application of radio geophysics to mining engineering

Copyright © 2012 by Larry Stolarczyk

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Application of Radio Geophysics to Mining Engineering

Larry G. Stolarczyk, Sc.D. Applied Radio Geophysics Institute for Mining Safety

and Productivity Raton, New Mexico 87740


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DEDICATION The inspiration for my 40 years of commitment to the application of radio geophysics theory in the solution of geotechnical communication and vision problems is attributed to the western mining environment, rich in sedimentary and volcanic mineralized resources. Most of the miners that brought this nation’s wealth to the surface emigrated from Europe and brought a cultural heritage of mom being the center of the family. Hard work was a virtue and man was only as good as his word. Mining camps replaced Indian wickiup villages that eventually became remote mining city centers, like Raton, New Mexico. Early landowners and steel and copper manufacturers provided capital for mine development while building infrastructure for a family-oriented living environment. The driving force underlying this inspiration is the heartbreak that mining families silently endure as the result of injuries and deaths of heads of households. The consequences linger on through generations and for many miners, a retirement ending in a smothering death. The Raton Coal Basin is approximately 50 miles wide and extends 80 miles along the eastern escarpment of the Sangre de Cristo Mountain range. The basin was formed during the Cretaceous period, 145.6 to 65.5 million years ago, with minable strandline and deltaic coal deposits. Volcanic rock capped mesas with sloping terraces of interbedded layers of sedimentary rock tell a story of plate tectonics and up lift resulting in the south eastern transgression of the in-land Cretaceous period sea with road cuts revealing meandering paleo river channel flow through this delta region. The upper floodplain river system flowed into the delta region from the west. The Raton area has long been a destination and field laboratory for this nation’s brightest young mining engineers and geologists training in sedimentary geology. The iridium layer, observable in sedimentary layers of the mesas, marks the end of the Cretaceous period. The absence of spores in the overlying rock layers give testimony to the theory of the Cretaceous period mass extension of life. Below the iridium layer, the world's largest dinosaur, Tyrannosaurus Rex, was found by Charles Pillmore in his study and fascination with the regional geology. The westward movement of the North American plate over upward welling tongues of magma reached the surface through the stress fractures in the Earth’s crust. Volcanism partially coked some of the basin coal seams resulting in one billion tons of the highest quality metallurgical coking coal in the entire world. Volcanism created dykes and sills alterations in the coal seam that can be seen in road cuts in the area. The upward welling of the magma carried with it fluidized elements in the periodic table. Upon reaching the upper regions of the Earth’s crust, cooling of the magma and the thermodynamic processes of exothermic solidification, selectively formed mineralized deposits of gold, silver, molybdenum, which is important ingredient in making stainless steel, copper, and the rare earth minerals. The Raton Coal Basin has been mined since 1881 to provide fuel for the railroad trains crossing Raton Pass on their way to bringing manpower needed to create wealth in the western smelting of copper and iron. Underground mines, within a day’s drive from Raton, featured adit entries into coal, uranium, gold, and silver deposits. Shaft and spiral declines provided access into deeper ore deposits featuring high production rate (e.g., 87,000 tons/day) block caving and


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vertical crater retreat (e.g., 8,000 tons/day) mining methods. The open pit mines complete the entire spectrum of modern mining methods. Like many of the mining regions in the U.S., Raton Coal Basin mining family members have suffered the consequences of mine injuries and disasters. In 1913, the Phelps Dodge Corporation's Stag Canyon No. 2 mine suffered a methane ignition and energetic coal dust explosion that claimed 263 lives. Again in 1923, the Stag Canyon No. 1 mine claimed 122 lives. The two disasters claimed 385 heads of households. These events are comparable to the worst U.S. mining disaster in Monongah, West Virginia, that claimed 361 lives on December 6, 1907. Raton is the home to the New Mexico State Miner’s Hospital and funded by miner’s trust land revenues. Here miners suffer the consequences of the occupational "black lung" disease, pneumoconiosis. Like roof-fall accidents, this hideous killer has not awakened the national conscience, as has the recent dramatic accidental entrapments of miners. The recent rash of mine accidents awakened the national conscience, initiating congressional action that enhanced mining law, rule making, and regulatory enforcement. Congressional appropriations funded improvements in mine safety technologies including the development of communication and tracking systems for trapped miners. Many of my long time personal friends are members of well-respected mining families that came to the western mining country extending throughout eastern Arizona, southeastern, western and southern Colorado, Wyoming, and New Mexico. My friends in mining also reside in the eastern states of Ohio, Pennsylvania, and West Virginia, as well as internationally from Canada and beyond North America to Chile, South Africa, New Zealand, Australia, China, and Russia. This work is dedicated to the many memories of the technical pioneering work of Dean Bryner, Utah Power & Light Company (UPL); Ed Moore, Kaiser Steel Corporation’s York Canyon Mine; John “Jack” Katlic, Nelson Kidder; Steven Doe and Craig Miller, American Electric Power (AEP) Fuel Supply and Ohio County Coal and Southern Ohio Coal Meigs mines; Greg Hasenfus, John Burr, and Dr. Bruce Bancroft, Consolidated Coal; Al Hillard, Blue Mountain Deserado Mine; Tim Acton, Magma Copper Company; Art Coca, Molycorp, Questa, New Mexico; and their mining division staff members. The advancement in applied radio geophysics was made possible only because these companies and staff members leaned forward and invested treasure, made underground facilities available, and applied human resources in the early adopter belief that radio geophysics would some day be a factor in advancing mine safety and productivity. A special dedication of this work is to the loss of my friends in the Wilberg Mine fire. In loving memory of Lori and Jedrek Stolarczyk.


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TABLE OF CONTENTS Page Dedication …………………………………………………………………………………… ii Foreword …………………………………………………………………………………….. x Acknowledgments ………………………………………………………………………….. xii 1.0 Introduction ………..……………………..……………..…………………………….. 1 1.1 Mining Industry Outlook and Technology Road Mapping ……………………... 1 1.2 Coal Resource Data ……………………………………………………………... 5 2.0 Mine-Wide Wireless Emergency, Post-Accident, and Operational Communications ... 8

2.1 Impact of the Farmington Mine Disaster ……………….…….…………………. 8 2.2 Impact of the Wilberg Disaster …………………..……….…………………….. 10 2.3 Quecreek Mine Inundation ….…………………………………………………... 15 2.4 Sago Mine Explosion …………………………………………………………… 16 2.5 Congressional Response to Mine Disasters ……………………………………... 20 2.6 Properties of Underground Distributed Antenna and Transmission Networks …. 24 2.7 Technology Gaps ………………………………………………………………... 30 2.8 Lessons Learned in Medium-Frequency Communications ..……………………. 34 2.9 Methane Ignition Susceptibility to Radiating Magnetic Dipoles ……………….. 49 2.10 Feasibility of High Magnetic Moment Intrinsically Safe Antennas …………….. 52 2.11 Susceptibility of Mine Equipment and Personnel to Electromagnetic Fields …... 53 2.11.1 Blasting Cap Susceptibility ……………………………………………… 53 2.11.2 Electronic Equipment Susceptibility ……………………………………. 54 2.11.3 Mine Personnel Susceptibility …………………………………………... 55 2.12 Through-the-Earth Transmission Loss ………………………………………….. 55 2.13 Wave Reflection and Absorption in Through-the-Earth Communications ……... 58 2.14 Through-the-Earth Transceivers ………………………………………………… 61 2.15 Transceiver Design ……………………………………………………………… 62

3.0 Horizon and Look-Ahead Coal Seam Sensors…...….……..…………………………. .. 65 3.1 Background……………………………………………………………………….. 65 3.2 Formation of Coal Deposits…………………………………………………….. .. 65 3.3 Horizon Sensor Design Considerations…………………………………………... 67 3.4 Technology Gap…………………………………………………………………. . 73 3.5 Look-Ahead Radar Technology………………………………………………… .. 75 3.5.1 Surface-Based Electromagnetic Gradiometer Surveys…………………..... 75 3.5.2 Cross Well Radio Imaging Method Surveys……………………………... . 79 3.5.3 Technology Gap………………………………………………………….... 79 3.5.4 Deep Look Ground Penetrating Radar Gradiometer …………………… .. 80 3.6 Technical Innovations of the Deep Look Radar Gradiometer……………………. 81 3.7 Deep Look Ground Penetrating Radar Gradiometer……………………………... 85 3.8 Seismic and Acoustic Wave Detection of Non-Linear Stress Fields...…………. .. 91 4.0 Making the Earth Transparent ………………………………………..……………….. 93 4.1 Electromagnetic Fields in Coal Seams …………………………………………. 94 4.2 Advanced Radio Imaging Method Instrumentation …………………………….. 100 4.3 Recent Longwall Mapping Case Studies ………………………………………... 104 4.4 Future Considerations …………………………………………………………… 108 4.5 Technology Gap in Subsurface Imaging ………………………………………... 109


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5.0 Sterilization of Coal Reserves .…………..……………………………………………. 111 5.1 Technology Gap ………………………………………………………………… 111 6.0 Destruction of Fresh Water Aquifers ………………...………………………………... 113 7.0 Horizontal Directional Drilling ……………………………..………………………… 116

7.1 Problems in Horizontal Drilling ………………………………………………… 116 7.2 Technology Gap in Horizontal Directional Drilling ……………………………. 117

8.0 Uranium Fuel In-Situ Mining …………………………………………………………. 118 8.1 History of Acoustic Stimulation for In-Situ Uranium Mining ………………….. 118 8.2 Uranium Market Analysis ……………………………………………………….. 119 8.3 In-Situ Leaching Uranium Mining ……………………………………………… 124 8.4 Technology Gap in In-Situ Leaching Processes ………………………………… 126 9.0 Concluding Remarks and Recommendations …………………………………………. 129 10.0 Bibliography and References …………………………………………………………. 131 11.0 Stolar Research Corporation Patent Portfolio ………………………………………… 137 Appendix A …………………………………………………………………………………. 140 Appendix B ………………………………………………………………………………… 144


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LIST OF FIGURES Figure Page 1-1 U.S. Electric Power Industry Net Electrical Generation by Fuel Type ……….…….. 1 1-2 Map of U.S. Coal Reserves ………………………………………………………….. 6 1-3 U.S. Coal Resources and Reserves ………………………………………………….. 7 2-1 Wilberg Mine Escape Route ………………………………………………………… 10 2-2 Third-Generation Intrinsically Safe Medium Frequency Transceivers Installed in a Western U.S. Coal Mine …………………………………………………………. 12 2-3 Cross Section of the High Energy Cutback Region of a Paleochannel ……………... 14 2-4 Location of the Trapped Miners in the Quecreek Mine Disaster …………………… 15 2-5 Saxman Mine Breach …..……………………………………………………………. 16 2-6 Stress Field Surrounding a Developed Entry ………………………………………... 16 2-7 Location of Barricaded Miners ……………………………………………………… 17 2-8 Transmission Network ………………………………………………………………. 25 2-9 Traveling Electromagnetic Waves Composed of Electric and Orthogonal Magnetic Field Components ………………………………………………………………….. 25 2-10 Bit Error Rate Versus Ratio of Energy per Bit to Noise Spectral Density for Coherent Binary Phase Shift Keyed, Non-Coherent Differential Binary Phase Shift Keyed, and Non-Coherent Frequency Shift Keying Modulation Schemes ………... 28 2-11 Receiver Specifications of Detection Sensitivity ……………………………………. 29 2-12 Mine Communications and Tracking System …...………………………………….. 33 2-13 Cap Lamp Transceiver ………………………………………………………………. 35 2-14 Radio Frequency Identification Tag Tracking System ……………………………… 35 2-15 A F1/F1 Transmit-Receive Transmission System …………………………………... 37 2-16 Electromagnetic Wave Field Component Produced by a Vertical Magnetic Dipole Antenna with the Loop in the Equatorial X-Y Plane ………………………………. 39 2-17 Geological Component of Magnetic Field Intensity Versus Distance Scaled in Skin Depths ………………………………………………………………………... 43 2-18 Geologic Field Component Phase Shift Versus Distance Scaled in Skin Depths 43 2-19 Radio Geophysics Earth Model ……………………………………………………... 45 2-20 Electrical Conductivity and Relative Dielectric Constant for Natural Media ………. 45 2-21 Attenuation Rate and Phase Constant for a Uniform Plane Wave Propagating in a Natural Medium with a Relative Dielectric Constant of Ten ……………………….. 47 2-22 Reflection Occurring at an Air-Natural Media Interface ……………………………. 47 2-23 Intrinsically Safe Current and Magnetic Moment Versus Circumference for an Air- Core Loop Antenna ………….……………………………………………………. 52 2-24 Intrinsically Safe Phased Array with QCKT < 1 ……………………………………… 52 2-25 Transmission (Heat-H) and Reflection (Loss-R) at Media Interfaces ……………… 55 2-26 Typical Ionospheric-Earth Radio Frequency Interference Noise Spectral Density …. 56 2-27 Air-Earth Transmission Loss Versus Frequency ……………………………………. 59 2-28 Total Attenuation Through 1,500 Feet of Overburden ……………………………... 59 2-29 Propagation Loss of the Radio Waves Traveling 1,500 Feet Through the Earth …… 60 2-30 Through-the-Earth Communications Hardware …………………………………….. 61 2-31 F1/F1 Digital Transceiver Block Diagram (Physical Layer) ……………………….. 62 3-1 Delta Region Illustrating Sand Levees, breaching in a Levee, and Meandering Flow and Splay Deposits …………………………………………………………... 65


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3-2 Illustration of a Meandering Paleochannel ………………………………………….. 65 3-3 Resonant Detection Impedance Plot ………………………………………………… 69 3-4 Cutaway View of a Resonant Microstrip Patch Antenna Sensor …………………… 69 3-5 Horizon Sensor Mounted on a Mining Machine Cutting Drum ……….…………... 70 3-6 Comparison of Deaths in the U.S. and Australia per Million Population …………... 71 3-7 Stratigraphic Cross Section Illustrating Contamination in a Coal Bed ……………... 71 3-8 Pick Tip Horizon Sensor mounted on a Cutting Drum ……………………………... 74 3-9 Horizon Sensor Mounting Options on a Longwall Shearer and Continuous Miner … 74 3-10 Ground Wave Field Components Propagating Away from an AM Band Radio Station ……………………………………………………………………………… 76 3-11 Gradiometric Response of the Illuminating and Scattered Fields …………………... 77 3-12 Electromagnetic Gradiometer Response ……………………………………………. 78 3-13 Hand-Held Electromagnetic Gradiometer ………………………………………….. 78 3-14 Gradiometric Response Measured Over an Abandoned Section of the Emery Mine .. 79 3-15 Cross Well Fence Line Imaging to Detect Unmapped Abandoned Mine Entries …... 80 3-16 Electromagnetic Wave Energy Flow in the Horizon Sensing and Abandoned Mine Detection Problem …………………………………………………………………. 81 3-17 Classical Ground Penetrating Radar Schematic and Waveforms …………………… 82 3-18 Time Domain of the Reflected Energy from an Object a 17 Feet …………………… 82 3-19 Detection Depth Versus Frequency for Near Zone Signal Suppression ……………. 85 3-20 Block Diagram of the Deep Look Radar Gradiometer ……………………………… 86 3-21 Double Sideband Suppressed Carrier Waveform …………………………………… 86 3-22 Phasor Representation of the Gradiometric Heterodyne Process and Quadrature Detection of the Far Zone Reflected I and Q Signals …………………………….... 87 3-23 Bausov Suppression Factor …………………………………………………………. 89 3-24 Bausov Deep Look Ground Penetrating Radar Response with First Interface Reflection Suppression Versus Variation in the Modulation Frequency ………….. 89 3-25 Continuous Mining Machine with the Deep Look Radar Gradiometer Installed …… 90 3-26 Shear Wave Transmission Through Non-Linear Stress Fields ……………………... 91 3-27 Detection of Heterodyne Signals …………………………………………………… 92 4-1 Subduction, Upwelling, and Solidification Temperature of Ore Bodies …………… 93 4-2 Tomographic Images of a Massive Iron-Nickel Ore Body …………………………. 95 4-3 Anomalies and Electromagnetic Field Components Found in a Coal Seam Waveguide …………………………………………………………………………. 96 4-4 Coal Seam Electromagnetic Wave Attenuation Rate Versus Frequency …………… 97 4-5 Coal Seam Electromagnetic Wave Attenuation Rate Versus Boundary Rock Conductivity …………………………………………………………………. 98 4-6 Sensitivity of Radio Waves to Changes in Coal Layer Thickness ………………….. 98 4-7 Longwall Mapping with In-Mine Radio Imaging …………………………………... 100 4-8 Digital RIM-6 Instrumentation ……………………………………………………… 102 4-9 Digital RIM-6 In-Mine Survey Instrumentation and Tomography Image of Coal Seam Anomalies …………………………………………………………………… 103 4-10 Radio Imaging Method Data Collection Techniques ……………………………….. 104 4-11 Initial Series of Multi-Stage Radio Imaging Method Surveys ……………………… 106 4-12 Final Series of Multi-Stage Radio Imaging Method Surveys …..…………………... 107 4-13 Radio Imaging Method Mapping of Intrusions into a Coal Seam ………………….. 108


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4-14 RIM-5 Studies ……………………………………………………………………….. 109 6-1 Coal Bed Methane Extraction with Cavitation or Horizontal Drilling ……………… 113 6-2 Cavitation Method of Coal Bed Methane Production ……………………………….. 114 6-3 Coal Bed Methane Production Enhanced by a Focused Acoustic Beam Tool ……… 115 7-1 Cross Section of a Coal Bed Illustrating Radar Controlled and Uncontrolled Drilling into the Floor ……………………………………………………………… 116 7-2 Acoustic Flow Permeability Intensification ………………………………………… 117 8-1 Acoustic Flow ……………………………………………………………………….. 119 8-2 Uranium Supply by Country for 2000 through 2008 ………………………………... 122 8-3 Production and Demand for Uranium ……………………………………………….. 124 8-4 In-Situ Leaching Uranium Mining Method …………………………………………. 125 8-5 Well Pattern in an In-Situ Leaching Project …………………………….................... 126 8-6 Focused Acoustic Beam Tool ……………………………………………………….. 127 8-7 Stress Field in Coal Mine Pillars ……………………………………………………. 128 A-1 Conductor Mode Attenuation Rate Versus Frequency for Conductor to Rock-Mass Air-Path Distances of 1 Centimeter, 10 Centimeters, and 1 Meter …….…...……... 142 A-2 Receiving Magnetic Field Constructive and Destructive Interference Zones Created by Mono-filar and Bi-filar Modes of Current Flow ………………………. 142


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LIST OF TABLES Table Page 1-1 Needed Technologies Identified by the National Mining Association and the National Research Council …………………………………………………………. 4 1-2 U.S. Coal Reserves by State ………..………………………………………………... 7 2-1 Comparison of Attenuation Loss as a Function of Travel Distance …………………. 27 2-2 Electrical Parameters for Coal, Shale, Water, and Air ………………………………. 46 2-3 Attenuation Rate ……………………………………………………………………… 46 2-4 Electromagnetic Wave Transmission Parameters ……………………………………. 48 2-5 Standard Annealed Copper Wire Resistance …………...……………………………. 50 2-6 Intrinsically Safe Magnetic Moment of a Magnetic Dipole Antenna ………………... 51 2-7 Surface Signal-to-Noise Ratio for Vertical Magnetic Dipole Antennas …………….. 57 2-8 Electromagnetic Wave Transmission Factors ………………………………………... 58 2-9 Magnitude of Radial Magnetic Field Components for a Normalized Magnetic Moment of 1 ATM2 Operating at a Frequency of 2,000 Hz in 20 mS/m Overburden ………………………………………………………………………….. 60 2-10 Intrinsically Safe Radial Magnetic Field Components Above a Surface ……………. 61 3-1 Comparison of Gradiometric Deep Look Ground Penetrating and Classical Radars ... 90 4-1 RIM-6 Performance Versus Previous RIM Technology ……………………………... 101 8-1 Uranium Production by Extraction Method in 2009 ………………………………… 120 8-2 In-Situ Leaching Uranium Mines …………………………………………………….. 120 8-3 World Uranium Production by Company ……………………………………………. 121 8-4 Uranium Production by Country for the Period 2003 through 2009 ………………… 121 8-5 Known Recoverable Resources of Uranium in 2007 ………………………………… 123


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FOREWORD Mining industry executives and members of the Special Committee of the Earth Resources Engineering, Section 11 of the National Academy of Engineering (NAE), share a common objective but from a different point of view. These individuals are dedicated to meeting society’s requirements for minerals and energy resources in a manner that also meets society’s needs for sustainability and Earth stewardship. For many years into the future, U.S. energy demands will gradually transition from our dependence on carbon fuels to an economy that is based on hydrogen and renewable energy. Throughout the transition period, mined natural resources of coal, uranium, and non-fuel minerals, including the rare earth minerals, will be needed. As part of the mining life cycle, environmentally friendly mineral process engineering, water quality preservation, and disposal of large amounts of waste will also need advanced and enhanced technology development. The mining executives and members of the NAE recognize that all of the engineering and applied science disciplines will be needed to advance mining technology beyond the current state of the art as mines encounter deeper resources surrounded by more complex geology. Understanding the origin of valuable resources requires the science and field experience of a geologist. Deposition and extraction issues require the addition of the specialized contributions of chemistry, biology, and mining engineering. Processing needs metallurgical innovation and discovery involves the complex mathematics of wave propagation, imaging, and geophysics. Mining executives, engineers, and applied scientists must be in full communication. Their point of view changes when mining personnel transition from a role dominated by engineering and applied science to management, who must then deal with public opinion and politics, which are necessarily based on non-scientific understanding. Interestingly, executives of space vehicle, aircraft, train, and car manufacturing companies encountering accidents are not judged as mining executives are, that is, by unsound science. The American way of life begins with mining and our future depends on mining. The future of cost-effective and environmentally small footprint mining depends on the executives defining their vision of the mine of the future (MOF) and technologists overcoming identified technology gaps preventing the realization of safe, environmentally friendly, and productive future mining. Taking engineering and applied science underground following the MOF road map is an exciting adventure. Like man and his machines traveling into the hostile outer space, traveling into inter space will create new technology challenges and opportunities for innovation and discovery by this nation’s scientific brain trust. The national commitment and investment in space adventure paved the way for unimaginable advancements in science and technology that made the world “flat.” Space-age advancements enabled our nation to create a secure and healthy place to live, infrastructure for a productive work force, high paying jobs, and incredible wealth. Some unintended consequences created manufacturing opportunities for our trading partners, like China, to manufacture and create wealth as our nation did during the industrial revolution. Like Alexander Hamilton advised George Washington, manufacturing creates wealth. A national commitment and investment in engineering, applied science, and technology for the inner space of mining will continue the pace of exciting leading edge technology innovations, but this time, the benefits will more directly apply to sustainable wealth creation in the U.S. economy.


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This paper presents an historical account of mining executives, in full communication, developing the first unified vision of the mine of the future along with mining industry technologists prioritizing the advanced technology development road map to the future. The mining industry road map is very similar to the map developed by the Special Committee of the Earth Resources Engineering, Section 11 of the National Academy of Engineering. Unlike the national commitment and investment in the space program, the national technology development investment in mining is driven by society’s reaction and congressional action to mine disasters. Public policy must change to recognize that national investment in mining should range between $4 and $8 billion per year, based on industry rules of thumb, with $400 to $800 million for coal extraction alone. The public and industry’s share of the investment must be debated and quasi-government mining research organizations established like in China, Australia, and South Africa.


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ACKNOWLEDGMENTS

I was fortunate to have begun my electrical engineering research and development (R&D) career in a region where my friends were employees of the Kaiser Steel Corporation (Kaiser) York Canyon underground coal mine. My daytime job was with a pioneering radio communications R&D firm that started up by contributing electrical engineering genius and theoretical physics understanding to the WWII development of radar jamming transmitters used in the Normandy Beach invasion and became leaders in the development of electronic warfare equipment, military communications for our fighting men, and spy radios for the Polish underground war fighters. The spy radios are on prominent display in the Spy Museum in Washington, D.C. Advanced development in my daytime job included designing and manufacturing precision electromagnetic phase coherent missile tracking system hardware for White Sands Missile Range, command destruction receivers for missiles, multiple channel very high frequency (VHF)/ultra high frequency (UHF) transmission equipment for military communications linking battlefield Air Force bases, and wireless garage door controls and home security systems. Other projects included the development of biological oxygen demand (BOD) respirometers and electromagnetic wave filters and the design of analytic chemistry instruments.

The Kaiser Steel Corporation executives, like many mining executives, were willing to invest in evolutionary and revolutionary mining technologies. Kaiser management was influenced by Stanford University's Dean of Engineering Frederick E. Terman's success in technical outreach, by educating the founders of Hewlett Packard and the many brilliant technologists that led the evolutionary and revolutionary development of Silicon Valley. Kaiser installed some of the first U.S. longwalls in the York Canyon Mine near Raton, New Mexico, and the Sunnyside Coal Mine near Price, Utah. Consolidation Coal (Consol) installed the first longwall in about the same time frame. One of the first walking draglines ripped coal from shallow coal deposits at the York Canyon mine site. Funding for advanced mining technology development was made available from profitable steel production and was applied to improving mining safety and productivity. Being a personal friend of the Kaiser maintenance team members, John Bizyak and Fred Rivera, we worked closely with the Mine Safety and Health Administration (MSHA) Denver Technical Support staff member, Merile Venter, to develop and implement the first fail-safe machine trailing cable grounding conductor monitor. The Pilotone monitor essentially eliminated the potential for electrocutions of maintenance personnel working near underground mining machines. The underground York Canyon Mine became our laboratory for understanding structural mining geology, mechanical and electrical requirements for safe and productive continuous miners (CM), and longwall mining machines and supporting systems. Mr. Ed Moore, Mine Manager and honors graduate of the Colorado School of Mines, was my professor of mining engineering and depositional geology. When designing, developing, and making the trailing cable monitor work correctly, I became aware of the shortcomings of the wired pager telephone and VHF communication systems used by miners that must be on the move. The trailing cables grounding conductor monitor development work frequently occurred in the coal and silica dust plumes of operating continuous mining and longwall machines. Dust induced coughing quickly convinced me that technology was needed to solve the " black lung" health related issues. I was self-educated in the cause of my retired miner friends needing to carry oxygen tanks as they visited stores in the city. I was sure that radio geophysics sensors could be


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designed to remotely determine when the rotating coal cutting drum picks approached the coal seam boundary rock by real-time radar measurement of uncut coal thickness.

The trailing cable grounding conductor monitors were installed in the section power centers throughout the mining complex. A slide mounted transformer converted 7,200-volt mains power to 440-volt machine power. The power center supplied three-phase electric power to each of the mining face equipment. Each piece of mining equipment required a separate circuit breaker, trailing cable, and ground conductor monitor. The power center side monitor was designed with high withstanding voltage AC blocking capacitors forming a coupler. The coupler capacitor leads were attached to each of the three insulated phase conductors in the trailing cable. The opposite ends of the capacitors were each tied together and driven by the monitor's 2,000-Hz pilot signal. The pilot signal returned from the distant mining machine through a machine side capacitor coupler and the continuous-grounding conductor in the trailing cable. If any of the three trailing cable phase conductors or motor field insulated copper windings faulted (i.e., shorted) to the motor frame ground, short circuit phase current would flow back to through the intact grounding cable conductor causing the power center circuit breaker trip out the three-phase AC supply. If the grounding conductor was inadvertently separated or cut, the fault causes the mining machine frame to rise to the phase voltage potential. If any miner touched the machine and Earth ground, electrocution was immediate.

During the in-mine development and trials of the monitor, I discovered that the pilot signal sensing frequency was within the spectral bandwidth of the radio frequency interference (RFI) electrical noise generated in the power distribution system and operating equipment. The high level of RFI noise caused the monitor to fail to sense fault conditions. To solve the RFI problem, I connected a spectrum analyzer instrument to the grounding conductor and determined that the grounding conductor noise spectrum density was rich in frequency components that were identified as harmonics of the power system frequency (especially the 6th harmonic of the supply frequency), CM induction motor slip frequency, power system switching transients frequency components, substation switching control signals generated by the utility grid control center 200 miles away, lighting strikes and the KRTN radio station 20 miles away. The supply-switching transients were oftentimes greater than 2,000 volts and destroyed the coupler and monitor electronics. I became aware that low frequency (i.e., 30 to 300 kHz) and medium frequency (i.e., 300 to 3,000 kHz) band electromagnetic (EM) waves traveled on the electric power system electrical conductors, with extremely low attenuation rate in the bi-filar mode, throughout the entire underground mining complex. By observing the spectrum, it was possible to determine which machines were operating and at what load factor. In 1970, having just completed my doctorial studies in theoretical physics, EM wave propagation, and electrical engineering, it was obvious that the "long wavelength scattering limit" of theoretical physics explained the phenomena of the AC power distribution system fulfilling the role of a distributed antenna and transmission facility for EM signals in the low and medium frequency bands. The U.S. Bureau of Mines (USBM) under the very capable leadership of Drs. John Murphy and Kenneth Sacks and staff members Robert Chufo, Harry Dombrowski, Jim Means, and William Schiftbauer established the programmatic development and confirmation of the radio geophysics theory of remote sensing and communications. The theory was formulated by Drs. David C. Chang, David A. Hill, and James R. Wait, professors and adjunct professors in the Electrical,


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Computer, and Energy Engineering (ECEE) Department at the University of Colorado in Boulder, Colorado. The Kaiser Steel Corporation York Canyon underground coal mine experience enabled the writing of a successful technical proposal for the development of the first mine wide MF frequency modulated (FM) communications system for underground mines. The USBM scope of work included the design, development, and underground demonstration of prototypes of MF FM transceivers. The USBM management encouraged a marketing, sales, and distribution partnership with the Mine Safety Appliance Company (MSA), a world leader in developing and marketing of safety products to the mining industry. The lessons learned in the York Canyon Mine development of the trailing cable grounding conductor monitor and MSA’s 20-year knowledge base and experience in marketing, sales, and service of the trolley phone and pager telephone product lines were combined to create synergism in the productization of the USBM MF communication equipment. A number of MF transceiver prototype demonstrations were carried out in the U.S. Eastern, Midwestern and Western MSA sales districts including world-mining regions where MSA had established market dominance. MSA sales organization members were on call 24/7 to provide in-mine technical assistance and training. MSA’s service above “self” relationship effectively made mines throughout the world our underground demonstration laboratories. The first prototype MF communications equipment demonstrations were carried out in the York Canyon Mine and with James Zappanti in the Colorado Fuel and Iron Allen Coal Mine near Trinidad, Colorado. The manager of MSA's Salt Lake City Regional Marketing Center took the lead in arranging demonstrations in Utah, Colorado, Wyoming, and Arizona mining regions. Demonstrations were conducted in Eastern and Western Canada, and South Africa underground coal and metalliferous underground mines. During the South African demonstrations, Dr. Nigal Middleton, a graduate of the University of Witwaterstand and a member of the technical staff of the South African Chamber of Mines, who later was an engineering professor at West Virginia University and the Colorado School of Mines, described the design and in-mine evaluation of the second generation of the single sideband MF transceiver in both coal and metalliferous underground mines. During the in-mine demonstration at the York Canyon Mine, Mr. Gary Boese, carrying an MF transceiver, communicated with the portal transceiver inadvertently turned into the electrical power distribution cable free entry of a longwall panel. Communications were still possible while advancing in-by along the gate road entry. It was clear that the MF radio communication system had switched modes from the distributed antenna and transmission conductor waveguide mode to the coal seam waveguide mode of transmission. Our demonstration team exited the mining complex and briefed Mr. Ed Moore about the 10,000-foot conductor waveguide communications range and the 700-foot coal seam waveguide range. It occurred to me that the coal seam mode and MF equipment could possibly be developed into a transmission tomography mapping method for detection of coal seam anomalies. The mine fresh air entry had been developed through a full seam displacement fault. An experiment was set up the next day to determine if the fault would simulate a "textbook" discontinuity in the coal seam waveguide. By setting up the transmitter and radiating the quasi-transverse electromagnetic wave (i.e., the quasi-TEM waveguide mode) in the coal seam, the reflected measured signal increased in front of the fault and significantly decreased in magnitude on the far side of the fault. The exact phenomenon expected in a microwave laboratory waveguide as taught by Dr. Carl T. Jonk, professor at the University of Colorado, Boulder ECEE department. This experiment suggested that coal seam


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anomalies could be detected and possibly imaged with EM waves. Because of MSA's market dominance, MF communications demonstrations were conducted worldwide and always included clandestine evaluation of the radio imaging method (RIM) anomaly detection. Clandestine RIM surveys were conducted throughout coal fields in the U.S. and abroad. Prior to U.S. and foreign patent filings, the clandestine demonstrations confirmed that coal seams throughout the world are altered by faults, dykes, rapidly thinning seams, paleochannels, and burns. The only problem with the rediscovery of the coal seam waveguide was that neither my daytime company, USBM, MSA, nor Kaiser Steel Corporation would fund development of RIM technology. The USBM was funding development of radar technologies at that time and was apparently unable to redirect the development effort. Dr. James Wait in his 1963 paper had predicted that natural waveguides existed in the layered subsurface. Even when approached about the existence of the coal seam waveguide, it was not obvious to Dr. Wait that the waveguide existed. Demonstrations of the USBM MF communications technology in underground mines seemed to frequently be diverted away from radio communications to focus on the radio remote control of mining machines. The main reason for this marketing phenomenon was that pager telephones systems had a very long prescriptive acceptance history and the product reached the mature phase of the product life cycle. Commodity pricing had been established in the worldwide market and the pager telephone was approved by the mine safety regulators. There was no enthusiasm for adopting mine-wide wireless MF communications in operating mines. Radio communications demonstrations at the block caving copper mine operated by Magna Copper’s San Manual Division caused Mine Manager Tim Atkins to approve the development of MF remote controls for loading ore train cars from the pony set to improve the safety and productivity of the block caving mining method. Maintenance staff members, Messrs. Kent Bilheartz and Al Metcalf, spent many underground hours discussing and participating in the project to develop wireless MF system equipment for full automation of the pony set train car loading system. The block caving molybdenum mine operated by Molycorp, Questa, New Mexico, funded the advanced development of the wireless MF radio remote control, tracking via wayside UHF sign post burst transmitters, and automated rail haulage system over the entire 17,000-foot haulage system. MF control extended from the surface control room via the 1,700-foot shaft conductor waveguide to repeaters on the haulage level. Drs. Steven Besenger and Michael Nelson, both graduate students of Dr. Syd Peng of West Virginia University, developed the first U.S fully automated longwall. The MF data transmission technology via the shearer trailing cable replaced the problematic fiber-optic link built into the cable. The radio data link was an important factor in reliably linking the computer-generated machine control signals to the longwall subsystems. Utah Power & Light Company (UPL) Mining Division geologists Rodger Fry and Chuck Semboyski were early adopters in evaluating, validating, and developing the radio imaging method (RIM). Dr. Ray Radosevich, who at that time was a member of the faculty of the Robert O. Anderson School of Business at the University of New Mexico, mentored the start-up and early development of the business. The New Mexico Energy Research and Development Institute, directed by Dr. Larry Icerman, funded the development of the RIM instrumentation. Messrs. Fry and Semboyski were joined by Mr. David Loreski, who later became the administrator of MSHA, in the development and demonstration of the third-generation mine-wide wireless MF radio communications system


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following the Wilberg Mine fire. Wireless communications were installed in a total of 15 underground mines.1 Later in the history of the UPL's mining division, Mr. Brett Harvey, who is now Chief Executive Officer of Consol Energy, funded the development and initial trials of the horizon sensor (HS) technology integrated into an automated high wall miner control system. Mr. Al Hilard of the Blue Mountain-Deserado Coal Mining Company installed and evaluated the HS on a high-production shearer cutting drum. Mr. Mark Bunell and Windel Koontz of Arch-Sufco and Arch-West Mining Company assisted in development of RIM and evaluated the HS on continuous miners. Mr. Charles Stumpher of Sasol-Brandspriut sponsored and evaluated the development of the HS for use in South African coal fields. Working closely with Drs. Sid Peng and Yi Luo of the Department of Mining Engineering at West Virginia University, HS and RIM technologies were improved with funding provided by the Department of Energy (DOE) Energy Efficiency (EE) program administered by Morgan (Mike) Mosser and Mike Canty. Mr. Greg Hasenfus, John Burr, and Dr. Bruce Bancroft of Consol Energy installed and evaluated the HS on a high-production rate shearer cutting drum. The RAG Twenty Mile Mine also evaluated the HS. Murray Energy Corporation’s Ohio Valley Coal Mine installed and evaluated the HS on a longwall shearer. The Massey-Highland, Monterey, and Oxbow mines evaluated the HS. Projects supported by the DOE EE received five R&D 100 Awards, the “academy awards” for innovative technology development. Look-ahead radar trials were conducted at Consol’s Emery, Arch-Sufco’s Mine 84, Mountain Coal, Ry Stone Bowie Resources and Deer Creek coal mines. Revised RIM, evolving from the second to sixth generations of equipment, were trialed by individuals at the following mines: John McGauhe of Noranda Mining, Allen King and Glenn McDowell of Inco, Dr. Asbjiorn Christenson and Michael Barlow of BHP/Metals, Rod Doyle and Roger Byyrnes of BHPB/Illawarra, Dr Steven Bessenger and John Mercier of San Juan Coal, Scott Pryerson and Brian Schaffer of Alpha Natural Resources, Ed Pitrolo of Monterey, Lane Dair of West Ridge Resources, Robert Koch and Jens Lange of Oxbow Mining, Marc Silverman, Phil Ames, and John Rusnak of Peabody Coal, Ernie Thacker and John Popp of Alliance Mines, Phil Ames and Richard Reisinger of Black Beauty Coal. The RIM equipment has also been tested in Arch-Sufco’s Dotiki, Farmrburg, Vermillion Grove, Mine-84, Big Run, Cannington, West Ridge, Daw Mill mines as well as in the San Juan Coal Company’s underground mine. I have had long discussions with Dr. Pramod Thakur and Scott Thomson about degassing of coal beds ahead of mining and using the degasification boreholes for RIM tomography investigations of coal seam structural geology. Dr. Peter Hatherly and Scott Thomson introduced RIM into Australian coal fields. Special thanks goes to Dr. Syd Peng, Dr. Larry Icerman, and David Chirdon for editing and revising the text. I have included their change recommendations to make complicated subjects of radio geophysics easier to understand. The opinions and recommendations expressed in the text are my own and may not have been endorsed by the editors. 1 J. Mike Mishra installed the first MF communications system in Wyoming.


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Radio geophysics consolidates the following: structural geology of Fry, Semboyski, Miller, Doe, Thomson, and Moore, petrophysics of Von Hipple and Parkhomenko; theoretical physics of Morse and Feshbach; mathematics of the complex variable of Churchill; scattering theory of Harrington, Van Bladel, and Kelly; electromagnetic wave theory of Maxwell and Heavsides; transmission line theory of Jonk, Jordan, and Balmain; EM wave propagation underground by Wait, Hill, Chang, and Delogne; statistical communications theory of Middleton and Lee; pioneering satellite networks of Cardin, Osborne, and G.L. Stolarczyk; network synthesis of Gillman and Lucky; pioneering development of software definable receivers of Bausov, Davis, Botla, and Sanchez; organizational behavior theory of longwall miners; mining engineering of Peng; and radio imaging of Löwy and Duncan.


SRC-2011-09 Application of Radio Geophysics for Mining Engineering 1

1.0 INTRODUCTION

1.1 Mining Industry Outlook and Technology Road Mapping There are 325 coal, metal and non-metal mining and service companies represented by the National Mining Association (NMA). The mining industry revenue is approximated at $450 billion/year or 3% of the U.S. gross national product (i.e., ~ $15 trillion). Mined coal and uranium fuels 65% of the nation’s base load electric power demand or 2.61 trillion kWh (see Figure 1).

Figure 1-1. U.S. Electric Power Industry Net Electrical Generation by Fuel Type.2 The NMA was primarily organized to combat the environmental movement in the U.S. Congress, enhance public relations in the media, and improve mining safety by working constructively with the Mine Safety Health and Administration (MSHA). The cooperative partnership with MSHA paid off measurably by significantly improving U.S. mine-safety records. The bumper sticker for the mining industry is "A SAFE MINE IS A PRODUCTIVE MINE." Mining makes America work. Across the nation, nearly 1.5 million people work in high paying mining related jobs. Mining generates nearly $22 billion in government revenue. In 2007, the mining industry reported an incident rate of 3.7 injuries per 100 workers, giving mining the second lowest injury rate in American industry. However, the industry does not report the significant health-related issues of retired miners. Mine managers and supervisors are dedicated to ensuring that miners return home safely. 2 U.S. Energy Information Administration, Annual Energy Outlook Report, April 2011.



The mission of MSHA is to promulgate and enforce regulations under mining laws enacted by the U.S. Congress as a result of national concerns for miner safety. Congressional hearing testimony and research conducted by staff members are essential in drafting mine-safety legislation. MSHA has mine inspection and enforcement responsibilities to ensure a safe working environment. As such, MSHA inspectors document unsafe working mining conditions by issuing citations with an infraction resolution time limit. In the past, MSHA's technical support groups worked constructively with mining company personnel to resolve safety problems in a timely manner. Many safety and equipment design issues are unique to mining and not solvable with commercial off-the-shelf (COTS), surface-based technologies. The problems arise because of the confining infrastructure of the underground mining complex; operations spread out over tens of miles of tunnels, drifts, and entries; power distribution restrictions; transportation limitations; nearly 100% humidity; and accumulation of aerobic and anaerobic bacteria producing carbon dioxide and methane gas. Mining problems can include the accumulation of bacteria and the release of dangerous gas, which requires ventilation, when cutting near hydrocarbon sources. Flame proof or intrinsic safety certification is a requirement of equipment when operated in mines with the possibility of explosive atmospheres. In the past, difficult mining problems were referred to the U.S. Bureau of Mines (USBM) scientists, engineers, and technicians for resolution. These technologists were specially trained in developing and monitoring safety research and development (R&D) programs for the mining industry. More recently, the MINER Act of 2006 reestablished mine safety and health technology development responsibility within the National Institute of Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR). Beginning in 1998, the NMA President and Chief Executive Officer, U.S. Army General Lawson (ret) and the Board of Directors expanded the NMA mission statement to include support for R&D directed at developing technology that addresses long-standing "upstream" mining problems. The NMA coal mining companies already supported the U.S. Department of Energy (DOE) "downstream" clean coal initiative enabling electric utilities to fuel boilers with run-of-the-mine (ROM) washed coal. Selected NMA members were appointed to the technology committee chaired by a technology-oriented Chief Executive Officer, Arthur Brown, a mining engineering graduate of South Africa's Witwatersrand University. Mr. Brown was directly involved in the Lucky Friday mine fire rescue effort and experienced the consequences of failed voice communications with trapped miners. The NMA technology committee worked with the DOE to establish the primary goal of prioritizing and developing "needed technologies" for energy conservation, enabling the mining industry to satisfy the DOE Office of Energy Efficiency (EE) program objectives. In the spring of 1989, Chief Executive Officers (CEOs) from the mining industry met in Phoenix, Arizona, and presented their vision of the Mine of the Future (MOF). Later in the fall, the CEOs sent mining technology specialists to a DOE facilitated Road Mapping event in Denver, Colorado. The Road Map identified and prioritized needed technologies that, if available, would significantly increase mine safety and productivity. Guided by the Road Map, DOE EE program staff prepared procurement packages for developing each of the "needed technologies." The NMA technical committee insisted that each of the development objectives of the technologies be consistent with the NMA Road Map. The statement of work (SOW) for each



project was to be approved by mining company personnel assigned to the project and demonstrated at the mine site. To accelerate the program, the DOE National Laboratories submitted proposals without necessarily consulting with the NMA technical committee or partnering with a mining company. Later in the program, solicitations for cost-shared proposals were accepted from private industry with mining company partners. The NMA technical committee believed that the DOE laboratories and mining industry focused on different goals and objectives that would not result in sustainable functionality in the mining environment. The program was funded at a level of $5 million/year until defunded by the George W. Bush administration. Defunding prevented in-mine demonstrations for many promising MOF technologies developed with cost-shared DOE EE funding. During the 1989 NMA/DOE visioning conference, the mining CEOs appealed for help in reducing the unreasonable length of time required by the federal and state mine permitting processes. They stated that consolidation of mining companies was beginning to occur, as mineral prices were declining due to foreign producers entering the market. In some notable cases, especially in the rare earth minerals industry, predatory pricing and business practices were used. Electric utility franchises granted large service areas to public and municipal utilities enabling efficient generation, distribution, energy pricing, and a reasonable return on investment. Franchising serves the public good while creating monopolistic and spot market purchasing practices in the fuel supply chain. Supply competition decreased margins in coal pricing with the unintended consequence of minimizing funding for investing 1 to 2% of mining revenues in R&D. According to this guideline, the R&D investment in mining technology should range between $4.5 and $9 billion. The combined government investment in mining-related research sharply declined from $160 million/year in 1988 to $5 million/year in 1998 and ultimately vanishing in 2001. Declining enrollment and research grants made maintaining staffing and graduate programs difficult for mining engineering and geophysics colleges. This trend, combined with the "graying" of the work force, was a concern. The mining company CEOs stated that the easy-to-mine coal reserves were nearing exhaustion and future mining would occur in deeper, thinner seams, with more complex geology, and in areas near abandoned mines. The CEOs were concerned that the general public believed that electricity comes from wall sockets. The mining industry contribution to the U.S. economy (i.e., ~3% of the gross national product) is not appreciated by the general public as well as by many environmentally sensitive members of Congress. The DOE facilitators privately stated that the mining industry CEOs participating in the visioning conference appeared to be "pistol whipped" by the environmental movement to a much greater degree than any other industry in the DOE EE program. The CEOs wanted to find ways to reach out to the public and make them aware of the critical importance of mining to the American way of life. The CEOs stated that coal reserves were being sterilized at an alarming rate. Sterilization is a mining industry term referring to the withdrawal of minable coal reserves from mine development. Examples include the withdrawal of the Kaiparowits Plateau in southern Utah and the Valle Vidal in northern New Mexico coal fields from mine development. Federal mine laws requiring barriers of coal surrounding metal gas well pipe and



near abandoned mines as well as restrictions on mountain-top mining add to the sterilization issue. Wealthy environmentally conscious landowners are withdrawing large tracks of land from energy development. The CEOs believed that development of detection technology would reduce the sterilization problem. The 1989 National Mining Association (NMA)/Department of Energy (DOE) Energy Efficiency (EE) and 2010 NRC/National Engineering Academy (NEA) Road Map technology gaps are prioritized in Table 1.1. Table 1-1. Needed Technologies Identified by the National Mining Association and the National

Research Council.

1989 NMA/DOE 2010 NRC/NEA Mine-wide wireless emergency, post-accident, and operational radio communications.

Protect people.

Resource characterization: develop borehole and in-mine instrumentation and 3-D tomography imaging technology to map geologic structure in and surrounding a deposit. Map paleochannels in coal deposits, and faults, dikes, and rapidly thinning coal seams. Map non-linear fields in deposits.

Make the Earth transparent.

Remote sensing of boundaries of low-grade ore and boundaries contaminated with toxic waste such as mercury, arsenic, and heavy metals.

Mining beyond boundaries leads to layer contamination and unprofitable extraction. Reducing the environmental footprint by preventing mining beyond boundaries that lead to contamination of the run-of-mine product.

Preventing rotating cutting drum picks from striking sandstone seam boundaries.

Detecting abandoned mines to prevent water inundation (e.g., Quecreek).

Guided directional drilling for degasification of coal beds ahead of mining. In-situ leaching and metallurgical processing. Undertake, engineer, and control subsurface processes.

Protect fresh water aquifers.

The CEOs are made villains by the news media, United Mine Workers of America (UMWA) lobbying, and family members during the days following a mine disaster. The news media asks, "Where are the miners trapped, and why can we not communicate with them?” The CEOs were appealing for a wireless communications system that would remain functional in emergency and post-disaster conditions. If the emergency is not resolved within the first few minutes, the problem gets out of control and post-accident communications are needed. Miners in motion must be in wireless voice contact and their location known during emergencies, when trapped, and when following escaping miners out of the mine.



The CEOs stated that imaging ahead of mining was essential in mapping geologic anomalies in the coal bed, such as faults; partial seam faults (i.e., displacements of less than 6 inches); dikes; margins of changing roof boundary rock, which is the leading cause of roof-fall injuries and roof collapse; burnt coal zones; and paleo sandstone channels, which cause scouring and roles in the coal seam. Imaging between boreholes is needed to map halos of mineralization (i.e., ore grade) and the structure of intrusive magmatic mineralization. Drilling and coring is still required for reserve confirmation, delineation and, exploration. The CEOs stated that imaging between exploration and delineation holes would increase the value of the drilling program in developing a mine plan. In-situ mining requires the detection and mapping of horizontal mudstone lenses in permeable aquifers. Lenses deflect leachant flow, altering the zone of hydraulic depression established between the injection and production wells, which contributes to contamination of the aquifer and disruption of remediation. Leachant flow restrictions are a problem in heap leaching recovery.

1.2 Coal Resource Data Coal provides 27% of the world's energy demand and fuels 41% of the global electricity generation. Global demand and consumption of electricity is forecasted to increase during the next 20 years at the rate of about 2.5%/year. This rate compares to the expected increase in U.S. coal demand of 1.1%/year. World coal consumption was 10 billion tons in 2010 as compared to 6.7 billion tons in 2006. China's coal production in 2008 was 2.7 billion tons (i.e., 42% of world production) followed by the U.S. with 1.062 billion tons (18%), with 40% coming from underground mining. U.S. coal accounts for 94% of this nation's fossil energy. The U.S. has 571 underground coal mines averaging a production rate of 709,000 tons/mine-year. The 19 western U.S. mines have an average production rate of 2,877,053 tons/mine-year. The 800 continuous mining machines (CM) produce 58% of the underground coal. In Australia, 48 underground mines have an average production rate of 2,522,356 tons/mine-year. China is fueling its economy with coal and has 460 plants under construction. China is building steel mills on offshore islands using metallurgical coal from the Rocky Mountain, Appalachian, and Australian coal fields. There are approximately 600 coal-fired generating facilities in the U.S., including 1,470 generating units and 1,000 manufacturing facilities burning coal. Production from more geologically complex deposits will require significant advances in technology and its utilization to continue the trend toward safer and more productive mining. In 1970, the U.S. was the "Saudi Arabia" of world coal resources, with 36% of reserves and 350 years of coal production remaining. By 1998, the CEOs agreed that less than 250 years remained. The Special Committee of the Earth Resources Engineering Section 11 of the National Academy of Engineering reported in November 2010 that there are 200 hundred years of coal production remaining. The U.S. Energy Information Administration (EIA) Annual Energy Outlook, published in April 2011, concluded that U.S. recoverable reserves would be exhausted in 119 years if no new reserves were added. Between 1970 and 2011, 231 years of coal production vanished with an annual average sterilization rate of 5.6 years per year. The rate of sterilization can be decreased with technology advances. The 1970 baseline estimate of reserves may have been wrong. The actual rate needs to be recognized by coal energy policy makers.



Figure 1-2 illustrates the coal reserves distribution in the lower 48 states. Coal formed in the late ceuitantous period appears in the western states, while Pennsylvanian period coals were deposited in the east. Table 1 summarizes the underground and surface coal reserves in 10 states with the largest total reserves. Figure 1-3 illustrates the U.S. coal resources and reserves.

Figure 1-2. Map of U.S. Coal Reserves.

There are several measures of how much coal is left, based on various degrees of geologic certainty and economic feasibility. The total resources including estimates of undiscovered coal is 4 trillion tons. The amount of recoverable coal reserves at producing mines is estimated to be 17.5 billion tons. The demonstrated reserves base that can be commercially mined is 486 billion tons. The recoverable reserves that can be mined with current technology considering accessibility constraints and recovery factors is 261 billion tons, about 54% of the demonstrated reserve base. U.S. coal demand will increase at 1.1%/year for the period 2009 to 2035. If that growth rate continues, recoverable coal reserves will be exhausted in 119 years. There are an uncountable number of reasons that coal reserves may not be safely and profitably mined even with advanced and enhanced technology. Each person in the U.S. uses 3.7 tons of coal annually as compared with Europe with per capita use of 1.2 tons/year. Energy policy makers should realize that the coal fields of Utah, New Mexico, and the Appalachian region are rapidly becoming sterilized and withdrawn from production. Coal will not continue as an abundant low cost (i.e., $2.27 per million Btu in 2011) fuel supply.



Table 1-2. U.S. Coal Reserves by State (Billions of Tons).

Figure 1-3. U.S. Coal Resources and Reserves.



2.0 MINE-WIDE WIRELESS EMERGENCY, POST-ACCIDENT, AND OPERATIONAL COMMUNICATIONS

2.1 Impact of the Farmington Mine Disaster The Farmington Mine disaster, the 1968-high energy methane gas and energetic coal dust explosion probably caused by mining into an abandoned gas well casing, trapped and killed 79 miners. Days went by while families, news organizations, and rescue teams wondered why they could not communicate with the trapped miners. The disaster awakened the national conscience and Congress took action by tasking the National Research Council (NRC) to investigate and recommend a course of action to improve underground mining safety. Congress enacted the Federal Coal Mine Health and Safety Act of 1969, which was amended in 1977, and appropriated funds for the U.S. Bureau of Mines (USBM) to develop programs that overcome technology gaps. Through the 1970s to 1995 when the USBM was defunded, the USBM formulated and conducted well-conceived programs for improving mine communications, including post-accident signaling (i.e., text messages) and voice communications with trapped miners. The programs included ground control, ventilation, fire suppression, and many other relevant safety issues. Unfortunately, the challenge of providing cost-effective wireless mine-wide emergency, post-accident, and operational communications has remained unsolved since the Farmington Mine disaster. The USBM leadership recruited the National Bureau of Standards (NBS), now the National Institute of Standards and Technology (NIST), theoretical scientists Drs. James C. Wait and David A. Hill, both fellows of the Institute of Electrical and Electronics Engineering (IEEE), to develop the "radio geophysics" theory underlying the propagation of electromagnetic energy through slightly conductive media as well as the five robust natural waveguides created by underground mine infrastructure. Hill and Wait were adjunct professors of the University of Colorado College of Engineering and Applied Science. The collection of Wait and Hill (Hill 1984, 1985, 1989, 1990a, 1990b, 1992, and1994; Wait and Hill 1974; and Wait 1963, and1983) papers established the technical guidelines for the USBM technology development road map. It is important to stress that these commercially independent scientists "got the physics right" on the forward development path. The USBM contracted with universities and industry research and development (R&D) teams to design and build experimental (i.e., received MSHA experimental approval) hardware for in-mine validation, verification, and demonstrations of the Wait/Hill radio geophysics theory. The USBM leadership recognized that development and demonstrations can be successfully achieved with government programs; however, effective implementation and sustainability requires partnering with the mine-service sector of the mining industry. Prestigious laboratories, R&D organizations, and consultants often fail to recognize that the natural media dielectric constant is complex. Their inexperience contributes to underestimating the very time-consuming and difficult problems of conducting validation and verification experiments in an operating mine located in a remote area of the U.S. The problem is magnified by the interactive redesign process required in achieving MSHA intrinsic safety (IS) approvals of battery-powered, signaling devices, which involve challenging technical innovations such as replacing current limiting resistors with ultra fast acting triply redundant electronic switches, often require as much



as 36 months. This lengthy approval process is a testimony to the difficulty and thoroughness required to ensure that equipment will operate in a fail-safe manner in the dangerous and explosive environment of an underground mine. Unfortunately, IS design theory is not taught in accredited university-based engineering and applied science departments. The commercial surface-based telecommunications industry was expected to manufacture, market, and service the equipment for the small U.S. underground mining market, which presently consists of 550 coal mines, of which 150 are located in West Virginia, as well as 102 metal underground mines. The technology teams successfully validated and demonstrated the Wait/Hill expectation of wireless ultra low-frequency band (i.e., 300 to 3,000 Hz) through-the-Earth (TTE), mine-wide wireless low-frequency band (i.e., 30 to 300 kHz), and medium-frequency band (i.e., 300 to 3,000 kHz) emergency and operational communications prototype equipment in the five robust natural waveguides associated with the underground mine infrastructure. Accident investigations found that three-phase AC electrical power distribution and supporting messenger cables survived catastrophic events. This finding ensured that a robust EM signal distribution antenna and transmission facility taught by Hill/Wait for wireless medium frequency (MF) communications with miners on the move was already available in underground mines. After completing the first in-mine demonstration of prototype MF transceivers, the leading telecommunications company in the U.S. found the underground mining environment to be too difficult and costly to continue development activities. From a business point of view, the market was too small to achieve the business objectives of the company and they withdrew from the market. The USBM issued a second contract to engage a well-respected mining industry supplier of pager and trolley phone communications products as well as an R&D organization with military radio experience to design and build prototype narrow-band, medium-frequency FM transceivers for demonstrations in fresh-air entries. Hill and Wait examined leaky-feeder cable technology for underground mine applications and concluded that the system would not withstand a mine fire or explosion and could not be relied on for use in post-accident communications. Because leaky-feeder equipment operating in the very high frequency (i.e., 30 to 300 MHz) band was already in use in tunnels and hard rock mines, prototype equipment was not included in the USBM hardware development program. For completeness, in-mine EM propagation studies were conducted in the MF, very high frequency (VHF), and ultra high-frequency (UHF) bands (i.e., 300 to 3,000 MHz). The test demonstrated that air-filled entries and tunnels are waveguides that exhibit a cut-off frequency. Below the cut-off frequency, the propagation constant is imaginary and evanescent modes EM waves cannot propagate. The cut-off frequency depends on the physical dimensions of escape-way entries. The dimensions of a typical entry place the cut-off frequency in the VHF band allowing wave propagation at higher frequencies in the UHF band. The propagation constant becomes imaginary in accidents that cause squeezing and structure collapse. The attenuation rate of VHF/UHF band EM waves through a roof fall is approximately 10 dB/foot, while attenuation rate through mine water inundations increases to over 400 dB/foot.



2.2 Impact of the Wilberg Mine Disaster The December 1984 Wilberg Mine fire, in which 27+1 miners died, was caused by an exploding air compressor and fire in the First North Mains No 4 fresh-air entry at crosscut 34.

Figure 2-1. Wilberg Mine Escape Route. The 1986 MSHA fire investigation report stated that mine management was attempting to set a production record at the time of the fire. If emergency mine-wide radio communications has been available, the only escaping miner could have given direction for the 3,000-foot walk to safety through the belt and dogleg entries then through a man door into the No. 5 return entry of the mains, shown by dark lines in Figure 2-1. Issues related to self-contained self-rescuer (SCSR) failure and training would have prevented escape of some of the miners. Following the accident, Dean Bryner, a M.S. graduate of the California Institute of Technology and Vice President of Utah Power & Light Company (UPL), whose health rapidly deteriorated, died of a broken heart. The opportunity for escape lasted for only a very few minutes requiring direct voice radio communications between miners on the move in the entries. The fire in the No. 4 intake entry of the First North Mains followed the air current injecting dense smoke, soot, and poisonous gases into the fifth right intake entry and by “stopping” leakage into the belt entry. The trapped miners were in a state of confusion and desperately tried to find alternate escape-ways. The miners on the move knew that the designated tailgate escape-way was blocked by a roof fall. Dense smoke and soot blocked the intake and belt entries near the mouth of the panel. They needed wireless radio transceivers that could communicate by voice while on the move in escape-ways while engulfed in low visibility dense smoke, soot, and dangerous gases. The SCSR mouthpiece would have prevented voice communications from the



miner on the move. That is why microphones need to be built into the mouthpiece, face mask, or pressed against the throat. The theory of organizational behavior can be applied in studying the self-rescue of the miners’ behavior during escape. The Wilberg Mine accident report gave a detailed account of the human behavior of the longwall crew during the first few minutes of the event. The mine management team received a pager telephone report from the surface that a cloud of smoke was seen by the parts deliveryman in the fresh air entry travel way. They initially thought the cloud was steam rising from the wet floor of the intake entry. The management team was at the headgate of the longwall and overheard the pager telephone information. Blake, the only survivor, just arrived at the headgate location. He donned his SCSR and proceeded with the management team, who were not wearing SCSR’s out-by to the mouth of the longwall panel where they encountered smoke at cross cut 5 (XC5). After testing man doors for heat, they entered the dogleg entry. Dense smoke engulfed the management team. The mine was managed by a pyramid organizational structure. When the management team was lost in the first few minutes of the fire, “centrality” of information flow was significantly altered, leaving every miner to find an unorganized way out. Becoming separated from the management team, Blake returned to the headgate to obtain a replacement SCSR. The investigation was able to track movements of the miners by noting the locations of discarded component parts of filter self rescuers (FSRs) and SCSRs as they were placed in service by each miner. Some SCSRs were found that were either defective or that did not properly initiate oxygen generation. This initiated significant frustration and anxiety. The account shows a state of confusion, and uncertainty during the on slot of becoming aware of being trapped. Some miners attempted escape through the bleeder and collapsed tailgate. Others just sat in a prone position along the longwall machine and wrote farewell notes to their families. Blake returned to the mouth of the panel and the dogleg encountering dense smoke. Testing man doors for heat, he discovered the way out through First North Main returns, escaping in a shocked and soot-covered condition. Brave rescue teams, essentially following Blake’s escape route, searched, located, and identified the 25 miners while fire crews battled the fire. Dean Bryner appeared before the Utah State Legislature and the Public Utilities Commission, making the case that underground mining safety and productivity development funding would be an element in the electricity rate base charged to customers. Immediately following the disaster, Dean Bryner approved UPL’s appropriation of emergency funding for designing third-generation personal carried (i.e., wearable), portable, vehicular, and repeater transceivers operating in the low frequency (LF)/MF bands. The design (see Figure 2-2) capitalized on the lessons learned in the USBM MF transceiver development program (Sacks and Chufo, 1978; Stolarczyk and Dabroski, 1989; Stolarczyk, 1991). The MF transceivers achieved the first MSHA intrinsically safe (IS) approval and created a mine-wide wireless communications system. The term “wireless” refers to the connecting link between a miner on the move and the distributed antenna and transmission facility. Mine-wide wireless and LF/ MF communication systems were installed in the InterWest, a subsidiary of UPL, remaining operating underground coal mines. The system achieved 20,000 feet of transmission distance from an IS portable transceiver at the face out-by to a base station at the



portal without requiring repeaters. Repeaters were designed to amplify the radio signal and increase the coverage area for voice communication between roving miners and miners in diesel pickups moving along 10 miles of travel-ways. Because of the 2 dB/kilometer attenuation rate in the lower end of the MF band of the already installed conductor waveguide, the repeater separation ranged between 5,000 and 10,000 feet. The repeater access frequency (F2), the distribution frequency (F1), and the intra-repeater transmission frequencies (F3 and F4) required four separate resonate loop antennas at each repeater site.

Figure 2-2. Third-Generation Intrinsically Safe Medium-Frequency Transceivers Installed in a

Western U.S. Coal Mine. (U.S. Patents 4,777,652; 4,879,755).

Repeaters are required to amplify the MF signals coming from the miners’ transceiver to overcome the transmission path attenuation and the 17 dB of transmission loss when MF signals pass by power centers. These MF systems were installed in a total of 15 coal and hard rock mines in the western U.S., which allowed many important lessons to be learned about practical system operations. Budgeting problems prevented the USBM and MSHA technologists from visiting the western demonstration sites and learning first hand the advantages, disadvantages, and limitations of the MF communications technology. This knowledge would have been useful in the drafting of a specific section (e.g., the requirement for life lines) of the MINER Act as well as directing and prioritizing the technology development road map implied by the Act. Following the publication of the MSHA Wilberg Mine accident report, MSHA, not being in full communications with UPL’s mine-wide MF communications initiative, believed that wireless communications equipment was not commercially available. MSHA interpreted "wireless” communications to mean a "redundant wired pager telephone system." Thus, redundant and inexpensive (i.e., ~ $40/phone instead of $100,000 for a wireless MF system) wired pager



telephone systems were rapidly installed in all U.S. underground mines connecting the operating face to the surface-monitoring center. In 1995, the "Contract with America" movement in the U.S. Congress defunded the USBM, leaving the mining industry without R&D support for safety and health projects. The leading factor influencing the congressional defunding action occurred because the USBM cut back travel funds for mine visits, which left mining executives with the impression that the USBM was just a duplication of MSHA. In contrast to the situation in the U.S., Australia, where mining revenues are 14% of gross national product (GNP), technology development organizations were formed, such as the Australian Coal Research Industries Laboratory (ACRIL) and the Australian Mining Industry Research Association (AMIRA). These organizations include technology representatives from the mining industry, universities, and government laboratories, such as the Commonwealth Scientific and Industrial Research Organization (CSIRO), which has a mission similar to that of National Institute of Standards and Technology in the U.S. The national scientific brain trust of Australia is brought together in full communication with the mining industry. These quasi government-industry-university organizations are organized to develop, broker, and facilitate collaborative research projects, which are jointly funded with shared benefits. Similarly, in China, the Coal Research Institute conducts research, development, and production activities related to underground mining. Mines in the U.S. are production organizations with highly developed safety, health, and operational training programs. Miner's tasks and responsibilities are directed at out-shift to in-shift coordination meetings. When performing duties underground, miners follow prescribed directives and ordinarily do not participate in experimental R&D activities. In-mine verification and validation activities are rare, very costly, and disruptive to the mining company. Early adopter companies need to receive tax credits for “needed technology” development, demonstration, and installation of unproven equipment. The 1991 MSHA redundant wired pager telephone rule making gave the mining industry no compelling reason to complete development (lesson learned guidelines) and adopt the intrinsically safe mine-wide, wireless Wait/Hill communications technology. The August 1987 MSHA Wilberg Mine accident report could have been of lasting importance in improving mine safety if the root cause of the disaster had not been blamed on managers of the Wilberg Mine attempting to set a longwall production record and the focus placed on the faulty air compressor. A common thread among mine accidents is the dust cloud of non-science that obscures the science underlying the root cause of the accident. Accident investigations should not only include MSHA, the mining company, state regulators, geologists and representatives of the miners (e.g., United Mine Workers of America), but should emulate the Challenger Accident Investigation Commission chaired by eminently qualified and independent scientists like physicist, Richard Feynman.3

3 Richard P. Feyman (1918-1988) was an American physicist, educator and Nobel Prize winner known for his work in path integral formulations of Quantum mechanics. Chair of the 1986 space shuttle challenger disaster.



No more than 13 miners were required to operate InterWest longwalls. The reason 27 miners died was the fear that the longwall could become "iron bound" when mining through the difficult mining conditions caused by a sandstone paleochannel (see, for example, Figures 2-3 and 2-6). The mine management and crew attempted to maximize the mining advance rate to reduce the roof-rock-fall hazard.

Figure 2-3. Cross Section of the High-Energy Cutbank Region of a Paleochannel.

The cross section shown in Figure 2-3 illustrates the fracturing of the roof rock and scouring of the high-energy channel into the coal seam. The roll in the seam is caused by differential compaction and thinning of the coal seam directly under the channel. Oftentimes, the sandstone is a freshwater aquifer that increases the water content in the fractured and compacted coal. The UPL mine management and longwall crew experienced “iron bound” conditions in their very first longwall panel. The “iron-bound” conditions occur when the machines intersect a full face of sandstone and roof caving immediately behind the roof supports trapping the machine. This experience taught the crew to advance as fast as possible when bad roof conditions are evident. Along the eastern edge of the Wilberg coal mine paleochannel, the tailgate return entry roof fall blocked this escape-way. From the point of view of an advancing longwall shearer operator, the horizon of the roof coal-rock boundary appears to suddenly drop down exposing a wall of hard sandstone in the face. In Figure 2-3, the longwall is advancing from right to left as denoted by the red dashed lines. The coal seam roof horizon drops below the normal floor coal-rock boundary caused by a "roll" in the coal bed. One of mining’s worst nightmares, the machine must move quickly forward because stress forces rapidly increase with time as the seam structural geology begins to fail. Caving migrates upward into the strata creating “cathedral-like” space above the entry. Dangerous drilling, roof bolting, and injection of resin is required to stop the caving. If the sandstone is hard, the "face" sandstone must be drilled to insert explosives into the rock face. Blasting paleochannel face rock may create high-energy rock projectiles that can damage the



longwall machine roof supports and shearers. When the roll is known in advance, the machine shearer operator initiates a floor rock cut sequence, as indicted by the yellow dashed lines, before reaching the roll to provide machine clearances. Along the margin of the channel, the roof rock is fractured by the non-linear stress fields. Mine safety could be advanced if remote stress detection (e.g., via acoustic waves) and imaging (e.g., via radio waves) technologies were an adopted routine in “operational best practices.” As the longwall retreats forward, the stress field increases in advance of the face. The Wilberg Mine fifth right longwall crew installed wooden cribbing to reduce “squeezing” and floor heave. The longwall crew was drilling and injecting Roklok resin into the fractured rock to strengthen it when the air compressor (at XC34) over heated and blew up causing a flash fire in the fresh Mains No. 4 air intake of the First North Mains. Even through the air compressor temperature sensor was defective, the air compressor was operating during 69 shifts prior to the accident. The MSHA report should have concluded that paleochannel geology was the root cause of the accident. Longwall panel tomographic imaging in advance of mining could have detected and mapped the paleochannel, giving guidance to applying appropriate ground control measures in advance of mining.

2.3 Quecreek Mine Inundation The Quecreek Mine disaster was caused by mining into the water filled abandoned Saxman Mine. The Quecreek miners retreated into the compressed air entries of the seven entry developments. Compressed air was created by the Saxman Mine water flooding of the escape entries and backing up into the upper right-side entries. The No. 1 development entry intersection with the Saxman Mine is shown on the lower right side of Figure 2-4. The Saxman Mine breach is shown in Figure 2-5.



Figure 2-4. Location of the Trapped Miners in the Quecreek Mine Disaster.

Figure 2-5. Saxman Mine Breach.

The continuous mining machine rotating cutting drum stopped approximately two feet from the water filled void in the Saxman Mine. The machine operator left the machine shortly before the



breach occurred. The modeling of the stress field by Dr. Yi Lui of West Virginia University is shown in Figure 2-6. The stress field reaches a maximum approximately two feet into the rib, which is approximately where the breach occurred. Often, the ribs are fractured up to a depth of four feet in a developed entry.

Figure 2-6. Stress Field Surrounding a Developed Entry. (After Dr. Yi Luo, Mining Engineering

Department, West Virginia University).

2.4 Sago Mine Explosion The Sago Mine owned by International Coal Group experienced a methane gas explosion behind seals in an abandoned part of the mine in 2006. The explosion trapped 12 miners without a means to communicate with the surface. Trapped 13,000 feet from the surface, they erected their barricade, harboring their oxygen generators (i.e., SCSRs) and scribbling notes to their families. If post-accident communications were available, there could have been instructions for a 1,500-foot walk to fresh air.



Figure 2-7. Location of Barricaded Miners.

The following text is from the MSHA investigation report.

Many of the following details concerning the events of the 2nd Left Parallel miners were obtained from physical evidence gathered during the investigation and from interviews of various mine rescue team members. Other details were provided by Randal McCloy, Jr. the lone survivor He provided investigators with valuable information that only he would know. However, McCloy was still recovering from the effects of the accident at the time of his interview. As the crew made their way to the 2nd Left Parallel section, McCloy did not recall speaking to or seeing Helms. The crew arrived on the section and exited the mantrip. The crew was walking toward the face when the explosion occurred. The initial effects of the explosion were noise, pressure, wind, and a haze. McCloy stated he was not knocked over. There was pressure, but his ears did not pop. McCloy stated that Martin Toler took charge and gathered everyone together after the explosion. McCloy indicated that no one tried to call out because all of the communication devices were damaged. He did not know if anyone tried to use the handheld radio communication system but he did not think it would have worked. McCloy stated that they boarded the mantrip operated by Martin Toler and started out-by on the track entry in an attempt to escape. During their travel out-by, they encountered an atmosphere filled with smoke. They continued out-by until the mantrip hit debris on the track at 10 Crosscut, No. 6 Belt. They exited the mantrip.



A mine rescue team later indicated that the mantrip appeared to have encountered an Omega block that had been blown into the center of the track between the rails. The mantrip appeared to have come in contact with the block and moved it in the out-by direction. As the block moved forward, the soot deposited on the gravel between the track rails was disturbed. It also appeared that the mantrip was then moved in-by away from the block about two to three feet. The crew donned their SCSRs, but McCloy could not remember exactly where or when. The top and bottom covers from 12 SCSRs were found at 11 Crosscut, No. 6 Belt in the No. 7 entry. According to McCloy, Martin Toler suggested that they don their SCSRs because they were in a small amount of smoke. McCloy stated that his SCSR worked fine, but that the SCSRs used by Groves, Anderson, Jesse Jones and Martin Toler did not work. McCloy indicated that he thought the other miners seemed to know how they worked, and indicated that they had been trained in their use numerous times. McCloy indicated that when they discovered that the SCSRs did not work, there was some yelling and there was a lot of controversy. When asked how he knew that the SCSRs did not work he stated that it was a “no-brainer,” since the miners had been trained extensively. He also indicated that the crew had to remove the mouthpieces from their SCSRs in order to communicate. At some point, Groves gave his SCSR to McCloy because Groves could not get it started. McCloy worked with the unit in an unsuccessful attempt to get the unit to work. McCloy stated the 2nd Left Parallel crew attempted to evacuate, and Martin Toler encouraged everyone to stay together. They tried several places to get out but everywhere they went it was smoky. However, McCloy said the visibility was never so poor that it was necessary to place their hands on each other or attach themselves in some manner like mine rescue teams. A mine rescue team found footprints in the soot on the mine floor indicating that the 2nd Left Parallel crew traveled to 11 Crosscut, No. 6 Belt in the No. 7 entry where they apparently donned their SCSRs. The team continued to follow the footprints out-by in the No. 7 entry a crosscut or two until they could no longer see the footprints. Due to the smoke filled atmosphere limiting visibility, toxic gases, destroyed stoppings, and the debris on the track, the crew may have felt that all their options were exhausted, and there was no way out. They may have theorized that to try to travel on foot as a group in an attempt to escape would be extremely difficult. Although all of the information that was available to the 2nd Left Parallel crew as they were considering their options is not known, it is possible to consider what information they may have had. They knew that the 1st Left crew had entered the mine after them. They knew that the mine had been idle the previous shift. They knew the mine was not very gassy. Although they knew the results of the preshift examination for the 2nd Left



Parallel section, they may not have known the results for the preshift examination for the 1st Left section. History has indicated that most explosions are the results of the actions of men or machinery. Based on these considerations, it is possible they believed that an explosion occurred in the 1st Left section as the crew entered the section or just shortly thereafter. It would not have been likely that they would have considered an explosion originating from behind the sealed area. Although explosions had occurred in the past damaging seals, there was no history of an explosion of this magnitude or level of destruction. There was no obvious ignition source present, such as spontaneous combustion or an active fire. If they considered that the explosion had originated in the 1st Left section, then the conditions observed on the 2nd Left Parallel section would not be as destructive as what they may have expected to encounter in the mains as they attempted to escape. They may have considered the distance that they would have to travel and speculated that it would be impossible for them to accomplish it safely. Martin Toler suggested that they go back to the section. Everyone agreed to go back to the section. As they traveled back toward the section in the belt line, they initially could not see very well. They decided to build a barricade. McCloy recalled Martin Toler directing the installation of the barricade curtains. Toler, Anderson and McCloy assisted in the installation of the curtains. He thought that there could have been additional miners helping but could not recall who. They tried to make them “leak-free.” They decided to use curtain material from the face area since some of the crew indicated their SCSRs were not working. Although there was concrete block nearby, they felt that using block would take more work and “it would just not work.” McCloy recalled that visibility was good during installation of the curtains. He said that he removed his SCSR during the installation process. Once behind the barricade, it took several hours before the miners calmed down. They turned all their cap lamps off except for one, as Martin Toler suggested. There was conversation between them. The area they were in was large, and they would have to shout to each other at times. McCloy indicated that the crew thought they would be rescued. They took turns using a sledgehammer to bang on a roof bolt. McCloy said that as each miner took his turn, he would take off his SCSR because he would get exhausted. McCloy said that this was the only time he removed his SCSR. McCloy thought that rescuers would bring the machine that locates people to the mine. According to McCloy, the crew thought that they would hear shots on the surface, rescuers would drill a hole in the right spot, and they would be taken out. They thought that they would be rescued, and discussed how long it would take. However, as time passed it did not look good. They were waiting for the borehole but felt that the rescuers must not have had the right equipment. McCloy indicated that about an hour and a half after entering the barricade, Martin Toler



and Anderson exited it. They walked to the power center across from the tailpiece. He thought that they did not have SCSRs with them. He believed that they were looking to see if the air was clearing and to see how far they could get. They made it to the power center but then returned. When they re-entered the barricade, they were coughing and gagging, and were exhausted. McCloy said that Toler and Anderson said that there was too much smoke and that it was hard to breathe. While in the barricade, McCloy removed his goggles. McCloy shared his SCSR with Groves while in the barricade. He was aggravated that Groves’ SCSR would not work, so he again made an unsuccessful attempt to get it to function. McCloy said that his and other miners’ SCSRs were depleted, but he could not recall whose.

Following the explosion, the trapped miners believed that the mine’s escape-way was blocked. The pager telephone communications cable had been disabled. They were unable to receive information that the escape-way was not blocked. Like the Wilberg accident, mine-wide wireless communications were needed with miners in a state of confusion, in low visibility conditions, wearing SCSRs, desperate, and on the move.

2.5 Congressional Response to Mine Disasters Devastating underground mine disasters starting with Jim Walter Resources No. 5 (2001; methane ignition), Quecreek (2002; water inundation), Sago (2006; lighting ignition of methane), Alma No 1 (2006) and Darby No. 1 (2006) shocked the national conscious, initiating congressional action and mandates for the installation of mine-wide wireless post-accident communications and tracking facilities. Most recently, Crandall Canyon (2007; pillar failure), Upper Big Branch (2010; cutting edges strike sandstone and ignition of methane and energetic coal dust) and Jellico (2011; water inundation) demonstrated that the mandates of the laws of radio geophysics theory need to be considered when validating communications and tracking networks as a solution to the post-accident problem. Congressman George Miller, Chairman of the Education and Labor Subcommittee, and his staff conducted hearings with testimony by MSHA, UMWA, NMA, family members, and other stakeholders. Absent from the hearings was Dr. David A. Hill, who has the ability to provide unbiased and experienced testimony about the "golden rules of radio geophysics theory" that he and the late James C. Wait developed for underground radio communications. He would have explained why commercial off-the-shelf (COTS) wide bandwidth VHF/UHF communication equipment, such as leaky-feeder communications equipment, cannot be relied on in emergency and post-accident conditions. He would have said that leaky-feeder cable is favorable for operational communications and creates a distributed antenna and a transmission facility enabling a wireless link to miners in motion. He would have recommended that leaky-feeder technology be advanced in design to improve the current state-of-the-art and installed in U.S. mines for operational communications. The system will improve safety and productivity. As in the Wilberg Mine disaster, the national news organizations and hearings were hostile to the management of the Sago mining company, vilifying the management and emphasizing a consistent pattern of violations. Along with the mining families, the mining industry suffered



through a tragic nightmare. Criminalization was lobbied for in Congress for managers and supervisors receiving multiple citations. Yet, MSHA citations convey a notice that a dangerous condition must be addressed and is not an indictment of wrong doing. During this time period of congressional action, the NMA safety committee followed a constructive policy to support the post-accident communications and tracking requirement proposed in the drafting of the MINER Act. The MINER Act states that:

“Not later than 3 years after the date of the enactment of the Mine Improvement and New Emergency Response Act of 2006, a plan shall, to be approved, provide for post accident communication between underground and surface personnel via a wireless two-way medium and provide for an electronic tracking system permitting surface personnel to determine the location of any persons trapped underground or set forth within the plan the reason such provisions can not be adopted. Where the plan sets forth the reasons such provisions can not be adopted, the plan shall also set forth the operator’s alternative means of compliance. Such alternative shall approximate, as closely as possible, the degree of functional utility and safety protection provided by the wireless two-way medium and tracking system referred to in this subpart.”

The term “wireless” in the context of underground mining means a radio link between the miner on the move and the distributed antenna and transmission facility of the conductor waveguide lifeline installed in every entry. Because post-accident wireless communications equipment was not commercially available, the MINER Act language was once again interpreted by MSHA to mean redundant communications facilities. The West Virginia Office of Miner's Health, Safety, and Training established early mandates for installing wireless communications and tracking equipment. Leaky-feeder cable communication systems, developed in Europe for tunnel communications in the 1970s, were installed in the mine passageways of some underground coal mines (Martin, 1978). By 2009, redundant "wired” communication systems were installed at a cost to the industry of more than $1 billion. In 2007, the MSHA administrator wrote a letter to Congress saying that if leaky-feeder cable technology were to be installed in underground mines, there would be no compelling reason to develop and install wireless communications systems when they became available in the future. The MINER Act of 2006 recreated the USBM safety and health research and development function under the Secretary of the Department of Health and Human Services, the Director of the Centers for Disease Control and Prevention (CDCP), the Director of the National Institute of Occupational Safety and Health (NIOSH), and finally the Office of the Associate Director of Mine Safety and Health Research (OMSHR). The NIOSH OMSHR technologists and their advisors, all eminently qualified scientists, engineers, technicians, and mining industry technologists, established a program that held promise in realizing the technical research objectives set forth in the congressional mandate of the MINER Act. Because of budget limitations, the OMSHR staff and their advisors, many of whom were former USBM employees, did not fully appreciate the lessons learned in the mine installations and operational experiences associated with the MF communications system developed earlier.



The NIOSH communications and tracking equipment, mine seals research, self-contained rescue devices, and refuge chambers development programs were funded by the Emergency Supplemental Appropriations Bills of 2007 and 2008 at a level of $21 million and were directed by an Associate Director of OMSHR for mining, a highly respected former professor from a leading university with a mining school. The communications and tracking system deadline for installation was June 15, 2011. Three working groups were established with one group providing advice on priorities in mine safety and health research, including grants and contracts for research. See, for example:

www.CDC.gov/NIOSH/mining/miner act/communicationandtracking.htm Twenty-three projects directed at exceeding the prevailing state-of-the-art in underground mine communications and tracking equipment were completed at an average project expenditure of $913,000, including an estimated direct cost expenditure of $304,000. Discounting material purchases, an average of one full-time equivalent technologist was allocated to each project. Breakthroughs in the state-of-the-art in the research phase and overcoming acceptance resistance in the introduction phase of the underground mining product life cycle are costly and can easily exceed $10 million per in-mine project. Congress seriously underfunded the MINER Act technology development needs. A total of $70 million was authorized in the Senate Energy and Water Bill for the NMA technology development roadmap with $20 million appropriated and then misplaced somewhere within the U.S. Department of Energy. Five NIOSH contracts supported the design and evaluation of through-the-Earth (TTE) emergency communications devices. Three contracts were directed at the development of MF band technologies. For example, interagency funding was provided for the National Institute of Standards and Technology (NIST) to develop MF and UHF modeling tools for mesh networks. Interagency funding to the U.S. Army Communications-Electronics Research, Development and Engineering Center (CERDEC) to take advantage of an ongoing military program supported a consulting organization to develop production ready analog MF radio equipment including cross over repeaters with digital capabilities. The remaining two contracts were focused on well-developed physics and very successful commercialization of office/surface UHF band mesh networks, using an IEEE protocol, and enhancing leaky-feeder communications and tracking equipment. Novak, Snyder, and Kohler (2010) describe the operation, application, advantages, and disadvantages of enhanced leaky-feeder, wireless mesh, and MF systems developed by the OMSHR contractors. In addition, how to accomplish the wireless communications and tracking objectives of the MINER Act in OMSHR’s view is explained. The leaky-feeder and mesh network enhancements were designed for operational as well as emergency communications and tracking with the additional benefits of expanded capabilities. For example, a roving miner wearing a UHF radio, which is in the MSHA IS approval process, can establish a wireless communications link with the distributed antenna and transmission facility of the leaky-feeder and mesh networks. One of the stated disadvantages of MF systems is that such systems cannot be used for primary communications except in small mines. Another disadvantage is that the MF transceiver carrying case is the size of a brief case and cannot be worn like a VHF/UHF radio. Furthermore, an MF system cannot facilitate the tracking objective of the MINER Act.



Under an Interagency Agreement, the Joint Spectrum Center of the Defense Information Systems Agency developed and commented on the EM propagation models for the frequency bands and modes supported by the infrastructure of an underground mine. With a more thorough understanding of the in-mine propagation data and experience acquired in operational communications in western U.S. mines, the transmission line theory could have been expanded to include a full understanding of the fundamental laws governing mode conversion from bi-filar to mono-filar, or vice versa, and how dead zones can be avoided by changing the way electrical cables are deployed in a mine. This information would have been exceedingly important in formulating the MINER Act requirement for lifeline conductor waveguides and how they are deployed. Why shielded parallel resonant loop antennas are used in receiver circuits and series resonate loop antennas are used when radiating should have been known, which could have provided an understanding of the radio geophysics governing intrinsic safety of radiating magnetic and electric dipole antennas. Souryal, Valoit, Guo, Moayer, Damiano, and Snyder (2010) describe MF mesh network modeling tools applied in determining performance metrics such as end-to-end delay and packet delivery rate. Mesh networks are designed with " nodes " that receive and then re-transmit digital data following a protocol. Bandwidth efficient minimum shift key (MSK) modulation methods have been of great importance in the digital data transmission for control and automation of mining equipment. Mesh network protocols enable routing of information through other nodes in the network to the destination. The protocol establishes an alternative (i.e., self-healing) path in case the direct path becomes disabled. Transmission requires sufficient bandwidth to support digital modulation schemes and may operate in the MF and UHF bands. The MF mesh network that was analyzed operated at a transmission bit rate of 26 kHz. Development of a digital repeater is reported now underway. Commercially available analog, in contrast to digital, VHF/UHF band leaky-feeder cable system equipment was ruggedized and enhanced in OMSHR projects to include IS features and UHF capabilities. The MSHA IS approved, commercial-of-the-shelf, wearable radio transceivers established a VHF/UHF wireless communications link between miners on the move and the distributed antenna and transmission facility of the leaky-feeder system. The leaky-feeder cable is installed in the fresh-air, man and material entries with "T" couplers inserted at several-hundred-foot intervals along the cable. A coupler with an attached long coaxial cable passes through crosscuts to a directional antenna, extending the radio coverage area into nearby entries. These antennas are not likely to withstand an explosion or fire. The OMSHR technologists believed that the leaky-feeder cable was not robust enough and needed a redundant path to the surface to comply with MSHA's interpretation of the MINER Act. A VHF/UHF to MF bridge repeater was added to the robust conductor waveguide to provide a robust redundant signal path to the surface. Working sections or face areas in coal mines are rapidly moving forward, creating a challenge for the timely extension of the leaky-feeder cable. The bridge repeater is connected to the end of the leaky-feeder cable and converts the radio signal to MF for transmission on the cables serving the power needs of the face. A second repeater converts the signal back to the VHF/UHF band to establish communications with the roving miners in the face area. Roving miners working in the vicinity of the face use the wireless VHF/UHF radio link to communicate with the network.



Special amplifiers are under development to improve redundancy in leaky-feeder cable systems. The UHF mesh and leaky-feeder system technical teams partnered with mining companies in "early-adopter" demonstrations in the introduction phase of the product life cycle. Some of the mines rejected the UHF mesh network system because of the very short distance spacing requirements between nodes (i.e., 1,000 feet) and the consequential requirement of a significant number of nodes in the average mine. Because the mesh node equipment are repeaters, the data rate slows down when received and re-transmitted in passing through a node, making the operational aspects of mesh network transmission systems non-competitive with fiber-optic transmission of video and high speed data. Fiber-optic transmission systems are ideal for transmitting video and high-speed data, but such systems are not likely to remain operational following a Farmington accident-like methane ignition, a high-energy coal dust explosion, or a Wilberg-like fire. Unfortunately, the mining industry did not have to wait very long before the next mine disaster occurred along with the proof that wide bandwidth leaky-feeder technology is not appropriate for emergency and post-accident communications. On August 5, 2010, the Massey Energy Company Upper Big Branch coal mine exploded killing 29 miners. The MSHA administrator4 for coal mine safety, Kevin Strickland, concluded that the likely cause of the accident was a coal dust explosion that propagated from a methane ignition. The longwall shearer rotating cutting drum steel cutting edges (i.e., picks) intersected the aluminum oxide (the story of Saint Barbara, the patron saint of miners) and created an energy release of greater than 0.25 millijoule, causing ignition of methane gas and energetic coal dust. The partially installed leaky-feeder communication equipment could not be made to function during the rescue and recovery efforts. Early in the NIOSH equipment development program, focus group members commented on the obvious fact that leaky-feeder cable would not likely survive an event and communication is needed in entries and escape-ways that are not in travel transportation entries. Nonetheless, the installation of leaky-feeder cable systems are now at or near 100% in U.S. coal mines. The Jellico water inundation trapped three miners for 14 hours. The UHF communications and tracking mesh network failed when the access point equipment was immersed in mine water. The network features algorithmic code to self-heal and establish redundancy in the network. More than $3.5 million was invested in the development of the technology. The laws of radio geophysics mandate that electromagnetic waves are reflected at the air-water interface causing a transmission loss of 17 dB when crossing through the interface. Mine water has very high electrical conductivity because of chemical reactions causing the EM wave transmission attenuation rate to be 55 dB/foot.

2.6 Properties of Underground Distributed Antenna and Transmission Networks The fundamental radio geophysics properties of all types of underground radio frequency distributed antenna and transmission networks are illustrated in Figure 2-8.

4 “MSHA Provides Update on UBB Explosion,” Coal Age, July 2011.



Figure 2-8. Transmission Network.

The transmitter antenna radiates energy that travels along the transmission path to the receiving antenna. The radio frequency interference (RFI) and thermal noise spectra density appearing in the receiver bandwidth as noise (N) are added to the signal (S) in the receiver signal path. The electromagnetic wave electric (E) and magnetic (H) field components phase varies along the path (x) as illustrated in Figure 2-9.

Figure 2-9. Traveling Electromagnetic Waves Composed of Electric (E) and Orthogonal Magnetic (H) Field Components.

The electric and magnetic field components are “in phase” when traveling along the transmission facility. However, they are orthogonal (90°) to each other. Each field component varies sinusoidally in time at a fixed location (x). Also at a fixed instant of time (t), there is a sinusoidal variation in space along the direction of propagation (x). The distance traveled for one complete cycle is a wavelength (λ), which is represented mathematically by

rf

cε

λ = in meters, (2-1)



where c = 3 x 108 is the speed of light in meters/second, f = frequency of the energy exchange between the elctric (E) and magnetic fields (H)

in hertz, and εr = relative dielectric constant of the natural media. The electric and magnetic fields can be mathematically represented by sinusoidal waveforms that shift in phase by 360 electrical degrees when traveling a distance of one wavelength. The fields illustrated in the Figure 2-9 are detected with receiving antennas. A short vertical electrical conductor is called an vertical electric dipole (VED) and will reproduce an electromotive force (emf) voltage waveform similar to the electric field sinusoidal waveform mathematically expressed as

!

emf = hef E = C cos "t #2$x%

+ &'

( )

*

+ , , (2-2)

where hef = effective height of the antenna, E = amplitude of the electric field in volts/meter, C = maximum magnitude of the sine wave signal, ω = 2πf is the radiant frequency and f is the frequency in Hz, x = travel distance, ϕ = initial phase angle when leaving the transmitter, and t = continuing time. A small coil of wire is called a magnetic dipole and will reproduce an electromotive force (emf) voltage sinusoidal waveform similar to the magnetic field waveform illustrated in Figure 2-9. The emf voltage is derived from Faradays Law as

dtdNdAB

dtdNemf φ

−=•∫−= in volts, (2-3)

where N = number of turns of magnetic wire in building the coil, Φ = flux (webers) of the magnetic field threading the area (A) of the coil, and A = area vector enclosed by the parameter of the coil wire in square meters. The flux has a time dependence given by tie ω and given by the scaller dot product of the magnetic field and area vectors as =φ A•B in webers, (2-4)

where B = µH the magnetic field density vector in webers/square meter, H = magnitude of the magnetic field intensity in amperes/meter, and == orµµµ magnetic permeability; µo = 4π × 10-7 henries/meter and µr is the relative

magnetic permeability of the natural media. The transmission facility may be a VHF leaky-feeder cable, UHF mesh air transmission path, or MF lifeline and messenger cable waveguides. Along the path, energy is lost because of the spreading of the wave front on an expanding surface area when traveling away from the



transmitted antenna, which is the spreading loss in dB. For distance greater than 1/3 wavelength, the wave front appears to be an expanding toroidal surface expanding away from an electrically short antenna, resulting in an omni-directional antenna pattern. Arrays and configuration of antennas can be made to alter the wave front into a beam and reduce the spreading loss, known as the called antenna gain. For a uniform media, the transmission path total loss (TL) is given as TL = spreading loss + the media attenuation rate x (separation distance). (2-5) When the transmission path is through free space, the TL is due to spreading loss. With the exception that reflections will alter the TL. A comparison of attenuation loss for different media is given in Table 2-1.

Table 2-1. Comparison of Attenuation Loss as a Function of Travel Distance.

Media Attenuation Rate (dB/km) Mine water @ 300 MHz At least 180,000 Rock @ 2000 Hz 180 Coal @ 300 kHz 161 Coaxial Cable @ VHF or UHF 30 or 60 Clean air 0 dB Conductor waveguide (lifeline) 2 dB

Entries driven into natural media to create the mine infrastructure became natural waveguides for transmission of VHF/UHF band EM waves. The rectangular waveguide with dimensions a (width) and b (height) have cut-off frequencies given by

!

fcmm = c ma

"

# $

%

& ' 2

+nb"

# $ %

& ' 2(

) *

+

, -

1/ 2

in Hertz. (2-6)

For the transverse electric (TE) modes, m and n may be zero, but not simultaneously. The cut-off frequency is given by

!

fc =c2a

in Hertz, (2-7)

which means the free space wavelength at cut off frequencies is twice the largest side of the rectangle. Below the cut off frequency, evanescent EM waves will not propagate. Equation (2-7) is highly idealized and there will be attenuation loss due to finite conductivity of the tunnel walls (Delogne, 1982). Electromagnetic waves are reflected at boundaries of contrasting impedance. Constructive (destructive) interference occurs when the reflected wave is in phase (180° out of phase) with the transmission path EM wave arriving at the receiving antenna. The apparent path attenuation decreases (increases). Oftentimes, the post-accident conditions dramatically increase the path loss with the effect of decreasing the destination signal (S) to noise (N) ratio (S/N).



The separation distance (D) illustrated in Figure 2-8 is determined by maximum path loss in dB anticipated in the link budget of the communications system design. Network transmission paths (i.e., links) are designed to achieve a destination signal-to-noise (S/N) ratio of at least 10 to 15 dB depending on the modulation scheme and bit error detection/correction algorithm as illustrated in the Figure 2-10. The bit error rate (BER) rapidly improves when the S/N ratio improves from 10 to 15 dB. For example, the BER improves from 1 bit in 300 bits to 1 bit in 10 million bits when the destination S/N ratio improves from 10 to 15 dB. The communications network goes below threshold and fails when the destination S/N ratio decreases below 10 dB.

Figure 2-10. Bit Error Rate Versus the Ratio of Energy per Bit to Noise Spectral Density for

Coherent Binary Phase Shift Keyed (red trace), Non-Coherent Differential Binary Phase Shift Keyed (dashed-blue trace), and Non-Coherent Frequency Shift Keying (dashed-

green trace) Modulation Schemes. Algorithmic error detection and correction codes have been developed to improve BER; however, most link budgets are designed to achieve destination S/N ratio greater than 20 dB. The decrease in S/N ratio occurs when additional attenuation (i.e., loss in dB) is added along the transmission path through the media. The link budget for UHF mesh communication networks are designed and installed for the conditions of a minimum entry cross-section area and air-filled entries. The separation distance (D) is limited to less than 1,000 feet. Geologic “squeeze” and roof falls reduce cross-section area. Fire and mine water-filled entries dramatically increase the attenuation rate as described in Table 2-1. The electrical noise (N) illustrated in Figure 2-8 is the sum of the radio frequency interference (RFI) and thermal noise generated in the receiver signal path. The amplifiers in the signal path introduce additional noise and are accounted for by the receiver noise figure (NF). Designing transmission facilities that can remain operational in post-accident conditions require minimizing the receiver detection bandwidth. Solving the post-accident communications and



tracking problem requires a thorough understanding of importance of minimizing (i.e., optimizing) the detection bandwidth to maximize the destination S/N ratio and minimize bit error rate. Middleton’s (1987) work in communications theory describes signal detection processes that are optimum in the sense of maximizing receiver threshold detection sensitivity. The detection sensitivity ( iS ) dependence on the noise figure (NF) and the detection bandwidth (BW) of the radio frequency (RF) receiver can be mathematically determined using the block diagram shown in Figure 2-11.

→⎟⎠

⎞⎜⎝

⎛

iNS

oNS⎟⎠

⎞⎜⎝

⎛→

Figure 2-11. Receiver Specifications of Detection Sensitivity. The noise figure is defined as

o

i

NSNS

NF⎟⎠

⎞⎜⎝

⎛

⎟⎠

⎞⎜⎝

⎛

= , (2-8)

where iS is the detection sensitivity power for a specified output (S/N)o and

iN is the noise power spectral density generated in the resistive input circuits of the first stage radio frequency amplifier.

The receiver detection sensitivity is derived from the above definition of noise figure (NF) as

io N

SNSNF ⎟

⎠

⎞⎜⎝

⎛+⎟⎠

⎞⎜⎝

⎛−= 101010 log10log10log10 (2-9)

and

o

ii NSNFNS ⎟⎠

⎞⎜⎝

⎛+=− 10101010 log10log10log10log10 . (2-10)

The Johnson noise power spectral density ( )iN is given by

KTBWReN n

i ==2

, (2-11)

where K is the Boltzmann Constant Kelvinjoules o/638.1 23−× and T is the temperature in degrees Kelvin (300o K).

Combining Equations (2-10) and 2-11) gives

RF Amplifier

NF



o

i NSBWNFKTRS ⎟⎠

⎞⎜⎝

⎛+++= 1010101010 log10log10log10log10log10 . (2-12)

For an output (S/N) o = 20dB

dBm NF log 10 log 10 8.166 101020 ++−= BWST , (2-13)

where BW is the detection bandwidth of the receiver in Hz and NF is the noise figure of the receiver.

The received signal 20TS produces a 20-dB S/N ratio in the receiver detection signal path.

The first right-hand term (-166.8 dBm) represents a signal of 1.02 nanovolts that produces a S/N ratio of 20 dB in the receiver signal detection path. The far right-hand term represents the threshold detection sensitivity degradation due to receiver noise figure. Typically, a well-designed receiver will exhibit a noise figure near 2 dB. The middle term shows that the detection bandwidth (BW) is the predominant factor in the receiver design problem. Radio geophysics requires the understanding of Equation (2-13). Modulation processes that require wide occupied bandwidth significantly degrade detection sensitivity. Increasing the detection bandwidth by a factor of ten, requires an increase in transmit power by a factor of ten when compared to a companion receiver design optimized for minimum occupied bandwidth detection. A10-watt transmitter will need to be increased to 100 watts when the detection bandwidth is increased from 300 to 3,000 Hz. However, a 100-watt transmitter cannot be made intrinsically safe. The detection sensitivity of the radio frequency method (RIM) (see Section 4.0), through-the-Earth (TTE) (see Section 2.7), MF analog, and MF digital receivers is

Si20 =

!164.8dBm BW =1Hz RIM!154.8 dBm BW =100Hz TTE

!126.8 dBm BW =10 kHz MF ana log!118.8 dBm BW = 25kHz MF digital

"

#

$$

%

$$

. (2-14)

2.7 Technology Gaps A clear distinction must be drawn between operational communications, emergency, and post-accident communications. Operational communications require wide bandwidth VHF/UHF transmission facilities. Wide bandwidth facilities support transmission of multiple voice channels in man and material travel ways, continuous video coverage of belt transfer points, and monitoring/control of equipment. Because automated machines move faster than miners can react high-speed data transmission, networks are required. The wide bandwidth VHF/UHF facility will increase operational safety and productivity. Emergency and post-accident communication requirements are vastly different because of the multitude of ways that dangerous situations occur and miners escape or become trapped in underground mining complexes. Mine-wide coverage is required in post-accident communications and tracking of miner on the move. Escaping miners often must travel in smoke-filled, soot, and low visibility



conditions in escape-ways with breathing apparatuses in the facemask or mouthpieces. In the Wilberg Mine disaster, one of the miners tried to escape through the paleochannel induced roof fall in the longwall tail gate entry, while another successfully escaped through return air entries (see Figure 2-1). Experience gained in the installation, operation, and maintenance of communications systems in 15 western U.S. underground mines, suggests that voice communications and tracking functionality must be integrated on miners in motion. The surface situation-awareness center (SAC) must know the escape route and current location being taken by each escaping miner. In emergency and post-accident conditions, underground miners are escaping or trapped in an undetermined number of ways and following an unpredictable number of escape-ways. Medium frequency, distributed antenna and transmission facilities, integrated with the conductors or lifeline waveguides, must be installed in every entry. Escaping miners require tracking, text, and/or voice communications with the surface along the entire escape-way. Voice communication through the face and mouthpiece apparatus must be solved. In the case of the Wilberg Mine escape, the dense smoke, soot, and poisonous gas required the use of self-contained self-rescuers (SCSRs). Only voice communication would have been possible for the miners on the move. Existing VHF/UHF communication network installations in U.S. mines are being augmented by MF to VHF/UHF bridge repeaters that provide wireless links to miners on the move except in return entries. The differing points of view could be resolved by eminently qualified academic physicists and scientists who are members of the JASONs5, the independent brain trust of the U.S. Department of Defense and intelligence agencies. The two candidate solutions are: 1. Combined operational and post-accident communications and tracking network installed in

man and material transportation entries with working face area coverage. Because of the high attenuation rates of UHF/UHF EM waves traveling along the transmission path, the network electronics and back-up batteries and chargers are installed at 500-foot intervals to compensate for path attenuation in the UHF mesh network configuration or VHF leaky-feeder coaxial cable creating a distributed antennas and transmission facility in transportation entries with face area coverage. The redundancy and self-healing requirements are met by employing an algorithmic code. Miners in motion wear wireless VHF transceivers and VHF/UHF radio frequency identification (RFID) tag data are transmitted through the VHF/UHF networks. Portable ultra low frequency (e.g., 2,000 Hz) through-the-earth transceivers with text messaging and synthetic-voice transmission at SCSR caches or refuge chambers are employed. Bridge repeaters create a wireless link between VHF/UHF and the ultra low frequency (ULF) transmission facilities.

2. Operational and post-accident communications and tracking networks are separated.

5 JASON, The MITRE Corporation, 1800 Dollet Madison Boulevard, McLean, VA 22102-‐3481.



The operational UHF mesh and VHF leaky feeder network electronics and batteries and charger equipment are installed at 500-foot intervals in man and material transportation entries with face-area coverage. Post-accident communications and tracking medium frequency F1/F1 digital repeaters and network equipment are installed in roof bolt holes or in buried flameproof enclosures installed at 5,000 to 10,000-foot intervals because the attenuation rate is only 2dB/ km in the MF band. Lifeline and messenger cables are installed in every entry except the transportation entries creating a distributed antenna and transmission (i.e., mode conversion) facility. The installation creates a physical self-healing and redundant network. Passive LF RFID tags with Braille or reflective tape way-in and way-out indicators are integrated with the cables. Miners on the move wear a cap lamp with built-in battery or as monitor with an integrated LF/MF transceiver. The transceiver periodically powers up (i.e., burst-beacon transmission) the nearby passive RFID tag. Transmission from the tag to the cap lamp transceiver conveys location information. The cap lamp transceiver digital packet switching transmission includes time stamp and location information. The cap lamp transceiver includes a detachable hand-held display for text messaging with an audio interface. Portable ULF through-the-Earth transceivers with text messaging and synthetic-voice transmission at SCSR caches or refuge chambers are employed. Bridge repeaters create a wireless link between MF and ULF transmission facilities.

The unintended consequence of the exceedingly large number of rechargeable batteries required in VHF/UHF networks creates a post-accident methane gas ignition source when ventilation systems are disabled following an accident, which endangers rescue teams.

If the emergency and post-accident communications facility is not a necessary functionality of every shift, the communications facility will not be maintained. The way to ensure maintenance of the communications and tracking facility is to require the emergency and post-accident communication system to include tracking. Tracking is a natural addition, since passive RFID tags are powered up by the LF/MF band transmissions. The mine infrastructure development plan for metal and non-metal mines is different from coal mines. Metal and non-metal mines develop a single or few adits or shafts into the working levels of the ore body In contrast, coal mines are developed with multiple parallel entries into a block of virgin coal. In metal and non-metal mines, the UHF leaky feeder facilities provide mine-wide coverage areas. Underground personnel are predominately located in the working face area (i.e., at the end of an MSHA compliant mine communication system) and scattered in construction and maintenance tasks. Emergency conditions often occur in locations with concentrations of energy in the mining complex where fire, roof collapse, or explosions are most likely to occur. Accidents are most likely to occur in travel ways, product transportation entries, and/or the work face area. An MSHA compliant communications system, commonly utilizing a leaky-feeder radio system or a hard-wired pager telephone system, will most likely be destroyed or disabled in a mine emergency, easily cutting off all means of communication with trapped or miners in motion.



Figure 2-12 illustrates a comprehensive mine communications and miner tracking system.

Figure 2-12. Mine Communications and Tracking System. (U.S. Patents 5,146,621, 5,301,082,

6,993,302 B2; 8,115,622). Market research and the lessons learned in the Wilberg Mine accident, and through-the-Earth (TTE) wireless communication development and installation in 15 western U.S. mines, determined that the mining industry requires robust wireless, two-way text and voice emergency communications between the face or refuge chamber and the surface. Because the miners may be trapped at the working-face area, a TTE system must be located in the refuge chambers. The industry requires transmission facility between the face or refuge chamber to the portal using the mining infrastructure and the correctly installed lifeline waveguides. Roof bolt hole or buried flameproof enclosure repeater transceivers facilitate a wireless link between the miner in motion and the distributed antenna and transmission facility of the conductor waveguides. Conveyor belts, AC power distribution and messenger cables, rail, and telephone cables create the remaining entries conductor waveguide. The Wait/Hill lifeline cable waveguide must be installed



in the remaining entries to create a robust, redundant, passive, self-healing mesh network with roof bolt hole or buried transceivers. Miners in motion wearing cap lamp or gas monitor with integrated MF transceivers provide a wireless link with the distributed antenna and transmission facility of conductor waveguide. The conductor waveguide installed in the transportation entries includes a fiber-optics link for operational communications of wide bandwidth data.

2.8 Lessons Learned in Medium-Frequency Communications Medium-frequency radio systems were installed, maintained, and operated in 15 western U.S. coal and metal/non-metal mines. The systems provided radio coverage in the passageways of both large and medium-sized mines. Electric locomotive cars and diesel powered vehicles provided transportation in these mines. These installations provided the following experience: 1. The already installed electrical conductors in the man and material entries, conveyor belt

entries, shafts, and tunnels created a robust MF band distributed antenna and signal transmission system.

2. More than 100 intrinsically safe (IS) wearable transceivers and 50 repeaters were built. The MF band radios established a wireless communications link for roving miners via the MF band distributed antenna and signal transmission system. The installed communications system enabled voice communications to coordinate maintenance and change priorities in the underground mining operations during a shift. In one underground coal mine, record keeping proved that the communications with roving maintenance personnel resulted in downtime saving over a three-month period equal to the cost of the entire system. Portable transceivers were installed in the face, lunch rooms, and service areas.

3. Escape through smoke, soot, and dangerous gases required a microphone integrated in the facemask and mouthpiece of SCSRs. Skull, facemask, mouthpiece, tooth, throat, and noise cancelling microphones were trialed for use with miners on the move. Skull devices created headaches, while throat microphones were judged to be satisfactory. Facemask microphones caused voice signals to be muffled and difficult to understand.

4. Miners in motion considered the wearable vest and bandolier transceivers to be an extra

burden given the bulkiness of SCSR units and service items carried by roving miners. The wearable radios were designed with replaceable battery packs to enable multiple shifts of operations with shared transceivers. The charging docks were different from the cap lamp charger with some battery packs remaining uncharged at a shift change. The miners requested that the transceivers be integrated within the cap lamp battery or preferably, with the miner’s cap lamp.

A cap lamp transceiver can be integrated into the light emitting diode (LED) lamp and battery assembly. The transceiver, lamp, and battery can be mounted on the miner’s helmet as illustrated in Figure 2-13. The air core vertical magnetic dipole (VMD) is also mounted on the miner’s helmet (see Figure 2-13).



Figure 2-13. Cap Lamp Transceiver.

The cap lamp transceiver must periodically burst 134 kHz transmission to power up a Texas Instruments (RT-IRP-W9UR) passive RFID disk transponder or tag encoded with the miner’s location (see Figure 2-14).

Figure 2-14. Radio Frequency Identification Tag Tracking System.

Re-transmission from the passive tag conveys location information to the cap lamp transceiver. The wearable transceiver appends identification along with location and transmits a digitally encoded data stream (i.e., application data) to the surface SAC display. The passive LF RFID tag has the functionality of the red/blue (i.e., way-in/way-out) reflective indicator disks that are installed in underground mine passageways. A communications system that is not required to be in use on every shift will not be maintained. The tracking capability must be built into the MF mesh network.

5. Portable transceivers were installed at power centers supplying power to the face area.

Repeater transceivers were installed at the power centers supplying power to conveyor belt drives of the longwall panels. Repeaters were installed in man and material roadways at



separation distances of approximately 5,000 feet because the attenuation rate is only 2 dB/km. Vehicular transceivers communicated via the installed infrastructure of large diameter, three-phase power distribution and messenger cables. Pager telephone cables also provided a transmission facility. The installed cables and conveyor belt structure created a distributed antenna and signal transmission path for the communications system. Repeaters supported push-to-talk transmission in the simplex/half-duplex mode. Separate transmit and receive frequencies were supported in the roadway distribution system by sets of transceivers with four separate operating frequencies each with a resonant-loop antenna. Even trained miners were confused when reconnecting the four separate loop antennas during a required relocation change. Repeaters are required in the conductor waveguide to overcome the 17 dB MF signal loss when passing through a power center. The MF signals couple to nearby conductors experiencing a few dB of coupling lost. The miners requested that a single antenna be used at the repeater site. Metal cabinets resembling stainless steel attaché cases were used as enclosures for the portable and repeater transceivers. The miners recommended that the transceivers be designed for installation in two-inch diameter stainless steel tubular enclosures and installed in roof bolt holes. This installation method was expected to survive an explosion or fire.

6. The MF transceivers worn by miners included a digital data transmission capability employing frequency shift key (FSK) modulation for digital data transmission of the application data with bit error detection and correction protocols. Miners found that digital control and monitoring communications required high signal-to-noise ratios resulting in shorter distances than analog voice communications.

7. As Wait/Hill taught, mono-filar and bi-filar propagation modes are supported on electrical

conductors installed in the construction of underground mine infrastructure. There are N - 1 propagation modes supported by an ensemble of electrical conductors where N is the number of conductors. The ground or sedimentary rock surrounding the coal bed is one of the conductors. The 23-dB/km attenuation rate of the mono-filar mode implies that only the bi-filar mode survives at great distance. The high attenuation rate of the mono-filar mode is due to the return current flow through the sedimentary rock surrounding the entry or tunnel. The bi-filar mode attenuation rate exhibits an exceeding low attenuation rate approaching 2 dB/km. In this case, the return current flows through the nearby conductor. The mono-filar mode is excited by the electric field component of the illuminating EM wave that is polarized tangential to the ensemble of conductors.

Twisted pairs are used to suppress the radio frequency interference (RFI) noise coupling in the communications cables connecting sensitive electronic components. The electric field that is tangential to the twisted pair induces mono-filar mode current flow in each conductor that is cancelled in the destination differential devices. Twisted pairs suppress the magnetic field noise induced in the cable. Miners found that by installing separate parallel conductors in entries without conductor infrastructure, coupling loss of MF signals to the distributed antenna decreased.



8. Mono-filar and bi-filar propagation modes occur simultaneously in the ensemble of electrical

conductors. Mode conversion is due to changes in the characteristic impedance of the wire pair installed in mine entries and tunnels. The characteristic impedance depends on the physical distance between conductors in the ensemble of conductors, including the rock conductor. Along the length of the lifeline, intentional separation changes are required. If the conductors in the MF distributed antenna and signal transmission system are installed on opposite corners of the passageway, reflections lead to magnetic field cancelation in the receiving magnetic dipole antenna. Vertical magnetic dipole antennas exhibit deep nulls directly under a cable. Nulls are not encountered when the conductors are installed on only one side of the entry and facilitate mode conversion by intentional change in the separation distance between conductors. The lifelines should be installed with periodic "braille" devices indicating the way out. Unfortunately, the MINER Act missed the opportunity to have lifelines installed in escape-ways that support mono-filar and /bi-filar modes of communications to roving miners wearing cap lamp transceivers. The MINER Act should be amended to require that the mono-filar and bi-filar modes of propagation, coupling, and mode conversion be supported by the lifeline cables installed in conductor-free entries (see, for example, Figure 2-15). The physical spacing between the conductors must periodically change along the entry to facilitate mode conversion.

Figure 2-15. A F1/F1 Transmit-Receive Transmission System. 9. The Accreditation Board for Engineering and Technology (ABET) procedure must

encourage a class segment in radio geophysics in mining engineering schools. The Wait/Hill radio geophysics theory for the design of robust mine-wide communications system has been set forth in the document “Radio Geophysics: "Emergency and Operational Communications and Tracking (RadCAT) System for Underground Mines”. The document must be edited for mining engineering school access.

10. Maintaining mine-wide radio communications experience gained in the maintenance of radio

transceivers in underground mines was a problem even after training. The mines do not have



the type of test equipment needed to trouble shoot problems in the distributed antenna transmission system and equipment. A solution was found by negotiating maintenance contracts for the mining complex. Mines now operate with independent contractors and service organizations.

11. Through-the-Earth subsurface transceiver location is problematic in the Wasatch Mountains

of Utah and regions where landowners only own the surface rights. Wait taught that in a slightly conductive media, energy is dissipated in the near field of a radiating electric dipole and stored in the vicinity of a magnetic dipole implying that energy is available for transmission into the far field. This condition is the technical reason that magnetic dipoles must be applied in the design of subsurface emergency EM communication systems. Radiating magnetic dipole antennas are characterized by their magnetic moment (M). The magnetic moment of a resonating loop antenna is given by M = NIA in Ampere turn meter square (ATM2) (2-15) and

M =

!A!µ

!

"#

$

%&

PBW!

"#

$

%& ferrite rod

RA

µ !n 8Ra

!

"#

$

%&'74

(

)*

+

,-

PBW!

"#

$

%& air' core loop

.

/

000

1

000

Ampereturn meter2 , (2-16)

where N = number of turns of copper wire used in construction,

I = peak value of the circulating current in the coil in Amperes, A = is a vector normal to the enclosed area of the loop in square meters, R = radius of the loop antenna,

= length of ferrite rod in meters, a = radius of copper wire in meters, P = essentially the power applied by the transmitter to the antenna, and

BW = 3-dB bandwidth of the resonating magnetic dipole antenna in Hz. The magnetic moment increases with the square root of power or by reducing bandwidth of the resonating magnetic dipole. The transmission of electromagnetic waves through the subsurface waveguides are described in electrodynamics. The electric and magnetic field components radiating from an oscillating magnetic dipole are illustrated in Figure 2-16. The spherical coordinate system (r, ϕ, θ) is used to describe the general orientation of the field components. When the physical dimension of the loop is small relative to the wavelength (λ), the magnetic dipole field components are described by Wait as:



Figure 2-16. Electromagnetic Wave Field Component Produced by a Vertical Magnetic Dipole

Antenna with the Loop in the Equatorial X-Y Plane. azimuthal (θ) component of the magnetic field in Amperes/meter

( ) ( ) ( )

, sin ekr1-

kri+

kr1

4Mk=H ikr-

23

3

!"#

$%&

'

(! (2-17)

radial (r) component of the magnetic field in Amperes/meter

, cos e)(kr

i+)(kr

12

Mk=H ikr-23

3

r !"#

$%&

'

( (2-18)

and longitudinal (φ) electric field component in Volts per meter

!E = iµ" 2Mk4#

-1(kr 2)

+ 1i(kr)

!

"#

$

%& -ikre sin $, (2-19)

where ω = 2πfo is the radian frequency in radians per second and fo is the operating frequency in Hz,

i = 1! , r = radial distance from the radiating antenna in meters, and k = β - iα, is the propagation constant with β being the phase constant in radians/

meter and α the attenuation rate in nepers/meter.

The magnetic field vectors lie in the meridian plane. The electric vector (Eϕ) is perpendicular to the meridian plane and subscribes concentric circles around the z-axis magnetic dipole moment vector. The terms in the magnetic dipole field component Equations (2-17) through (2-19) have been arranged in the inverse power of r. The radial distance r = λ/2π defines the near field (one skin depth) spherical surface surrounding the radiating dipole antenna. The natural media space



surrounding the magnetic dipole can be divided into three regions: the near or static zone, induction zone, and far or radiating zone. The near or static zone exists when the radial distance (r) is less than one skin depth, that is

πλδ 2/=<r , the reactive near fields drop off as 1/r 3 . Energy is stored in the reactive impedances and available to flow into the far field. Wait has shown, in the case of an electrically small electric dipole, the impedance is real and energy is dissipated in this zone. When the radial distance (r) is one skin depth (i.e., πλ 2/=r ), the fields drop off as 1/r 2 . When the far distance is much greater than one skin depth, the fields drop off as 1/r. These fields exhibit non-planar spherical spreading wave front. The radiation far-field fields are given by

!H = - 2Mk4"

!

"#

$

%&

-ikrer

sin ! (2-20)

and

θπ

µωφ

re

4Mk=E

-ikrsin⎥⎦

⎤⎢⎣

⎡ in volts/meter. (2-21)

The radiation fields are transverse (i.e., orthogonal), which is expected of spherical wave propagation at great distances from all electromagnetic wave sources. The sine θ and cosine θ terms describe the antenna pattern for the dipole fields. The fields of infinitesimal magnetic and electric dipoles embedded in infinite homogenous medium with electrical constants of conductivityσ , magnetic permeability µ , and dielectric constant ( )ε can be expressed in terms of the propagation constants of attenuation rate ( )α (nepers per meter) and phase constant ( )β (radians per meter). For the magnetic dipole

( ) θβββα

ββα

βββ

απ

ββ

βα

θ sin2114

2

3ri

reerrirr

rrMH −⎟⎟

⎠

⎞⎜⎜⎝

⎛−

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛++

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛+−+⎟⎟

⎠

⎞⎜⎜⎝

⎛= (2-22)

and

( ){ } 134/ φθ π ieArMH −= (2-23)

and

!

Hr =M2"r2

#$

%

& '

(

) * +

1$r

%

& '

(

) * + i

+

, -

.

/ 0 $r( )e

1#$

%

& '

(

) * $r2

3 4

5 4

6 7 4

8 4 e1i$r cos9 (2-24)

and

( ){ } 222/ φπ ir eBrMH −= . (2-25)



For the electric dipole

( ) ( ) θβββ

αωµ

πββ

α

φ sin14 3

rieerir

irM −⎟⎟

⎠

⎞⎜⎜⎝

⎛−

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎦

⎤⎢⎣

⎡++⎟⎟

⎠

⎞⎜⎜⎝

⎛−=Ε (2-26)

and

( )( ){ } 234/ φφ ωµπ ieBirM −−=Ε . (2-27)

In the limit as frequency approaches zero, the attenuation rate ( )α , phase constant )(β , and electric field ( )φE vanish and the magnetic fields θH and rH approach the static (DC) value. For the electric dipole

( ) θβββα

ββα

βββ

ασπ

ββα

θ sin21114

2

3ri

reerrirr

rrIdE −⎟⎟

⎠

⎞⎜⎜⎝

⎛−

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛++

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛+−+⎟⎟

⎠

⎞⎜⎜⎝

⎛⎟⎠

⎞⎜⎝

⎛= (2-28)

and

( )( ){ } 13 /14/ φ

θ σπ ieArIdlE = (2-29)

and

( ) θβββ

ασπ

ββ

βα

cos112 3

rir

r eerirr

IdE −⎟⎟⎠

⎞⎜⎜⎝

⎛−

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎥⎦

⎤

⎢⎢⎣

⎡+⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠

⎞⎜⎝

⎛= (2-30)

and

( )( ){ } 283 )/12/ θσπ ir eBrIdE −= . (2-31)

For the magnetic dipole

( ) θβββ

απ

ββ

βα

φ sin14 2

rireeri

rrIdH −⎟⎟

⎠

⎞⎜⎜⎝

⎛−

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎦

⎤⎢⎣

⎡++⎟⎟

⎠

⎞⎜⎜⎝

⎛=

(2-32)

and

( ){ } 224/ φφ π ieBrIdH −= . (2-33)

Each field in Equations (2-22) through (2-33) has been separated into the magnetic ( 34/ rM π or ) or current ( 24/ rId π or 22/ rId π ) spatial-excitation term and the geologic terms (A

and B). The magnitude of the azimuthal magnetic field component H θ can be expressed in terms of the propagation factor ratio βα / and the space scaling factor β r as

22/ rM π



(2-34) and phase by

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛+−

⎟⎟⎠

⎞⎜⎜⎝

⎛+

+−= −

βα

ββα

ββ

ββα

βφ

rrr

rTanr 2

11

1

21. (2-35)

The magnitude of electric field is mathematically

( )21

2

3 114

11⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

+⎥⎦

⎤⎢⎣

⎡+⎟⎟⎠

⎞⎜⎜⎝

⎛=

rrME

ββα

ωµπφ (2-36)

and

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

++= −

r

Tanr

ββα

βφ1

112 . (2-37)

The magnitude of the magnetic ( )θH and electric field ( )θE components can be expressed in decibels (dB) with respect to one ampere per meter (dB re A/m) or volt per meter (dB re v/m) by taking the logarithm to the base 10 of both sides of the above equations and multiplying by 20. The magnitude of the azimuthal magnetic field component is expressed as

!

20log10H" = 20log10M4#r3

+ 20log10 A{ } dBre A /m

= spatial-excitation +geologic contribution (2-38)

The variable rβ represents the distance scaling factor from the radiating magnetic dipole to the point in the medium. The magnitude and phase of the component fields depends on the ratio of the propagation factors

⎟⎟⎠

⎞⎜⎜⎝

⎛

βα and the geologic space scaling factor ( )rβ as illustrated in Figure 2-17.

The ratio of propagation factors ranges 10 ≤≤βα .

The curve labeled 0/ =βα and 1/ =βα in Figure 2-17 represents propagation through free space and slightly conducting natural media, respectively. The azimuthal component phase shift versus skin depth distance is illustrated in Figure 2-18.

21

222

3 2114 ⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛++

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟⎠

⎞⎜⎜⎝

⎛+−

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡=

⎟⎟⎠

⎞⎜⎜⎝

⎛−

rrrr

errMH

rβ

βα

ββα

βα

ββ

βπ

ββα

θ



Figure 2-17. Geological Component of Magnetic Field Intensity Versus Distance Scaled in Skin

Depths.

Figure 2-18. Geologic Field Component Phase Shift Versus Distance Scaled in Skin Depths.

The attenuation rate (α) and phase (β) rate of EM waves traveling through natural media was developed by Oliver Heavysides (Bollen 1989) and is expressed by



1-+12

=2 2

1 21

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠

⎞⎜⎝

⎛εωσµε

ωα nepers per meter (2-39)

and

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠

⎞⎜⎝

⎛ 1++12

=2 21 2

1

εωσµε

ωβ radians per meter, (2-40)

where ! = 2! f is the radian frequency and f is the frequency in Hz and ! = electrical conductivity in Siemens per meter (S/m)

The dimension less quantity

!

" /#$ is the loss tangent. When the loss tangent is greater or less than unity, the wave constants simplify and separate as

!

" =

#µ$2; $#%

>>1

$2

µ%; $#%

>>1Nepers per meter (multiplyby8.686&dB)

'

( ) )

* ) )

(2-41)

and

!

" =2#$

=

%µ&2; &%'

<<1

% µ' ; &%'

>>1radians permeter

(

) * *

+ * *

. (2-42)

The velocity of the traveling wave in the media is given by

!

" =#$

=

2#µ%; %#&

>>1

c& r; %#&

<<1meters /second

'

( ) )

* ) )

. (2-43)

Radio geophysics Earth model can be formulated as a parallel resistor and capacitor as shown in Figure 2-19. Expressions for the electrical conductivity and dielectric constant of natural media are also given in the Figure 2-19. The range conductivity and relative dielectric constant values or natural media is illustrated in Figure 2-20. The electrical conductivity of mine water is like seawater because of ionization of argillaceous matter in coal. The attenuation rate of electromagnetic waves through mine water with electrical conductivity ranging between 1 and 10 S/m is shown in Table 2-2.



Figure 2-19. Radio Geophysics Earth Model.

Figure 2-20. Electrical Conductivity and Relative Dielectric Constant for Natural Media. (The width of the horizontal bars indicates the effect of frequency.)



Electrical parameters for coal, shale. lake water, and air are given in Table 2-2. Table 2-3 reveals why VHF/UHF field component transmission through mine water decreases the destination S/N ratio by 55 dB/foot (i.e., a factor of over 500).

Table 2-2. Electrical Parameters for Coal, Shale, Lake Water, and Air. (After Van Baldel 1964).

Surface

Electrical Parameter

Frequency (1 MHz) (100 MHz)

σ εr ωεσ Z

ωεσ Z

Dry coal 0.0005 4 2.247 120.1 0.022 188.3 Saturated shale 0.05 7 128.4 12.6 1.284 111.6 Lake water 0.02 81 4.44 19.6 0.044 41.8 Limestone 0.001 9 2.00 84.0 0.020 125.6 Air 0 1 0 376.7 0 376.7

Table 2-3. Attenuation Rate.

Frequency (MHz)

Conductivity (S/m)

Attenuation Constant (Neper/m)

Attenuation Constant (dB/m) Loss Tangent

100 1 15.98 138.80228 2.220 300 1 19.77 171.72222 0.741

1,000 1 20.81 180.75566 0.222 3,000 1 20.92 181.71112 0.074

Frequency

(MHz) Conductivity

(S/m) Attenuation

constant (neper/m) Attenuation

constant (dB/m) Loss Tangent 100 10 61.40 533.3204 22.22 300 10 101.75 883.8005 7.470

1,000 10 159.77 1387.76222 2.222 3,000 10 197.70 1717.2222 0.741

When the loss tangent (σ/ωε) is greater than unity, the attenuation and phase rate increase with the first power of frequency because conductivity increases with the first percent of frequency. The lowest possible frequency should be used in emergency communications. The LF /MF bands attenuation rates through natural media depend on electrical conductivity and frequency. At 300 kHz and through a 5 milliseimens/meter (mS/m) media, the attenuation rate is less than 5 dB/100 feet. By way of contrast, the VHF/UHF bands attenuation rate is 10 dB/foot, preventing communications through rock and roof falls. Attenuation rate and phase constant for a uniform plane wave propagating in a natural medium with a relative dielectric constant of ten is shown in Figure 2-21.



Figure 2-21. Attenuation Rate and Phase Constant for a Uniform Plane Wave Propagating in a

Natural Medium with a Relative Dielectric Constant of Ten. (The curves from bottom to top represent increases in natural media conductivity from 10-5 to 101 S/m.)

The transmission path link budget is complicated by the reflection of EM waves from air-water interfaces. The reflections and attenuation occurring at the air interface are illustrated in Figure 2-22.

Figure 2-22. Reflection Occurring at an Air-Natural Media Interface.



Table 2-4 lists the EM wave propagation parameters for a wide range of natural media electrical conductivity (εr=10).

Table 2-4. Electromagnetic Wave Transmission Parameters.

Frequency (MHz) Loss Tangent Attenuation

Rate (dB/ft) Phase Constant

(radian/m) Wavelength (=2π/β) (m)

Wavelength (ft)

σ = 0.0005 S/m εr = 4 1 2.25 0.09 0.06 113.97 373.93 3 0.75 0.12 0.13 47.11 154.58 10 0.22 0.12 0.42 14.90 48.88 30 0.07 0.12 1.26 4.99 16.38 60 0.04 0.12 2.52 2.50 8.20 100 0.02 0.12 4.19 1.50 4.92 300 0.01 0.12 12.58 0.50 1.64

σ = 0.005 S/m εr = 4 0.002 11,250 0.016 0.006 1,600 3,280 0.02 1,250 0.053 0.02 316 1,036 0.2 112 0.159 0.06 100 328 1 22.47 0.36 0.14 43.74 143.50 3 7.49 0.60 0.26 24.16 79.26 10 2.25 0.95 0.55 11.40 37.39 30 0.75 1.18 1.33 4.71 15.46 60 0.37 1.23 2.56 2.46 8.06 100 0.22 1.24 4.22 1.49 4.89 300 0.07 1.25 12.58 0.50 1.64

σ = 0.05 S/m εr = 4 0.002 112,500 0.05 .020 316 1036 0.020 11,250 0.167 .063 100 328 0.2 1125 0.53 .20 31.6 104 1 224.69 1.17 0.45 14.11 46.29 3 74.90 2.02 0.77 8.11 26.61 10 22.47 3.64 1.44 4.37 14.35 30 7.49 6.03 2.60 2.42 7.93 60 3.74 7.98 3.93 1.60 5.25 100 2.25 9.48 5.51 1.14 3.74 300 0.75 11.76 13.34 0.47 1.55



The reflection coefficient is given by

12

12

ZZZZ

EE

i

R

+

!==" , (2-44)

where Ei = incident electric field component, ER = reflected electric field, Z2 = impedance natural media in region 2, and Z1 = impedance of the natural media in region 1.

The impedance in any media is given by

!

Z =

µ"

1 # i $%"

µ" # i$ /%( )

&

' (

)

* +

1/ 2

,

-

.

.

.

/

.

.

.

Ohms. (2-45)

The magnitude of impedance is given by

41

2

1!!"

#

$$%

&'(

)*+

,+

=

-./

.µ

iZ Ohms, (2-46)

which separates to

Z =

i!µ"

=!µ"!45o ; "

!#>>1

377#r; "!#

<<1Ohms

"

#$$

%$$

. (2-47)

2.9 Methane Ignition Susceptibility to Radiating Magnetic Dipoles When a radiating magnetic dipole antenna is operating in the resonant condition, a circulating current (Ic) flows in the antenna circuit consisting of a series connection of a capacitor and inductor, both energy storage devices. The relationship between the peak energy stored to energy dissipated in the antenna coil series resistor per cycle is called the quality factor (Q) and given by

!

QCKT =peak energy stored in the inductor

energy dissipated percyclein thecoil resistance (2-48)

When the QCKT of the antenna is less than unity, the stored energy is dissipated in the coil.



The resonating antenna circuit QCKT is given by

QCKT =foBW

, (2-49)

where fo = resonant frequency of the antenna in Hz and BW = 3-dB bandwidth in Hz. From circuit theory, the unloaded Qu of the conductor is

!

Qu =QCKTQLP , (2-50)

and

Qu =!LRS

, (2-51)

where Rs is modeled as a lumped, although it is actually distributed, DC resistance value. The low-pass prototype filter quality factor (QLP) is used to determine energy dissipation loss in resonate circuit. A through-the-Earth transmission bandwidth (BW) of 100 Hz is required to achieve a symbol transmission rate of 2 symbols/second. From equation (2-49) the quality factor of the loop antenna is 20. The lumped non-physical DC resistance can be determined from the standard annealed wire table in series with the inductor and is presented in Table 2-5. As the resonant frequency increases, the current flow crowds toward the surface of the conductor increasing the value of the “lumped” resistance. Radiation of EM energy away from the coil is accounted for by adding a non-physical radiation resistance value to the “lumped resistance value. When viewed as a receiving loop antenna, the radiation resistance includes the effect of the slightly conducting media being transformed into the loop antenna.

Table 2-5. Standard Annealed Copper Wire Resistance.

American Wire Gauge

Resistance (Ohms/1,000 ft)

Diameter (meters)

12 1.59 2.040x10-3

14 2.53 1.619x10-3

16 4.01 1.284x10-3

18 6.39 1.016x10-3 20 10.15 0.808x10-3 22 16.11 0.641x10-3

24 25.67 0.508x10-3

26 40.81 0.396x10-3 28 64.90 0.319x10-3



In typical communications systems, the antenna circuit Q ranges between 20 to more than 100. The current applied to the resonating antenna is multiplied by Q and represents the peak circulating current (IC). The peak energy (ε) stored in the inductors and capacitors is given by

!

" =1/2LIC

2 inductiveenergy1/2CV 2 capactiveenergy

# $ %

in Joules. (2-52)

The rate of exchange of inductive to capacitive energy is the operating frequency. If the resonating series circuit of the radiating antenna were to become an open circuit at the peak of the energy storage cycle, an incendiary spark with 0.25 millijoules of energy would ignite methane gas. The inductance (L) of coils used in building magnetic dipole antennas is given by

L =

µ!

!

"#

$

%&AN 2 ferrite rod

µoR !n8Ra

!

"#

$

%&'74

(

)*

+

,-N

2 air' core loop

.

/00

100

Henry , (2-53)

where R = radius of the air core loop antenna in meters, a = radius of the magnetic wire in meters, N = number of turns,

!

! = length of the coil in meters, A = area of the antenna in square meters, and μr = relative magnetic permeability. The intrinsically safe magnetic moment (M) limit of a resonating magnetic dipole antenna is given by

M =

102 !A4!µr

ferrite rod

102 !R3

8 !n 8Ra

!

"#

$

%&'74

(

)*

+

,-

air' core loop

.

/

000

1

000

Ampere turnm2 . (2-54)

The magnetic moment is independent of the number of turns. The intrinsically safe magnetic moment for an air core coil is given in Table 2-6.

Table 2-6. Intrinsically Safe Magnetic Moment of a Magnetic Dipole Antenna.

Intrinsically Safe Magnetic Moment for Loop Antenna (16 AWG) a = 0.508 x 10-3m

Loop Circumference (feet [meters])

Radius (meters)

Magnetic Moment (Ampere turn meter2)

10 [3.04] 0.483 8.309 50 [15.243] 2.426 83.158



100 [30.481] 4.852 225.749 200 [60.975] 9.704 614.753

The safe limit maximum magnetic moment of the radiating antenna (e.g., one-inch diameter ferrite rod with a µr of 120, built with 22 turns, an inductance of 95 microhenries, and operating with a peak circulating current of 2.29 Ampere) is 3 ATM2. The safe limit circulating current (Ic) and magnetic moment (M) of a radiating air-core loop are illustrated in Figure 2-23. The magnetic moment increases with circumference of the loop. The surface receiving antennas must be constructed with electrostatic shields to suppress the horizontally polarized electric field component of noise.

Figure 2-23. Intrinsically Safe Current and Magnetic Moment for an Air-Core Loop.

2.10 Feasibility of High Magnetic Moment Intrinsically Safe Antennas The definition of QCKT given in Equation (2-48) suggests that a radiating magnetic dipole with Q of less than unity internally dissipates all of the stored energy on each oscillation cycle in the equivalent series resistance of the coil wire. When the low Q inductor is open circuited, there will be no energy discharge. An intrinsically safe phased array is shown in Figure 2-24.

0 50 100 150 200 250 3000

500

1000

1500

2000

2500

circumference of air core loop in feet --->

Intrinsically safe current and Magnetic moments for an Air core loop

Current - mAMoment - ATm2



Figure 2-24. Intrinsically Safe Phased Array with QCKT < 1.

Each radiating magnetic dipole antenna magnetic moment (M) generates a magnetic field that by superposition is the sum magnitude of fields. 2.11 Susceptibility of Mine Equipment and Personnel to Electromagnetic Fields The susceptibility of mining personnel and various types of equipment to electromagnetic (EM) fields has been investigated by the Franklin Institute. The Franklin Institute investigation included blasting caps. During Stolar’s development of an intrinsically safe mine-wide wireless low-to-medium frequency underground radio systems for the Bureau of Mines in the 1980s, analytical studies and field tests were conducted with blasting caps that corroborated the Franklin Institute results. The investigation concluded that blasting caps and machine control electronics were not susceptible to long wavelength signals. 2.11.1 Blasting Cap Susceptibility Blasting caps are shipped to the mine site with the insulated copper wire leads emanating from the cap and stripped approximately one inch from the end of each copper wire. The ends of each copper wire are twisted together to form a short circuit. The leads are closely spaced and folded together to eliminate the possibility of forming a loop (i.e., magnetic dipole) with an enclosed area between the two leads or an electric dipole when both leads are separated and pulled apart. Blasting caps have lead length of approximately one meter with an internal blasting cap resistance of 200 ohms. The safe blasting cap current limit is one ampere and the blasting cap ignition current, IEXP, is 50 amperes. The blasting cap is designed to have a safety factor of 50 to 1. Considering the blasting cap leads as a dangerous antenna when illuminated by an electromagnetic wave, the open circuit condition of the leads will create an electric dipole with two one-meter electrically conductive elements. The short circuit condition of the leads with maximized area (1/π meter2) will create a circular loop magnetic dipole with a circumference of two meters. At a distance of one meter from the subsurface radiating TTE antenna (i.e., 839 ATM2), the electric field (E) is 1.11 volts/meter and the magnetic field (H) is 2.94 x 10-3 Ampere/meter (A/m). The field strength depends on the first power of the magnetic moment. If the radiating



antenna has a moment of 419 ATM2, the field strength would be reduced by 50%. The wavelength at 2 kHz is 150,000 meters. For the open circuit condition of leads, the effective antenna height (heff) is the physical length of antenna element related to wavelength = 1.33x10-5 meter. The electromotive force (emf) generated by an antenna is given by

emf = electric field x heff = 1.33x10-5m x 1.11 v/m = 1.476x10-5 volt. (2-55)

The induced current is ID = emf/200 ohms = 0.0074 microamperes. (2-56) Thus, the safety factor (SF) becomes SF = IEXP/ID = 6.75x109 to 1. (2-57)

For the short circuit condition of leads, the magnetic dipole loop area (A) is A = πr2 =1/π m2. The electromotive force (emf) is

emf = -iNωAμH = -i1(2π x 2,000)(1/π)(4πx10-7)(2.94x10-3) = -i4.35x10-8 volt. (2-58) The induced current (I) is I = emf/200 ohms = 9.9 milliamperes. (2-59) Thus, the safety factor (SF) becomes

SF = IEXP/ID= 5.05x103 to 1. (2-60) In the extreme, if the blasting cap were connected in series with the antenna, the safety factor becomes 501/216 = 231 to 1. For a remote detonation device, with a blasting cap cable length of 1,000 meters, the effective antenna height, he, is the length of the cable relative to the wavelength, which is he = 0.007 (2-61) The electromotive force (emf) is emf = heE = 7x10-3(1.11) = 7.4 x 10-3 microvolts. (2-62) The induced current is ID = emf/200 ohms = 37 microamperes. (2-63) Thus, the safety factor (SF) becomes SF = IEXP/ID= 1.35x105 to 1. (2-64) Note that the detonation cable supports the simultaneous transmission of the mono-filar and bi-filar modes. The electric field component that is tangential to the cable induces mono-filar current flow in each conductor. As the characteristic impedance changes along the cable, mode



conversion occurs and bi-filar mode (i.e., differential) current flows through the blasting cap igniter. 2.11.2 Electronic Equipment Susceptibility The susceptibility of electronic equipment follows from the same basic analysis. Electronic equipment has shielding that will reduce the magnitude of the electric field applied to the electronics. Lead lengths are typically 0.01 meter. The induced voltage would be 0.07 microvolts. Logic switching signals are in the 100-millivolt to 1.01-volt range. The safety factor of 1.35x104 to 1 is large enough to ensure complete safety. The frequencies used by continuous miners and shearer remote control transmitters are generally between 78 MHz and 1.5 GHz. The operating frequencies of TTE (i.e., 2 to 10 kHz) are far enough below those of the remote control frequencies to avoid interference. The TTE signal will not cause interference and under no circumstances will the system affect any solid-state equipment, including stationary, portable, or remote control. 2.11.3 Mine Personnel Susceptibility The biological effects of the EM waves of the TTE and caplamp transceivers can be determined from an article in the Microwaves and RF publication, September 1999, entitled “Study Antenna Positioning and EM Biological Effects,” by Cellai and Ferrarotti, which states that the specific absorption rate limit is 0.08 watts/kilogram of body tissue. The TTE transmitters produce an electric field of 1.11 volt (peak)/meter for radiating antenna with a magnetic moment of 839. The power is given by P = (1.11)2/377= 3.27 milliwatts. (2-65) If a typical underground miner weighs 100 kilogram, the specific absorption rate is 3.27x10-3/100 = 3.27x10-5 watts/kilogram. The safety factor is 2,446 to 1. As a result, the TTE equipment will not cause any health effects. The camp lamp IS magnetic moment is 1.1 ampere than meter2. The magnitude of the electric field component is 22.2 volts/meter. The power is 1.3 watts. The absorption rate for a miner weighing 100 kilograms is 1.3x10-2 watts/kilogram and the safety factor is 6.12 to 1.

2.12 Through-the-Earth Transmission Loss The horizontally stratified Earth overlying the underground mining complex causes the EM wave to be guided vertically, as illustrated in Figure 2-25.



Figure 2-25. Transmission (Heat-H) and Reflection (Loss-R) at Media Interfaces. The TTE transmission signals from trapped miners with cap lamp transceivers and ULF band F1/F1 repeaters are subjected to very high reflection loss (R) at the air-earth surface boundary, the roof entry boundary on downward trave, and to a lesser extent, at each interface in a layered Earth geologic model. When reaching the interface, the EM wave is reflected back into the soil or overburden. The radiating condition of a TTE subsurface transmitter antenna requires an N-turn magnetic dipole antenna with a resonant circulating current (I) and enclosed area (A). The intrensically safe magnetic moment (M = NIA) is presented in Table 2-6. The TTE communications problem is dominated by the surface electrical noise spectral density and required transmission bandwidth (i.e., 100 Hz) for text message transmission. The RFI noise transmission in the ionosphere-Earth waveguide limits the upward transmission distance (see Figure 2-26).



Figure 2-26. Typical Ionospheric-Earth Radio Frequency Interference Noise Spectral Density. Measured at San Antonio, California (gamma=1 nanotesla).

(After Labson et al., Geophysics, Vol. 50, No 4, April 1985.) The typical measured surface electrical noise measured in a 100-Hz bandwidth is -144 dB re one Ampere/meter (dB re A/m). The noise originates from one-half millisecond duration lighting discharges in the ionosphere-Earth waveguide and exhibits a noise spectral density minimum near 2,000 Hz. Because the RFI is oftentimes generated by sources that are several wavelengths (λ ) from the mine, the far field wave fronts are plane surfaces. The EM gradiometric method of suppressing plane wave front RFI noise is discussed in Section 3.5.1. The up-link TTE EM from a trapped miner must be much greater than the RFI noise spectrum shown in Figure 2-26. The destination signal-to-noise (S/N) ratio must be greater than 20 dB for intelligible transmission

dB =10 log10 SNR(power ratio)20 log10 SNR(voltageratio)!"#

, (2-66)

where SNR is the S/N ratio. The RFI noise magnetic field density (B = Hµ ) is stated as the magnetic flux in webers/meter2. The magnetic field noise spectral density exhibits a local minimum in the ULF band (i.e., 300 to 3,000 Hz) near 2,000 Hz. If the RFI noise was the only consideration, then the TTE communications system operations frequency should be near 2,000 Hz. Because the transmission loss through the Earth surface boundary decreases with increasing frequency while the absorption (i.e., attenuation) loss decreases with frequency, the selection of the optimum operation frequency requires further analysis. The lightning generated noise quasi-transverse electromagnetic (quasi-TEM) wave exhibits a vertically polarized electric field emanating from negative build up charge on the Earth’s surface. The charge polarity alternates every half wavelength of radial distance from the lightning strike, causing a horizontally polarized electric field on conductive boundaries. By the Poynting vector theorem (P = E x H), the horizontally-polarized field components travel downward into the soil with propagation constant (κ). The horizontal electric field component causes the vertically polarized electric field to tilt with angle θ given by

!

" = tan#1 1$ r

1

1+%&$

'

( )

*

+ , 2-

. /

0

1 2

14

; %&$

>>1. (2-67)

Three-phase AC power transmission systems operate with unbalanced phase currents causing ground currents to flow within one skin depth (i.e., 100s of miles) from the transmission line. The fundamental and harmonics flow in higher electrical conductivity underground layers. The underground current flow generates magnetic fields observable in the measured noise data.



The destination signal must be at least 10 dB above the noise for the TTE system to exhibit a BER of at least 1 in 100. The magnetic field noise can be suppressed by 30 dB by employing a cross-polarized vertical magnetic dipole (VMD) receiving antenna. An electromagnetic gradiometer (EMG) antenna suppresses the surface noise by at least 60 dB. The TTE communication depth through 20 milliseimen/meter soils for IS transmission magnetic moment (M) VMD antennas in the mine is given in Table 2-7 for VMD and EMG receiving antennas.

Table 2-7. Surface Signal-to-Noise Ratio for Vertical Magnetic Dipole Antennas.

The average depth of cover in U.S. mines is about 1,000 feet. Gradiometer receivers will achieve a BER of better than 1 bit in 10 million bits. Equation (2-48) suggests that a phase coherent VMD array built with QCKT antenna of less than unity can achieve IS operation with very high magnetic moments. Such arrays are under development. A review of U.S. Bureau of Mines RFI data gathered for many U.S. mine company properties and Stolar’s data show a noise minimum near 2,000 Hz, which would appear to be the optimal frequency for TTE two-way data and text message transmission. The transmission loss (i.e., absorption into heat) is very high in passing through each geologic layer. The ULF transmission parameters are given in Table 2-8. Radiating magnetic dipoles near interface boundaries have equivalent circuits that include the reflected impedance of the boundary. For this reason, the first reflection interface is substantially in the near field. The near reflection loss is omitted from the total path loss.

Table 2-8. Electromagnetic Wave Transmission Factors ( mS /05.0=σ and 10=αε ).

Frequency (Hz)

Loss Tangent

Attenuation Rate (dB/foot)

Phase Constant (radian/meter)

Wavelength [meter (feet)]

Skin Depth [meter (feet)]

30 3,000,000 3104.6 −× 21043.2 −× 2,582 (8469) 411 (1348) 300 300,000 21004.2 −× 21069.7 −× 817 (2680) 130 (426) 500 180,000 21062.2 −× 3109.9 −× 632 (2073) 101 (330) 1000 90,000 21073.3 −× 21041.1 −× 447 (1466) 71 (232)

Depth (ft)

Surface Signal-to-Noise Ratio (dB) Circumference of a Vertical Magnetic Dipole Antenna (ft) 50 100 140 300

VMD EMG VMD EMG VMD EMG VMD EMG 500 27 47 36 56 40 60 50 70

1,000 -4 16 5 25 9 29 19 39 1,500 -28 -9 -19 1 -15 5 -5 15 2,000 -39 -19 -30 -10 -26 -6 -16 4 2,500 -62 -42 -53 -33 -49 -29 -39 -19



1,500 60,000 2105.4 −× 2107.1 −× 365 (1197) 59 (192) 2,000 45,000 21026.5 −× 21099.1 −× 316 (1036) 50 (164)

2.13 Wave Reflection and Absorption in Through-the-Earth Communications The frequency and electrical conductivity influence on air-earth interface transmission loss is illustrated in Figure 2-27.

The reflection loss increases significantly as the frequency is decreased, while the transmission through the air-earth interface improves as the frequency is increased. The transmission path absorption (i.e., attenuation) versus frequency is shown in Figure 2-28.

The total attenuation (i.e., reflection and absorption) along a 1,500-ft path through the Earth is illustrated in Figure 2-29. From petrophysics, the attenuation rate increases with the first power of frequency. The TTE waveguide up and down transmission paths illustrated in Figure 2-24 can be analyzed to determine the destination signal to noise ratio. Intrinsic safety considerations limit up-link transmit power and magnetic moment (M) so the magnetic dipole coil inductance and peak circulating flow lies under the UL913 ignition curve. The intrinsically safe loop antenna current and magnetic moment versus loop circumference are illustrated in Figure 2-22. The down-link transmit magnetic moment is not limited, which allows this communications link to be realizable with commercially available technology. Equations (2-17) and (2-18) can be compared to show that the radial component of the magnetic field versus mine entry depth will result in the largest vertically polarized magnetic field component at the surface.

Figure 2-27. Air-Earth Transmission Loss Versus Frequency.



Figure 2-28. Total Attenuation Through 1,500 Feet of Overburden.

The normalized magnitude of the magnetic field component is increased by 20 log M in dB where M is the IS value of magnetic moment (see Table 2-9). Intrinsically safe radial magnetic field components above a surface are given in Table 2-10.

Figure 2-29. Propagation Loss of the Radio Waves Traveling 1,500 Feet Through the Earth. Losses Include Reflection from One Air-Earth Boundary, Losses in Earth, and Spreading Losses.

(The Relative Dielectric Constant of the Earth Is Assumed to be 4.)

Table 2-9. Magnitude of Radial Magnetic Field Components for a Normalized Magnetic Moment of 1 ATM2 Operating at a Frequency of 2,000 Hz in 20 mS/m Overburden.



Depth [feet (meter)]

Magnetic Field (dB re 1 A/m) Just Below

Surface Above Surface

500 (152) -152 -175 1,000 (304) -183 -206 1,500 (457) -207 -230 2,000 (609) -228 -241 2,500 (762) -249 -262

The magnetic moment can be increased from the IS value as

20 logM =

10 log A!!µ

!

"#

$

%&+10 log

PdBW!

"#

$

%& ferrite core

10 log2!R3 '10 log Ln 8Ra'74

(

)*+

,-+10 log Pd

BW!

"#

$

%& air core

.

/00

100

. (2-68)

The magnetic moment can be increased by decreasing bandwidth (BW). Doubling the power (Pd) applied to the antenna only increases magnetic moment (M) by 3 dB for the same BW. The price paid for higher power is increased demand for battery capacity. This condition is one of the reasons that the system design goal is to decrease required bandwidth, thereby increasing detection sensitivity.

Table 2-10. Intrinsically Safe Radial Magnetic Field Components Above a Surface.

Depth (ft)

Circumference of a Vertical Magnetic Dipole Antenna (ft) 50 100 140 300

Intrinsically Safe Radial Magnetic Field Components (dB re 1 A/m)

500 -137 -128 -124 -114 1,000 -168 -159 -155 -145 1,500 -192 -183 -179 -169 2,000 -203 -194 -190 -180 2,500 -226 -217 -213 -203

2.14 Through-the-Earth Transceivers The through-the-Earth (TTE) transceiver is being evaluated by MSHA for flameproof approval with IS circulating current in the radiating antenna. Photographs of TTE communications equipment development by Stolar and Lockheed-Martin are shown in Figure 2-30.



Figure 2-30. Through-the-Earth Communications Hardware. Stolar Research Corporation,

Pending MSHA Approval (left and bottom). Lockheed-Martin, MSHA Approved (right).

The TTE transceiver weighs 35 pounds and features text messaging and synthetic voice conversion. 2.15 Transceiver Design The mine communications and tracking system, illustrated in Figure 2-12, and fulfilling the Option 2, features transceivers designed with identical circuit modules. The software definable transceiver block diagram is illustrated in Figure 2-31. Bluetooth transmission enables the transceiver to communicate with external gas monitors and text messaging keyboards. A personal digital assistant (PDA) enables wireless modification of the software code for specific applications. The magnetic dipole antenna is switched to series resonant condition when the push-to-talk (PTT) voice or data transmission is requested. The transceiver provides simplex/half duplex wireless communications between a miner on the move and the distributed antenna and transmission facility. The transceiver series-to-parallel switch connects the magnetic dipole antenna in a parallel resonant condition. This design allows the transceiver to monitor the distributed antenna and transmission lifeline conductor waveguide for radiated signals, including the modulated carrier frequency traffic and radio frequency interference (RFI) spectral density



generated by electrical equipment powered from the mine AC power distribution cables.

Figure 2-31. F1/F1 Digital Transceiver Block Diagram (Physical Layer).

The antenna received electromotive force, emf, is applied to a variable gain amplifier optimized for minimum noise spectral density. The 24-bit analog-to-digital (A/D) converter enables the receiving mode of the transceiver to operate over a dynamic range of 144 dB. The A/D converter signal is applied to a field-programmable, gated array (FPGA). The physical layer employs multi-level frequency (4FSK) modulation and demodulation of each carrier frequency in the ultra low, low, or medium-frequency bands. The modulation scheme enables multiple communication channels to be available in the MF communications system. The dispatch channel is used to net mining groups together. Carrier frequencies in the ultra low frequency (ULF) band are used in through-the-Earth (TTE) communications. The instantaneous transceiver bandwidths are either 100 Hz or 30 kHz for packet transmission rates of 80 bites/second or 26 kilobits/second, respectively. The topology of the distributed antenna and transmission lifeline conductor waveguide facility illustrated in Figure 2-12 is physically, not algorithmically, redundant. The termination ends of the waveguide (i.e., at working face area) employ ULF-band carrier frequency transceivers for two-way text and synthetic voice transmission for TTE communications. The termination ends include a second repeater-transceiver operating with a low-to-medium frequency band carrier frequency, determined by the RFI spectrum analyzer layer to monitor busy channels and RFI noise bands. The transmission signal is a multi-level frequency modulated with a packet message. The transmitted packet signal reaches the portal via bi-filar mode propagation on the distributed antenna and transmission lifeline conductor waveguide. The face area termination end transceivers operate as a bridge between the surface for ULF data messaging (e.g., text or sensor data) and the low-to-medium frequency distributed antenna and transmission lifeline waveguide for mine-wide coverage. A miner on the move can communicate data messages to the surface and portal. Miners in motion wear either a cap lamp or gas monitoring transceiver. Either transceiver periodically bursts a 134-kHz radio wave energy to power-up and then listen to the 134-kHz reply from nearby passive reverse radio frequency identification (RFID) tags integrated with the lifeline waveguide. The spectrum analyzer and tracking layer imbedded codes are distributed between the FPGA, digital signal processor, and microprocessor integrated circuits. The periodic burst from the cap lamp or gas monitoring transceiver can be used by mine rescue team members



carrying a Fox Hunter direction finding antenna to locate down and trapped miners. Transceivers feature fixed-length digitally encoded packet messages for voice and data (i.e., text, location, or ID sensor values). The base band processor decodes and assembles the packet message. The messages are 48 bytes in length with 4 bytes to identify the type of message and provide control information. The synchronization preamble requires 8 bytes for a total packet length of 52 bytes for the application payload. The transceiver, transmission facility traffic monitoring mode, employs a media access control (MAC) layer. The carrier sensing, multiple access with collision avoidance protocol is applied in the traffic-monitoring mode. Detecting a traffic null, a dithered time period elapses before a packet transmission starts. The random back-off time period reduces the likelihood of packet collisions in the transmission facility. The MAC layer adds a header to each packet transmission containing the destination address and other information. The physical layer overhead adds 10 bytes bringing the packet to 71 bytes. The 26-kilobits/second data rate requires a packet transmission period of 22 milliseconds. The Stolar transmission facility repeater-transceivers shown in Figure 2-30 operate with circuits that are separated by 5,000 to 10,000 feet. Parallel entries driven into the coal block each have installed lifeline conductor waveguides. The conductor waveguides are connected together at the specified separation distance. Each parallel conductor waveguide is brought together at a common point, but insulated from each other. A repeater-transceiver is installed in a protective borehole near the common point such that the magnetic dipole antenna inductively induces approximately an equal carrier frequency signal current in each conductor. Reciprocity applies and the packet traffic carrier frequency signal current flowing in each conductor waveguide, by Ampere's law, generates a magnetic field along the distributed antenna. The magnetic field component near by the antenna induces electromotive force signals in the magnetic dipole antenna during the monitoring mode. The conductor waveguides are also inductively coupled together when installed in a confined area and couple across breakers in otherwise continuous cables. A break of at least 50 feet is required to create a radio frequency signal block. The repeater network provides radio coverage over miles of entries. An advantage of the 5,000- to 10,000-foot repeater separation is that only one rechargeable battery pack is required per mile of entries. This compares favorably with very high frequency (VHF)/UHF networks. The repeater-transceivers have been designed with 1.66-inch diameter cylindrical enclosures for insertion into roof bolt holes. The enclosures have achieved MSHA flameproof approvals. The cylindrical enclosures have internal rechargeable batteries protected by redundant current trip circuits. The flameproof enclosures shown in Figure 2-30, which include a graphical display for text messaging, are designed for protective burial.



3.0 HORIZON AND LOOK-AHEAD COAL SEAM SENSORS

3.1 Background The mining industry Chief Executive Officers identified remote rock boundary sensing as an urgently "needed technology." Real-time boundary sensing will increase safety, improve retirement health, reduce waste, and improve run-of-mine (ROM) product quality. Since the development of the first continuous cutting drum mining machine by Joe Joy in 1948, machine operators and worldwide research and development (R&D) organizations have searched for a means of remotely detecting the roof and floor rock boundaries (i.e. horizons) and looking ahead for dangerous mining conditions. Coal, trona (sodium carbonate-Na2CO3), potash (sylvinite-KCl), and salt (halite-NaCl) layers are bounded by layers of contaminated minerals. Look-ahead sensing is needed for the detection of abandoned mines, and oil and gas well casings ahead of the mining machine and halos of mineralization.

3.2 Formation of Coal Deposits Coal beds are formed in different sedimentary ways. The most common are strandline and deltaic deposits of a transgressing sea. Deltaic deposits from in the delta legions of river systems. The upper floodplain, mud-water flow, and delta regions of river system are illustrated in Figure 3-1.

Figure 3-1. Delta Region Illustrating Sand Levees, Breaching in a Levee, and Meandering Flow

and Splay Deposits. The upper floodplain is an oxygen-rich environment where water flow carries metal oxides into the river system. Vegetation grows in the swamp region of the delta forming peat-coal. During the time sequences of mudflow deposition and delta region burial of the peat-coal swamp, the environment of the upper layer of peat-coal changes to a septic condition. Accumulation of anaerobic bacteria creates a reducing (i.e., oxygen-reduction reaction) environment. Upper floodplain mud-water flow into the peat-coal swamp carries oxides of the heavy metals that precipitate when encountering the reducing environment, contaminating the upper peat-coal layer. Subsequent burial and 50:1 compaction forms a thin boundary layer of coal contaminated with sulfur, selenium, and heavy metals, such as mercury, uranium, and arsenic.



Oftentimes, sequences of dry and wet periods during the initial burial sequence create a gradational boundary with higher ash and density. Continuing with mudflow, the mud-water flow during burial creates sealing shale and mudstone layers, which are aqua strict. The sealing layer contains ions creating a high electrical conductivity contrast with the coal layers. In deltaic deposits, flooding through breaches in the levees creates porous sandstone paleochannels that meander in the boundary layers surrounding the coal layer. Deltaic deposits typically have a contaminated layer at the top of the coal layer (see Figure 3-2).

Figure 3-2. Illustration of a Meandering Paleochannel. Oftentimes, the high-energy "cutbank" segment of the channel scours into the coal layer replacing coal with porous sandstone paleochannels (see Figure 3-2). Differential compaction occurring in the overlying strata of the coal bed by uncompressible sandstone paleochannels creates fracturing, rolls, and rapid thinning (i.e., compaction) in the coal layer. One of the important features of coal is its microporous and fracture nature, which plays an important part in many of the physiochemical properties of coal, such as methane gas retention capacity and highly adsorbing and absorbing properties. Trapped methane gas is released during the mining process when the coal is fractured and the micropores open allowing transport of gas to the atmosphere and chemically adsorbed gas becomes available for liberation into the micro-porous structure or fracture system. The flow of gas stored in the microporous structure is governed by Flick’s Law. The free gas in the fracture system flows according to Darcy’s law. These two modes of transport are interdependent. The physics of gas in coal during mining is complex and conventional gas field methods of reservoir engineering analysis are not applicable. The internal surface area of coal can be as high as 1.5 million square feet/pound of coal and 0.34 standard cubic feet of methane/pound of coal can be adsorbed on the internal surface area at the saturation pressure of 1,500 psi. Depending on the rank of the coal and integrity of the overburden, the amount of methane adsorbed and absorbed can reach as high as 28 times the volume of coal. Each pound of coal fuels the generation of one kilowatt hour (kWh) of electric power in a typical coal-fired power plant. At atmospheric pressure, the most explosive concentration of methane in air is 9.5% by volume. Methane also has a tendency to stratify and form horizontal layers near the roof of mine workings where there are insufficiently high ventilation velocities to prevent layering. This phenomenon occurs because methane is lighter than air, with a density of only 0.55 that of air. In



many instances, a ventilation air velocity of 1.6 feet/second will prevent layering, but there are some circumstances where this air velocity will be insufficient as barometric pressure decreases. These changes are created by storm fronts as they approach, decreasing barometric pressure as they pass. Charles McIntosh of Eastern Illinois University conducted the earliest detailed study of methane gas in coal seams in the late 1950s. The rate of gas liberation from coal mining depends upon age, depth, and the structure of the coal seam; the mining technique; and the rank of the coal (i.e., the higher the fixed carbon content of the coal, the higher the methane liberation). Geologically induced stress fields create fractures and butt and face cleats form gas and water pathways through the coal matrix. Cutting machines are oriented to cut (i.e., fracture the coal) at an angle to the butt cleats to maximize roof-rock stability. The anisotropic gas-flow permeability and relative dielectric constant is maximized when horizontal production wells are drilled such that long face cleats drain gas and water into a well. Adsorbed (i.e., bound to the matrix ~67%), absorbed (i.e., pressurized cleat volume ~27%), and micro fracture (free ~6%) methane gas concentrations range up to 1,000 cubic feet/ton, with a typical value being about typically 360 cubic feet/ton. The coal seam water content resides in fractures and cleat structure. During degassing, water is pumped from the well to reduce pressure and facilitate gas flow. There is a thermodynamic mass transfer problem that suggests acoustic stimulation may increase the gas flow rate. Acoustic stimulations within degasification boreholes ahead of high-production-rate longwalls should reduce methane ignition potential. The shale and mudstone layer bounding the coal seam seals the coal bed from nearby porous sandstone fresh water aquifers. The sealing layer of the coal bed is oftentimes scoured by an overlying sandstone paleochannel, which creates a dangerous margin of weak rock. The electrical conductivity and impedance contrast between the bounding rock and the coal layer creates waveguides for electromagnetic and acoustic wave transmission. The acoustical resonance of the coal seam depends on thickness and is typically near 760 Hz. Quasi-transverse electromagnetic transmission has a "sweet spot" in the medium frequency band. Tomographic mapping of paleochannels ahead of mining can locate where ground control should be intensified by roof bolting and installing screening and/or trusses. Oftentimes, the roof rock fails when entries are driven under margins of paleochannels. Roof fall injures will be reduced significantly when images of margins are mapped and ground control measures are intensified.

3.3 Horizon Sensor Design Considerations To provide machine clearance, a precise rock cut is needed to minimize waste rock in the mined product. Cutting causes coal dust plumes that obscure the machine operator’s vision of cutting edges, thereby allowing accidental cutting through the contaminated coal layers and into boundary rock. This problem is heightened due to the machine operator’s location, which is 20 to 80 feet away from the cutting edges to remain out of the dust plume and under "bolted" roof rock. Skilled machine operators judge the cutting horizons by "marker bands" in the rib (i.e., side wall of the immediately cut entry or face). Oftentimes, the marker bands vanish or the horizon changes due to differential compaction and rolls in the coal bed.



Horizon sensors (HS) must be mounted underneath the loading buckets, blades, or on the surface of cutting drums of mining machines. The measurement must be accomplished in real time (i.e., within 17 milliseconds) and must accurately determine the uncut layer thickness adjacent to mudstone, shale, sandstone, and salt (i.e., halite) rock layers. Sensing the cut-off ore grade in the halo of mineralization can reduce waste rock. Dr. Harrison "Jack" Schmitt, the Apollo 17 commander, was the first scientist trained as a geologist to walk on the moon’s surface. Following his lunar mission in 1971, he influenced the National Aeronautics and Space Administration (NASA) to transfer space exploration technology to the mining industry. Automation of a mining machine operating in an undulating coal seam cannot be achieved without coal boundary rock detection from the cutting edge location. The solution was beyond the then state-of-the-art. Technologists at NASA investigated sensitized picks (i.e., vibration sensors), ultra/acoustic ranging, and gamma detection techniques. All but gamma detection was ruled out as infeasible. Gamma detector electronics are not fast enough to be used for real-time measurements. Gamma sensors, including a calibration algorithm, were developed for mounting on the body of a mining machine. Today, gamma sensors are in use on mining machines and coal seam degasification drills. Gamma sensing is based on the decay of potasium-34 occurring in shale and mudstone rock. Gamma emissions occur at varying rates near 60 bursts or more per second. This rate was considered too slow to make measurements in the 17-millisecond time duration associated with a rotating coal drum. Undulations in the coal bed are likely to occur under sandstone paleochannels as illustrated in Figure 3-2. Sandstone roof rock has a very low concentration of potassium-34 and is a very poor gamma emitter. Horizon sensing is most beneficial under sandstone paleochannels to keep cutting edges from striking sandstone. Gamma emission rates increase when the cutting bits strike a shale and mudstone rock boundary. Coal is argillaceous (i.e., containing trace amounts of clay) with natural potasium-34 emissions that limit the uncut thickness measurements to less than 18 inches. Following Schmitt’s work, the Jet Propulsion Laboratory (JPL) established the Advanced Coal Extraction (ACE) project that considered the machine automation problem using NASA technology. Technologists at JPL also concluded that a state-of-the-art advancement in interface detection would be needed to achieve a satisfactory automation solution. Stolar Research Corporation (Stolar) began work on this problem in 1986 with a view that more than interface detection was needed because of the reducing biological environment in the peat-coal swamp occurring during deposition. The oxygen-reduction reaction created a thin boundary layer of coal contaminated with heavy metals, ash, and organic sulfur. Dr. James Wait became aware of the uncut coal-rock boundary detection problem when consulting with the U.S. Bureau of Mines (USBM) on underground communications problems. In the Wait and Chang (1977) paper, “An Analysis of a Resonant Loop as an Electromagnetic Sensor of Coal Seam Thickness,” they developed the theory mandating that a resonating wire loop with an infinitesimally small gap exhibited driving point impedance Zin that varies with the thickness of the uncut coal layer adjacent to the boundary rock as illustrated in Figure 3-3. Chang



developed the underlying theory during his graduate studies at Harvard University under R.W.P. King.

Figure 3-3. Resonant Detection Impedance Plot.

The Wait/Chang wire loop features a back lobe that couples radio frequency energy into the metallic hub of the rotating cutting drum, which prevents its direct application on a cutting drum. Mechanical designs of wire loops were believed to be unable to withstand the 100-g force environment of the rotating cutting drum. A laboratory measurement of impedance variation over simulated uncut coal layer thickness bound by sandstone rock confirmed the Wait/Chang expectation. Consultation with David Chang, who was the head of the University of Colorado Electrical Engineering Department and is now President of the Polytechnic Institute of New York University, suggested that a resonant microstrip patch antenna (RMPA) with the TM11 mode electric field lines (see Figure 3-4) would exhibit identical impedance variations with thickness.

Figure 3-4. Cutaway View of a Resonant Microstrip Patch Antenna Sensor. (U.S. Patents

5,072,172; 5,186,426; 5,474,261; 5,686,841).



Conventional radars cannot be made to measure thin layers close to the radiating antenna. Development work conducted in a NASA Johnson Space Flight Center program, focused on the shuttle booster rocket fuel tank ice build-up detection, found that a RMPA exhibited a driving point impedance and scattering frequency that varied with ice thickness. The NASA Space Act award recognized the importance of the sensor for fuel tank ice build-up detection. The sensor was adopted for automation of automobile windshield wipers. The RMPA was developed into a hand-held device and trialed in several underground coal mines. In-mine test sites were constructed by “mining” various uncut roof coal thickness layers into the roof coal. The layered uncut coal thickness varied from 1 to 30 inches. The sensor impedance versus uncut coal thickness measurements confirmed the Wait/Chang HS expectations. The U.S. Department of Energy (DOE) Mine of the Future program awarded funding for the Wait/Chang HS development and field trials. The West Virginia University Mining Engineering Department conducted a design evaluation, Stolar designed the electronics, and InterWest Mining Company built a highwall mining machine for test and evaluation in an open-pit coal mine. Sandia National Laboratories’ staff members and the Mine Safety and Health Administration (MSHA) assisted the mechanical design team with the approval of the drum-mounted enclosure. The enclosure featured built-in vibration frequency band rejection mechanical filters. The design was evaluated at Sandia's warhead test center and withstood the 100-g forces shock and vibration profile previously recorded on an operating continuous mining machine. An R&D 100 award was received for the development of the horizon sensor. The drum mounted horizon sensor photographs are shown in Figure 3-5.

Figure 3-5. Horizon Sensor Mounted on a Mining Machine Cutting Drum (U.S. Patents 4,753,484; 5,146,661; 5,769,503; 6,43,052 B2;).

A pendulum driven dynamic generator provides 50 watts of power for the horizon sensor.



The HS will enable real-time automation of the machine. Since the HS technology is not commercially available, machinery manufacturers have developed "last cut" memory control algorithms. The algorithm is problematic in undulating coal beds unless real-time uncut coal thickness measurements are included in the control algorithms. Inhalation of coal and silica dust by machine operators is a long-standing regulatory issue and an end-of-life smothering death sentence for miners (see Figure 3-6). The dust plume is known to contribute to the occurrence of pneumoconiosis (i.e., black lung disease) and silicosis resulting from long-term exposure to coal and silica dust, respectively.

Figure 3-6. Comparison of Deaths in the U.S. and Australia per Million Population. Coal mining requires a cutting drum mounted HS to reduce silica in the residual dust and significantly reduce silicosis as an occupational disease. Sulfur and heavy metals (i.e., mercury) are typically concentrated in thin (i.e., less than 6 inch) boundary layers of the coal seam as illustrated in Figure 3-7.

Figure 3-7. Stratigraphic Cross Section Illustrating Contamination in a Coal Bed.



The HS enables mining machines to leave the heavy metals behind and greatly reduces the operating cost of the " downstream " technology installed at the electric utility. Because the HS technology is not commercially available, the National Mining Association (NMA) supported the DOE's "downstream " initiative because lower quality contaminated coal can be supplied to the power plants. Downstream technologies enable mining companies to cut “rock to rock.” The current DOE focus on the clean coal research and development initiative is directed at the development and demonstrations of "downstream" smokestack emissions, scrubbing, and carbon dioxide sequestration technologies at a level of about $500 million annually. There are a number of safety and economic benefits to a mine using HS technology, namely:

• Cutting into sandstone roof and floor rock creates incendiary sparks that have more than 0.25 millijoule of energy that will ignite liberated methane. The HS significantly reduces this mine explosion source. The Mine Safety and Health Administration (MSHA) briefing indentified the source of the 2010 Upper Big Branch Mine methane ignition as the spark trail caused by the cutting drum bits striking sandstone rock.

• When the cutting bits strike sandstone, silica enters the cutting process dust stream and miner inhalation of silica particles lodge in the lung tissue. The acid produced by the silica particles produces lung scar tissue and the damage called silicosis. The HS technology allows the cutting machine operator to operate the machine from dust free areas.

• As shown in Figure 3-7, the stratigraphic cross section, thin boundary layers of coal are contaminated by heavy metals and ash. The contaminated layers should be left behind in the mine. For example, reducing ash by 1.5% has a power plant economic value of $2.5 million in annual savings for an 800-MWe coal-fired plant.

• Oftentimes, as little as one inch of boundary rock must be cut to provide clearance for the mining machine. Estimates and analysis show that a 1% improvement in yield over a one-year mining period is worth $75 million.

• Cost analysis of high production longwalls shows that a HS can save $47,000/day. The Office of Surface Mining and Regulation Enforcement (OSM) has initiated a process for regulating the re-use or disposal of fly ash at mine sites. Environmental assessment is now underway to determine if an environmental impact statement will be needed to regulate fly ash and mined waste rock as a toxic waste. Combustion of contaminated coal layer reverses the oxygen-reduction reaction occurring during coal seam deposition. Earth Justice and other environmental groups argue that National Pollution Discharge Elimination System (NPDES) permits should include selenium, arsenic, mercury, and other constituents of coal ash. The coal ash and heavy metal contamination of run-of-mine (ROM) coal are made worse when the density of the thin boundary layer is included in the calculation. The disposal of fly ash containing oxides of heavy metals will result in the contamination of nearby groundwater. Leaving the thin boundary layer of coal containing higher concentrations of ash, sulfur, and heavy metals, such as mercury and arsenic, in the mine yields cleaner ROM coal. Cleaner coals also improve power plant efficiency, which results in lower maintenance costs, lower coal consumption for the same level of electricity generation, and lower electricity prices for U.S. consumers. In addition to minimizing the level of contaminants in ROM coal that



contribute to environmental concerns, boundary-rock sensing can allow miners to operate in safer and healthier underground conditions. This benefit is achievable in three ways by: (i) enhanced automation of mining machinery thereby reducing the chance of an accidental ignition of methane gas by sparks generated by mining into boundary rock; (ii) allowing miners to operate further from the coal face and out of the dust plume; and (iii) reducing the potential for roof fall injuries. Environmental restrictions will require that ROM coal quality be improved. By cutting more coal and less boundary rock, which yields cleaner ROM coal, the cost of coal production can be reduced as well as the coal preparation costs. Moreover, cleaner ROM coal results in environmental degradation mitigation by reducing aboveground fly ash waste disposal and sulfur dioxide and heavy metals emissions from power plants. At the start of the introduction phase of the HS product life cycle, "early adopter" installations were completed on 10 different continuous miners and two longwall cutting drums. The machines were operated by mine personnel with varying degrees of training. In some mines, calibration and operation met the mine operator’s expectations. Other mines experienced cutting conditions where the eight-inch gaps between the cut coal interface and the hub of the cutting drum varied from air, water, cut coal, and rock. The varying dielectric constant of the natural media overlying the RMPA created a calibration problem. The drum-mounted sensor withstood 12 months of coal and rock cutting with no mechanical failures. The machine operator human interface characteristic was well received by machine operators. The product life cycle cost through the research phase was $3 million. Another $12 million was invested at the beginning of the introduction phase before withdrawing the HS product from the market. When finally perfected, the HS product will prevent the cutting drum picks from striking the sandstone layer especially in undulating coal seams. When the rotating steel "fracturing" picks strike the sandstone layer, incendiary sparks are produced with more than 0.25 millijoule of energy, which is enough energy to cause ignition of liberated methane gas, which typically amounts to about 350 cubic feet/ton of cut coal, with propagating pressure waves. The pressure wave picks up coal dust creating an extremely high-energy, coal-dust explosion condition. The propagating super-pressure wave continues to develop unless quenched by previously applied rock dust. These powerful explosions can create twisted rail, destroy conveyor belts, and piles of cable in the impacted entries. Following an explosion, the mine ventilation system is shutdown, which prevents removal of toxic and explosive gas from the mine passageways. The presence of these gases delays the re-entry of rescue teams.

3.4 Technology Gap The gap in HS technology can be eliminated by reconfiguring the Wait/Chang sensor. The sensor would be designed to have the functionality of a pick block. The pick block surface mechanical design coincides with the outer pick tip ring circle, located at the far end of the drum (see Figure 3-8).



Figure 3-8. Pick Tip Horizon Sensor Mounted on a Cutting Drum.

The ranging arms of longwall shearers and booms of continuous mining machines have been designed to withstand the dynamic forces of cutting rock and extremely hard layers in the coal bed (see, for example, Figure 3-9). The HS bit block sensor will cause the dynamic forces to change and may negatively impact the reliability of the gear trains. An analysis of this problem will be needed in the design of the bit block sensor.

Figure 3-9. Horizon Sensor Mounting Options on a Longwall Shearer and Continuous Miner.



Cutting drums are manufactured by small machine shops and not by the mining machine manufacturers. Drum lacing patterns (i.e., pick placement) are specifically designed according to the experience in a given mine with the fracture cutting process. The alignment of the butt and cleat structure is determined by regional stress fields, which determine the optimal pick-fracturing pattern. The sensor would be mounted at the end of spline during the rebuild time of the cutting drum.

3.5 Look-Ahead Radar Technology On July 24, 2002, Black Wolf Coal Company’s Quecreek No. 1 Mine section development unexpectedly breached the barrier pillar of the Saxman Coal Mine trapping nine miners for 78 hours. Following the Quecreek accident, Pennsylvania Governor, Mark Schweiker’s commission reported on “Abandoned Mine Voids and Mine Safety” (Ramani, R.V. et al). The report contained 48 recommended changes to prevent future mine accidents in Pennsylvania. One of the recommendations was “continuing to research existing and developing geophysical techniques to locate abandoned mine void boundaries in addition to horizontal drilling.” The report recommended returning to the 200-foot from the 50-foot width barrier coal pillar requirement between the entries of an abandoned mine and an operating mine. For a mine producing 1.7 million tons/year and a 10-year life, the barrier contains 48,000 tons of sterilized coal per mile. Under the barrier pillar width regulation of 50 feet, approximately 95 million kWh of electricity is lost per mile for each mine operating near an abandoned mine. The U.S. Congress funded the MSHA Technical Support, Mine Waste, and Geotechnical Engineering Division to establish the a programmatic plan for development and demonstrations of promising technologies for abandoned mine detection ahead of mining. For 20 years preceding the Quecreek accident, 449 incidents of intersecting abandoned mines had been reported, a rate of approximately two per month. The Marion County impoundment dam failure and inundation of an abandoned mine causing breakout flooding and destruction of river ecology heighten MSHA’s interest in advancing the state-of-the-art of look-ahead radar detection technology. Three of the MSHA projects were based on the transmission of electromagnetic (EM) waves with detection based on surface EM gradiometer (EMG) surveys, cross well radio imaging method (RIM) surveys, and advanced development of the deep look (i.e., ground penetrating) radar.

3.5.1 Surface-Based Electromagnetic Gradiometer Surveys Electromagnetic gradiometer (EMG) technology illuminates the surface overlying underground structures, such as abandoned mines, tunnels, bunkers, and clandestine facilities. The illumination may be the ground wave traveling from a distant AM radio station or the field components of a radiating magnetic dipole. Electromagnetic waves in the ultra low frequency (ULF) band have been generated by heating of the polar region electrojet. Heating and displacement of current was accomplished by megawatt transmission from a phased array antenna of VHF band energy. The transmitter is located near Genoa, Alaska and directs energy upward to the Aurora Borealis. The down range (i.e., 120 miles) delta tunnel conductors were illuminated by the downward propagating horizontally polarized electric field component (EH) of the 2,000-Hz EM ground wave. The scattered fields were detected with the EMG instrument by



acquisition of data along travels over the tunnels. Figure 3-10 illustrates EM ground wave field components illuminating the surface overlying an electrically conductive current flow concentrator (i.e., a subsurface anomaly).

Figure 3-10. Ground Wave Field Components Propagating Away from an AM Band Radio

Station. The Ionosphere-Earth surface waveguide supports the propagation of ground EM waves that exhibit a horizontally polarized electric field component (EH), which is tangential to the Earth's surface and polarized in the radial direction from the radiating transmitter. The magnitude of the horizontally polarized electric field component is dependent on the electrical conductivity (σ) of the layered geology. The horizontally polarized electrical field component (EH) is caused by the boundary electronic surface charge induced by the vertically polarized electric field component (Ev) emanating from a negative boundary charge. There is a horizontally polarized magnetic field component (Hϕ) in the ground wave. A detailed illustration of the field components is shown in Figure 3-11. By the Poynting Vector Theorem (P = EH X HH), the horizontal components travel through the Earth’s surface and downward into the layered Earth with propagation constant (κ). The downward travelling electric field component that is tangential to an anomaly of contrasting electrical conductivity, by the " long wavelength scattering limit" of theoretical physics, induces current flow (I). By Ampere's law, the current flow creates a cylindrically spreading EM field components that travel up and through the reflecting interface of the Earth's surface, which is observable on or above the Earth's surface. The magnitudes of the observable EM field components are several orders of magnitude less than the magnitudes of the illuminating ground wave field components. Detection of the observable fields in the presences of the very large illuminating fields is a formidable, but not intractable problem that has been solved with



innovative gradiometric technology. As illustrated in Figure 3-11, the illuminating fields exhibit a plane wave front while the observable scattered fields travelling upward from the object exhibit a cylindrical spreading wave front.

Figure 3-11. Gradiometric Response of the Illuminating and Scattered Fields.

The EM gradiometer is built with oppositely polarized magnetic dipole antennas. Plane wave fronts induce identical electromotive (emf see page 26) signal voltages in each of the oppositely polarized magnetic dipole (i.e., loop-coil) antennas (see Figure 3-10). The series connection of magnetic dipole antennas causes the cancelation of the emf voltage. By the Taylor series expansion theorem, differentiation of the constant plane wave fronts suppresses plane wave front EM fields by more than 60 dB because a derivative of a constant is zero. Cylindrically spreading scattered fields induce non-zero emf voltages in each dipole except directly over the object. The magnitude of the gradiometer signal along a traverse crossing over the long electrically conductive object resembles a capital M with the peak-to-peak separation distance proportional to distance to the object and the minimum emfT value of the M occurs directly over the object as shown in Figure 3-12.



Figure 3-12. Electromagnetic Gradiometer Response.

The photograph in Figure 3-13 of the gradiometer shows two spatially separated antennas that are connected in series but opposite polarity.

Figure 3-13. Hand-Held Electromagnetic Gradiometer.

Electromagnetic gradiometer (EMG) surveys were conducted over the shallow buried (i.e., 180 feet deep) entries of Consol's Emery Coal Mine near Price, Utah. The gradiometric response is shown in Figure 3-14. The wet floor of the coal mine entries releases free ions from the soluble salts and sulfides in the fire clay floor, which significantly increase the electrical conductivity of mine water to between 1 and 10 Siemen per meter. The electric field component of the downward traveling EM wave induces current flow that, by Amperes law, causes scattered fields to be observable on the Earth's surface with the EMG instrumentation. The surface EMG response agreed favorably with the



mine map. A confirmation drilling plan was prepared, and approved by federal and state agencies. Drilling permits were obtained and then drilled to intersect the void (i.e., entries). Ambiguity in the global positioning system (GPS) coordinates and drill drift prevented conformation of the void detection. Funds were not available to acquire and use high resolution GPS technology.

Figure 3-14. Gradiometric Response Measured Over an Abandoned Section of the Emery Mine.

3.5.2 Cross Well Radio Imaging Method Surveys Presently, the MSHA requires horizontal directional drilling in mines operating near abandoned mining complexes. MSHA has also approved vertical drilling of a fence line of boreholes and cross well RIM detection of voids with the radio imaging method (RIM). Cross well RIM imaging of a fence line of boreholes is illustrated on the mine map of an abandoned coal mine in Figure 3-15. The cross well RIM path crossing through the abandoned mine entries illustrated a significant increase in attenuation rate. The paths through virgin coal exhibits lower total attenuation. The existence of an abandoned mine entry is illustrated by the sharp increase in attenuation rate (see Figure 3-15).

3.5.3 Technology Gap Horizontal in-mine directional drilling slows down mining processes because it requires relocating and repositioning a drilling machine for each 40 feet of entry development into virgin coal. The efficiency of long hole horizontal directional drilling to probe for abandoned mine



boundaries increases if the borehole can be accurately guided and maintained within the coal bed.

Figure 3-15. Cross Well Fence Line Imaging to Detect Unmapped Abandoned Mine Entries.

The technology gap is caused by the paleochannels and differential compaction illustrated in Figure 2-3. A horizontal drill cannot respond to a role in the coal seam caused by a paleochannel. The role causes the drill to intersect the seam boundary and drill out of seam. An obvious solution is to incorporate radar technology into the drill navigation system.

3.5.4 Deep Look Ground Penatrating Radar Gradiometer Advanced radar development work for clandestine tunnel and abandoned mine detection ahead of mining resulted in a new class of ground penetrating radar. The deep look ground penetrating radar gradiometer (DLRG) was designed, developed, and demonstrated with gradiometric suppression concepts originally developed for detection of scattered fields from tunnels as illustrated in Figure 3-10. The DLRG was adapted to look ahead of the face for a distance at least 50 feet to detect abandoned mine entries and/or gas well casings. Technology improvements and demonstration efforts for the DLRG were funded by MSHA as a direct result of the Quecreek accident. The first interface near reflection zone (see Figure 2-22) of the DLRG radar design achieved 60 dB of suppression of the reflected wave. In-mine demonstrations conducted at the Oxbow Coal Mine near Paonia, Colorado, confirmed void detection beyond 50 feet. A detailed illustration of multiple internal reflections and attenuation (i.e., heat loss) along the round trip path from the transmitter to receiver sections of the radar are illustrated in Figure 3-16.



Figure 3-16. Electromagnetic Wave Energy Flow in the Horizon Sensing and Abandoned Mine Detection Problem.

The attenuation and internal reflections decrease the magnitude of the observable electric (ER1 and ER2) and magnetic (HR1 and HR2) field components by several orders of magnitude below the illuminating fields (Ei and Hi). There are lateral surface waves (EL) that propagate along the free space-media interface. Lateral waves that intersect nearby surface obstacles are reflected and add to clutter signals arriving back to the radar. Each order of magnitude equals a 20 dB reduction in the magnitude of the electric (E) and magnetic (H) field components.6 For simplicity, the magnetic field components are not shown in Figure 3-16. DLRG with gradiometric detection technology operating in the low frequency (i.e., 30 to 300 MHz) band is required to achieve the required void detection depth of 50 feet.

3.6 Technical Innovations of the Deep Look Radar Gradiometer The evolutionary and revolutionary development history of radio detection and ranging (Radar) during WWII at the Massachusetts Institute of Technology (MIT) Radiation Laboratory as well as other laboratories in England, Germany, Russia, and Japan has been chronicled by Brown (2008). The classical ground penetrating radar radiates a stream of very short-time duration pulses illustrated Figure 3-17.

6 The electric field component is divided by the characteristic impedence (z) of the media to arrive at the value of the magnetic field component.



Figure 3-17. Classical Ground Penetrating Radar Schematic and Waveforms. The Fourier transform of the time domain radar pulse can be represented in the time domain as a spectra of frequency components with a sin x/x envelope as illustrated in the lower right side of the figure. The first minimum in the frequency domain spectra occurs at the inverse of the pulse time duration (f = T/t). The short time duration pulse is reflected at the air-natural media interface and when arriving at the radar receiver, “blinds the radar” by occupying most of the useful dynamic range of the receiver. The blinding effect is shown in Figure 3-18.

Figure 3-18. Time Domain of the Reflected Energy from an Object at 17 Feet. First Interface

Reflection Not Suppressed (Trace A). First Interface Reflection Suppressed (Trace B).



The reflection reduces the operating distance (R) of the radar. A more complex problem is that each frequency component in the frequency domain spectrum travels along the path at a different velocity (v) [see, for example, Equation (2-43)], distorting the waveform and making it difficult to accurately determine the range to object. The short-time duration pulse radar receiver instantaneous bandwidth (BW) must accommodate the occupied frequency domain spectral bandwidth (BW) illustrated on the lower right corner of Figure 3-17. The maximum theoretical threshold detection sensitivity of a receiver -168 dBm [see, for example Equation (2-42)] for a 10-dB detection signal-to-noise (S/N) ratio and a noise figure near unity can be achieved with synchronous (i.e., phase coherent) detection (Middleton 1981). Short-time duration pulse radars require multiple megahertz bandwidths with more than 60 dB loss of detection sensitivity. Digitization and signal processing of wide bandwidth signals can restore some of the loss in detection sensitivity. The stepped frequency continuous wave (SFCW) ground penetrating radar technology was developed to overcome the wide spectral bandwidth required by short-time duration pulse radar by Steve Koppenjan and his colleagues at the DOE Special Technologies Laboratory. Each frequency component in the required frequency domain spectrum is sequentially transmitted requiring processing time at each step in frequency. The price for insignificant improved detection sensitivity is the time required to step through the required frequency band. For the SFCW radar, the frequency band of the spectra components must be large to achieve detection spatial resolution as evident in Equations (3-1 and 3-2). Range resolution is mathematically given by

!

"R =C

2BW #r in meters, (3-1)

where C = speed of light 3 x 108 meters/second and BW = spectral bandwidth in Hz. Unambiguous range is mathematically given by

!

Rmax =C

2"f #r in meters, (3-2)

where Δf = step in frequency step in Hz and εr = relative dielectric constant. The SFCW radar can detect multiple objects as defined by the range resolution (ΔR). The SFCW radar inherently high (-168 dB) detection sensitivity is compromised by the transmitter to receiver antenna cross coupling (i.e., cross talk) shown by the red-colored path and the reflection from the first interface in Figure 3-17. The magnitude of the reflected signal (ER2) from the second interface (i.e., object) illustrated in Figure 3-16 must be larger than the near zone signal arriving from the first interface (ER1). The



change in elevation of the radar antenna and ground electrical conductivity (σ) along the traverse creates non-deterministic near zone arriving signals. The non-deterministic clutter and lateral wave reflection signal cannot be averaged to zero and appear as additive noise in the arriving near zone signal. However, installing absorption boundaries around the antenna can minimize lateral reflection noise. The dynamic detection range of the receiver A/D converter is predominated by the vector sum of the cross talk and first interface reflection signals leaving only a small segment of the receiver A/D conversion range to digitize the coherent far zone second interface reflection signal and the non-deterministic near zone clutter and lateral signals. The design concept of the DLRG is vastly different than the design concept of conventional radar instruments, for example:

• Conventional radar operates in free space requiring high-range resolution (ΔR) to detect multiple targets. The traveling EM waves frequency components encounter spreading and object cross section reflection losses along the round-trip transmission path. The round-trip travel time in free space (εr=1) is 0.914 nanoseconds/foot. The transmit to receiver signal path cross talk (see Figure 3-17) isolation is typically near 30 dB requiring that the arriving signal from the buried object be greater than the cross talk signal by at least 10 dB (see, for example, Figure 2-10). Short-time duration pulse radar achieves isolation by gating the received signal path off for the on-time period of the radar pulse and the ring-down time period of the receiver input circuits. Signal processing algorithms have been developed to increase the detection signal path S/N ratio and by incorporating matched filters in the intermediate frequency signal path. Change detection algorithms can be applied to minimize clutter signals.

• Ground penetrating radar directs the transmitted energy directly into the ground creating a number of issues that must be overcome to achieve deep object detection. The ensemble of reflected signal components arriving at the radar receiver input circuits are each phase coherent with each transmit frequency component and can be represented as the linear superposition of all signals identified as:

o Cross talk arriving in less than a nanosecond of travel time. o Air-soil interface impedance miss match causing reflections from the first

interface to be greater the magnitude of cross talk arriving in less than a nanosecond travel time.

o Lateral waves reflected from nearby surface objects arriving within a nanosecond time period.

o Non-deterministic antenna height and soil impedances changes add phase coherent clutter variations to the first interface reflection signal.

o The signals transmitted through the first interface are attenuated by the media, undergo spreading, attenuation, cross section reflection, and internal reflection losses. The observable detection signals exhibit magnitudes that can be more than 47 dB below the cross talk and first reflection signals for object distances of 50 and 20 feet, respectively, foe example, through a coal-barrier pillar or electrically conductive clay soils.



Each arriving signal component can be represented as a stationary phasor with the length of the phasor vector equal to the magnitude of the signal component. Components that are phase coherent and identical in radian frequency can be vectorially summed with a phase rotation equal to the round-trip travel time (τ) multiplied by the radian frequency (ω) of component. Each component phasor exhibits phase jitter (

!

"•

) that depends on the signal to noise (S/N) ratio given as

!

"•

=1

S /N . (3-3)

3.7 Deep Look Ground Penetrating Radar Gradiometer The advanced development of the deep look ground penetrating radar gradiometer (DLRG) has overcome the blinding problem of the traditional ground penetrating radar by gradiometric suppression of the near zone signals, cross talk coupling, first interface reflection, and clutter. Partial to 60 dB clutter rejection is an important contribution to ground penetrating radar technology. This result has been achieved by transmitting double sideband (DSB) suppressed carrier frequency components to achieve greater detection depth by gradiometric suppression (i.e., 60 dB) of arriving near zone signals as shown in Figure 3-19.

Figure 3-19. Detection Depth Versus Frequency for Near Zone Signal Suppression.

The EM gradiometer (EMG) operates in the ultra low frequency (i.e., 300 to 3,000 Hz) to medium frequency (i.e., 300 to 3,000 kHz) bands for detection of scattered waves from abandoned mine entries, clandestine tunnels, weapons caches, and water filled paleochannels. The DLRG incorporates the same EMG primary wave suppression concept but operates as a classical ground penetrating radar in the very high frequency (i.e., 30 to 300 MHz) and ultra high frequency (i.e., 300 to 3,000 MHz) bands for detection of reflected waves from abandon mine entries, gas and oil well casings ahead of a mining machine, and shallow buried tunnels and weapons caches.



The block diagram of DLRG is illustrated in Figure 3-20.

Figure 3-20. Block Diagram of the Deep Look Radar Gradiometer. The digital section is designed around an ARM microprocessor and synchronized with a highly stable, low phase jitter crystal controlled oscillator. Four direct digital synthesizers generate the transmit and heterodyne frequencies for the lower and upper sideband ensemble of signals. The heterodyne signals appear at the same intermediate frequency and are amplified before being applied to the synchronized analog-to-digital converter (A/D) and field-programmable, gated array (FPGA). The DLRG detection is achieved by the spectral transmission of a double sideband suppress carrier waveform illustrated in the Figure 3-21.

Figure 3-21. Double Sideband Suppressed Carrier Waveform.



The DLRG transmit and receive radian frequency (i.e., ω = 2πf) signals applied to the mixer are phase coherent with heterodyne signals. The gradiometric functionality is achieved by down converting each of the arriving lower and upper sideband signals to an ensemble of signals each down converted to the same intermediate frequency as illustrated in Figure 3-22. The modulation frequency (ωm) is given by

!

"m =" 2 #" 2

2 (3-3)

The ensemble of lower sideband frequency components is represented by the vector sum of phasors, each with nearly identical phase shift (i.e., ω1τN). The ensemble of upper sideband frequency components is represented by the vector sum of phasors each with nearly identical phase shift (ω2τN). The ensemble of lower sideband signals is subtracted from the upper sideband signal in the heterodyne down conversion (i.e., mixer) process. The subtraction occurs because the heterodyne process causes the lower and upper ensemble of signals to be 180° out of phase with each other. The lower and upper sideband signals reflected from the far zone interface are each shifted in phase by the radian frequency of each component multiplied by the round-trip travel times (i.e., ω1τF and ω2τF).

Figure 3-22. Phasor Representation of the Gradiometric Heterodyne Process and Quadrature

Detection of the Far Zone Reflected I and Q Signals. (U.S. Patent 6,522,285 B2). The reflection signals arriving from the second interface are also represented as a phasor and add to the vector sum of the lower and upper sideband phasors but with a phase differences (i.e., ωmτF) that is varied by the microprocessor as represented by the dashed circles at the end of each summation of phasors in Figure 3-22. The gradiometric subtraction of the second interface phasors is carried out by the microprocessor varying the phase of the upper and lower heterodyne frequency components with an optimization algorithm that minimizes (i.e., nulling) the magnitudes of the ensemble of intermediate frequency signals. Measurements show that near zone cross talk, first interface, and clutter signals are suppressed by at least 60 dB, an



improvement of 30 dB over non-double side band processing methods. The ensemble of intermediate frequency signals is applied to a quadrature detector where the in-phase (I) and quadrature (Q) components of the intermediate frequency signal are recovered and algorithmically processed to display detection and range to an object. The quadrature detector in-phase (I) and quadrature (Q) signals are mathematically represented by

In-phase (I)

!

I = cos "m# +$m( )cos " cm# +$cm( ) (3-4)

and

Quadrature (Q)

!

Q = cos "m# +$m( )sin " cm# +$ cm( ) , (3-5)

where

!

" cm = 2# fcm is the radian frequency of the suppressed carrier signal and fcm is in Hertz. The magnitude of quadrature detection signal is

!

M = I2 +Q2 1/ 2= cos "m +#m$( ) (3-6)

and the phase of the suppressed carrier is given by

!

" cm# +$cm = tan%1Q&

(3-7)

The microprocessor controls the sideband separation frequency (ωm) to determine the range (distance) to the reflecting object. Since the round trip travel time to the second reflecting interface is invariant, the change in modulation frequency (Δω) required for the I,Q signals to vary from maximum to minimum determines the range given by

!

R =12"#F =

$"4%&m

, (3-8)

where the velocity, v, in the natural media is given by Equation (2-43) and is, for example, approximately 1.5x108 meters/second through coal. Each heterodyne double side band signal coherent phase difference is shifted in phase (θm) to π/2 radians, which changes the magnitude coefficients of the I, Q signals from cos(ωmτ) to the sin(ωmτ). As the Bausov suppression chart illustrates, near zone (i.e., small τ) signals are suppressed by the sin(ωmτ) as illustrated in Figure 3-23. The DLRG in-phase (I) and quadrature (Q) signals acquired along a traverse over a 2x2x4-foot empty wooden crate buried at a depth of eight feet in clay soil with an electrical conductivity of 20 mS/m at 150 MHz and an attenuation rate of 2.5 dB/foot for frequencies above 100 MHz are shown in Figure 3-24. The arriving second interface signal is approximately 46 dB below the magnitude of the first reflection signal. The derivative (labeled magnitude) of the magnitude response (1), if the absolute value of the processed magnitude response were taken, would exhibit the typical M shape of the gradiometric response. The modulation frequency (ωm) was varied by changing the sideband separation radian frequency over 15.43 MHz and observing the magnitude change from minimum to maximum. The data closely agrees with the burial depth of eight feet.



Figure 3-23. Bausov Suppression Factor. The Blue Circles Represent the Near Zone

Suppression Dependence on Modulation Frequency (ωm).

Figure 3-24. Bausov Deep Look Ground Penetrating Radar Response with First Interface

Reflection Suppression Versus Variation in the Modulation Frequency.



Figure 3-25 shows a deep look radar gradiometer installed on a continuous mining machine.

Figure 3-25. Continuous Mining Machine with the Deep Look Radar Gradiometer Installed.

Table 3-1 gives a comparison of the DLRP and classical radars for a number of operating parameters.

Table 3-1. Comparison of Gradiometric Deep Look Ground Penetrating and Classical Radars.

Operating Parameter

Deep Look Ground Penetrating Radar

Gradiometer

Short Pulse or Stepped Frequency Continuous Wave

Radar

First interface reflection suppression

60 dB 30 dB max

Clutter rejection 60 dB Algorithmic signal processing methods that improve detection probability

Additional A/D converter dynamic range

30 dB for deeper detection

Required antenna Narrow bandwidth Wide bandwidth Distance range to an object Varying modulation

frequency Directly measures round-trip time

Transmission wave form Two continuous waves Wideband spectra Useful on a rotating cutting drum

Yes No



3.8 Seismic and Acoustic Wave Detection of Non-Linear Stress Fields Tunnels and boreholes driven into natural media create non-linear stress fields surrounding the void. The stress fields surrounding a tunnel or entry are illustrated in Figure 3-26.

Figure 3-26. Shear Wave Transmission Through Non-Linear Stress Fields.

The formula for a logarithmic pressure field distribution in a one-dimensional radial distance from a circular locus of points with radius (Rc) and pressure (Pc) to a concentric well bore with effective radius (rb) and face pressure( Pb) is

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛

−=−

rR

In

rR

n

PPPrP c

b

c

cbc

1 . (3-9)

The natural logarithm (ln) power series expansion is mathematically given by

!

Ln 1+ x( ) = x "x 2

2+x 3

3"x 4

4+x 5

5... . (3-10)

A narrow band near the borehole experiences most of the pressure differential. For example, Rc ≈ 100 m, and rb ≈ 0.1 m, more than one-third of the pressure differential occurs across the 1 meter nearest to the borehole core. More than one-half of the pressure differential occurs across a zone with a radius of Rc ≈ 3 m. The situation is even more pronounced for boreholes with smaller radii, rb. In general, the stress field can be represented by a Taylor series expansion. When two or more sinusoidal seismic S (i.e., slow traverse) waves, seismic P (i.e., fast longitudinal) waves, or acoustic frequency signals travel along a refraction path crossing through a non-linear stress field, the heterodyne of the two signals generates at least a sum and difference frequency signal given by

!

f"

= nf1 ± mf2 . (3-11)



When the stress field is strongly follows a square law, the best product frequencies

!

f"

are predominately the sum (i.e., upper heterodyne) and difference (i.e., lower heterodyne) frequency. The magnitudes of the generated signals depend on the coefficient of the power series expansion. The “double sideband” seismic or acoustic detection process is similar to the DLRG illustrated in Figure 3-22 except that the heterodyne process occurs in the non-linear stress field surrounding the void as illustrated in Figure 3-27.

Figure 3-27. Detection of Heterodyne Signals.

The receiver geophones are built with a magnetic wire coil surrounding a permanent magnetic.7 The coil is mounted to an Earth contact plate. The mounting configuration can be on three orthogonal axes. The media movement along each axis generates an electromotive force, emf, voltage measured by instruments. The transmitter may be a piezoelectric ceramic radiator driven by a series of short time domain pulses that are synchronized to a direct digital synthesizer and controllable in frequency steps from 3 to 30 kHz, which receives the spectra components including the transmitted frequencies ω1 and ω2 and the non-linear stress field heterodyne frequencies. Each of the frequency components may be a unique spectrum for each individual source. The received heterodyne signals can be re-heterodyned in electronic circuits to create a common intermediate frequency enabled by a detection process described in Figure 3-22. The path range can be determined by varying the modulation frequency. The clutter, in this case, consists of cultural signals that can be suppressed by applying the Bausov suppression factor (see Figure 3-23). The transmitted spectrum, F(ω), of each source can be detected and auto correlation processing of the media heterodyne signals can be used to detect the non-linear stress fields of voids.

7 Mems sensors may also be used in detection vibrations caused by pressure (P) and shear (S) waves. Non-ground contact lasers have been developed for soil movement detection.



4.0 MAKING THE EARTH TRANSPARENT Formation of ore bodies and geothermal reservoirs by magmatic injection into the Earth crust are illustrated in Figure 4-1.

Figure 4.1 Subduction, Upwelling, and Solidification Temperature of Ore Bodies.

The drift, collisions, uplift, and subductions of continental plates making up the Earth’s crust give rise to volcanism. Drift, collision, and uplift create non-liner stress fields, micro and macro fractures and faults in the crust. Subduction carries valuable elements of the periodic table, previously deposited on the sea floor, into the thermal region of the Earth. Welling up of tongues of magma into the upper Earth crust creates geothermal reservoirs, mineralized ore deposits, and alters layered beds of coal and evaporates. Thermodynamic processes occurring during magmatic injection through the temperature gradient in the upper Earth’s crust separate elements according to their temperature of solidification. The element solidification temperature ranges are illustrated on the right side of the Figure 4-1. The exothermic processes of the elements giving up their heat of fusion causes stress fields to develop in the solidified rock mass. When the stress fields become high enough, the solidified rock fractures. Fluid elements are injected into the fracture space, creating complex mineralization. Basic metal ore bodies and fluid elements of geothermal reservoirs exhibit higher electrical conductivity than the host rock with few exceptions like sphalerite, the resistive zinc containing ore. Exploration departments of today’s mining companies employ the skills of geologists in surface mineralization studies and apply surface-based geophysical instruments (e.g., seismic, long wavelength electromagnetics, Earth’s magnetic field, temperature, and gravity) to discover promising deposits. Similar techniques are used in geothermal resource exploration. To prove



reserves, exploration activities include slim-hole drilling, core log analysis, and running a set of wireline or measurement-while-drilling instruments. Contouring software (e.g., Rock Works, Surface Arc View, QuickSurf Map info) is applied in mapping mineralization between drill holes. Oil-field service companies offer limited services to the mining companies. There are very few geophysicists employed in the mining industry. Mineralization and mineability assessments are oftentimes provided by a geologist’s interpretation of borehole cores and geophysical logging data. The problem that the oil-field service company faces in providing services to the mining industry is that of the Mine Safety and Health Administration (MSHA) flame proof or intrinsically safe (IS) approvals are time consuming and difficult to achieve for equipment that must operate in gassy mines. The problem is complicated in that oil-field tools are not sized in accordance with standards established by the mining industry. Depth requirements are seldom greater than a few thousand feet because entries are difficult or impossible to be maintained below a few thousand feet of cover. The service companies have applied surface seismic high resolution imaging with favorable results in locating full seam displacement faults. Partial seam faults and paleochannels have proven to be problematic for detection by seismic technology. This type of subtle geologic anomaly commonly creates unexpected ground control problems that impact coal extraction. Mining companies drive tunnels and multiple entries into the deposit achieving visual confirmation of the anomaly that is seldom in agreement with seismic or acoustic imaging. On the other hand, oil-field geophysical logs and images are seldom validated by confirmation. In an oil-field geologic setting, sandstone reservoirs may have meandering paleochannels that only slightly interfere with oil production, but are catastrophic in the mining environment. Seismic velocity depends on rock density and changes by less than an order of magnitude when passing through mineralized rock. Seismic imaging is not useful in determining the halo of mineralization and cut-off ore grade. The electromagnetic wave attenuation rate (see Figure 2-21) is dependent on frequency and electrical conductivity, and a change by orders of magnitude in crossing the mineralized ore zone, which accounts for the high detection sensitivity and imaging resolution. An image of mineralization in host rock is shown Figure 4-2. 4.1 Electromagnetic Fields in Coal Seams Medium-frequency (MF) mine-wide radio communications demonstrated in the late 1970s discovered that the coal seam waveguide supports the transmission of electromagnetic waves in the low-frequency range of the AM radio broadcast band. Radio wave transmission experiments carried out in the world’s coal seams exhibit "text book" wave propagation results similar to those found in microwave transmission laboratories of applied science and electrical engineering colleges. Transmissions of radio waves through faults in the coal bed create near-side reflections and far-side reduction of the magnitude of the radio signal (see Figure 2-22). Radio waves are refracted when passing near anomalous geologic structures in the coal seam. Oftentimes, meandering paleochannels (see Figure 3-2) scour through sedimentary boundary layers and create non-linear stress fractures and slickenside geology along the margins of a channel.



Figure 4-2. Tomographic Images of a Massive Iron-Nickel Ore Body.

Differential compaction of the coal seam resulted in seam thinning and undulations. The fractures allow the radio signal energy to leak out of the coal-seam waveguide and become observable as increased signal attenuation between the radio transmitter and receiver. Oftentimes, a sandstone paleochannel becomes an aquifer for local groundwater and scouring of the sealing boundary layer allows water to seep into the waveguide. Because of the clay content of coal, ionization of the bulk coal increases the electrical conductivity and the attenuation rate of the radio wave when traveling through anomalous zones. These coal seam anomalies can be detected via real-time reconnaissance and rapid tomography scanning of the coal seam with in-mine or slim-hole radio imaging method (RIM) instrumentation. Natural coal, trona, gilsonite, tar-sands, and potash seam waveguides occur in layered sedimentary geology because the sealing boundary layer electrical conductivity of shale, mudstone, and fire clay ranges between 0.01 and 0.1 Siemens per meter (S/m) or 100 and 10 ohm-meters. Marine strandline environment deposition processes have boundary layer conductivity as high as 0.16 S/m. The conductivity of coal, trona, and potash depends on the amount of bentonite clay and moisture in the seam. The conductivity ranges from 0.001 to 0.0005 S/m or 1,000 to 2,000 ohm-meters. The more than 10-to-1 conductivity contrasts between the boundary layer and the natural seam forms a waveguide that causes electromagnetic (EM) waves to travel within the seam (see Figure 4-3). The electric field, EZ, component of a traveling EM wave is polarized in the vertical direction and the magnetic field (Hy) component is polarized horizontally in the seam. The energy in this part of the EM wave travels laterally in the coal seam from a transmitter to a receiver. There is a horizontally polarized electric field (EX) that has zero value in the center of the seam and reaches a maximum value at the sedimentary rock-coal interface. Because of the boundary charge



(++++,----) illustrated in Figure 4-3, the Ex component is responsible for transmission of the EM wave signal into the boundary rock layer. The energy in this part of the EM wave travels vertically and out of the coal bed (i.e., the coal seam is a leaky waveguide).

Figure 4-3. Anomalies and Electromagnetic Field Components Found in a Coal Seam

Waveguide. (U.S. Patents 4,691,166; Re. 32,563; 5,408,182; 6,549,017 B2; 6,593,746 B2; 6,744,253 B2; 6,927,698 B2).

Energy in the EM wave “leaks” into the fractured rock overlying the seam; thus, weaker roof rock can be detected by mapping rapid increases in attenuation rate (i.e., gradient) across the plane view of the seam. Fractures in the boundary layer will increase the roof fall hazard (see Figure 2-3). In rock fall hazard areas, ground control measures should be intensified in these areas. Due to the EM waveguide behavior, the magnitude of the coal seam radio wave decreases because of two different factors, namely, the attenuation rate and cylindrical spreading of wave energy in the coal seam. The cylindrically spreading factor is mathematically given by 10log r, where r is the distance from the transmitting to the receiving antenna. This factor compares with the non-waveguide far-field spherically spreading factor of 20log r. Thus, at 100 meters, the magnitude of the EM wave within the coal seam decreases by a factor of only 10 in the waveguide and by a factor of 100 in an unbounded medium. An advantage of the seam waveguide is greater travel distance. Another advantage is that the traveling EM wave predominantly remains within the coal seam waveguide (i.e., the coal bed) except when the sealing mudstone or shale laver is fractured by an overlying paleochannel. Rolls caused by differential compaction decrease seam height. The injection of water into a coal seam significantly increases the attenuation rate.



A coal seam EM wave is very sensitive to changes in the waveguide structural geology. The horizontal electric field component reaches minimum value at the vertical elevation of mid seam when the roof and floor conductors are identical. The horizontal electric field component or “null” rapidly changes from near mid seam elevation when passing under the margins of a paleochannel. A hand-carried survey tool can be developed to detect margins of paleochannels crossing development entries. The radio-wave attenuation rate in decibels and phase shift in electrical degree/100 feet of travel were determined by Dr. David Hill (Hill 1984) at the National Institute of Standards and Technology (NIST). Dr. James Wait (Wait 1963) was the first to recognize that natural waveguides exist in the Earth’s crust. The science underlying the traveling of an EM wave in a coal seam waveguide is well known. Hill and Wait have theoretically investigated the seam waveguide EM wave transmission described in Figure 4-3. The propagating wave is called a zero order mode quasi-transverse EM wave. All waveguide modes above the zero order are cut off and will not propagate in the seam. This phenomenon means that an EM wave does not bounce from the roof to the floor as it would in a multi-mode case. Multipath propagation is suppressed by the relatively high attenuation rate within the coal seam. The effect of attenuation in the seam waveguide is to reduce the magnitude of the EM wave along the path. The coal seam attenuation rate increases with frequency is illustrated in Figure 4-4,

Figure 4-4. Coal Seam Electromagnetic Wave Attenuation Rate Versus Frequency.

The wavelength increases as frequency decreases. The effect of changing coal seam boundary sedimentary rock on attenuation rate is illustrated Figure 4-5. Under sandstone sedimentary rock, the attenuation rate increases because part of the RIM signal energy travels vertically into the boundary rock (i.e., leaks from the waveguide). If water is injected into the coal from an overlying paleochannel, then clay in the coal causes the electrical conductivity and attenuation rate and phase shift to increase. The attenuation rate significantly increases under sandstone paleochannels (see Figure 2-3). Along the margins of paleochannels, the channel scours into the bounding shale or mudstone sedimentary rock. Differential compaction rapidly degrades roof rock strength. Roof falls are



likely to occur along the margin, suggesting that ground control should be increased in this segment of mine entries.

Figure 4-5. Coal Seam Electromagnetic Wave Attenuation Rate Versus Boundary Rock Conductivity.

The attenuation rate and phase shift rapidly increase with decreasing seam height as illustrated in Figure. 4-6.

Figure 4-6. Sensitivity of Radio Waves to Changes in Coal Layer Thickness.

Seam thinning can be detected by transmitting an EM signal in the waveguide and measuring the attenuation rate. The graphical presentation of coal seam waveguide attenuation and phase constants represents the science factor in the art and science of interpreting EM sensor wave

Fractured shale

SandstoneShale

Fractured shale

SandstoneShale



tomographic images. Higher attenuation rate zones suggest that the coal seam boundary rock is changing, the seam is rapidly thinning, and/or water has been injected into the coal seam. The seam waveguide is effective in the frequency range above 10 kHz to at least 500 kHz. Near the low-frequency limit, in-mine experiments suggest that exciting the seam transmission mode with reasonable size loop (i.e., magnetic dipole) antennas is difficult. At the high-frequency limit, the attenuation rate of the wave increases and limits the operating range. Faults and dykes cause reflections to occur in the waveguide. The reflections can appear as excess or very low path loss. Total phase shift measurements are useful in detecting reflection anomalies. Geologic anomalies and ground control problems are prevalent in all of the world’s coal deposits. Coal production can come to an abrupt halt when a longwall machine becomes trapped or "iron-bound" in bad geology such as along the margins of a channel (see Figure 2-3) intersecting a fault or a dyke. Tomographic radio wave mapping around anomalous geologic structures assists in geotechnical planning and operation. Imaging of paleochannels ahead of mining can locate where ground control should be intensified by roof bolting and installing screening or trusses. Oftentimes, the roof rock fails when entries are driven under margins of paleochannels. Roof fall injuries could be reduced significantly if images of margins were mapped and ground control measures were intensified. The primary function of RIM instrumentation is to send radio waves from a transmitter, along a straight ray path through the area-of-interest to a receiver as illustrated in Figure 4-7. The RIM instrumentation leverages the natural waveguide effect of signal propagation in layered strata to produce the observable, cylindrical spreading attenuation rate and refraction within the coal bed. Signal analyses allow for the detection of conductivity changes and material boundaries, while the geometric distribution of signal ray paths allows for the generation of reconstructed images through tomographic inversion. RIM applications go beyond coal mining, and have proven to be powerful tools in metalliferous mining, environmental research, civil engineering, environmental research, and security applications. Radio geophysics applies methods in computerized axial tomography (CAT) in the processing of RIM data to effectively reconstruct geologic images. Advanced 3D algorithms include corrections for complex refraction and reflections in the coal seam waveguide. The development of practical RIM technology has had to evolve to keep pace with the ever-growing scale of mining. Longwall panels in particular have increased in width to more than 1,500 feet in the last decade, nearly three times wider than those first mapped with RIM in the 1980’s. H. Löwy’s 1911 work applying computerized axial tomography (CAT) in processing EM wave attenuation data to reconstruct images of ore bodies preceded, by more than four decades, Godfrey Hounsfield’s work, who received the Nobel Prize in 1979 for his part in developing the diagnostic technique of X-ray computed tomography. In recent years, slim hole single and cross well acoustic and EM imaging instrumentation have been developed to acquire data for tomographic reconstruction and mapping of anomalous geologic structures in coal and mineral deposits. For low contrast anomalies, reconstructed images are in close agreement with geologic



mapping conducted while mining through the anomaly. In the present art, EM data sets are acquired between boreholes and physically constrained by two-sided tomographic reconstruction, which distorts the image in the direction of wave propagation. Computerized axial tomography, as well as ray path refraction correction, algorithms that process data sets acquired in scanning higher contrast anomalies exhibit artifacts in the reconstructed images.

Figure 4-7. Longwall Mapping with In-Mine Radio Imaging.

4.2 Advanced Radio Imaging Method Instrumentation The radio imaging method (RIM) has a long history of applying the well-proven methods of computerized axial tomography (CAT) in the processing of EM wave attenuation data to effectively reconstruct images of both coal seams and ore bodies. The algorithms required for these reconstructions have been continuously developed to include corrections for complex refraction and reflections in the coal seam waveguide. Using advanced image processing, RIM tomography has been successfully applied in evaporite deposits and mineralized ore zones as well as in coal seams. The evolutionary development of RIM technology has continued since the early 1980s as longwall panel width has increased to more than 1,500 feet. Given the need for longer range and better resolution, slim-hole cross well and in-mine RIM imaging instrumentation required technical innovation in digital receiver design to lower its own internal noise floor, combat environmental electrical noise generated in the mines electrical power system. These improvements and enabled RIM signal detection at the one-Hz bandwidth theoretical limit, (i.e. -168 dB re 1 Ampere/meter).



In-Mine RIM-6 survey equipment is man-portable and consists of receiver units (RX) and transmitter (TX) units. During operation, the transmitter must be used in the headgate entry (i.e., beltway, intake) of the longwall block and the receivers must be used in the tailgate entry (i.e., return). The RIM-6 instrumentation operates at discrete frequencies between 10 kHz and 1 MHz. Typically, the frequency used is the highest possible given the range of the signal in a specific coal seam and panel width. The TX unit broadcasts a continuous-wave radio signal to the RX units at a fixed radiated power level. The TX and RX units are not connected by any type of cable or wire. Thus, the signal passes entirely through the coal seam. The principal key to the digital RIM-6 success is the narrow bandwidth and wide dynamic range of the radio-frequency (RF) receiver, which provides greater detection sensitivity and a lower noise floor than any previous RIM system. A secondary contribution is in the improved transmitter antennas, which generate larger magnetic moment magnitudes and couple greater signal into the coal seam. These improvements provide greater operational range, higher signal-to-noise (S/N) ratios, and ultimately improve the image resolution of the tomographic reconstructions enabling imaging in super wide longwall panels. In addition to improved RF performance, the current RIM-6 hardware uses a modern personal digital assistant (PDA) and Bluetooth technology as the primary command and control interface, which increases data rates, and allows wireless communication and onboard data storage and processing. By way of example for performance improvements, a recent digital RIM-6 survey at a Colorado coal mine in the U.S. provided a 70-dB S/N ratio at 700-kHz, while a previous RIM-4 survey in the same mine provided a 40-dB ratio at only 300-kHz. These improvements have the potential to increase resolution by an order of magnitude. In addition, the fully digital RIM-6 receiver can also provide: (i) more stable and accurate measurements, (ii) wide-band spectral noise analysis, (iii) multi-channel, multi-frequency measurements, and (iv) two-way transceiver functionality, although the TX function is currently not implemented for demonstration. Table 4-1 lists RIM-6 performance improvements in frequency and S/N ratio for the demonstrations projects completed in the first few months of use.

Table 4-1. RIM-6 Performance Versus Previous RIM Technology (February to May 2011).

Demonstrations of in-mine RIM-6 will continue in 2012 with the process of identifying longwall sites, reviewing possible in-seam target anomalies, and working with coal operators to organize

Coal Mine Location Longwall Width Frequency Signal-‐to-‐Noise Frequency Signal-‐to-‐Noise

Colorado, USA 900-‐ft 672-‐kHz 70 290-‐kHz 40

NSW, Australia 1320 302-‐kHz 15 52-‐kHz 18





2011 In-‐Mine RIM-‐6 Previous Best RIM (2, 4, or 5)

RIM-‐6 Performance vs. Previous RIM Efforts (Feb to May 2011)

Many more demonstrations of RIM-‐6 are planned for 2011.



underground logistics, scheduling, and approvals for the use of the new instrumentation on current and future panels. The process for surveying a longwall panel includes five steps:

• Plan the survey; timing, proper instruments, budget, and mine-site preparations; • Collect the field data; including equipment calibration to the specific seam, a

reconnaissance scan, and tomographic scans as needed. • Analysis of the data, which includes construction of 2-D or 3-D tomogram images; • Confirmation as required, in some cases drilling or mining into anomalies to confirm

targets is prudent; and • Integration of geologic intelligence into mine planning.

In addition to longwall mapping with hand-held instruments, the RIM-6 system is also constructed into a slim line borehole package for mapping from drill hole to drill hole. The range of the borehole RIM-6 system is somewhat less than the in-mine system, due to antenna inefficiencies, but the ability to maximize the information garnered from drilling efforts can be invaluable. Using widely spaced boreholes to detect and image in-seam structure without intersecting with the drill bit can provide a large cost savings and better direct exploration efforts. Figure 4-8 shows a current borehole RIM-6 system during recent survey efforts.

Figure 4-8. Digital RIM-6 Instrumentation.

The graphic in Figure 4-9 illustrates the process and results of a RIM longwall mapping operation. A sample tomographic image (i.e., tomogram) is shown. The tomogram is a 2-D plan-



view representation of signal-loss within the coal seam block. The blue areas are normal signal quality representing “clean coal,” while the red areas are excess signal loss indicative of “hazardous” structures or severely disturbed coal. The image uses hundreds of ray paths to create a general size, shape, trend, and severity for the in-seam anomalies.

Figure 4-9. Digital RIM-6 In-Mine Survey Instrumentation and Tomography Image of Coal

Seam Anamolies. Each coal seam is unique and thus the RIM system should be calibrated to establish baseline attenuation rates (i.e., rate of signal decay per unit lateral distance). Once established, it is fairly efficient to send a signal directly across the panel every 20 to 40 feet along the panel’s length. This is known as a real-time reconnaissance or RECON scan. If no anomalies are present, the attenuation rates of the signals should be fairly consistent. However, if an anomaly is encountered, there will be a general loss of energy in the signal with an increase in the attenuation rate. Once encountered, a more in-depth evaluation can take place around this anomaly by conducting diagonal scans across the panel to increase the density and orientation of the signal’s ray paths, which generates greater resolution. This detailed survey is called a tomography or TOMO scan. These two survey methods are illustrated in Figure 4-10. In-seam anomalies not only create higher attenuation rates, but cause reflections in the signals, which are measured by the signal phase shift. These two variables are used to create reconstructions of the survey area using inverse tomographic algorithms. A tomogram is a color-coded image based on these reconstructions. Tomograms provide mine planners and geologists with important intelligence about the location and severity of thinning seams, faults, sandstone channels that can impede longwall advancement. Factoring this information into production forecasts provides management with the necessary tools to better assess financial, production,

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maintenance, and safety performance. Eliminating “surprises” during production, or ahead of development, reduces risk and enables greater productivity.

Figure 4-10. Radio Imaging Method Data Collection Techniques.

4.3 Recent Longwall Mapping Case Studies A major Australian coal producer has recently utilized several types of RIM techniques for borehole exploration and longwall mapping. This mine has encountered a number of geological anomalies that have created great difficulty during the mining process. In some cases, large coal seam structures were intersected without prior knowledge or warning, causing production to temporarily stop and only be recovered at a substantial cost. Some of the structures typically intersected were igneous plugs, dykes, or diatremes. Using both the in-mine and borehole versions of RIM-6, the mine can detect hazards early in development and image the anomaly before production passes through the hazardous zone, enabling supplemental ground control methods to be employed, such as surface-deployed long strata bolts and grouting to improve stability. The mine uses traditional exploration processes such as aeromagnetic or ground magnetic surveys, and then further investigates the coal seam through drilling. However, the mine has found that this process has a number of limitations because these techniques can only identify



large anomalies with strong magnetic signatures at the surface. Since the opposite is often true, exploration drilling is often guided by more direct and mundane techniques. Longwall mapping with older versions of in-mine RIM was able to indentify large anomalies within longwall blocks prior to mining, but due to some technical requirements, conducting the RIM survey was disruptive. Power had to be cut to the panel and infrastructure (e.g., metal pipes) had to be broken. These requirements created downtime not only for the shifts RIM was utilized, but over several shifts as preparation and remediation was performed. Additionally, as the width of the longwall blocks continued to increase and the older RIM systems were not providing sufficient results over the new extended distances. So poor performance, combined with the disruption to production, came to be considered impractical and the mine looked for advanced RIM technology. With the RIM-6 instrumentation, the mine realized it did not need to disrupt the mining process, Moreover, the improved performance of the RIM-6 equipment created more opportunities to discover a broader range of geological anomalies that could impact both development and production. Recently, a number of RIM-6 surveys were conducted over an area initially identified from a reconnaissance survey of a longwall block. Progressive exploration was undertaken further utilizing RIM-6 at each stage, which included borehole-to-borehole, borehole-to-gate road, and gate road-to-gate road surveys. The result was detection and scaling of an anomalous area well before interaction with the mining process. This advance information permitted timely communication to the mine site, preparation of geological information plans encompassing the RIM-6 images, and preparation for additional support of the area prior to mining through the anomalous area. The project began with a rapid real-time RECON scan along the longwall block. The 1-D results indicated that an unknown anomaly existed at the center of the longwall block. A focused 2-D tomography survey was performed in the anomalous area and further refined the size, shape, and location of the structure. A drill hole was then developed from the surface into the anomaly to explore the source of the disturbance. Unfortunately, the drill hole missed the anomaly due to severe deviation of the drill hole. However, the drill hole provided an opportunity to image from the borehole to the in-mine entries to further refine the image from within the block. Using the drill hole at mid-block, the required signal propagation distances are 50% less than normal, allowing for the use of higher frequencies with better resolution. This initial series of RIM imaging efforts is shown in the upper image in Figure 4-11. The results of this borehole-to-gate road survey method provided a two-dimensional shape to the unknown anomaly and it was decided that the anomaly would be surrounded by a small grid of boreholes for additional mapping. A significant borehole-to-borehole mapping survey commenced and led to the creation of dozens of vertical image planes crisscrossing the anomalous area. The survey predicted severe fracture zones in the roof strata and upper sequences of the multi-bench coal seam. The resulting image was used to plan a dense drill-hole pattern for the purposes of supplemental strata control, including long cable, anchors, and grouting from the surface holes. In the end, the longwall passed beneath the fracture zone with no disruption to longwall mining. Had the RIM survey not been conducted, the mine may have battled severe ground control issues for more than 300 feet of longwall advance. The final series



of imaging efforts leading to geotechnical intervention, and subsequent longwall mining, is shown in the lower images in Figure 4-12.

Figure 4-11. Initial Series of Multi-Stage Radio Imaging Method Surveys.

During the mining process through the anomalous zone, geologists mapped the longwall face 24-hours a day to reconcile the RIM-imaged anomaly with actual longwall face conditions. What was determined and visually mapped on the longwall face was a seam roll of significant undulation (i.e., up to 2 meters). Related to the fold was a clear increase in jointing directions and frequency. The start, finish, and trending direction of this seam roll and associated jointing coincided with the RIM-6 tomogram. Consequently, information was provided to production crews regarding the likely distance of the anomaly and, therefore, when mining conditions were likely to improve. The RIM-6 instrumentation clearly has the ability to identify a wide variety of geological anomalies. In addition, RIM-6 surveys can identify large igneous plugs or diatremes that have low magnetic signatures within limited sized longwall blocks. Without disruption to the mining process, RIM-6 surveys enable detection of finer-scale structure within larger longwall blocks, such as the roll and jointing that was encountered. A second major Australian coal producer has been able to utilize and document the benefit of progressive advancements in RIM using imaging on successive longwall panels over several years. As improvements in the technology are brought into the district, mine engineers have been able to document the improved detection sensitivity and image resolution of RIM advancement over five years (e.g., from RIM-4, to RIM-5, and, finally, to RIM-6) by tracking significant in-

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seam anomalies across entire mining districts, including faults, igneous intrusions, sills, and paleochannels. Each new longwall panel showed increased RIM performance from frequency gains and better signal-to-noise ratios. The graphics in Figure 4-13 show several recent multi-panel case studies. In general, the use of improved RIM platforms has increased sensitivity to in-seam structure, increased signal range (i.e., maximum imaging distance), and improved image resolution.

Figure 4-12. Final Series of Multi-Stage Radio Imaging Method Surveys.

The choice to use RIM by this coal producer occurred when a volcanic plug was encountered in the middle of their longwall block, which had a massive effect on business, and from which a six-month recovery period was required. The decision was made to use RIM as a predictive tool to better understand any significant geological features and prevent a similar outcome to operations. This decision has lead to the use of RIM for longwall mapping as a standard practice to assist in the location and definition of geological structures. The series of three consecutive longwall tomograms shown in Figure 4-13 from this mine have been verified through mining history to correlate with the actual structure encountered during production. To date, the majority of anomalies in the tomograms have been explained and confirmed. There have been a few small tomographic anomalies that did not correlate to severe structures, but no structure has been encountered that was not identified by the RIM surveys. This coal producer has also utilized high-resolution RIM around pillars to locate ancient surface boreholes, providing invaluable information to assisting with locating potential water in-rush hazards. The mine does do a significant amount of in-seam drilling to de-gasify and de-water the coal seams, however, the mine is quick to point out that they no longer depend on existing

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drilling to fully map the longwall. Other mines have argued that their existing in-seam drilling efforts for degassing should typically locate anomalous structures. However, this major coal producer has documented two significant events in which there were numerous in-seam drill holes that did locate a small number of dykes but missed their source plug entirely. In fact, the mine actual drilled two holes beneath the silled section, but the zone was misinterpreted by the drillers as simply being “hard coal,” while it was actually the base of a massive plug which grew in width, thickness, and hardness moving away from the drill holes. These events proved to the coal producer that in-seam drilling was not reliable for detection and scaling of these structures. Since adapting RIM-6 as standard practice, this mine site has been able to document intrusions and avoid unknown pitfalls. Figure 4-13 shows several intrusions mapped with successive versions of RIM, each with its own unique results.

Figure 4-13. Radio Imaging Method Mapping of Intrusions into a Coal Seam.

The improvement in imaging resolution with frequenvy is illustrated in Figure 4-14.

4.4 Future Considerations For the past decade the underground coal mining industry has been moving toward a reality of “super panels,” that is wider mining faces and greater longwall lengths. An obvious economy of scale exists and super panels have certainly enabled the industry to keep pushing the limits of productivity. However, an important consideration of panel size, now and especially in the future, will be driven in large part by geological factors. While larger panels capture economies of scale, the fact that super panels contain several times the coal volume, the probability of encountering serious anomalies is several times greater than with conventional panel sizes. Given the increased probability of encountering anomalies, improved assessment of geology is important for future longwall panels. Also, the quality of coal reserves are, or have been, declining so in the future mining will be in deeper and most likely thinner seams. These seams also appear to contain greater anomalies that threaten efficient operations. To counter the impact of reserve deterioration, the industry must move toward greater use of geophysical tools and services.

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Figure 4-14. RIM-5 Studies.

The results of the case studies confirm that the RIM-6 system provides additional intelligence about the coal geology of large and geologically complex longwall panels; however, the images are not an end in and of themselves. Images of the seam need to be integrated into mine planning and production forecasting. If serious anomalies are identified, management then must chart a course to deal with the geologic challenges. Knowing that geological obstacles lay ahead can improve the chances of positive outcomes.

4.5 Technology Gap in Subsurface Imaging Integrating acoustic with EM wave transmission and destination measurement technology in slim hole single and cross well instrumentation is a natural evolutionary and revolutionary advancement in the state-of-the-art in geothermal energy development. The instrumentation brings the state-of-the-art forward because EM propagation constants are sensitive to changes in electrical conductivity whereas the transmission of multiple-frequency acoustic waves through non-linear rock stress fields and anomalies generates an observable acoustic frequency domain spectra. The amplitude of each acoustic spectral component depends on the coefficients of the power series expansion mathematically representing the non-linear effects of stress fields and anomalies. Effects of non-linear stress fields, micro fractures, and pore space fluid geochemistry on methane gas and geothermal fluid flow permeability can be investigated with the combined instrumentation. Mechanical stresses in natural media change the fracture aperture that functions as a filter. Chemical reactions affect fluid flow mobility and dissolution of the pore surface lining minerals can create debris and clog the filter, thereby reducing permeability. The geological and



geochemistry factors predominating flow permeability can be more accurately determined with acoustic spectrum analysis and tomographic imaging. A downhole tool designed with radiating focused acoustic beam forming resonators holds promise for increasing flow permeability and thermodynamic mass transfer, possibly paving the way for new discoveries in geothermal reservoir development and management. Non-linear image reconstruction algorithms and instrumentation capable of synchronized magnitude and phase (i.e., full wave) measurement of the destination acoustic and EM wave are required. The non-linear reconstruction algorithms require forward solvers as part of the reconstruction process. Forward solvers are three-dimensional models that assign acoustic velocity electrical conductivity values to the boxel in the image volume. The non-linear inversion problem is a scattering problem that has been worked on by Drs. Gregory Newman and Peter Petrov of the Lawrence Berkeley National Laboratory. The algorithms have not been developed sufficiently to allow straightforward application by the mining industry.



5.0 STERILIZATION OF COAL RESERVES The sterilization of the U.S. coal reserves as well as contamination and destruction of freshwater aquifers are occurring at an alarming rate. Technology gaps if identified, validated, and overcome, may prevent coal from becoming a strategic mineral in the East. Safe and productive mining complex development plans require driving multiple entries into virgin coal. Coal pillars with cross cut stoppings separate the entries to provide fresh and return air-flow passageways, coal haulage by rail or conveyer routes, AC power and communications cable pathways, and man and material travel passageways. The approved mine ventilation and ground control plans define the infrastructure of the underground mine. The mine infrastructure sterilizes from 20 to 50% of the coal reserves located on the mine property. Modern longwall (e.g., 1,200-foot wide and 10,000-foot long panels) mining approaches the lower end of the sterilization range. The average U.S. coal mine produces 0.71 million tons/year. During the 10-year life cycle of the mine, 1.4 million tons, which is equivalent to about 2.8 billion kWh of electricity are unavoidably sterilized. Taken together, all U.S. mines annually sterilize 80.3 million tons of coal or 160 billion kWh of electricity equivalent. Over the past 20 years, the number of operating longwall machines has declined from 103 to 49. This decline is offset by increased production rates of more than 20,000 tons/shift. The number of longwalls will continue to decline as the easy to mine coal becomes exhausted. The unavoidable sterilization rate will continue to increase as mining occurs in more complex geologic settings. The Quecreek mine disaster occurred when development entries were driven near the abandoned, water-filled Saxman Mine. The problem occurred because older mine maps were not accurate and some entries may not have been recorded on the mine map. As a result of the disaster, the Mine Safety and Health Administration (MSHA) requires that a 50-foot wide barrier pillar be maintained between an abandoned mine and the boundary of a new mine to ensure safety in the new mine development. For a coal bed thickness of seven feet, the reserve sterilization for each mile of barrier is 48,000 tons of coal or 95 million kWh of electricity equivalent.

5.1 Technology Gap The cross section shown in Figure 2-6 illustrates the stress field for the Quecreek entry where rib failure occurred approximately two feet from the abandoned Saxman Mine. Interestingly, the mining crew reported increased water in the developed cut prior to the collapse of the rib. Underground mines could use look-ahead radar and reduce barrier width to 20 feet (i.e., a safety factor of more than 2.5 when depth allows). As a result of the Quecreek disaster, look-ahead radar technology was developed with MSHA funding and successfully evaluated in an underground mine. However, radar detection of abandoned mines ahead of mining was not made a mining law requirement. The production of coal bed methane (CBM) from coal beds with vertical drilling and cavitation recovers only about 5% of the energy content and leaves 95% behind. Many U.S. coal reserves



have multiple seams with each seam pierced by vertical metal casings. The Farmington Mine disaster is believed to have been caused by mining into the metal casing of an abandoned gas well. The MSHA regulations require that mining stop before reaching a 150-foot radius of a gas well. This regulation results in the sterilization of 20,600 tons or 41 million kWh of electricity equivalent. Thus, each gas well in a coal seam destroys the electricity generation that could supply a city of 8,500 people for one year. The Raton Basin, which is 50 miles wide and 80 miles long, in southern Colorado and northern New Mexico has 5,346 developed CBM wells, sterilizing 110 million tons of coal or 220 billion kWh of electricity equivalent. The basin includes two seams of high-quality metallurgical coal with an estimate of 1 billion tons of minable coal. Abandoned gas wells are located and plugged. Mining plans specify where the well barrier coal will be located. The Stolar RIM imaging and radar detection has been used to locate abandoned wells, which are then exposed by mining and cut-off, which enables the mining machine to recover otherwise sterilized coal. The withdrawal of public and private lands from mining also reduces the minable coal reserves. Each square mile withdrawn from mining sterilizes 8.2 million tons of coal or deprives the nation of 16.2 billion kWh of electricity equivalent. The main landowner in the Raton Basin has withdrawn one billion tons of metallurgical coal. There are 800 continuous mining (CM) machines and 49 longwall shearers cutting underground coal in the U.S. that need advanced technology to detect anomalies ahead of mining. The rotating cutting drum of continuous mining machines and longwall shearers need to be equipped with look-ahead radar technology that can prevent mining into steel well casings and water and/or gas filled voids. The unproven technology needs to be validated by MSHA and proven in three mining regions.



6.0 DESTRUCTION OF FRESHWATER AQUIFERS Production of methane from coal beds (CBM) and shale gas is having a negative effect on near-surface freshwater aquifers. High-pressure hydraulic fracturing with propants (e.g., sand) provides high permeability pathways into overlying and underlying aquifers. Pumping of contaminated water to the surface followed by deep disposal depletes freshwater supplies for cattle, agriculture, and human populations. Oftentimes, the recharge rate of near-surface aquifers is slow because of the aqua strict nature of the overlying strata. Vertical drilling and cavitation and horizontal drilling procedures into a coal bed are illustrated in Figure 6-1.

Figure 6-1. Coal Bed Methane Extraction with Cavitation (left) or Horizontal Drilling (right).

Mining under fractured roof rock creates "block caving" conditions that resemble "cathedrals" that are several 10s of feet high. Roof bolting and screening in these dangerous structures is required to stabilize the roof to prevent roof fall injures. Safety and cost issues cause sterilization of the coal reserves. Vertical drilling to depths greater than the lower elevation of the coal seam is accomplished by setting steel casing in the well. Explosive shape charges perforate the walls of the casing for a vertical distance equal to the seam height (see Figure 6-2). The cavitation method injects very



high-pressure (e.g., 17,000 psi) hydraulic fracturing fluids with propants to create high permeability pathways for fluid flow from the coal bed into the cavitation void. Mining near a hydraulic fracturing well discovered propants 1,000 feet away from the well. Rock fractures at 2,000 to 2,500 psi. When the pressure is suddenly released, the explosive force creates a cavity of fractured coal and seam boundary rock surrounding the wellbore. Water with included gas flows into the cavity releasing pressure in the natural cleat and micro fractures of the coal bed. Pumping contaminated water to the surface has the effect of lowering pressure in the coal bed. Methane adsorbed on the surface of the coal matrix is released and along with absorbed gas in the cleats and fractures. Chemical reactions and fine particle flow clog the filtering action of the fractured cavity walls and cleat structure.

Figure 6-2. Cavitation Method of Coal Bed Methane Production.

A focused acoustic beam tool needs to be built into a conventional drill string mud pump as illustrated in Figure 6-3. The pump exhausts water and methane gas through a 2-inch diameter pipe to the surface. An internal rod shaft drives the mud pump from a surface motor. Piezoceramic resonators, manufactured in the form of separate thick washers, surround the exhaust pipe and are driven at the resonant frequency (e.g., 770 Hz) of the coal bed, which depends on the seam thickness. The resonance assists in increasing the gas-flow permeability.



Figure 6-3. Coal Bed Methane Production Enhanced by a Focused Acoustic Beam Tool.



7.0 HORIZONTAL DIRECTIONAL DRILLING Radar control horizontal drilling at mid seam along with acoustic gas-flow permeability intensification can resolve the technology gap. In the case of horizontal drilling, methane gas production method, the wellbore is preferably navigated down dip in the center of the coal bed. Water and gas is recovered through a second well at the end of the drill wellbore. The method can be applied by drilling up dip as illustrated in Figure 7-1.

Figure 7-1. Cross Section of a Coal Bed Illustrating Radar Controlled and Uncontrolled

Drilling into the Floor. (U.S. Patents 6,497,457 B2; 6,633,252 B2; 6,778,127 B2; 6,892,815 B2).

7.1 Problems in Horizontal Drilling Several problems are commonly encountered in horizontal directional drilling, for example:

• drilling into contaminated boundary layers brings heavy metals to the surface; • floor fire clay cuttings and coal fine coats the wall of the wellbore, decreasing gas flow

permeability; and • without radar controlled drilling at a specified distance from the coal-rock interface, seam

roll can cause drilling into sandstone aquifers. To counteract these problems, drillers sometimes use dull drills and underpowered mud motors to keep the wellbore within the coal seam.



7.2 Technology Gap in Horizontal Directional Drilling Horizontal directional drilling radar technology needs to be developed and demonstrated to navigate the directional drill mud motor in the middle of the coal seam. The U.S. Department of Energy (DOE) supported the development of the horizontal directional drilling technology shown in Figure 7-1. The radars were designed to operate in the 0.2 to 2.5 GHz band and were successfully trialed in degasification boreholes. Funding cuts prevented in-mine drilling demonstration tests. Acoustic gas-flow permeability intensification technology was developed in the DOE non-proliferation program employing former Russian weapons of mass destruction scientists. Under this program, acoustic resonators (see Figure 7-2) were designed to operate at the resonant frequency of the coal seam waveguide. The resonator increases gas-flow permeability through the wall of the wellbore by clearing the wellbore of the fine clay layer and the stress field filter surrounding the wellbore. During resonance, the adsorbed methane may be released when vibration amplitude exceeds 20°A.

Figure 7-2. Acoustic Flow Permeability Intensification.



8.0 URANIUM FUEL IN-SITU MINING

The different ways in which to mine uranium include open pit, underground mining, and in-situ leaching (ISL). In-situ leaching, also known as solution mining, involves leaving the ore deposit in place and recovering the minerals by dissolving them and pumping the pregnant solution to the surface. The minerals are recovered in a surface processing plant. The process reverses the oxygen-reduction reaction occurring during formation of the groundwater guide and the creation of the deposit. The mining method results in little surface disturbance and no tailing or waste rock to be reclaimed when extraction is completed. During reclamation, the leachant is flushed from the aquifer, which returned to the original groundwater quality. The ore body needs to be permeable to the leaching fluid, which is contained within the guide to prevent contamination of local groundwater supplies. The design of the leaching pad injection/recovery field wells and operational plan must be approved by the applicable regulatory agencies. Metal oxides (e.g., uranium) occurring in the oxygen-rich environment of the upper floodplain are soluble and flow with the river system to stagnant swamp regions. Decreased oxygen in stagnant water enables the acclimation of anaerobic bacteria, producing enzymes that assist in creating the reducing environment. When the fluid oxides of the metals reach the stagnant reducing environment of the river system, precipitation occurs. The uranium minerals are usually present in the form of uraninite (i.e., oxide) or conffinite (i.e., silicate) coatings of the individual grains of sand. The sand was deposited because of wave action along a shoreline or paleochannel flow in a river system. Subsequent burial of the sand deposits by mudflow and subsidence caused sandstone layers and paleochannels to be bounded by impervious layers of mudstone or shale. Natural guides for groundwater flow were created by this deposition phenomenon. In-situ uranium mining was first trialed on an experimental basis in Wyoming during the early 1960s. The first commercial mine began in 1974. Today, most Kazakhstan and U.S. uranium production comes from ISL processing. Several operations are licensed in Wyoming, Nebraska, and Texas. These operations are small (i.e., under 1,000 tons/year) but account for most of the U.S. uranium production. About 36% of the world uranium production comes from ISL, including production from Kazakhstan and Uzbekistan.

8.1 History of Acoustic Stimulation for In-Situ Uranium Mining During the fall of the Soviet Union in the early 1990s, the Radiophysical Research Institute in Nizhny Novgorod, Russia, designed and evaluated a borehole acoustic tool for application in recovery of in-situ uranium at a Kazakhstan site. The increase in concentration of the pumped fluids (see Figure 8-1) was due to the interaction of the elastic fields with the physical and chemical processes occurring in the uranium deposit. Borehole acoustic tools have been developed for two classes of applied problems. One relates to the studies of rocks near or between boreholes. Another is associated with the study of stimulation of geotechnical processes, such as oil and gas production or underground leaching, by elastic fields.



Figure 8-1. Acoustic Flow. Common to these two classes of problems is the configuration of divergent fields of elastic oscillations produced by the borehole radiators. More often, spherically divergent fields are produced by point sources and less often by cylindrically divergent fields produced by an extended quasi-linear borehole antenna. In the near borehole region, the extended antenna creates a focusing of the axial phase distribution of field amplitudes with drastically increasing amplitude of the elastic field in the collector region of the in-situ recovery well. The estimates of the acoustic power flux thresholds required for intensification of heat- or mass-transfer processes in porous media ranges between 0.03 to 0.1 watts/cm2. The borehole piezoceramic resonating focusing antenna effective range is 20 to 30 m. The wellbore face zone strata (FZS) of the productive area and the filtration characteristics always impact fluid flow. Acoustic stimulation is one of the advanced methods of FZS stimulation. Increasing amplitudes of the acoustic field are known to enhance the acoustic stimulation mechanisms substantially. This condition is a general characteristic of physical and chemical processes. The heat conduction of a saturated collector is increased by a multiple five to 20 times. In the experimental work conducted in Kazakhstan, the concentration of pump-off fluids continued to increase for some period after the stimulation. The tool has not been applied in the West, partly because the technical description of the process was not translated into English until 2002. The tool needs to be redeveloped, integrated with a pump, and demonstrated in a U.S. in-situ mining field (see Section 8.4). The primary market for the focused acoustic beam tool will be mining operations specializing in ISL uranium production. However, adaptation of the tool should be able to be applied in a heap leaching pile of open-pit mines and surface mills and processing facilities. In-situ leaching is considered the most economical and environmentally acceptable method in which to mine uranium in the U.S. Most uranium mining in the U.S. and Kazakhstan utilizes the ISL method.

8.2 Uranium Market Analysis Forecast uranium production for 2010 is about 55,000 tons, as production ramps up in Kazakhstan and Namibia. A breakdown of the 2009 world uranium production by extraction technique is given in Table 8-1. Table 8-2 lists the ISL major mines throughout the world. Mining methods have been changing. In 1990, 55% of the world uranium production came from underground mines, but this percentage decreased dramatically by 1999 to 33%. Since 2000, new Canadian mines increased production again and Australia’s Olympic Dam Mine is coming on line. Mining via ISL has been steadily increasing its share of the total world uranium production.



Table 8-1. Uranium Production by Extraction Method in 2009.

Mining Method Percentage of Total Production (%)

Conventional underground and open-pit mining 57% In situ leaching (ISL) 36% By-product 7%

Note: Olympic Dam production is included in the by-product rather than the underground category.

Table 8-2. In-Situ Leaching Uranium Mines.

Mine Name

Location

Operator

Mine Type

Production Rate (ton/year)

McClean Lake Canada Cameco Open pit 1,388 Langer Heinrich Namibia Paladin Open pit 1,108 Central Mynkuduk Kazakhstan Kazatomprom ISL 1,104 Akdala Kazakhstan Uranium One ISL 1,039 Karamuran Kazakhstan Kazatomprom ISL 1,011 East Mynkuduk Kazakhstan Kazatomprom ISL 1,001 Zafarabad - Central Mining Uzbekistan Navoi ISL 900 South Inkai Kazakhstan Uranium One ISL 831 Inkai Kazakhstan Cameco ISL 715 Smith Ranch, Highland, Crow Butte

USA Cameco ISL 705

Uchkuduk - Northern Mining Uzbekistan Navoi ISL 700 Nurabad - South Mining Uzbekistan Navoi ISL 700 Beverley Australia Heathgate ISL 583 Vaal River South Africa AngloGold By-product 554 Kanzhugan Kazakhstan Kazatomprom ISL 545 Irkol Kazakhstan Kazatomprom ISL 502 Underground mines have a surface mill where the ore is crushed, ground, and then leached with sulfuric acid to dissolve the uranium oxides. At the mill of an underground mine, or the treatment plant of an ISL operation, the uranium is separated by ion exchange before being dried and packed, usually as U3O8. Some mills and ISL operations use carbonate leaching instead of sulfuric acid, depending on the characteristics of the ore body. Where uranium is recovered as a by-product of copper or phosphate mining, the treatment process is likely to be more complex. Since the early 1990s, takeovers, mergers, and closures have consolidated the uranium production industry. In 2009, ten companies marketed 89% of the world's uranium mine production (see Table 8-3). The world uranium supply by country is given in Table 8-4 and Figure 8-2.



Table 8-3. World Uranium Production by Company.

Company

Production (Tonnes/Year) Production Fraction (%)

Areva 8,623 17 Cameco 8,000 16 Rio Tinto 7,963 16 KazAtomProm 7,467 15 ARMZ 4,624 9 BHP Billiton 2,955 6 Navoi 2,429 5 Uranium One 1,368 3 Paladin 1,210 2 GA/Heathgate 583 1 Other 5,550 11 Total 50,772 100%

Table 8-4. Uranium Production by Country for the Period 2003 through 2009.

Country 2003 2004 2005 2006 2007 2008 2009 Kazakhstan 3,300 3,719 4,357 5,279 6,637 8,521 14,020 Canada 10,457 11,597 11,628 9,862 9,476 9,000 10,173 Australia 7,572 8,982 9,516 7,593 8,611 8,430 7,982 Namibia 2,036 3,038 3,147 3,067 2,879 4,366 4,626 Russia 3,150 3,200 3,431 3,262 3,413 3,521 3,564 Niger 3,143 3,282 3,093 3,434 3,153 3,032 3,243 Uzbekistan 1,598 2,016 2,300 2,260 2,320 2,338 2,429 USA 779 878 1,039 1,672 1,654 1,430 1,453 Ukraine (est.) 800 800 800 800 846 800 840 China (est.) 750 750 750 750 712 769 750 South Africa 758 755 674 534 539 655 563 Brazil 310 300 110 190 299 330 345 India (est.) 230 230 230 177 270 271 290 Czech Republic 452 412 408 359 306 263 258 Malawi 104 Romania (est.) 90 90 90 90 77 77 75 Pakistan (est.) 45 45 45 45 45 45 50 France 0 7 7 5 4 5 8 Germany 104 77 94 65 41 0 0 Total world 35,574 40,178 41,719 39,444 41,282 43,853 50,772 Tonnes of U3O8 41,944 47,382 49,199 46,516 48,683 51,716 59,875 Percentage of world demand 65% 63% 64% 68% 76%



Figure 8-2. Uranium Supply by Country for 2000 through 2008. (Source: World Nuclear Association)

The only significant commercial use for uranium is to fuel nuclear reactors for electricity generation. Worldwide, there are 440 commercial nuclear power reactors in 30 countries and a total of 100 reactors under construction or planned for completion in the next ten years. Before uranium is ready for use as a nuclear fuel in reactors, it must undergo a number of intermediary processing steps, which are identified as the front end of the nuclear fuel cycle, namely:

• mining and milling to produce U3O8 (yellow cake); • refining and conversion to produce UF6 and UO2; • enrichment to produce low -enriched uranium; and • fuel fabrication to produce fuel assemblies and bundles.

Nuclear utilities purchase uranium in all three of the intermediate forms prior to conversion into fuel assemblies. Typically, a fuel buyer from an electric utility will contract separately with the suppliers at each step of the process. Sometimes, the fuel buyer may purchase enriched uranium product, the end product of the first three steps and contract separately for fabrication, the fourth step. Sellers consist of suppliers in each four processing steps as well as brokers and traders. In addition to being sold in different forms, uranium markets are differentiated by geography. The global trading of uranium has evolved into two distinct marketplaces shaped by historical and political forces. The first is the western-world marketplace comprising the Americas, Western Europe, and the Far East. A separate marketplace comprises countries within the former Soviet Union or the Commonwealth of Independent States (CIS), Eastern Europe, and China. Most of the uranium fuel requirements for nuclear power plants in the CIS are supplied from the CIS's own stockpiles. Often, producers with in the CIS also supply uranium and fuel products to the western world, increasing competition. There are fewer than 100 companies that buy and sell uranium in the western world.



Worldwide, approximately 5.5 million tons of uranium that could be economically mined have been identified. The known uranium supply is enough to sustain nuclear power generation for more than a century. Spent fuel rods contain 95% of the original energy and can be reprocessed to increase fuel supply well into the future. Advanced fast reactor designs could extend the fuel supply for nuclear power for at least 1,000 years. Since the recovery of uranium prices beginning in about 2003, there has been a lot of activity in preparing to open new mines in many countries. The World Nuclear Association (WNA) reference scenario projects the world uranium demand to be about 77,000 tons of uranium in 2015. Most of this uranium will need to come directly from mines. For comparison, in 2009, 24% of the uranium fuel supply came from secondary sources. A large nuclear power station with a net generating capacity of 1,300 MW requires 11,636 pounds of enriched uranium annually. The worldwide known recoverable resources of uranium in 2007 are shown in Table 8-5.

Table 8-5. Known Recoverable Resources of Uranium in 2007.

Country

Known Recoverable Resources

(Tons of U)

Percentage of World Known Recoverable

Resources (%) Australia 1,243,000 23 Kazakhstan 817,000 15 Russia 546,000 10 South Africa 435,000 8 Canada 423,000 8 USA 342,000 6 Brazil 278,000 5 Namibia 275,000 5 Niger 274,000 5 Ukraine 200,000 4 Jordan 112,000 2 Uzbekistan 111,000 2 India 73,000 1 China 68,000 1 Mongolia 62,000 1 Other 210,000 4 World total 5,469,000 100

For many years, uranium traded for less than $15/pound but the increased interest in nuclear power together with the forthcoming end of the agreement to source uranium from dismantled nuclear warheads and speculation led to a spike in price. Starting from $10/pound in May 2003, the price reached $138/pound in July 2007. As of December 2009, 382 tons, equal to 15,000 warheads, have been turned into about 11,000 tons of fuel, for which the Russian government



received more than $8 billion. The dismantled warhead supply represents about 50% of the U.S. reactor fuel supply. Interestingly, one in ten U.S. light bulbs are lit by electricity generated from uranium contained in nuclear warheads originally targeted at our homes. Russian highly enriched uranium (HEU) deliveries will continue until 2013. At the present time, the price ranges between $40 to $60/pound because of increased supply. The International Atomic Energy Agency (IAEA) has projected nuclear power to increase from 372 GWe today to 509 to 563 GWe by 2030, which will require an increase in uranium demand from 66,599 tons/year to between 94,000 and 122,000 tons/year (i.e., an increase in demand of 43 to 83%). The typical uranium fuel requirements of a nuclear power plant are shown in Figure 8-3.

Figure 8-3. Production and Demand for Uranium. (Source: World Nuclear Association)

8.3 In-Situ Leaching Uranium Mining U.S. uranium mines produced 4.1 million pounds of U3O8 in 2009. Fourteen underground mines produced uranium in 2009 along with four ISL operations. The ISL operations were Alta Mesa Project, Crow Butte Operations, Kingsville Dome, and Smith Ranch-Highlands Operations. Shipment of concentrate from these facilities was 3.6 million pounds in 2009. The leaching process uses native groundwater fortified with a complex agent, which is in most cases an oxidant. Natural bacteria play a role in the reduction-oxygen process. Once the pregnant solution returns to the surface, uranium is recovered in much the same way as in the uranium milling plant-processing operation. In Australian ISL mines (i.e., Beverly and Honeymoon), the oxidant is hydrogen peroxide and the complexing agent is sulfuric acid. The Kazakhstan ISL mines do not use an oxidant but use high acid concentrations in the circulating solution. In U.S. ISL operations, an alkali leach is used where gypsum and limestone occur in the host aquifer. The presence of more than a few percent carbonate minerals requires an alkali leach to be used.



The geologic cross section of a typical deposit suitable for ISL recovery is characterized by porous sandstone layers or paleochannels bounded by sealing layers of mudstone and shale (see Figure 8-4). The structure forms a guide for water flow within the deposit. The high electrical conductivity contrast of the bounding mudstone (i.e., shale) and sandstone layer forms a natural waveguide for transmission of electromagnetic and acoustic waves. The waveguide can be used to create tomography images of the structural geology of the deposit. Oftentimes, impermeable mudstone lenses occur in the deposit, interfering with leachant fluid flow. The interference decreases the efficiency of leaching process. The tomography technique known as the radio imaging method (RIM) can map the lenses.

Figure 8-4. In-Situ Leaching Uranium Mining Method.

The leaching method drills a constellation of injection and recovery wells into the porous sandstone layer. The surface layout of the drill holes or well field could be designed by analyzing three-dimensional tomography images generated by the RIM system. The pattern of injection wells surround the recovery wells is designed so as to confine the leaching solution in the immediate zone of the recovery well. Pumping of the leachant fluid creates a pressure gradient and cone of depression surrounding the recovery well. The most common patterns of wells are a five-spot pattern, which typically has 20- to 30-meter well spacing, and a seven-spot pattern, which has 30- to 40-meter well spacing (see Figure 8-5). In most western operations, closer spaced patterns are employed to achieve faster recovery rates. The acoustic intensification technology would provide added value by enabling the spacing to be increased for the same operating time interval. The drill holes are typically low-cost water wells. In the U.S., the production life of an ISL uranium mining project is typically one to three years. Most of the uranium is recovered in the first six months of operation. The most successful operations recover 80% of the ore and the minimum recovery rate approaches 60%. The progressive flow of the leachant through the aquifer traps clay and silt in the permeable sandstone sediments. The trapped material can be dislodged to some extent by using higher-pressure injection or by reversing the flow. The flow capacity generally declines through the life of the injection well.



Figure 8-5. Well Pattern in an In-Situ Leaching Project.

A leaching solution is injected and circulated through the bounded sandstone layer, re-oxidizing the metal into a fluid form. Aerobic bacteria accumulate in the oxygen-rich environment and assist in the oxidizing process. This process is the reverse of the reduction process that formed the deposit. The dissolved ore is pumped out of the recovery well and processed on the surface recovering the metal oxide. During restoration of an in-situ uranium site near Beeville, Texas, cross borehole electromagnetic (EM) tomography was used to map clay lenses that interfered with the cleanup flow through the deposit. Drilling an additional drill well solved the problem.

8.4 Technology Gap in In-Situ Leaching Processes The acoustic tool field demonstration work conducted in the former Soviet Union resulted in some valuable lessons. For example, the acoustic tool should be combined with the pump and made more automatic when it comes to cleaning the filtration screens. Electromagnetic imaging should be applied during actual construction of the leaching field and images used in the design of the field. One advantage of the tool is that the cone of depression will need to be maintained for a much shorter time. This procedure should reduce the potential for groundwater contamination. Larger spacing can be designed into the drill hole pattern to increase total extraction. In addition, the experimental data indicated that:

• acoustic resonance occurs with 75 gallon/second drilling mudflow with a 15 psi drop across each resonator;

• the resonator cleans the filtration region and fine coating on the wall of borehole thereby clearing the flow pathway;

• methane adsorption release occurs with molecular displacement of one methane molecule diameter; and

• chemical reactions occurring in matrix and cleats decrease flow permeability over time.



The focused acoustic beam (FAB) tool (see Figure 8-6) increases methane gas-flow permeability. The antenna modules shown in left-hand image of Figure 8-6 were used in underground leaching mining. The antennas are non-compensated, consisting of piezoceramic cylinders, shown in the right-hand image of Figure 8-6, and are intended for use at depths down to 500 meters. A real borehole zone lens used in geotechnical processes for intensification had the following characteristics:

• resonant frequency in water of 15 kHz; • antenna diameter of 80 mm; • initial energy flux density is up to 2 W/cm2; • antenna length of 5 m, with five different module lengths ranging from 0.5 to 1.5 m; • operating depth of 170 to 210 m; • focus distance in water was 7.5 m; • amplification factor in water was 0.45 for an antenna consisting of seven Fresnel zones;

and • two frequency modes existed in the productive borehole ƒ = 13.8 kHz, F = 5.5 m,

estimated πf ~ 0.1 W/cm2; ƒ = 8.2 kHz, F = 3.2 m, estimated πf ~ 0.25 W/cm2.

Figure 8-6. Focused Acoustic Beam Tool.

Typically, the productive collector of the borehole is equipped with slot screens (i.e., filters). The filters are plates with thin slots between them and the leaching solution flows through the thin slots. Very often these slots become blocked and the pump begins to operate in an irregular mode, which can cause damage to the pump thereby decreasing leachant flow into the borehole. Acoustic transducers with internal generators, which can be initiated by a command, can replace some of the plates.

! !



The simultaneous transmission of two acoustic frequency wavelets can map stress fields in pillars as illustrated in Figure 8-7.

Figure 8-7. Stress Field in Coal Mine Pillars.



9.0 CONCLUDING REMARKS AND RECOMMENDATIONS Policymakers need to become aware that mineable coal resources are being sterilized at a rapid rate and easy to mine coal reserves are nearing exhaustion. Coal resources can no longer be thought of as an abundant and low cost resource able to fuel more than 45% of the base-load electric power demand of this country for 250 years into the future. The Energy Information Agency (EIA) recently stated that 119 years of coal production remain with current mining technology. The EIA failed to consider the sterilization rate and the estimation that only 60 years remain. Tomorrow’s mining will be conducted in deeper, thinner, more geologically complex reserves near abandoned mines. Unless policymakers recognize that mine safety and productivity are now strongly dependent on the geotechnical vision factors of mining, the mine accident rate will only be weakly influenced by increased enforcement of mining laws and regulations. To combat sterilization of the coal reserves, new mining technologies are needed. Emphasis on and the scope of advancing mine safety and productivity needs to be broadened to include the development of geotechnical vision technologies. Although mine accidents are tragedies for miners, their families, mining companies, and the mining industry, a tragedy of even greater importance is the smothering death of retired miners because horizon sensor technologies have not yet been developed to operate reliably. Since the defunding of the U.S. Bureau of Mines (USBM), there has been no enthusiasm for completing the mining technology development road map formulated by the National Mining Association (NMA) chief executive officers, which was recently affirmed by the National Research Council. A quasi-government and mining industry partnership responsible for mining technology development must be organized to include mining university members. An important consideration is the issue of technology development oversight, which must be provided by the JASONs8, the fearlessly independent brain trust of the Department of Defense. There needs to be greater focus on the appropriate level of cost sharing between Congress and the mining industry for advanced technology development applicable to the mining industry (e.g., horizon sensing for mine machine cutting drums). Tax policy must continue to provide tax credits for mining companies to participate in authorized partnership safety and productivity improvement projects and the installation equipment. The failure of this nation to invest in the development of evolutionary and revolutionary technologies needed to mine in difficult geology is a key factor underlying the rash of recent mining accidents and the heartbreak of mining families, the Mine Safety and Health Administration (MSHA), and the mining industry. The laws of radio physics are not well understood or even taught in our accredited university mining engineering and applied science programs. The mandated laws of radio geophysics are not difficult to comprehend and should be included as part of the Accreditation Board for Engineering and Technology (ABET) requirements for certified university mining engineering curriculums. Mine maintenance of distributed antennas and transmission facilities require the use

8 JASON, The MITRE Corporation, 1800 Dollet Madison Boulevard, McLean, VA 22102-‐3481.



of test instruments. Standard practice should include routine testing of the operational status of any installed communications and tracking systems. Too often, manufacturer’s technicians find that an installed system has deteriorated in performance and the mine’s technicians had not detected the change.

The NMA mining company employees and MSHA officials, along with technical support and enforcement personnel, have worked constructively together to bring down the mining industry injury rate to the second lowest in U.S. industry. Imagine what could be achieved in improved safety and productivity if full and productive communications were established between policymakers in Congress, NMA member companies, MSHA, accredited universities with mining engineering and applied science departments, and research organizations. One focus of these communications should be working together to follow an evolutionary and revolutionary technology development road map, which was developed in 1998 by mining industry technologists and confirmed by the November 2010 National Academy of Engineering (NAE) study identifying mining technology gaps. The NMA mining company executives and technologists should be asked to participate in an updated vision statement creating a technology road map for the future. Funding sources for the revised mining technology development road map effort appropriations need to be debated by the stakeholders. However, by appropriating 1% of the tax revenue paid by the mining industry to the government (i.e., $22 billion), $220 million could be made available each year. The MINER Act of 2006 must be amended to require that the adoption of wireless technology means that miners on the move must have a two-way voice and text radio link of at least 10 feet within a mine-wide distributed antenna and transmission facility. Policymakers must read the Wilberg, Quecreek, and Sago mine accident reports to understand why narrow bandwidth Hill/Wait conductor waveguide lifelines must be installed in every entry except cross cuts. Wide bandwidth very high frequency (VHF)/ultra high frequency (UHF) distributed antennas and transmission facilities must be installed in transportation roadways and provide working face area coverage. A real-time tracking resolution of 200 feet will be realizable with medium frequency technology. The wide bandwidth UHF mesh distributed antenna and transmission facility failed at the Jellico Mine when inundated with mine water. Focus group meetings conducted with miners following the writing of the MINER Act of 2006 concluded that leaky-feeder communications facilities would fail in most post-accident scenarios. The definition of “wireless” in the context of underground mining should mean a voice and text radio link between miners of the move and the distributed antenna and transmission facilities is installed in every entry of the underground mining complex except in crosscuts



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Colorado. Wait, J.R., 1982, Geo-Electromagnetism, Academic Press, a subsidiary of Harcourt Brace

Jovanovich Publishers, New York, New York. Wilson, D.D., 1997, John Barkley Dawson: Pioneer, Catteman, Rancher. 2nd edition, Wilson.



11.0 STOLAR RESEARCH CORPORATION PATENT PORTFOLIO

Product Line Patent Title Patent

Number Subsurface Radio Imaging

Drilling, image, and coal-bed methane production ahead of mining 6,497,457 B1

Method and system for radio-imaging underground geologic structures 6,593,746 B2

Synchronous radio-imaging of underground structures 6,744,253 B2

Shuttle-in receiver for radio-imaging underground geologic structures 6,927,698 B2

Horizon Sensing

Method for controlling the thickness of a layer of material in a seam 5,188,426

Method and apparatus for a rotating cutting drum or arm mounted with paired opposite circular polarity antennas and resonant microstrip patch transceiver for measuring coal, trona and potash layers forward, side and around a continuous mining machine 5,769,503

Ground-penetrating imaging and detecting radar 6,522,285 B2

Earth-penetrating radar with inherent near-field rejection 7,548,181 B1

Double-sideband suppressed-carrier radar to null near-field reflections from a first

interface between media layers Radar mining guidance control system Horizontal Drilling Ground-penetrating imaging and detecting radar 6,522,285 B2 Radar plow drillstring steering 6,633,252 B2 Drillstring radar 6,778,127 B2




Double-sideband suppressed-carrier radar to null near-field reflections from a first interface between media layers

Coal Bed Methane Production

Coal bed methane borehole pipe liner perforation system 6,892,815 B2

Increasing media permeability with acoustic vibrations 7,350,567 B2

Data Transmission Slickline data transmission system 7,224,289 B2 Electromagnetic Gradiometer

Radio system for characterizing and outlining underground industrial developments and facilities 6,549,012 B2

Aerial electronic detection of surface and underground threats 7,336,079 B2

Subsurface Conductor Detection

Aerial electronic detection of surface and underground threats 7,336,079 B2

Subsurface Anomaly Detection



Borehole Radar



Landmine and Explosives Detection Landmine locating system 6,473,025 B2



Method for locating a concealed object 6,501,414 Mine Communications Current limiter circuit 5,301,082 Class L power amplifier 6,993,302 B2 Multimode mode communication system 8,115,622 Medium frequency mine communication system 4,879,755 Mine communication cable and method for use 5,146,611 Ice Detection Ice detection apparatus for transportation safety 5,474,261

Apparatus and method for the detection and measurement of liquid water and ice layers on the surfaces of solid materials 5,686,841



Appendix A

Lifeline Conductor Waveguide Transmission Hill (1990b) developed a simple formula for the induced current (I) in long, thin electrical conductors when illuminated by the electric field component (E) of an electromagnetic (EM) wave. The total current is given by

I= EZ=

!Zm " (i!µ / 2" )!n kb/a( )

, (A-1)

where ω = 2πf and f is the frequency in hertz of the primary EM wave, a = radius of the conductor in meters, b = radius of the conductor insulator, and Zm = the series impedance of the conductor. The denominator in Equation (A-1) is the axial impedance of the conductor waveguide. For a thin electrical conductor in an entry, Equation (A-1) indicates that the induced current increases with the magnitude of the primary EM wave electric field component, E, that is tangential to the electrical conductor and is inversely related to the frequency (ω). Therefore, lower frequency EM waves induce higher current in these electrical conductors. Actual measurements conducted at the Colorado School of Mines-U.S. Army Belvoir Research and Development Engineering Center tunnel proved that the induced current increased as frequency decreased (Stolarczyk 1991). For a magnetic dipole source, the longitudinal electric field component is given by

!! =iµ" Mk2

4#"1kr( )2 +

1i kr( )

#

$%%

&

'(( e"ikr sin! . (A-2)

Because of the ω term in Equation (A-2), the electric field vanishes at zero frequency. The vertical magnetic dipole (VMD) antenna integrated with a cap lamp battery will radiate horizontally polarized electric field components for maximum induction of current into a conductor installed on the entry ribs. Harrington (1961) goes on in his formulation to show that the EM field components scattered from the electrical conductor will slowly decay with distance from the conductor at radial distances that are large compared with the skin depth. Burrows (1978) also develops similar formulations as

Hs ( )( )krH

4iI

- 21

sk!= (A-3)

and

Es=-Z ( )( )krH4I 2

Osωµ

, (A-4)



where Hs is the scattered magnetic field, Es is the scattered electric field, Is is the secondary current, f and Z are unit vectors, and Ho

(2) and H1(2) are Hankel functions of the second kind (order 0 and 1), and

r is the radial distance in meters to the measurement point. At radial distances that are large compared with the skin depth, the asymptotic formula of the Hankel function leads to the simplified expressions

Hs e2ik

2I ik-2

1

s r

r!"

#$%

&'(

) (A-5)

and

Es ≈ -Z ek2i

2I ik-2

1

s r

r⎟⎠

⎞⎜⎝

⎛π

ωµ. (A-6)

The secondary magnetic field component radiating (i.e., scattered) from a lifeline cable decays with the first power of distance, r, and decreases in magnitude by the attenuation factor e-αr. Hill (1990) reformulated the problem for finite length conductors and non-uniform illumination by a magnetic dipole source. In this case, standing waves occur on the underground conductors. In a passageway with multiple conductors, the standing wave pattern is not observable because of multiple reflections in the ensemble of electrical conductors (Harrington 1961). Bartel and Cress (1998) used forward-modeling codes developed by Gregory Newman to show that current flow is induced in reinforced concrete. Hill and Wait (1974) have theoretically shown that the passageway conductors form low-attenuation-rate transmission networks (i.e., waveguides) for distribution of induced current throughout a mining complex. Hill and Wait analyzed the bi-filar and mono-filar modes of transmission. Figure A-1 shows that the bi-filar attenuation rate is less than 3.0 dB/kilometer at 3,000 kHz. The current flow appears on the conveyor belt structure, electric power lines, and telephone cables. The illumination of a pair of thin electrical conductors by the electric field component of a transmitting magnetic dipole of the cap lamp transceiver or F1/F1 repeater transceiver is illustrated in Figure A-2. The radiating electric field component ( )φE that is tangential to each conductor induces mono-filar current flow (see Figure A-2). During the receiving time period, the magnetic dipole antenna of the cap lamp or F1/F1 repeater transceiver coupling to the conductor or lifeline cable is via the magnetic field (H) scattered from the thin wire and threads the enclosed area of the antenna. The mono-filar (i.e., common) mode induction current flow is attenuated at a much higher rate than the bi-filar current flow. The current return path is through the finite electrical conductivity (i.e., higher absorption) of the sedimentary rock surrounding the coal seam. Although the bi-filar



and mono-filar current flow exist at the same time in the electrical conductors, the bi-filar current will predominate as transmission distances increase.

Figure A-1. Conductor Mode Attenuation Rate Versus Frequency for Conductor to Rock-Mass Air-Path Distances of 1 Centimeter, 10 Centimeters, and 1 Meter.

Figure A-2. Receiving Magnetic Field Constructive and Destructive Interference Zones Created by Mono-filar and Bi-filar Modes of Current Flow.



Installing conductors on only one side of the entry can eliminate the dead zone caused by destructive interference of the mono-filar mode currents. At the end of a conveyor or cable waveguide, the transmission facility appears to be an open-ended wire pair exhibiting no current flow. The reflection from the open circuit creates a standing wave that reduces coupling to a roving miner’s transceiver, which extends for a distance of about 100 feet. However, standing waves are not apparent in most passageways as a result of the existence of multiple reflections in the multiple conductors that are inductively coupled together. The vertical magnetic dipole antenna pattern exhibits a vertical null directly above the cap lamp transceiver resulting in less sensitivity to dead zones.



APPENDIX B

About The Author As the Founder and President of Stolar Research Corporation (Stolar), Larry Stolarczyk has made extensive and pioneering contributions to the field of electromagnetic remote sensing, including the development of radio imaging method (RIM) technology for underground mining and detection of anti-personnel landmines. Stolarczyk has been awarded more than 52 patents related to electromagnetic sensing to bring about safer, more environmentally friendly coal mining and technologies related to military applications. He received a National Aeronautics and Space Administration Space Act Award for his method of locating concealed objects and the National Award for Energy Innovation presented by the U.S. Secretary of Energy for the development of RIM for scanning of coal bed waveguides and ore bodies. He developed the first transistorized super-regenerative receivers for garage door controls and residential home security systems, and phase-coherent Doppler velocity and position missile tracking equipment for White Sands Missile Range. Since 1994, he has served as President of Stolar, a multimillion-dollar research and development company in Raton, New Mexico, specializing in radio geophysics development for the underground mining industry. The applications include emergency and operational wireless communications and post-accident, through-the-Earth communications with trapped miners. He served as Vice President and Trustee of Raton Public Service Co., a coal-fired, municipally owned electric generation and distribution utility. He co-founded the Arkansas River Power Authority, securing low-cost electrical power for seven southern Colorado and New Mexico cities. From 1991 to 1994, he served as Vice President of Research for RIMtech, Inc. before returning to Stolar. He also co-founded and has been an officer in the U.S. Department of Energy (DOE)/National Nuclear Security Agency (NNSA)-funded United States Industry Coalition for Russian Non-Proliferation Programs. He was one of the first western scientists to visit the closed Russian nuclear cities following the collapse of the Soviet Union. He was the principal scientist on five advanced electromagnetic imaging and detection projects in partnership with the Russian Minatom institutes and DOE laboratories. Stolar has won numerous technical and business awards, six R&D 100 awards, eleven New Mexico Technology Flying 40 Awards, and two New Mexico Business Weekly Fast Trackers Awards. Dr. Stolarczyk has written more than 60 technical papers and presentations and chapters in mining geophysics books. He is a member of Institute of Electrical and Electronics Engineers (IEEE), the Society of Mining Engineers (SME), and was elected to Sigma Pi Sigma, the National Physics Honor Society. He was also named an Outstanding Engineering Alumnus of New Mexico State University. In 2011, the University of Colorado College of Engineering and Applied Science honored Dr. Stolarczyk as a Distinguished Alumnus.



Stolarczyk earned his bachelor’s degree in electrical engineering at University of Colorado-Boulder in 1960, and went on to earn master’s and doctor of science degrees at New Mexico State University in 1965 and 1970. He also completed the Executive Program at the University of New Mexico Robert O. Anderson Graduate School of Management.

application of radio geophysics to mining engineering

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