micropower impulse radar - lawrence livermore … science & technology review january/february...

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Science & Technology Review January/February 1996

ADIO detection and ranging(radar) was first developed in the

1920s. Most of us associate radar withcombat scenes in movies or an occasionalspeeding ticket. Conventional radar usesbeamed and reflected microwave energyto detect, locate, and track objects overdistances of many miles. Almost alltypes of radar were developed fordefense applications, and they continueto be used by the military and a fewcivilian organizations. Commercial usehas been limited primarily because mostradar systems are large, and they can becomplex and cost $40,000 or more. Adramatic change in radar use is imminent,resulting from work done at LLNL.

We have invented and patented a fundamentally different type ofcompact, low-power radar system calledmicropower impulse radar (MIR), whichis orders of magnitude less expensive toproduce than other conventional radars.Unlike conventional radar, which sendsout continuous waves in bursts, MIRuses very short electromagnetic pulsesand can detect objects at much shorterrange. The new technology has become

MicropowerImpulse Radar

R

16

A new pocket-size radar that operates

up to several years on AA batteries and

costs only a few dollars is stimulating

Laboratory research efforts and a

variety of industrial products. Its many

potential uses include security, rescue

operations, and health monitoring.


Figure 2. In an MIR motion sensor,

a transmitting antenna radiates a

pulse that is about 0.2 nanoseconds

long. Reflections from targets return

a complex series of echoes to the

receiving antenna. The return signal

is sampled at one range-gate time

by an impulse receiver containing

a voltage sampler along with an

averaging circuit and amplifier. The

detector listens at the appropriate

time for an echo. For an object about

3 m from the MIR, the sampled

gate at 20 nanoseconds after

transmission would just

capture it.

19


Micropower Impulse Radar18


Micropower Impulse Radar

beam pulsed Nova laser generatessubnanosecond events that must beaccurately recorded. In the late 1980s,Laboratory engineers began to developa new high-speed data acquisitionsystem to capture the data generated byNova and the next-generation lasersystem, the National Ignition Facility.The result was a single-shot transientdigitizer—a 1993 R&D 100 Awardwinner described in the April 1994issue of Energy and Technology Review.1

The LLNL transient digitizer, whichis the world’s fastest, functions as ahigh-speed oscilloscope combined witha digital-readout device. The instrumentrecords many samples from singleelectrical events (a brief signal called a “transient”), each lasting only 5 nanoseconds (5 billionths of a second).Compared to competitive products, suchas the best oscilloscopes, the transientdigitizer is much smaller and morerobust, consumes less power, and costsfar less.

While developing the transientdigitizer, project engineer McEwan hadan important insight. The samplingcircuits developed for it could form thebasis of a sensitive receiver for anextremely small, low-power radarsystem (Figure 1).

MIR Components

The principal MIR components areshown in Figure 2: a transmitter with apulse generator, a receiver with a pulsedetector, timing circuitry, a signalprocessor, and antennas. The MIRtransmitter emits rapid, wideband radarpulses at a nominal rate of 2 million persecond. This rate is randomizedintentionally by a noise circuit. Thecomponents making up the transmittercan send out shortened and sharpenedelectrical pulses with rise times asshort as 50 trillionths of a second (50 picoseconds). The receiver, whichuses a pulse-detector circuit, only acceptsechoes from objects within a preset

Figure 1. The micropower impulse radar

(MIR) proximity sensor board. distance (round-trip delay time)—from afew centimeters to many tens of meters.

The MIR antenna determines muchof the device’s operating characteristics.A single-wire monopole antenna only 4 cm long is used for standard MIRmotion sensors, but larger antennasystems can provide a longer range,greater directionality, and betterpenetration of some materials such aswater, ice, and mud. Currently, themaximum range in air for these low-power devices is about 50 m. With anomnidirectional antenna, MIR can lookfor echoes in an invisible radar bubbleof adjustable radius surrounding the unit(Figure 2). Directional antennas can aimpulses in a specific direction and addgain to the signals. We can separate thetransmitter and receiver antennas, forexample, to establish an electronic“trip-line” so that targets or intruderscrossing the line will trigger a warning.We are also exploring other geometrieswith multiple sensors and overlappingregions of coverage.

Behind MIR Technology

Impulse RadarConventional radar sends out short

bursts of single-frequency (narrow-band) electromagnetic energy in themicrowave frequency range. Otherradars step through multiple (wide-band) frequencies to obtain moreinformation about a scene. An impulse,or ultrawide-band, radar such as MIRsends individual pulses that containenergy over a very wide band offrequencies. The shorter the pulse, thewider the band, thereby generating evengreater information about reflectedobjects. Because the pulse is soshort, very little power isneeded to generate the signal.MIR is unique because itinexpensively generatesand detects very fast(subnanosecond) pulses.The drawback of usingshort, low-power

NoisePulse-repetition

interval

Impulse generator

Delay

Motion processor

Sensitivity control

Impulse receiver

Alarm

Transmitting antenna

Receiving antenna

Range control

Range gate

Target

0.2-nanosecond impulse

Radar echoes

Radar bubble

Wall

government sponsors are interested inlow-cost, lightweight MIR sensors inareas of defense, law enforcement,transportation infrastructure, and theenvironment. Envisioning perhapshundreds of other uses, Tom McEwan—the electrical engineer who inventedMIR—has compared the newtechnology to the Swiss Army knife.

The Genesis of MIR

MIR, with origins in LawrenceLivermore’s Laser ProgramsDirectorate, is now being developed bythat directorate’s Imaging and DetectionProgram. The Laboratory is home to the100-trillion-watt Nova laser. Developedfor nuclear fusion research, the ten-

LLNL’s fastest growing technology transfer activity

primarily because of its low costand extraordinary range of applications.

Among the scores of uses underinvestigation for MIR are new securityand border-surveillance systems;underground, through-wall, and oceanimaging; fluid-level sensing; automotivesafety, including collision-avoidanceand intelligent cruise-control systems;“smart” devices such as lights, heaters,and tools that automatically turn on oroff; and medical diagnostics.

The technology has potential use infinding earthquake survivors underrubble and in monitoring for sudden-infant-death syndrome. Various

Http://www.llnl.gov:80/etr/etr.html

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after each transmitted pulse, called arange gate. If we choose a delay timeafter each transmitted pulse correspondingto a range in space, then we can openthe receiver “gate” after that delay andclose it an instant later. In this way, weavoid receiving unwanted signals.

The MIR receiver has a very fastsampler that measures only one delaytime or range gate per transmitted pulse,as shown in Figure 3a. In fact, we usecircuitry that is similar to the transmitimpulse generator for this range-gatedmeasurement, another unique featureof our device. Only those returnpulses within the small range gate—corresponding to a fixed distance fromdevice to target—are measured. The gatewidth (the sampling time) is always fixedbased on the length of the pulse; but thedelay time (the range) is adjustable, asis the detection sensitivity. Averagingthousands of pulses improves the signal-to-noise ratio for a single measurement;i.e., noise is reduced, which increasessensitivity. A selected threshold on theaveraged signal senses any motion andcan trigger a switch, such as an alarm.

Randomized Pulse RepetitionAs mentioned earlier, a noise source

is intentionally added to the timingcircuitry so that the amount of timebetween pulses varies randomly around2 MHz. There are three reasons forrandomizing the pulse repetition rateand averaging thousands of samples atthose random times. First, interferencefrom radio and TV station harmonicscan trigger false alarms; but withrandomizing, interference is effectivelyaveraged to zero. Second, multiple MIRunits can be activated in one vicinitywithout interfering with each other ifthe operation of each unit is randomlycoded and unique. Each unit creates a pattern recognizable only by theoriginating MIR. Third, randomizingspreads the sensor’s emission spectrumso the MIR signals resemble backgroundnoise, which is difficult for other sensors

to detect. Emissions from an MIR sensorare virtually undetectable with aconventional radio-frequency receiverand antenna only 3 m away. In otherwords, randomizing makes the MIRstealthy.

Equivalent-Time SamplingMore sophisticated MIR sensors,

such as our MIR Rangefinder, cyclethrough many range gates. As shownin Figure 3b, the delay time is swept, orvaried, slowly with each received pulse(about 40 sweeps per second) toeffectively fill in the detection bubblewith a continuous trace of radarinformation. In essence, we are takingsamples at different times, thus differentdistances, away from the device. Theresult is an “equivalent-time” record ofall return pulses that can be correlatedto object distance. The equivalent-time

echo pattern exactly matches theoriginal “real-time” pattern, except thatit occurs on a time scale slowed by 106.We can easily display the equivalent-timeecho pattern on an oscilloscope or readthe data into a computer. We are applyingthis sampling technique to many short-range applications, such as lightweightaltimeters or reservoir-level measurement,as well as all MIR imaging applications.

Forming ImagesWith equivalent-time sampling,

we can form images by moving theRangefinder in front of a target areaor by using a stationary array ofRangefinders. Figure 4a showsunprocessed radar information weobtained along a concrete floor in theNova facility. Each vertical trace is areturn signal from a different position

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pulses is that less energy can bemeasured on the radar returns. Wesolved this problem by transmittingmany pulses rapidly and averaging allreturns.

The advantages of producing anddetecting very brief radar impulses areconsiderable:• The target echoes return muchinformation. With short pulses, thesystem operates across a wide band offrequencies, giving high resolution andaccuracy. The system is also lesssusceptible to interference from otherradars.• Battery current is drawn only duringthe short time the system is pulsed, sopower requirements are extremely low(microamperes). One type of MIR unitoperates for several years on two AAbatteries.• The microwave power associated withpulsed transmission is exceedingly low(averaging tens of microwatts) and ismedically safe. MIR emits less thanone-thousandth the power of a cellulartelephone.

Range-Gated RadarTransmitted energy from any radar

is diffracted and scattered by objects inthe field of view, such as cars, trees, orpeople. Larger and more conductiveobjects generally produce larger returns.Because the wavelength of MIR signalsin air is currently about 15 cm, we caneasily detect objects of that size orlarger at distances of about 15 cm orgreater. Distorted, low-amplitudereflections of the transmitted pulse arepicked up by the receiving antenna inthe time it takes for light to travel fromthe MIR to the object and back again.

The operating principle of MIRmotion sensors is based on therelatively straightforward principle ofrange gating. In looking for the returnsignals, MIR samples only those signalsoccurring in a narrow time window

Range gate

Fixed round-trip delay time

Transmitted MIR impulses (about 2 million/second)

Radar echoes received

500 nanoseconds

200 picoseconds

Distance

Time

25 milliseconds

Incr

easi

ng r

ange

Swept range delay

Time-equivalent record of returns

Figure 3. (a) Following

an impulse transmitted by

MIR, a range gate opens

briefly after a fixed delay

time to sample the

received radar echoes.

(b) To obtain a more

complete record of returns

for more sophisticated

applications, we sweep

the range delay over

various delay times to

obtain target information

at different distances. We

have effectively slowed

down the radar signal by

about a factor of 1 million

to get an “equivalent-time”

record of radar returns

that can be correlated to

object distances. (Pulses

pictured here are not to

scale.)

(a)

(b)

(a) Unprocessed data

(b) Reconstructed image

7.5 ns

33 cm

Figure 4. (a) Unprocessed radar information we obtained along a concrete floor in the Nova facility.

(b) After applying a specialized image-reconstruction algorithm to the unprocessed MIR data, buried

rebar and conduit shown in a cross section become clear.

Rebar

Conduit

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Commercially Ready MIR

Table 1 lists some of the commercialapplications of MIR. One key factor invirtually all commercial markets for MIRis cost. Most of our sensor units can bemanufactured at a fraction of the costof existing technology—indeed, theyare typically hundreds of times lessexpensive. In many cases, there simplyis no practical alternative technologyon the market that is as robust, accurate,and inexpensive.

Security SystemsHome security systems now on the

market can cost thousands of dollars,require regular maintenance, and bedisrupted by interference from aneighbor’s system. At a projected costof $20, an MIR sensor (Figure 6),powered by AA batteries, operateswithout frequency channels or wiring

and is simple to install. Motion sensorscan be adjusted for sensitivity and rangeso that a pet, for example, would nottrigger an alarm and could roam freelyanywhere below a ceiling-mounted MIRsensor. Installations of MIR sensorsalready exist in the DOE nuclear weapons

22



system and its intended purpose, thefollowing features are common to mostunits:• Low cost, using off-the-shelfcomponents.• Very small size (circuit board is about4 cm2).• Excellent signal penetration throughmost low-conductivity materials, so it isable to “see through” walls, concrete, andother barriers, including human tissue.• A sharply defined and adjustable rangeof operation, which reduces false alarms.• Long battery life, typically severalyears, because of micropower operation.• Simultaneous operation of many unitswithout interference.• Randomized emissions, making thesensor difficult to detect.

Current MIR prototype units atLLNL are made with low-cost, discretecomponents. In the planning stages aresingle chips—application-specificintegrated circuits (ASICs)—that willreplace most of the discrete parts andresult in even lower cost and smaller size.

One limitation is that the penetrationof MIR signals through a materialdecreases as that material’s electricalconductivity increases. Thus, the

technology cannot see through thickmetal, such as a ship’s hull, or sea water,but it still can penetrate substances withmoderate electrical conductivity, suchas the human body.

MIR as a Sensor Technology

MIR technology opens up manypossible low-cost sensor systems formotion detection or proximity, distancemeasurement, microwave imageformation, or even communications. Forexample, in some cases it has advantagesover many kinds of conventionalproximity and motion sensors, such aspassive infrared (heat sensors), activebeam-interruption infrared, ultrasound,seismic, and microwave Doppler devices.Many of these sensors are adverselyaffected by temperature, weather, andother environmental conditions, makingthem prone to false alarms. Passiveinfrared sensors can be triggered by lightand heat, and their detection range is notwell defined. Even a thin sheet of paperblocks both infrared and ultrasoundsignals.Similarly, ultrasound motion andDoppler microwave sensors interferewith one another when several units areco-located. Without range gates, thesesensors can trigger as easily on distantobjects as on nearby insects. They canalso have limited material penetration,detectable emissions, and expensivecomponents. MIR technology providesan attractive alternative to these devices.

We are following two paths indeveloping and applying MIR technology.For well-developed products, weencourage commercial applications,and we are licensing the technology toqualified manufacturers in the U.S.using a procedure that ensures fairnessof opportunity. For ideas that requiremore research and systems development,we are continuing to explore electronics,antennas, signal processing, and imagingconcepts as we develop programs thatwill apply MIR technology to supportLaboratory missions and addressproblems of national interest.

Table 1. Some commercial applications of MIR.

CommercialSector Application of MIR

Automotive Parking assistance; backup warning; precollision detection;cruise control; airbag deployment; electronic dipstick for all fluid levels

Security Home intrusion and motion sensor; keyless locks, automatic doors;child monitoring; vehicle theft alarm; radar trip wire; perimeter surveillance

Appliances Stud finder; laser tape measure; wireless thermostat; automatic dispenser;automatic tool shutoff; toys, games, and virtual reality

Manufacturing Fluid-level, proximity, and harsh-environment sensing;robotic sensor; industrial automation

along the floor. When many individualvertical views into the floor are stackedside-by-side, resembling slices of breadmaking up a loaf, we can reconstruct across section of the floor. As expected,features are obscured by the clutterinherent in all radar measurements. Toresolve the locations of buried objects,such as rebar and conduit shown inFigure 4b, we apply a specializedimage-reconstruction algorithm usingdiffraction tomography.2

Many such slices stacked togetherform a full 3-D view of the subfloor orother concrete structure (Figure 5).This unique combination of the MIRsensors and imaging software isspurring new, low-cost nondestructiveinspection methods.

Summary of Features

As MIR technology has evolved, aunique combination of featuresresulted. Although certainspecifications—signal strength,operating range, and directionality—can vary depending on the type of

MIR Recognition and Awards• Thirty U.S. patent applications.

• Twelve industry licensees and many more expected.

• Popular Science, cover story March 1995 and Best of What’s New Award 1994.

• New Scientist, cover story August 1995.

• Electronic Design News, 100 Hottest Products of 1994.

• Intellectual Property Owners, Distinguished Inventor of 1994.

• Federal Laboratory Consortium Award for Excellence inTechnology Transfer 1995.

Figure 5. Imaging steel

in concrete with MIR.

(a) The internal elements

of a concrete slab before

pouring. (b) Reconstructed

3-D MIR image of the

elements embedded in

the finished, 30-cm-thick

concrete slab.

(a)

(b)

25



imaging, highway and bridge-deckinspection, and hand-held wall surveying.In defense and law enforcement, we areexploring MIR in scenarios such asborder control and surveillance systems,mine and ordnance imaging, the imagingof individuals behind walls, and proximityfuses. We also envision potential usesin environmental and medical research.

Many of these applications ofnational interest are government-sponsored, involving signal processing,computations, and communicationsexpertise along with hardwaredevelopment, and we draw onLaboratory experts in all those fields.Following are a few areas in which wehave already made substantial progress.

Border SurveillanceBorder and perimeter surveillance

pose serious technical problems for thenation and many industries and agencies,including drug enforcement, landmanagement, and military security.Among many other issues, visible devicessuch as antennas or cameras are often

targets for vandalism or attack. TheLaboratory is working with the U.S.Border Patrol to demonstrate anautomated, covert surveillance systemfor international borders as well as formilitary sites and police boundaries.

By combining an array of concealableMIR units with advanced, low-costcomputation and communicationtechnologies, we plan to deploy anautomated surveillance method. Wecan monitor a localized area or establishan unattended, electronic trip-line thatwould cover a few kilometers andeventually extend across perhapshundreds of kilometers. MIR modulesplaced up to 100 m apart would measurehuman movement—discriminatingbetween people and other sources ofmotion—and rapidly communicate anintrusion down the chain of modules tothe nearest base station. We now havesensor units in place at the BorderPatrol station in El Centro, California,at an International Atomic EnergyAgency facility, and at Sandia NationalLaboratories, Albuquerque.

Detecting MinesLandmine detection is a serious

military and humanitarian problem.One thousand people are killed ormaimed every week worldwide bymines left from previous wars. MIRcan detect both plastic and metallicland mines buried in most soils. Ourtechnology is attractive because itssmall size and low cost allow eitherhand-held or vehicle-mounted arraysand because images formed by an arrayaid in discriminating mines from groundclutter.3,4 Currently, a laptop computercan reconstruct an image in less than10 seconds, but much higher speeds arefeasible. Field tests at the Nevada TestSite show conclusively that the MIRsensor readily detects buried minesthrough 2-D imaging, but full 3-Dimaging (Figure 8) may be necessary tomore reliably discriminate between amine and other buried features, likerocks of similar size and shape. A lineararray of MIR modules mounted on thefront of a remote-controlled vehicle, oron a boom extending beyond the vehicle,

can detect antitankand antipersonnelmines. Even inareas of roughterrain or densefoliage, portablemine-detectionsystems operatingin the look-aheadmode are feasiblewith currenttechnology.

24



complex, DoD Special Forces, U.S.Border Patrol, and the intelligencecommunity. At Livermore, an MIRsecurity system is now being installedin the lobby of the Nova building.

Automotive SensorsMIR motion sensors placed on the

side of vehicles can alert drivers aboutother cars in blind spots, warn whenanother vehicle is too close, and activateside air bags. A sensor placed on therear bumper, for example, providesparking assistance or warns when a curbis very close. In one test, a sensor unitinstalled in a car’s taillight sectionfunctioned perfectly even when wesmeared mud over the taillight or placed

30 cm of ice in front of the sensor unit.One licensee is expected to equip carswith MIR proximity sensors by the1997 or 1998 model year. Otherautomotive uses include securitysystems, traffic flow sensors, distanceand speed indicators, and dipsticks(described below).

Tools to ManufacturingDo-it-yourself tools based on MIR

can locate wooden or steel studs in awall, steel within concrete (Figure 5),plumbing lines, or electrical wiring. We envision electronic tape measures,automatic thermostats, automaticdispensers, games, and toys thatincorporate the new MIR technology. Inmanufacturing, we are exploring roboticsensors, harsh-environment sensors, andindustrial automation equipment basedon MIR.

One application in particular, the“electronic dipstick,” has the potentialto revolutionize the way fluid levels aremeasured in virtually every industry.The electronic dipstick, a low-cost,solid-state sensor that has no movingparts, is impervious to wetting, corrosion,sludge, and condensation. The deviceshown in Figure 7 launches a signalalong a single metal wire, rather thanthrough air, and measures the transittime of reflected electromagnetic pulsesfrom the top of the dipstick down to aliquid surface. Our tests show that theelectronic dipstick can resolve fluid-level changes smaller than a millimeterand is accurate to within 0.1% of itsmaximum length. The dipstick candetect all fluid levels in a car, measureoil levels in supertankers, and remotelymonitor water levels in reservoirs,among many other uses.

Projects in the Works

Some of our ongoing projectsinclude specialized motion sensors,short-range altimeters, radar ocean Figure 7. The electronic dipstick is a metal wire connected by cable to an MIR electronic circuit.

As a highly accurate fluid-level sensor with no moving parts, this device has myriad applications

in manufacturing and is significantly lower in cost than laboratory equipment performing the

same task.

Figure 6. An MIR concealable

intrusion sensor detects

intruders at ranges up to 6 m.

Units can be mounted on the

ceiling, located behind objects,

or hidden in shelves, closets, or

drawers. The system detects

motion by repeatedly monitoring

the echo pattern to see if it

changes. A change signifies

that an intruder has penetrated

the invisible radar bubble.

27


Micropower Impulse Radar26



Inspecting the Infrastructure More than 40% of the 578,000

highway bridges in the U.S. havestructural deficiencies or are obsolete.Corrosion of steel reinforcing bars(rebar), hidden by concrete and asphaltlayers, leads to fracturing anddelamination, which can result infailure. Visualizing the details of manystructures such as bridge decks hasrequired destructive techniques, such ascoring.

We are developing MIR devices tonondestructively image bridges androadbeds, evaluate civil structures,inspect power poles, and locate buriedpipes. We received funding from the

Asphalt surface

Delamination

Corrosion products

Concrete deck

Front-mounted transceiver array

Survey wheel

Rebar

Figure 8. A typical plastic

antitank mine is shown (top)

before burial at the Nevada

Test Site. MIR technology

was used (bottom) to image

the mine at three depths, or

horizontal “slices.”

Federal Highway Administration tobuild a vehicle for highway and bridgedeck inspection. In that project, we havedesigned a prototype vehicle-mountedinspection system (Figure 9) thatacquires data at speeds approachingthe normal flow of traffic. Speed isimportant because a large portion ofinspection costs arise from trafficcontrols. We envision three modes ofinspection: a quick mode at the highestvehicle speeds for preliminaryassessments, a limited-depth mode forhigher-resolution data, and a detailedmode at slower speed to inspect theentire deck thickness (up to 40 cm).Deployment of the full system isscheduled for fall 1996.

Medical ApplicationsOur radar’s average emission level

is about a microwatt—about 3 orders of magnitude lower than mostinternational standards for continuoushuman exposure to microwaves. Thus,MIR is a medically harmless diagnostictool. In addition, the sensors we aretesting remotely measure human vitalsigns much like the medical tricorderenvisioned in Star Trek, withoutinterfering with computers, digitalwatches, FM radio, or television.

Our MIR heart monitor (Figure 10a)measures muscle contractions(responses of the heart) rather than theelectrical impulses (stimuli) measuredwith an electrocardiogram (EKG).Figure 10b shows the output waveformof a prototype heart monitor comparedto that obtained from a standard EKG.The MIR output is complex and rich in detailed information, and we areactively working with physicians tounderstand its significance.

As a medical monitor, a very smallMIR unit built into a single chip couldsubstitute for a stethoscope. The U.S.Army is interested in a portable devicethat could be worn inside clothing sothat a soldier’s vital signs can be relayedfrom the field to a medical command post.

Depth of 4 cm

Depth of 5 cm

Depth of 6 cm

An MIR-based breathing monitor(Figure 11) does not have to makecontact with a person’s body, and it can operate through a mattress, wall, or other barriers. The detection ofbreathing motion can be a valuableasset in hospitals and homes, couldguard against sudden-infant-deathsyndrome, and might be used by peoplewith breathing disorders such as sleepapnea, in which the affected individualoccasionally stops breathing.

We are exploring the use of MIR foradditional medical devices, includingspeech-sensing devices and a polygraphsensor. Devices for the blind could warnof obstacles and variations in terrainand help to train individuals in usingcanes. We are initiating clinical studiesto optimize medical radars for heart,respiration, and speech applications.The potential payoffs are enormousnot only in financial terms but also in benefits to society.

Rescue OperationsCameras, dogs, and acoustic

equipment tuned to signs of lifecurrently help rescuers to findsurvivors buried after an earthquake,avalanche, or other disaster. Soon,wall- and rubble-penetrating portableMIR devices could assist in search-and-rescue operations. We have testedunits that detect respiration andheartbeats at a range of about 3 m. Inthe midst of wreckage too unstable tosupport rescuers, miniature radardevices could be tossed into the debrisfrom a safe distance and signalpersonnel when physiological signs aredetected. We are working with the U.S.Army Corps of Engineers EarthquakePreparedness Center (San Francisco)and with the NASA Disaster ResponseTeam (Ames) to develop such devices.

Figure 9. Vehicle-mounted

radar imaging for bridge-deck

inspection. Arrays of MIR

modules mounted on the front

and rear allow the vehicle to

cover a 2-m-wide swath with

each pass. Radar images are

reconstructed and processed

at an on-board workstation.

The current maximum range forMIR is about 100 m using high-gainantennas. Our intent is to extend therange to about half a kilometer. Longerrange will require an improved signal-to-noise ratio. We are looking at higher-power systems and improved antennadesigns to extend the range and atbetter signal and image processing toreduce noise.

Key Words: electronic dipstick;micropower impulse radar (MIR); radarheart monitor; ultrawide-band radar, radarimaging, microwave sensors.

References1. T. E. McEwan, J. D. Kilkenny, and

G. Dallum, “World’s Fastest Solid-StateDigitizer,” Energy and TechnologyReview, UCRL-52000-94-4, pp. 1–6(April 1994).

2. J. E. Mast and E. M. Johansson, “Three-dimensional Ground-penetratingRadar Imaging using Multi-frequencyDiffraction Tomography,” SPIE Vol.2275: Advanced Microwave andMillimeter Wave Detectors, pp. 25–26(1994).

3. D. T. Gavel, J. E. Mast, J. Warhus, andS. G. Azevedo, “An Impulse RadarArray for Detecting Land Mines,”Proceedings of the AutonomousVehicles in Mine CountermeasuresSymposium, Monterey, California, April4–7, 1995, Section 6: 112–120 (1995).

4. S. G. Azevedo, D. T. Gavel, J. E. Mast,and J. P. Warhus, “Landmine Detectionand Imaging using Micropower ImpulseRadar (MIR),” Proceedings of theWorkshop on Anti-personnel MineDetection and Removal, July 1, 1995,Lausanne, Switzerland, pp. 48–51 (1995).

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Looking to the Future

We continue to develop MIR for a variety of applications, and we are exploring ways to increase itsperformance in difficult situations.Even though the new radar technologyperforms very well, we still need toaddress issues such as reduced clutter,enhanced resolution and contrast,electromagnetic attenuation by differentmedia, multiple scattering, shadowing,dispersion, real-time operation, andfull 3-D imaging speed.

For some applications, we want toextend MIR from the centimeter-waveregion into the higher-frequency,millimeter-wave region. Higher-frequency MIR will provide betterresolution and give greater signaldirectionality with divergence of onlya few degrees. Higher frequency willalso mean that MIR could detectsmaller objects of 2 cm or smallerdiameter, such as concealed weaponsor bullets, and even tiny asteroidsapproaching a spacecraft. MIR usingmillimeter waves could replaceultrasound motion sensors, such asthose used for automatic door openers.

28



About the Researchers

–0.75

–0.50

–0.25

0

0.25

0.50

0.75

Res

pons

e, V

0 5 10 15 20 25 30 35 40Time, s

–2.0

–1.5

–1.0

–0.5

0

0.5

1.0

1.5

2.0

Res

pons

e, V

0 1 2 3 4 5Time, s

MIR

EKG

(b)

(a)

Figure 10. (a) An MIR

cardiac monitor.

(b) Its output (upper

trace) is distinctly different

from that obtained by a

conventional EKG (lower

trace). We are working

with physicians to

correlate the radar signals

with physiological

functions.

Figure 11. An MIR breathing monitor detects the respiratory cycle through a 10-cm-thick chairback. The higher-frequency waveforms are cardiac activity.

For further information contact Stephen Azevedo (510) 422-8538([email protected]).

For licensing and MIR partneringinformation contact (510) 422-6935([email protected]). Also see ourhomepage (http://www-lasers.llnl.gov/ lasers/idp/mir/mir.html).

STEPHEN AZEVEDO, currently the Program Group Leader ofthe Microradar Project in the Laser Programs Directorate, has abackground in digital signal and image processing. Concentrating inelectrical engineering, he received a B.S. (1977) from the Universityof California at Berkeley; an M.S. (1978) from Carnegie-MellonUniversity; and a Ph.D. (1991) from the University of California atDavis. Azevedo joined LLNL in 1979 and since has been a principalinvestigator in computed tomography research and radar remotesensing; he also has done work in signal processing, modal analysis,

x-ray inspection, nondestructive evaluation, and imaging. He is the author or coauthor ofover 40 publications on these subjects.

THOMAS E. MCEWAN has been a member of the Laser ProgramsDirectorate in the Imaging and Detection Program since joining theLaboratory in 1990. His accomplishments here include inventing themicropower impulse radar (MIR) and developing the world’s fastestsolid-state transient digitizer and a palm-size impulse generator. Hereceived his B.S. (1970) and M.S. (1971) degrees from the Universityof Illinois (Chicago Campus) in electrical engineering. From 1970 to1985, he was a design engineer at Nanofast Inc. From 1986 to 1989,McEwan led the design of high-speed microelectronics at NorthropCorporation, where he supported programs in radar jamming,electronic countermeasures, and computer-chip development. In

addition to the MIR recognitions listed on p. 23, he has six patents in widebandelectronics.

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micropower impulse radar - lawrence livermore … science & technology review january/february...

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