1 department of physics terahertz imaging and detection of suicide bombers* j. f. federici, d. gary,...
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Department of Physics
TERAHERTZ IMAGING and DETECTION OF SUICIDE BOMBERS*
J. F. Federici, D. Gary, B. Schulkin, F. Huang, H. Altan Department of Physics
R. Barat Department of Chemical Engineering
K. Walsh
Picatinny Arsenal
*Funded by US Army and NSF
http://physics.njit.edu/~federici
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Outline
• THz Basics
• Basics of Interferometric Imaging
— Spectral Information
— Spatial information
• Simulated Images
— cm resolution at 100m distances
— Spectral Resolution of Explosives and Metals
— Analysis of Images
• Current and Future Work
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What is Terahertz (THz)?
1 THz frequency = 300 m wavelengthor 33 cm-1 or 4.1 meV or T = 48 K
Radio Microwave T-rays Infrared UV X-rays
Frequency (Hz)
108 109 1010 1011 1012 1013 1014 1015 1016 1017
Visible
Also known as Far-Infrared or sub-millimeter
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THz at NJIT
• 1997-2001 Developed various THz sources, detectors, and imaging techniques
Two PhD students graduated, 9+ publications in THz technology
• 2000-2001 Developed concept for Detection of explosives, chemical and biological weapons using new THz imaging methodology.
• Spring 2001 - Proposal for cargo screening submitted to FAA
• Post 9/11 - National Science Foundation and US Army Funding
8 publications since 2002, 2 patents pending
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Wide Area Surveillance
NJIT Team is developing THz imaging techniques for Stand-Off Detection of concealed Explosives, Chemical/Biological Agents
• Development of Technique/ Hardware for Imaging
• Development of Image Analysis
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Comparison with Other Techniques
X-Ray, Neutron Scattering - Uses high energy radiation
• damages biological systems - eg. damages DNA/ tissues
• permissible exposure limited - more difficult for use on people.
THz - low energy radiation - “non-ionizing”
• no damage to biological tissue
• differentiation of target compounds based on THz “color”
• Imaging and “color” information combination will reduce false alarm rate.
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Disadvantages of THz for Scanning for Explosives / BioAgents
• Metals are opaque to THz– will reflect the THz
• THz strongly absorbed by water– will not detect explosives inside the body
• THz scanners will likely be used in conjunction with other detection techniques.
• Not a forensic technique - looking for 1cm2 size blocks of material
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Application of High-Resolution X-Ray Raman Scattering to Homeland SecurityT. A. Tyson, Q. Qian (NJIT), Z. Zhong, C.-C. Kao and W. Caliebe (NSLS)
X-ray absorption spectroscopy of is one method that can be used to identify chemical systems by threshold spectra. The resonance features in x-ray absorption spectra are uniquely related with the molecular structure enabling rapid chemical identification. Utilizing 100 KeV x-rays with high penetration power and a transmission x-ray analyzer system based on a working design (left), we will develop a system for detecting explosives and chemical weapons by fingerprinting their spectra.
260 280 300 320 340 360
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Inte
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Energy(eV)
Carbon K-Edge of Graphite (X-Ray Raman)
The upper and lower left panels show the full spectrometer and blow up of the analyzer array, respectively. Each of the nine x-ray focusing mirrors can be independently aligned with micro radian precision in the horizontal and vertical planes. The lower left panel show the carbon K-edge spectrum of graphite measured in energy loss mode (x-ray Raman spectrum) with a resolution of ~ 0.5 eV.
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Advantages of THz for Scanning for Explosives / Bio and Chemical Agents
• THz transmits through most non-metallic materials: plastic, paper , clothing
• THz yields transmission / reflection spectra of targets*
ExplosivesKemp (2003)
Transmissive Bas.Sub. SpectraWoolard et al (2003)
* See papers from Proc. SPIE 5070, (2003)
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Interferometric Imaging - Motivation
Therefore
• To image in the THz, one must generate images using only a few to a few hundred detector elements.
Possible Solution: Interferometric imaging
A THz digital camera would be ideal for THz imaging:
However
• consumer digital cameras imaging arrays of 1024 by 768 pixels or 780,000 individual detector elements in the array.
• That high density of detectors in THz range not technologically possible.
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Sample Array Geometry
)1( nobradDetector Distance
to Origin:
Exponential Distances Ensure Non-redundant Spacing of Detector Pairs
66 detector pair combinations
Rotation of 90o with data acquired every 1o:
66*90 = 5940 points in u-v plane
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Estimated Angular Resolution
b (meters)
10 1 0.1 0.01 0.001
0.1 62" 10' 1.7o 17o 170o
1.0 6.2" 62" 10' 1.7o 17o
(THz)
10.0 0.6" 6.2" 62" 10' 1.7o
Field-of-View determined by either Field-of-View of individual Detectors or Bandwidth of Detectors.
Angular (Spatial) Resolution determined by spacing between Detector Pairs.
A 1m baseline array has a spatial resolution of 3cm at 100m!
Scaling down to cargo unit or hand-held size of smoke detector!
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Simulation of THz Imaging Array
Detection of RDX and Metal at a distance of 30m
Objects 1.5cm in size
Composite Image combination of THz images taken at 5 different frequencies
Spectral and Spatial Images
Objects with spectral content of RDX colored Red
Objects reflecting all THz radiation colored white
RDX Metal
Sidelobes
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Focusing of Image
ImagingArray
Object
Focal Length
Single frequency, uncleaned image
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Image Analysis - Neural Networks
U A A A A U A A A U A A U A F A S S A S S U A A U U A S S U A A A A U A S F U U F U A A A A F F F A A U S U U S F F F F F F F A U M M M M M S A A U F F F A M M M M M M S U U U M M M M M M U U M M M M M U S M M M M U A A S S U
BLUE = metal coinPINK = bioagentGREEN = flourORANGE = starch
THz Image at 1 frequency
Neural Network Analysis
U U U U S S A S S A S S F A F F A F F U F F A U F A A U U A U A A U A A A U U A A A A A A A U U A A U U A A
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Present and Future Work
• Development of Benchtop model underway to demonstrate key technological components
• Detect C4 versus peanut butter hidden in clothing.• Scale up to imaging system for suicide bombers
(system size about 1m)• Scale to hand-held/ cargo container unit (10cm size,
battery operated unit)