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
Federici@adm.njit.edu
http://physics.njit.edu/~federici
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Department of Physics
*Funded by US Army and NSF
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)?
Visible
Radio Microwave
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109
1010
T-rays
1011
Infrared
1012 1013
UV
1014
1015
X-rays
1016
1017
Frequency (Hz)
1 THz frequency = 300 m wavelength
or 33 cm-1 or 4.1 meV or T = 48 K
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 Security
T. 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.
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0.95
Intensity
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.
Carbon K-Edge of Graphite (X-Ray Raman)
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0.90
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0.75
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Energy(eV)
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Tyson@adm.njit.edu
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*
Explosives
Kemp (2003)
Transmissive Bas.Sub. Spectra
Woolard et al (2003)
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* See papers from Proc. SPIE 5070, (2003)
Interferometric Imaging - Motivation
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.
Therefore
• To image in the THz, one must generate images using only a few to a few
hundred detector elements.
Possible Solution: Interferometric imaging
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Sample Array Geometry
Detector Distance
to Origin:
d  a rob
( n 1)
Exponential Distances Ensure Nonredundant 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
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.
b (meters)

(THz)
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1
0.1
o
0.01
o
0.001
0.1
1.0
62"
6.2"
10'
62"
1.7
10'
17
1.7o
170o
17o
10.0
0.6"
6.2"
62"
10'
1.7o
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
RDX
Metal
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
Sidelobes
Objects reflecting all THz radiation
colored white
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Focusing of Image
Focal Length
Object
Imaging
Array
Single frequency, uncleaned image
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Image Analysis - Neural Networks
THz Image at 1 frequency
Neural Network Analysis
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BLUE = metal coin
PINK = bioagent
GREEN = flour
ORANGE = starch
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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)
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