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

Federici@adm.njit.edu

http://physics.njit.edu/~federici

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Department of Physics

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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Department of Physics

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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Department of Physics

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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Department of Physics

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

0.75

0.80

0.85

0.90

0.95

1.00

Inte

nsity

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.

Tyson@adm.njit.edu

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Department of Physics

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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Department of Physics

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)