Explosives Detection

By Joseph Straw


Vapor trace. The greatest chemical detector in the world is a dog’s nose. Ross Harper, a senior staff scientist with ICx Technologies, lists the various factors that make dogs such effective sensors, whether they’re looking for table scraps or explosives: The surface of a dog’s olfactory membrane is up to four times larger than a human’s, and roughly 40 percent more of a dog’s brain is devoted to detecting scent. As a result, dogs can detect substances even if they are only present at 2 parts per trillion.
Researchers at various universities and the Defense Advanced Research Projects Agency have been working for decades to duplicate what nature has achieved with the canine nose. Those efforts have borne fruit, in particular the ion mobility spectroscopy and chemiluminescence technologies used in today’s explosive trace detection devices, like the hand-held and bench-top machines already in use at airports and security checkpoints around the world.
Other technologies that function at the micro and nano levels have also shown promise at detecting small quantities, and, at least one researcher says that they hold the promise of exceeding the sensitivity of canine olfaction.
Microelectromechanical systems, or MEMS, 1/1000th the width of a human hair can be engineered to bind to only one type of molecule, TATP for example. When that molecule binds to the device, the sensor detects the distortion of the fiber and registers a hit. More recent research conducted by scientists from Germany’s University of Bonn and the Max Planck Institute in Mainz have used “microbalances” made of quartz crystals, which vibrate at a known frequency, to detect contact with TATP with a sensitivity of 1 part per million.
Susan Hallowell, director of the U.S. Department of Homeland Security’s (DHS) Transportation Security Laboratory, acknowledged the promise of quartz microbalances, but noted the challenge of collecting enough air, quickly enough, to produce a high degree of selectivity from a sample.
Another research effort that is making progress is headed by scientist Tom Bruno at the National Institute of Standards and Technology (NIST). That team is developing what Bruno calls “headspace analysis,” meaning simply a sampling of the air over a test substance.
NIST’s technology relies on the attraction of certain molecules of an explosive to specially treated, supercooled metal coils. A test sample is combined with helium, then passed over the coils. If present in the sample, the targeted molecules will bind to the coils.
The coils are rinsed with a solvent, which can then be tested for the presence of the target substance. The sensitivity of the test, which according to NIST could be adopted for use outside the laboratory, is currently two parts per billion. Bruno, however, tells Security Management that the technology holds the promise of detection at 10 parts per trillion, which would exceed canine sensitivity by a factor of five.
Terahertz scanning. Another technology that has government’s attention is that of Terahertz radiation, a band that is non-ionizing and eye-safe, which means that it could be used safely to scan both liquids and individuals for explosives.
More recent research on liquid-explosives detection at the Jülich center involves radiation at a higher frequency, in from the gigahertz to the terahertz range. Using a newer method of spectroscopy called Hilbert spectroscopy, the technology can measure transmission, reflection, and absorption of substances being tested, which increases accuracy. The test also takes less than a second, according to Jülich researcher Yuri Divin.
Divin and his fellow researchers are working toward development of a compact commercial prototype for the Hilbert spectrometry technology. He thinks it could be fully commercialized within two to four years.
Technology employing terahertz scanning, developed by TeraView Ltd. of Cambridge, England, holds the promise of scanning individuals for either trace or bulk explosives, even those concealed under clothing, according to TeraView CEO Don Arnone.
TeraView’s product, called the TPS Spectra 3000, is housed on a pair of wheeled carts, each about the size of an airline beverage cart. One cart bears a display monitor and the system’s analytic hardware; the other holds the equipment necessary for actual sampling via a sensor placed at the end of a fiber-optic cable.
As with all forms of spectroscopy, the process involves reading radiation. In this case, TeraView’s device emits a beam of radiation that passes unencumbered through clothing. At specific frequencies, however, the energy is absorbed by specific explosive molecules. The technology is already under evaluation at the U.S. Naval Surface Warfare Center at Indian Head, Maryland. It is scheduled for field tests by British aviation security authorities, Arnone tells Security Management.
Integration and Automation
Time and again, investigations by government watchdogs have demonstrated the limitations of human screeners to spot threats when they appear in images on machine monitors. This may be the result of natural shortcomings in human observation and cognition as much as the fault of apathy or distraction after too much time spent staring at the screen.
The Transportation Security Administration (TSA) wants automation that will remove the human element and, thus, the potential for human error. One solution may be what the agency calls automated target recognition (ATR).
Many vendors tout their products as offering ATR, because their software superimposes a box over an anomaly detected on a full body scan or over a large, potentially organic object detected by the dual-energy advanced technology (AT) x-ray machines currently used at TSA checkpoints for carry-on baggage. Mitchell Laskey, president and CEO of Brijot Imaging Systems, which sells massive millimeter wave scanners, notes that these capabilities are not truly ATR as much as “automated human assist.”
True ATR could mean an end to the volume restrictions on carry-on liquids, and it might mean an end to the requirement that travelers remove computers from all carry-on bags. But ATR for finding threats on humans is trickier, because of the health and safety issues. Luggage can be screened using relatively high levels of ionizing x-ray radiation, which is most effective at detecting chemical compositions. Human travelers cannot.
The likely solution for scanning people is technology integration, according to Hallowell and Jim Tuttle, director of the explosives division of the Department of Homeland Security’s Science and Technology Directorate. Hallowell acknowledges the potential for an integrated, automated system to provide ATR for that purpose. She notes the prospect of a checkpoint screening device that combines full-body scanning, such as millimeter wave or backscatter, and a sophisticated, non-ionizing and eye-safe explosives detection technology like terahertz radiation (as mentioned earlier). The integrated device could use a full-body scanner to detect an anomaly, then automatically direct a terahertz beam at the highlighted anomaly to determine its composition.
That concept, mated with real-time devices like Smith Detection’s new eqo millimeter wave full-body scanner, could bring security agencies like TSA closer to what some call a “lane of truth,” in which subjects simply pass through an automated screening portal without slowing their gait, let alone stopping and removing articles from bags or shoes from feet.
Another integrated solution would involve mounting terahertz sensors on traditional portal magnetometers, which typically cost less than $5,000 apiece, compared to the $170,000 price tag of the typical full-body scanner, says Arnone.
Mark Laustra, of Smiths Detection, says his firm is collaborating with Analogic, manufacturer of the computed tomography (CT) explosives detection systems used to scan checked airline bags, to develop a belt-fed scanning device for checked baggage that combines both CT and AT technology.
The combined detection capability of the two technologies could mean higher sensitivity and greater speed. That could move aviation security operations closer to another goal: integration of EDS into the existing automated systems used to move checked bags from curb or check-in counter to aircraft. TSA calls the concept “in line” screening of checked bags.
DHS has set a goal of fielding new technologies like terahertz within four years and fielding integrated technology systems within eight years, Tuttle tells Security Management


EMIT Technologies already has a Bottle Scanning Device

You can view a video of a similar bottle scanner by going to the following link and the EMIT Technologies website:


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