Defense Technology International - June 2008 - (Page 12)

SCIENCE WATCH MICHAEL DUMIAK SEE-THROUGH SCANNERS German federal research chief Thomas Rachel has set a security agenda with an array of projects weighted toward probing the terahertz spectrum in an effort to develop see-through scanners that detect weapons and explosives. Rather than go for a home run with one detector that does it all, Berlin is making small bets around the country, with teams looking to produce different devices that do well-deﬁned jobs. For a nation with a limited and sensiabout 1 mm. in length. Scanners that work in the millimeter-wave range also show promise. Terahertz waves penetrate clothes, ceramics, wood, paper and plastic, but are blocked by metal and water. Waves change when going through gases, solids or liquids, and in doing so emit a terahertz “signature” readable through refined spectroscopy. The scan is hard to do outside a lab—signals are weak, hard to resolve and quickly absorbed by air. someone is hiding something, but that something—a cell phone, knife, bomb—usually looks like a blob,” New Jersey Institute of Technology physicists John Federici and Dale Gary wrote last summer in IEEE Spectrum. The best way to get terahertz scanning is with a particle accelerator. Indeed, the U.S. military is researching an electron accelerator compact enough to ﬁt in a Humvee. Another method uses liquid helium. The most promising way, commercially, is to use a femtosecond laser, which pulses at rates measured in quadrillionths of a second. But this raises other issues— the laser’s cost (extremely expensive), portability (very limited) and the need for a highly stable base. At Braunschweig Technical University in Germany, spectrometry expert Martin Koch says terahertz scanning has a lot of promise. “The problem is people are promising things that aren’t there yet,” he remarks. “There’s one image of a tooth, and the idea is, you can use a scanner to show decay. What’s not said is that the tooth is extracted, cut into thin slices and dried because otherwise it would contain too much water at terahertz frequencies to show anything.” Berlin gave Koch’s team $450,000 to build a hand-held terahertz scanner to examine bottled liquids at airports. “It is specialized and focused,” he says. “You press it against an object and hold it for one or two seconds. It’ll bleep and tell you [if the liquid is] dangerous or Coca-Cola.” Because the scanner isn’t looking over a mass of moving people, trying to resolve video, it gets around some of the harder terahertz issues. Rachel’s research budget, which totals about $40 million, also lays out terahertz projects for scanning passengers’ shoes. And amid the larger research mix of broadband sensors for drinking water, epizootic detection in case of agro-terrorism and risk communication, $480,000 goes to ethical research into terahertz applications. “Right now, this is more in the lab than in the airport,” says Regina Ammicht Quinn, a security ethics expert at the University of Tubingen in Germany. “But a system that is not accepted by passengers is of little use.” I AviationWeek.com/dti FOTOSEARCH Terahertz scanners can penetrate most materials to detect if weapons or explosives are being transported. tive defense appetite, and great engineering and scientiﬁc talent, there is logic to this approach. The hunt for a terahertz scanner, a device able to scan and detect—at a distance—weapons, explosives and other dangerous substances concealed beneath clothing or in suitcases, emerged in recent years as a controversial security pursuit. It’s sparked a contentious debate over privacy rights: Some scanners produce body images that critics claim are equivalent to a strip search. Lost in the fray is the science and whether these machines are ready for use. The scanners work in various ways, but all probe a part of the electromagnetic spectrum starting in the far infrared and pressing up to the border with microwaves, which begin at 12 American and British security ofﬁcials have tried pilot projects with terahertz and terahertz-like machines going back to 2004. A few models of see-through spectrum scanners are on the market. The U.S. Transportation Security Administration recently bought 12 millimeter-wave scanners for $3 million after tryouts at the Staten Island Ferry terminal in New York City. But researchers are far from unanimous on whether terahertz scanning is ready for security work. Resolution, clarity, expense, power supply and speed of imaging are issues, says Ullrich Pfeiffer, a high-frequency expert at Wuppertal University in Germany. The millimeter-wave scanner is further developed but has drawbacks. “These are capable of discovering if DEFENSE TECHNOLOGY INTERNATIONAL JUNE 2008 http://AviationWeek.com/dti

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Defense Technology International - June 2008 Contents Around the World Science Watch Tech Watch Basic Black Self-Defense Fire-Resistant Perfezione Hyperspeed Trial Big Sky Cashing In Digital Links Hang Ten Sea Change Programs Update Two Steps Back Direct Hit Staying Power Potent Stinger Do No Harm Guard Duty The Net Cutting Edge First Person In Review Insight

Defense Technology International - June 2008

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