Detecting explosives hidden within clothing

12 November 2010

Near infrared (NIR) spectroscopy could be used to detect hazardous chemicals hidden behind clothing, and could improve security screening technology in places such as airports, say UK scientists.

Celine Canal, David Hutchins and colleagues from the University of Warwick detected the explosive ammonium nitrate hidden behind a layer of various clothing materials, from light acrylic to thick denim. 'Light in the NIR wavelength range is invisible to the naked eye, allowing unnoticeable remote detection,' explains Hutchins. The optical components of a spectrometer in the NIR wavelength range are less expensive than for alternative remote detection systems, which use X-rays or terahertz signals, he adds. Unlike X-rays, NIR radiation is not ionising so it is also a safer option for human screening.

The group showed how a person could be screened for hidden chemicals from a remote distance. They set up a light source to illuminate a sample, which consisted of the chemical in a glass container hidden behind a layer of clothing material. The light was transmitted through the clothing and signals were reflected by the chemical and back through the clothing to the detector. The signal was then passed into a spectrometer, which analysed the intensity of the light at each wavelength. By comparing the intensities of light diffused by the clothing material and the hidden chemicals, the group were able to work out a 'fingerprint' for the chemical. They hope that by using statistical methods, this fingerprint can then be recognised automatically in screening applications.

The explosive ammonium nitrate was detected behind a layer of clothing, from light acrylic to thick denim

'Identifying materials hidden under clothing is an unsolved challenge for existing security technologies. NIR spectroscopy combined with powerful analysis tools might be a promising answer,' says Jürgen Popp who develops innovative spectroscopic techniques at Friedrich Schiller University in Jena, Germany. However, he points out that that dealing with influences such as perspiration, scent and pollution will be a challenge.

Hutchins' group are working on how to process the data to remove influences from the environment, the packaging around the chemical and multiple clothing layers. They hope that in the future, the system could be added to CCTV cameras, providing a warning from the spectroscopic analysis of a hidden suspicious chemical and an image of the suspect.

Fay Nolan-Neylan


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