Beating the gun

A portable device capable of detecting concealed guns on people at key locations, such as airports and entertainment venues, is being developed by UK researchers in a two-year project.

Police currently have scanners and portals that can detect the carrying of metal objects, but there is no discrete portable system that allows detection from a stand-off distance of more than one metre.

The team — from Manchester Metropolitan University, Manchester University, Huddersfield University and Queen Mary University of London, plus an expert in pattern recognition from Leeds Metropolitan University — will begin work on the device within the next three months, with the help of a £530,000 EPSRC grant.

The initiative is the latest in an array of UK projects looking into explosivees and weapons detection. Others include the use of Ultra Wide Band Radar.

Establishing the sort of electromagnetic radiation that best penetrates clothing will be the team’s first task — and could be the key to the project’s success.

Wavelength capability

‘There’s a lot of literature on the propagation of electromagnetic radiation at various wavelengths through the atmosphere. We are interested in the capabilities of various wavelengths to penetrate not only the atmosphere, but also various kinds of clothing and fabrics,’ said the project’s leader Dr Nicholas Bowring, of Manchester Metropolitan’s Department of Engineering and Technology,

The researchers’ initial investigations show that millimetre waves penetrate most clothing samples. But one of their design challenges will be to establish the water content of different fabrics as this could affect readings.

‘Leather, for instance, has a higher water content than modern fabrics and as such will require higher power to penetrate, but what we’re talking about is well below safe limits,’ said Bowring. The team will explore a range of solutions, one being to increase the sensitivity of the detectors using standard radio receiver techniques.

Atmospheric conditions pose another challenge, as the damper it is, the more the attenuation — especially at frequencies above one millimetre. But Bowring said that there are plenty of places in the electromagnetic (EM) spectrum where sufficient power can get through to be effective.

A major part of the project will focus on studying and recording a wide range of readings using different types of electromagnetic radiation to penetrate different fabrics and detect myriad metal objects. The team will build a comprehensive range of patterns before it can establish the most effective combination of EM waves.

Microwaves are a form of electromagnetic radiation, but other forms include light, infrared, terahertz and millimetre waves — and they all differ in their fabric penetration ability. The team will also explore the use of ultrasound to detect metal objects concealed under clothing. The body absorbs some of these forms of electromagnetic radiation, whereas others are reflected back depending upon the precise wavelength.

Detect reflections

Although the detector will be able to penetrate clothing to locate a concealed metal object, the device will not take any images of the body. Rather it will detect reflections off the surfaces of the gun — in a similar manner to that of a radar detecting the bright echoes from ships and aircraft — while filtering out the body’s lower level reflections.

So that the detector can distinguish between a gun and other metal object, such as mobile phones and portable music players, the team aims to use features unique to a gun, such as the barrel and other cavities, to identify signatures in the reflected signals. A gun’s barrel acts as a resonant cavity rather like air blown over a musical wind instrument, and the researchers are looking to detect these resonances remotely.

‘We want to know whether other unique features such as the presence of gun barrel cavities will alter the reflected signal sufficiently to be an identifying factor,’ said Bowring.

The team might be a long way from manufacturing a hand-held gun detection system, but, if the project goes according to plan, they should have identified the most efficient blend of technologies by the end of the year.

They will then concentrate on fusing together the most promising technologies to manufacture a prototype that can operate effectively at stand-off distances.