Bomb sight

Suicide bombers could be spotted in a crowd before they carry out their deadly mission, thanks to a combination of ultrawideband radio technology and an obscure law of physics, according to a UK project team.

Researchers at Birmingham University and the UK R&D division of Thales hope to develop portable sensors based on UWB to detect hidden weapons and explosives in an open area without having to channel people though security gates — which is a major logistical headache.

Tests have already identified a grenade-shaped object hidden in a pocket, and the system could eventually even be able to distinguish between different types of weapons, according to researchers evaluating the technology.

The system uses one-nanosecond radio pulses from a UWB sensor that occupy the 1GHz band.

UWB sensors are not new in themselves, but the research team, based in Birmingham’s engineering department, plans to use a littleknown principle of physics known as Late-time Response (LTR) to analyse the signals.

The signal from conventional radar is nearly always longer than the target it is striking, reflecting back as a single point. In contrast, a UWB radar signal is so short that each part of the body acts as a separate point, each reflecting a pulse back at a slightly different time.

Dr. Mikhail Cherniakov, who is leading the project, said: ‘The duration of the signal is 15 times smaller than the time it takes for it to propagate itself around the human body. It is this peculiarity of UWB that we hope to use to develop the sensor.’

When any radio signal strikes an object most of the signal is reflected straight back while some is partially absorbed. Because of a UWB signal’s short length, this absorption produces a gradually diminishing signal or ‘tail’ effect as it decays.

According to Cherniakov, it is this ‘tail’ that can be used to identify any object via a unique signature based on its shape and electrical properties.

‘Every single object has its own signature that it reflects back,’ he said. ‘These are like fingerprints; no one is the same. Different sizes and different materials all produce different signatures, which we can then analyse and categorise.’

Cherniakov and his team use sophisticated processing software to identify the signals and check them against a database of known suspicious signatures.

‘It is similar to the way a dog picks up a scent. Because it knows the characteristics of the scent it is looking for it can disregard the millions of other signals it is receiving,’ he said.

Used in tandem with known imaging techniques, the sensor could identify a suspect and then target them for more detailed scanning, for example using terahertz imaging.

Conventional imaging systems also rely on people passing through a security gate, or allowing themselves to be examined, which is not practical in the case of a suspected suicide bomber.

The UWB sensor should be able to pick up the signal of a concealed weapon in a crowd from up to 30m away. The sensors have already performed well in tests, most notably by successfully detecting the grenade-like object, said Cherniakov.

‘In time we might even be able to determine if the weapon is a shotgun or kalashnikov, and know exactly how many metres from the sensor the suspect is,’ he said.

Airport security companies and the MoD have already shown interest in the technology. The army, for example, could use it to help military police based in Iraq to detect potential suicide attackers from a safe distance.

The two-year project, which is backed by the EPSRC, will evaluate the technology further and attempt to lay the foundations for products that are low cost enough to be commercially viable.

Barry Darby, business development manager at Thales Research, said that the project team hoped to have a working prototype within two years. ‘This technology has great potential and needs to be explored further. We’re all quite excited about it here,’ he added.