Friday, 31 October 2014
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Dolphin 'sonar' inspires clutter-penetrating radar

Scientists in the UK have taken inspiration from the natural world to develop a new kind of radar that can detect hidden surveillance equipment and explosives.

The twin inverted pulse radar (TWIPR) is reportedly able to distinguish true ‘targets’, such as certain types of electronic circuits that may be used in explosive or espionage devices, from ‘clutter’ (usually other metallic items) that may be mistaken for a genuine target by traditional radar and metal detectors.

The new system has been developed by a team led by Prof Tim Leighton from Southampton University’s Institute of Sound and Vibration Research and is based on twin inverted pulse sonar (TWIPS).

TWIPS exploits the natural abilities of dolphins to process their sonar signals to distinguish between targets and clutter in bubbly water. Some dolphins have been observed to blow ‘bubble nets’ around schools of fish, which force the fish to cluster together, and their sonar would not work if they could not distinguish the fish from the bubbles.

The technique uses a signal consisting of two pulses in quick succession, one identical to the other, but phase inverted. Prof Leighton, along with Prof Paul White and students Dan Finfer and Gim Hwa Chua, showed that TWIPS could enhance linear scatter from the target, while simultaneously suppressing nonlinear scattering from oceanic bubbles.

Prof Leighton’s team proposed that the TWIPS method could be applied to electromagnetic waves and that the same technique would work with radar.

They teamed up with Prof Hugh Griffiths and Dr Kenneth Tong of University College London and Dr David Daniels of Cobham Technical Services to test the proposal, by applying TWIPR radar pulses to a ‘target’ (a dipole antenna with a diode across its feedpoint - typical of circuitry in devices associated with espionage or explosives) to distinguish it from ‘clutter’ (represented by an aluminium plate and a bench clamp). In the test, the target showed up 100,000 times more powerfully than the clutter signal from an aluminium plate measuring 34cm by 40cm.

The study, ‘Radar clutter suppression and target discrimination using twin inverted pulses’ is published in the journal Proceedings of the Royal Society A.

In a statement, Prof Leighton said: ‘As with TWIPS, the TWIPR method distinguishes linear scatterers from nonlinear ones. However, in scenarios for which TWIPS was designed, the clutter scatters nonlinearly and the target linearly - while in situations using TWIPR, these properties are reversed.

Given that the diode target measured 6cm in length, weighed 2.8g, costs less than €1 and requires no batteries, it allows the manufacture of small, lightweight and inexpensive location and identification tags for animals, infrastructure, and for humans entering hazardous areas.

These tags could then be tuned to scatter-specific resonances to provide a unique identifier to a TWIPR pulse.

Buried catastrophe victims not carrying such tags might still be located by TWIPR, as it can carry the bandwidth to search for mobile phone resonances, offering the possibility of locating victims from their mobile phones, even when the phones are turned off or the batteries have no charge remaining.

Professor Leighton said: ‘Such technology could be extended to other radiations, such as magnetic resonance imaging (MRI) and light detection and ranging (LIDAR), which, for example, scatters nonlinearly from combustion products, offering the possibility of early fire detection systems.’


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