Life Goes Full Circle

Now approaching the ripe old age of 70, your Editor was delighted to see a solution announced to the first research project he undertook when fresh out of University. This was in 1967, when starting work at the sensor/detection systems research laboratory of Plessey Electronics at West Leigh, near Portsmouth. The project was on advanced detection aids for the Home Office Police R&D Branch, and the broad feasibility studies looked at methods of improving Police search methods by introducing scientific aids.

One notable idea was that possibly hidden bundles of banknotes might be recognized and located by using an adapted form of ground radar to detect the resonance of the dipole formed by the metal strip embedded in UK banknotes. Various experiments were undertaken that involved dangling bundles of GBP100 in GBP1 notes within a radar beam, but the effective reflective area was still insignificant compared to the background clutter. The conclusion was that detection might be possible if the metal strip was built with an embedded diode junction, which might enable some sort of mixing of dual frequency waves, but this was dismissed as impractical.

TWIPR Twin Inverted Pulse Radar

A Report by Jason Ford in the Engineer suggests that a new type of radar could be used to detect hidden surveillance equipment, explosives, or any other tagged items. Developed by a team led by Prof Tim Leighton from Southampton University’s Institute of Sound and Vibration Research, the idea is based on the technique used by dolphins to help their sonar signal processing. Their system, called TWIPS, twin inverted pulse sonar, can enhance scattering from a linear target, such as a fish, while suppressing non-linear scattering from oceanic bubbles. The technique uses a transmitted signal consisting of two pulses in quick succession, one identical to the other, but phase inverted. The Engineer reports:

“The Southampton researchers 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.”

Useful Applications

In fact, it is said that TWIPR would work the opposite way round to TWIPS, in that it would look for non-linear scattering by the target. Given that the diode target measured 6cm in length, weighed 2.8g, cost 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 also be tuned to scatter-specific resonances to provide a unique identifier to a TWIPR pulse.

The technique could also be used by skiers, to enable quicker location after avalanche burial, although the technique could be adapted to look for resonances from within standard objects like mobile phones.




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