Landmine clearance breakthrough

A new landmine detection system, which claims rapid and 100% accurate detection, has been revealed by the US Naval Research Laboratory (NRL).

In preliminary tests, the system cleared small areas 30 times faster than metal detectors, which are plagued by the false alarms caused by bullet casings and other battlefield debris.

Mine facts
120 million mines buried worldwide
One million mines were buried in 1997
100,000 mines were made safe in 1997
To clear all the mines in Croatia at current rates would take 690 years
One in 237 people in Cambodia have lost limbs to mines

The device uses radio waves to specifically detect the explosives.

Regina Dugan, from the US Defense Advanced Research Projects Agency, which provided about $10m for the research, said both hand-held and vehicle-borne applications would be developed.

She said: "It is quite difficult to put an eventual price on the device, but the value of a system which could clear 100% of mines would be very high."

However, she estimated that the hand-held devices would cost "thousands or tens of thousands of dollars".

Pointed sticks

Until recently, according to Dr Dugan, mine detection technology was only barely better than in the 1940s. The main tools were metal detectors and pointed sticks. However, with modern mines containing very little metal, the detectors have to be so sensitive that many false alarms result. It can take 10 minutes to resolve a false alarm and often only one signal in 1,000 is genuine, making clearance extremely slow.

The new approach is called nuclear quadrupole resonance (NQR) and was created by Allen Garroway, who led the research team at NRL in Washington DC.

The technique is similar to magnetic resonance imaging (MRI) but uses radio waves rather than a magnet to detect a signal. Radio waves of a frequency specific to the explosive result in a measurable disturbance.

However, the background noise in the signal is high and so a powerful and energy-hungry radio pulse is needed - hundreds of watts for the hand-held device.

The current configuration resembles a metal detector, with a 30-cm loop to wave over the ground.

It is too large for a backpack, but miniaturisation of the electronics and improvements in power use should make that goal possible.

Bosnia test

The first devices are expected to be military versions and available in three years' time. Another possible problem is that the NQR system cannot detect mines which have less than 50g of explosives. This is currently at the lower limit of typical anti-personnel mines, which have ranges of 50g to 200g. Typical anti-tank mines contain 5kg of explosives in them.

In a test in Bosnia, an area 10ft by 10ft was set out, giving 100 one-foot squares. Eight mines of different types were buried, along with spent bullet cartridges.

The NQR device found all the devices in 15 minutes.

However, the metal detector suffered false alarms in 34 of the 92 empty squares, meaning the total time for clearance would be seven hours.

The new mine-clearance system was announced at the annual meeting of the American Association for the Advancement of Science.