Electronic Design

Quadrupole Resonance Detects Landmines With 100% Accuracy

From World War II to Somalia, the percentage of casualties caused by landmines has risen sharply. These explosives have indiscriminately killed and wounded soldiers and civilians for over six decades. Sadly, the problem only seems to be getting worse. According to one estimate, almost 60 million landmines are buried across four continents.

The Defense Advanced Research Projects Agency has responded by funding research in quadrupole resonance (QR) technology, also known as nuclear quadrupole resonance (NQR). Current detection methods are slow, expensive, and dangerous because metal fragments scattered across battlefields produce many false alarms. But early tests have shown QR to be 100% effective.

A variation of magnetic resonance imaging (MRI), QR has been around for nearly 30 years. Yet the recent availability of powerful, low-cost DSP processors has made it viable for landmine detection. Substantial improvements in RF pulse sequencing, QR coil designs, and RF hardware also have contributed. While proper RF pulse sequencing has curtailed the effects of magneto-acoustic and piezoelectric ringing, improved QR coils have cut interference and ground signal artifacts to achieve better receiver sensitivity. And, the RF hardware tolerates variations in coil electrical properties due to ground proximity.

The new system applies an electromagnetic field pulse at a frequency specific to individual explosive compounds. When the pulse is aimed at landmine-filled ground, it excites the molecules of any explosives present. The explosive generates or re-emits a characteristic response that is measured and identified by the detection system, which is comprised of a tuned antenna and a very sensitive receiver (see the figure). Recently, researchers have pushed to develop a QR-based system that can detect metal, RDX, TNT, and composition B (part TNT and part RDX), which represent the vast majority of landmines deployed throughout the world. Also, the QR-based detection system can operate in almost all soil conditions, as well as through water.

Quantum Magnetics, a subsidiary of InVision Technologies of Newark, Calif., has built a prototype system for detecting antipersonnel (AP) and antitank (AT) landmines. Key QR patents used in the development of this prototype system were licensed from the Naval Research Laboratory.

According to Lowell Burnett, Quantum's CEO, the prototype successfully detected 100% of AP and AT landmines during field trials at the Army Combat Engineering School test facility at Fort Leonard, Mo. In a series of blind tests, Quantum's prototype detected and precisely located seven out of seven plastic TNT AP mines. The same system was able to detect all of the RDX landmines in the same lane. Each of the three separate attempts on the AP test lane resulted in 100% detection of all mines.

Remarkably, Burnett notes, there were no false alarms after a rescan of initial alarms. In a separate test of the system's performance on a 20-m AT landmine test lane, the system was put to work searching for 20 plastic TNT, two plastic composition B, and one metal-cased AT landmines. It accurately located all 23 buried explosives.

Under a two-year engineering program, Quantum plans to convert the prototype into a manufacturable unit that's rugged enough for field use in a variety of settings. Concurrently, there's a project under way to develop a battery-operated backpack-mounted version. Quantum also is seeking a sponsor to extend the QR detection capabilities for humanitarian demining applications.

Additional details are available at www.darpa.mil.

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