Land mines are terrifying and indiscriminate weapons, harming soldiers and civilians alike. Even long after the conflict in which they were deployed has ceased they end up killing and injuring civilians and render land impassable and unusable for decades. There are a variety of methods used to detect mines by both humanitarian and military groups, but many are dangerous, most are less than 100 percent reliable and some of the more reliable detection methods are prohibitively expensive. Physicists have now built a relatively inexpensive land mine detection system using off-the-shelf components – including some sourced from online auction sites.

In a project sponsored by the U.S. Army Research Laboratory's Army Research Office, Physics professor John Scales, his collaborator Martin Smith, and students at the Colorado School of Mines have built a new system using microwave-based sensors to detect vibrations in the ground (or other structures) remotely. Using microwaves also has many other advantages, including the ability to “see through” foliage.

"Land mines are an enormous problem around the world for both military personnel and civilians," explains Scales. "We've developed an ultrasound technique to first shake the ground and then a microwave component to detect ground motion that indicates location of the land mine. We hope that the two components together enable us to detect the land mines in a safe fashion, from a distance."

With so many unexploded land mines located in developing countries, cost was a key factor in building the new system. Using off-the-shelf parts and online auction sites to source system components the team was able to keep the cost of the system down to around US$10,000. That might still sound pretty steep, but it’s a fraction of the cost of laser-based Doppler remote detection systems that sell for upwards of US$1 million.

Multiple approaches exist for land mine detection, from trained dogs and rats that detect chemicals used in explosives to biosensor plants that change colors in response to soil conditions altered by mines. But, according to Scales, “there is no one scheme that works well all the time. You need an arsenal of tools.”

According to Landmine Monitor, over 75 countries and territories in all regions of the world are affected by land mines and at least 5,197 casualties were caused by mines, ERW (Explosive Remnants of War), and victim-activated IEDs (Improvided Explosive Devices) in 2008. So, it is both depressing that there is a need for such a system, but encouraging that there are people working on new ways to rid the world of such indiscriminate weapons.

The team says there are also many other applications for remote vibration sensing, including monitoring the structural integrity of buildings, bridges and dams.

The article detailing the novel acoustical/microwave detection system, "A low-cost millimeter wave interferometer for remote vibration sensing" by John A. Scales et al, will appear in the Journal of Applied Physics.