Radar Provides New Means To Detect, Disable Buried Land Mines

Recent advances to emerge from the university's efforts to develop anti-mine technology include two new radar antenna designs and a hands-off technique for disabling land mines.

Researchers described a dish antenna in a recent issue of the journal IEEE Transactions on Geoscience and Remote Sensing, and have applied for a patent on a second, rod-shaped antenna.

"Our goal is to have radar identify mines the way fingerprints identify people," said Chi-Chih Chen, senior research associate in Ohio State's Electroscience Laboratory.

Chen is also working on an apparatus to disable mines as they lay in the ground. Ultimately, he and his colleagues want to develop a hand-held device that detects mines with radar and then -- at the push of a button -- injects material into the ground to stifle the mines' triggering mechanism.

Chen's university collaborators include Leon Peters, Jr., professor emeritus of electrical engineering and former director of the ElectroScience Laboratory; Walter Burnside, professor of electrical engineering; and Soumya Nag, a graduate student. The Ohio State researchers worked together with Jennifer Halman, principal research scientist, and Keith A. Shubert, senior research scientist, at Battelle Memorial Institute of Columbus.

Unlike the steel land mines that emerged from World War II, today's half-pound plastic mines are invisible to metal detectors, Chen and Peters explained.

Mines are a bigger problem than ever before, Chen said, because the hockey-puck-sized disks cost only a few dollars to make, and are easy to mass-produce. Any political faction or terrorist group anywhere in the world can afford to seed a field with land mines, he said. That's why mines are as common in Bosnia and Kosovo as they were -- and still are -- in Cambodia.

"NATO governments are putting tens of millions of dollars into technology to identify and neutralize land mines. It's a very difficult problem, and the whole world is dealing with it," said Chen.

The researchers turned to ground penetrating radar (GPR) because even a plastic mine filled with explosive possesses electrical properties that make it detectable to the right technology.

Their major obstacle: to keep from setting off those same land mines, the researchers had to design a GPR system that could see underground without touching the earth.

Traditional GPR antennas are designed to send signals through solid ground, not open air. Commercially available GPR devices press down against the earth, and move by sliding along the ground.

"Obviously, if you're hunting for land mines you don't want to put the radar on the ground," Peters said.

The researchers' first dish antenna design appears in the IEEE paper; they've since constructed a second rod-shaped antenna and a paper on that design has been accepted for publication in the journal IEEE Transactions on Antennas and Propagation.

"Our dish antenna system represents a big step forward from traditional ground penetrating radar, but it has one big disadvantage: it's difficult for one person to carry," said Chen.

He should know -- he's worn the 28-inch dish and 50-lb radar pack on a shoulder harness. The size and weight of the system is more suited to being mounted on the front of a tank, he said, but the U.S. military needs a portable system, "something a soldier can swing along the ground like a metal detector."

That led to the researchers' latest device -- a rod-shaped Plexiglas antenna. Sweeping its 5-lb hand-held frame across the ground feels like waving an umbrella or broom, Peters said.

"The rod-shaped antenna has the advantage that when you detect something, you're pointing right at it," he added.

The basic technology behind the two antennas is the same. The researchers designed them to focus radar energy to a point just below ground a few feet in front of the person carrying the antenna. They programmed the control device to ignore signals that bounce back from the surface, and developed software to make buried objects shine brighter in the radar image.

In the IEEE paper, the researchers describe how they tested the dish antenna on a generic target, a 3.5 inch sphere. The signal the antenna received matched the expected signal for a sphere to excellent accuracy.

They then took the dish antenna to the U.S. Army land mine test lanes at Fort A.P. Hill, VA. The test range was filled with authentic land mine cases, the explosives replaced with a waxy filler that has similar radar properties as TNT.

The dish antenna was able to detect two common models of land mines buried 2 inches below ground -- a typical depth for mines in combat -- among the clay, sand, and small rocks of the test lanes.

For those tests, the researchers mounted the dish antenna on a cart. While the weight of radar system must decrease if a single person is to carry it in combat, Peters isn't worried.

He pointed to advances in computer microchips that are constantly making many electronic devices smaller and lighter. "That weight of the radar pack will ultimately go away, I'm sure," he concluded.

Chen has applied for a U.S. patent for methods of detecting mines with radar and then deactivating them.

Today, the only way to render a land mine inoperative is to detonate it remotely, or carefully disable the trigger.

Chen proposes a device that would shoot a special chemical agent into the soil to deactivate mines in place. One agent would solidify the triggering mechanism along with surrounding soil so that soldiers in combat could cross a field very quickly. Another chemical agent would take longer to harden, but would solidify the mine and the soil permanently.

"Then you could just shovel the mines out and throw them away," Chen said.

Currently, the researchers are working to improve the device's ability to tell the difference between explosive devices and rocks or other buried debris.

The dish radar work described in the IEEE paper was supported by the United States Government Office of Special Technology.