By Candace Stuart
Small Times Senior Writer
July 9, 2001 — Scientists in national and university laboratories are developing small tech devices that remotely detect land mines.
They predict no single approach will provide the solution, but are optimistic that nations one day will have an inexpensive tool for reclaiming land that has been made inhospitable by abandoned mines.
One American company is poised to join in the cause. Sense Holdings Inc., a Fort Lauderdale, Fla.-based company that specializes in safety technologies, said it might market the devices once they become more affordable and reliable.
Land mines are just one potential application. Bombing test grounds such as Puerto Rico’s Vieques Island, which the U.S. Navy has agreed to abandon in 2003, could benefit from similar small tech advances.
“For a land mine detector, we will need a technology that is as cheap as a transistor radio and that can be taken anywhere without much infrastructure,” said Thomas Thundat, a senior research scientist at the U.S. Department of Energy’s Oak Ridge National Laboratory in Oak Ridge, Tenn.
Thundat is trying to adapt MEMS sensors he designed as explosives detectors for airport security systems into land mine detectors. He is among several physicists testing and refining various MEMS sensors with the goal of using them in the field. Last year Discover magazine gave him its Humanitarian Award for the endeavor.
More than 100 million land mines remain buried in 64 countries such as Cambodia and Bosnia, according to the Demining Technology Center in Lausanne, Switzerland. The United Nations estimates these remnants of civil and world strife kill or main 2,000 people a month, many of them children.
Public support for demining has been strong since the mid-1990s, in part because of high-profile campaigners such as the late Princess Diana and Jody Williams, who won the 1997 Nobel Peace Prize for coordinating the International Campaign to Ban Land Mines. In 1997, 120 nations signed a treaty to ban land mines. To date, 139 nations have signed the pact and 112 have ratified it.
But many nations can’t afford conventional detectors, which cost up to $20,000. Instead they rely on dogs trained to alert handlers when they smell explosives or human scouts who scour fields and unearth the mines. A field can be littered with mines, which themselves cost a mere $10.
Cleanup expenses are not the only barriers. Metal detectors, a common and decades-old technology, cannot spot land mines made of plastic. Many modern explosives makers now use plastics.
Sensing technologies can skirt that problem by honing in on other physical properties, said Michael Naughton, a physicist at Boston College. MEMS offer a solution to the cost problem, said Naughton, who has had success making and marketing a MEMS magnetometer.
“You can easily go into a fab and crank out 100,000 at a low cost,” he said. “There’s the potential to make them relatively inexpensively.”
Both Thundat and Naughton use cantilevered MEMS devices to detect land mines, but their approaches are different. Thundat’s device reacts to trace chemical vapors that rise from the land mines, while Naughton’s responds to acoustic waves that penetrate the soil and reverberate back off the mine.
Both are still in testing stages.
Naughton’s system emits audible sound waves that travel through grains of soil and bounce back when they encounter a surface such as the plastic covering of a land mine. Cantilevers similar to tiny diving boards in the MEMS sensor are calibrated to respond to the backscattered sound waves.
“The main detection mechanism is density,” he said. “Almost always there is sufficient difference (between soil and the land mine) that it can be detected.”
Naughton has tested his device using a deactivated land mine buried in a sandbox. He not only successfully detected the mine, but he also calculated its dimensions as some sound waves reflected off the top while others traveled through the land mine and bounced off the bottom.
“That separation of waves can give size information,” he said.
Naughton’s project this summer is to broaden the detection parameters to better reflect the vagaries of the real world. He will begin gathering readings from objects buried in various types of soil and amid rocks and manmade debris. He also wants to extend the range of the device, which now can detect objects imbedded half a meter or more in sand.
“The real question is how far away can you be,” he said, adding he’d like to get that figure to at least 10 meters.
But he cautions his device can never stand alone as a land mine detector. He sees it as a complement to other technologies such as radar devices. The two readings together give a reliable image of what lies beneath the soil. “I don’t see this technology as the be all and end all.”
Thundat’s MEMS sensor uses cantilevers coated on top with chemicals that react with trace fumes from TNT and other explosives. Energy is released when the reaction takes place, which forces the cantilever to curl upward.
“It creates stress, which manifests itself as bending,’ he said.
The cantilevers are so sensitive they vibrate in the presence of explosives, with the intensity of vibration corresponding to the number of molecules they’re exposed to. “Bending tells us the molecule is in the environment and the frequency will tell us the amount,” Thundat said.
In June, Oak Ridge National Laboratory licensed Thundat’s technology to Micro Sensors Technologies, a subsidiary of Sense Holdings. The company plans to develop it for security applications, according to Sense Holdings President Dore Perler.
Naughton and Thundat said their MEMS technologies work in controlled environments but not in the outdoors, where wind, temperature, moisture and other factors can come into play.
“Airports are much easier,” Thundat said. “Land mines will be much harder because they are in the field.”
Thundat believes he and other researchers eventually will be able incorporate various MEMS sensors on a chip to measure those environmental conditions and devise an intelligent system that accounts for them. The key will be to keep cost low and reliability high.
Perler is also cautious about the prospects of getting a MEMS-based land mine detector that is cost-effective. He predicts it will take years of research and lots of investment dollars to make it viable. But he sees the basic technology as socially important and broadly applicable for detecting all types of explosives.
“When it matures, we want to take it to market,” he said. “All these kinds of things are premature at this time.”
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CONTACT THE AUTHOR:
Candace Stuart at [email protected] or call 734-994-1106, ext. 235.