AUGUST 13, 2004 -- The secret to ferreting out land mines in pastures and bombs in suitcases could very well lie in "a really bad" antenna.
Physics professor Bryan Suits has built just such a device as part of an ongoing study funded by the Naval Research Lab. Encased in clear plastic, it's made of two back-to-back copper spirals. Like a regular antenna, it receives radio waves. Unlike a regular antenna, it detects radio waves only from sources that are very, very close, such as luggage in an airport inspection station.
Bombs don't broadcast radio waves on their own. However, scientists can induce certain atoms--including the nitrogen in explosives--to emit a specific radio frequency using a technique known as nuclear quadropole resonance. Like the MRI used in medicine, NQR causes atoms to realign briefly and emit characteristic radio waves as they return to normal.
Generating that signal is the simplest part of finding a mine or a bomb using NQR. The hard part is filtering that tell-tale signal out of all the background noise, of which there is a lot: NQR radiation is smack dab in the middle of the AM band.
The problem isn't limited to talk radio. "We also get interference from lightning strikes, the ignition noise from cars . . . all sorts of noise, much of it manmade," Suits says. "The question is, how can you make a radio receiver that can see something next to it really well but is blind to things that are far away?
"That's the challenge. You have to understand enough about antenna theory to make a really bad one for something far away."
Thus the two coils. One is nearer the target and designed to pull in signals only from very close range. The second coil is a little farther away, picking up the interference. Subtract the interference from the first coil's reception, and you should have narrowed the signal down to the explosive you're looking for.
The technology should provide a major advantage over existing methods of finding land mines, which rely on old-fashioned metal detection.
"In battlefield conditions, there's metal all over the place," Suits notes. "So there are a huge number of false alarms, and you have to treat every one like it's a land mine, or you miss the land mine." For example, de-mining operations in Cambodia dug up 200 million items, of which 500,000, less than 0.3 percent, were land mines.
In a minefield, a technique that's even 90 percent effective would be a major step forward. However, in the realm of airport security, the issues are vastly different.
"Suppose you had one false alarm out of a thousand bags," Suits says. "That's 99.9 percent effective. In the typical large airport, you're talking one alarm every minute, and you'd have to treat each of those alarms as if someone's trying to blow up the plane." For luggage, eliminating all the false alarms is made more daunting due to the presence of non-NQR radio signals which can mimic the NQR signals--signals that can arise from the "panoply of junk" found in people's luggage.
However, NQR does have an advantage over most current inspection techniques, which rely on human judgment. "These devices are basically red-light green-light," Suits says. "Put the suitcase through. If the red light comes on, you know you've got to do something. It's not as if you've got to interpret anything."
Since perfection in the detection of explosives would be difficult to achieve using just one system, Suits believes NQR could be one of a number of methods used to weed out potential threats. "Terrorists will try to exploit the weaknesses in every technique, and we need to make that as hard as possible," he says.
Suits works closely with the Naval Research Lab on both the land mine and luggage problems, and the knowledge and technology developed are shared with Quantum Magnetics, Inc., a California company, for possible incorporation into a final product. However, Suits' heart is particularly drawn toward solving the land-mine problem.
"Land mines bother me the most," he says. Every year, they kill or maim an estimated 15,000 to 20,000 victims, many of them children. "Very few are soldiers, and it happens principally in Third World countries.
"Globally, it makes the World Trade Center disaster, as bad as it was, look pretty minor, and the SARS epidemic like nothing."
The U.S. invests about $100 million a year in humanitarian mine clearance, more than any other country. Yet, at the current rate, it could take 450 to 500 years to eliminate all existing mines, never mind the ones being laid down daily in trouble spots such as Afghanistan.
"It's frustrating," Suits adds. "Because it's not happening in the United States, and it's not contagious, we don't worry about it."
He, however, does worry about it. And he hopes his "really bad" antenna can one day play a role in turning the mine fields of the world back into farm fields.
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