New remote sensing system can detect explosives and drugs

Rensselaer Polytechnic Institute researchers developed a remote sensing technology to sniff out chemical, biological, and explosives. The remote sensing systems can be used for commercial and defense purposes.

Ever since the underwear bomber on a Northwest Airlines flight failed to ignite a powdery substance Christmas Eve, airport security regulations have been put into question.

When airport authorities claimed high-tech security scanners could have prevented this from ever happening, the scanning devices that used terahertz (THz) technology attracted some eyeballs.

A number of the new body scanning machines have been deployed in major airports in the United States. However, privacy advocates worry the see-through-your-clothes scanning machines reveal way too much.

Besides exposing the outline of a person's nude body, THz waves can penetrate and see almost any material that isn't liquid or metal.

THz waves essentially pick up where metal detectors fail and detect images that x-rays and microwaves can't.

Currently, people must go through specialized machines, so the THz waves can be measured.

Rensselaer Polytechnic Institute researchers may have a way around that. The scientists discovered how to use THz technology to detect explosives, drugs, and chemical spills 20 meters away.

"It will be very competitive technology. Terahertz can immediately tell you the fingerprint of the chemical compounds,"  the Center for THz Research's Jingle Liu says. "We can extend the sensing range of current machines."

While the device has only been tested in the lab, the researchers want their device to be portable in the future. For instance, the device could be used to search luggage for illegal drugs.

"With our new technique, you don't have to stand close to the machine because our method remotely detects terahertz," Liu says. "Before this method was invented, there was no single method that could do that."

Two years ago, Liu and his adviser, kept trying different methods. "We failed first several times until we thought of using fluorescence," he admits.

Fluorescence has high atmospheric transparency and emits in every direction. Liu found THz waves could emit waves in a plasma. This made it easy to read the waves indirectly. The plasma emitted a fluorescent spectrum that could be read using a spectrometer to identify the questionable substance.

Liu says he wants to make the mission impossible, possible. "Right now we can offer a solution for the problem with our broadband THz sensing method. This was considered pretty challenging before."

The problem with measuring THz directing is a humidity problem — THz waves can not propagate in the air and moisture absorbs them.

"This new method can circumvent this limitation," Liu says. Instead of sending the THz from the operator to the object, the researchers test it indirectly.

When the researchers send laser beams in the air, they create a plasma which then emits florescence. The signal is read from a computer monitor and identifies the chemical's unique fingerprint.

The research group has been heavily funded by The U.S. Army, The Department of Homeland Security, The Defense Threat Reduction Agency, and the U.S. Air Force as well as a number of commercial entities.

"It's very useful because it can penetrate clothes and suitcases. It's used in a noninvasive security screening. It works because there are a lot of chemical compounds and drugs that have a clear signature," Liu says.

But it's by no means perfect. The water content in the human body absorbs THz waves, so it's hard to detect if illegal drugs are indeed stuffed up someone's cavities.

Photo, top: Rensselaer Polytechnic Institute

Illustration, bottom: iStockPhoto

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