Student Uses Sound Waves To Boost Distance Terahertz Technology Can Remotely Detect Dangerous Materials

Benjamin Clough is dedicated to making the world a safer place for emergency first responders, police and military personnel, chemical plant employees, and many others. The Rensselaer Polytechnic Institute doctoral student has developed a novel method for extending the distance from which powerful terahertz technology can remotely detect hidden explosives, chemicals and other dangerous materials.

A student in the Department of Electrical, Computer, and Systems Engineering at Rensselaer, Clough has demonstrated a promising, cost-effective technique that employs sound waves to boost the effective distance of terahertz spectroscopy from a few feet to several meters.

For this innovation, Clough has been named the winner of the 2011 $30,000 Lemelson-MIT Rensselaer Student Prize. He is among the four 2011 $30,000 Lemelson-MIT Collegiate Student Prize winners announced recently.

“We live in an age of continuous innovation, where technologies come together in unexpected and serendipitous ways. This mash-up culture, where data and applications constantly are being combined to bring value in ways that exercise the imagination, is where many stellar Rensselaer student researchers find their inspiration,” said Rensselaer President Shirley Ann Jackson. “Benjamin Clough is a prime example, with his invention of a new method that combines mature audio technology with leading-edge research to extend the operational usefulness of terahertz sensing. We congratulate him, and applaud all of the winners and finalists of the Lemelson-MIT Collegiate Student Prize for innovating a brighter, better future.”

Clough is the fifth recipient of the Lemelson-MIT Rensselaer Student Prize. First given in 2007, the prize is awarded annually to a Rensselaer senior or graduate student who has created or improved a product or process, applied a technology in a new way, redesigned a system, or demonstrated remarkable inventiveness in other ways.

With his project, titled “Terahertz Enhanced Acoustics,” Clough has developed a method to circumvent one of the major fundamental limitations of remote terahertz spectroscopy.

The Rensselaer Center for Terahertz Research is one of the most active groups worldwide to apply terahertz wave technology for security and defense applications. Sensors using terahertz waves can penetrate packaging materials or clothing and identify the unique terahertz “fingerprints” of many hidden materials. Terahertz waves, or T-rays, occupy a large segment of the electromagnetic spectrum between the infrared and microwave bands. Unlike X-rays and microwaves, T-rays pose no known health threat to humans.

A key practical limitation of terahertz technology, however, is that it only works over short distances. Naturally occurring moisture in air absorbs terahertz waves, weakening the signal and sensing capabilities. This distance limitation is not ideal for applications in bomb or hazardous material detection, where the human operator wants to be as far away as possible from the potential threat.

Clough’s patent-pending solution to this problem is a new method for using sound waves to remotely “listen” to terahertz signals from a distance. Focusing two laser beams into air creates small bursts of plasma, which in turn create terahertz pulses. Another pair of lasers is aimed near the target of interest to create a second plasma for detecting the terahertz pulses after they have interacted with the material. This detection plasma produces acoustic waves as it ionizes the air.

Clough discovered that by using a sensitive microphone to “listen” to the plasma, he could detect terahertz wave information embedded in these sound waves. This audio information can then be converted into digital data and instantly checked against a library of known terahertz fingerprints, to determine the chemical composition of the mystery material.

So far, Clough has successfully demonstrated the ability to use acoustics to identify the terahertz fingerprints from several meters away. He has separately demonstrated plasma acoustic detection from 11 meters, limited only by available lab space. Along with the increased distance from the potentially hazardous material, an additional advantage is that his system does not require a direct line of sight to collect signals, as the microphone can still capture the audio information. Potential applications of Clough’s invention include environmental monitoring of atmospheric conditions, monitoring smokestack emissions, inspecting suspicious packages, or even detecting land mines -- all from a safe distance.

 

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