Detecting Dangerous Chemicals from Afar

Thursday, April 7, 2011 @ 04:04 PM gHale


Benjamin Clough wants to make the world a safer place for emergency first responders like chemical plant employees, among others.

Clough created a method for extending the distance from which powerful terahertz technology can remotely detect hidden explosives, chemicals, and other dangerous materials.

A doctoral student at Rensselaer Polytechnic Institute’s Department of Electrical, Computer, and Systems Engineering, Clough showed a 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 won the 2011 $30,000 Lemelson-MIT Rensselaer Student Prize. He is among the four 2011 $30,000 Lemelson-MIT Collegiate Student Prize winners.

Benjamin Clough at work in the RPI lab.

Benjamin Clough at work in the RPI lab.


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

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 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 aims 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 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 convert 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 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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