T-rays triumph over X-rays in bomb detection

MY NOTE: I'VE HAD A VIDEO RELATED TO THIS STORY ON THE BLOG FOR A FEW DAYS.  
http://www.punemirror.in/article/26/201103112011031101432792152d7a50c/Trays-triumph-over-Xrays-in-bomb-detection.html

New York: Benjamin Clough, a student of Rensselaer Polytechnic Institute in New York, has demonstrated a promising, cost-effective technique that employs sound waves for bomb detection, physorg .com has reported.

With his project, titled Terahertz Enhanced Acoustics, Clough has developed a method in which 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.

Benjamin Clough

The problem
A major limitation of T-rays is that they work over short distances. Moisture in air absorbs them, weakening the signal and sensing capabilities.

This is not ideal for applications in bomb or hazardous material detection, where the human operator wants to be away from the potential threat.

The solution
Clough’s patent-pending solution to this problem is using sound waves to remotely ‘listen’ to terahertz signals from a distance.

Focusing two laser beams into air creates small bursts of plasma, which create terahertz pulses. Another pair of lasers is aimed near the target 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 ionises the air. Using a sensitive microphone to ‘listen’ to the plasma, one can detect terahertz wave information embedded in these sound waves.

This audio information can be converted into digital data and instantly checked against a library of known terahertz fingerprints, to determine the chemical composition of the material.

Distance covered

So far, Clough has demonstrated the ability to use acoustics to identify the terahertz fingerprints from several metres away. He has separately demonstrated plasma acoustic detection from 11 metres, 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.