One of the most promising methods for detection of trace vapors is via micro-mechanics. Very small cantilevers oscillate so precisely that the deposition of just a few molecules upon one can change its frequency of vibration.
Unfortunately, while this method reveals the mass quite precisely, that's just about all it reveals. For engineers trying to build detectors capable of sniffing out traces of explosive chemicals, that isn't good enough. Some devices using this technique have a hard time discriminating between high explosives and innocuous gasoline residues.
A team of researchers at Oak Ridge National Laboratory in Tennessee and elsewhere recently published findings that suggest a better way to detect potentially explosive chemicals. The key is to heat the suspect molecules while on the cantilever.
The method, which is now being developed into a prototype for field testing, was published in the March 2009 edition of The Review of Scientific Instruments.
The key is the thermal characteristics of certain molecules. The research team, led by Thomas Thundat of Oak Ridge and consisting of scientists from there and the Technical University of Denmark, wanted to make a micromechanical sensor that could be a cheaper alternative to an ion mobility spectrometer, which ionizes minuscule amounts of chemicals and measures how quickly they move through an electric field. While such spectrometers are fast, sensitive, and reliable, they are also cumbersome and expensive.
Thundat and his colleagues realized that they could get the best of both approaches by modifying a standard cantilever-based device so that it could be heated. When air introduced to the chamber passed over the cantilevers, some molecules of vapor stuck to them. The researchers then heated the cantilevers for just 50 milliseconds. While non-explosive material didn't react over that short span, the explosives tested responded in an easily identifiable manner.
In the published results, Thundat and his colleagues claim to be able to detect less than one billionth of a gram of such explosives as trinitrotoluene, pentaerythritol tetranitrate, and cyclotrimethylenetrinitromine. The team is working to improve and optimize the experimental device, and hopes to begin field tests as early as this fall.
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|Title Annotation:||TECH FOCUS: Instrumentation And Control; trace vapors|
|Date:||Jun 1, 2009|
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