Sensor could identify limitless chemical agents in real time

The new system is said to be based on the photoacoustic effect, in which the absorption of light by materials generates characteristic acoustic waves. By using a laser and very sensitive microphones — in a technique called laser photoacoustic spectroscopy (LPAS) — vanishingly low concentrations of gases, at parts per billion, can be detected.

According to a statement, the drawback with traditional LPAS systems is that they only identify one chemical at a time.

‘Photoacoustics is an excellent analytic tool, but is somewhat limited in the sense that one traditionally only measures one absorption parameter at a time,’ said Kristan Gurton, an experimental physicist at the US Army Research Laboratory (ARL) in Adelphi, Maryland. ‘As I started looking into the chemical/biological detection problem, it became apparent that multiple LPAS absorption measurements — representing an “absorption spectrum” — might provide the added information required in any detection and identification scheme.’

To create such a multi-wavelength LPAS system, Gurton, along with Melvin Felton and Richard Tober of the ARL, designed a photoacoustic cell. This hollow, cylindrical device holds the gas being sampled and contains microphones that can listen for the characteristic signal when light is applied to the sample.