October 20, 2009

Superconducting Spectrometer Could Detect Explosives and Let You Carry Water onto a Plane Again

Plane passengers have not been able to carry bottles of liquid through security at airports, leaving some parched at the airport and others having expensive toiletries confiscated, but work by a group of physicists in Germany is paving the way to eliminate this necessary nuisance.

Success might also mean that we can leave our shoes on when going through security checks as well.

An article in Tuesday, 20 October, in IOP Publishing’s Superconductor Science and Technology explains how a new form of spectroscopy, a scientific method that uses electromagnetic radiation to identify materials, and a novel nanoelectronic device to detect signals, can identify explosive liquids, or liquid components for the fabrication of explosives, in usual plastic bottles almost instantly.

Liquid identification by Hilbert spectroscopy
by M Lyatti, Y Divin, U Poppe and K Urban

Abstract. Fast and reliable identification of liquids is of great importance in, for example, security, biology and the beverage industry. An unambiguous identification of liquids can be made by electromagnetic measurements of their dielectric functions in the frequency range of their main dispersions, but this frequency range, from a few GHz to a few THz, is not covered by any conventional spectroscopy. We have developed a concept of liquid identification based on our new Hilbert spectroscopy and high- Tc Josephson junctions, which can operate at the intermediate range from microwaves to THz frequencies. A demonstration setup has been developed consisting of a polychromatic radiation source and a compact Hilbert spectrometer integrated in a Stirling cryocooler. Reflection polychromatic spectra of various bottled liquids have been measured at the spectral range of 15–300 GHz with total scanning time down to 0.2 s and identification of liquids has been demonstrated.

While the idea of using electromagnetic radiation to inspect the properties of liquids is already thought a viable route to detecting explosive liquids, previous devices, working at single fixed frequencies within a small frequency range, cannot unambiguously distinguish mixtures of different liquids containing dangerous components which can be used as an explosive.

The researchers from Jülich have suggested a fast and reliable way to increase the range of frequencies that their spectrometer can analyse, thereby verifying the molecular signature of the liquid and creating a much more detailed ‘thumbprint’ that can be checked against the range of possibly dangerous liquids available to terrorists.

The researchers’ new method of spectrometry is called Hilbert spectroscopy. It works over a wider range of frequencies, from a few gigahertz to a few terahertz. With the incorporation of a nanoscale electronic device, a Josephson junction, the researchers have undertaken practical detection experiments which directly transform the electromagnetic spectrum received by the spectrometer into an electrical signal which warns of suspicious fluids.

As the researchers write, “Our first experiments showed that with simple measurements at four frequencies ranging from microwave to terahertz we are able to perform fast and reliable identification of various widespread liquids, such as water, ethanol, propanol and acetone, placed in a plastic container. We have made and continue to make significant steps towards a practical device.”

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