Liquid identification

If you have travelled by aeroplane recently you will probably have been annoyed by the rules limiting the liquids you can take onto the plane. The problem is that there are various liquids that can be used to make explosives or just a fire, which are hard to detect quickly and easily in the security check.

A group for Julich in Germany think they may have a solution. They are looking at the frequencies reflected in the GHz to 10 THz region of the spectrum, which is the frequency of your mobile phone and upwards. Different liquids have different spectra so you can detect which one is in a bottle, however these frequencies are difficult to deal with and conventional spectrometers are very slow, or they only use a single frequency.

Their solution is to use a Josephson junction, which is a small gap between two pieces of superconductor. The relationship between the voltage across the junction and the current flowing through it changes when you apply GHz  and THz frequencies. So they have been able to shine a variety of different frequencies onto a suspicious liquid and the focus the reflections onto the Josephson junction and work out what frequencies were reflected.

At the moment they have only distinguished 5-6 liquids including water and a variety of alcohols, ketones and water but there is no reason it shouldn't work for more, and they can take a spectrum in a second or so which getting towards a practical speed for testing baggage.