System detects liquids in luggage

Restrictions on carrying liquids on commercial airlines could soon be lifted with the development of a system that can quickly identify dangerous substances in passenger luggage.

German researchers at the Forschungszentrum Jülich claim that they have been able to do this using an optical approach that detects all existing and future harmful liquids within one fifth of a second.

The technique uses electromagnetic waves that are able to reflect information about a substance’s internal molecular dynamics. The method is known as Hilbert spectroscopy and operates in the frequency range of 10GHz to 1THz.

This range is what Prof Knut Urban, head of microstructure research at the centre, believes sets the system apart from other detection devices. Existing detectors are largely based on electromagnetic theory, but are also restricted to working in the lower gigahertz scale and can only analyse certain features of a liquid’s molecular structure.

Researchers at Jülich have overcome this problem by using a nano-electric device known as a Josephson junction. This accumulates the frequencies of light reflected from the liquid when exposed to monochromatic electromagnetic radiation. As a result, the device is able span low and high frequencies to provide a far more detailed ‘fingerprint’ of the liquid.

According to Urban, systems that measure only a small part of the complex fingerprint could prevent security authorities from assessing all potential threats. He cited the example of the 2006 terrorist attempt to detonate peroxide-based liquid explosives on board aircraft travelling from the UK.

‘It is very difficult to distinguish between hydrogen peroxide and water,’ he said. ‘They have a similar chemical make-up and look exactly the same. Fortunately, the plot in London was foiled before it was carried out, but the technologies developed since then would still struggle to identify the difference between the two liquids without separating them from other luggage.’

A number of competing technologies exist that that are based on conventional gigahertz and infrared techniques, low-energy X-ray spectroscopy and the Raman effect. With the latter approach, Urban argues that the method is critically obstructed by non-transparent material and cannot be used to assess liquids in bottles carrying a label or placed in hand luggage.

He added: ‘As far as we know, no other concept at the moment allows for identification of liquids regardless of container… You really need to be able to measure the entire molecular fingerprint and our approach can do this. I believe the technical device that comes out of this will be flexible enough to identify harmful substances that have not yet been invented by the terrorists.’

Since publishing their research in the Superconductor Science and Technology journal, the team in Jülich has received interest from industrial partners to develop an advanced prototype of the system.

Urban is skeptical about whether the technology will be ready in time for the European Community’s 2012 target of having a routine liquid identification system installed at larger airports. However, he believes that if industrial partners are forthcoming, the technology could see widespread use within the next five years.

Ellie Zolfagharifard