Although airline passengers find it annoying, tight control of liquids and gels in onboard luggage is claimed to be essential for safety. Researchers at the Institute of Solid State Research in Jülich, Germany have developed a technology that holds promise for reliably detecting potentially explosive substances and differentiating them from harmless liquids.
The device developed by the German–Russian research team is based on the dielectric permittivity profiles of each material, which depends on the frequency of the electromagnetic waves impinging on the material. A permittivity response measured over a very wide frequency spectrum in the gigahertz to terahertz range forms a ‘fingerprint’ for every liquid substance. In particular, it allows quick and exact determination of the type of material.
In order to achieve the very broad frequency range necessary to obtain exact profiles, the research team chose Hilbert spectroscopy, a technique developed at the Russian Academy of Sciences in Moscow. The critical element in Hilbert spectroscopy is the Josephson detector, a nanoelectronic component based on a high-temperature superconductor. Operating at a temperature of minus 200 degrees Celsius (about 70 Kelvin), the Josephson junction detects the electromagnetic waves received from the material under test and generates an output signal proportional to the frequency.
The prototype built by the Jülich research team uses commercially available external devices to generate the electromagnetic signal and maintain the operating temperature of the Josephson junction in the desired range. The Josephson junction was fabricated at the Institute of Solid State Research, which specializes in thin-film physics. For the Hilbert spectrometer, the researchers used material based on YBa2Cu3O7.
According to the researchers, the Hilbert spectroscope can generate a valid material scan in less than one second, which they said is much faster than competing technologies using nuclear magnetic resonance or conventional high-frequency radio or and infrared waves.
To prove the feasibility of the approach, the researchers used an oscillator that can produce frequencies up to 500 GHz. To improve the reliability of the measurements, they said that an oscillator that can cover the range up to the 1 THz or more is necessary, and this should have top priority. However, they said that the European Commission's aim of establishing a system for routine identification of dangerous liquids by 2012 will be difficult to achieve.
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