MUNICH, Germany Air passengers find it annoying, experts claim it is indispensible for flight safety: Entrainment of liquids and gels on board of airplanes is subject to tight restrictions. The Juelich Research Center (Juelich, Germany) has developed a promising technology to reliably discriminate explosives from harmless liquids.
The German-Russian research team made use of the dielectric permittivity profile of materials. This physical value varies with the frequency of electromagnetic waves directed to it. The permittivity response, measured over a very wide frequency spectrum in the GHz to THz range provides a 'fingerprint' for every liquid matter tested. In particular, it allows quick and exact information as to the material examined.
In order to achieve the very broad frequency range necessary to gain exact profiles, the research team chose Hilbert spectroscopy, an approach 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 element detects the electromagnetic waves reflected by the material under test and generates an output signal proportional to the frequency.
The prototype built by the Juelich research team uses commercially available external appliances to generate the electromagnetic spectrum as well as to keep the operating temperature for the Josephson junction in the desired range. The Josephson device, the most critical element in the setup, has been created at the Juelich Research institute which is said to excel in the field of superconducting thin-film devices. For the Hilbert spectrometer, the researchers used material on basis of YBa2Cu3O7.
The Hilbert spectroscope generates valid material scans within less than one second, the researchers claim. This would be much faster than competing technologies using nuclear magnetic resonance or conventional GHz and infrared waves, an institute spokesperson said.
In order to prove the feasibility of the approach, the researchers used an oscillator covering frequencies of up to 500GHz. In order to cover the range of up to 1 THz and even beyond that limit for better significance of the measurement results, the researchers now grant the development of a radiation source the highest priority. Nevertheless, the European Commission's intention to establish a identification system for routine identification of dangerous liquids by 2012 will be "difficult to realize", the researchers said in a statement.
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