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'T-ray' breakthrough signals next generation of security sensors
Feb 5, 2008 - 5:00:00 AM
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Dr Andrews says that although the results of their study are very
promising, more work is needed to refine the technology before such
surfaces can be used for sensing applications. At the moment only a
small number of the frequencies that make up a pulse of T-ray radiation
are closely confined by our metamaterial. More sophisticated designs are
needed in order to make sure that the whole pulse is affected by the
surface structure, so that absorption features of molecules can be
clearly identified.
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By Imperial College London,
[RxPG]
A new generation of sensors for detecting explosives and poisons could
be developed following new research into a type of radiation known as
T-rays, published today (3 February) in Nature Photonics.
The research shows that these T-rays, electromagnetic waves in the far
infrared part of the electromagnetic spectrum that have a wavelength 500
times longer than visible light, can be guided along the surface of a
specially designed material, known as a metamaterial. Being able to
control T-rays in this way is essential if this type of radiation is to
be used in many real world applications.
Researchers believe one of the areas with the most potential to use
T-rays is security sensing and scanning, because many of the molecules
in explosives and biological agents like anthrax strongly absorb this
radiation. If T-rays are tightly confined on surfaces in contact with
such molecules then the detection sensitivity is greatly increased.
Simple metallic surfaces have been used to control T-ray propagation
before, but these only weakly guide the radiation, which extends as a
weak field many centimetres above the surface of the material, thus
rendering it less effective for sensing. The new study has now shown
that a metamaterial surface draws T-rays close to it, creating a very
strong field less than a millimetre above the surface. This greatly
enhances the absorption by molecules on the surface making highly
effective sensing techniques possible.
The study was performed by a team of UK and Spanish physicists led in
the UK by Dr Stefan Maier from Imperial College London's Department of
Physics, and Dr Steve Andrews of the University of Bath. Dr Maier
explains why their metamaterial design is so important:
T-rays have the potential to revolutionise security screening for
dangerous materials such as explosives. Until now it hasn't been
possible to exert the necessary control and guidance over pulses of this
kind of radiation for it to have been usable in real world applications.
We have shown with our material that it is possible to tightly guide
T-rays along a metal sheet, possibly even around corners, increasing
their suitability for a wide range of situations.
A metamaterial is a man-made material with designed electromagnetic
properties which are impossible for natural materials to possess. The
metamaterial created for this new research consists of a metallic
surface textured with a two-dimensional array of pits. The researchers
chose the dimensions of the pits so that T-rays are drawn closely to
them as they travel along the surface.
Dr Andrews says that although the results of their study are very
promising, more work is needed to refine the technology before such
surfaces can be used for sensing applications. At the moment only a
small number of the frequencies that make up a pulse of T-ray radiation
are closely confined by our metamaterial. More sophisticated designs are
needed in order to make sure that the whole pulse is affected by the
surface structure, so that absorption features of molecules can be
clearly identified.
Dr Maier and Dr Andrews designed the metamaterial together with
colleagues from Universities in Madrid and Zaragoza, with financial
support from the US Air Force and the Royal Society. Their breakthrough
is based on previous theoretical predictions obtained by the Spanish
team together with Imperial's Professor John Pendry, published in
Science in 2004.
Publication:
Nature Photonics
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