Terahertz camera takes snapshot of the future

StarTiger, a European Space Agency project, has taken the first terahertz picture of a human hand. Terahertz radiation lies on the boundary between radio and light waves and is far more difficult to detect and analyse than either, but is of huge interest for medical, security, environmental and communication uses; the technology could, for instance, theoretically carry wireless data at terabit speeds.

ESA originally investigated the radiation for sensing atmospheric and ground phenomena from satellites, but it is now examining terrestrial applications of the new frequencies. "We have recognised the huge potential in non-space applications, and in parallel to exploiting the use of terahertz waves and the StarTiger technology in space, we have kicked-off a commercialisation study to identify the best way of transferring it into terrestrial systems," said Pierre Brisson, head of ESA's Technology Transfer and Promotion Office.

One terahertz is 1,000 gigahertz, and most current radio technology stops at around 100 GHz: 0.1THz. Everything gives off terahertz radiation naturally, and like radio waves -- but unlike heat or light -- the waves can pass through some solid objects. Like light, it is possible to focus the radiation and create images as if the intervening material were translucent, and by analysing the frequencies given off the chemical and physical characteristics of the object can be worked out.

Terahertz radiation has wavelengths too short for normal radio antennae to pick up but too long for normal optical techniques and thus the band has been closed to experimenters and scientists. Until now, the only known user of the frequencies has been a species of moth. By using nano-engineering techniques to create micro-machined arrays of minute antennae, the StarTiger team has created a sensor array that can image objects at 0.2THz and 0.3THz.

"The final version was an enhanced imaging system incorporating a two-colour 16-pixel detector array of the size of a postage stamp. This advanced system incorporated revolutionary silicon micro-electrical-mechanical systems (MEMs) technology," said Chris Mann, the project manager at Rutherford Appleton Laboratories (RAL) in Oxfordshire, where most of the work has been done. "The enhanced system delivered images that confirmed the nature of terahertz waves. An imager can show details of features under the skin, confirming the potential of this technique." The project has released images of a hand taken through 15mm of paper, while related work by UK technology company Qinetiq shows pictures of the human body imaged through clothing.

Because the field is so new and unexplored, many applications are still to be tested. Detecting explosives or biological agents in parcels, cancers beneath the skin, the state of wounds beneath dressings, and seeing through fog: all have been suggested by StarTiger and other researchers.

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