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Ice sensor protects aircraft

05 Sep 2003

A European consortium develops an optical fiber sensor that detects the formation of ice.

Flying in bad weather could soon be safer thanks to a highly sensitive optical ice sensor designed for use on aircraft and helicopters. The sensor, developed under a European Framework 5 project called “ACIDS”, can detect a layer of ice that is as little as 100 microns thick.

The sensor is not only more sensitive than existing solutions but is also much lighter and far more durable, according to Cambridge Optical Sciences (COS), UK, one of the project partners which is now commercializing the device.

Martin Lawrence from COS told Optics.org that the sensor is currently undergoing trials for flight approval and will be tested on several aircraft, including a Nimrod, at the end of next year.

“There’s a real need for sensors that are robust and light enough for fitting into surfaces such as tailplanes and helicopter blades,” explained Lawrence. “Our sensor weighs a few ounces, has no moving parts and is made from stainless steel and glass.”

In contrast, traditional electro-mechanical sensors rely on ice altering the dynamics of an exposed mechanical part such as a vibrating wire and a rotating spindle. The drawback of these devices is that their size and weight (around a kilogram) can limit their use.

Put simply, the ACIDS sensor consists of an infrared semiconductor laser, a parallel array of seven optical fibers, some detection electronics and a sapphire window. Light from the laser is coupled into the central fiber and directed onto the glass window. The reflection is picked up by the neighbouring fibers and analyzed. Ice forming on the window alters the intensity pattern of the reflected light.

According to Lawrence, by analyzing the pattern of the reflection the sensor is able to distinguish between water and different types of ice. “Glazed ice with a smooth surface reflects the light very strongly whereas rime ice which is composed of spiky crystals gives far more scatter and a weaker reflection,” he told Optics.org.

If the sensor works well in flight trials next year it could turn out to be a lucrative venture for COS. A plane may need up to 10 or more sensors fitted over its fuselage and impending legislation from the US’s federal aviation authority (FAA) is likely to require that from 2005 all new light aircraft are fitted with tailplane ice sensing equipment.

Lawrence believes the sensor also has applications outside the aerospace sector, such as road and rail transport links, for example. He may be contacted at sales@cos.co.uk

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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