17 Jun 2002
Ultra-thin optical fibers overcome the interference problems that haunt electronic vibration sensors.
Scientists at Japanese company Photonic Science Technology (PST) have developed an extremely sensitive sensor that uses the flexibility and light leakage of very fine optical fibers to measure acceleration or vibration.
Soichi Kobayashi, president of the Chitose Institute of Science and Technology spin-off company, says that the new PST sensor would likely see its first application in detecting abnormalities in accelerometers and other precision instruments aboard passenger airliners.
The PST device uses 1550 nm diode lasers. This frequency, Kobayashi says, makes any bending or vibration of the optical fibers easily detected. The light from the lasers is sent through optical fibers 7 cm long and only 1 to 3 microns thick. This light is detected by optoelectronic transformers and analyzed to determine any deviation from the normal signal.
Kobayashi pointed out that the thinnest optical fibers commonly available are about 25 microns thick. Such thicknesses make it impossible to detect tiny vibrations. He also said it was difficult to produce very thin optical fibers with sufficient strength, but that PST achieved this with a proprietary manufacturing process that employs very precise temperature control.
Most conventional vibration sensors use electronic signals to detect vibration. However, interference from other electronic circuits can make sensitive detection impossible. Electronic components may also be expensive. Optical fibers, on the other hand, are inexpensive and they are not subject to interference from electronic noise.
Lockheed Martin, US, has already expressed interest in the new vibration sensor for possible use with its accelerometers. PST has shipped samples to Lockheed and says that the company is considering incorporating PST sensors in the wings and vertical stabilizers of its airplanes.
In addition to aeronautical uses, PST is developing vibration sensors for use in highrise buildings and other such structures.
Charles Whipple is a freelance journalist based in Japan.