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10 Aug 2005
An optical vibration sensor could help detect structural damage even in high electromagnetic fields.
Using pieces of microscope glass and a femtosecond laser, researchers from Japan and the US have made a vibration sensor that they believe could ultimately withstand extreme conditions found in space craft, atomic reactors and electrical power plants. Developed for monitoring structural damage in machines, vehicles and buildings, the device is immune to electromagnetic interference thanks to its optical principle of operation. (Appl. Phys. Lett. 87 051106)
The 25 x 20 x 3 mm sensor consists of a single, straight waveguide written across a series of three pieces of glass. Mounted on a cantilever beam, the central glass structure moves in response to mechanical vibration, which disrupts the continuity of the waveguide.
By hooking the device up to a light source such as a laser diode, the researchers can monitor vibration via a loss in transmission. According to the team, measurements are insensitive to variations in temperature as vibration is detected by relative rather than absolute changes in transmission.
The sensor has a linear response over the frequency range 20 Hz to 2 kHz and can detect accelerations as small as 0.01 m/s2.
Made from readily available soda-lime and borosilicate glass, the unit is said to be affordable and straightforward to assemble. The group from Keio University, Japan, and Harvard University, US, used a 25 MHz train of 55 fs pulses from a Ti:sapphire laser to induce a permanent refractive index change in the sensor and create an embedded waveguide.
With a working prototype complete, the scientists are seeking partners to help commercialize the sensor and continue to develop the device back in the lab. "[Currently] we are trying to extend the sensor's frequency range by changing the cantilever beam material," researcher Minoru Obara from Keio University, Japan, told Optics.org. "Silicon would be a good candidate because of its very high Young's modulus."
Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.
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