Detection of Ultrasonic Waves by using a Dual-cavity Fiber Fabry-Perot Interferometer for Structural Health Monitoring

초록

A Fiber Fabry-Perot Interferometer (FFPI) can be used as an ultrasonic transducer for the evaluation of structural health status. Especially, a quadrature-phase-shifted fiber Fabry-Perot interferometer (QPS-FFPI) generates two sinusoidal signals of which phase difference should be 90 degrees for the exact measurement of thedisplacement induced by ultrasonic wave. If the phase difference is not exactly 90 degrees, it would be hard to detect the ultrasonic waves effectively. In order to guarantee the condition of the phase difference of 90 degrees, the relative adjustment of the cavities of two pair ofoptical fibers is needed. However, the precise adjustment is very hard to be made to the proper difference of the two cavities for the quadrature-phase-shifting. In this paper, a dual-cavity fiber FFPI is used to detectanultrasonic signal. Then, a novel phase-compensation algorithm is applied to signal processing in order to force the phase difference to be exactly 90 degrees without any physical adjustment of the two cavities. As a result, the paper shows that the phase-compensated dual-cavity FFPI can effectively detect ultrasonic waves and the dual-cavity FFPI could be a good ultrasonic sensor for structural health monitoring.