Abstract
Transverse misalignment of optical fibers was applied to detect an acoustic emission (AE) signal. A pair of single-mode fibers was placed facing each other using elastic blocks which were adhered to a specimen. Since misalignment causes loss of optical transmission between two fibers, the amount of offset from the initial position of fibers can be determined by measuring the power of light which has been propagated through the fiber splice. It is demonstrated that the blocks with different elastic properties are effective to detect the surface displacement of the specimen which is induced by AE wave. Because inverted-U shaped blocks act as a phase delay line, these blocks are useful in improving the sensitivity as a large amount of offset can be generated. Based on these results, we made a new type of optical fiber AE sensor experimentally. Using pencil lead break as the simulated AE source for calibration, it is found that the developed sensor is capable of detecting AE wave of less than 150 kHz in frequency, and has a resonant characteristic at the frequency of 30 to 40 kHz.
