Acoustic emission sensor based on a tapered single-mode fiber

This paper reports, on the use of a tapered single mode fiber as a sensing element for the detection of acoustic emission (AE) and ultrasound. When an acoustic wave impinges on the mode-coupling region of a fiber, the coupling coefficient is modulated via the photo-elastic effect. Therefore, the transfer function of the fiber is modulated by an acoustic wave. The sensitivity of the sensor at 156 kHz was approximately 1.2 V/mbar. Because of the resonant condition of the coupled-mode theory, this sensor is almost immunity of the environment perturbations, and the output is a DC signal instead of AC, so it is very suitable for those situations such as faulty protection which need very fast responsibilities.