The Study Of Optical Fiber Acoustic Emission Detection Technology

Fiber optic ultrasonic detection technique is one of the focus issues in the field of smart structure and health monitoring. In this thesis, the development of acoustic emission detecting using fiber optic sensing techniques in recent years are overviewed, and acoustic emission mechanism and ultrasonic pulses transmission characteristic in isotropic and anisotropic medium is also evaluated. The linear-elasticity mechanics interaction model of acoustic wave and fiber optic sensor has been established, and the fiber cladding interaction to acoustic wave and fiber optic based on photo-elastic effect is concerned. The ultrasonic stress field wave transfer function between matrix material and sensing fiber are obtained. Based on the experimental setup, the detected acoustic emission signals are analyze by the FFT (Fast Fourier Transform) method, which can implements frequency identification. In this work, all-fiber optical Fizeau interferometer has been constructed for acoustic emission detecting. The basic principle and experiment scheme of several type optical fiber interferometers such as Sagnac and Mach- Zehnder individually in ultrasonic stress wave detection are realized and discussed in detail. Theoretically, the output signals of the sensing system are simulated and discussed in our work so that induces system optimum state. From above fiber optic sensing system, the experiment results of ultrasonic wave transmitting through artificial marble are given. Compared it was agreement with the computer simulation results. Based on Sagnac optical fiber interferometer, a novel configeration called Sagnac-like optical fiber interferometer is proposed and demonstrated, the optical signal output characteristic and its working principle of the Sagnac-like fiber optic interferometer is analyze systematically, and a coil sensor is also be designed in order to improve its sensitivity. This coiled fiber...