Fiber Bragg Grating Sensors for Detection of Acoustic Wave Emission and Seismic Activities

摘要

A systematic study of acoustic emission detection and seismic activity sensing using fiber Bragg grating sensors has been carried out recently in our laboratory. In this, we attempt to use the fiber Bragg grating to sense the dynamic strain created by a passing ultrasonic wave signal. Our goal here is to see if such a sensor is possible, and if so, what the detection sensitivity and limitations will be. To answer these questions, we carried out several experiments involving the detection of simulated acoustic emission events, in the first experiment, we attach fiber Bragg grating to the surface of a piezoceramic resonator which is driven by a signal generator. We were able to detect the resulting surface vibration of the resonator up to 2.1 MHz. In the second experiment, we attach a fiber Bragg grating to the surface of an aluminum plate. We excite an acoustic wave using an ultrasonic transducer located at various positions of the aluminum plate. In this way, we demonstrated that the fiber Bragg grating sensor is capable of picking up the signal coming from a distance (up to 30 cm) for up to 2.5 MHz. In a third experiment, we use the same fiber Bragg grating on aluminum plate set up, but set up an acoustic signal by either a gentle knock on the plate by a pin, or by breaking a pencil lead on the plate. We were able to detect acoustic emission set up by pencil lead breaking up to a frequency of 100 kHz. Higher frequency components were not detected mainly due to the limitations of the available electronic equipment at this time (high frequency bandpass filters and amplifiers). In yet another experiment we use the fiber Bragg grating to detect low-frequency seismic activities set up by vehicular traffic. In all the above-mentioned experiments we use a matching Bragg grating to demodulate the detected optical signal and use a dual channel scheme for electronic data acquisition and processing (a signal channel and a reference channel). Our experimental results have shown great promise of the fiber Bragg grating as a highly sensitive and accurate detector of vibrations of high and low frequencies. Furthermore, with WDM technology, multiple sensors can be deployed with little or no complication or new requirement.