Acoustic Emission Detection Using Fiber Bragg Gratings

A systematic study of acoustic emission detection using fiber Bragg grating sensors is presented. In this, we attempt to use the fiber Bragg grating to sense the dynamic strain created by a passing ultrasonic wave signal. Our goal 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 a 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 30 kHz. Higher frequency components were not detected mainly due to the limitation of available electronic equipment at this time (higher frequency band-pass filters and amplifiers). In all the above-mentioned experiments we use a match 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).