Acoustic emission (AE) is an effective technology that can be used for structural health monitoring. One of the most attractive features is the ability to locate AE sources. Characteristic parameters of waveform importing Artificial Neural Network (ANN) model is proposed for acoustic emission source location. The waveform of AE signal is apperceived by sensors, and decreases dispersion effect by wavelet transform. Input of ANN includes characteristic parameters of AE signal, waveform data and characteristic quantities which have been preprocessed. Time difference of signals and other parameters acts as sample which can decrease the influence of wave speed. Based on the agreement that ANN has the ability approximate any nonlinear mapping, it is feasible to build a model of time difference of signals and other characteristics with AE source position. This locating method can be widely used in AE source location on account of high accuracy, practicality and reliability.
A method using fiber Bragg grating (FBG) array-based shape sensing is proposed for structure health monitoring of cylindrical marine structures in this paper. Because of the characteristics of FBG, any strain applied on the FBG is encoded as a wavelength shift of the light reflected by FBG. FBG sensors, with flexibility and small size, are bonded on the surface of the cylindrical shell structure to measure the strain of each fiber Bragg grating on the same certain points. And then we analyze the relationship of each parameter between FBG sensors and cylindrical structure. Experimental results prove that it is feasible for this method using FBG array-based shape sensing to monitor the deformation of the cylindrical structure. This method can be widely adopted in structure health monitoring of curved structures due to high precision, simple operation and low cost.
In this paper, we propose a semiconductor optical amplifier (SOA)-fiber ring laser (FRL) for fiber Bragg grating (FBG) dynamic strain sensing system with an adaptive demodulator based on two-wave mixing (TWM) photorefractive interferometry. Any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The wavelength modulation is perfectly converted to intensity modulation by splitting the light into signal and pump beams and interfering the beams in an photorefractive InP:Fe crystal. The classical beam-combiner was replaced by a dynamic hologram continuously recorded in the InP:Fe crystal. The results demonstrate that TWM interferometer has the characteristics of adaptability and multiplexing. To investigate multiplexability, a three-channel SOA-fiber ring laser sensor system is presented to detect dynamic strain signals from three FBG sensors simultaneously. Experimental results prove that true multiplexing of several FBG dynamic strain sensors with a single adaptive source is feasible. This technique is expected to be suitable for the monitoring of external impact as well as acoustic emission in structures.
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