The Study Of Acoustic Emission Detection And Location Based On Fiber Laser Sensors

Acoustic emission (AE) detection, which is used to monitoring the stability of the rock mass, the stress field of the complex rock and exploration the instability mechanism of rock mass, have played an important role in rock mass failure and micro earthquake prediction. In the past twenty years, optical fiber acoustic emission sensing technology have attracted widespread attention in structure health monitoring and nondestructive testing, as they have considerable advantages over conventional piezoelectric (PZT) sensors, such as immunity to electromagnetic interference, embeddability, ease of installation and multiplexing.According to the low-frequency characteristics of the rock mass acoustic emission, this paper a AE detection and location system based on distributed feedback (DFB) fiber laser sensors. The purpose of this study is to provide a practical and advanced measurement means in large civil structural health monitoring. The main content of this article is as follows.(1) Firstly, the paper review and summarize the current domestic and international development situation of rock mass AE detecting technology and AE detection and location based on optical fiber sensors. Then mechanism and characteristics the rock mass AE, transmission characteristics in the solid and optical fiber sensing principle are introduced. The response of DFB fiber laser under the surface wave is analyzed primarily. The theory of wavelet denoising for AE detection and location is given.(2) Secondly, the fabrication and sensing principle of DFB fiber laser and the basic principle of DFB fiber laser sensor acoustic emission demodulation system based on phase generated carrier (PGC) algorithm is introduced. The demodulation system test results are presented. DFB fiber lasers are bonding on the surface of the marble plate with three different coupled modes, such as two head bonding, transparent adhesive joint,353ND fiber adhesive and their different response to AE wave is analyzed. The dynamic strain sensitivity of DFB fiber grating laser bonded with353ND fiber adhesive is calibrated by a comparison with PZT AE sensor.(3) Thirdly, the acoustic emission directional characteristics of the DFB fiber grating laser are investigated by two kinds of analyzing method. In the first experiment, the relationship between the wavelength drift and the angle of a continuous acoustic emission source is determined. In the second experiment, the relationship between the percentage of wavelet packet energy and the angle of impact response is established. Their acoustic emission directional characteristics make them suitable for determining principal strains and the direction of propagation of acoustic waves. Then a DFB fiber laser strain rosette using three DFB fiber grating lasers and the DFB fiber laser strain rosette array are constructed on the marble plate. And a new algorithm based on DFB fiber laser rosette for AE source location is given.(4) Finally, the direction and location of continuous acoustic emission source and low-impact signal are achieved by DFB fiber laser strain rosette and DFB fiber laser strain rosette array. In addition, the linear array and planar array of DFB fiber lasers are built and they can be used to low-impact signal location based on high-precision time delay estimation method.