Research Of Acoustic Emission Sensor Based On Acoustic Coupling Cone Fiber Bragg Grating

Acoustic emission detection technology has been widely used in many fields such as pressure vessel,aerospace,railway transportation,industrial manufacturing process,construction,petrochemical.Compared with the traditional technology,it can detect the abnormal vibration of the structure as early as possible.Therefore,it plays a significant role in national defense construction and production.At the same time,due to its small size,good flexibility and durability,anti-electromagnetic interference ability,good corrosion resistance and so on,FBG has attract many academic researchers and engineers at home and abroad in recent years.However,the existing FBG acoustic emission sensors can detect sound waves with low ultrasonic response sensitivity and narrow frequency band,due to the high frequency and serious attenuation of ultrasonic wave.Accordingly,this dissertation aims to propose an acoustic emission sensor based on a coupling cone to solve the above-mentioned problems.The main contents were included as follows:(1)The basic principle of FBG ultrasonic sensor is theoretically explained,such as the propagation and attenuation characteristics of ultrasonic,the interaction mechanism between FBG and ultrasonic and its resonance characteristics.The work provides the theoretical basis for the design of FBG ultrasonic sensor.(2)A kind of fiber Bragg grating ultrasonic sensor based on acoustic coupling cone is designed.The acoustic coupling cone focus the ultrasonic wave to the tip of the cone,and then the sound wave with higher energy transmit to the optical fiber.Thus,the detection sensitivity of the ultrasonic sensor is improved.(3)The cone material of fiber Bragg grating acoustic emission sensor is simulated and analyzed by COMSOL software.The influence of Young's modulus,Poisson's ratio,cone angle on the sensor is analyzed.The results show that the cone with large Young's modulus and Poisson's ratio provide the more concentrated energy and the greater displacement amplitude of the fiber.When the steel AISI 4340 alloy steel cone with120 ° cone angle is used,FBG sensor has a good response to ultrasonic wave and the wider frequency response range ranging from 200 k Hz to 1 500 k Hz.This work solves the problems of low coupling efficiency and narrow dynamic frequency response range of the existing sensors.Furthermore,the sensor structure is more compact and is easy to be produced.