Research On Acoustic Signal Acquisition And Positioning Technology Based On Fiber Laser Sensor Array

With the rapid development of today's industrialization,the structural health of materials has attracted much attention.Ultrasonic testing is used to evaluate and locate internal defects in materials.However,traditional piezoelectric sensors are gradually incapable of meeting the needs of modern applications.Fiber laser acoustic sensors show very good development prospects in ultrasonic sensing,relying on the outstanding advantages of active devices such as high stability,low threshold,narrow line width,and high signal-to-noise ratio.The related research is still in the initial stage,and the application of fiber lasers in ultrasonic non-destructive positioning detection needs to be improved.The sensing mechanism of fiber laser ultrasonic sensor was studied in this paper.The characteristics of ultrasonic sensing were analyzed,and the high-precision demodulation method of non-equilibrium Mach-Zehnder interferometer was studied.The length of the interference arm in the optical path interferometer was discussed,in a compromise,and the interference arm of 120 m was selected in a compromise.The 3×3coupler demodulation algorithm was used to build a high-precision sensing optical path.A multi-channel demodulation software was developed based on the Microsoft basic class library to realize high-precision acoustic signal acquisition and real-time demodulation,and the performance of fiber laser sensor and demodulation system were analyzed experimentally.The experimental results showed that the system can stably demodulate ultrasonic signals from 20 k Hz to 2 MHz,and it was detected that the sensor has directivity,and the responsiveness in axial direction was large,and the responsiveness in vertical direction was small.Finally,the location detection of acoustic emission fiber laser sensor array was carried out,and the particle swarm optimization algorithm was used to improve the positioning accuracy.The experimental results showed that the minimum error of this method is 0.14 cm,the maximum error is 0.68 cm,and the average error is0.41 mm.The positioning accuracy is higher than that of the traditional hyperbola algorithm.The acoustic acquisition and demodulation system of fiber laser sensor built in this paper can be effectively applied to nondestructive testing technology.