Design And Applied Research Of Integrated Fiber Optic Acoustic Detection System

Optical fiber acoustic probe is a typical application of optical fiber sensing technology,which has the technological advantages of small size,light weight,simple structure,high reliability and stability,anti electromagnetic interference,corrosion resistance,high sensitivity,low loss,and has a broad application prospect in the field of monitoring and security.In this thesis,based on the principle of optical phase modulation,a simple and sensitive optical fiber acoustic probe based on grapheme thin membrane is designed and manufactured.The research contents are as follows:First,this thesis expounds the principle and characteristics of three kinds of optical fiber sensing technology,and introduces the basic working principle of the three modulation modes of the fiber optic acoustic sensor technology and the development trend of the fiber optic acoustic sensor.Secondly,from the two-beam interference phenomenon of parallel plate,the working principle of optical fiber micro interference cavity acoustic sensor based on two-dimensional thin membrane is described.This thesis analyses and compares two kinds of main signal demodulation methods of the fiber micro interference cavity acoustic sensor,namely intensity demodulation method and phase demodulation method.And this thesis introduces the design scheme of fiber optic acoustic probe based on grapheme thin membrane,completes the manufacture and performance test of the probe,and completes the structural design and hardware implementation of two demodulation systems based on intensity demodulation method.In addition,two signal processing methods about optical fiber acoustic detection system are described in detail.The fiber micro interference cavity acoustic detection system is very sensitive to external environment noise and the circuit noise components of the system,so this thesis proposes an adaptive filtering method based on LMS(least mean square)algorithm to effectively reduce the noise of the sound signal on the system.In the sound signal processing,blind source separation algorithm is applied to the fiber optic acoustic sensing system for the first time.That can be achieved separation and recovery relatively independent source signals from the collected multi source mixed signals.In this thesis,the blind source separation method is used to separate or recover the relatively independent source sound signal.In this thesis,for linear instantaneous mixture model,the algorithm of blind source separation based on the Fast ICA algorithm is analyzed and studied,and for linear convolution mixture model,the frequency domain blind source separation sorting algorithm based on the influence factor is analyzed and studied.Moreover,the effectiveness of the proposed algorithm is proved by simulation and experiment.Finally,the test experiment of optical fiber micro interference cavity acoustic detection system is introduced in a practical project.Through the field test and the comparison test with the electric microphone,it is proved that the system can effectively detect the defects of the train wheel axle,and there is a large space for performance improvement.This thesis the sound signal processing methods of optical fiber micro interference cavity acoustic detection system based on two-dimensional thin membrane of design and implementation are studied in detail.It provides a new way to apply blind source separation algorithm in fiber optic acoustic sensing system.