Highly Sensitive Signal Detection Methods And Experimental Study Based On Optical Fiber Acoustic Detection System

As one of the core of the optical fiber acoustic detection system,the optical fiber acoustic sensor is widely used in acoustic detection,pipeline leakage monitoring and related fields because of its good reliability,relatively simple structure,high stability and high sensitivity.However,the methods of demodulation of the signal in the fiber-optic acoustic detection system will directly affect the entire system sensitivity,signal to noise ratio and other parameters,and indirectly affect the performance of the entire system.This thesis is based on developing a fiber acoustic detection system that can be applied to acoustic detection and pipeline leakage monitoring with stable,high sensitivity and simple structure and convenient multiplexing and expansion.The fiber-optic acoustic sensor and signal demodulation methods based on the optical fiber acoustic detection system are performed and studied,and design and integration of the entire system are performed.The research content of this thesis mainly includes the following points:1.Use graphene oxide solution to make a vibration film for sensing external sound signals.Based on this,employ the Fabry-Perot micro-interference chamber in the structure,a graphene oxide-based acoustic sensor is fabricated in which the two reflective end faces of the interference cavity are the graphene oxide film and the single-mode fiber end face inside the sensor.2.Combined with graphene oxide-based optical fiber acoustic sensors,singlewavelength intensity demodulation,PGC phase generated carrier demodulation,and 3x3 coupler demodulation were used to perform experiments.That the experimental processes and results were obtained in the time and frequency domain are analyzed and the advantages and disadvantages of the three demodulation methods are compared.Finally,a hybrid three-wavelength demodulation method is designed in combination with the three-wavelength demodulation method and the 3x3 coupler demodulation method.The hybrid three-wavelength demodulation method combined with graphene oxide sonic sensors were experimentally studied.The experimental results show that the demodulation method not only has the characteristics of high stability,but also has the advantages of high sensitivity and high signal to noise ratio.Moreover,the demodulation method solves the defect that the previous system cannot be actually applied to the actual environment of the project.Finally,According to the experimental principle structure diagram,the overall construction of the fiber-optic acoustic detection system was completed,and the test and package were performed.3.The windproof and waterproof package before the on-site experiment of the graphene oxide-based acoustic sensor was designed and actually packaged.Finally,a single sensor field experiment was performed with the optical fiber acoustic detection system to make sure that the system can effectively monitor leakage of molybdenum tail sand waste liquid pipelines and achieve how long can be monitored by a sensor.Then multiple sensors are used for multiplexing,and an optical switch is used to control sensors to achieve long-term monitoring of pipeline leakage.