Research On Sensitization Enhancement Of Fiber Bragg Grating Sensor For Underwater Sound Detection

In recent years,the development of marine resources has accelerated,and research on sensors used in the ocean has also entered a high-speed development stage.As a new type of sensing material,fiber optic sensor has been widely studied and applied.Among them,the fiber Bragg grating hydrophone,as an underwater sound signal acquisition device,has been widely concerned because of its advantages of corrosion resistance,high temperature and pressure resistance,anti-electromagnetic interference,light weight,WDM and easy array formation.In engineering applications,there are higher requirements for the acoustic sensitivity of fiber Bragg grating hydrophones.Therefore,this paper studies the sensitization of fiber Bragg grating hydrophone probe.First,this paper introduces the research progress of fiber grating hydrophone probe packaging technology at home and abroad.Then,the working principle of fiber Bragg gratings are studied,and the cross-sensitivity characteristics of stress and temperature sensing principles and temperature strain of fiber Bragg gratings are analyzed.Based on the above,it is proposed to use two types of structures: side compression type and end tension type to enhance the fiber Bragg grating,and this two sensor structures are calculated and optimized by the finite element analysis method.The research results found that the side-pressed hydrophone designed in this paper has a small resonance frequency,which can achieve higher sensitivity in the range of 10Hz-2000 Hz.The sensitivity gain at the resonance can reach up to 145 d B.The high sensitivity at the resonant frequency can be used to detect the corresponding sound frequency.The designed end-face hydrophone has a higher resonance frequency,which can reach 30 k Hz,and the highest sensitivity gain at the resonance frequency is 115 d B,so this hydrophone can detect sound signals at higher frequencies.Based on the above,temperature compensation is carried out for the side-stretched structure with high sensitivity gain.A compensation material is used in the structure: polymethyl methacrylate(PMMA).The material's thermal expansion effect is used to modulate the fiber Bragg grating to reduce the effect of temperature on the Bragg grating,Finally,the temperature compensation with wavelength offset less than 0.01 nm in the range of ocean temperature(-2?-30?)was realized.