| The development of optical fiber acoustic sensing system puts forward the miniaturization requirement for sound pressure sensor.The conventional fiber-optic acoustic sensor with long-arm type is difficult to meet in the miniaturization direction.The combination of MEMS technology and extrinsic Fabry-Perot sensor technology is expected to break the bottleneck.At present,the technology is in the initial stage,facing many problems,such as the long-term ignore the sound pressure sensor probe structural design theoretical analysis;the lack of low-cost,high-performance sound pressure sensor processing methods;underwater acoustic detection can not take into account anti-Water pressure and high sensitivity.In this thesis,several key technologies of micro-EFPI fiber-optic acoustic sensor are studied,and the main work is as follows:1.Perfect the theoretical analysis model of EFPI fiber optic sound pressure sensor.The optical,mechanical and acoustic properties of the sensor are anal yzed theoretically.In the optical analysis,the transmission and coupling characteristics of the optical fiber are analyzed theoretically.The rationality of the Gaussian coupling model is verified by experiments.The effect of the tilt and mislocation loss on the interference fringes is analyzed in detail.In the mechanical property analysis,the amplitude distribution of the diaphragm is deduced from the vibration equation of the diaphragm,the analytical expressions of the plate model and the membrane model are obtained,and the mechanical properties of the diaphragm structure after the introduction of the corrugated structure are analyzed.In the acoustic analysis,The equivalent circuit model of the acoustic pressure sensor is established,and the expression of the acoustic impedance of each component is analyzed.The influence of the diaphragm material properties,working environment and sensor structure parameters on the acoustic performance of the acoustic pressure sensor is discussed in detail,which provides theoretical guidance for structural design of sound pressure sensor.2.A high-quality metal film dry transfer process based on sacrificial layer is proposed.A low cost positive photoresist,which is easily soluble in acetone solution,is used as the sacrificial layer.The metal film is processed on the surface of the sacrificial layer by magnetron sputtering.The wrinkles of the membrane is effectively reduced by the residual stress in the diaphragm.The experimental results show that the machined metallic silver film has a flatness of less than 14 ?m at a diameter of 2.5 mm.Aiming at the problem that the stress of the silver film is high and difficult to be controlled by the magnetron sputtering,the stress of the diaphragm is reduced by introducing the corrugated structure.The experimental results show that the sensitivity of the sound pressure sensor based on the silver film is about 1 time higher than that of the flat membrane structure.The sensitivity of the acoustic pressure sensor based on the silver film is about 1 time higher than that of the flat film structure sensor.3.Design and manufacture a variety of EFPI fiber optic pressure sensor structure.Short cavity length co-axial type flat/corrugated diaphragm fiber microphone,short cavity length cross-axial type flat diaphragm fiber microphone,long cavity long co-axial type flat film fiber microphone,etc.are respectively processed by a silver metal diaphragm.The micro-fiber hydrophone based on micro-channel anti-hydrostatic structure was fabricated by silver diaphragm and PET diaphragm.The characterization parameters of optical fiber sensor are discussed.The intensity demodulation device is built by using ASE light source and DFB light source respectively.The phase demodulation device based on PGC-DCM algorithm is built with EDFL light source.At last,the performance of four optical fiber microphones and two kinds of optical fiber hydrophone are tested and analyzed in detail. |
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