Research Of Fiber-optic Low-frequency Acoustic Pressure Sensor

Since the advent of optical fiber,the technology of fiber optic sensing has been changing with each passing day due to its sensitivity to external physical quantities.Fiber optic acoustic pressure sensor is a very important field in optical fiber sensing technology.Compared with the traditional electroacoustic sensors,it has the characteristics of simple structure,low cost,high sensitivity and anti-electromagnetic interference.Now fiber optic acoustic pressure sensors are widely used in medical diagnostics(hospital CT rooms),natural disaster warnings,and some inflammable and explosive environments(oil wells).It is precisely because of these special needs that people pay more and more attention to highprecision,small-volume,low-frequency and high-sensitivity fiber optic acoustic pressure sensors.In this paper,combined with the development needs of low-frequency fiber optic acoustic pressure sensors,some application scenarios of sensors were introduced,and the significance of the research was expounded.Their research conclusions were summarized by reviewing the previous research progress of fiber optic acoustic pressure sensors.Based on this,the theoretical analysis of the reflective intensity modulated fiber optic acoustic pressure sensor have been carried out on the deformation of the diaphragm.Combined with the related simulation,the effects of the material,thickness and the size of the diaphragm on the sensitivity and frequency response of the sensor were discussed.Considering the sensitivity reduction caused by the fiber divergence angle,an acoustic sensing scheme based on fiber collimator was proposed.The coupling effect of various fiber collimators was tested.Then the whole transducer was designed which included the studies of the diaphragm's optical and mechanical properties.The structure of the transducer was also designed and optimized.The circuit of the key parts of the sensor was classified and described,including the selection and generation of the light,the photodetector,and the processing of weak signals.This paper also tested the linearity,stability and frequency response of the sensor in the audible band,and tested the response of the infrasound band by using the nonlinear effects of the sound and the beat frequency principle.The results showed that the fiber acoustic sensor has a linear response in the range of 0-2 Pa at 0.5 KHz with linear correlation coefficient of 0.9995.The frequency response of 10 dB bandwidth is 1-1000 Hz,and the sensitivity is up to 320 mV/Pa.