Research On Diaphragm-based Optical Fiber Sound Pressure Sensing Technolog

As a carrier of energy and information,acoustic waves can be detected and moni-tored to realize the early warning of volcanoes,earthquakes,tsunamis and other natural disasters.It is also widely used in medical diagnosis and daily life.This research is of great significance in improving the quality of life of residents and preventing natu-ral disasters.Acoustic waves are transmitted by perturbing the medium volume element pressure form of energy,the medium volume element is perturbed by the pressure change is the acoustic pressure,therefore,by monitoring the relationship between the change of Acoustic pressure with time can complete the monitoring of the measured acoustic waves.Fiber optic acoustic pressure sensing system is to achieve acoustic pressure detec-tion by monitoring the change of the characteristic parameters of the carrier wave in the fiber,the sensitivity of this method is several orders of magnitude higher than the traditional electrical acoustic sensors,and has the advantages of low noise level,large dynamic range,anti-electromagnetic interference,light size and high stability.In this paper,the research on diaphragm-based fiber optic acoustic pressure sensing technolo-gy is carried out,and its goal is to obtain a highly sensitive,simple structure and low cost fiber optic acoustic pressure sensing scheme by studying the principles related to diaphragm vibration,photoacoustic conversion mechanism and the relationship between fiber optic mode change and acoustic pressure sensitivity.The main research contents of this paper are as follows:Firstly,the basic theory of acoustic pressure sensing is studied,and the diaphragm is designed and simulated based on the theoretical research and analysis.To begin with,the principle of sound receiving and the vibration performance of the diaphragm are an-alyzed.In addition,the demodulation techniques commonly used in fiber optic sensing technology are studied.By comparing and analyzing several different acoustic receiving devices and discussing their acoustic receiving principles,the piezometric acoustic receiv-ing principle was chosen to design and fabricate the acoustic pressure receiving device,followed by the theoretical analysis of the vibration characteristics of the diaphragm in the acoustic receiving device.In the end,the vibration characteristics of the diaphragm were simulated using finite element software,and the simulation results showed that the theoretical results of the diaphragm vibration characteristics were consistent with the simulation results.Secondly,an optical fibre acoustic pressure sensing scheme based on a large-angle tilted fibre grating is proposed and validated based on theoretical analysis and simula-tion experiments.The core-cladding mode coupling in the tilted optical fibre grating is easily changed when the fibre is bent,and it is glued to the polyethylene terephtha-late（PET）diaphragm to form an acoustic pressure sensor.The diaphragm of the sensor vibrates in response to the acoustic signal,which causes the tilted fibre grating glued to the surface of the diaphragm to bend dynamically,causing its cladding mode spectrum to drift back and forth periodically.The sensor is demodulated using edge filtering,and the corresponding acoustic signal is demodulated by tracking the change in laser output power caused by the wavelength drift.Experimental results show that the sensor can achieve high sensitivity acoustic detection in the range of 45²20Hz,with a maximum acoustic pressure sensitivity of 115.88m V/Pa@54Hz,corresponding to a minimum de-tection acoustic pressure of 539.2Pa/Hz^1/2.Therefore,the sensor has the advantages of high sensitivity,simple structure,easy processing and modification,and has a good development prospect in weak acoustic detection related applications.