Design And Experiment Of All-fiber Low-frequency Vibration Sensor Based On FPI

Low-frequency vibration measurement has been playing important roles in monitoring engineering machinery,vehicles,instruments,building structures,earthquake etc.Optical fiber vibration sensor has become a new research hotspot of vibration sensing field owing to its wide measurement range,high resolution,corrosion resistance and electromagnetic immunity.Low-frequency optical fiber vibration sensor mainly depends on external vibration structures nowadays,leading to huge volume and temperature crosssensitivity.With the advent of the era of intelligence,device miniature is a kind of trend,and the fabrication of practical micro optical fiber low-frequency vibration sensor is of great value.This thesis focuses on the decrease of volume of optical fiber vibration sensor,the improvement of its sensitivity and the reduction of its temperature cross-sensitivity.The vibration model of the vibration sensor is studied and vibration response curves of displacement sensor,velocity sensor and acceleration sensor are obtained.According to vibration response curves,when the testing frequency is greater than the resonance frequency of the system,displacement sensor should be applied,otherwise,the acceleration should be applied.So,as to low-frequency vibration sensing,the acceleration sensor should be used.As for the acceleration sensor,the eigenfrequency and the damp are two key factors.The lower the resonance frequency of the system,the higher sensitivity of the sensor.Greater damp can expand the measurement range but decrease the responsivity and the sensitivity.Based on the problems existing in optical fiber vibration sensors,and in order to reduce the size,improve the sensitivity and eliminate the temperature cross-sensitivity of the sensor,an all-fiber low-frequency vibration sensor head based on micro cantilever beam with tip mass(MCBTM)and FPI is designed.The fabrication process,the measurement and demodulation system of the sensor is introduced in detail.The characteristics of the sensor head is analyzed by using COMSOL Multiphysics software.Experimental system is set up and low-frequency vibration experiments of three sensors are studied.To verify the quartz capillary can effectively isolate the temperature influence of the sensor,temperature experiment is conducted in one of the three sensors.The experimental results show that tip mass can improve the sensitivity of the sensor and the quartz capillary tube can isolate external temperature effectively,reducing temperature cross-sensitivity of the sensor.The all-fiber low-frequency vibration sensor based on FPI and MCBTM has small volume,high sensitivity and anti-temperature cross-sensitivity,which can be embedded in composite material to detect vibration after being encapsulated.Besides,the sensor has easy fabrication process and high repeatability,which is of great practical value in the field of low-frequency vibration measurement.