Optical Acoustic Pressure Sensor Based On MEMS Cantilever Beam

The measurement of acoustic pressure,the reduction of acoustic waveforms,and the determination of acoustic frequency are of great significance in the application or development of an acoustic system.At present,the acoustic pressure sensors on the market are mostly capacitive sensors based on suspending membranes.The problems with this type of sensors are that,on the one hand,the sensing sensitivity of the suspending membrane to the sound pressure is low;on the other hand,the electrical sensor has poor anti-electromagnetic interference capability and limited sensitivity.In view of the above problems,this paper studies the optical acoustic pressure sensor based on MEMS cantilever beam.In this paper,the one-dimensional harmonic oscillator model is used to analyze the dynamic process of the cantilever beam.The expression of the first-order resonant frequency is given.Then the frequency response function is derived and the size parameters of the cantilever beam are designed.Subsequently,this paper uses COMSOL software to simulate the resonant frequency of the cantilever beam,the resonant mode and the deformation under static pressure.Based on the above theory,this paper designs a F-P cavity acoustic pressure sensor based on a cantilever beam.The principle of measuring the deformation of cantilever beam by F-P cavity is analyzed.Subsequently,the cantilever beam device is fabricated and the F-P cavity sensor is built with the device,and the stripe contrast of 12dB is obtained.Next,the acoustic pressure test of the sensor is carried out.At the eigen frequency,the sensitivity of the sensor is 3.404 V/Pa,and the minimum detectable sound pressure is 1.6mPa/Hz.In addition,the vibration test is carried out in this paper.At 150 Hz,the sensitivity of the sensor is 8.08 V/g,which is 156 times that of the reference accelerometer.During the test,operating point the F-P cavity sensor appears to be fluttering,which in turn causes the output to be unstable.Aiming at the above problems,this paper designs a cantilever beam ridge waveguide-single mode fiber coupled sensor.In this part,the principle of measuring the deformation of cantilever beam by coupling attenuation is described.The mode field simulation of ridge waveguide and single mode fiber is carried out by OptiBPM software,and energy coupling ratio of waveguide and fiber in different axial misalignment and longitudinal misalignment is present.According to the simulation results,the structure of the sensor is designed and the size parameters are optimized.Subsequently,the cantilever beam device is processed by MEMS technology,and the sensor sample was built with the device.Finally,the paper performs acoustic pressure test and photoacoustic test on the sensor.The acoustic pressure test results show that the sensor's test sensitivity is 8.34V/Pa and the minimum detectable sound pressure is 51.7mPa/??? at the eigen frequency.Both of these results are more excellent comparing with F-P cavity sensor.In the photoacoustic test,the photoacoustic signals in time domain at 150Hz and 25Hz modulation frequencies are obtained with CO₂ in the air as the target gas,and the linear relationship between the photoacoustic signal intensity and the power of the light source is obtained.