Study On The Low-Frequency Sensitivity Modeling And Key Calibration Technology Of Microphones

In recent years,the quantitative study on low-frequency sound(infrasound especially)has aroused a wide concern.Therefore,the accuracy of the low-frequency sensitivity of the microphone is put forward more and more high,but in the primary calibration process of the widely used microphone,the dual effect of leakage and the heat conduction coupling attenuation(the first coupling mechanism)in the chambers of the microphone and the calibration device,and the sound pressure coupling excitation(the second recoupling mechanism)on both sides of the microphone’s sensitive cell causes nonlinear fluctuations of the low-frequency sensitivity of the microphone.Therefore,accurate modeling of low-frequency sensitivity of the microphone is the premise of quantitative study on the low-frequency acoustic and the key of breaking through the bottleneck of air pressure reference at low frequencies.In this thesis,based on the National Natural Science Foundation of China Youth Fund Project “Low-frequency sensitivity modeling and parameters identification of acoustic-electrical transducers considering the dual coupling mechanism”,firstly,the low-frequency sensitivity modeling of the microphone and key calibration techniques are studied.Secondly,the lowfrequency sensitivity calibration experiment platform of the microphone is established.Then low-frequency sensitivity model of the microphone is established.Finally,a further theoretical,simulation and experimental study of the low-frequency sensitivity model of the microphone is presented.The main study work is as follows.(1)The experimental platform of low-frequency sensitivity calibration of the microphone based on pistonphone technology is designed.Firstly,the main bodies and driving mechanisms of the pistonphone device are designed,and the parameters of each mechanism of the pistonphone device are determined.Secondly,the dynamics and kinematics analysis of the driving mechanism are carried out,and the main working resistances and motor driving parameters of the system are calculated and studied.Finally,the rigid-flexible coupling model of the drive mechanism is established in ADMAS,and the driving parameters of the drive mechanism are calculated and compared with the results of analytical calculation.The results of the simulation analysis verified the correctness of the results of the analytical calculation and provided a reference for motor selection.(2)The dual coupling mechanism in the primary calibration process of the microphone is studied,and the low frequency sensitivity model of the microphone is established.Firstly,the dual coupling mechanism in the primary calibration process of the microphone is briefly introduced.Secondly,the time constant expression and temperature transfer function expression of the microphone are derived,and the air leakage and heat conduction coupling model of the microphone cavity in the two sound fields is established.Then,based on the force balance characteristic of the microphone sensitive cell under two sound fields,its deformation function is established,and the parameterized model of the low-frequency sensitivity of the microphone under the corresponding sound field is established.Finally,the frequency response of the microphone is calculated,and the influence of each parameter on its sensitivity is analyzed.(3)The simulation software of acoustical finite element method is used to study the pressure field and the diffuse field low-frequency sensitivity of the microphone in the primary calibration of the pistonphone.Firstly,the finite element model of the pistonphone cavity is established in COMSOL Multiphysics respectively,and the sound pressure corrections in the cavity under the action of wave,leakage,heat conduction,leakage and heat conduction coupling which are basically consistent with the theoretical method are obtained by calculated.Then,the unidirectional coupling model of the microphone and the pistonphone is established in COMSOL Multiphysics.The low frequency sensitivity model and the diaphragm displacement frequency response of the microphone which are basically consistent with the trend of the theoretical method are obtained by calculated.(4)An experimental study on the low-frequency sensitivity calibration platform of the microphone.Firstly,the structure and composition of the experimental platform are briefly introduced.Secondly,the step pressure response experiment of the cavity is performed on.And the tightness of the cavity is tested.Finally,the low-frequency sensitivity calibration experiments of the microphone and the pressure transducer are performed on.The experimental results show that: 1.The developed pistonphone device has a good sealing performance,the measured time constant is 27.5 s,and the sound pressure attenuation is less than 3 d B at 0.01 Hz;2.The obtained sound pressure sensitivity curve of the microphone is smooth,and in the infrasound frequency band,the sensitivity level of the microphone with a pressure equalization hole has a certain difference in diffuser field and the pressure field;3.The sensitivity level of the pressure transducer is basically a straight line below 2 Hz.