Research On Some Theoretical And Technical Problems For Very-Low-Frequency Finite-Amplitude Sound Pressure Calibations

Based on the National Natural Science Foundation of China "Research on the mechanism and related technology of a very-low frequency standard infrasonic generator",the theoretical and technical problems for very-low-frequency(VLF)finite-amplitude sound pressure calibrations were studied.In chapter 1,the research background,significance and content of this dissertation were presented.First,the content,method and significance of acoustic measurement and microphone calibration were pointed out.Secondly,primary calibration methods of microphones and their research status were presented.Thirdly,the significance and research status of VLF finite-amplitude sound pressure calibration was pointed out.Finally,research contents of this dissertation were summarized.In chapter 2,the analytic theories for the linear sound pressure in the membrane-sealed coupler were studied.First,the distributed parameter model for the linear sound pressure in the membrane-sealed coupler was built under airtight and adiabatic conditions,and the lumped parameter expression and its wave motion correction expression were derived.Secondly,the pressure step response model was built under leaky and adiabatic conditions,and expressions for the adiabatic time constant and pressure leakage correction were derived,and effects of the equalizing tube on the lower limiting frequency were studied.Finally,the leakage and heat conduction coupling model was built,and its amplitude-phase frequency characteristics were studied,and the expression for the leakage and heat conduction coupling correction was derived.In chapter 3,the nonlinear theories for the finite-amplitude sound pressure in the membrane-sealed coupler were studied.First,linearized sound wave equations based on the Euler system and the Perturbation method were built starting from three basic acoustic equations.Secondly,the first and second order distributed parameter expressions for the finite-amplitude sound pressure were built under airtight and adiabatic conditions,and nonlinear distortion characteristics of the finite-amplitude sound pressure were studied.Finally,the first and second order intermodulation expressions for the finite-amplitude sound pressure were built under airtight and adiabatic conditions,and effects of the intermodulation on the sound pressure distortion were studied.In chapter 4,the related design techniques for the VLF finite-amplitude sound pressure calibration device were studied.First,the structural proposal for the membrane-sealed coupler was presented,and the deformation characteristics and dynamic characteristics of the membrane under static load were studied.Secondly,the electromechanical coupling model of an electromagnetic vibrator was built,and its voltage-displacement characteristics and displacement output capacities were studied.Thirdly,electro-mechanical-acoustical coupling models of the calibration device with the feedback control were built,whose voltage-acoustical characteristics were studied,and acoustical output capacities of the coupler were determined.Finally,the attenuation characteristics of the sound pressure in the coupler,which were induced by the factors such as the leakage,heat conduction,nonrigid wall,etc.,were studied,and the structure parameters of couplers were confirmed according to the designed specifications.In chapter 5,the experimental studies were conducted for the VLF finite-amplitude sound pressure calibration device.First,the calibration device and its measurement and control system were set up,and their main components were introduced.Secondly,the pressure step responses in the calibration modes of membrane sealing and clearance-gap sealing were tested,and their time constants were measured and their corresponding adiabatic time constants were obtained though correction,and finally their corresponding leakage correction values and correction errors from traditional correction methods were presented.Thirdly,the piston displacement distortions of each calibration modes were tested,and the distortion of the sound pressure were theoretical calculated and verified by the test results from microphones.Finally,the effect of the coupler vibration on the sound pressure output was studied.In chapter 6,the primary calibration and uncertainty evaluation of microphones were conducted based on the VLF finite-amplitude sound pressure calibration device.First,primary calibrations of working standard microphones were conducted in the calibration modes of membrane sealing and clearance-gap sealing,and the finite-amplitude calibration capacities and distortion characteristics of each calibration modes were evaluated and compared at low,medium and high pressure levels.Secondly,the inner and outer pressure-balance calibrations of working standard microphones were conducted,whose results proved that they are different from each other.Thirdly,very-low-frequency calibratons down to 1 mHz of pressure sensors were conducted,and the leakage and heat conduction coupling correction theory were verified.Finally,uncertainty evaluations of pressure sensitivity calibrations of microphones based on the membrane sealing VLF finite-amplitude sound pressure calibration device were conducted,whose evaluating results were presented.In chapter 7,the achievements of this dissertation were summarized,and the future research work for further study was prospected.