Research On The Mechanism And Related Technology Of A Standard Infrasound Generating Device

In this thesis, the mechanism and related technology of a standard infrasound generating device were studied, which associated with the project of the National Institute of Metrology in P.R. China.In chapter 1, the destination and significance of the thesis were presented. First, the characteristic and application of infrasound were introduced. In addition, the classification and calibration of microphone were shown. Then present research status and developing trends both at home and abroad of the device were analyzed. At last, the main research aim and content of the thesis were pointed out.In chapter 2, the infrasound generating mechanism was studied. First, the acoustic theory in the infrasound generating cavity and its acoustic simplified model were researched. Then, the sound field in the infrasound generating cavity was calculated based on the finite element analysis method, and the acoustic simplified model was verified, and the optimum mounting position of a calibrated transducer in the infrasound generating cavity was analyzed. Finally, the influence of the dimension of the infrasound generating cavity on the distribution of sound pressure was analyzed based on the finite element analysis results.In chapter 3, the related technology problems in the infrasound generating device was studied. First, the configuration and principle of the infrasound generating device were introduced. Then, an electromagnetic vibration exciter was analyzed based on the technology of the displacement feedback control, and the low distortion of the displacement of the piston in the cavity was realized. Finally, the structure of the infrasound generating cavity and the sectional fixture of microphones were designed, and the modal analysis of the infrasound generating device and the moving element was carried out, which verified that the resonance would not occur when the device worked within the woring frequency range.In chapter 4, some experiments were taken on the infrasound generating device. First, the distortion of the piston displacement and the sound pressure at the different frequency in the device was tested. Secondly, the sound pressure in the infrasound generating cavity was calculated after the piston displayment was measured by the laser interferometer, and modified values were got according to the correction of the heat conduction, wave-motion and pressure leakage. Finally, the acoustic comparison for the whole calibration device was carried out by the standard microphone of the model 4160 made by B&K, and the accuracy of the device was given. Then, the distribution of the sound field in the middle and end of the cavity was tested and analyzed, and the optimum position for the calibration in the infrasound generating cavity was decided. Experimental results show that the finite-element analysis of sound field in the infrasound generating cavity is reliable and the infrasound generating device can meet the design requirements.In chapter 5, the achievements of the thesis were briefly summarized and the further research work was expected.