Research On The Mechanism And Related Technologies Of Infrasonic Pistonphones

Pistonphone is the most suitable method for infrasonic microphone calibration at present. In order to establish a national infrasound standard for our country, the mechanism and related technologies of infrasound pistonphones were investigated to solve the problems in the current research on pistonphones.In chapter1, the significance of the research and contents of this dissertation were presented. First, the hazards and applications of infrasound were analyzed, and the significance of infrasonic microphone calibration was pointed out. Secondly, the main contents of microphone calibration, the common microphone calibration methods and their research status were presented. Thirdly, the research and development of infrasonic pistonphones at home and abroad were overviewed. Finally, the main contents of this dissertation were generalized.In chapter2, the theory of the infrasonic sound field in an ideal chamber was researched. First, the distributed parameter model of the infrasonic sound field in an ideal chamber was conducted, and the expression for the wave correction of the sound pressure in infrasonic pistonphones was presented. Secondly, the effects of the chamber sizes on the purity and uniformity of the sound field were researched. Thirdly, the effects of the non-rigid chamber walls on the sound field were researched. Finally, the lumped parameter model of the sound field in a chamber with a microphone was conducted; the effects and correction method of the microphone on the sound field in the chamber were researched.In chapter3, the theory of infrasonic sound field in a leaky chamber was researched. First, the pressure step response of a leaky and adiabatic chamber was conducted and the expression for the adiabatic time constant of a pistonphone was presented. Secondly, the lumped parameter model for the sound field in a leaky chamber was conducted, and the expression for the leakage correction of the sound pressure in infrasonic pistonphones was presented. Thirdly, a method of obtaining the adiabatic time constant in the expression for leakage correction by modifying the measured time constant was researched. Finally, the distributed parameter model for the sound field in a leaky chamber was conducted, and the principle for the wave and leakage coupling correction of the sound pressure in infrasonic pistonphones was researched.In chapter4, the theory of infrasonic sound field in a non-adiabatic chamber was researched. First, the thermal effects of the sound field in a non-adiabatic chamber were researched, and the single series expression for the heat conduction correction of the sound pressure in infrasonic pistonphones was presented; it was pointed out that the single series expression for the heat conduction correction given in this dissertation was more accurate than the current dual series expression for the heat conduction correction. Secondly, the thermal effects of the sound field in a leaky and non-adiabatic chamber were researched, and the expression for the leakage and heat conduction coupling correction of the sound pressure in infrasonic pistonphones was presented, and the error brought in by the current theory of the leakage correction and the heat conduction correction was analyzed.In chapter5, an infrasonic pistonphone based on an electromagnetic vibration exciter with displacement-feedback was developed. First, the structure of the infrasonic pistonphone was presented, and an automatic-centring small-gap sealed structure for the piston and its guide was designed. Secondly, according to the research on the infrasonic sound field in a chamber, the chamber for the infrasonic pistonphone was designed. Finally, the impact of the piston displacement distortion and the acoustic nonlinear effects on the sound pressure distortion in the developed infrasonic pistonphone was assessed.In chapter6, the experimental research of the developed infrasonic pistonphone was carried out. First, the pressure step responses and the adiabatic time constants of two chambers were investigated experimentally, which verified the correctness of the pressure step responses of the leaky and adiabatic chamber and the leaky and non-adiabatic chamber, as well as the expression for the adiabatic time constant. Secondly, the performance of the developed infrasonic pistonphone was tested at the frequency range from0.001Hz to20Hz. Thirdly, the sound pressure sensitivity levels of three different types of microphones and their preamplifiers were calibrated in the developed infrasonic pistonphone at different sound pressures and different frequencies, and the calibration results were compared with the sound pressure sensitivity levels obtained by other methods. Finally, the uncertainties of the calibration results of sound pressure sensitivity levels of the calibrated microphones and their preamplifiers were evaluated.In chapter7, the achievements of this dissertation were summarized, and future research work for further study was prospected.