Research On The Measurement Of Reflection Coefficient Of Underwater Acoustic Materials

It is a kind of common and effective method that puts the sound absorption material onthe route of transmission of the sound wave in the noise control field. The acoustic reflectioncoefficient is a significant parameter of the acoustical behavior of the characteristicsound-absorbing material. It directly guides the placement and use of the sound absorptionmaterial. The issue of “How to get the acoustic reflection coefficient quickly and accurately”has been discussed hotly in the field of acoustic testing.In this thesis, the model of spherical wave reflection is founded firstly. Then the authorcounts the correction relation of the spherical wave between reflection coefficient of thesurface of layered medium and reflection coefficient of the plane wave. And the author alsoresearches the source of error based on the test method of the acoustic reflection coefficientof the surface impedance method. The influence of diffraction effect of material edge on theerror of test result is analyzed and calculated. The regularities of distribution of the diffractedsound field are also analyzed. Size dimension of the material and the source of sound arediscussed. The influence of reception of the vector hydrophone at different positions on thetest error is discussed. And the impact of the phase equalization of the vector hydrophone onthe testing error is also discussed. At last, the influence of the experimental background noiseand the incorrectness of the placement of experimental system on the accuracy of the testresult are researched.Then this thesis detailed studies the compression technology of wide-band pulse. Andthe author employs the theory to deduce theoretical formula of compression of the wide-bandpulse, and counts the transmission rules of the impulse wave at near field when sphericalwave expanded. Then the compression technologies of wide-band pulse and cepstrum methodare combined, and the separated technology method of the time domain of diffracted wave isclarified. Simulation studies are conducted from three aspects: the pressure informationprocessing, particle vibration information processing, acoustic pressure and particle vibrationcombined processing. The author analyzes three kinds of handling methods respectivelyabout the test result of different SNR and different incident angle of the sound wave, andcontrasts and analyzes the good and bad of three kinds of handling means. At last, the authordesigns the experimental program of the surface impedance method and the method of thecompression of wide-band pulse, and sets up the experimental system. According to theoriesof two kinds of experiments, the author conducts several experiments about the various conditions experiments and data processing, and provides the results of processing ofexperimental data. Then the author contrasts and analyzes two kinds of results of the dataprocessing, and analyzes the source of the error. The theoretical simulation results are verified.Superiority of the acoustic reflection coefficient of the underwater acoustic material measuredby the compression technology of wide-band pulse is proved.The compression technology of wide-band pulse is a kind of useful separated technologymethod of the time domain of diffracted wave. The method of cepstrum avoids the errorsresulted from the sound pressure of the vector hydrophone and the consistency of vibrationspeed channel and sound pressure channel. The acoustic reflection coefficient of the fullspectrum band can be obtained from the perspective of acoustic incident by using broadbandsignal which can be tested one time. Therefore, experimental procedure is simplified, and theoperation will be more simple and convenient. The test result is accurate, which has thehigher reference value of the project.