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Research on the Measurement of Reflection Coefficient of Underwater Acoustic Materials Based on Vector Hydrophone in Free Field

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Tutor: ShiShengGuo
School: Harbin Engineering University
Course: Underwater Acoustics
Keywords: vector hydrophone,reflection coefficient,free field,sound intensity
CLC: TB565.1
Type: Master's thesis
Year:  2011
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Nowadays, by the noise pollution worsening, the sound absorption material has been widely applied. The Characterization of acoustic reflection coefficient is an important characteristic of sound-absorbing material parameter. It makes the sound absorption properties to be quantified and provides a theoretical basis for the proper application of sound-absorbing material. Therefore, how to effectively obtain the reflection coefficient of acoustic materials becomes the focus of study.This dissertation studies the method of measuring large sample reflection coefficient of acoustic materials in free field with vector hydrophone. First it describes the theoretical formula of reflected sound field produced by spherical wave incident upon plane baffle and analyzes the approximate geometric conditions for geometrical acoustic. Second, it gives the basic principle of the surface impedance method and discusses the formula for calculating the reflection coefficient from perpendicular incident and inclined incidence. The measuring error that come from experiment parameter are discussed.This dissertation mainly presents a completely new measurement technique of sound absorption properties of materials, based on the measurements of active intensity and sound energy density. It discusses the effect of the source position, the distance between the hydrophone and baffle and SNR on calculation results. The numerical analysis method is used to discuss the influence of sound source direction, the sensitivity of each channel of underwater sensor and inconsistent phase between the sound pressure and vibrating velocity aisle. This dissertation built a measurement system which is based on sound intensity method and surface impedance method. The surface impedance method and sound intensity method are proved feasible through the experiments. Data processing results are given by various conditions experiments. And this paper tested the conclusion of simulation and compare with the result of surface impedance method; analysis the advantage and disadvantage of the methods.The sound intensity method could use the advantage of vector hydrophone that could obtain field sound pressure and vibrating velocity information at the same time to measure materials of reflection coefficient fastly.This can simplify instruments and equipment. Experimental operation is simple and easy. This could satisfy site test requirements. Because of the advantages of the low frequency measurement and the fine directivity of the vector hydrophone, the test band could extend to the low frequency. This conforms to modern underwater acoustic technology development trend. Vector signal processing technology could provide reference to the inversion of the material reflection coefficient.
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