| The measuring method of underwater finite rectangle elastic steel plane's sound reflection coefficient, which is obtained by sound holography, has been studied in the paper. The sound field of the elastic steel board excited by sound source is calculated by the combination of FEM (Finite Element Method) and IBEM (Indirect Boundary Element Method). The reflection coefficient of the steel plane has been reconstructed by the calculated data, which is obtained by the adoption of sound holography method. Those factors that may have influence on the reconstruction of steel board reflection coefficient, such as the structure parameters, the measure parameters, the source types, the multi-source combination, are discussed. It provides the reference for the parameters selection in the practical engineering measurement.In the paper, the elastic structure vibration problems can be solved by FEM. The sound radiated field of structure can be calculated by BEM (Boundary Element Method). If the discrete nodes of elastic structure and fluid interface are matched in FEM and BEM, the coupled motion equation of the structure and sound field can be obtained. The scattering field near field holography sound pressure distribution of elastic steel board can be obtained by further numerical calculation. The data is handled by the combination of the software VC++, MATLAB. Then, the sound reflection coefficients, the graphics of wave-number spectra and angle spectra are obtained.The reconstruction of sound reflection coefficient by Near-field Acoustic Holography is based on the theory of wave acoustics. This method is based on the measurement of complex pressure distribution on the holography surface of the test material and the source. The plane wave sound reflection coefficient of the test material at arbitrary oblique incidence can be obtained by using spatial Fourier transform. The wave-number spectra and the angle spectra are obtained by the application of sampling theory on wave-number area.
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