Investigation On Low-Frequency Reflection Coefficient Measurements From Big Acoustic Material Samples

With the development of science and technology and the application of sound absorption material, the research on sound absorption material is attached increasing importance to every country correspondingly. The sound reflection coefficient of the material is one of the important sound characteristics. Then, the reflection coefficients measurement is also being paid more attention to.In this thesis, the principle of near-field acoustic holography (NAH) in semi-space and the advantage and disadvantage based on Spatial Fourier Transforms in Semi-space, are described. The measuring system is set up. The affection of parameters, such as the location and distance between measurement points, the distance between sound source and test material, on the errors of the reconstructed field is analyzed by means of experimental investigation. The measured results are generally in good agreement with the theoretical value. Then, an experimental verification of this method is given in the paper.The experimental results show that this method eliminates the effect of the scattered sound field of the water surface completely. Because the sound source and the test material are set near the water surface during the experiment, it is very easy to set the measuring system, and this is very useful in practice.