Simulated And Experimental Research On The Reconstruction Technology Of Reflection Coefficients At Oblique Incidence

The reconstruction of reflection coefficients using active Near-field Acoustical Holography is based on the theory of wave acoustics. The method involves the measurement of complex pressure distribution on two parallel planes lying between the surface of a test material and the source, and decomposing each of the complex pressure distributions into plane-wave components by using 2-D spatial Fourier transform. By doing so, the reflection coefficients at arbitrary oblique incidence could be reconstructed.The theory of this method is described in this paper, and the measuring model is provided. It is demonstrated that it could obtain the complex reflection coefficients at a number of incidences by calculating once with applying the wave number sampling theorem.Systematical simulation is deduced, which result shows the influences of various factors on the reconstruction, such as the source, the reflection medium, the measure parameters, the measure noise and the channel mismatch. It is verified that the dipole source is the preferred source for active NAH measurement. The optimum parameters and scanning method are also proposed based on the result of simulation. Specially, it is demonstrated that the distance between the holography plane and the reflection surface is the most important parameter.Experiments are carried out, which results testify that the method is applicable. Base it, the measurement of acoustical superstratum is performed to reconstruct its reflection coefficient.