Spatial Fourier transform method incorporated with Johnson-Champoux-Allard model to determine absorption coefficient of materials

This paper describes spatial Fourier transform method which is based on calculation of complex pressure distributions on two parallel surfaces and decomposing the complex pressure distributions into plane-wave components by using two-dimensional spatial Fourier transform which is used to separate the incident and reflected plane wave components. Johnson-Champoux-Allard model is utilized to predict effective density and bulk modulus of the air in the material, which are used to calculate wave number and characteristic impedance. Consequently, they are used to determine reflection coefficient of the porous materials at a range of angle of incidence.