Spatial Fourier transform method to determine reflection and absorption coefficient of porous rigid materials applying Johnson-Champoux-Allard model

Sound absorption and reflection coefficients of the materials are two important parameters to understand the capacity of the materials to store acoustical energy. Spatial Fourier transform method 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 absorption and reflection coefficient of the porous materials at oblique angles.