POLES AND ZEROS OF THE PLANE-WAVE REFLECTION COEFFICIENT FOR POROUS SURFACES

A study of the location of the singularities of the reflection coeffic ient, and the related acoustic fields, at the plane contact surface be tween a fluid layer and a porous layer, is performed in two cases. In the first case, the porous layer is thin (the product of the thickness by the wavenumber is much smaller than one), and the layer is set on an impervious rigid backing. In a second case, the porous layer is sem i-infinite. In the first case, one of the poles, predicted after more approximations, is related to a slightly inhomogeneous wave in air whi ch has recently been observed by nearfield acoustical holography. In t he second case, it is shown that the singularity is related to a zero of the reflection coefficient observable at high frequencies. New resu lts concerning the location of the pole relative to the steepest integ ration path can be obtained from a physical model of sound propagation in the porous medium.