Acoustic Impedance at Oblique Incidence in Fluids, and Highly Porous Materials

Abstract

The dilatational plane waves studied previously have equiphase planes and equiamplitude planes which are both perpendicular to the direction of propagation. These waves are called homogeneous plane waves. They have been used to represent the acoustic field in layered fluids having plane boundaries perpendicular to the direction of propagation. Transmission and reflection at oblique incidence may be described by inhomogeneous waves, with non-parallel equiphase and equiamplitude planes. A short description of these waves is presented in this chapter, both in isotropic and in anisotropic fluids. Next, these waves are used to calculate the surface impedance and the absorption coefficient of both isotropic and anisotropic highly porous materials according to the laws of Delany and Bazley [1].