The computation of backward-scattered acoustic field using the Kirchhoff approximation for a convex curved body coated with multiple acoustic layers

This paper applies the Kirchhoff Approximation (KA) method to compute the scattered acoustic field produced by a convex scatterer. The surface impedance of this convex shape is formed by multiple layers of acoustic media. The impedance value is calculated based on the interaction of two-dimensional plane incident waves with the multilayered acoustic media. According to the KA method, the backscattered acoustic field on the illuminated side of the scatterer is composed of monopole and dipole sources, whose amplitudes correspond to the surface acoustic pressure and surface normal velocity, respectively. These two quantities are determined based on the high-frequency approximation, in which the incident and reflected waves on the curved surface can be treated as locally planar acoustic waves. Thus, the surface pressure and normal velocity can be determined using the impedance values computed from the two-dimensional layered model. An analytical solution for a spherical object coated with multiple acoustic layers is used to compare with the results obtained by the KA approximation method proposed in this study.