FFT-accelerated analysis of scattering from three-dimensional structures residing in multiple layers

An extension of the adaptive integral method (AIM) is presented for fast analysis of scattering from three-dimensional (3D) structures located in multiple layers of a planar layered medium. The proposed scheme accelerates the iterative method-of-moments solution by employing 3D auxiliary regular grids, each of which encloses the parts of the structure in a different layer, and 2D auxiliary regular grids, each of which is located at a different interface of the layered medium. The auxiliary grids are used to execute the standard four-stage AIM procedure (anterpolation, propagation, interpolation, and correction) but the propagation stage of the procedure is divided into intra-layer and inter-layer components. Only the 3D grids and both 3D and 2D grids are used for intra- and inter-layer propagation stages, respectively. Numerical results validate the accuracy and efficiency of the proposed method.