| The method of moments (MoM) is applied to the problem of electromagnetic scattering from general three-dimensional lossy dielectric targets in an arbitrary lossy, dispersive multi-layered environment. The dyadic Green's function for stratified media is computed via the method of complex images, and the Galerkin MoM solution is effected by employing triangular patch basis functions. Applications to radar-based sensing of plastic land mines are presented in both the time-domain and frequency domain. Due to the high requirements of RAM and CPU for the MoM solution, a multi-level fast multi-pole algorithm (MLFMA) has also been developed for electromagnetic scattering problems involving electrically large, arbitrary-shaped dielectric targets situated in the presence of a lossy, dispersive half-space. The near MLFMA terms are treated rigorously, via a complex-image-technique-based evaluation of the Sommerfeld integrals inherent to the half-space Green's function. The Green's function components for the far MLFMA terms are evaluated approximately, but accurately, via an asymptotic analysis. The MLFMA solution has O(NlogN) and O(P · NlogN) complexity for the RAM and CPU, respectively, for dielectric targets in the vicinity of a half space, where N is the number of unknowns and P is the number of iterations for the conjugate gradient solver. Numerical results from three different methods, namely, body of revolution (BoR) based MoM, general 3D MoM and dielectric MLFMA are compared extensively, and excellent agreement has been achieved in general. Several example applications utilizing the MoM and MLFMA to remote sensing are addressed, particularly on electromagnetic scattering from tree trunks or tree-shaped targets in the presence of a half-space environment. |
