TIME DOMAIN INVERSE SCATTERING OF A TWO-DIMENSIONAL HOMOGENOUS DIELECTRIC OBJECT WITH ARBITRARY SHAPE BY PARTICLE SWARM OPTIMIZATION

This paper presents a computational approach to the two- dimensional time domain inverse scattering problem of a dielectric cylinder based on the finite difference time domain (FDTD) method andthe particle swarm optimization (PSO) to d etermine the shape, location and permittivity of a dielectric cylinder. A pulse is incident upon a homogeneous dielectric cylinder with unknown shape and d ielectric constant in free space andthe scatteredfieldis record ed outside. By using the scattered field, the shape and permittivity of the dielectric cylinder are reconstructed. The subgridding technique is implemented in the FDTD code for modeling the shape of the cylinder more closely. In order to describe an unknown cylinder with arbitrary shape more effectively, the shape function is expandedby closedcubic- spline function insteadof frequently usedtrigonometric series. The inverse problem is resolvedby an optimization approach, andthe global searching scheme PSO is then employedto search the parameter space. Numerical results demonstrate that, even when the initial guess is far away from the exact one, goodreconstruction can be obtained . In addition, the effects of Gaussian noise on the reconstruction results are investigated. Numerical results show that even the measured scattered E fields are contaminated with some Gaussian noise, PSO can still yield goodreconstructedquality.