SUMMARYWe address time-domain inverse electromagnetic scattering for determining unknown characteristics of an object from observations of the scattered field. Applications include non-destructive characterization of media and optimization of material properties, for example, the design of radar absorbing materials. Another application is model reduction where a detailed model of a complex geometry is reduced to a simplified model.The inverse problem is formulated as an optimal control problem where the cost function to be minimized is the difference between the estimated and observed fields, and the control parameters are the unknown object characteristics. The problem is solved in a deterministic gradient-based optimization algorithm using a parallel 2D FDTD scheme. Highly accurate analytical gradients are computed from the adjoint formulation.The inverse method is applied to the characterization of layered dispersive media and the determination of parameters in subcell models for thin sheets and narrow slots.
SUMMARYWe present a new approach to time domain hybrid schemes for the Maxwell equations. By combining the classical FD-TD scheme with two unstructured solvers, one explicit ÿnite volume solver and one implicit ÿnite element solver, we achieve a very e cient and exible second-order scheme. The secondorder accuracy of the hybrid scheme is veriÿed through convergence studies on perfectly conducting as well as dielectric and diamagnetic circular cylinders. The numerical results also show its superiority to the FD-TD scheme.
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