Modeling of arbitrarily shaped resistive objects with a finite-difference time-domain electromagnetic field solver

An implementation of surface-impedance boundary conditions in finite-difference time-domain electromagnetic field solvers was described by Oh and Schutt-Aine. This algorithm allows for modeling of the effects of objects with finite conductivity which lie along grid-conformal surfaces. Here we describe the extension of the algorithm to allow for modeling of arbitrarily shaped objects. This is accomplished by combining the model of Oh and Schutt-Aine with the locally conformal method for modeling of perfectly conducting objects developed by Dey and Mittra. The resulting hybrid algorithm yields a second-order accurate implicit field solution, in which the standard orthogonal grid is deformed only locally at the conductor-vacuum interface, which is modeled by partially filled grid cells. Field solutions inside the conductor are not sought and the approximate boundary condition is used to set the nonzero tangential electric fields along interfaces. This method obviates the need to resolve skin depths on the grid. We briefly review the Oh and Schutt-Aine algorithm and describe its implementation in the Dey-Mittra partial-cell treatment. The use of the model is then demonstrated by performing several test problems involving objects with finite conductivity in both relatively simple and more complex geometries.