FDTD Modeling of Impedance Boundary Conditions by Equivalent LTI Circuits

A circuit-based implementation of the Leontovich impedance boundary condition (IBC) is proposed. The surface impedance of a lossy medium is approximated by a series of first-order rational functions using the vector-fitting technique. Thus, an equivalent analogical circuit with lumped linear time-invariant parameters is derived, which is simply analyzed in time domain without performing any convolution. The implementation of the equivalent circuit in the finite-difference time-domain method is detailed for different circuit configurations. Finally, the advantages of the proposed method are presented and compared with those of other numerical procedures for the solution of the IBC in time domain.