A surface impedance approach for modeling multilayer conductors in FDTD

Surface impedance boundary conditions (SIBC´s) are implemented in the finite-difference time-domain (FDTD) method to analyze the electromagnetic field around multilayer conductors. The conducting region is replaced by an equivalent surface where SIBC´s are applied locally. To incorporate the equivalent surface impedance into the FDTD code, at first the surface impedance is determined in the frequency domain by replacing the multilayer conductor by a cascade of transmission lines and calculating the total impedance matrix of the network. Following this, a wide-band polynomial approximation of the SIBC´s leads to an efficient and recursive solution of the convolution integrals in the time domain. As a numerical example, the impedance matrix of a symmetric three layer conductor is derived and the scattering parameters are compared to the analytical solutions.