Transient finite-element analysis using a surface admittance boundary condition to incorporate eddy-current effects

We present a time-domain finite-element formulation for modeling electromagnetic fields in two-dimensional regions containing conductors, dielectrics, and magnetic materials. Such an analysis is needed to determine terminal parameters (equivalent to resistance and inductance per unit length) for multiconductor transmission lines excited with time-varying signals. We use a novel separation of the excitation and response within the formulation and a surface admittance boundary condition to provide a time-domain solution capable of incorporating both proximity-effect and skin-effect eddy currents over a wide range of material parameters. We use a Prony expansion to convert the inherent convolution integral into a recursive expression, resulting in an efficient numerical procedure that can incorporate nonlinear material effects.