Novel Surface Impedance Formulation via FILT and Prony Method for FDTD Analyses of Lossy Media

Surface impedance method has been utilized in many electromagnetic problems involving high-loss media. In this letter, a new finite-difference time-domain formulation unified for the surface impedances of both metals and biological media is derived using the fast inverse Laplace transform and the Prony method. The proposed formulation is capable of treating many kinds of surface impedance without in-advance knowledges of their analytical expressions in the time domain. It is demonstrated that the reflection coefficients of both metal and biological tissues calculated using our proposed formulation agree well with the theoretical values with errors less than 1.2% in the frequency range between 1 and 100 GHz, confirming the validity and effectiveness of the method.