Surface impedance modeling using the finite-difference time-domain method

The finite-difference time-domain (FDTD) technique has been used to model the one-dimensional (1-D) surface impedance of a lossy earth plane having discontinuities in two and three dimensions. Using a horizontal magnetic field aperture source located five cells from an absorbing boundary and 35 cells above the lossy earth plane, the surface impedance was accurately modeled at a distance of 0=5000 from the source using both grazing and normal incidence. The technique was validated by comparison with a number of two-dimensional (2-D) analytical models. The surface impedance profile in the vicinity of a vertical conductive water filled shaft that extends from the earth’s surface to a conductive basement is presented. Unlike modeling in the frequency domain, a single FDTD solution yields accurate multi frequency surface impedance data providing a number of standard cell size constraints are met. For common earth electrical constants, the FDTD approach is limited to frequencies above 500 Hz.