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 (1D) 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 λ₀/5000 from the source using both grazing and normal incidence. The technique was validated by comparison with a number of two-dimensional (2D) 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