SURFACE IMPEDANCE MODELING USING THE FINITE-DIFFERENCE TIME-DOMAIN METHOD

The finite-difference time-domain (FDTD) technique has been used to mo del the one-dimensional (1-D) surface impedance of a lossy earth plane having discontinuities in tno and three dimensions, Using a horizonta l magnetic field aperture source located five cells from an absorbing boundary and 35 cells above the lossy earth plane, the surface impedan ce was accurately modeled at a distance of lambda(0)/5000 from the sou rce using both grazing and normal incidence, The technique was validat ed by comparison with a number of two-dimensional (2-D) analytical mod els, The surface impedance profile in the vicinity of a vertical condu ctive water filled shaft that extends from the earth's surface to a co nductive basement is presented, Unlike modeling in the frequency domai n, a single FDTD solution yields accurate multi frequency surface impe dance data providing a number of standard cell size constraints are me t, For common earth electrical constants, the FDTD approach is limited to frequencies above 500 Hz.