Evaluating the Ground Impedance-A New Methodology Based on EM Reciprocity

The electromagnetic reciprocity theorem of the time-convolution type is applied to introduce a general methodology for constructing approximate expressions for the ground impedance parameter. The methodology is first illustrated on expressing the ground impedance concerning a thin conductive strip above a homogeneous, lossy half-space, which yields the classic ground-impedance approximate expressions due to Carson and Vance. Second, the proposed methodology is applied to the corresponding strip-ground configuration in which the effect of the ground is modeled via the surface impedance approximation. This leads to a new ground-impedance approximate expression given in terms of the exponential integral. The validity of the latter approximation is assessed numerically and its relation to the well-known approximations is briefly discussed. Finally, the corresponding two-layer ground problem configuration is analyzed. The result is a correction of the ground impedance accounting for the contrast in soil stratification.