Through-the-earth magnetic field propagation: Modelling for underground applications

A finite-element method (FEM) model of a through-the-earth (TTE) magnetic field propagation field experiment is developed using COMSOL multiphysics. The geometry of the model is obtained from the topographic data of the test site. The soil description is set from the literature concerning the region interpreted by means of a vertical electric sounding and the geophysical analysis of the electromagnetic measurements and computations. A frequency range of 1 to 100 kHz, for seven emitter station points along 200 m was covered. In this paper, the coefficient of variation of the root of the mean squared error (CVRMSE) is studied. The results are compared with the computations of analytical propagation models. Free-space, infinite dissipative, semi-infinite and three-layered models for linear, homogeneous and isotropic horizontal mediums are considered. As a result, the accuracy of the analytical models is highly improved by the FEM model. Therefore, FEM modelling can successfully be used for improving TTE propagation predictions for environments of complex geological structure.