Study on Electrical Properties of Multilayered Spherical Earth by Wireless Electromagnetic Method

Abstract

The wireless electromagnetic method (WEM), a new method combining geophysics and radio physics, can be used for seismic monitoring, ionospheric structure exploration and electrical structure detection within a depth of 10m underground. As the wavelength of an electromagnetic wave can be equal the circumference of the earth, the influence of ionosphere and earth curvature on electromagnetic waves shall be considered. Considering that the earth is a multi-layer geoelectric medium, a multi-layer ''Earth-ionosphere'' model is established to simulate the electromagnetic field more accurately in the actual complex underground structure. By combining the W.K.B method and the impedance recursion method, we initially obtained the response formula under such a model, calculated the Schumann Resonance within the low frequency range of 1-30Hz, and verified the correctness of the algorithm proposed by this paper; we subsequently obtained the propagation characteristics and the frequency characteristics of the electromagnetic field under different electrical structures by simulation and calculation, and analyzed the propagation law of the electromagnetic field at different times and at different equivalent heights of the ionosphere. The results revealed that the influence of the ionosphere and the earth curvature must be accounted for in large-scale deep detection, and different underground structures and the equivalent heights of ionosphere at different times may lead to differences in the value of the electromagnetic field. Therefore, the multi-layered spherical ''Earthionosphere'' model can better meet the requirements of high-power WEM for the forward calculation of underground complex electrical structure detection and assist the refined exploration by such a method. INDEX TERMS Extremely low frequency electromagnetic method, spherical coordinate system, ''earth-ionosphere'' model, multilayered sphere, refined electrical structure.