Numerical Simulation Of Electromagnetic Field Excited By Electric Dipole Source In The Earth Spherical Cavity

The earth and the ionosphere can form a resonant cavity, called the earth spherical cavity. The electromagnetic method using controlled-source extremely low-frequency (CSELF) wave is a technology is based on large power alternating electromagnetic field generated by electric dipole source placed on the surface of the earth. This method has great application value and development potential in geophysics. CSELF method is characterized by strong signal, constant character, broad coverage, Small attenuation, strong penetrating power and large exploration depth and so on, it can be applied to earthquake monitoring, geological exploration, surveys for mineral resources, treatment of waste nuclear material, detection to ionosphere structure in space as well as land and marine undersea communication and a large area of emergency command and control communications in wartime. The Extremely Low Frequency Engineering project for Underground Exploration is one of the "major national science and technology infrastructure project" approved by the Chinese government. Need to calculate the distribution of electromagnetic field in the earth spherical cavity, some scholars studied the earth-air-ionosphere coupling case layered model, some scholars studied the earth-air-ionosphere coupling case spherical model. However, some scholars only gives approximate solution, some uses boundary conditions only for radio communications, some gives expression of electromagnetic field use non-Earth-Air-ionospheric model but did not give corresponding results, some analytical solution is given confined to the surface, there is no corresponding space and plane distribution. Overall, our research and application of electromagnetic fields excited by electric dipole in the earth spherical cavity have certain results, but these studies were conducted in ideal model of simple cases. For heterogeneous sphere earth, unable to calculate electromagnetic field, we need to use the numerical simulation method. So use numerical simulation method to study the extremely low frequency electromagnetic wave propagation characteristics is of great significance.At present there are few scholars use electromagnetic simulation software to numerical simulation of electromagnetic field excited by electric dipole source in the Earth spherical cavity. How electromagnetic wave propagation and distribution in the earth, the air layer, the ionospheric, what differences between the various target and the impact of different interference factors on the electromagnetic field is worth further study. Provide support for the application and development of CSELF method in geophysics. This paper firstly introduces the principle of CSELF method, then based on previous studies, from classical electromagnetic sounding theory, finishing analytical solution under impedance boundary conditions and general boundary conditions. Mapping and analysis of the distribution and propagation of the electromagnetic field. The most important research of this paper is the use of three-dimensional electromagnetic simulation software CST to numerical simulation of electromagnetic field excited by electric dipole source in the Earth spherical cavity. From simple to complex set four models:Horizontal homogeneous earth model, Sphere earth model, Earth-ionosphere three layer model, Earth-ionosphere five layer model. Compared the numerical results of horizontal homogeneous earth model with the theoretical results show three-dimensional electromagnetic simulation software CST can simulate electromagnetic wave propagation and distribution of electric dipole source. Then numerical simulation of electromagnetic field excited by electric dipole source in the Earth Spherical Cavity, prove CST can offer certain forward support for CSELF technology and can be used for geophysical electromagnetic exploration areas.