Modeling and Measurement of Through-the-Earth Communication Based on ELF Magnetic Signals From Permanent Magnet Mechanical Antennas

Through-the-earth communication (TEC) technology is irreplaceable in geological exploration and mine safety communication. However, conventional TEC systems use a multiturn coil as the transmitting antenna, which occupies a large space and is less flexible. Therefore, this article trials a TEC method based on extremely low frequency (ELF) signals generated by large-volume rotating permanent magnets. This method not only detects ELF signals at large depths in the Earth because ELF signals attenuate less in consumptive media, but also allows smaller communication system size and power consumption based on mechanical antenna (MA) technology. Theoretical analysis, simulation model, and experimental verification were also established on this basis. The question of optimal frequency selection for magnetic signals on Earth with different conductivities is also discussed. The results of theory, simulation, and experimental analyses show that the TEC model proposed in this article is highly feasible and lays a foundation for the future realization of small-size TEC system devices. Finally, we placed the MA with a permanent magnet volume of $1~{\text {dm}}^{{3}}$ and the receiving antenna on both sides of the mountain to establish a frequency sweep experiment with a frequency range of 32–77 Hz and a step frequency of 5 Hz. The test results show that the optimal communication frequency of the mountain at the experimental site is 67 Hz, and thus the relevant electromagnetic parameters of the mountain at the experimental site can be deduced.