## 2 Related Work  
In the early 20 th century, the famous German physicists [PERSON] and [PERSON] carried out a large number of theoretical analyses and long-term mathematical formula derivations, and finally described the theoretical knowledge of through-the-ground wireless communication in detail, which is based on the assumption of conductive and semi-conductive media. It was proposed on the premise of having uniform electrical properties. In 1930, the U.S. Bureau of Mines set up a research group. Through a large number of experiments, the research group tried to use different sizes and shapes of loop antennas and radio waves of different frequencies, and they finally successfully carried out a 200 m wireless through-the-ground communication experiment. An engineer in South Africa successfully developed the first true penetrating communication system in 1949. The operating frequency of the system was 300 kHz. It also used a loop antenna as a transceiver antenna and its electromagnetic waves to successfully achieve an effective distance of 300 m of penetrating information communication. In 1974, the United States proposed and published a research report entitled \"Electromagnetic Communication Through Conductive Strata\", in which the authors reported that they achieved reliable information transmission during underground nuclear explosions via electromagnetic signals through the stratum. Then, the U.S. Bureau of Mines developed an electromagnetic positioning system for locating miners trapped in mines and planned to develop a transmitter with low transmission power and a transceiver with high sensitivity and that was lightweight, which could be attached to the miner. The receiver and the transmitter could maintain communication between the up-hole and the down-hole by penetrating the ground. The 722 nd Research Institute of the CSIC is a high-tech engineering technology research institute under the CSIC that specializes in equipment research, manufacturing, and the development and design of communication electronics engineering. The institute is heavily involved with the development and design of integrated communication systems and communication equipment. The wireless chamber emergency rescue communication system is widely used in the field of wireless information transmission under complex geological conditions in coal mines as well as in other mines. In 2013, a through-the-ground communication system was independently developed by the Institute, and a successful experiment was carried out in a mine in Xinzheng, Henan Province, at a depth of 469 m [8; 9; 10; 11; 12; 13; 14; 15; 16]. In 2013, the Air Force Engineering University conducted a study on the miniaturized antenna of the ground-penetrating information transmission system. When the input power is 0.25 W, the effective transmission distance of the antenna is 30 m, and the maximum transmission distance is 180 m. In 2015, Taiyuan University of Technology conducted research on the propagation characteristics of very low frequency electromagnetic waves at the interface between a mine roadway and ore bed, in the ore bed, and between the ore bed and ground, and established a propagation model of very low frequency electromagnetic waves in the ore bed. In 2016, Beijing Jiaotong University conducted a study on the propagation and attenuation characteristics of electromagnetic waves in the layered media channel and established a layered media model and calculation model. In 2016, Beijing University of Science and Technology conducted research on a very low frequency-coupled information transmission system based on ring antennas and coupled waveguides, proposed an active noise reduction method based on dual-ring antennas, which can achieve 323 m of two-way