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The electromagnetic wave energy emitted by wireless communication equipment in coal mines can be coupled and absorbed by surrounding metal structures, which poses a risk of igniting explosive gases in the mine. The existing research on the safety of underground metal structure coupled electromagnetic waves only focuses on the analysis of the energy of metal structure equivalent impedance model coupled electromagnetic waves. It lacks research on the energy storage process of metal structure coupled electromagnetic wave energy accumulated over time. In order to solve the above problems, an equivalent energy storage structure model suitable for studying the coupling-accumulation-release electromagnetic wave energy of metal structures is proposed, namely the metal structure equivalent capacitive energy storage model and the metal structure equivalent inductive energy storage model. Firstly, by using a low attenuation transmission line model, the relationship between the output power of the transmitting antenna, the distance between the transmitting antenna and the metal structure, and the induced voltage at the receiving end is derived. Secondly, an equivalent energy storage model of metal structure is established. The mathematical relationship between the receiving end parameters and the discharge spark energy is derived. The influence of the receiving end parameters on the discharge spark energy is analyzed. Finally, the mathematical relationship between the output power of the transmitting antenna, the distance between the transmitting antenna and the metal structure, and the discharge spark energy is derived by analyzing the relationship between the induced voltage at the receiving end and the effective value of the induced voltage. The influence of the output power of the transmitting antenna and the distance between the transmitting antenna and the metal structure on the discharge spark energy is analyzed. The theoretical reference safety points of the equivalent energy storage models of the two metal structures are given under the condition of other parameters being determined. The simulation results show the following points. ① For the equivalent capacitive energy storage model of metal structures, the discharge spark energy increases with the increase of the effective values of the equivalent energy storage capacitor and the induced voltage at the receiving end, and the safety point shifts to the left. The safety requirements for the effective values of the equivalent energy storage capacitor and the induced voltage at the receiving end become stricter. ② The energy of the discharge spark increases with the increase of the transmitting antenna power, and decreases with the increase of the distance between the transmitting antenna and the metal structure. The theoretical reference safety point of the equivalent capacitive energy storage model of the metal structure is obtained. ③ For the equivalent inductive energy storage model of metal structures, the discharge spark energy increases with the increase of the effective values of the equivalent energy storage inductance and the induced voltage at the receiving end, and the safety point shifts to the left. The safety requirements for the effective values of the equivalent energy storage inductance and the induced voltage at the receiving end become stricter. ④ The energy of the discharge spark increases with the increase of the transmitting antenna power, and decreases with the increase of the distance between the transmitting antenna and the metal structure. The theoretical reference safety point of the equivalent inductive energy storage model of the metal structure is obtained. ⑤ Comparing the theoretical reference safety points of two metal structure energy storage models, it is concluded that the danger of the metal structure equivalent capacitive energy storage model is much greater than that of the metal structure equivalent inductive energy storage model.

When the metal structures distributed in the underground roadway are in the near-field of the large loop transmitting antenna, they will couple the electromagnetic wave energy of the large loop transmitting antenna. Once the metal structure has a breakpoint and friction occurs, it may produce friction discharge spark and ignite gas. This poses a threat to the safety of coal mine. In order to solve this problem, the safety of electromagnetic wave energy of underground metal structure near-field coupled large loop transmitting antenna is analyzed from two aspects of near-field coupling risk coefficient and safe distance. By establishing the equivalent circuit of electromagnetic wave energy of metal structure near-field coupled large loop transmitting antenna, the expressions of near-field coupling risk coefficient and safe distance between metal structure and large loop transmitting antenna are derived. The influence of the radius of the large loop transmitting antenna, the radius of the equivalent receiving coil of the metal structure, the friction discharge spark load and the distance between the metal structure and the large loop transmitting antenna on the near-field coupling risk coefficient and the safe distance are analyzed. The simulation results show that the near-field coupling risk coefficient increases slightly at first and then decreases slightly or increases all the time with the increase of the radius of the large loop transmitting antenna. Under certain conditions, the friction discharge spark load can make the near-field coupling risk coefficient reach the peak value. When the radius of the large loop transmitting antenna is greater than or equal to the radius of the equivalent receiving coil of the metal structure, the near-field coupling risk coefficient at the peak value may exceed the critical value 0.46 of the near-field coupling risk coefficient. This may cause danger. When the radius of the large loop transmitting antenna is smaller than the radius of equivalent receiving coil of the metal structure, the near-field coupling risk coefficient at the peak value is less than the critical value 0.46 in most cases. This will not cause danger in most cases. Under certain conditions, the radius of the large loop transmitting antenna can make the near-field coupling risk coefficient reach the peak value. The near-field coupling risk coefficient at the peak value first increases and then decreases with the increase of the radius of equivalent receiving coil of the metal structure. It is more likely to exceed the critical value 0.46 of the near-field coupling risk coefficient, which is likely to cause danger in the gas environment. The safe distance increases with the increase of the radius of the large loop transmitting antenna. The safety of the electromagnetic wave energy on the friction discharge spark load decreases with the increase of the radius of the large loop transmitting antenna. When the radius of the large loop transmitting antenna is greater than or equal to the radius of the equivalent receiving coil of the metal structure, the safe distance increases with the increase of the radius of the equivalent receiving coil of the metal structure. The safety of the electromagnetic wave energy on the friction discharge spark load decreases with the increase of the radius of the equivalent receiving coil of the metal structure. When the radius of the large loop transmitting antenna is smaller than the radius of the equivalent receiving coil of the metal structure, the safe distance first increases slowly and then decreases with the increase of the radius of the equivalent receiving coil of the metal structure. The safety of the electromagnetic wave energy on the friction discharge spark load first decreases and then increases with the increase of the radius of the equivalent receiving coil of the metal structure.

The metal structures distributed in underground coal mine roadways can be equivalent to the receiving antenna to absorb electromagnetic wave energy and release the energy in the form of discharge sparks under specific conditions. The accumulated energy has the risk of igniting explosive gas. In order to solve the problem, the conditions of ignition of gas by discharge spark when the metal structure is equivalent to the receiving antenna are analyzed, and the calculation expression of the maximum power that can be absorbed by the discharge spark as load is derived. It is concluded that when the gas volume fraction is 8.5% and the metal structure is equivalent to the receiving antenna, the maximum allowable power that the discharge spark will not ignite the gas is 2.8 W. Wireless Insite electromagnetic simulation software is used to simulate the maximum power that can be absorbed by the discharge spark as load under different working conditions of the radio frequency equipment. The results show that the greater the output power of radio frequency equipment, the lower the working frequency of radio frequency equipment, the closer the metal structure to radio frequency equipment, the greater the load maximum power that can be absorbed, the greater the potential safety hazard of gas ignited by discharge spark. When the minimum safety distance between the transmitting antenna of the radio frequency equipment and the metal structure is 0.1 m, the discharge sparks generated by the radio frequency electromagnetic radiation energy in the frequency band below 800 MHz of the radio frequency equipment have the possibility of igniting gas. The discharge sparks generated by the radio frequency electromagnetic radiation energy in the frequency band above 890 MHz of the radio frequency equipment in the metal structure are intrinsically safe and will not ignite gas.