Analysis of electromagnetic wave energy safety of underground metal structure near-field coupled large loop transmitting antenna

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.