Safety power analysis of metal oscillator structure in mine 5G radiation field
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摘要:
煤矿井下存在瓦斯等易燃易爆气体，5G无线通信系统基站天线辐射出的电磁波被井下金属结构吸收，在金属结构断点处产生放电火花，当电火花能量达到瓦斯气体的最小点火能时可能发生爆炸，限制了5G技术在煤矿井下的应用。为了评估5G无线通信基站射频功率的安全性，通过分析金属结构耦合电磁波的方式，得到射频功率、最大辐射场强与距离的关系；以最小点火能为安全判定标准，得出天线负载的接收功率小于2.625 W时，可确保不会引起瓦斯爆炸；分析得出煤矿井下应优先选择700 MHz作为5G工作频段；通过分析方向性系数，得出应选择臂长与波长比为0.65的对称振子天线金属结构进行研究，对称振子天线金属结构安全电场强度为202.9 V/m，最小安全距离为0.2 m。仿真结果表明：在距离发射天线小于0.2 m的区域电场分布极不均匀，在距离发射天线大于0.2 m的区域电场分布较均匀；在距离发射天线大于0.2 m的区域导致瓦斯爆炸的最小射频功率为27.45 W。
Abstract:There are flammable and explosive gases such as gas underground in coal mines. The electromagnetic waves radiated by the 5G wireless communication system base station antenna are absorbed by the underground metal structure, generating discharge sparks at the metal structure breakpoint. When the energy of the electric spark reaches the minimum ignition energy of gas, an explosion may occur, which limits the application of 5G technology in coal mines. In order to evaluate the safety of the RF power of 5G wireless communication base stations, the relationship between RF power, maximum radiation field strength, and distance is obtained by analyzing the coupling of electromagnetic waves with metal structures. Using the minimum ignition energy as the safety criterion, it can be concluded that when the receiving power of the antenna load is less than 2.625 W, it can ensure that it will not cause gas explosions. The analysis shows that 700 MHz should be given priority as the 5G working frequency band in coal mines underground. By analyzing the directional coefficient, it is concluded that a symmetrical oscillator antenna metal structure with an arm length to wavelength ratio of 0.65 should be chosen for research. The safe electric field strength of the symmetrical oscillator antenna metal structure is 202.9 V/m, and the minimum safe distance is 0.2 m. The simulation results show that the electric field distribution is extremely uneven in areas less than 0.2 m away from the transmitting antenna. The electric field distribution is relatively even in areas more than 0.2 m away from the transmitting antenna. The minimum radio frequency power that causes a gas explosion in an area greater than 0.2 m from the transmitting antenna is 27.45 W.
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图 1 金属结构耦合电磁波的过程
Figure 1. The process of coupling electromagnetic waves with metal structures
图 5 电场强度与发射天线距离的关系
Figure 5. The relationship between electric field strength and transmitting antenna distance
表 1 仿真参数设置
Table 1. Simulation parameter settings
项目 参数 射频功率/W 6，24，48 电磁波频率/MHz 700 巷道厚度/m 0.1 巷道材料 混凝土 电磁波极化方式 垂直极化 巷道相对介电常数 5.31 巷道电导率/（S·m−1） 0.066 
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