Radiation Safety Analysis of Metasurface Antennas in Underground Space Electromagnetic Environments

To improve the quality of wireless communication in underground spaces, this study designs a metasurface antenna based on a circular ring structure. The antenna operates in the 4.717～5.206 GHz frequency band, with a bandwidth of 489 MHz and a peak gain of 9.7 dBi. The distributions of electric field strength and received power for both the metasurface antenna and a conventional antenna are comparatively analyzed in above-ground and underground environments. Furthermore, the electromagnetic exposure safety of the human body in these environments is investigated. The results demonstrate that in above-ground environments, the metasurface antenna increases the maximum electric field strength by 67% and the peak received power by 12.24 dBm, providing broader coverage. In underground environments, it enhances the maximum electric field strength by 263.1% and the peak received power by 11.62 dBm, leading to a more uniform signal distribution. The average signal coverage area under specific thresholds is improved by 5.66% on the second above-ground floor and 9.25% on the second underground floor, respectively. Additionally, under metasurface antenna radiation, the peak electric field strength on the first underground floor reaches 3.254 V/m, where the maximum 10 g averaged Specific Absorption Rate (SAR) for the human body is only 4.433×10-6 W/kg, far below the public exposure limits specified by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). In summary, the proposed metasurface antenna effectively overcomes the rapid attenuation of wireless signals in underground spaces, enhances communication coverage, and ensures the safety of the electromagnetic environment, providing a new perspective for optimizing wireless communication deployment in enclosed underground areas.