Research on the frequency penetration characteristics of wireless communication in coal mine goafs

At present, for fire detection in the goafs of coal mines, the main methods employed are beam tube gas analysis and optical fiber temperature measurement. These detection methods encounter difficulties in arranging protective measures for the beam tubes and optical fibers in the collapsed environment of goafs. Meanwhile, with the development of wireless communication technology in coal mines, this technology has played a significant role in specific aspects such as wireless positioning, communication, and sensing in the underground mines. However, the structure of goafs of coal mines is complex. Traditional wireless communication technology generates electromagnetic wave signals that rapidly attenuate when penetrating the media of goafs, making it difficult to achieve effective wireless communication coverage of goafs. Further research on wireless communication technology in the goafs is needed, and in-depth studies on the transmission characteristics of different frequency electromagnetic waves in the media of goafs should be conducted, and wireless through-the-ground communication systems with medium and short distance （>50 m） suitable for goafs of coal mines should be developed. Three communication systems with different working frequencies, namely very high frequency, high frequency and medium frequency, are designed and built. The attenuation characteristics of electromagnetic wave signals of different frequencies are analyzed theoretically and the actual communication system tests buried tests in the ground soil are conducted. The results show that the medium frequency communication system is consistent with the theoretical attenuation characteristic analysis results. The electromagnetic wave signal attenuation decreases with the decrease of frequency, and the actual penetration effect is the best, with the communication distance reaching up to 160 m, which is feasible for application in goafs.