Objective and Methods Ultra-wideband (UWB) radars can transmit electromagnetic waves that penetrate coal and rock media, thereby addressing the challenge of detecting and localizing personnel trapped in shielding environments during mine collapse. However, key parameters for UWB radar detection are difficult to determine due to complex mine environments, diverse media, and unclear dispersion characteristics. To deal with this issue, this study determined the frequency-dependent dielectric properties of various coal and rock media, as well as human tissues, through experiments and fitting. In combination with actual rescue scenarios, this study established the electromagnetic equivalent model of shielding environments in coal mines. Through numerical simulations using GprMax, this study determined the optimal pulse waveform function, center frequencies, and frequency ranges of electromagnetic waves penetrating coals, rocks, and coal-rock mixed media for human body detection.
Results and Conclusions Under frequencies ranging from 100 MHz to 1 GHz, coals, rocks, and human tissues exhibited progressively decreasing relative dielectric constants and gradually increasing conductivities as the frequency increased. In the case of identical frequencies, the relative dielectric constants and conductivities of human tissues were 1−2 orders of magnitude higher than those of coals and rocks. Comparison of B-scans, A-scans, and the amplitudes of echoes from the human body among Gaussian, Ricker, Sine, and Cosine pulse waveforms in coals, rocks, and coal-rock mixed media reveals that Ricker was the optimal waveform for life detection. Furthermore, comparison and analysis of the amplitudes of the echoes of Ricker waves from the human body under 400 MHz, 500 MHz, 600 MHz, 800 MHz, and 1 000 MHz reveals that the amplitudes decreased with increasing frequency for media with high and medium conductivities, while the opposite is true for low-conductivity media. This finding suggests the medium conductivity represents a key factor influencing the amplitude of echoes from the human body. The optimal center frequencies for media with high, medium, and low conductivities were determined at 400 MHz, 400 MHz, and 800 MHz, respectively, corresponding to frequency ranges of 400‒600 MHz, 400‒800 MHz, and 600‒1 000 MHz. Based on these optimal parameters, a UWB radar device for life detection was designed and manufactured. Using a shielding environment of non-caking coal, established in combination with actual mine rescue, the applicability of the optimal detection parameters was verified through experiments on the UWB radar detection of a single moving person. Overall, the results of this study provide a reference for basic research and equipment R&D related to UWB radar technology for life detection in mine rescue.
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