It is vital to understand the electromagnetic radiation’s time-frequency characteristics in the process of coal and rock failure with different joint angles in order to reveal the generation mechanism of the electromagnetic radiation (EMR) and improve the accuracy of EMR early warning. We studied the time-frequency characteristics of EMR signals of coal samples with different joint angles. The study finds that, (1) with the increase of joint angle, the failure time and peak load of samples decrease first and increase later, and the postpeak failure time decreases gradually. The EMR counts’ peak value showed a slow rise, a sharp rise, and a slow rise in the three intervals of α = 0° to 45°, 45° to 60°, and 60° to 90°, respectively. The accumulated EMR counts showed a steady upward trend. The duration of the EMR waveform, the dominant frequency of the EMR, and the peak number of the frequency spectrum of coal samples are on the rise. (2) As the joint angle increases, the samples’ failure mode changes from the stage fracture dominated by tension cracks to the rapid fracture with the coexistence of shear and tension cracks and finally to the burst fracture which produces a large number of fragments. This is also the main reason for the difference of the EMR generation mechanism and the signal of samples with different joint angles. (3) According to the experimental results, we established the modified formulas for calculating the EMR threshold value and deviation of coal and rock with joints under different stress environments and revealed that the longer the EMR waveform duration, the higher the dominant frequency, and the more the number of spectrum peaks, the greater the burst risk of coal and rock.

中文翻译：

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不同节理角煤体电磁辐射的时频特征及影响机制

了解不同节理角煤岩破坏过程中电磁辐射的时频特性对于揭示电磁辐射的产生机制，提高电磁辐射预警的准确性至关重要。研究了不同关节角煤样的EMR信号时频特性。研究发现，（1）随着接头角度的增加，样品的破坏时间和峰值载荷先减少后增加，峰值后破坏时间逐渐减少。EMR计数的峰值在α的三个区间呈现缓慢上升、急剧上升和缓慢上升 = 分别为 0° 至 45°、45° 至 60° 和 60° 至 90°。累积的 EMR 计数呈稳步上升趋势。EMR 波形的持续时间、EMR 的主导频率和煤样频谱的峰值数呈上升趋势。(2)随着接头角度的增加，试样的破坏模式由以拉裂为主的阶段断裂转变为剪切与拉裂并存的快速断裂，最后转变为产生大量碎片的爆裂断裂。这也是造成EMR产生机制和不同关节角度样本信号不同的主要原因。(3) 根据实验结果，