Research on the variation law of coal electrical parameters under different temperatures and detection frequencies
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摘要: 现有针对煤电性参数影响因素的研究大多为在固定频率或低频率、高温条件下进行的,缺少对超宽带频率和常温条件下煤电性参数影响因素的研究,这对煤电性参数的影响因素研究有一定局限性。针对该问题,为了研究煤电性参数对不同条件下超宽带雷达波井下探测频段选择的影响,利用Concept-80超宽带介电谱测试系统,在0~80 ℃温度和500~1 000 MHz探测频率下测试不同变质程度煤(褐煤、长焰煤和贫瘦煤)的相对介电常数、电导率和损耗角正切值的大小并分析其变化规律。分析结果表明:煤的相对介电常数随着煤变质程度增大而增大,煤的电导率和损耗角正切值随着煤变质程度增大而减小;不同变质程度煤样的相对介电常数均随测试频率的增加而先减小、后增大、再减小,相对介电常数与温度呈正相关关系;电导率与测试频率和温度均呈正相关关系;损耗角正切值与温度呈正相关关系,但测试频率不能很好地反映损耗角正切值的变化。根据3种电性参数在不同温度与探测频率下的变化规律,综合对比3种电性参数对超宽带雷达波在煤中传输的影响,得出在0~80 ℃条件下使用500~1 000 MHz超宽带雷达波穿透煤体进行探测时选择550~650 MHz频率为最佳,且探测频率的选择应随着温度升高而降低。该结论可为在不同条件下超宽带雷达波井下探测频段的选择提供参考。Abstract: Most of the existing research on the influencing factors of coal electrical parameters are carried out under fixed frequency or low frequency and high temperature conditions. There is a lack of research on the influencing factors of coal electrical parameters under ultra-wideband frequency and normal temperature conditions. Therefore, there are certain limitations in the research on the influencing factors of coal electrical parameters. To address this problem, in order to study the influence of coal electrical parameters on the selection of ultra-wideband radar wave mine detection frequency band under different conditions, the Concept-80 ultra-wideband dielectric spectrum test system is applied. The system is set to detect the relative permittivity, electrical conductivity and loss angle tangent values of coals with different metamorphic degrees (lignite, long-flame coal and lean coal) at 0-80 ℃ and 500-1 000 MHz detection frequency and analyze their variation laws. The analysis results show that the relative permittivity of coal increases with the increase of coal metamorphic degrees, and the electrical conductivity and loss angle tangent values of coals decrease with the increase of coal metamorphic degrees. The relative permittivity of coal samples with different metamorphic degrees decreases, then increases and decreases again with the increase of detection frequency, and the relative permittivity is positively correlated with temperature. The electrical conductivity is positively correlated with both detection frequency and temperature. The loss angle tangent value is positively correlated with temperature. However, the detection frequency does not reflect the variation of loss angle tangent value well. Based on the variation law of three electrical parameters at different temperatures and detection frequencies, and the comprehensive comparison of influence of three electrical parameters on the transmission of ultra-wideband radar waves in coal, it is pointed out that the frequency of 550-650 MHz performs best when using 500-1 000 MHz ultra-wideband radar waves to penetrate the coal body for detection at 0-80 ℃, and the detection frequency should decrease as the temperature increases. The conclusion of this study can provide a reference for the selection of ultra-wideband radar wave mine detection frequency band under different conditions.
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