Experimental study on microwave propagation characteristics of different coal-gangue mixtures
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摘要:
煤矸识别问题是煤炭行业内长期未能有效解决的技术难题之一。通过分析现有煤矸识别方法的特点及局限性，探讨基于微波探测技术进行煤矸识别的可行性。首先，开展了对不同煤种和矸石的电磁参数测量分析，为后续的样本测试结果分析提供依据。然后，为探讨煤矸尺寸参数对微波传播的影响，开展了不同厚度、不同截面积的煤矸介质样本对不同频段电磁波的传播规律研究。由于煤矸混合物是由煤、矸石和空气组成的多尺度介质，其体积不等、形状各异，且空间分布及混合形式复杂多变，在微波照射区域内的散射效应非常复杂，导致电磁波在不同煤矸混合物中的传播特性具有明显的差异性。最后，为探究煤矸不同介质混合状态流的微波传播特性变化规律，开展了不同微波频段、不同煤矸粒度、不同含矸率工况下的煤矸混合物微波探测试验。结果表明：煤矸介质的电磁参数、厚度和截面积对微波在介质中的传播规律有明显影响；不同的粒度和含矸率对微波在煤矸混合物的传播规律有一定的影响。当频率大于4 GHz的微波照射在煤矸混合物时，粒度的增大会使回波损耗S11、插入损耗S21强度值和时域透射波O21信号幅值逐渐增大。当混合介质中煤和矸石的电磁参数差异较大时，在频率大于3.5 GHz后，粒度的增大使S21强度由−35.3 dB降低至−38.2 dB，O21信号幅值由1.6 mV减小至1.26 mV，且具有一定的时延特性。通过试验分析可以掌握敏感频点下透射波信号强度值、时域透射波信号幅值或透射波信号时延等特征的差异性，为放顶煤开采的煤矸精准识别提供一种新的思路和方法。
Abstract:The problem of coal-gangue identification is one of the technical problems that have not been effectively solved for a long time in the coal industry. By analyzing the characteristics and limitations of existing coal-gangue identification methods, the feasibility of coal-gangue identification based on microwave detection technology is discussed. Firstly, the electromagnetic parameters of different coals and gangues are measured and analyzed to provide a basis for the subsequent analysis of sample test results. Then, in order to explore the influence of coal gangue size parameters on microwave propagation, the propagation law of coal gangue dielectric samples with different thickness and cross-sectional area on different frequency bands is studied. Because the coal-gangue mixture is a multi-scale medium composed of coal, gangue and air, the volume and shape are different, and the spatial distribution and mixing form are complex and changeable. The scattering effect in the microwave irradiation area is very complex, resulting in obvious differences in the transmission characteristics of electromagnetic waves in different coal-gangue mixtures. Finally, in order to explore the variation law of microwave propagation characteristics in different coal-gangue media, some microwave detection experiments of coal-gangue mixture under different microwave frequency bands, different particle sizes and different gangue contents are carried out. The results show that: the electromagnetic parameters, thickness and sectional area have obvious influence on the propagation law of microwave in the media. Different particle size and gangue rate have certain influence on microwave propagation in coal-gangue mixture. When microwave with frequency greater than 4 GHz irradiates the coal gangue mixture, the increase of particle size will gradually increase the intensity values ofS11 andS21 and the amplitude ofO21 signal. When the electromagnetic parameters of coal and gangue in the mixed medium are quite different, after the frequency is greater than 3.5 GHz, the increase of particle size reduces theS21 intensity from −35.3 dB to −38.2 dB, and theO21 signal amplitude from 1.6 mV to 1.26 mV, with certain time delay characteristics. Through the experimental analysis, the differences of the transmitted wave signal intensity value, the time-domain transmitted wave signal amplitude and the transmitted wave signal delay at the sensitive frequency points can be mastered, so as to provide a new idea and method for accurate identification of coal and gangue in top coal caving face.
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图 4 电磁波在煤矸试样中的反射与传输情况
Figure 4. Reflection and transmission of electromagnetic wave in coal-gangue sample
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图 5 不同煤矸试样的电磁参数测量结果
Figure 5. Measurement results of electromagnetic parameters of different coal-gangue samples
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图 7 不同煤矸介质的O21时域波形
Figure 7. Time domain waveform of O21 with different coal-gangue medium
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图 13 不同粒度下煤矸混合物的S11曲线
Figure 13. S11 curves of coal-gangue mixtures with different particle sizes
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图 14 不同粒度下煤矸混合物的S21曲线
Figure 14. S21 curves of coal-gangue mixtures with different particle sizes
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图 15 不同粒度下煤矸混合物的O21曲线
Figure 15. O21 curves of coal-gangue mixtures with different particle sizes
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图 17 煤矸混合物中不同含矸率的S11曲线
Figure 17. S11 curves with different gangue ratios in coal-gangue mixture
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图 18 煤矸混合物中不同含矸率的S21曲线
Figure 18. S21 curves with different gangue ratios in coal-gangue mixture
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图 19 3.5 GHz处不同煤种中不同含矸率的信号强度
Figure 19. Signal strength at different gangue-containing rates at 3.5 GHz
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图 20 煤矸混合物中不同含矸率的O21曲线
Figure 20. O21 curves with different gangue ratios in coal-gangue mixture
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图 21 12.4 ns左右不同含矸率O21曲线峰值点特征
Figure 21. Characteristics of the peak point of t he O21 curve with different gangue ratios around 12.4 ns
表 1 煤和矸石的微波探测试验方案
Table 1 Experimental scheme of coal-gangue microwave detection
试验参数 煤样类别 无烟煤 肥煤 工作频率/GHz 1～8 试样厚度/cm 10 20 40 试样截面积/（cm×cm） 10×10 20×20 40×40 煤矸粒度/cm 3～5 8～12 15～20 含矸率（矸石占比）/% 0 10 20 30 40 50 
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表 2 不同粒度的微波照射参数
Table 2 Microwave irradiation parameters of different particle sizes
编号 质量占比/% 煤类别 粒度/cm 频率/GHz 煤块 矸石 1 60 30 无烟煤 3～5 1～8 2 60 30 无烟煤 8～10 1～8 3 60 30 无烟煤 15～20 1～8
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表 3 不同含矸率的微波照射参数
Table 3 Microwave irradiation parameters of different rate of gangue
编号 质量占比/% 煤类别 粒度/cm 频率/GHz 煤块 矸石 1 90 0 无烟煤 8～12 1～8 2 80 10 3 70 20 4 60 30 5 50 40 6 40 50 7 90 0 烟煤 8 80 10 9 70 20 10 60 30 11 50 40 12 40 50
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