【作者】 刘鑫明；

【导师】 刘树才；

【作者基本信息】 中国矿业大学 ， 地质资源与地质工程， 2013， 博士

【摘要】 煤矿地质预测预报工作是保证矿井安全高效生产的基本环节。矿井生产受地质构造及煤层结构等因素的制约，轻则影响采掘效率、降低效益，重则威胁煤矿的安全生产甚至人员的生命。以中高频电磁波传播规律为基础的矿井无线电波透视技术作为一种矿井物探方法，通常用于探测陷落柱、火成岩侵入区、断层等地质构造，多年来在各大矿区的实际应用中取得了较好的效果。但该方法也存在着诸如理论研究滞后、探测精度低等现实问题。因此研究中高频的电磁波在煤岩介质中的传播规律，对于提高无线电波透视的精度，满足实际生产的需求具有重要的理论价值和应用价值。本文主要研究内容如下：1）以麦克斯韦方程为基础，从“源”出发，将无线电波透视系统中的环形天线等效为磁偶极子，建立球坐标系，利用格林定律并引入位函数A计算求得了环形天线辐射场的表达式，采用微分电流方法验证等效磁偶极子法计算的辐射场，并将天线辐射的球面波等效为平面波，进而建立了煤岩介质中的中高频电磁波传播规律的研究基础。2）以等效后的平面电磁波为切入点，建立平面直角坐标系，针对定点工作方式下的无线电波透视技术远端接收点相对发射点存在相对入射角度的问题，考虑电磁波脱离天线自巷道空间（空气介质）入射到煤岩介质（有耗媒质）这一过程，推导出与入射角度有关的振幅衰减常数p。验证了在入射角等于零度时，即沿z方向传播的经典振幅衰减常数与p的等价性。研究了振幅衰减常数p随入射角度、电导率、相对介电常数和电磁波工作频率之间的关系并指出线天线辐射场的初始场强振幅与入射角的正弦之间具有正比关系。3）根据全反射定律推导了理想状态下的煤岩介质产生波导的条件即煤岩折射率要小于上下围岩的折射率。利用纵向场法给出了矩形（煤与上下围岩层状沉积）波导内电磁波各分量的表达式，分析了在波导中传输的电磁波的截止波长和截止频率。指出在兆赫兹频段，长壁开采工作面中应存在H10和H20两种波导模式。得出了导体衰减常数c与频率的关系，即当工作频率接近截止频率时，导体衰减常数c剧增，随频率继续增高，导体衰减常数c逐渐减小，后又继续增大，在某一频率下有最小值。此外，当工作频率不变时，导体衰减常数c随波导尺寸的减小而增大；而介质衰减常数d主要取决于波导内所充填的介质（煤层）的特性，并与波长有关，工作波长趋于截止波长时，振幅损耗大。4）利用天线的辐射场标定并归一化初始场强，采用振幅衰减常数p、经典振幅衰减常数以及界面效应分别计算不同电阻率的陷落柱、规模不一的火成岩以及倾角较大且存在组合关系的多重断层模型的电磁波衰减值。基于直射线理论进行场强衰减法成像，使用代数重建算法（ART）对不同振幅衰减常数计算得到的衰减值分别进行相对和绝对层析成像及图像重建工作。分析不同振幅衰减常数、不同成像方式以及构造的物性变化对电磁波吸收的影响，结果表明：（1）对于绝对层析成像方式而言，采用振幅衰减常数p时，构造的横向位置定位较为准确、衰减值更为明显；对于相对层析成像方式，采用振幅衰减常数p时冗余构造少，因此修正后的振幅衰减常数p更适合于相对层析成像方式。（2）绝对层析成像方式在纵向上将构造“扩大”的趋势明显；相对层析成像方式有将构造“缩小”的趋势，易造成真实构造的局部缺失。（3）低阻介质计算得到的衰减值要大于高阻介质，对异常构造的定位也要优于高阻介质，更利于构造的地质解释，探测高阻构造时，使用衰减常数p和绝对衰减层析成像方式效果要更好。（4）对于较大型的构造，以本文为例，当模型规模为30m40m时，无线电波透视结果有较好的反应，随着模型减小为15m20m时，仅对构造的横向位置定位精度尚可满足需求。（5）对于断层构造而言，当仅存在单一断层构造时，尽管断层面近垂直巷道，但断层的实际位置和走向基本可以准确判定；而存在组合关系的多重断层构造时，采用任何一种振幅衰减常数的无线电波透视方法效果均不明显。综合分析比较两种振幅衰减常数和成像方式的效果图可知，振幅衰减常数p和绝对衰减层析成像方式效果要优于振幅衰减常数和相对衰减层析成像方式。最后通过无线电磁波透视技术探测工作面内隐伏构造的三个实例，从实用性方面进一步说明了采用振幅衰减常数p的无线电磁波层析成像技术可以在一定程度上提高预测预报采煤工作面内隐伏构造的准确性。更多还原

【Abstract】 Geological forecasting work is the basic link in coal mine production. Geology andcoal seam structure factors influence the exploitation efficiency, and even threaten lives.Radio wave perspective as a coal mine geophysical method can effectively detect thegeological structures. But there are also issues in this method. Therefore, study thepropagation of electromagnetic wave in the coal-rock medium has important theoreticaland practical value. The main contents of the thesis are as follows:1) Based on Maxwell equations and from the "source", keep the linear loop antenna asa magnetic dipole, and established spherical coordinate system. Then computation theradiation field by make use of the Green theorem and the potential functionA. Using thedifferential current method to verify the equivalent magnetic dipole radiation field.Spherical wave equivalent to the plane wave, and established the basis for further study ofthe propagation rule of electromagnetic wave.2) When adopted a plane rectangular coordinate system and fixed point mode, remotereceiver point relative to emission point had a problem of incident angle. Thought aboutelectromagnetic wave from roadway space (air medium) incident into coal-rock media(lossy medium), calculated the attenuation constantpthat involved incident angle, andverified the equivalence of the classic attenuation constant andpwhen the incident angleequal to zero degree. The relationship between attenuation constantpand incident angle,conductivity, relative permittivity and the working frequency were presented. Also therelationship between incident angle and initial field intensity was discussed.3) Based on the total reflection law, when the refractive index of the coal is less thanthe surrounding rock’s the waveguide phenomenon was produced Then the expression ofeach component of the electromagnetic wave in the rectangular waveguide were given byusing longitudinal field method. Two kinds of waveguide modesH10andH20existed in thelong-wall mining working face. The relationship between attenuation constant ofconductor and working frequency were discussed, and conductor attenuationconstant csharp increasing when working frequency approached the cut-off frequency,with the working frequency increasing the cdecreases gradually and then increasing withthe working frequency continued rising and at a certain frequency chad an minimumvalue. When working frequency was constant, cincreased with the waveguide dimensionsdecreased. While attenuation constant dof medium depended on the characteristics of themedium which filling the waveguide and working wavelength, the amplitudes loss largerwith working wavelength approached cut-off wavelength. 4) The initial electric field intensity were calibrated and normalized which radiated bythe antenna. Then various models’ electromagnetic wave attenuation value wererespectively calculated using decay constant p, classic decay constant and interfaceeffect. Based on direct ray theory, the imaging of electromagnetic field intensityattenuation was completed by using Algebra Reconstruction Technology (ART). Andcompleted two different kinds of tomography imaging for different decay constants.Analysis the electromagnetic waves absorption of different decay constants, differenttomography imaging methods, and structures with different electrical resistivity, Theresults shown that,(1) For absolute tomography imaging, horizontal location was moreaccurate and decay value was more obvious by using decay constant p, but for relativetomography imaging, there was less redundant structures. Therefore, the constant p was moresuitable for relative tomography imaging.(2) For absolute tomography imaging, it waseasily to enlarge the range in vertical direction. While for relatively tomography imaging it waseasily to shrink the range in horizontal direction, and conduced losing real structure.(3) Theattenuation value of low resistivity model is greater than the high resistivity model, and thelocation was also better.(4) For3040mmodel, it got a good result, but as the dimension wasreduced to1520m, only the horizontal location accuracy can still meet the need.(5) When singlefault with vertical plane existed, the actual location and direction can be accurately confirmed. Whenmultiple faults existed. the effect was not obvious.Comprehensive analysis and comparison two attenuation constants and the imagingmethod, it can be seen that the attenuation constantpand absolute tomography method areeven better. Finally, three experiments and practical perspecting work were done by usingelectromagnetic perspective technology to detect the concealed structures which in thework face. Accuracy and usefulness were credible by using attenuation constantpinelectromagnetic tomography technique.更多还原