偶极子假设引起的大回线源瞬变电磁响应偏差分析  

Theoretical study on the errors caused by dipole hypothesis of large-loop TEM response

作　　者：薛国强[1] 闫述[2] 周楠楠[1] 

机构地区：[1]中国科学院矿产资源研究重点实验室、中国科学院地质与地球物理研究所,北京100029 [2]江苏大学计算机科学与通信工程学院,江苏镇江212013

出　　处：《地球物理学报》2011年第9期2389-2396,共8页Chinese Journal of Geophysics

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-YW-Q04-07);国家自然科学重点基金(41030750);国家自然科学基金项目(474090)资助

摘　　要：偶极子假设下的场点近似解与场点的瞬变电磁精确解存在一定的误差,文中对偶极子假设引起的误差进行了探索性研究.首先分析了由恒定电流偶极子公式"比拟"出的谐变偶极子位函数解.分别计算了静态场中磁偶极子和电偶极子的近似解与各自对应的未做偶极子假设的电流环和载流导线的精确解之间的误差值,然后分析了谐变偶极子微元与点电荷微元的误差.结果表明,在发射回线内,均不满足偶极子的条件,由此造成的解析表达式的误差不可忽略.为此探讨了以时变点电荷微元作为解析求解基本单元的可行性,以时变点电荷假设代替偶极子假设,将时变点电荷解直接"比拟"到时域场中,给出了时间域瞬变电磁场的推迟矢量位函数,为进一步研究时变点电荷微元假设下的精确解、直接时域求解瞬变场问题探索了新方法.There is some error between field approximate solution and loop-source exact solutions. In this paper, the error caused by dipole approximation is researched. The vector and scalar potential function was analyzed by ＂matching＂ the result of constant current field to TEM response. The error between dipole approximate solution and loop-source exact solutions of magnetic dipole source and electric dipole source was calculated in the condition of static field. Then, we analyzed the error between harmonic dipole and point charge. We draw the conclusion that the condition of dipole is not met in the loop and the calculation error can not be omitted. After that, we discuss over the ability of using transient point charge as the basic solution. Based on the theory that time-varying point electric charge can transmit electromagnetic wave, it is found that point charge infinitesimal instead of dipole infinitesimal is the smallest unit. This paper gives the important idea of ＂matching＂ the study result of electrostatic field point charge to the result of time-domain field. After the analysis of possibility of point charge infinitesimal hypothesis, and ＂matching＂ the solution of point charge infinitesimal in microwave antenna theory to time domain electromagnetic field, the Postpone vector Potential function of pointcharge infinitesimal is obtained at last which makes the foundation for the studying of the exact solution based on the point charge and searching for the direct transient-field solution.

关 键 词：大回线源瞬变电磁法 中心回线 大定源回线 偶极子微元 点电荷微元 

分 类 号：P631[天文地球—地质矿产勘探]