中文摘要：

针对大回线源中心装置在回线内场非中心位置处场点响应表达式复杂,视电阻率计算困难,只能套用中心回线装置计算公式,导致解释精度下降问题,给出了圆回线的响应公式。提出对发射回线沿边框进行电偶极子源分解,通过对各个边框的偶极子源产生的响应进行叠加;讨论了圆回线与圆内接多边形发射回线的等效性问题;完成了大回线内任意点的场值计算,并对基于电偶极子近似的大回线内场的分布特征进行了分析,得出了大回线源内非中心点探测的可行性结论。研究成果具有理论价值和实际指导意义。

英文摘要：

In order to realize the aim of rapid,efficient and large-depth exploration,we utilize the in-loop device with large rectangular transmitter in transient electromagnetic exploration.That is,the TEM（transient electromagnetic method） detects the target in some range of the loop.However,the response equation of the non-central point in the loop is complex and does not have the analytical resolutions,leading to the difficulty to get the apparent resistivity.In most circumstances,we use the calculation equation of in-loop to calculate the non-central point,leading to the decrease of the interpretation accuracy.This paper gives the response equation of the circular loop and separates the transmitting loop into electric dipoles.Then,we discuss the superposition response from the dipole and equivalence between the circular loop and inscribed polygon,calculate the response value of any point in the loop and analyze the distribution characteristic of large-loop based on the electric dipole approximation.At last,we realize the conclusion that observation at the non-central point in the large-loop is feasible,which has the theory and application importance.