激发极化观测中电磁耦合的时间特性

Time characteristics of EM coupling in induced polarization

为了克服激发极化观测中经常遇到的电磁耦合干扰,以往研究大多基于电磁耦合的频率特点.本文从电偶极子电磁耦合的基本公式出发,借助拉普拉斯变换和数值积分,着重研究了电磁耦合的时间历程及特点.研究表明,在足够长时间的矩形电流激励下,偶极装置电磁耦合的响应电位差表现为矩形激励电流开通时的上升斜坡和关断时的下降斜坡,并且使电磁信号到达的时间推迟;中间梯度装置的电磁耦合响应表现为矩形激励电流开通时的正尖脉冲和关断时的负尖脉冲,同时也使电磁信号到达的时间推迟.与激电法常用矩形电流的接通(关断)时间相比,不论采用何种观测装置,电磁感应耦合终归是一种"短命"的瞬变现象.不同装置的电磁耦合既有不同之处,又有相同之点.在固体矿产勘查常见的地电条件下,就激电法常用的中间梯度和偶极装置以及供电波形而言,电磁耦合的时间一般不超过10-2s,利用这些时间特点能够达到区分并克服电磁耦合的目的.

In order to remove the electromagnetic coupling interference which was encountered frequently in IP measurement, most previous studies were based on the frequency characteristics of EM coupling. According to the basic formulas of electric dipole EM coupling and by means of Laplace transform and numerical integration, the time course and characteristic of EM coupling were studied in this paper. The research has shown that： （1） the response voltage difference of dipole array shows as a rising slope when rectangular current is turned on and a dropping slope when current is turned off, which both defer the arrival time of EM signal. （2） the middle-grads array response of EM coupling shows as a positive sharp pulse when rectangular current is turned on and a negative sharp pulse when the current is turned off, which defer the arrival time of EM signal too. No matter what kind of array, compared with the on-off time of IP, EM coupling is eventually a short-lived transient phenomenon. EM couplings of all kinds of configurations have dissimilarities as well as similarities. Under the general geoelectric conditions of solid mineral prospecting, the time course of EM coupling does not exceed 10^-2s using middle-grads or dipole array. Utilizing these time characteristics, we can distinguish and remove EM coupling from IP data.