Time Characteristics of EM Coupling in Induced Polarization

Abstract

In order to remove the electromagnetic coupling in IP measurement, previous studies were mostly based on the frequency characteristics of EM coupling. According to the basic EM coupling formulas of electric dipole and by means of Laplace transform and numerical integration, the time course and characteristic of EM coupling are studied in this paper, and the result of 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 −2 s using middle-grads or dipole array. Utilizing these time characteristics, we are able to distinguish and remove EM coupling from IP data.