It is known that the electromagnetic coupling effect is a disturbance factor in induced‐polarization measurements. Based on the different appearances of EM coupling effect and IP effect in measured dual‐frequency waveform, a direct decoupling scheme by chop‐wave is presented in this paper. The method is able to eliminate EM coupling effect directly during the field data acquisition, and it does not suffer loss of IP information by and large. This paper has mainly discussed several aspects, which include the fundamentals of chop‐wave, the distortion of normal dual‐frequency wave resulting from chopping wave, chopper of existing pure EM coupling effect and IP effect's loss due to chop‐wave. The numerical results show that the scheme reduces and eliminates EM coupling effect markedly and can provide some parameter bases for the development and design on the correlative instrument. Thereby, it is worth generalizing the chop‐wave for decoupling scheme in the induced polarization method.
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.
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