Experimental Research On The Repression Of EM Coupling Effect In Dual-Frequency IP Method

Abstract:Since ’the Variable Frequency Measurement’ was advanced, the repression and elimination of electromagnetic induction coupling effect (EM effect) has become an important research topic in the frequency-domain induced polarization method (IP method). By summarizing the previous researches in the mechanism and repression of EM coupling effects in the IP method, this paper designs two electrical circuits to simulate IP effect and EM effect, and uses the PXI-5922system from the NI Corporation for data acquisition, and also programs a corresponding LabVIEW data acquisition program. Using four solutions (sampling-FFT, sampling-coherent detection, low-pass filter and square-wave coherent method), we extract IP effects and repress EM effect.By this means, a variety of solutions to extract IP effects and repress EM effect are proposed and comparatively evaluated.When the EM effect is weak, each of the methods, FFT, coherent detection and square-wave coherent method, can achieve the goal of extracting the IP effect and repressing the EM effect. Because the EM coupling appears once in every high-frequency period, the period of EM coupling effect is the same as period of the high-frequency in dual-frequency. Therefore, the low-pass filter cannot repress the EM coupling effect effectively. Square-wave coherent method can extract the IP effect and EM coupling effect at the same time aiming at the Dual-frequency IP Method. It can calculate the percent frequency effect (PFE) of IP effect and EM effect by measurements in two different frequency groups of dual-frequency. However, because of the limit of the present dual-frequency transmitter, only four given group can be used in the experiment, and the difference among the four low-frequency groups is little, so the calculated PFE is small.