Transient process and optimal design of receiver coil for small‐loop transient electromagnetics

Abstract

Distributed parameters of the receiver coils greatly affect transient electromagnetic signals over short time periods, causing a delay in the signal's effective sampling time and the loss of shallow exploration information. This paper investigates the influence of transient process on apparent resistivity calculation and analyses the relations between the error of apparent resistivity and receiver coil design. We find that, under the same effective area, different radii of the receiver coils lead to different levels of impact on the estimation of the apparent resistivity. An optimization model is proposed to determine the optimal receiver coil size that gives rise to the smallest estimation error of the apparent resistivity. The relationship between the optimal radius and the effective areas is developed, which serves as a guideline for the optimal receiver coil design. The results may provide a useful means for improving the accuracy of the small loop transient electromagnetic instrumentation for shallow‐depth mapping.

A Novel Method for Fault Diagnosis of Grounding Grids

“…4. We observe that the magnetic intensity value at point 1, 5,9,13, and 17, which lies in the center of the grounding mesh, is much higher than that at other points; whereas the magnetic intensity value at point 3, 7, 11, and 15, which lies right above the grounding conductor, is significantly smaller than that at other points when grounding grids have no fault. In situation 2, the magnetic intensity value at point 8, 9 and 10 which lies within the corrosion mesh has a maximal drop of about 5.81%, while that at other points has no significant change.…”

“…Instead, the equivalent resistivity reflects the ability of underground media (e.g., grid, soil) forming the eddy current and the impact of transient process of the receiver loop [13]. The corresponding equivalent depth does not exactly reflect the actual depth either.…”

Research on Precise Damping Matching for Transient Electromagnetic Transmitter

“…Literature [10] pointed out that each coil can be equivalent to one node, and the node-to-node capacitance is calculated by a finite element model using the Maxwell 2-D electrostatic axisymmetric solver. The equivalent lumped distributed capacitance C between two terminal nodes can be calculated by calculating the parasitic capacitance of each turn and using Matlab software proper matrix operation to eliminate the intermediate nodes.…”

Break-Point Diagnosis of Grounding Grids Using Transient Electromagnetic Apparent Resistivity Imaging

“…Remark: In the fault diagnosis of grounding grids, the calculated equivalent resistivity is not the actual resistivity of the ground. Instead, the equivalent resistivity reflects the ability of underground media (e.g., grid, soil) forming the eddy current and the impact of transient process of the receiver loop [21]. The actual resistivity of underground can be obtained by using the direct current method [25].…”

“…The TEM technique is effective in determining the electrical resistivity of the underground layers and has been widely used in shallow geological exploration [21]. A typical TEM system is a transmitter-receiver pair that records the secondary magnetic field for inversion imaging.…”