Three-component TEM Response On Thin Plate Conductor

With the study of the TEM response of three-component, this paper proposed the importance of its application in Geophysical prospecting. This paper mainly studied the TEM response of three-component in four conditions: (1) the response for plate in two commonly used configurations, central loop configuration and large fixed source loop configuration; (2)the response for multi-plates model; (3) the response for plates target with conductor overburden on its top;(4) the response for plates with topography.According to the field expressions of all the electromagnetic components in frequency domain, it derives the mathematical expression of the three-component response on the surface in homogeneous half-space in time domain, for both the vertical magnetic dipole source transient field and the horizontal electronic dipole field. The eigencurrent equivalent simulation principle is introduced to calculate the TEM response of three-component for the various models.Results show that: (1)the X-component response roughly determines the projection position of the plate's center on the ground, the Y-component response reflects the dip direction which does better than The Z-component response, while the Z-component response obviously imply the anomaly. (2) For multi-plates model in the two configurations, the central loop configuration has higher resolution than the large fixed source loop configuration in detecting transverse multi-model. For the latter, when P/h<3, the response curve is similar as the single plate model, when P/h>3, all the three response curves demonstrated double peaks; while for the former, when P/h>2 the multi-model can be prospected. (3)when the ratio factors of the longitudinal conductance between the target (S₂) and the overburden (S₁)equals (S₂/S₁ ), the X-component and the Y-component response reflect the target under the central loop configuration, while under the large fixed source loop configuration there is no reflection. When S₂ /S₁≥5 , the reflection is obvious. (4) The topography influence on the response of three-component is that: hill and valley terrain mainly affects the response amplitude, with little influence on the response curve shape. However, for step topography, the response amplitude and shape will be changed significantly, it becomes more complex. The vertical component is less affected by terrain than the horizontal component, and large fixed source loop configuration is less affected by terrain than central loop configuration.