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Abstract

In this paper it is shown that a plane wave source, an infinite line source and a vertical magnetic dipole source<br>generate approximately equal peak responses from a thin three dimensional (3-D) conductor. The main difference between<br>source types come in the layered response. In general the plane wave source is greater than the infinite line source layered<br>response which in turn is larger than the dipole layered response. For the anomaly index, as measured by the ratio of<br>secondary to layered response, the magnetic field component is largest for the dipole source and smallest for the plane wave<br>source whereas for the electric field the magnetic dipole has the smallest anomaly index. This is true both when the dominant<br>mode of excitation is current gathered into the scatter from the surroundings (channeling currents) and current induced in<br>the scatter (vortex currents).<br>We consider large and small transmitter loops with in loop and out of loop receiver configuration in both the<br>frequency and the time domain, Most of the currently used prospecting system configurations in either mining or<br>environmental work are thus covered. In the time and the frequency domain we find that a system which measures the<br>horizontal magnetic field has a anomaly index one to two orders of magnitude larger than a system which measures the<br>vertical magnetic field. Furthermore, conclusions regarding the optimum source-receiver configuration are dependent on<br>the target orientation. In the time domain, for a vertical thin sheet, the anomaly index is largest when the loop size is of the<br>order of the depth to the conductor whereas in the frequency domain a much larger loop can be employed.

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/content/papers/10.3997/2214-4609-pdb.205.1996_010
1996-04-28
2020-04-04
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