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Electromagnetic induction using powerlines Fisk, Lynda Elaine


The possibility of obtaining information about subsurface conductivity structure using powerlines as a source has been investigated. Powerlines have been modelled as purely inductive sources over a layered earth. Solutions for the field components produced by an elevated straight line source of current over a layered earth are presented. Exact solutions are in the form of a (inverse) Fourier transform. These expressions are evaluated numerically using Fast Fourier Transform (FFT) algorithms. Preliminary interpretations of magnetic field data gathered in the vicinity of a powerline have been made using these expressions. Emphasis at this stage is on forward model results. For the case of a bent line of current the computation of exact solutions becomes costly, so that approximate solutions are used employing complex image theory. Image theory results agree with exact solution results throughout the quasi-static range, except at distances less than the order of a skin depth from the source. Effects due to lateral inhomogeneities in a homogeneous half space were modelled with the use of an electrolytic tank. A cylindrical wave analogue model was used to study the effect of a rectangular structure embedded in a homogeneous half space. Inphase and quadrature measurements of the total field are obtained.

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