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TRANSIENT EM RESPONSE OF A LARGE LOOP ON A LAYERED GROUND *
Author(s) -
Lee T.,
Lewis R.
Publication year - 1974
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1974.tb00097.x
Subject(s) - conductivity , radius , loop (graph theory) , amplitude , voltage , electrical resistivity and conductivity , physics , ground state , current (fluid) , excited state , materials science , geometry , mechanics , optics , atomic physics , mathematics , thermodynamics , computer security , combinatorics , quantum mechanics , computer science
A bstract The voltage induced in a horizontal loop on a layered ground has been calculated for the case where the loop is excited by a step current and measurements are made during the off‐cycle. The expressions derived for a uniform ground show that for large time t the induced voltage E(t) is approximately given by E(t) ≃— ( Ib αμ/20 t ) (σμ 2 / t ) 3/2 where σ is the conductivity of the ground, μ the permeability, b the loop radius, and I the amplitude of the current step. For small times the corresponding result is E(t) ≃— Ib μ/2 t. When the ground is composed of a number of layers a numerical procedure for calculating the induced voltage is described. The calculated responses of various multilayered structures show that at short times the induced voltage is asymptotic to that produced in the case of a uniform ground of conductivity equal to the top layer. Interference effects in the top layer can lead to anomalous decay curves which may result in the underestimation of the conductivity of a buried layer.