HARMONIC AND TRANSIENT FIELDS ON THE SURFACE OF A 2-LAYER MEDIUM

The article deals with the behaviour of the quasi-static electromagnetic (EM) fields created by currents in a two-layer medium when the source is a vertical axis circular loop. This analysis is of use for determining the depth of investigation of induction methods in mining prospecting. The relationship of the active and reactive components of the fields with the geoelectrical parameters is different, depending on the range of frequencies. Unlike the case of a confined body, the low-frequency part of the spectrum is presented as a series made up of integral and fractional powers of frequency omega and also logarithmic terms of omega. The late stage of a transient process is described with a sum of terms, proportional to the inverse power of time t. These representations are useful for determining the host rock effect against which the signal from an ore body of finite extent must be detached.-Author