Transient electromagnetic field in magneto-viscous medium

When using Transient Geo-Electromagnetics (TEM) unusually slow decaying transients are sometimes observed in the absence of well-conductive objects. Many researchers explain this phenomenon by presence of material with magneto-viscous or superparamagnetic (SPM) properties. The analysis of electromagnetic (EM) field equations in conductive SPM medium is suggested in the present paper. It is shown that in a simplest case of small size single-domain magnetic particles with relative higher potential barrier energy, the SPM-medium is characterized by a very slow decaying exponential transient magnetic field, the level of which is much more as compared to that of due to non-magnetic medium of the same conductivity. This situation is traced up to the late transient time like 0.1 s and more. SPM and Induction fields are in the near zone additive. They depend in a different way on the superparamagnetic and electric properties of the SPM-medium. They also depend in different ways on the transient time and on the size of the transmitter–receiver configuration. These characteristics make it possible to recognize the presence of SPM-effect and to separate these fields.

► Superparamagnetic particles in rocks create very slow exponential transients.
► The cause of this is the frequency/time dispersion of the magnetic susceptibility.
► SPM and Induction fields are in the near zone additive.
► They depend differently on configuration and size of transmitter-receiver assembly.
► It makes possible to recognize SPM-effect and separate it from the Induction one.