MAGNETIC RELAXATION AND THE ELECTROMAGNETIC RESPONSE PARAMETER

Abstract

Relaxation processes are important in the study of electromagnetic prospecting techniques. These processes can be the result of magnetic fields due to eddy currents in electrical conductors or due to displacement currents from dielectric processes or magnetic fields associated with direct magnetic loss phenomena. In the past, most attention has been focused on eddy‐current losses since this is the dominant effect. Dielectric losses also may be of importance, particularly at high frequencies, where the conductivity is extremely low or where the dielectric properties become anomalously high. In general, however, little attention has been given to magnetic losses and the effect they might have on the electromagnetic response parameter. Magnetic minerals do have a measurable magnetic loss due to various mechanisms. This effect has been measured in a frequency range from 125 to 5000 hz for a variety of samples. In synthetic samples with varying amounts of magnetite dispersed in a nonmagnetic matrix the effect is linearly proportional to the magnetite content. The magnetic loss causes a distinct, but small, change in the electromagnetic response of a body. The effect can be detected, provided the peak frequency of magnetic loss is lower than the peak frequency of electrical loss. The most diagnostic feature is the reversed phase relationship from the electrical response (for constant geometries).