THE TRANSIENT ELECTROMAGNETIC RESPONSE OF A CONDUCTING SPHERE IN AN IMPERFECTLY CONDUCTING HALF‐SPACE*

Abstract

AbstractThe presence of a conducting environment about a spherical ore body must be considered when calculating the transient electromagnetic response of the ore body due to a step current flowing in a large circular loop at the earth's surface. Failure to do this can easily lead to errors in excess of 10% in numerical calculations. Moreover, there is only a limited time interval in which the response of the spherical conductor is easily seen.In a poorly conducting ground the resonance response of the sphere is the first to be excited. Later, however, the non‐resonance or wave‐type response is excited. These waves destructively interfere and finally the response of the sphere decays with time as t−7/2.For a range of times and depths the best loop for detecting the sphere has about the same radius as the sphere.