The quantitative advantages of using B-field sensors in time-domain EM measurement for mineral exploration and unexploded ordnance search

The use of simple models for decay of conductive targets under conductive overburden and for the decay of magnetically permeable conductive steel objects allows quantitative consideration of the advantages of the use of magnetic-field detectors in time-domain electromagnetic (TEM) measurements, or more generally, the advantage of step response over impulse response TEM systems. We identified eight advantages of the step response versus impulse-response systems. The first two advantages relate to the inductive limit (early time) decay behavior, in which a target response amplitude is largely dependent on geometrical rather than conductivity parameters. Five further advantages occur when measuring response of a target in a conductive host or under conductive overburden; the maximum target-to-overburden response occurs 25 -30 earlier in time, the earliest target detection time occurs a factor 2-4 earlier, and the amplitude advantage of target-to-overburden response is a factor in the range of 1-10 for the step versus impulse-response systems, respectively.