A preliminary investigation of the effects of soil electromagnetic properties on metal detectors

Abstract

Some soils can adversely affect the operation of sensitive metal detectors widely used to detect buried landmines. Although there has been some related work in geophysics, researchers in metal detection techniques, until very recently, seem to have largely ignored the issue of problem soil. As a result, rigorous scientific investigations of how soil electromagnetic properties may affect the operation of metal detectors are lacking. Thus, there is a need for theoretical and experimental studies to clarify which electromagnetic properties are important and to what extent they affect the performance of metal detectors of various designs. The paper presents a systematic analytical framework, based on existing work in geophysics and non-destructive testing, for studying the effects of soil electromagnetic properties on the functioning of metal detectors. For this initial study the burial medium is modelled as a half-space. While soil electrical conductivity has been assumed to be real and independent of frequency, soil magnetic susceptibility has been modelled as complex and frequency dependent. Simplified versions of the analysis techniques have been applied to three selected cases of practical importance, namely, non-conducting soil with constant susceptibility, non-conducting soil with frequency-dependent susceptibility and non-magnetic soil with constant conductivity. Results from a preliminary analysis of even these simple cases explain a number of previous experimental observations, for example, the greater influence of magnetic properties than of electrical conductivity on the performance of metal detectors.