Electromagnetic induction response of a target buried in conductive and magnetic soil

Abstract

Soils that are conductive or magnetic or both can adversely affect the operation of induction metal detectors widely used to detect buried landmines. Although this effect has been known for a long time, it is only recently that efforts to rigorously characterize and quantify it has been initiated. The work reported in this paper is a part of on-going studies to clarify which properties of soil are important and to what extent they affect the performance of metal detectors which operate on the principle of electromagnetic induction. The electromagnetic response of a buried small metallic sphere is analyzed and computed. The results are used to investigate the influence that electrical conductivity and magnetic susceptibility of the host soil have on the signal produced by a target and hence on its detectability by a metal detector. The burial medium is modelled as a halfspace. While soil electrical conductivity has been assumed to be real and independent of frequency, its magnetic susceptibility has been modelled as complex and frequency-dependent in general. Results include three specific 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.

Effects of magnetic soil on metal detectors: preliminary experimental results

“…The geometry employed to analyze the metal detector problem is the same as the one used previously [1][2][3][4] and is repeated in Figure 1. The soil is modelled as a homogeneous half-space and the metal detector head is taken to consist of a pair of concentric and coplanar circular coils.…”

“…As discussed in earlier papers [1][2][3] the voltage, normalized by the product N t N r I, induced in the receiver coil by a non-conducting (σ 1 = 0) but magnetic half-space is given by…”

“…As well, the permittivity of soil will be assumed to be frequency-independent, the same as that of free space and will be not be considered in the results (i.e., displacement currents will be ignored). The starting point for the assumed magnetic behaviour of the soil is the following well-known general model [1,2,[6][7][8][9][10].…”

“…In a series of papers [1][2][3][4], the author has reported on various aspects of the influence of soil electromagnetic properties on the functioning of the metal detector. Most of the discussion in these previous papers has been on analytical results, which included response calculations in the frequency domain and the consideration of the response to an idealized step-current pulse.…”

Study of the influence of the plastic casing on the electromagnetic induction response of a buried landmine

“…In a series of papers [1][2][3][4][5], the author has reported on various aspects of the influence of soil electromagnetic properties on the functioning of the metal detector. Most of the discussion in these previous papers as well as the work of others on the electromagnetic induction (EMI) response of a low-metal landmine buried in soil have not considered any influence that the plastic casing may have on such response.…”