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

摘要

Most studies of the electromagnetic induction (EMI) response of a low-metal landmine buried in soil ignore any influence that the plastic casing may have on such response. In most cases such treatment is adequate since only the metal components of a landmine are expected to contribute to such a response. However, when the landmine is buried in a soil that has significant conductivity and/or magnetic susceptibility, the electromagnetic void created by the casing may have an influence on the EMI response of the landmine. That possibility is investigated using a simple analytical model and an experiment. A sphere is chosen as a simple prototype for the small metal parts in low-metal landmines, and a concentric spherical shell, made of foamed polystyrene, encasing the sphere is used to represent the plastic landmine body. The time-domain EMI response is measured using a purpose-designed system based on a modified Schiebel AN19/2 metal detector. Responses of the metallic sphere, the polystyrene shell and the metal-polystyrene composite target are measured with the targets buried in magnetic soil half-spaces. The particular soil type for which data are presented in this paper is Cambodian "laterite" with dispersive magnetic susceptibility, which serves as a good model for soils that are known to affect the performance of metal detectors. The metal sphere used has a diameter of 0.0254 m and is made of 6061-T6 aluminum, and the polystyrene shell has an outer diameter of 0.15 m. For the specific soil and targets used, theoretical results show that a small effect on the time-domain response is expected from the presence of the polystyrene casing. Experimental results confirm this for the case of the buried polystyrene shell. However the small difference in the example of the composite target is masked by experimental errors.