Synthetic magnetic soils for landmine detector testing

This study aims to move towards a reliable method for synthesizing artificial soils that emulate the effect of real soils on pulse-induction metal detectors. The signals resulting from some mineralized soils can greatly impair the effectiveness of mine detectors. We analysed a sample of one such soil from Cambodia, using resistivity measurement, X-ray diffraction, magnetic susceptibility measurement and electron microscopy. The physical origin of the soil signal was found to be high proportions of small grained magnetite. By mixing a U.K. topsoil with finely crushed magnetite, a synthetic soil with similar magnetic susceptibility to the real Cambodian soil was created. Other problematic soils from around the world were also synthesized. Comparative tests with a pulse induction metal detector showed decay characteristics for the artificial soils to be within 13% of those for the real soil. We achieved close susceptibility matching between artificial and real soils, either for a 2kHz measurement or a pulse-induction measurement. In our experiments it was not possible to match with both measurements at once. We propose that this discrepancy is due to differences in the average properties of magnetic grains between those in real soil and the magnetite concentrate used for the synthesis tests.