The detection of buried plastic land-mines by electro-magnetic induction?

A prototype detector has been constructed that is intended to be capable of locating a nonconducting object (e.g. a plastic land-mine) shallowly buried in earth. The detector consists of an inductive probe, the coil of which is mounted with its axis vertically, in a manoeuvrable search-probe. This, plus the associated circuitry and a battery power supply comprises the complete instrument. The inductive probe and capacitor form a tuned circuit which is self-excited at resonance; if placed in close proximity to the earth, the circuit Q (=ωL/R) is reduced because of the energy loss incurred as a result of eddy currents induced in the comparatively conductive soil. When the coil is moved above a buried nonconducting object the losses are reduced and the increase in Q results in an appropriate increase in the output signal