Discriminating metal detector with compensation for ground minerals

Claim 1

A metal detector for discriminating between treasure and junk metal objects in a high mineral soil having a probe, a resonant circuit (with) including an inductive coil (in) within the probe, the improvement comprising: means connected to the resonant circuit for generating a signal to drive the resonant circuit at a predetermined frequency higher than the natural resonant frequency of the resonant circuit, said means further including at least two attenuating coils of opposing magnetic fields operating at a substantially higher frequency than said inductive coil and operating without magnetic effect on said inductive coil, said attenuating coils positioned adjacent the inductive coil in the probe so that the attenuating coils are exposed to the same soil conditions as the inductive coil which results in the attenuating coils shifting in frequency proportionally to the shift in frequency of the inductive coil to avoid effects of ground minerals, said attenuating coils operating at a high enough frequency as to have a rise in frequency for ferrous and non-ferrous metal objects and a decrease in frequency for minerals; (and) a frequency divider connected in series between the generating means and resonant circuit for lowering the higher frequency of the generating means to the lower predetermined frequency of the drive signal required to discriminate between treasure and junk metal objects(.); said resonating circuit being driven by the drive signal to provide several different types of output signals, a first output signal when the probe is proximate mineral soil, a second output signal when the probe is proximate junk objects and a third output signal when the probe is proximate treasure objects; and means responsive to said third output signal for indicating that the probe is sensing treasure in the mineral soil area.