A two-loop frequency-domain electromagnetic induction system for detection of anomalous objects

We discuss a two-loop frequency-domain electromagnetic induction sounding system which allows vertical focussing of the primary magnetic field thus reducing the disturbance from shallow subsurface. The frequency dependence of apparent resistivity estimated from the real part of the measured magnetic field turns out to be more sensitive than that found from the absolute total field. The advantage of the suggested FD EMI system has been validated by experiments.