The reduced impedance function for cup-core eddy-current probes

Eddy-current nondestructive evaluation makes use of ferrite-core probes for exciting alternating currents in the test piece. The effectiveness of the probe for detecting flaws in the material through changes in its impedance may be assessed from its interaction with an unflawed conductor. For an important class of eddy-current probes, those with ferrite cup-cores, the measured impedance characteristics are governed by a rule-based behavior found from experiments. These findings are in conflict with the elementary circuit theory model of probe-workpiece interaction but are confirmed by a general field-theory probe model