In an eddy current probe, an alternating (AC) electric current flows through a wire coil producing an oscillating magnetic field (Figure A).









The eddy current produces a separate magnetic field which interacts with the wire coil in the probe. This process is called mutual inductance. Any defects or deviations in thickness will affect the pattern of the eddy current and its magnetic field. In turn, these changes in the eddy current are picked up by the wire coil which a skilled NDT technician can detect using eddy current technology (Figure C).



When the probe is brought near an electrically conductive material, electrons invisibly pass through the material like a swirling pool of water. These swirling electrons are called the eddy current (Figure B).