Eddy-Current Testing (spelled with or without the hyphen) is a nondestructive testing method that makes use of electromagnetic induction to detect defects or faults in conductive materials. In standard eddy current testing, a circular coil that carries current is positioned close to the test subject (which should be electrically conductive). The magnetic field produced by the alternating current in the coil interacts with the test subject to generate eddy current. To perform an NDT with this method is to monitor variations in the phase and magnitude of the generated currents using a second "search" coil or by measuring changes in the current flowing in the primary "excitation" coil. Flaws or defects are determined through the variations observed in the electrical conductivity or magnetic permeability of the conductive object being tested.
Though limited to testing conductive objects only, eddy current testing as an NDT method has the advantage of minimal preparation, immediate feedback, and (typically) small size and portability of the testing device used.