Eddy current testing uses the principle of electromagnetic induction to detect flaws in conductive materials. An excitation coil carrying current is placed in proximity to the component to be inspected. The coil generates a changing magnetic field using an alternating current, which interacts with the component generating eddy currents.
Variations in the phase and magnitude of these currents are monitored either by using a second coil, or by measuring changes to the current flowing in the excitation coil. The presence of any flaw will cause a change in the eddy current field and a corresponding change in the phase and amplitude of the measured signal. In the case of nondestructive testing (NDT), these are displayed on an eddy current flaw detector as a distinct change in signal (see figure 1).