Mostly in eddy current technique single element probe & a coil conductive wire is excited with an alternating electrical current. This wire coil produce an alternating magnetic field around itself. The magnetic field oscillates at the same frequency as the current running through the coil when coil approaches a conductive material, current opposed to the ones in the coil are induced in the material- eddy current.

Variations in the electrical conductivity and magnetic permeability of the test object and the presence of defects causes change in eddy current and corresponding change in phase and amplitude that can be detected by measuring the impedance changes in the coil which is a telltale sign of the presence of defects.

Technique is very sensitive and can defect small/tight cracks surface inspection can be performed both on ferromagnetic & non ferromagnetic materials, also useful in making electrical conductivity & coating thickness measurement.

Modern NDT method for controlling quality of component for aerospace, automotive, heat exchanger tubes, pipes for oil gas in manufacturing & in service inspection for only surface & subsurface, another widely used application is Material sorting for bulk quantity. Portable equipment & inspect complex shapes & sizes of conductive materials.