This NDT method is based on the principles of electromagnetic induction. The flow of electricity, under certain circumstances, can cause magnetism. Magnetism under certain circumstances causes the flow of electricity. When an alternating current (AC) is passed through a coil, a changing magnetic field is generated.

This method can be applied to tubing, sheets, cylinders and coatings and provides a means for measuring conductivity, detecting discontinuities, and determining the thickness of coating or plating on articles. Since a continuous indication is a part of the basic testing system, automatic production testing is particularly feasible.

The signal indicating the status of the material is obtained almost instantaneously. There is no requirement for allowing time for the indication to develop. The testing procedures are readily adaptable to go/no go situations. The method is sensitive to many physical and metallurgical variables- thus it has wide application provided the variables, not of interest can be eliminated or suppressed. The only link between test equipment and the item under test is a magnetic field – there is no possible harm to the item. The equipment, for the most part, can be self –powered and there for a portable.