Eddy-current testing uses electromagnetic induction to detect flaws in conductive materials. It can detect very small cracks in or near the surface of the material.
Parts capable of inducing current are put in contact or near a probe that emits electromagnetic currents through the part. The probe also looks for changes in how the current travels through the part. It picks up the changes and shows the irregular flow. This process can detect slight changes in the piece being inspected. The changes may be due to hardness difference, changes in material, or a void or crack in the part.
The material surface needs minimal preparation, and physically complex geometries can be investigated. It is also useful for making electrical conductivity and coating thickness measurements.