It is widely known that eddy current measurements can provide useful information on the properties of ferrous materials. Modifications of the micro structure and of the dislocations distribution caused by heat treatment or work hardening result in variations of the magnetic domain wall motion, which affect the electromagnetic response of the sample. While the underlying microscopic mechanism relating these quantities is difficult to describe quantitatively, the relation between the electromagnetic response and the micro-structure is a very efficient empirical tool to sort parts, both by comparison with reference batches or by statistical analysis of samples. 

There is a growing interest for the application of this technique to the quality control (QC) of parts with complex geometries and/or manufactured using exotic techniques such as EDM, SLS, or water jet. Moreover, eddy currents can prove an attractive complementary technology for the detection of subsurface porosity.