Imaging surface conditions of ferromagnetic steel using Barkhausen technique

When ferromagnetic materials are magnetized, the resulting hysteresis curve consists of discontinuous changes in magnetization. This Barkhausen effect is produced by discontinuous domain mechanisms such as the domain wall breaking away from pinning sites due to the application of a magnetic field. For this reason, the Barkhausen effect is very useful for analyzing the microstructure of a material, since inhomogeneities in the microstructure act as pinning sites which restrict domain wall motion. It can be shown that Barkhausen data, in the form of an rms Barkhausen signal amplitude, can be used to image flaws on the surface of ferromagnetic steels. The material surface conditions, such as stress, cracking, oxidation, plastic deformation and pitting produce signal changes which ran be visualized through a computer generated image of the related Barkhausen parameters.>