The magnetic Barkhausen noise (MBN) measurement technique is a popular magnetic method used for non destructive detection of microstructural changes in ferromagnetic materials. The MBN parameters depend on the gap between the excitation yoke and measured object. To suppress the negative influence of lift off, we tried to find a parameter of the MBN, which could be independent of lift off changing in a practical range. The lift off effect was analysed experimentally on construction steel samples with various levels of carbon content. We found that the amplitude distribution is a promising parameter of MBN in this regard. Measurement results showed that the slope of amplitude distribution was roughly independent of lift off.
The magnetic Barkhausen noise (MBN) measurement method is a widely used non-destructive evaluation technique used for inspection of ferromagnetic materials. Besides other influences, the excitation yoke lift-off is a significant issue of this method deteriorating the measurement accuracy. In this paper, the lift-off effect is analysed mainly on grain oriented Fe-3%Si steel subjected to various heat treatment conditions. Based on investigation of relationship between the amplitude distribution of MBN and lift-off, an approach to suppress the lift-off effect is proposed. Proposed approach utilizes the digital feedback optimising the measurement based on the amplitude distribution of MBN. The results demonstrated that the approach can highly suppress the lift-off effect up to 2 mm.
Hopkinson Effect Study in Spinel and Hexagonal Ferrites
The magnetic susceptibility shows a Hopkinson peak just below the Curie temperature TC when heating the selected hexagonal and spinel ferrite samples. It is proposed that this peak can be associated with a transition from stable magnetic state to super-paramagnetic relaxation above the blocking temperature up to the TC. The Hopkinson effect results are compared with SEM micrographs of both studied hexagonal and spinel ferrites.