Anisotropic flux density dependence of magnetic Barkhausen noise in oriented 3% Si-Fe steel laminates

This paper compares the anisotropy of surface magnetic Barkhausen noise (MBN) and pulse height distributions between two samples of oriented 3% Si-Fe steel laminate at equivalent flux densities. One sample had lower core loss (0.83 W/kg) than the other (0.97 W/kg). The MBN_Energy (square of the MBN voltage signal integrated with respect to time) was investigated parallel and perpendicular to the samples´ easy axis. The highest levels of MBN_Energy and magnetization were achieved in the parallel orientation in the low-core-loss sample. The considerable anisotropies observed under similar field conditions were largely removed when the MBN_Energy was considered as a function of peak flux density. Differences between the two samples were observed in the anisotropic behavior of the MBN_Energy and pulse height distributions for flux density amplitudes between 1.3 and 1.6 T, the typical operating range of transformer laminates. These were attributed to differences in the number and structure of 180° domain walls. The low-core-loss sample was interpreted as having a finer domain-wall structure that produced abrupt changes in the magnetization projected out of the sample plane, thereby reducing the microscopic eddy-current contribution to losses.