High resolution magnetic Barkhausen noise measurements

Abstract High resolution magnetic Barkhausen noise (MBN) measurements of slits in steel have been made using a small magnetic disk read head mounted in a U-shaped laminated sweep field core. Detection occurred for sweep fields oriented both parallel and perpindicular to a slit or through-cut. For sweep fields oriented parallel to slits with widths from 0.25 mm to 0.7 mm, a maximum depression of 62% to 95% of the MBN signal was found. The corresponding width of the signal at 50% depreciation ranged from 2 to 4 mm. The range of depression was a factor of 2 to 5 times larger for sweep fields applied perpendicular to the slit. Through-cuts demonstrated similar depression of the MBN signal but with the distance of the suppression at 50% ranging from 4 to 11 mm. An observed increase in the MBN signal at the edges of slits cut with a blade was associated with increased residual stress induced by the blade at the edges. Results are interpreted in terms of the ability of the small magnetic disk read head to resolve small regions of non-uniform magnetization that produced MBN.