Influence of applied magnetic field strength and frequency response of pick-up coil on the magnetic barkhausen noise profile

Abstract

The influence of applied magnetic field strength and frequency response of the pickup coil on the shape of Magnetic Barkhausen Noise (MBN) profile have been studied. The low frequency MBN measurements have been carried out using 5 different MBN pickup coils at two different ranges of applied magnetic field strengths on quenched & tempered (QT) and case-carburised & tempered (CT) 18CrNiMo7 steel bar samples. The MBN pickup coils have been designed to obtain different frequency response such that the peak frequency response varies from ~ 4 kHz to ~32 kHz and the amplitude of low frequency signals decreases gradually. At lower applied magnetic field strength of ±14000 A/m, all the pickup coils produced a single peak MBN profile for both QT and CT sample. However, at higher applied magnetic field strength of ±22000 A/m, the MBN profile showed two peaks for both QT and CT samples for pickup coils with peak frequency response up to ~17 kHz. Also, there is systematic reduction in peak 2 for QT sample and asymmetric reduction in the heights of peak 1 and peak 2 for CT sample with increase in peak frequency response of the pickup coils. The decreasing sensitivity of pickup coils with increasing peak frequency response to MBN signal generation is indicated by the gradual reduction in width of MBN profile and height of peak 2 in QT sample. The drastic reduction in peak 1 as compared to peak 2 in CT sample shows the effect of decreasing low frequency response of the pickup coils on lowering skindepth of MBN signal detection. This study clearly suggests that it is essential to optimise both maximum applied magnetic field strength and frequency response of the MBN pickup coil for maximising the shape of the MBN profile for appropriate correlation with the magnetisation process and hence the material properties.

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