Relationship between AC Barkhausen noise and losses in electrical steel

• Main Author: Patel, Harshad Virji
• Published: Cardiff University 2008
• Subjects: 669
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584374

The magnetic Barkhausen effect, which appears as abrupt changes in magnetisation, occurs when a ferromagnetic material is subjected to an external varying magnetic field. The origin of the effect is known to be primarily due to the discontinuous domain wall motion through a material caused by imperfections in the material. The Barkhausen effect is very sensitive to the changes in the microstructure and stress. Owing to this sensitivity, Barkhausen measurements can be used for the non destructive evaluation of a ferromagnetic material. Previous research has been mainly based on low frequency magnetisation to generate Barkhausen noise with a typical excitation frequency less than one Hertz. In this work, a measuring system is presented which is capable of capturing Barkhausen noise signals at a magnetisation frequency up to 100 Hz. Enwrapping coils and the ferrite cored surface sensor methods were used to measure Barkhausen noise, and although the surface sensor was oriented perpendicular to the sample, all the sensors produced very similar trends. Due to the Barkhausen noise signal being of stochastic nature, methods of analysing Barkhausen noise signals was investigated. RMS, total sum of amplitudes, power spectrum and kurtosis all showed repetitive characteristics and were used to analyse Barkhausen signals. A relationship between Barkhausen noise and the hysteresis component of total power loss is presented. The variation of Barkhausen noise signals and the tangential component of surface field over the surface of a grain-oriented 3%SiFe electrical steel was also examined and it was found that there is a strong indication that surface Barkhausen noise activity is influenced by grain-to-grain misorientation. In addition, the results infer that the hysteresis component of loss varies spatially with grain structure. An ancillary study was conducted on cold rolled low-carbon steel and thermally aged Fe lwt%Cu alloy to examine the effects of Barkhausen noise due to rolling reduction.