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Title: Dynamic domain observation in grain-oriented electrical steel using magneto-optical techniques
Author: Hoshtanar, Oleksandr
ISNI:       0000 0004 2748 9467
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2006
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Direct, real time domain observations in electrical steel during its magnetisation at 50 Hz and 75 Hz was limited due to low the limited sensitivity and frame sampling rate of the camera systems available. In this work, a high efficiency Kerr magneto-optic microscope was coupled to a recent commercially available high speed intensified camera. The superior efficiency of the developed system enabled domain dynamics measurement to be made at magnetisation frequencies up to 100 Hz in the real time mode and up to 1.8 kHz in stroboscopic mode. The application of the system was focussed on the study of grain-oriented electrical steel. Observations in this work revealed that the behaviour of the domain walls under sinusoidal excitation is far from being ideal sinusoidal motion. The deviations from the ideal behaviour can be summarised as non-sinusoidal, non uniform and non-repetitive domain wall motion. The dependence of the non- uniformity of wall motion and cycle-to-cycle non-repeatability on magnetisation conditions studied by direct real-time observation revealed that under certain conditions the non-uniformity and non-repeatability is much higher. Recommendations have been made on how to reduce losses by adjusting the magnetisation conditions and "magnetic history" of the steel core. The observations confirmed previous researchers' suggestions that the perfection of grain-to-grain orientation and grain size uniformity would improve wall motion uniformity, hence reducing power loss in the material. In addition to Kerr-microscopy observations, the application of a magnetic indicator imaging technique was demonstrated. Moving domains under the insulating, opaque coating on commercial grain-oriented electrical steel were observed using this method. The influence of surface roughness and the effect of coating tension on the domain structure and distortion of bar domains under dynamic magnetisation was observed. New experimental techniques and image processing programs have been developed such as the first attempt of automatic domain wall recognition and analysis by computer vision methods. It was demonstrated that the system and software tools were flexible for use with other materials such as steel, NiFe and CoFe alloys, amorphous ribbons and wires, ferrites and magnetic films.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available