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Abstract: This work describes a specially designed setup for magnetic hysteresis and Barkhausen noise measurements. The setup combines two main elements: an improved fast algorithm to control the waveform of magnetic induction and simultaneous direct determination of the magnetic field. The digital feedback algorithm uses only the previous measurement cycle to correct the magnetization voltage without any additional correlation parameter; it usually converges after several tens of cycles. The magnetic field is measured at the sample surface using a vertically mounted array of sensitive Hall sensors. Linear extrapolation of the tangential field profile to the sample surface determines the true waveform of the magnetic field. This unique combination of physically based control for both parameters of the magnetization process provides stable and reliable results, which are independent of a specified experimental configuration. This is illustrated for the industrially attractive measurements of non-oriented electrical steels with a 50Hz sinusoidal induction waveform. [Copyright &y& Elsevier]

Abstract: Surface decarburization of steel was non-destructively and quantitatively investigated by magnetic hysteresis. Flat samples were prepared from spring steel 54SiCr6 and decarburized layers of different thickness were produced on their surfaces by annealing at 800°C in air for 1, 4, 8 and 20h. Three types of treatment were applied on different samples in order to remove the simultaneously appearing surface oxides. The decarburized layers were examined magnetically by hysteresis loops measurements and the results were related to their optically determined depths. The magnetic measurements showed high sensitivity with respect to free ferrite and mixed ferrite/pearlite layers detection even without removal of the oxide layer. The free ferrite layers were easily and quantitatively detected by minor loops measurements with low field amplitude. [Copyright &y& Elsevier]

Abstract: The paper is devoted to the establishment of experimental conditions, which ensure the repeatability of magnetic Barkhausen noise testing in practice. For this task, the measurements were performed on open flat samples using different experimental configurations, including: different magnetization frequencies, sampling rates, and filter cut-off frequencies; using a sample-wrapped coil and using attached pick-up coils of various dimensions, with different lift-offs of a single yoke magnet and of the attached coil. The sample magnetization was controlled by a vertical array of three Hall sensors; their readings were extrapolated to the sample surface to precisely define its field. After analysis of the results, a scheme for an optimized sensor with a controlled field waveform was suggested to improve the measurement repeatability. The important issues of signal processing and parameter applicability were also discussed in detail. [Copyright &y& Elsevier]

Abstract: This work studies the conditions of controllable sample magnetization for local hysteresis and Barkhausen noise measurements. These non-destructive techniques usually utilize the sensor, based on a U-shaped single yoke magnet. Its magnetization potential, however, is too dependent on the measurement conditions. To investigate this problem, we performed the measurements on magnetically different samples with varied dimensions. The magnetization was controlled by a vertical array of two Hall elements measuring the tangential surface fields. The sample field was evaluated by a linear extrapolation of the surface field profile to the sample face. It was showed that the big-sized samples are magnetized in a strongly heterogeneous way. Therefore, it was recommended to use the single yoke, equipped with the local field and sensing elements. The magnetization conditions were suggested to stabilize by means of a feedback loop controlling the local magnetic field/flux waveform, measured by these integrated sensors. [Copyright &y& Elsevier]