Dependence of Barkhausen Noise in Plastically Deformed Steel on Frequency and Nonlinearity of Magnetizing Field

The Barkhausen noise was measured in plastically deformed low-carbon steel at various frequencies of the magnetizing fleld. Strip samples magnetized by a yoke were used for investigation. The measured amplitude distributions and power spectra are compared with the results of the Alessandro, Beatrice, Bertotti, Montorsi model of the Barkhausen noise. The measurement results at the triangular magnetizing current and the triangular magnetic fleld in the sample were compared and the difierences will be discussed. The Barkhausen noise (BN) method of nondestructive testing provides good sensitivity to residual stress levels and changes in the microstructure of a magnetic material. In this work, the BN was measured in plastically deformed low-carbon steel. Plastic deformation changes the average number of individual pulses in large Barkhausen jump due to the change of the dislocation density and distribution of residual microstresses in the sample. The in∞uence of the plastic deformation on the BN is usually investigated using the deflned (triangular or sinusoidal) magnetizing current with some low frequency [1]. In this paper, we tried to investigate the in∞uence of the magnetizing frequency on the measurement results. In addition, when the triangular current from the power amplifler is used as magnetizing current in coils of the yoke, the nonhomogeneity of magnetic circuit causes that the magnetic fleld in the sample is not proportional to the current, and therefore the fleld rate is not constant [2]. Further, the magnetizing frequency and the deformation of samples heavily in∞uence the nonlinearity of the sample magnetization characteristic, so the samples are not measured with the same fleld amplitude. To impose the constant fleld rate with the deflned fleld amplitude, the fleld was measured by the tangential Hall probe on the sample surface and the digital feedback was used. The impact of this feedback on measurement results will be discussed.