Analysis of Barkhausen effect signals in surface-modified magnetic materials using a hysteretic-stochastic model

The effects of microstructural variations with depth on Barkhausen effect (BE) signals in surface-modified ferrous materials have been studied through measurements and simulations based on a hysteretic-stochastic model. The BE signals measured from an unhardened sample show a peak near zero field. In contrast, the BE signals in surface-hardened samples with different case depths exhibit low-amplitude pulses near zero field and a peak at a high reverse field, which are attributed to irreversible magnetization processes in the soft core and the hardened surface layer, respectively. Theoretical analysis showed that the model parameters k and ξ, which describe the domain-wall pinning strength and the range of interaction of a domain wall with pinning sites, respectively, are related to each other as ξ = a ρ−1/2 = b/k via the pinning site density ρ, where a and b are constants. The relationship was used to simulate BE signals of the surface-hardened samples as a sum of signals generated at different depths by taking into account signal attenuation due to eddy current shielding. The simulated results were found to exhibit the general features observed in the experimental results.