Optimization of single-yoke magnetic testing by surface fields measurement

Abstract

The main aim of the work is to discuss ways of optimizing a single-yoke magnetization set-up with respect to fluctuations of the measurement results due to imperfections of the yoke–sample contact. The nondestructive testing method is proposed to be optimized by simultaneous multi-point determination of surface magnetic fields of the investigated sample. The presented measurements of the surface fields are accompanied by computational modelling of the magnetic system by the finite element method.

Measurement of Barkhausen noise and its correlation with magnetic permeability

“…At such a yoke-sample configuration the specimens were magnetized homogeneously in the depth in the central part between the yoke poles [20]. Therefore, the Hall sensor for the surface field measurements H sur was placed at the yokefree side of the samples, where the surface field gradients are much smaller than at the opposite side between the yoke poles [21].…”

“…The first one was wound directly around the samples (laboratory condition), and the other one was wound around the yoke pole near to the edge (NDT configuration) [20]. The number of turns n were 55 and 20 for the sample and for the yoke coils, respectively.…”

“…2(b). In case of the current method, the m dif ðH i Þ is proportional to the induction rate: [19,20]. However, evaluation of the m dif ðH sur Þ requires digital derivation: dB=dH sur was calculated and gently smoothed to obtain the differential permeability.…”

“…These profiles were evaluated versus the sample field, measured directly by a near-surface Hall sensor (the surface field method of the sample field determination) [5,14]. This method was applied by analogy with our previous works, devoted to optimization of the hysteresis measurements [20,21]. It was shown there that control of the sample magnetization by the Hall sensor/s increases the results stability and the physical accuracy of the hysteresis measurements in comparison with the ordinary current method.…”

Magnetic adaptive testing—low magnetization, high sensitivity assessment of material modifications

“…FEM analysis of such measuring systems together with a number of experimental plots can be found, e.g., in Ref. [8].…”