Field distributions in rotational single sheet testers

Abstract
This paper concerns rotational single sheet testers (RSST) as applied for investigations of laminated soft magnetic materials. Most RSSTs use a square 64 cm² sample with rather small sensor element. They yield effective average loss values for fine-grained SiFe rotationally magnetized up to 1.2 T. For highly grain oriented (h.g.o.) SiFe sheets, characterized by large grain size and high crystallographic order, we have developed a 3-phase existed RSST which uses a hexagonal sample of 166 cm² area. It allows for increased induction values and for the application of large, well averaging sensors, the degree of flux homogeneity however being questionable. The aim of this study was a numerical estimation of the actual conditions of homogeneity for the two set-ups. Calculation was performed for the whole apparatuses by means of 2-dimensional FEM. The material was assumed to show uniaxial anisotropy with orthogonal principal directions for the permeability tensor. For both RSSTs, the results indicate good homogeneity of the induction vector B for the entire sample area. Effects of air gaps between sample and yokes prove to be less critical in the hexagonal case. In a second step, a heterogeneous model was used to simulate the magnetically hardest 55°-direction of Goss-textured material. With respect to the areally averaged vector interdependence between B and H, a comparison with measured results shows good qualitative agreement.