The permanent magnet systems generating strong stray fields with large localization region

Abstract

Three systems of permanent magnets, which produce strong magnetic stray fields (SFs) with H> B r=4 πM r were studied in this work. Remarkable feature of the developed systems is localization of the strong fields in large region with linear dimension Δ r comparable to characteristic magnet dimension a. The first system composed of uniformly magnetized magnets generates sufficiently homogeneous strong SFs, which amounts up to 1.5 of magnets induction B r. The second system with nonuniform magnetization is represented by cylindrical and hemispheric magnets their magnetization vector directed at every point along the radius. Such distribution of magnetization is assumed to be the consequence of magnet radial crystal texture resulting in a high uniaxial anisotropy field H K . It is shown that maximal SFs can exist on the flat surface of cylindrical magnet at the distance r from its axis and their limiting value equals to 4 πM r ln(2 a/r). Here, the localization region of the fields is comparable to diameter of cylindrical magnet Δ r≈2 R. As for the hemisphere its SFs are less than corresponding SFs for the cylinder. The third so-called quasi-nonuniform system consists of uniformly magnetized cylindrical sectors their magnetization vector is directed along the sector bisectrix. The strong SFs and their localization region are calculated in details for this case. The passage to radial magnetized cylinder is considered.