1 Intensity Distribution of Strong Magnetic Fields Created by Opposing Linear Halbach Assemblies of Permanent Magnets Václav Žežulka 1 , Jaromír Pištora 2 , Michal Lesňák 3* , Pavel Straka 1 , Dalibor Ciprian 3 , Jaroslav Foukal 3 1 Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i. V Holešovičkách 41, 182 09 Prague 8, Czech Republic 2 Nanotechnology Centre, VSB – Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba, Czech Republic 3 Institute of Physics, VSB – Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba, Czech Republic Abstract The work is devoted to a geometrical configuration of permanent magnets on the basis of opposing geometrically linear assemblies (e.g. Halbach arrays) for the generation of strong magnetic fields, which have been theoretically modeled and experimentally verified. The implementation of these opposing assemblies using NdFeB magnets of a total weight of 3.75 kg provided a value of magnetic flux density in the middle of an air gap of a width of 20 mm that was higher by 56% in comparison with the simplest possible design. When the air-gap width was 3 mm, the flux density reached a value of 2.16 T, which represents an increase of more than 100%. Simultaneously, however, unlike in the simplest possible parallel configuration, opposing Halbach assemblies have shown, in the middle of an air gap, a significant decrease of the magnetic flux density values when passing from the middle of the assemblies in the direction parallel to the x-axis. Keywords: Magnetic field, Permanent magnets, Halbach arrays. Introduction Numerous applications require the usage of magnetic fields with high values of magnetic flux density, or with an extreme gradient of this parameter. Thanks to their high values of remanent magnetization and energy density, permanent magnets on the basis of rare earths are predetermined for these purposes. In the 1970s, the first work concerning the so-called one-sided magnetic fluxes with planar magnetic geometries was published [1]. Subsequently, Halbach described a new quadrupole configuration using cobalt permanent magnets [2]. Marble claims [3] that through a relatively simple arrangement of permanent magnets it is possible to achieve more than 80% of the maximum possible magnetic field. The authors in the work [4] describe a geometric arrangement of NdFeB-type permanent magnets for magnetic resonance, which in the implemented device of a total weight of 790 kg (of which 290 kg is the weight of the NdFeB magnets from the material N42) generates, in an air gap of 0.06 m and a pole diameter of 0.2 m, a magnetic field of an induction of 1.6 T. In the same work, the authors mentioned that using the Halbach ring structure would make it possible to attain high fields and reduce the weight of the device, but this structure is too complicated to be manufactured and assembled. With simplified Halbach cylinders, values of up to 1.8 T were attained [5]; with Halbach cylinders with iron pole magnetic-flux concentrators, the maximum level shifted to a value of 3.9 T [6]. The work [5] describes also an original source of a magnetic field on the basis of permanent magnets (Halbach sphere), where the calculated value of magnetic flux density in the central area (ø 6 mm x h 2.8 mm) exceeded the level of 4.3 T. Besides the size of the field generated, in many cases it is important to monitor the uniformity of this field as well. The Journal of magnetism and magnetic materials. 2013, vol. 345, p. 7-12. http://dx.doi.org/10.1016/j.jmmm.2013.05.047 DSpace VŠB-TUO http://hdl.handle.net/10084/101260 8/1/2014