Design and construction of a dipolar Halbach array with a homogeneous field from identical bar magnets:: NMR Mandhalas

Magnets of the Halbach layout are interesting for the use in mobile NMR/ MRI devices. Therefore, the ideal Halbach magnet was iterated using identical bar magnets, which are positioned and oriented based on analytical equations. These configurations were simulated with two-dimensional finite-element methods. Performance factors were defined to relate field strength with homogeneity and mass. A geometry of 16 magnets provided a good compromise between performance and special requirements for the desired use to store hyperpolarized xenon. The construction of such a magnet required the design of dedicated support frames and procedures to mount them. The field strength and homogeneity in the finished magnet were measured by a Hall probe and agreed well with the simulations. The calculation and construction are described in detail and together with the tabled field values for n magnets with n less than or equal to 80 may prove helpful for building similar devices, which were named NMR Mandhalas (Magnet Arrangements for Novel Discrete Halbach Layout). (C) 2004 Wiley Periodicals, Inc.