Simulation and Optimization of an Octagonal Halbach Permanent Magnet Array for Small-Size NMR

Halbach magnet array has advantages of its small size and yokeless, so it has been widely used in various areas. In this paper, two Halbach permanent magnet arrays for small-size NMR with cube and octagonal shape, respectively, were compared in parameters of average magnetic field strength, field homogeneity and volume with the same material consumption. It was found that the octagonal shape magnet has better performance than the cube one. Then the field homogeneity optimization for octagonal magnet was performed. By analysis of magnetic field strength, the best homogeneity in 5mm DSV (Diameter of Spherical Volume) with 133.4ppm was achieved when the height of magnetic blocks is 16.25mm. After optimization, the magnetic field homogeneity has been significantly improved when the shape of magnet has small volume. This result laid a foundation for the design and manufacture of the octagonal Halbach permanent magnet array in small size.