Theoretical foundation for designing multilayer Halbach array magnets for benchtop NMR and MRI

Multilayer Halbach array magnets support portable NMR and MRI, but optimizing their design to maxi-mize performance and minimize the use of expensive magnet materials is challenging. This is partly because our theoretical understanding of such arrays is incomplete and computationally intensive. Here we provide a theoretical description of the magnetic field distribution and we demonstrate that inhomogeneity is greatest along the z axis in multilayer Halbach array magnets. This allows the config-uration of the multilayer Halbach array magnets to be optimized in a way that takes into account homo-geneity, magnet volume, and magnetic flux density. At the same time, our description simplifies the design of multilayer array magnets, while accommodating the possibility of different outer radii, lengths for each layer array, or the presence of separation between the rings. We validated the theoretical description in simulations of a three-layer Halbach array magnet, then with a prototype three-layer 1-T Halbach array magnet. After adjusting the position of magnet blocks in the neighboring rings, we achieved homogeneity of 220 ppm for a standard 5 mm NMR tube while the inner diameter of the mag-net is 20 mm. Our work provides a theoretical foundation for designing multilayer Halbach array magnets to maximize homogeneity and minimize the use of magnet materials.(c) 2022 Elsevier Inc. All rights reserved.

Automated summary

In this study, we provide a theoretical description of multilayer Halbach array magnets and demonstrate that the greatest inhomogeneity occurs along the z axis. Based on this, we optimize the configuration of multilayer Halbach array magnets, taking into account homogeneity, magnet volume, and magnetic flux density, while simplifying the design process.