A passive shimming method for Halbach magnet based on magnetic sheet arrays

Halbach magnet has great potential in nuclear magnetic resonance device, where the field homogeneity requirement puts heavy demands on high efficiency passive shimming (PS) technique. Conventional PS involves a tedious iteration process of the magnetic block/sheet number and positions optimization. In this paper, we propose a PS method based on magnetic sheet arrays (MSAs) targeting at spherical har-monic basis up to the 3rd order including dedicated composition of Y(4Z2-X2-Y2), Z3 and X(4Z2-X2-Y2) (n = 3, m =-1,0,1) with cross terms to implement structural field compensation. With this approach, the homogeneity of a 0.5 T Halbach magnet was improved from the original 811 ppm to 4.7 ppm in a L15 mm x R2.5 mm water sample. Rough shimming in another 0.93 T Halbach magnet also improved the homogeneity from 1103 ppm to 125 ppm in R2.5 mm sphere. This work provides a flexible, convenient PS method based on MSAs for compact Halbach magnet, which can be applied in NMR spectrometers and other high homogeneity application circumstances. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

This paper proposes a passive shimming method based on magnetic sheet arrays (MSAs), aiming to improve the field homogeneity requirement of Halbach magnet and implement structural field compensation. The method achieves good results in experiments and provides a feasible approach for the application of compact Halbach magnet in NMR devices and other high homogeneity applications.