A Passive Shimming Method for Halbach Magnet Based on Numerical Optimization Algorithm

doi:10.11938/cjmr20233091

Abstract

Abstract:

In recent years, Halbach magnet has been extensively used in miniaturized NMR spectrometers. However, the inhomogeneity of the magnetic field of permanent magnets poses a challenge to passive shimming method. In this paper, we conducted a passive shimming study of Halbach permanent magnet array structure which is mechanically adjustable. We modeled the relationship between the radial position of the magnetic blocks and magnetic field homogeneity. Then, an optimization algorithm combining the Levenberg-Marquardt method and quasi-Newton method was utilized to optimize the magnetic field homogeneity by adjusting the radial positions of the magnetic blocks. With this approach, the homogeneity of a 1.03 T Halbach magnet was improved from 7 391×10^-6 to 154.23×10^-6 in a sphere with a radius of 2.5 mm. This work provides a flexible and convenient passive shimming method for compact Halbach magnet, which has the potential to be applied in NMR spectrometers and other instruments that require high magnetic field homogeneity.

Key words: nuclear magnetic resonance spectrometer, Halbach magnet, passive shimming, Levenberg-Marquardt method, quasi-Newton method

CLC Number:

O482.53

LI Zhengzhe, GUO Liang, REN Xuhu. A Passive Shimming Method for Halbach Magnet Based on Numerical Optimization Algorithm[J]. Chinese Journal of Magnetic Resonance, 2024, 41(2): 128-138.

Figures/Tables 8

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参数	匀场前	匀场后
磁块1径向移动距离	0 mm	-1.13 mm
磁块2径向移动距离	0 mm	+0.76 mm
磁块3径向移动距离	0 mm	-0.35 mm
磁块4径向移动距离	0 mm	+0.53 mm
磁块5径向移动距离	0 mm	-0.48 mm
磁块6径向移动距离	0 mm	-1.25 mm
磁块7径向移动距离	0 mm	-0.45 mm
磁块8径向移动距离	0 mm	+1.20 mm
磁块9径向移动距离	0 mm	+1.34 mm
磁块10径向移动距离	0 mm	+0.85 mm
磁块11径向移动距离	0 mm	-1.96 mm
磁块12径向移动距离	0 mm	-1.40 mm
磁体口径	30 mm	27.6 mm
x方向均匀度	4 571 ppm	19.2 ppm
y方向均匀度	4 601 ppm	144.3 ppm
z方向均匀度	2 226 ppm	106.03 ppm
区域均匀度	7 391 ppm	154.23 ppm