基于数值优化方法的Halbach磁体无源匀场方法研究
收稿日期: 2023-12-11
网络出版日期: 2024-02-18
基金资助
山东省自然科学基金资助项目(ZR2021ME093)
A Passive Shimming Method for Halbach Magnet Based on Numerical Optimization Algorithm
Received date: 2023-12-11
Online published: 2024-02-18
小型化的核磁共振谱仪由于其便携性的优势，成了当下核磁共振领域的研究热点．近年来，Halbach磁体在小型化核磁共振波谱仪领域得到了广泛应用．永磁体磁场的不均匀性对无源匀场方法提出了较高的要求．因此，本文基于机械可调的Halbach永磁体阵列结构进行了无源匀场研究．首先研制了由12个机械可调的磁块构成的Halbach磁体，并建立了磁块位置和磁场均匀性的最小二乘问题，随后利用了一种结合Levenberg-Marquardt法和拟牛顿法的优化算法，通过改变磁块的径向位置来优化磁场的均匀性．通过这种方法，成功将1.03 T的Halbach磁体中心区域（半径为2.5 mm）的均匀度从7 391×10-6提升到154.23×10-6．本文提出的匀场方法相对于传统的无源匀场方法更加灵活和简便，有望应用于核磁共振波谱仪和其他需要高磁场均匀度的仪器．
关键词： 核磁共振波谱仪; Halbach磁体; 无源匀场; Levenberg-Marquardt方法; 拟牛顿方法
李正喆 , 郭亮 , 任旭虎 . 基于数值优化方法的Halbach磁体无源匀场方法研究[J]. 波谱学杂志, 2024 , 41(2) : 128 -138 . DOI: 10.11938/cjmr20233091
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.
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