Affiliations: [a] Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing 211189, China | [b] School of Mechanical Engineering, Southeast University, Nanjing 211189, China
Correspondence:
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Corresponding authors: Rongsheng Lu and Zhonghua Ni, School of Mechanical Engineering, Southeast University, Nanjing 211189, China. Tel.: +86 025 52090518; Fax: +86 025 52090504; E-mail:lurs@seu.edu.cn;nzh2003@seu.edu.cn
Abstract: Permanent magnet is the key component of nuclear magnetic
resonance (NMR) instrument. Based on the principle of Halbach array, this
study designs and optimizes a multilayer Halbach permanent magnet for human
finger NMR detection. The quality factor (QF) is introduced to represent the
performance of magnetic field, firstly. The impact on magnetic performance,
caused by various magnet heights, is analyzed using Finite Element Method
(FEM). In order to compensate the end effect, the radial adjustment method
is proposed, combining the adjustments of the radial size and the radial
position of the magnet blocks. Comparing the effect on magnetic field of
three different plans, the results show that combining the adjustments of
inner radius and outer radius shims the field dramatically. Finally the
designed construction is stacked by 11 layers of magic rings and each layer
is composed of 8 trapezoid-shaped magnets. The magnetic field of the center
cylindrical region (ϕ20 × 20 mm) of the structure is calculated, whose
final strength achieves up to 447 mT and homogeneity is within 500 ppm. The
designed magnet structure is manufactured and the measurement is finished in
the end. The proposed construction has the advantages of small size and high
uniformity, which has an extensive application prospect in portable NMR
system.
