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Halbach array magnets are permanent magnet configurations that are regularly assembled by multiple blocks with different magnetization
directions.
Thanks to the advantages of high magnetic material utilization, high uniformity and small fugitive field, Halbach array magnets are widely used
in scenarios where compact, movable, real-time and in-situ detection is required.
In recent years, thanks to the research and development of high-uniformity multilayer Halbach magnets, portable NMR systems have become a research hotspot
for low-field magnetic resonance systems.
However, due to the imperfect design theory, the current magnet design method mostly adopts approximate calculation or finite element simulation, which has problems such as
low calculation accuracy and time-consuming and laborious simulation optimization.
Core scientific questions such as how magnet geometric parameters affect magnetic field strength and uniformity, and how magnetic block errors affect uniformity, still need to be solved
.
Therefore, providing a more commonly applicable design theory method for the design of multilayer Halbach magnets has become an urgent problem
to be solved.
In order to solve this problem, the desktop magnetic resonance spectroscopy group of Yang Xiaodong's research team of Suzhou Medical Institute constructed the optimization theory of multilayer Halabch magnets, and proved the middle edge z of multilayer Halbach array magnets The shaft inhomogeneity is the largest, and the multilayer Halbach magnet design and optimization model
is established based on the derivation of the magnetic field distribution equation of the single-layer Halbach magnet.
At the same time, the design of multilayer Halbach array magnets is simplified, and the optimization results based on different radii, each layer of Halbach array length and the spacing of each layer magnet are verified by simulation.
Finally, a 1T-Halbach array magnet consisting of three layers of Halbach magnets is designed to verify the theoretical results
.
After adjusting the position of the movable magnetic block in the magnet, a uniformity of 220 ppm was achieved in a standard 5mm NMR tube.
This work provides a theoretical basis for the design of multilayer Halbach array magnets to maximize uniformity and minimize the use of magnet materials, improve magnet fabrication efficiency, reduce magnet processing costs, and promote high uniformity Halbach Research and application
of magnets in desktop spectrometers and small magnetic resonance equipment.
At the same time, based on this design theory, the team designed and produced multiple sets of Halbach magnets
such as 0.
5T and 1T.
Among them, the relevant teams of Huazhong University of Science and Technology and East China Normal University were provided with a compact permanent magnet desktop spectroscopy system based on multilayer Halbach, with a magnet weight of less than 6kg and a passive shim post-field uniformity of 20ppm Within; In addition, the team implemented an active shim on another 0.
5T magnet system with a field uniformity of 0.
5ppm.
Subsequently, it is expected that Halbach magnets with high uniformity of up to 2 T will be designed and fabricated based on this theory, laying the foundation
for the development of high-performance desktop NMR spectrometers and desktop NMR imaging instruments.
The results were published in the journal Journal of Magnetic, entitled "Theoretical foundation for designing multilayer Halbach array magnets for benchtop NMR and MRI.
" On Reaonance, Yang Xiaodong, director of the imaging room of Suzhou Medical Institute, is the corresponding author
.
The research work has been supported
by the National Natural Science Foundation of China, the Natural Science Foundation of Shandong Province and other projects.
Link to the paper: (DOI ）: https://doi.
org/10.
1016/j.
jmr.
2022.
107322
Figure 1 The theoretical model (a) and magnetic field uniformity compensation model (b) of multilayer Halbach array magnets are proposed
Figure 2 The magnet (a) designed based on this theory and the spectral line (b) collected based on the magnet
Figure 3 Desktop 0.
5T NMR magnet system
