Fig. 1

Schematic diagram of (a) ideal Halbach magnet, (b) compact Halbach magnet and (c) discrete Halbach magnet structure

Fig. 2

(a) Schematic diagram of magnetic block with dimensions of 40 × 25 × 25 mm3; (b) The influence of the number of magnetic blocks on the magnetic field strength; (c) Schematic diagram of a single-loop magnetic ring arrangement

Fig. 3

Effects of the number of magnet ring layers and the end ring structure on the magnetic field homogeneity in the ROI

Fig. 4

(a) Schematic diagram of magnetic block with dimensions of 30 × 20 × 20 mm3; (b) Schematic diagram of the double loop magnetic rings at the top and bottom ends of the magnet

Fig. 5

(a) The effect of adding magnetic rings at both ends of the magnet on the homogeneity of the ROI (seven magnet ring layers in total); (b) Simulation result of magnetic field distribution in the ROI when no magnetic rings are added at the top and bottom ends of the magnet; (c) Simulation result of magnetic field distribution in the ROI after adding magnetic rings at both ends of the magnet

Fig. 6

(a) Front view of the magnet; (b) Schematic of the final magnet structure; (c) Effect of the number of magnet layers on the magnetic-field homogeneity within the ROI

Fig. 7

Photographs of (a) single magnet ring, (b) double ring assembly, and (c) fully assembled Halbach magnet

Fig. 8

(a) ROI and the 100 mm field mapping lines along the X, Y, and Z axes; (b) Initial magnetic field profiles within a 100 mm range along the X, Y, and Z axes

Fig. 9

Flowchart of the passive shimming procedure

Fig. 10

(a) Photograph of the passive shimming cylinder; (b) Magnetic-field profiles along the X, Y, and Z axes within a 100 mm range after passive shimming

Table 1

Performance parameters for each component of the test platform

Fig. 11

NMR experimental system

Fig. 12

(a) Schematic illustrating the relationship between the ROI and the Φ 100 mm × H 100 mm test region; (b) NMR signal of a Φ 100 mm × H 100 mm CuSO4 aqueous solution before shimming (10 signal averages); (c) NMR signal of the same sample after shimming (single acquisition, no averaging)

Fig. 13

(a) Schematic illustrating the relationship between the ROI and the Φ 25 mm × H 25 mm test region; (b) Comparison of the NMR signals from a Φ 25 mm × H 25 mm CuSO₄ aqueous solution before and after shimming (normalized); (c) Zoomed-in view of the peak region in (b)

Fig. 14

(a) CPMG echo envelope decay curve of a two component CuSO4 aqueous solution (TE = 0.3 ms); (b) T2 distribution spectrum of the two component CuSO4 aqueous solution