Halbach永磁体因其无需轭铁、外杂散场小等优势，在低场核磁共振（LF-NMR）领域（例如岩芯分析）有着潜在的广泛应用前景．相较于小体积岩芯，大体积更容易保留原始内部结构与流体状态，但其测试时要求更大的磁场均匀区域．然而Halbach磁体的异型结构导致其初始磁场均匀度差，难以直接获得较大的磁场均匀区域．为此，本文结合Halbach磁体理论与有限元仿真方法，设计得到场强158.4 mT、均匀度22 502 ppm（1 ppm=10^-6，直径100 mm球形区域）的Halbach磁体．采用改进的谐波分析无源匀场法，将磁场均匀度提升至1 496 ppm（提升15倍）．无源匀场后采集直径100 mm、高度100 mm硫酸铜水溶液中¹H的FID，并采集双组分硫酸铜溶液CPMG信号，以T₂为依据分辨不同样品组分．上述结果表明，本文的磁体设计方案与无源匀场方法为大口径高均匀度Halbach磁体的构建提供了有效技术支持．

Halbach permanent magnets hold significant promise for low-field nuclear magnetic resonance (LF-NMR) applications, such as rock core analysis, owing to their yoke-free design and low external stray fields. Compared with small rock cores, large rock cores better preserve the original internal structure and fluid distribution, yet they demand a larger homogeneous region. However, the complex structure of Halbach magnets inherently yields inadequate initial homogeneity, making it difficult to directly obtain a sufficiently large homogeneous region. In this study, we defined a 100-mm-diameter spherical region of interest (ROI) and optimized the magnet structure using Halbach magnet theory and finite-element simulations. The final designed magnet provides a field strength of 158.4 mT and an initial homogeneity of 22 502 ppm (1 ppm=10^-6). We applied an improved harmonic-based passive shimming method and enhanced the field homogeneity to 1 496 ppm. After passive shimming, we acquired ¹H free induction decay (FID) signals from an aqueous CuSO₄ sample (Φ 100 mm × H 100 mm), and Carr-Purcell-Meiboom-Gill (CPMG) signals from a two-component CuSO₄ aqueous solution, and distinguished different samples based on their T₂. These results demonstrate that the proposed magnet design and passive shimming method are effective for constructing large-bore, high homogeneity Halbach magnets.