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，设计得到主磁场约158.4 mT、直径100 mm球形目标区域的初始磁场均匀度为22 502 ppm（1 ppm=10^-6）的大口径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 have potential wide application prospects in low-field nuclear magnetic resonance (LF-NMR), such as rock core relaxation analysis, because they require no iron yoke and produce small external stray fields. Compared with small rock cores, large rock cores retain the original internal structure and fluid distribution more completely, but they require a larger homogeneous region. However, the complex structure of Halbach magnets results in inadequate initial homogeneity, which makes it difficult to obtain a large homogeneous region directly. We defined a 100 mm-diameter sphere as the region of interest (ROI) and optimized the magnet structure using Halbach magnet theory and finite-element simulations. Finally, we designed a magnet, which provided a field strength of 158.4 mT and an initial homogeneity of 22 502 ppm. We applied an improved harmonic-based passive shimming method, and the field homogeneity was improved to 1 496 ppm. Then, we measured ¹H FID signals from an aqueous CuSO₄ sample (Φ 100 mm× H 100 mm), and we measured CPMG signals from a two component CuSO₄ aqueous solution, distinguished different samples through T₂. These results show that the magnet design and passive shimming method are effective for building large-bore, high homogeneity Halbach magnets.