M4a1x
commented
1 year ago Didn't know about Mandhalas, but about Halbach magnets. Fukushima/McDowell sind da eher kritisch:
Halbach magnets [21] would commonly be considered well suited for compact NMR because they are extremely efficient; the magnetic material itself provides the flux return path, thus eliminating the heavy steel of a traditional magnet design. However, the rare-earth magnet materials generally show piece-to-piece variations of a few percent so these multipiece magnets must undergo major adjustments (shimming). The challenge of shimming any magnet rises with decreasing size; shimming efforts and designs [22, 23] rapidly drive the cost and complexity of the small magnet out of the realm of practical applications (B. Lown, Aster Enterprises, Acton, MA, USA, pers. commun.). We prefer the use of precision steel pole-caps and steel flux return paths in our small magnets since this simpler approach can meet the homogeneity, cost, and environmental insensitivity requirements of industrial applications; the extra weight of the steel is inconsequential for small enough magnets.
One of the NMR spectrometers in #29 uses a Mandhalas Magnet configuration. There are 3D printable designs that reach homogenous fields of 0.3T that seem very inexpensive done by Merideth Ann Frey Am I missing something? Temperature stability? An updated version seems to reach 0.6T in the homogenous region Current final update on the blog
The original paper from 2004 can be found here