This is a Halbach NMR Mandhala (along with several attachments) to be used in small magnetic resonance imaging experiments.
The purpose of the Halbach NMR Mandhala [Magnet Arrangements for Novel Discrete Halbach Layout, created by Raich and Blümler, “Design and Construction of a Dipolar Halbach Array with a Homogeneous Field from Identical Bar Magnets: NMR Mandhalas”, Concepts in Magnetic Resonance part B (Magnetic Resonance Engineering), Vol. 23B(1) 16-25 (2004), DOI 10.1002/cmr.b.20018] is to provide a large, homogeneous magnetic field over a large and accessible volume made from identical and affordable permanent magnets. This design focuses on modularity and flexibility to generate a variety of different magnetic fields which can be easily modified depending on desired uses and sample sizes.
There are five individual pieces:
- NMR Mandhala
- 8 cm outer diameter, 4 cm inner diameter
- Eight 1/2” x 1/2” x 1/2” slots for the permanent magnets (N-52 ½” cubes from K&J Magnetics).Lip on top and bottom so that mandalas can be stacked for a greater field (~0.3 T at center)
- 4 cm inner diameter
- Four holes for bolts (Nylon ¼-20 hex bolt, 3” length)
- 3.8 cm divot to hold mandalas
- Four holes for bolts
- 3.8-cm diameter divot to hold NMR Mandhalas
- Sample Holder
- Five holes to hold 5mm NMR sample test tubes
- Arms slot into the lid to keep stable
- Center Mandhala
- 4 cm outer diameter, 2 cm inner diameter
- Eight 1/4” x 1/4” x 1” slots for the permanent magnets (BX044-N52 from K&J Magnetics).
- An additional NMR Mandhala to fit inside two stacked 8-cm Mandhalas to provide a stronger field (up to 0.45 T)
Stacking the Mandhalas can be tricky, as their magnetic fields will want to align in a way that isn’t conducive to creating the desired strong magnetic fields. Therefore we recommend securing the top Mandhala to the lid and the bottom Mandhala to the base using hot glue (and the glue can later be peeled off). Alternatively, you can enlist at least two friends to help hold everything together by brute force.
All the files here were made in SketchUp using designs from the article above for the NMR Mandhalas themselves and original designs for the base, sample holder, lid, and center Mandhala. They were converted to .stl files in MeshLab. Theoretical predictions were calculated and plotted using the open-source Finite Element Method Magnetics, FEMM 4.2 and magnetic field measurements were made with AlphaLab’s Gaussmeter Model 2.
This model was constructed by Jeremiah O’Mahony with guidance and good-natured mockery from Merideth Frey, PhD, in beautiful Yonkers, New York.