These are improved versions of 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 improved design uses longer magnets to provide stronger magnetic fields and more homogeneity along the central axis, aiming for samples that will roughly 1 cubic-centimeter in size. The permanent magnets used are still easily purchasable online.
This Thing has two distinct pieces which are designed to work together:
Outer Mandhala + 4cm inner diameter; 8cm outer diameter + Eight 1⁄2” x 1⁄2”x 2” slots for N52 magnets (K&J Magnetics: https://www.kjmagnetics.com/proddetail.asp?prod=BY088-N52) + Tracks and bar for Inner Mandhala (see below) + Holes in each slot to easily remove the magnets
Inner Mandhala + 1.8cm inner diameter; ~4cm outer diameter + Eight 1/4” x 1/4” x 1” slots for N52 magnets (K&J Magnetics: https://www.kjmagnetics.com/proddetail.asp?prod=BX044-N52&cat=168) + Rails on sides fit into rails on Outer Mandhala; the Inner Mandhala sits on the bar in the Outer Mandhala so the middle of the Inner’s magnets are aligned with the centers of the Outer’s magnets + The Inner Mandhala slots into the Outer Mandhala for a stronger field (Up to ~.45 T)
The magnets in both the Outer and Inner Mandhala should be oriented according to Raich and Blümer’s article (see photo in image above) to get a homogeneous magnetic field.
Inserting the magnets into the Outer and Inner Mandhalas and inserting the Inner into the Outer Mandhala can be difficult, as the magnets resist these orientations. For us, it has consistently been a two-person job. The magnets are strong and very fragile. We suggest using spacers to keep them from attracting each other and potentially breaking upon impact.
These Mandhalas are an improvement on a previous design: (https://www.thingiverse.com/thing:2474075). All the files generated in SketchUp with modifications using ThinkerCad (we are moving towards using ThinkerCad or AutoCad in the future.) 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 Nick Torres and Ken Zhu based on the earlier design by Jeremiah O’Mahony.