This is an updated version of the NMR Mandhala Gradient. You can find the new version here: https://www.thingiverse.com/thing:3799946.
Improving upon our previous permanent magnet gradient design, we decided to switch to a more modular design where multiple copies of the same magnet holder can be used to create linear gradients along the different axes of an NMR MANDHALA. This was designed to have an 8-cm inner diameter and hold four 1⁄2” x 1⁄4” x 1” magnets, specifically either magnets with poles on tall, narrow sides or magnets with poles on large faces. The measurements shown here use the N42 magnets provided in the links.
The center two holders hold 8 magnets arranged to create a quadrupolar field, as described on an article by Peter Blümler (“Permanent Magnet System for MRI with Constant Gradient mechanically adjustable in Direction and Strength”, Concepts in Magnetic Resonance Part B (Magnetic Resonance Engineering), No Vol. Number (2015), DOI 10.1002/cmr.b.21320). The angle of the two gradient pieces relative to each other changes the gradient strength along the external homogeneous field provided by the NMR Mandhala. The maximum gradient strength is observed when all the magnets are at 45-degree increments. We achieved a maximum gradient of ~11 Gauss/mm with this setup and the magnets given above.
The outer two holders generate a linear gradient along the cylindrical axis by orienting the magnets such that one side adds to the homogeneous magnetic field created by the NMR Mandhala and the other side subtracts. One can control the strength of the gradient field by adjusting the separation between the two sides, with the maximum gradient we measured being ~5 Gauss/mm.
For more information, check out the Summer Science 2019 summary blog post.