A Short and Light, Sparse Dipolar Halbach Magnet for MRI

Citations Over TimeTop 18% of 2021 papers

Abstract

Recently designed dipolar Halbach magnets used in portable MRI systems are much lighter and more compact than standard permanent or superconductive magnets. However, improved designs and manufacturing techniques aiming at lower weight and smaller external size are an area of continual interest especially for application to space flight. Most Halbach magnet design techniques aim to optimize homogeneity suitable for MRI over a diameter-spherical volume (DSV) that requires the aspect ratio (length/inner diameter) to be larger than 1.5:1. Furthermore, current magnet construction techniques often use low-coercivity magnetic pieces and imperfect formers that produce a mismatch in the intended designs. As a result, Halbach magnets require complex shimming methods to improve the magnetic field homogeneity, causing further size and weight increase. Here, we propose to reduce the weight and the aspect ratio of the Halbach magnet by optimizing homogeneity over a cylindrical region of interest (ROI) rather than a DSV, applying a genetic algorithm, high-coercivity ferromagnets (N40UH) and a robust construction technique. The assembled 67 mT magnet, with aspect ratio ~ 1:1, produces almost identical homogeneity (11152 ppm) as simulations (11451 ppm) within a 12.7 cm diameter, 1 cm long cylinder ROI. The magnet structure was 3D printed ring-by-ring and assembled coaxially. The magnet can be disassembled for transportation.

Related Papers

• → Permanent Magnets Design and Magnetic Field Analysis of a Novel Permanent Magnet Linear Motor(2012)1 cited
• The Effect of Magnet Structure Size on Halbach Array(2010)
• Design of dipole permanent magnet with high field strength(2003)
• → Study on a novel 1D Halbach permanent magnet array based on the analysis of the side shape of permanent magnets(2023)
• → Design of an Electromagnet Reaction Wheel With Halbach Array(2025)