Accounting for material imperfections in the design and optimization of low cost Halbach magnets

Abstract

We demonstrate an experimental method for the improvement of the magnetic field homogeneity in Halbach magnets by taking magnet material imperfection into account. This method relies on the determination of the magnetization magnitude only for individual magnet blocks based on nuclear magnetic resonance field measurements in a simplified system, which, in our case, consists of four blocks. Then, a set of configurations with highest homogeneities can be found from simplified field map simulations of all possible configurations or by applying sophisticated optimum search algorithms if the number of blocks is large. Finally, the residual effect of angular magnetization deviations can be reduced by the experimental selection of the best configuration from the set found on the simulation step. This selection strategy is based on the conclusions made from statistical analysis of simulated field maps. By applying the described method to our eight-element magnet, we experimentally achieved tenfold field homogeneity improvement. Thus, in the best configuration, we obtained an average value of the magnetic field of 598.0 mT and a half-width of 226.9 ppm for a sample with a diameter of 4 mm and a height of 10 mm. These parameters along with the compact magnet size (40 × 40 × 102 mm3) and weight (0.6 kg) provide reasonable magnet quality compared with analogous systems having more complex magnet arrangements and significantly higher costs.

Magnetic Guiding with Permanent Magnets: Concept, Realization and Applications to Nanoparticles and Cells

“…This arrangement is also named Mandhalas [54] and densely packed geometries for differently shaped sub-pieces are discussed in [55]. The main advantage of using identically magnetized sub-pieces is to determine their individual strength (remanence), sort, and orient them to optimize the homogeneity of the resulting magnet [56][57][58]. If the footprint of the sub-pieces covers an area A M , the strength of the resulting magnet is reduced by the ratio to the area of the ideal Halbach (i.e., π…”