Shimming of yokeless permanent magnets designed to generate uniform fields

Recently introduced yokeless permanent magnets are very suitable for generating uniform fields. Practical yokeless magnets must be shimmed or compensated for fabrication and magnetization tolerances. The particular shimming approach described exploits the magnetic transparency of yokeless structures. The method is based on the use of active elements of high‐energy‐product material. The logic for determining the distribution of active elements is based on measuring the departure from uniformity of the field sampled on a sphere surrounding the region of interest. The magnetic moments of the elements are determined by solving a system of linear equations representing the field generated by active elements on each sampling point.