Ferrofluids to improve field homogeneity in permanent magnet assemblies

• Halbach magnet adapted with rings for mechanical shimming. Novel passive magnetic field shimming method based on ferrofluid suspensions in microvolumes. Small size light-weight assembly suitable mobile resonance applications. A novel principle of permanent assemblies is introduced, defined amounts a suspension contained microliter volume plastic container that accurately positioned within the bore. The acts as micromagnet compensates inhomogeneities profile. proof shown assembly, derived from design, two additional movable magnets. These result an average strength 1.06 T inside bore, 19 % higher than alone. Two options ferrofluids are shown: changing material or choosing different saturation magnetization value. With tested simple single-cube implementation homogeneity improved 86 ppm to 8 over sampling length 5.5 mm. Better expected more sophisticated arrangements. complete has 5 × 4.2 cm 3 and weight 332 g. demonstrated concept particularly attractive systems, it does not require electrical power during operation.