Design and Realization of Large Dimension Ferrite Rings

Low leakage, low field, easy access flat hybrid magnets for MRI applications are being investigated. This configuration associates bobbins and ferrite permanent magnets having a Br field equal to 0.4 T. The complete magnet is designed using the laboratory-conceived CALMAG3D code[1] which allows us to simulate, in three dimensions, the various magnetic field producing elements (resistive bobbins, permanent magnets, ferromagnetic pieces) while taking into account their nonlinearity. A full-scale magnet should produce a sufficiently homogeneous field of a few ppm over a 30 cm sphere for whole body imaging purposes. For this reason we have elaborated a configuration of cylindrical [2] form with a revolution symmetry. The realisation of a 1/3 prototype requires some ferrite disks of big dimensions. We propose here a relatively low cost fabrication method with respect to that proposed by the manufacturers