Patent ID: 7256672

Claim:
A method for shimming a magnetic field generating device, comprising: positioning a plurality of permanent magnets (PM) to form an arrangement, each permanent magnet having a north end and a south end, and each aligned in the same north-south orientation, the plurality positioned to have a surface at the north polarity end of the PM arrangement, a surface at the south polarity end of the PM arrangement, or a surface at both ends of the PM arrangement; forming a shim assembly having a layer comprising a ferromagnetic material securely disposed at a pole face of a PM shim; and securely positioning the shim assembly at a surface of the PM arrangement, the layer of the shim assembly being positioned facing the surface of the PM arrangement, and the PM shim being positioned on a side of the layer opposite that of the PM arrangement; wherein the layer has a thickness equal to or less than about 15 millimeters.