Patent ID: 6225887
Filing Date: 2001-05-01
Classification: G01R,H01F

Abstract:
A magnetic structure for generating a uniform magnetic field within a region of interest, comprising:a) a pair of wedge-shaped blocks of permanent magnet material and of substantially identical shape and positioned within an arbitrary three-dimensional rectangular coordinate system consisting of perpendicular x, y, and z axes meeting at an origin such that the pair of wedge-shaped blocks are arranged symmetrically on either side of the xz plane and abut one another along a common edge extending along or parallel to the z axis, each wedge-shaped block having a first major side and a second major side subtending a first angle and which terminate at or near the common edge, each wedge-shaped block being substantially uniformly magnetized in a direction substantially perpendicularly to the z axis and a first wedge-shaped block of the pair having a magnetization J whose orientation forms a second angle .alpha. with respect to its first side and a second wedge-shaped block of the pair having a substantially similar magnitude of magnetization J,b) the first wedge-shaped block of the pair of wedge-shaped blocks being configured to define a third angle .phi..sub.a between the first side and the x axis and a fourth angle .phi..sub.b between the second side and the x axis,c) a high-permeability member having an edge substantially coinciding with the z axis and having a face substantially coinciding with the second side of each of the wedge-shaped blocks, the radial extent from the origin of the rectangular coordinate system of the high-permeability member being at least equal to that of the wedge-shaped blocks,d) the second wedge-shaped block of the pair of wedge-shaped blocks being magnetized such that components of its magnetization J along the x and y axes are related to corresponding x and y axis components of the magnetization J in the first wedge-shaped block of the pair of wedge-shaped blocks such that one of their respective x and y axis components extends in opposite directions and the other of their respective x and y axis components extend in the same direction,e) said region of interest being situated close to the common edge and being confined to a region of the cavity bounded by the first major sides of the wedge-shaped blocks, said wedge-shaped blocks being a major contributor to the uniform magnetic field in the region of interest,f) compensation means for reducing field distortions by the substantial elimination of selected harmonics of the uniform magnetic field in the region of interest, the compensation means comprising one or more pairs of compensating blocks of permanently magnetized material and uniformly magnetized perpendicularly to the z axis, the radial extent from the z axis of the compensation blocks exceeding that of the wedge-shaped blocks.