Abstract: A magnetic structure generating a substantially uniform magnetic field within a region of interest comprising at least one pair of magnetic wedges of substantially identical shape arranged symmetrically about a first axis and abutting one another along a common edge. Each magnetic wedge has a first side and a second side which terminate at the common edge. The first wedge of each pair is positioned to define a first angle between the first side and the first axis and a second angle between the second side and the first axis, and is uniformly magnetized in a direction relative to a second axis (perpendicular to the first axis) which is a function of the sum of the first and second angles.

Abstract: A hybrid permanent magnet structure for providing a uniform magnetic field within a region of interest while allowing access via open ends by a patient for NMR scanning and by a surgeon to the patient via a large opening at the top. The magnet structure comprises nested inner and outer magnetic structures separated by ferromagnetic material and surrounded by a ferromagnetic yoke. The inner magnetic sections comprise end blocks of triangular cross-section, and the outer magnetic sections comprise end blocks of trapezoidal cross-section. Field distortion compensating means is provided by a primary filter structure to the ferromagnetic material and by magnetic insertions or a secondary filter structure.

Abstract: A technique is provided for improving the homogeneity of the magnetic field within a cavity disposed inside a magnetic structure that has an opening to permit convenient access to an imaging region. The technique is based upon the step of inserting layers of magnetized material between plates of high magnetic permeability material. The layers are inserted at the boundary of the cavity. The technique includes the step of (1) computing the surface charges on the plates as used to derive the distribution of the magnetostatic potential, (2) analyzing the uniformity of the magnetic field within the imaging region as effected by the opening in the magnetic structure by expanding the magnetostatic potential in a spatial harmonic series, and (3) determining the geometry and the composition of the inserted layers based on the successive elimination of increasing orders of spatial harmonics in the potential expansion within the imaging region.

Abstract: A magnetic structure is provided having a pair of spaced apart magnetized elements having surfaces in a common plane that defines a wall of a cavity. The space between the first and second magnetized elements is formed with at least one slit extending perpendicularly to the common plane. In order to compensate for field distortion in the cavity, a magnetized element is provided in at least one of the slits, the material in the slit having a remanence that is different from the remanences of the spaced apart magnetized elements that define the structure. In modifications of the invention, the field distortion is compensated by including at least one component in the cavity that has a high magnetic permeability. This component, has a variable thickness. It may be formed of a single component, or of a plurality of plates. In a still further embodiment, for a yokeless magnetic structure, field distortion compensation is effected by positioning magnetized elements outside of the magnetic structure.

Abstract: A high field strength permanent magnet has a plurality of layers, with at least two of the layers being formed of materials of different remanence. The remanence of the material of each layer is no greater than that of the layers thereunder, and is preferably less than the remanence of all underlying layers.The inner layer may be formed of a magnetic structure in which all or part of a basic yoke has been replaced by a shunt of active material. Such a shunt may alternatively be employed in a single layer magnetic structure.

Abstract: The invention is directed to a method for determining the fields of permanent magnet structures with a surface or boundary solution method for the magnetic material with linear characteristics with small susceptibility and large permeabilities of the ferromagnetic materials.

Abstract: A magnetic structure defining a cavity includes a first member of high-permeability material having a flat surface defining a first wall of the cavity, and a member of permanent magnetic material spaced from the flat surface and producing a uniform magnetic field in the cavity. The permanent magnetic material member may have two or more layers, with the layers outward of the cavity being of a material having a remanence that is no greater than the adjacent inner layers.

Abstract: A permanent magnet structure comprising a longitudinally extending flux sce fabricated of magnetically rigid material. The flux source comprises a central cavity with a magnetic field being produced therein. Magnetic dipoles having predetermined magnitude and orientation for compensating nonuniformities in the magnetic field are symmetrically located within the plane of the flux source.