摘要:
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. The second wedge of each pair is magnetized such that the absolute values of components of the magnetization along the first and second axes are equal to components of the magnetization of the first wedge along the first and second axes, respectively, and one of the magnetization components of the second wedge is opposite to the respective magnetization component of the first wedge. The region of interest containing the substantially uniform field is between the first sides of the pair of wedges, the second sides of the pair of wedges, or both. To minimize or eliminate the surface charge density along the third side of each wedge, the third side of each wedge is preferably parallel to the direction in which the wedge is magnetized.
摘要:
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.
摘要:
An open unipolar magnetic structure allowing an arbitrary location of a region of interest which will contain a uniform magnetic field within a cavity. In a preferred embodiment, a yoked magnetic structure is modified to reduce the field perturbations in the region of interest when the latter is arbitrarily located within the cavity. The modification includes the provision of supplemental permanent magnetic members at the opening, the configuration of the supplemental permanent magnetic members being related to the configuration of some of the permanent magnetic members of the magnetic structure that provides the uniform magnetic field.
摘要:
A magnetic structure generating a uniform magnetic field within a region of interest using permanently magnetized prism-shaped blocks of magnetic material positioned around a cavity and which constitute the predominant generator of the uniform magnetic field in the desired region of interest. The magnetic structure has a plane surface comprising a high permeability ferromagnetic member interfacing with a first side of the cavity and forming a single pole piece of the magnetic structure. The magnetic structure produces within the cavity adjacent the single pole piece the uniform magnetic field and collects the magnetic flux flowing through the single pole piece and through the cavity, with the region of interest being located adjacent the single pole piece. A second side of the cavity generally opposite to the first side is open to a surrounding medium and forms an interface with the surrounding medium but not with a magnetic member. The magnetic structure is designed assuming a hypothetical high permeability membrane parallel to the single pole piece and located where the open second side of the cavity will be made, the high permeability membrane forming an equipotential surface at the interface with the surrounding medium. This minimizes the fringe field generated in the surrounding medium when the second side of the cavity is opened.
摘要:
A magnetic structure generating a substantially uniform magnetic field within a region of interest using permanently magnetized wedge-shaped blocks of magnetic material. In a preferred embodiment, the permanently magnetized wedge-shaped blocks are provided in pairs positioned on opposite sides of the x z plane of an arbitrary x,y,z coordinate system, and each of the blocks are magnetized in certain directions. The uniform field is created in the vicinity of the z axis. In another embodiment, the parts of the structure below the x-axis are replaced by a high-permeability, soft magnetic plate to form a so-called mirror system. In still another embodiment, permanently magnetized blocks positioned outside of the wedge-shaped blocks are employed as the main compensation means for field distortions arising from the practical need to truncate the wedge-shaped blocks to a practical size. An important application for the magnetic structure of the invention is MRI, as it can be configured as an open structure accessible to medical intervention during the MRI.
摘要:
Strapped open magnetic structure, particularly useful in nuclear magnetic resonance imaging applications, which provides a substantially uniform magnetic field within a region of interest while allowing access by a surgeon to a patient via an opening at the top of the magnetic structure. The magnetic structure comprises nested inner and outer magnetic structures separated by ferromagnetic material or pole pieces and surrounded by a ferromagnetic yoke. The structure contains one or more thin layers or straps of high magnetic permeability material aligned substantially along equipotential surface(s) of an associated closed magnetic structure of ideal properties. Structures and techniques are also provided for replacing thick, heavy blocks of ferromagnetic material with thin straps and for extending the magnetostatic potential of a component in a magnetic structure by connecting a thin strap thereto and embedding the strap in the magnetic structure along an equipotential surface of the magnetic field generated by the magnetic structure.
摘要:
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.
摘要:
A yoked magnetic structure has a pair of spaced magnetized members defining a cavity, and an end ferromagnetic structure closing said cavity and abutting an end of the magnetized members. The end structure comprising at least a first element of triangular cross section having one side abutting an end of one of said magnetized member and a second element of triangular cross section having one side abutting the adjacent side of said cavity. The first and second elements have second sides away from the magnetized member and cavity defining at least part of an equipotential line whereby the flux density on the side of the equipotential line away from the magnetized structure is zero. A region of .mu.=.infin. material is provided adjacent the magnetized member to minimize the effect of perturbations.
摘要:
A superconducting magnet, in which a static magnetic filed is generated in a region of interest, i.e. a predetermined volume in which the part under examination has to be placed for imaging characterised in that it is provided with means for generating a uniform annular distribution of electric currents enclosing the polyhedral cavity.
摘要:
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.