Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Patent
1990-09-24
1992-07-07
Harris, George
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
335304, 324318, H01F 700
Patent
active
051286432
ABSTRACT:
A magnetic shield is presented comprising a shell of ferromagnetic material, augmented by one or more shielding magnets. The shielding magnets may be permanent magnets, electromagnetic coils, or other sources of magnetic flux. These shielding magnets are placed in close proximity to the shell, on the surface facing the region to be shielded, and are arranged to cancel any magnetic flux penetrating through the ferromagnetic shell into the region to be shielded. This invention provides magnetic protection for an exterior region when the shield is assembled around a magnet whose external field is to be contained, such as an MRI magnet. This invention also provides protection within an interior volume which is to be protected from an exterior source such as the Earth's magnetic field. The method by which the invention is applied is an iterative one, in which the shielding magnets are applied to substantially cancel the leakage field and then adjusted to minimize the remaining field in the shielded region. The invention is expected to be useful in containing the fringing field of medical imaging magnets as well as other applications.
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