Cylindrical permanent-magnet structures using images in an iron shield

We report on cylindrical permanent-magnet structures that exploit the image effect in a surrounding circular soft-iron sheath. We present the theory for a general multipole ring, where the polarization direction /spl alpha/ = (n + 1)/spl psi/, n is a positive or negative integer, and /spl psi/ is th...

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Bibliographic Details
Published in:IEEE transactions on magnetics 2003-07, Vol.39 (4), p.1983-1989
Main Authors: Quanling Peng, McMurry, S.M., Coey, J.M.D.
Format: Article
Language:English
Subjects:
Applied classical electromagnetism
Boring
Cylinders
Electromagnetism
electron and ion optics
Exact sciences and technology
Ferrous alloys
Flux
Fundamental areas of phenomenology (including applications)
Iron
Magnetic anisotropy
Magnetic confinement
Magnetic field measurement
Magnetic flux
Magnetic materials
Magnetic shielding
Magnetism
Magnetostatics
magnetic shielding, magnetic induction, boundary-value problems
Multipoles
Perpendicular magnetic anisotropy
Physics
Polarization
Sheaths
Shields
Toroidal magnetic fields
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Summary:We report on cylindrical permanent-magnet structures that exploit the image effect in a surrounding circular soft-iron sheath. We present the theory for a general multipole ring, where the polarization direction /spl alpha/ = (n + 1)/spl psi/, n is a positive or negative integer, and /spl psi/ is the angular coordinate. For the uniformly magnetized case n = -1, a long cylindrical ring produces no field in its bore, and the field outside the cylinder is that of a linear dipole. When surrounded by the sheath, the field becomes uniform in the bore and zero outside the cylinder. Higher multipole fields can similarly be transformed from outward fields to inward fields by using the sheath. The field can be varied continuously by moving the sheath. We describe a small variable-field device using a Nd-Fe-B cylinder that produces a flux density of 0-400 mT.
ISSN:0018-9464
1941-0069
DOI:10.1109/TMAG.2003.814286