1. Cylindrical permanent-magnet structures using images in an iron shield
- Author
-
J. M. D. Coey, Quanling Peng, and Sara McMurry
- Subjects
Physics ,Permanent magnets ,Condensed matter physics ,Iron ,Magnetic shielding ,Magnetostatics ,Polarization (waves) ,Magnetic flux ,Electronic, Optical and Magnetic Materials ,Boron alloys ,Neodymium alloys ,Dipole ,Physics::Plasma Physics ,Magnet ,Iron alloys ,Electromagnetic shielding ,Cylinder ,Electrical and Electronic Engineering ,Atomic physics ,Multipole expansion ,GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries) - Abstract
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.
- Published
- 2003