A Halbach cylinder is a magnetized cylinder composed of ferromagnetic material producing (in the idealised case) an intense magnetic field confined entirely within the cylinder with zero field outside. The cylinders can also be magnetized such that the magnetic field is entirely outside the cylinder, with zero field inside. Several magnetization distributions are shown:
The direction of magnetization within the ferromagnetic material, in plane perpendicular to the axis of the cylinder, is given by
where Mr is the ferromagnetic remanence (A/m). A choice of +k gives an internal magnetic field and -k gives an external magnetic field.
Ideally, these structures would be created from an infinite length cylinder of magnetic material with the direction of magnetization continuously varying. The magnetic flux produced by this ideal design would be perfectly uniform and be entirely confined to the bore of the cylinder. Of course, the ideal case of infinite length is not realisable and in practice the finite length of the cylinders produces end effects which introduce non-uniformities in the field within the bore. The difficulty of manufacturing a cylinder with a continuously varying magnetization also usually leads to the design being broken into segments.
Read more about this topic: Halbach Array
Famous quotes containing the word cylinder:
“The outline of the city became frantic in its effort to explain something that defied meaning. Power seemed to have outgrown its servitude and to have asserted its freedom. The cylinder had exploded, and thrown great masses of stone and steam against the sky.”
—Henry Brooks Adams (1838–1918)