Torque in nested Halbach cylinders

Abstract

-Permanent magnet variable flux sources are produced by rotating two nested N-segment, permanent magnet, Halbach cylinders. Torque is primarily an end effect, determined by field non-uniformities due to the fmite length and' segmented structure of the cylinders. Due to symmetry, one cylinder experiences zero torque In a uniform applied field. Experiment and numerical simulation reveal that the torque is composed of a dominant term of frequency 1/(2n) and harmonics a t ( k N i l)/(Zn), where k is an integer.

An adjustable linear Halbach array

“…Practical magnetic designs also suffer from additional effects caused by the finite length of the magnetic components in the design (Ni Mhiochain, 1999;Bjørk , 2011).…”

“…Many configurations and permutations of such cylinder designs are possible. Nesting two Halbach cylinders allows a variable field within the bore of the device, which can be precisely controlled by the relative angle between the two cylinders (Ni Mhiochain, 1999). The magnetization distribution required for a Halbach array can, remarkably, even be created by induced magnetization in a highly permeable soft magnetic material (Peng, 2003).…”

Cylindrical permanent-magnet structures using images in an iron shield

“…When the polarization in the permanent magnet at is oriented so that (6) the field is an inward one, being zero outside the ring and having a pure -pole form inside it. For the case , illustrated in Fig.…”

“…Switchable magnets involve movement of the magnet relative to a soft-iron section. Rotatable nested Halbach cylinders were proposed by Leupold [3], and the structures have been built and analyzed in detail [6]. They are used as laboratory variable flux sources, superseding the electromagnet, and fields of up to 2 T can be achieved.…”

“…in nested cylinders [6]. The fields produced at the ends of a finite-length magnet depend on , when .…”