I. Introduction
A permanent magnetic coupling (PMC) creates synchronous torque transmission without physical contact. The study of the torque capabilities of magnetic couplings is fundamental to ones understand of the upper bound on the torque densities of magnetic devices, such as motors and magnetic gearboxes [1]. The axial and radial PMC, as illustrated in Fig. 1, form the two primary types of PMCs. The external field created by a PMC can be made close to sinusoidal in form if a Halbach rotor magnet structure is utilized. An example of an axial and radial Halbach rotor magnet arrangement is shown in Fig. 2. In order to compute the PMCs torque, the field from each individual magnet is typically first determined, and then the magnet’s fields are summed up and used to compute the torque. Examples of authors using this approach are given in [2]–[5]. Other authors have utilized the finite element analysis (FEA) technique to determine the optimal geometric design for a PMC [6], [7].
(a) Axial magnetic coupling. (b) Radial magnetic coupling.
(a) Eight-segment four pole-pair -axis directed (/2) axial Halbach rotor and (b) externally directed () radial Halbach rotor.