Halbach permanent magnet machines and applications: a review

Permanent magnet brushless machines employing multipole Halbach magnetised rotors are being developed for various applications, since they offer a number of attractive features. Alternative Halbach machine topologies are reviewed, and the realisation of Halbach magnetised magnets from pre-magnetised sintered rare earth magnet segments (which approximate the Halbach magnetisation distribution and thereby compromise their performance), and as bonded isotropic and anisotropic NdFeB ring magnets (which are subsequently impulse magnetised with a Halbach field distribution), is considered. Radial- and axial-field, slotted and slotless, rotary and linear (tubular and planar), and spherical Halbach magnetised brushless machines are described, and potential applications, including a motor/generator for a high-speed flywheel peak power buffer, high-performance linear and rotary servo motors, and passive magnetic bearings are considered