The stator comprises a steel yoke (4) inside which there is a ferrite cylinder (5). This is magnetised in a radial direction. Inside the bore of the ferrite cylinder are flux gathering plates (6, 7) corresponding to the number of poles, and, radially inward from these, flux concentrating plates (9, 10) of shorter arc. By the use of the gathering and concentrating plates a high effective gap flux density is achieved, which is higher than would be feasible with poles entirely made from permanent magnet material. Additionally the plates provide the formation of a pole arc of requisite length for optimum performance of the machine.
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