Electric generator having plural stators

An electric power generator comprising a rotor and a plurality of stators, wherein:

• the rotor and the plurality of stators are arranged coaxially and concentrically about a central axis;
• the rotor is provided radially inwardly of the plurality of stators;
• a first stator of the plurality of stators is provided concentrically around and adjacent to the rotor, the rotor and the first stator being separated by a rotor-stator airgap;
• a second stator of the plurality of stators is provided concentrically around and adjacent to the first stator, the first and second stators being separated by a stator-stator airgap;
• the rotor includes a plurality of magnetic pole structures configured to provide or generate a plurality of magnetic poles;
• a radially outer surface of each of the magnetic pole structures is curved with an average radius of curvature which is less than an average distance between the outer surface and the central axis, the rotor-stator airgap thus varying circumferentially in distance, with a shortest distance being at a circumferential centre of each of the magnetic pole structures and longest distance being at circumferential ends of each of the magnetic pole structures;
• wherein the stator-stator airgap is shorter than the shortest distance of the rotor-stator airgap;
• wherein the electric power generator includes a back-iron configured to provide a return path and assist in closing a magnetic circuit from the magnetic poles of the rotor, the back-iron is provided around the plurality of stators, in other words, around, the back-iron having a thickness of at least 2 mm;
• and
• wherein the stator-stator airgap is of uniform thickness and is at least 0.25 mm.