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A buried magnet rotor structure, which is supported only by permanent magnets, is proposed for medium-speed permanent magnet machines. Many design aspects of the dovetail-shaped rotor structure have been found. Various machine solutions, with pole numbers 6 to 14, are studied with electromagnetic and structural finite element simulations. A simple model is created for making comparison with the different pole numbers easier. Main dimensions of the machine are kept the same. Optimal solutions for various pole numbers are searched and discussed. It is shown that for lower pole numbers, the structure is electrically better, while for higher pole numbers, the structure is mechanically stronger against centrifugal forces. In addition, the optimal electromagnetic structures for each pole number are shown to be similar to the optimal mechanical structures. Electrically and mechanically critical areas are also shown to be almost the same. The optimized results are also compared to three manufactured prototypes. The obtained results demonstrate the feasibility of the construction and the design method.