Columnar solid body rotor

Claim 1

A rotor for d-c dynamo electric machines wherein said rotor is to be rotated at a high speed, has a relatively low loss, low inertia and is mechanically rigid and has an extremely low permeability; said rotor comprising, in combination: a rotor shaft rotatable around the axis thereof and made of a non-magnetic material; a cylindrical dust core of small volume compared to the volume of said rotor and symmetrically disposed around said shaft, said cylindrical dust core comprising a hollow cylinder having an outer diameter and having an interior diameter, said interior diameter being fixed to said rotor shaft, the length of said cylindrical dust core being greater than its said outer diameter; said dust core consisting of finely powdered ferromagnetic particles which are bound within and are interspersed within a solid insulation medium, whereby said dust core can have a high flux density while having a small eddy current loss; insulation sleeve means fixed to and surrounding and electrically insulating said outer diameter of said dust core; a winding fixed to the outer surface of said insulation sleeve means and closely wound around said dust core and having an outer diameter which encloses a given cross-sectional area which is perpendicular to said rotor shaft; the volume conversion permeability of said rotor as a whole, including said dust core, said rotor shaft, said winding and said insulation sleeve being at least several times higher than the permeability of free space; said outer diameter of said dust core enclosing an area A 1 which is perpendicular to the axis of said rotor shaft and wherein said given cross-sectional area enclosed by said winding is an area A 2 ; the ratio of A 2 /A 1 being in the range of 0.3 to 0.7.