Magnetization patterns of permanent ring magnets in brushless DC motors

The effects of the geometry of the magnetizing fixtures on the magnetization patterns of the permanent ring magnets are studied. The sample ring magnets are magnetized in magnetizing fixtures having various geometries. Each of the magnets creates a unique magnetic field due to the difference in the magnetization pattern of the permanent magnets. The prototype motors with the sample magnets were examined and the measured back electromotive force profiles and cogging torque profiles turn out greatly affected by the magnetization patterns. Using two-dimensional electromagnetic field theory, this article proposes a general closed form representation for the air gap flux density created by non-conventional magnetization pattern which has magnetic orientation in both radial and tangential directions. The results are compared with the finite element results for validity.