Permanent-magnet behaviour under `open-circuit¿ conditions

In general, the determination of the performance of permanent magnets in free air is a complex problem. Certain, clearly-stated assumptions having been made, an analytical solution for the open-circuit, cylindrical bar magnet is presented, this based on the solution of a partial differential equation for the magnetic scalar-potential distribution within the magnet itself. Rationalised characteristics are presented to enable the minimum axial-flux density within a magnet of given proportions to be determined from a knowledge of the magnet material´s relative permeability and operating characteristic. Hence, an indication may be obtained as to the advisability of leaving the material unkeepered in air. A theoretical characteristic is compared with some preliminary experimental results obtained using a flexible, bonded-ferrite permanent-magnet material.