Magnetic Circuits Employing Ceramic Magnets

Measurements of the field produced by a ceramic, brick-shaped magnet show that the assumption of fixed, uniform magnetization is a useful approximation to the physical state of the magnet. One consequence is that the magnetization is easily measured without disturbing the physical state of the magnet. Another consequence is that the incremental permeability of a ceramic magnet is approximately that of free space. This leads to a significant simplification in the equations describing the fields produced in magnetic circuits employing ceramic magnets. Several types of magnetic circuits are analyzed from this new point of view. A method of design optimization is developed which, in one particular case, violates the ancient criterion that the magnet operate at the point of maximum BH product. A generalized derivation of the BH energy theorem is given. The properties of steel magnets are contrasted with those of ceramic magnets. In an effort to make use of the leakage field of steel horseshoe magnets, a low-leakage ceramic-steel magnet is developed in which both magnetic materials operate at their respective points of maximum BH product. A method is described and analyzed by which the uniformity of the field produced by ceramic pole pieces is improved by covering the pole faces with thin sheets of iron.