General formulation of equivalent magnetic charge method for force density distribution on interface of different materials

The conventional force calculation methods can be applied only for the total force of the objects surrounded by air or vacuum. In this paper, a new general form of equivalent magnetic charge method is proposed for calculating force density and total forces of materials in contact including ferromagnetic and permanent magnet. It provides surface force density on the interface of different materials. The validity of this method is shown by direct observation of the formulas and numerical tests.