Figure 3

The tested force and FEA simulated force F_z vs. distance between two sets of N55 like poles. For the center-aligned like poles, the tested and simulated results are almost identical, with the same turning points TP and the zero force points δ. All these four curves of force vs. distance shown in Fig. 3(a) and (b) display an undisputable transition from a negative force, or a repulsion, to a positive force, or an attraction. This is a remarkable verification of the fact that the attraction can occur to these like magnetic poles. For the edge-aligned like poles, although the tested and simulated forces F_z shown in Fig. 3(a) and (b) do not completely coincide, the shapes of the curves are similar. Both the tested and simulated curves show the turning point TP at similar distances. It is believed that the difference between the tested F_z and the FEA simulated F_z for the edge-aligned pairs is due to the complication or the influence from the force in the x-axis direction, F_x. As shown in Fig. 3(c) and (d), the F_x is non-neglectable, and it produces a torque to affect the F_z. The fact of the turning point TP is unmistakable, and the simulated curves show a larger repelling force. The FEA successfully verified the attractive condition for unequally sized like poles.