Verification of pull-up force and electromagnetic spring to an aluminum ring using ac electromagnets

Magnetic levitation (maglev) systems for nonmagnetic conductive metals generally generate only repulsive force between the stator and the levitated body. To overturn the conventional common sense, we have fabricated a new maglev device that can generate 'attractive force' between the stator consisting of plural ac electromagnets and a nonmagnetic conductive metal ring. In this paper, we elucidate the electromagnetic phenomenon that appropriately arranged seven ac electromagnets continuously pulls up an aluminum (Al) ring, which has 120 mm outer diameter and 5 mm square cross-section, by using finite element analysis. The analysis results reveal the existence of an equilibrium gap where the electromagnetic pulling force balances with the weight of the Al ring without active control. Besides, the equilibrium gap was measured when different weights were added to Al ring to verify the validity of analysis results. The measured results show that the maglev device has a positive stiffness (i.e., electromagnetic spring) of 50 N/m.