Magnetic stiffness of a coupled high-T_c superconducting levitation system

High-T_c superconducting levitation systems, such as flywheels and linear-drives, have very small damping, because of their no contact support. Thus, they can show complicated phenomena of dynamics due to nonlinearity in their magnetic force or torque. In mechanical design of such systems, it is important to evaluate their nonlinear dynamics, though it has not been well studied so far. As one modeling of such an application system, we consider a magnetically coupled system of several permanent magnets and high-T_c superconducting bulks. It is a multi-degree-of-freedom dynamical system showing complicated motion caused by nonlinear interaction between levitated magnets and superconducting bulks. This research deals with magnetic stiffness of a coupled superconducting levitation system. As a fundamental dynamical property of the system, we evaluate the stiffness by doing experiment and analysis, and examine nonlinear effect on this property.