Analytical study of radial stability of permanent-magnet synchronous couplings

Magnetic couplings are used to transmit a torque through a magnetic separation wall without any mechanical contact between the two rotors. But the usual cylindrical-airgap magnetic coupling is radially unstable. This instability can be computed from the analytical formulas of the force components exerted between two magnets. The instability can then be analyzed. We present a structure for an astable coupling. Such a coupling does not generate any radial force when a radial displacement occurs. It is a perfect mechanical filter.