Fundamental analysis of magnetic damping force for a rotating machine

Magnetic dampers used in turbo-molecular pump and the like in order to reduce vibration sometimes generate unstable vibrations. In this report, the authors present a new modeling and a new method using an infinitesimal conductor loop for calculating magnetic damping force, which acts on a conductor disk moving and rotating in a static magnetic field. The advantages of this method are that it doesn't need a complicated calculation of scalar potential's distribution in the conductor and that the magnetic damping force is derived with ease from the static magnetic field analysis through FEM or some fairly simple measurements. In addition, the magnetic damping force computed by the present method is very useful for obtaining the solution to an unstable vibration of a rotating machine caused by a magnetic damper. In conclusion, the analytical results agreed well quantitatively with the experimental ones.