Eddy Current Damper Model of Ring Magnet and Coaxially Moving Conducting Disk

An eddy current damper comprising a magnet and a conducting plate moving perpendicularly to it is called a perpendicular-motion-type eddy current damper, whereas one with a magnet and a conducting plate moving parallel to it is called a parallel-motion-type eddy current damper. In this article, a method of using magnetic vector potentials in a stationary-conductor coordinate system to obtain easily the damping coefficient (the A method) is proposed and applied to a perpendicular-motion-type eddy current damper comprising a ring magnet and conducting disk. The previously proposed coil method is also applied. Because both methods utilize the magnetic flux densities and magnetic vector potentials obtained using a circular current loop, they cannot be considered to be the effect of the magnetic field generated by eddy currents on the damping coefficients. However, the damping coefficients were in good agreement with those obtained using a 3-D finite element method (3-D-FEM). Hence, the effect of the secondary magnetic field can be ignored. Moreover, the A method is as precise as the 3-D-FEM, is less complicated, and does not require an air region and boundary conditions for computation. In addition, although the errors of the damping ratios calculated from measured data and the A method were 17%, the error of the modified damping ratios obtained by applying the equivalent mass of the disk to the A method decreased to 6%.