Jae-Sung Bae/Jai-Hyuk Hwang/Jung-Sam Park/Dong-Gi Kwag
The Journal of Mechanical Science and Technology, vol. 23, no. 11, pp.3024-3035, 2009

Abstract : Eddy currents are induced when a nonmagnetic, conductive material is moving as the result of being subjected to a magnetic field, or if it is placed in a time-varying magnetic field. These currents circulate in the conductive material and are dissipated, causing a repulsive force between the magnet and the conductor. With this concept, eddy current damping can be used as a form of viscous damping. The present study investigates analytically and experimentally the characteristics of eddy current damping when a permanent magnet is placed in a conductive tube. The theoretical model of eddy current damping as the result of a magnet in a copper tube is developed from electromagnetics and is verified from experiments. The experiments include a drop test whereby a magnet is dropped in a copper tube to measure the damping force in a steady-state, and a dynamic test is used to measure the same phenomenon in a dynamic-state. The drop test shows that the present model can accurately predict the force of steady-state damping. From the dynamic test, although predictability is not accurate at high excitation frequencies, the present model can be used to predict damping force at low excitation frequencies.

Keyword : Shock absorber; Vibration suppression; Damping force; Eddy current; Eddy current damping; Electromagnetic damping