Evaluation of Overdamping Behavior of a Vibrating Conductive Cylinder in a Strong Magnetic Field

Magnetomechanically coupled problems of conductive structures are generally known, but the focus of interest has been on underdamping, not overdamping. The purpose of this study is to verify the applicability of unidirectional weak-coupling analysis to the overdamping behavior of a vibrating thin conductive plate in a strong magnetic field, which is a necessary procedure for designing magnetic resonance imaging (MRI) equipment. An impact vibration experiment was done with a thin conductive cylinder in the 3-T field of an MRI magnet. Magnetic modal damping ratios and accelerations of the cylinder were calculated by eddy current analysis and frequency response analysis. As a result, specified peaks of the acceleration curves were found to disappear and the corresponding eigenmodes were the same for both the experiment and analysis. Furthermore, relative errors of the acceleration amplitude decrease ratio were in the range of 9.2%-31.9%; hence the calculated acceleration was on the conservative side. Consequently, the analysis method was judged suitable as a practical calculation method for designing MRI equipment that considers the overdamping behavior.