Evaluation of Eddy-Current Effects on Diamagnetic Bearings for Microsystems

Diamagnetic materials could be utilized with permanent magnets to offer a simple passive solution to micro bearings as a result of scale reduction. In this paper, we investigate the eddy-current effect on the performance of diamagnetic bearings. Due to the good electrical conductivity of some of diamagnetic materials or the intentionally introduced eddy-current damper for vibration control, eddy current could be induced in the diamagnetic bearing with viscous forces opposing the relative motion between the rotor and the stator. Such damping mechanism is analyzed with a thin-sheet model and the image method and compared with that due to aerodynamic effects so as to give an idea of its significance at the microscale. Following the calculation, extracted damping coefficients are employed in a rotor dynamic model to investigate their influence on dynamic behaviors of the bearing. Results indicated that damping provided by eddy-current effects has pros and cons for the performance of the diamagnetic bearing which involves rotational motion. Finally, rundown characteristics of the bearing are evaluated, and the implication for operation scheme is discussed.