A Zero-Power Magnetic Bearing for Implantable Ventricular Assist Device

Conventional bearings require lubrication and regular maintenance, making them unsuitable for liquid environments. To expand the applicability of bearingless motors in ventricular assist device (VAD) pumps, this study proposes a passive, zero-power magnetic bearing using PMs repulsion for shaft support. Radial stabilization is achieved by arranging same-pole PMs on the stator and rotor; axial support uses stator PMs positioned between two rows of rotor PMs. To minimize blood-flow disturbance, the stator-rotor gap was increased to 5mm, and rotor PMs were overlapped by 1mm with the stator extension to enhance repulsive force. Three-dimensional finite-element method (3DFEM) under various operating conditions characterized bearing performance. Results show rotational speed doesn't affect bearing stiffness. Eccentric rotation around the rotor's axis generated a restoring force, and torsional loading in the radial direction confirmed system rigidity. However, instability was observed in the axial (thrust) direction. To address this, a correction mechanism combining a stator electromagnet and rotor electromagnetic steel was analyzed. Theoretical predictions matched 3DFEM results for radial force but deviated in axial. These findings suggest the need to integrate an active thrust-control structure into the motor. Future work will improve axial force correction methods and experimentally validate the proposed design.