Passive Magnetic Bearings With Ferrofluid Stabilization

Permanent-magnet rotary bearings with ferrofluid stabilization in the axial degree of freedom are undergoing development. These bearings are totally passive, yet stable in all degrees of freedom. In contrast, previously developed electromagnet and permanent-magnet bearings all exhibit instability in at least one degree of freedom, giving rise to the need for active electronic feedback and power-control circuitry. By making active control unnecessary, ferrofluid stabilization can enable reductions in the overall sizes, weights, and power consumptions of machines that contain permanent-magnet bearings. Unlike passive magnetic bearings based on superconductivity, which are restricted to operating temperatures far below room temperature, the developmental bearings are designed to function at temperatures from 0 to 50 °C.