Development of an active superconducting magnetic bearing

The potential use of YBa/sub 2/Cu/sub 3/O/sub 7/ as an active component in a magnetic bearing is being investigated. Measurements are being made of the load bearing capacity and related stiffnesses in comparison to predictions from the critical state model. Although the load bearing capacity is high and increases with the square of the magnetic field trapped, the stiffness is low. We report on a novel design concept to overcome this problem which uses superconducting bulk materials. In bulk materials where the magnetic field is produced by persistent currents trapped in the superconductor this option is not available. However the available force is a function of the flux density and the area over which it is applied. Thus even if the flux density remains constant then changes in available force may be made by changing the active area of the bearing i.e. increasing the area of overlap between the magnetic components. Using this method active control may be achieved using bulk materials and the inherently low stiffness of the materials is no longer a problem.<>