A Passive Magnetic Bearing

A novel design for a fully passive magnetic bearing is presented. In the proposed structure, non-contact suspension of a rotor is provided without additional electronic components or an external energy supply. Also, the bearing does not make use of superconducting materials and therefore can operate over a wide range of temperatures, including room temperature. Stable suspension of the rotor in the axial direction is provided by the interaction between permanent magnets and soft-magnetic elements, installed on the rotor and the stator. Consistent with Earnshaw's theorem, since this system is stable in the axial direction, it cannot also be stable in the radial directions. To overcome this radial instability, a passive radial electromagnetic suspension system is proposed, which provides radial centering of the rotor when rotating above some critical speed. The system exploits the interaction of currents induced in shorted conducting loops installed on the rotor with the axial component of a magnetic field emanating from permanent magnets installed on the stator. This type of bearing can provide adequate stiffness and load capacity for many applications. At the same time, the lack of mechanical contact between a rotor and a stator along with lack of external energy supplies and control systems will be significant advantages compared to other magnetic bearings. To give some numerical estimates of expected bearing performance: 60N/mm theoretical estimate of a radial stiffness and 120 N radial load capacity has been obtained for a radial suspension system with a outer diameter of 28 cm and a thickness of 3.3 cm. This suspension system will support a diskshaped 2.5-kg rotor rotating above 9000rpm.