Magnetic Suspension for Small Rotors

A magnetic suspension for small rotors has been developed which employs scattered light to regulate the vertical height of the rotor. Upon entering a horizontal beam of light the rotor scatters or reflects light into a photo-electron multiplier cell. This cell actuates an electronic circuit which in turn regulates the current through the supporting solenoid in such a way as to maintain the ferromagnetic rotor at the desired vertical position. Rotors with diameters down to 0.004″ have been stably supported. A 164′′ rotor was spun to an estimated speed of 800,000 r.p.s. which gave a centrifugal field in excess of one-half billion times gravity. Besides providing a support for rotors, the apparatus may be used as an analytical balance for weighing materials inside a vacuum chamber. It detects changes in mass of from 10−8 to 10−9 gram. Other uses also are indicated.