Surface acoustic wave bridge for rotation measurement

Abstract

A surface acoustic wave bridge for rotation measurement which uses acoustic waves propagated in opposite directions about the circumference of a rotor. The acoustic waves are generated by a transducer adjacent the rotor which is excited by an rf electric field. Clockwise and counterclockwise waves in the surface of the rotor interfere with each other adjacent the transducer to form a bridge system which produces a null when the waves are out of phase. The rf frequency of the electric field is varied to obtain the null and, thus, is a measurement of the rotation rate of the rotor. For the measurement of slow rotation rates two transducers are used to generate the counterrotating acoustic waves in a helical pattern such that the acoustic wave generated by one transducer is received by the other. The outputs of the transducers are detected and provide an approximately linear measurement of slow rotational rates.