Rotation sensing through electromagnetic-surface-acoustic-wave transduction

Rotation rates ranging from two rotations per day to one rpm have been measured by a novel but simple rotation sensor; rotary position can also be measured. This device utilizes a surface-acoustic-wave (SAW) standing-wave pattern on the circumferential surface of a rotating cylinder. The standing-wave nodes and antinodes are stationary in the rotating cylinder frame as they move past a separate sensing transducer. Electromagnetic transducers are used for the contactless transduction of SAW’s. The device sensitivity is effectively several orders of magnitude greater than for earlier SAW sensor designs. In addition, we foresee measurements of rotation rates of up to thousands of rpm and down to less than 0.1°/h. Design considerations and alternate sensor designs are discussed.