Sound Field Characteristics in Air Gaps of Noncontact Ultrasonic Motor Driven by Two Flexural Standing Wave Vibration Disks

Abstract

The sound field characteristics in the air gaps of the noncontact ultrasonic motor driven by two flexural standing wave vibration disks were analyzed by finite element method (FEM). Standing wave sound fields with an opposite phase were generated in the two air gaps by a single driving stator. Traveling wave sound fields in the two air gaps are formed as the superposition of the standing wave sound fields generated by two stators whose temporal phases and spatial positions are different from each other. The traveling direction of the calculated sound fields coincided with the rotating direction of the rotor observed in the experiments. The intensity of the sound field generated in the air gap by the single driving stator was measured by detecting the voltage induced in another stator. A gap distance wider than 0.5 mm is required for a high revolution speed because the sound field generated in the gap on the opposite side of the rotor is weak in an air gap narrower than 0.3 mm.