Optimum Design for Noncontact Ultrasonic Motor with Flexurally Vibrating Disk Using an Equivalent Circuit Considering Viscosity of Air

The optimum design for a noncontact ultrasonic motor with a flexurally vibrating disk has been investigated by analyzing the sound pressure in the air gap using an equivalent circuit considering the viscosity of air. The calculated results indicate that the sound pressure is affected by the viscosity and mass effect in the air gap, which are changed by the gap distance. The experimental results of revolution speed measured at various gap distances agree qualitatively with the sound pressure calculated using the equivalent circuit. In the case of wider gaps, a design satisfying the resonant condition of the air gap is necessary for optimizing the motor because the air gap resonates by the mass effect. However, in motors with an air gap narrower than about 50 lam, a higher speed rotation can be obtained for a wide range of rotor diameters and for a wide frequency range without consideration of the air gap resonance because the air viscosity effect becomes dominant. (C) 2009 The Japan Society of Applied Physics