Optimum operation conditions of an ultrasonic motor driving fluid directly

We proposed a new type of ultrasonic motor which consists of a fluid-filled ring stator and a rotor. The fluid is caused to flow in the circumferential direction by the ultrasonic vibration travelling along the ring stator. The operation mechanism was previously analyzed. In this paper, we present the results of experiments aimed at optimizing this motor. The acoustic streaming velocity of the motor can be increased by using the resonance of the fluid confined in the ring stator, employing a higher mode of stator vibration, and increasing the roughness of the stator wall. Also, it is clear that the nonlinearity of the acoustic field in the fluid is the main cause of the saturation of the acoustic streaming velocity, and that the saturated acoustic streaming velocity increases when the attenuation of the fluid acoustic field is increased.