A shear-mode ultrasonic motor using potassium sodium niobate-based ceramics with high mechanical quality factor

Abstract

(K,Na)NbO3-LiNbO3-CuO lead-free piezoelectric ceramics that show a high mechanical quality factor Qm were synthesized and used as a drive element of an ultrasonic motor. The Qm of the (K,Na)NbO3 ceramic could be enhanced by chemical modification using Li and Cu as well as microstructure control to obtain ceramics with fine grains. The grain size dependence of the Qm was consistent with a model based on the formation of internal bias field to stabilize the domain structure. A shear mode was used to drive the ultrasonic motor because the piezoelectric d31 and d33 constants of the ceramics were not sufficient for the motor applications. A shear-mode motor driven with four piezoelectric ceramic plates was developed using the lead-free ceramics with a high Q m of 1400, a high d15 of 207pC/N, and a high k 15 of 0.72. The highest revolution speed of 486 rpm was achieved at 34.5kHz with the input voltage of approximately 180Vp-p (peak to peak). © 2008 The Japan Society of Applied Physics.