Performance improvement of micro-ultrasonic motors using the thickness shear mode piezoelectric elements

We propose a one-millimeter-scale traveling-wave ultrasonic motor that uses a thickness shear mode (15-mode) piezoelectric elements with a high shear piezoelectric coefficient. This thickness shear mode makes the micromotor suitable for operating with higher energy efficiency than conventional micromotors and enables a low voltage operation and a high torque generation. In this study, we build a thickness shear mode-driven micro-ultrasonic motor and demonstrate the improvement in motor performance. A micromotor comprising a cube with a side length of 1 mm and four piezoelectric plates is fabricated, and its dynamic and static characteristics are evaluated experimentally. With an optimal preload mechanism, the micromotor obtains unprecedented performance measures: an efficiency of 2.1% and a torque of 40 µNm, which are 3–4 times larger than those of a comparable micromotor using typical expansion mode (31-mode) piezoelectric elements. Currently, the proposed motor is the most powerful micromotor in 1–2 millimeter-scale actuators and represents a new benchmark for micromotors.