Small piezoelectric fibers wound with helical electrodes on their outer surface will produce torsional displacement. A piece of piezoelectric tube with an outer diameter of 1mm, a wall thickness of 0.1mm, and an effective axial length of 40mm was used as a prototype actuator’s body, while two pieces of copper wires of 40μm diameter were used as the electrodes. After poled with 2kV∕mm electric field strength, the prototype actuator produces 1.7° torsional angle when it was driven from −500to500V. A resonant frequency as high as 10kHz was observed on this actuator.

A prototype small impact rotary motor has been fabricated based on a newly developed torsional actuator which is 15.0 mm long and 1.0 mm in diameter. The motor can rotate when it is powered with a saw-shaped voltage. The experimental results show that its angular speed is proportional to both the driving voltage's amplitude and the frequency under 1 kHz. The large nonlinearity occurs at higher driving frequency due to the resonance of the partial mechanical structure of the motor. The motor can rotate at a speed of 90 rpm with a saw-shaped driving voltage of 600 V(p.-p.) at 8 kHz, and produce a stall torque of 80 microN m with 1000 V(p.-p.) at 3 kHz.