Torsional displacement of piezoelectric fiber actuators with helical electrodes

A piezoceramic fiber wound with helical electrodes on its outer surface can be used as a torsional actuator. This paper explains the torsional actuator's working principles and points out that although such a mechanism can produce a large torsional strain, it will have a small axial strain. Detailed analyses are performed on the influences of the tubular fiber's wall thickness and the helical angle of the electrodes on the torsional strain. With the aid of the finite element analysis method, the electric field distribution in the actuator is illustrated. Theoretical analyses point out that to obtain the largest torsional strain, a 45° electrode helical angle is needed for an actuator with an ideal thin wall thickness, but the angle becomes smaller than 45° if the wall thickness cannot be ignored. Results of some deliberate experiments prove these analyses.