Coupled torsional and longitudinal vibrations of piezoelectric fiber actuator with helical electrodes

The vibration characteristics of a piezoelectric fiber actuator with helical electrodes are studied theoretically and experimentally. Its working principle indicates that the torsional, longitudinal, and tangential deformations of the fiber are coupled. A simplified dynamic model is deduced to investigate the properties of the coupled vibrations and their corresponding equivalent circuits are also provided. Resonant frequencies and mechanical coupling coefficients in free-free boundary condition are calculated. The trends of resonant frequencies as functions of the electrode helical angle and fiber length are discussed and validated in experiments.