Experimental Characterization and Modeling of Electro-Mechanically Coupled Ferroelectric Actuators

Abstract

Piezoelectric actuators used in nano-positioning devices exhibit highly non-linear behavior and strong hysteresis. The rate-dependence of piezoelectric materials resulting from the kinetics of domain switching is an important factor that needs to be included in realistic modeling attempts. This thesis provides a systematic study of the rate-dependent hysteresis behavior of a commercially available PZT stack actuator. Experiments covering full as well as minor loops are conducted at different electro-mechanically coupled loading conditions with polarization and strain recorded. In addition, the creep behavior at different constant levels of the electric field is observed. These experiments provide evidence of kinetics being characterized by strongly varying relaxation times that can be associated with different switching mechanisms. Finally, an electro-mechanically coupled free energy model for polycrystalline ferroelectrics is presented that is based on the theory of thermal activation. It is capable of predicting the hysteretic behavior along with the frequency-dependence present in these materials. The electro-mechanically coupled model also predicts the behavior of spring coupled actuators under various pre-stress levels. The model will be coupled with a SDOF model of a commercial nano-positioning stage (Nano-OP30, Mad City Labs) and is the basis for future control applications.