Electromechanical Response of Large Strain Ferroelectric Actuators

One of the desired properties of actuators is large actuation strains, which also correlates with large work output per volume. This property becomes especially important in micro systems where small devices are required to produce relatively large strokes. The existing mechanisms for electromechanical actuation are limited to small actuation strains and hence recent years have seen a variety of attempts at achieving larger strain actuation. One such attempt, basing on 90 degree domain switching in ferroelectric crystals subjected to compression load and cyclic electric field, has recently been demonstrated. In this presentation we explore the dynamics of 90 degree domain switching at high frequencies. For this purpose a novel ferroelectric actuator and experimental system were developed, which allow measuring the response of a BaTiO₃ single crystal to a combination of constant tensile stress and cyclic electric field at frequencies of up to 100 kHz. Experimental results are compared with theoretical calculations basing on a new model which considers the motion of discrete domain walls. Current results exhibit actuation strains of up to 0.8% (an order of magnitude larger than piezoelectric strains) and no decrease of actuation strains up to several kHz.