Evaluation Criteria for THUNDERTM Actuators

THUNDERTM (thin-layer composite unimorph ferroelectric driver and sensor) represents a new class of piezoceramicbased actuators capable of generating significant displacements and forces in response to input voltages. The performance capabilities of THUNDERTM actuators are due to the component materials and process used in their construction. A typical THUNDERTM actuator is composed of metallic backing materials (e.g., aluminum or stainless steel), a piezoceramic wafer, and adhesive in spray or film form. The materials are bonded under high pressures and temperatures and then cooled to room temperature after the adhesive has solidified. Due to the prestresses which result from the differing thermal properties of the component materials under cooling, the actuator is highly durable with respect to mechanical impacts and voltage levels. As a result of this construction, voltages in excess of 800 V can be applied to new actuator models without causing damage. This provides the actuators with significant displacement and force capabilities. In this paper, we discuss the development of evaluation criteria which are suitable for characterizing the actuator capabilities and provide a legitimate methodology for comparing THUNDERTM properties with those of other smart material actuators. For example, the concept of blocked force is often used to quantify the force capabilities of an actuator. However, due to the inherent curvature and mode of operation, standard techniques for measuring blocked forces are inappropriate for THUNDERTM actuators. Furthermore, changing operating conditions, frequency, etc., often make blocked force measurements ambiguous. We will discuss techniques for evaluating THUNDERTM properties in a manner which limits such ambiguities when comparing with other smart materials. We note that the evaluation issues discussed here are germane to a variety of high performance smart material transducers.