Development of high performance stress-biased actuators through the incorporation of mechanical pre-loads

Stress-biased actuators, commonly referred to as thin unimorph driver (THUNDER(R)) and reduced and internally biased oxide wafer (RAINBOW), were first invented in 1994, and have been the subject of intense investigation since that time. Despite the exceptional performance of these devices, actuators with even greater performance are needed to pursue new applications. In this study, mechanical pre-loads, in the form of elongated springs, were added to standard stress-biased devices to alter domain switching behavior, and thus increase electromechanical response. The incorporation of the mechanical pre-load also results in an increase in stored mechanical and elastic energy within the device, which likely also contributes to the improved response of the modified devices compared to the standard devices. The displacement performance of the new actuators is two times that of the standard devices. The pre-load forces may also be employed to shift displacement resonance peaks to give additional improvements in response. Results are reported for the increased resistance of the modified devices to deformation under applied mass, the effects of pre-load force on actuator displacement response, and the capabilities of the new devices to move large (>3 kg) masses over millimeter distances at low applied power. Indirect evidence is presented that suggests that at least part of the improved response of the new devices is due to greater 90degrees domain switching. (C) 2002 Elsevier Science B.V. All rights reserved.