Behavior of conducting polymer-based micro-actuators under a DC voltage

Conducting polymer-based micro-actuators are of great interest in soft MEMS as they exhibit large strains and forces in response to electrical stimulation. To date, these micro-actuators have very often been characterized by applying low frequency voltage to extract the electromechanical characteristics. However, many applications require maintaining the actuator's position for several minutes. A micro-camera tracking the displacements of an object, the actuation of a cochlear implant during surgery, or closing micro-tweezers to manipulate objects are potential applications for which actuation is achieved by applying a direct current (DC) voltage. Knowledge of the behavior of micro-actuators under and after a DC voltage is crucial for modeling and future control. Consequently, the kinetics to reach the maximum strain followed by back-relaxation are identified. It is shown that it is the result of competition between an elastic restoring force and the backflow of the ions inside the actuator. A residual strain is observed after a short circuit and studied as a function of the DC voltage applied. It is demonstrated that the voltage and the chronology of the power-ups affect the actuator position and strain amplitude. The interpretation of the experimental results linked directly to the intrinsic operation of micro-actuators is presented.