Normal stiffness calibration of microfabricated tri-layer conducting polymer actuators

Abstract

This paper reports on the stiffness characterization of microfabricated tri-layer conductingpolymer (PPy) actuators. The rectangular, polypyrrole microactuators, which couldoperate both in aqueous and non-aqueous media, were fabricated using an excimer laserablation technique that provided high throughput production and did not requirecleanroom facilities. The microactuators were fixed at one end with electricalcontacts and the other was end free to act as an electroactive microcantileverbeam. An atomic force microscope (AFM) was used to measure the microactuatordeflection under a range of normal forces applied by the AFM cantilever. A modifiedreference spring constant calibration method was employed to determine thestiffness constants of the microactuators. The stiffness of the microactuators in theelectroactive (electrically stimulated) and passive state (no stimulation) were evaluatedseparately and compared. In doing so, the study presents results leading to thestiffness characterization of the first air-operated polymer microactuators andimplementation of a simple, reliable and effective method for directly measuring thespring constant of polymer microactuators. This method is an alternative to theuse of mechanical modeling methods, which can be difficult to implement formulti-layer (composite) polymer actuators. Importantly, our results highlight severalrequirements for using the reference spring method to accurately determine stiffnessvalues of any microcantilever generally fabricated from soft, deformable materials.