Resonant frequency tuning of electroactive polymer membranes via an applied bias voltage

Vibration-based energy harvesting may hold tremendous impact for future applications of continuous machine and structural health monitoring. Here a novel resonant frequency tuning approach is proposed where the application of a bias voltage to a pre-stretched electroactive polymer (EAP) membrane results in changes in membrane tension which can be used to adjust the resonant frequency of the membrane. The effect of the bias voltage on the EAP membrane, which induces an electrostatic pressure and corresponding reduction in membrane thickness, is determined via an analytical model of the activation response of the EAP membrane, with the results confirmed using FEM simulation in ANSYS. Through a mass-loaded circular membrane vibration model, the effective resonant frequency of the membrane can be determined as a function of changes in membrane tension due to the applied bias voltage. In the case of an EAP membrane, pre-stretch contributes to the mechanical stiffness of the system while the applied bias voltage contributes to a change in electrical stiffness of the membrane. Experimental characterization of the EAP material VHB 4910 from 3M verified the resonant frequencies corresponding to the bias voltages predicted from the appropriate models. Given an effective system stiffness range between 598 N m(-1) (when lambda = 1.5, U = 0) and 266 N m(-1) (when lambda = 5, U = 5000), the corresponding resonant frequency tuning range for a particular circular central loaded EAP membrane device is between 31.4 to 21.8 Hz. The proposed bias voltage tuning approach for the EAP membrane may provide a novel strategy to enable resonant frequency tuning of energy harvesting devices in particular application environments.