Electromechanical Modeling of Encapsulated Ionic Polymer Transducers

Abstract

A model to allow the design and evaluation of encapsulated ionic polymer transducers is developed. This model in based on a linearly coupled, two port, electrical equivalent circuit model (Newbury, 2002). The proposed model incorporates multilayer beam theory to model the passive stiffness effects of the encapsulation layer and attempts to increase the prediction accuracy of the model by using distributed parameter system modeling to create the mechanical terms used in the model. Modal expansion is used to extend the applicability of the mechanical impedance terms through multiple resonances of the transducer. The test setup as well as the mathematical approach to characterize the viscoelastic properties of Nafion™ as they relate to this work is described and the results presented. The model simulation is then compared to measured experimental data taken for a number of ionic-polymer-metal composites before and after encapsulation. The applicable frequency range of the model is explored as well as data trends seen above previous frequency ranges (approximately 1 kHz).

Free deflection was predicted to reduce by an order of magnitude when the transducers were encapsulated with Kapton™. This trend was observed and correlates well with the measured response. Charge sensing and blocked force were found to increase for a transducer after encapsulation; this could be due to the higher coherence obtained in testing after encapsulation and is not predicted by the model. The model predicts charge sensing and blocked force should remain constant with encapsulation. Low frequency blocked force data for any given transducer was observed to be roughly an order of magnitude greater than the sensing response, before and after encapsulation. There is no explanation for this observation, future work should investigate this phenomena.