Derivation of a Continuum Model and Its Electric Equivalent-Circuit Representation for The Ionic Polymer-Metal Composite (IPMC) Electromechanics

Biomedical engineering applications of ionic polymer-metal composites like motion devices for endoscopy, pumps, valves, catheter navigation mechanisms and espinal pressure sensors makes it important to properly model IPMCs for engineering design. Particularly, IPMC continuum models and their electric equivalent circuit representation are critical to a more efficient design of IPMC devices. In this paper, we propose a new continuum electromechanical model to understand and predict the electrical/mechanical behaviour of the IPMC. An IPMC lumped-parameter circuit is derived from its continuum model to predict the relationship between its voltage and current signals. Although based on previous works of Shahinpoor and Nemat-Nasser, our model was derived on a macroscopic level, the water effects were assumed negligable when compared with the electrical effects of mobile ions for the IPMC motion, the model parameters were clearly identi&ed in its physical meaning, and an equivalentcircuit IPMC model was determined from the established continnum electromechanical model. Experiments are done with two IPMC pieces having different dimensions, which were previously immersed in a sodium solution. The IPMCs are current driven, being the transverse displacement and voltage signals measured for different current values, avoinding the water electrolysis phenomenon. Simulations using the analytic models derived are compared with the experimental results and they are found to predict the electrical and mechanical relations very accurately.