Derivation of a continuum model and its electric equivalent-circuit representation for ionic polymer-metal composite (IPMC) electromechanics

Biomedical engineering applications of ionic polymer-metal composites such as motion devices for endoscopy, pumps, valves, catheter navigation mechanisms and spinal pressure sensors make it important to properly model IPMCs for engineering design. In particular, 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 behavior 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 negligible when compared with the electrical effects of mobile ions for the IPMC motion, the model parameters were clearly identified in their physical meaning, and an equivalent-circuit IPMC model was determined from the established continuum 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, the transverse displacement and voltage signals being measured for different current values, avoiding 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.