Bias-Dependent Impedance Model for Ionic Polymer-Metal Composite Actuators

Ionic polymer-metal composites (IPMCs) are a novel class of soft sensing and actuation materials with promising applications in robotic and biomedical systems. In this paper we present a model for nonlinear electrical dynamics of IPMC actuators, by applying perturbation analysis on the dynamics-governing partial differential equation (PDE) around a given bias voltage. By approximating the steady-state electric field under the bias with a piecewise linear function, we derive a linear PDE for the perturbed charge dynamics, which has piecewise constant coefficients and coefficients linear in the spatial variable. Through power series expansion, we solve the PDE to get the charge distribution up to any prescribed order. The perturbed electric field and current are subsequently obtained, which results in a bias-dependent impedance model. This model captures the nonlinear nature of the IPMC electrical dynamics, and degenerates to the linear model when the bias is zero. Simulation results are presented to illustrate the modeling approach.