Ionic polymer-metal composites (IPMCs) have intrinsic actuation and sensing capabilities, and they need hydration to operate. For an IPMC sensor operating in air, the water content in the polymer varies with the humidity level of the ambient environment, which leads to its strong humidity-dependent sensing behavior. However, the study of this behavior has been very limited. In this paper, the influence of environmental humidity on IPMC sensors is characterized and modeled from a physical perspective. Specifically, a cantilevered IPMC beam is excited mechanically at its base inside a custom-built humidity chamber, where the humidity is feedback-controlled by activating/deactivating a humidifier or a dehumidifier properly. We first obtain the empirical frequency responses of the sensor under different humidity levels, with the IPMC base displacement as input and the tip displacement and short-circuit current as outputs. Based on physics-based model for a given humidity level, we then curve-fit the measured frequency responses to identify the humidity-dependent physical parameters, including Young’s modulus and strain-rate damping coefficient for the mechanical properties, and ionic diffusivity for the mechanoelectrical dynamics. These parameters show a clear trend of change with the humidity. By fitting the identified parameters at a set of test humidity levels, the humidity-dependence of the physical parameters is captured with polynomial functions, which are then plugged into the physics-based model for IPMC sensors to predict the sensing output under other humidity conditions. The latter humidity-dependent model is further validated with experiments.

Date Published: 9 April 2013
PDF: 10 pages
Proc. SPIE 8687, Electroactive Polymer Actuators and Devices (EAPAD) 2013, 868720 (9 April 2013); doi: 10.1117/12.2010612

Published in SPIE Proceedings Vol. 8687:
Electroactive Polymer Actuators and Devices (EAPAD) 2013
Yoseph Bar-Cohen, Editor(s)