Humidity-dependence of IPMC sensing dynamics: characterization and modeling from a physical perspective

Ionic polymer-metal composites (IPMCs) exhibit humidity-dependent sensing behavior when operating in air, which weakens the reliability of the IPMC sensors. To better understand the underlying physics of this behavior and capture the humiditydependence analytically, in this paper the influence of the ambient humidity on IPMC sensors is characterized and modeled from a physical perspective. In particular, we study a cantilevered IPMC beam subjected to baseexcitation inside a custom-built humidity chamber with controlled humidity level. The empirical frequency responses of the sensor dynamics under different humidity levels are first obtained. Charging experiments are also conducted under each humidity level, in order to identify the corresponding effective dielectric constant. At each given humidity level, the humidity-dependent physical parameters are identified by curve-fitting the measured frequency responses with the model predictions. These identified parameters indicate a noticeable dependence on the humidity, which is captured with polynomial functions. The polynomial functions are then plugged into the physicsbased model to predict the sensing output of the IPMC sensor under other humidity conditions. Additional experimental results are presented to support the effectiveness of the model.