Dynamics of Omnidirectional IPMC Sensor: Experimental Characterization and Physical Modeling

Typical ionic polymer-metal composite (IPMC) sensors are in the shape of beams, and only respond to stimuli acting perpendicular to the beam plane. In this paper, we present a novel, omnidirectional, tubular IPMC sensor that responds to all stimuli perpendicular to the tube axis. With one common inner electrode and four outer electrodes, the tubular IPMC sensor provides four routes of common-ground current outputs. With a custom-made setup, the response of each sensor route is characterized under tip deflection in different orientations at frequencies 1-20 Hz, which verifies the sensor's omnidirectional sensing capability and shows little mechanoelectrical coupling between neighboring sensor routes. An analytical dynamic model, in the form of an infinite-dimensional transfer function, is developed for the sensor, which captures the internal ion-transport physics and the effect of contact resistance. Experimental results show that the proposed model is able to capture the tubular sensor dynamics. Finally, the original model is reduced to a finite-dimensional one, based on which an inversion algorithm is used to reconstruct the mechanical stimulus given the sensor output. The effectiveness of the reconstruction approach is demonstrated experimentally.