Modelling compression sensing in ionic polymer metal composites

Abstract

Ionic polymer metal composites (IPMCs) consist of an ionomeric membrane, including mobile counterions, sandwiched between two thin noble metal electrodes. IPMCs find application as sensors and actuators, where an imposed mechanical loading generates a voltage across the electrodes, and, vice versa, an imposed electric field causes deformation. Here, we present a predictive modelling approach to elucidate the dynamic sensing response of IPMCs subject to a time-varying through-the-thickness compression (‘compression sensing’). The model relies on the continuum theory recently developed by Porfiri and co-workers, which couples finite deformations to the modified Poisson–Nernst–Planck (PNP) system governing the IPMC electrochemistry. For the ‘compression sensing’ problem we establish a perturbative closed-form solution along with a finite element (FE) solution. The systematic comparison between these two solutions is a central contribution of this study, offering insight on accuracy and mathematical complexity. The method of matched asymptotic expansions is employed to find the analytical solution. To this end, we uncouple the force balance from the modified PNP system and separately linearise the PNP equations in the ionomer bulk and in the boundary layers at the ionomer–electrode interfaces. Comparison with FE results for the fully coupled nonlinear system demonstrates the accuracy of the analytical solution to describe IPMC sensing for moderate deformation levels. We finally demonstrate the potential of the modelling scheme to accurately reproduce experimental results from the literature. The proposed model is expected to aid in the design of IPMC sensors, contribute to an improved understanding of IPMC electrochemomechanical response, and offer insight into the role of nonlinear phenomena across mechanics and electrochemistry.

Developing next generation ionic polymer–metal composite materials: perspectives for enabling robotics and biomimetics

“…10 Additionally, the theoretical underpinnings for compressive sensing in IPMCs have been developed which, under the modeling framework proposed, require the presence of inhomogeneity of the ionomer. 11 In a general robotics application, sensors may be required to detect inputs from a variety of stimuli, possibly simultaneously. The multimodal sensing capabilities of IPMCs have recently been demonstrated, wherein IPMC sensors have been shown as effective detectors of torsional twisting and axial extension or compression.…”

“…We have seen tubular geometry IPMCs used for the sensing of torsional deformation, with both theoretical modeling and experimental validation 10 . Additionally, the theoretical underpinnings for compressive sensing in IPMCs have been developed which, under the modeling framework proposed, require the presence of inhomogeneity of the ionomer 11 …”

A Compact Review of IPMC as Soft Actuator and Sensor: Current Trends, Challenges, and Potential Solutions From Our Recent Work

“…Additionally, Zhu et al investigated the effects of different cations on the electrical responses of IPMC sensors at different ambient humidities (Zhu et al, 2016c ). Volpini et al established a predictive model to explain the dynamic compression-sensing response (Volpini et al, 2017 ). In 2017, Gudarzi designed an IPMC dynamic pressure sensor based on the streaming potential hypothesis and then presented charge current-generation mechanisms that operate due to the external pressure in both compression and shear modes (Gudarzi et al, 2017a , b ).…”

Sensing and Self-Sensing Actuation Methods for Ionic Polymer–Metal Composite (IPMC): A Review

“…Based on [108,109], Volpini et al (2017) derived a one-dimensional model for IPMC compression sensing [112]. The model was solved analytically and validated against finite element modelling results.…”