A Finite Element Analysis Approach to Explain Sensitivity Degradation in Force Sensing Resistors Based on Conductive Polymer Composites

Abstract

Force sensing resistors (FSR) based in conductive polymer composites (CPC) are a cost-effective alternative to load cells for force measurement. Nevertheless, their physical characteristics related to rheological features provoke some drawbacks such as hysteresis, drift, low repeatability, and sensitivity degradation (SD), which is a concerning issue when final application involves periodic loading. Although it is already known that SD is a voltage-related phenomenon and practical considerations to avoid it have been published, a more theoretical approach was yet missing. This study provides a set of finite element analysis (FEA) simplified models to shed light on the situations that favor degradation based in a time-dependent mechanical study considering rheological parameters and how they influence interparticle tunneling conduction. Also, a stationary electrostatic analysis with special scope in contact resistance and its influence in equipotential surfaces arousal. Simulation results show how the effect of contact resistance bends equipotential surfaces favoring conduction through time-increasing interparticle gaps, which is a direct consequence of the low Poisson ratio of considered polymers.