Abstract
Force Sensing Resistors (FSRs) are manufactured by sandwiching a Conductive Polymer Composite (CPC) between metal electrodes. The piezoresistive property of FSRs has been exploited to perform stress and strain measurements, but the rheological property of polymers has undermined the repeatability of measurements causing creep in the electrical resistance of FSRs. With the aim of understanding the creep phenomenon, the drift response of thirty two specimens of FSRs was studied using a statistical approach. Similarly, a theoretical model for the creep response was developed by combining the Burger’s rheological model with the equations for the quantum tunneling conduction through thin insulating films. The proposed model and the experimental observations showed that the sourcing voltage has a strong influence on the creep response; this observation—and the corresponding model—is an important contribution that has not been previously accounted. The phenomenon of sensitivity degradation was also studied. It was found that sensitivity degradation is a voltage-related phenomenon that can be avoided by choosing an appropriate sourcing voltage in the driving circuit. The models and experimental observations from this study are key aspects to enhance the repeatability of measurements and the accuracy of FSRs.
Highlights
A Conductive Polymer Composites (CPC) is manufactured by randomly dispersing conductive particles along an insulating polymer matrix
Conductive particles are typically obtained from metals such as Nickel or Cooper [5,6], but more recently, carbon black or carbon nanotubes have been employed as the conductive phase in CPCs [7,8]
When a CPC is subjected to constant stress response in the electrical resistance of the specimen; this is a well-studied phenomenon that has been for an extended period of time, the rheological characteristic of the CPC produces a creep response in addressed by multiple authors [18,21,22], but the contribution from this study is to demonstrate that the electrical resistance of the specimen; this is a well-studied phenomenon that has been addressed the creep response in the electrical resistance is influenced by the sourcing voltage across the by multiple authors [18,21,22], but the contribution from this study is to demonstrate that the creep specimen
Summary
A Conductive Polymer Composites (CPC) is manufactured by randomly dispersing conductive particles along an insulating polymer matrix. The CPCs benefit from the insulating behavior of polymer materials to exhibit an electrical resistance dependent on both: particle concentration and mechanical stress [1]; this semiconductive response has been exploited in the manufacturing of tactile and pressure sensors to be integrated in multiple applications as later described in this article. To previous studies, the proposed model is capable of predicting sensor current under static loading at any operating voltage, and as later described in this article, the voltage-dependent behavior of the tunneling resistance is a key aspect for the appropriate modelling of the creep response. The rest of this paper is organized as follows: Section 2 reviews the authors’ proposed model for the quantum tunneling conduction of CPCs. A comparison with previous models is presented. Sensors was considered in order to yield representative results supported by statistical analysis
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