Screen Printed Silver/Carbon Composite Strain Gauge on a TPU Platform for Wearable Applications

A printed strain gauge based on silver/carbon composite was successfully fabricated and characterized for strain monitoring applications. The silver-carbon (Ag/C) composite ink was prepared by blending 81% wt. of silver with 19% wt. of carbon ink. The strain gauge was fabricated by screen printing Ag/C composite ink on a flexible and stretchable thermoplastic polyurethane (TPU) substrate in a meandering pattern to achieve a desired resistance of $\sim 350 \Omega$. The capability of the printed strain gauge to detect varying strains ranging from 0% to 5% was investigated. It was observed that the strain gauge had a linear response till 2.5% strain. At 2.5% of tensile strain a relative resistive change of 7.8% and a gauge factor of 3.1 was observed. However, as the strain increased beyond 2.5% the strain gauge had a non-linear response. It was observed that at a tensile strain of 5%, the strain gauge had a maximum relative resistive change of 285.6% resulting in 57.2 gauge factor. The results demonstrate that a screen-printed Ag/C composite ink-based strain gauge with on a TPU substrate can be utilized for strain monitoring. The electromechanical response of the fabricated strain gauge as a function of resistance is investigated and presented in this paper.