A Robust Printed Strain Sensor for Large-Area Structural Health Monitoring

Strain sensors are one of the most used sensors in structural health monitoring. Vapor deposition and screen printing are prominent for manufacturing strain sensors. However, the former offers poor scalability, while the latter does not provide “on-the-fly” design adjustments. Here, we present a digitally fabricated strain sensor using additive 3D direct writing, which offers high scalability and resolution. Furthermore, we use a hybrid design with stretchable carbon for enhanced sensitivity and stretchable silver for endurance. The optimized serpentine sensor structure features a carbon component with dimensions of 5 cm in length and 0.8 mm in width. The strain sensor provides a gauge factor of 2.45 and high robustness (i.e., only 0.01% change in resistance $(\Delta R/R_{0})$ after 1000 bending cycles to 5 mm radius of curvature). The sensor's performance is evaluated by comparing it with a commercial sensor for measuring foam and plastic PETG pipe strains. The results depict that both sensors measured similar strain for the soft pipe. However, the printed sensor, which is printed on $\mathbf{50}\ \mu m$ polyimide tape, is able to successfully measure 0.1% strain with 0.01% resolution on PETG pipes, while the $\mathbf{500}\ \mu m$ thick commercial sensor does not provide such high sensing resolution. Due to the excellent scalability and robustness, we hope the digitally manufactured strain sensors will encourage new structural health monitoring system developments spanning large areas, such as bridges or dams.