A stretchable strain sensor based on metal nanoparticle thin film for human motion detector

Abstract

Wearable strain sensors that can detect human motions are being spotlighted in various fields such as medical, entertainment, and sports industry. However, conventional strain gauges using stiff materials such as metal thin foil or silicon piezoresistor have limitation in stretchability. Therefore, many researchers have reported several strategies to extend the stretchability. However, most of these previous researches require multi-step and complicated fabrication processes. Also, they have demonstrated the sensing capability of only tensile strains. Therefore, we propose a new stretchable strain sensor that can detect both tensile and compressive strains and its extremely simple fabrication process in this paper. We fabricated a stretchable strain sensor by single-step direct transfer/patterning process, in which silver nanoparticle ink was used as the sensing material. We used micro-structured PDMS substrate as both stamp and target substrate to achieve transfer and patterning of silver nanoparticle thin film at the same time. Transferred silver nanoparticle thin film has many initial cracks induced by annealing process on the PDMS substrate. The working principle of the stretchable strain sensor is the changes in the resistance caused by opening/closure of cracks under mechanical deformation. The stretchable strain sensor can be stretched up to 50% strain with high strain sensitivity and high durability. Also, our stretchable strain sensor is sensitive not only to tensile but also to compressive strain. The maximum gauge factors are 10 for the tensile strain and 13 for the compressive strain. As applications, we demonstrated our stretchable strain sensor as human motion detector and sensitivity-controllable flexible pressure sensor. We developed a motion detection glove, bandage, and wrist guard with integrated strain sensors on the fingers, Adam’s apple, and wrist parts. Using continuous monitoring of the electrical resistance, we conducted real-time and ...