Highly durable yarn-based strain sensor with enhanced underwater monitoring capabilities and rapid drowning detection for safety applications

Abstract

Flexible strain sensors have garnered significant attention for their outstanding performance in fields such as telemedicine, motion management, and human–machine interfaces. However, in the demanding marine environments, these advanced sensors face challenges related to mechanical weakness, stability, and durability under wet conditions, which are critical for expanding their range of practical applications. In this study, a stable and durable yarn sensor was developed specifically tailored for underwater activity monitoring. This was achieved by using polydopamine to immobilize silver nanoparticles, thereby creating a highly conductive layer, followed by applying an impregnation coating to establish a hydrophobic layer. The resulting composite structure featured a micro-convex layer of silver nanoparticles, which provided a durable hydrophobic surface resistant to mechanical wear and capable of maintaining its electrical properties even under high-velocity water impacts. More significantly, a FWAS was engineered, which is activated by pre-stretching the yarn sensor using a water-soluble vinylon yarn. The FWAS automatically alters its resistance within 1.3 s upon detecting someone falling into the water, thereby sending out an accurate distress signal to the external world by transmitting Morse code signals via gesture movements. This innovation provides a straightforward and effective approach for timely rescue operations from drowning, demonstrating the versatility of yarn-based flexible strain sensors for use not only in air but also in underwater scenarios.