A spring-like fiber based strain sensor with a fast response and high sensitivity for precise detection of complicated human activities

Abstract

With the rapid development of intelligent electronic devices, there is a growing demand for flexible strain sensors with a fast response, high sensitivity, a large sensing range, a low detection limit, and good repeatability simultaneously. However, combining the excellent sensing performances into one sensor via special structures remains a great challenge. Herein, inspired by the special spring deformation process from contact to separation of the helixes, a strategy to build a fiber based strain sensor with tightly interconnected helixes has been presented. The sensor is composed of a spring-like polyvinyl alcohol (PVA) conductive fiber wound around a highly elastic substrate. The spring-like structure endows the sensor for stretching strain with a wide sensing range (200% strain), an ultralow detection limit (0.01% strain), and high repeatability (12 000 cycles). More importantly, the sensor exhibits high sensitivity (a gauge factor of about 66 in the small strain range) and a fast response (∼42 ms) due to the huge resistance difference caused by the separation process of the helixes from the tight contact state. Taking advantage of the superior sensing performance, the sensor can be applied for speech recognition, micro-expression detection, and pulse/respiration monitoring. In particular, the real-time monitoring applications for a series of complicated human activities have been developed to help infants, elderly people, and people with disabilities. This work will provide a universal and effective strategy for designing high-performance intelligent wearable devices.