Design of Helically Double-Leveled Gaps for Stretchable Fiber Strain Sensor with Ultralow Detection Limit, Broad Sensing Range, and High Repeatability.

Flexible strain sensors have attracted extensive attention in electronic skins and health monitoring systems. To date, it remains a great challenge for the development of a multifunctional strain sensor with simultaneous ultralow detection limit, broad sensing range, and high repeatability. In this paper, we report a new carbon nanotube/flexible fiber-shaped strain sensor. The fiber substrate has a novel microstructure where a highly elastic rubber fiber core is tightly wound by a continuous spring-like polypropylene fiber as the shell. Our sensor offers combined sensing performances of ultralow detection limit of 0.01% strain, wide sensing range of 200% strain, and high repeatability of 20 000 cycles by designing double-leveled helical gaps. This strain sensor shows a rapid response time of 70 ms under both stretching and releasing. In addition, it is available for a variety of other deformations such as bending and torsion. Due to the unique fiber structure, it can extend the torsion detection range to 1000 rad m. On the basis of the superior sensing performances, our sensor demonstrates to efficiently work for both subtle physiological activities and vigorous human motions. This work provides a general and effective strategy for designing smart wearable devices with high performance.