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

Abstract

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 fibershaped 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 doubleleveled 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 −1 . 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.

Wearable and Stretchable Strain Sensors: Materials, Sensing Mechanisms, and Applications

“…Durable strain sensors are ideal for wearable strain sensing applications where large and dynamic strains should be accommodated by them. Highly durable and stretchable strain sensors have been recently reported in which they have shown remarkable dynamic durability up to 20 000 stretching-releasing cycles [62,64,111,112,122,138,139,177,182,187,188] even at very high strain levels (150%). [72] Wang et al stepped even beyond this limit and developed a strain sensor based on CNTs/cotton/TPU core-spun yarn that was durable up to 300 000 cycles at 40% strain.…”

A Route Toward Smart System Integration: From Fiber Design to Device Construction

“…For fiber‐shaped resistive‐type strain sensors, a facile way is to use polymer fibers coated by conductive layers. These fiber substrates can be rubber fiber, polyurethane (PU) fiber, Spandex fiber, and so on. In Figure a, a spring‐like substrate is shown, which was achieved by winding PP fibers on a rubber fiber with controllable gaps.…”

“…The substrate was then coated by CNTs. Due to the designed double‐leveled helical gaps, the fiber showed ultralow detection limit of 0.01% strain, wide sensing range of 200% strain, and high repeatability of 20 000 cycles . Shown in Figure b, graphene‐coated PU fiber was fabricated as a fiber‐shaped strain sensor.…”

“…a) Schematic illustration of the large gaps formed between two neighboring knots of CNT/PP fiber bunches and small gaps formed among CNT/PP fibers. Reproduced with permission . Copyright 2019, American Chemical Society.…”

Multifunctional Fibers to Shape Future Biomedical Devices

“…Resistive sensors typically consist of a conductive fiber that change their geometries with a resistance change in response to an applied force. These fibers are usually fabricated by the incorporation of conductive CNTs, silver nanoparticles, or nanowires into elastic polymer fibers.…”