Abstract: Yarn-based flexible strain sensors with advantages in wearability and integrability have attracted wide attention. However, it is still a big challenge to achieve yarn-based strain sensors with a wide linear strain range, low hysteresis, and durability synchronously that can be used for full range detection of human body motions. Herein, a new structure, double-threaded conductive yarn with rhythmic strain distribution, is reported to markedly widen the linear strain range of microcrack-based stretchable strain sensors. A new method of winding and thermally adhering hot-melt filaments on the surface of the elastic fiber is used to achieve double-threaded yarn (DTY) with rhythmic strain distribution. The proposed strategy, the integration of heterogeneous materials, is reported to significantly reduce the mechanical hysteresis of composite yarns. Rhythmic strain distribution of the DTY during stretching causes multi-level microcracks in different regions of the carbon nanotube (CNT) conductive layer deposited on the surface of the DTY. Besides, the sensing performance of DTY-based strain sensor can be adjusted by designing the structural parameters. The final prepared flexible strain sensor has the advantages of a wide linear strain range (100%), great sensitivity (GF = 12.43), low hysteresis, rapid response (158 ms), high repeatability (> 2000 cycles at 50% strain), and hydrophobicity, etc. The sensor can monitor human motion repeatedly and stably well, and shows great advantages in flexible wearable devices.

Key words: Double-threaded yarn, Strain redistribution, Hysteresis, Human motion monitoring