Shape-adaptable and wearable strain sensor based on braided auxetic yarns for monitoring large human motions

As one of the flexible and wearable strain sensors, yarn sensors have shown promising applications in monitoring human motions. In this research, shape-adaptable, and wearable braided auxetic yarns (BAYs) sensors were designed and large-scale manufactured by a simple method. The auxetic behavior, mechanical and electrical properties of BAYs were measured and analyzed. The prepared BAYs demonstrated the obvious auxetic behavior (negative Poisson`s ratio >-3) and maintained the stability of negative Poisson`s ratio performance for long-terms, revealing excellent shape adaptability and structure stability. The auxetic BAYs sensors exhibited a fast response time (149.9 ms), a wide sensing range (0–40.7 %), and excellent cyclic stability. The deformation sensing mechanism of the BAYs sensor was proposed. The fabricated BAYs sensors were directly used to detect and recognize muscle and joint motions, showing outstanding accuracy, stability, repeatability, and shape fitting performance on large curved surfaces (e.g., human body parts like elbow and knee). The excellent performances and auxetic behavior of BAYs sensors would provide remarkable potential in shape-adaptable, flexible, and wearable electronics.