One-Dimensional Flexible Capacitive Sensor with Large Strain and High Stability for Human Motion Monitoring

Flexible capacitive sensors have attracted the attention of researchers owing to their simple structure, ease of realization, and wearability. Currently, flexible capacitive sensors mainly have three-dimensional and two-dimensional structures, which are subject to several limitations in their applications. A low-cost, high-efficiency, and continuously processable process was used to wrap nylon DTY (PA) filaments on the surface of silver-coated nylon (SCN) core yarns and impregnate them with waterborne polyurethane (WPU) to obtain SCN/PA/WPU composite yarns, which were then utilized in the design of SCN/PA/WPU for the preparation of one-dimensionally structured flexible capacitive sensors. The morphology and mechanical properties of the SCN core yarn, SCN/PA wrapped yarn, and SCN/PA/WPU composite yarn were characterized. The strain-sensing performance of the sensor was analyzed, and the sensor was used to monitor human physiological activities. The sensor exhibited excellent strain capacitance sensing performance with a strain range of up to 140%. With a gauge factor of 0.66 at 10% tensile strain, it can detect strains as low as 1% and has good repeatability, withstanding more than 3200 tensile-unload cycles at 80% strain. The one-dimensional structure sensor can be used to monitor the large-scale movements of joints and muscles in various parts of the human body and the physiological signals of tiny human movements, such as breathing, coughing, and facial expressions, which have potential applications in the fields of sports monitoring and smart wearable.