Wearable strain sensors based on electrically conductive natural fiber yarns

Highlights: • Highly conductive natural fiber yarns through a novel coating technique by an ultrasonication are produced. • The maximum value of 5.8 S.cm⁻¹ was achieved for the conductive yarns by hybrid of graphene nanoplatelets and carbon black. • New wearable strain sensors possessing good sensitivity, high durability, and stability were fully characterized. • The fabricated strain sensors were able to detect a full range of human motion, even the subtle movements. • A flexible grid structured pressure sensor was developed and characterized that could be applied as flexible touch panels. The demand for flexible and wearable devices based on novel nanomaterials is rapidly growing due to their applications in human motion detection, soft robotics, human-machine interface and similar applications. Herein, we report a systematic study on the fabrication of electrically conductive yarns made of natural fiber yarns coated with graphene nanoplatelets (GNPs) and carbon black (CB). The highly conductive yarns are then utilized to fabricate wearable, stretchable, and durable strain sensors. Our strain sensors demonstrate a good sensitivity with gauge factors (GFs) in the range of 1.46 to 5.62, depending on the magnitude of the applied strain and displacement rate. The strain sensors show reliable electromechanical response to strains as large as 60%, suggesting their potential application in human motion detection. They can successfully detect a range of human movements, such as finger, wrist, and knee joint movements, pronunciation, breathing, and swallowing. Finally, we propose a flexible grid structured pressure sensor to detect finger touch that could be utilized as flexible touch panels.