Highly sensitive flexible strain sensors with novel tubular fiber design for human motion monitoring

Flexible strain sensors with high flexibility, high sensitivity, and wide stress/strain detection range are critical for applications in wearable devices. This work discusses the performance of flexible strain sensors utilizing a novel tubular fiber composed of polycaprolactone (PCL), carbon nanotubes (CNTs), and thermoplastic urethane (TPU). The strain sensor exhibits excellent sensitivity in minor deformation (gauge factor of 3.05 with strain below 20%), fast response time (< 110 ms), and impressive durability (> 4000 times). When applied to eye movement monitoring, the strain sensor can detect small deformations with a saccade of 4°. Furthermore, due to the novel cross section structure, the strain sensors can detect radial compression deformations. The sensor can be used not only for monitoring joint movements of finger motions but also for detecting minor deformation muscle activity, such as arm muscle movements and even eye rotation, which has great significance for human motion monitoring.