Ultra-stable strain/ humidity dual-functional flexible wearable sensor based on brush-like AgNPs@CNTs@TPU heterogeneous structure

Wearable flexible sensors have a broad applications prospect in human motion and health monitoring. However, designing and manufacturing ultra-stable sensors with wide operating ranges and extremely low detection limits remain a challenging task. In this paper, a heterogeneous-structured fibrous membrane was constructed using the electrospinning process and subsequent ultrasonic homogenizer treatment. The fibrous membrane is composed of brush-like thermoplastic polyurethane (TPU) fibers, which are embedded with carbon nanotubes decorated with silver nanoparticles (AgNPs@CNTs). A dual-function sensor for strain and humidity based on the fiber membrane was designed. As a strain sensor, it has an ultra-low detection limit (0.05 %), an ultra-wide sensing range of 600 %, and excellent stability (100,000 cycles of stretch/release operation at 50 % strain). As a humidity sensor, it can achieve fast response as low as 1 s. With excellent sensing capabilities in terms of strain and humidity, the fiber membrane can be used to monitor breathing, pulse, and limb movement, as well as non-contact sensing, such as sensing the vibration of guitar strings or monitoring footsteps. The versatility and manufacturability of fiber membranes provide a new way for the application of wearable sensors in health monitoring and motion tracking.