Strain Sensors for Human Movement Detection Based on Fibrous Membranes Comprising Thermoplastic Polyurethane, Ag Nanoparticles, and Carbon Nanotubes

Abstract

Flexible wearable strain sensors are crucial in human–machine interfaces, electronic skins, and human movement detection. However, simultaneously achieving high sensitivity and a large response range persists as a significant issue, and trade-offs often exist between them. In this work, thermoplastic polyurethane (TPU) fibrous membranes are prepared by utilizing electrospinning technology and used as a flexible substrate. Silver nanoparticles (AgNPs) are securely sputtered on the TPU fibrous membrane by magnetron sputtering, which enhances the sensitivity due to their small dimensions. Meanwhile, CNTs were anchored through ultrasonication to serve as an additional conductive layer to expand the response range due to their large aspect ratio. The obtained TPU/Ag/CNT fibrous membrane possesses exceptional mechanical properties (stress up to 10.44 MPa, strain up to 606.7%). The TPU/Ag/CNT-based strain sensor exhibits remarkable sensing properties of high sensitivity (gauge factor up to 6834), a large response range (up to 604% strain), and fast response and recovery times (response time is 122 ms, recovery time is 164 ms), along with an extremely low detection limit (0.1%). Moreover, it shows remarkable cycling stability, maintaining its performance for over 1000 cycles. Due to these outstanding advantages, TPU/Ag/CNT strain sensors have exceptional capacity to detect human movement and demonstrate a certain potential in the development of flexible strain sensors.