Strain detection using long-length MWCNT buckypaper-based flexible strain sensor for large strain range

Flexible strain sensors are crucial in wearable devices, yet achieving both high sensitivity and a broad strain detection range simultaneously poses challenges, often leading to trade-offs. In this study, a flexible, sandwiched structured strain sensor has been developed using thermoplastic polyurethane (TPU) polymer and long-length multiwalled carbon nanotube (l-MWCNT) buckypaper. The l-MWCNT helps to keep the resistance steady as long as the strain stays within a certain limit. This greatly expands the strain detection range of the sensor to ∼427%. Additionally, the sensor exhibits notable sensing properties with a highest gauge factor of ∼150 and a rapid response and recovery time of 100 ms. It also demonstrates good stability and durability during cyclic stretching and releasing tests, owing to the reversible changes in the CNT conductive network under tensile and compression loading. This sensor enables real-time health monitoring and can detect various physiological activities such as swallowing, breathing, speech, pulse, and movements of the wrist and fingers. These advancements highlight the potential of flexible strain sensor technology in improving human movement detection.