High-performance wearable strain sensors based on fragmented carbonized melamine sponges for human motion detection

Strain sensors with a large strain sensing range and high sensitivity are in high demand due to their various potential applications ranging from human motion detection to soft robotics. In this study, high-performance strain sensors are developed by fragmenting carbonized melamine sponges that are commercially available. The strain sensors, based on fragmented carbonized melamine sponges (FCMS), demonstrate high sensitivity with a gauge factor (GF) of 18.7 at an FCMS density of 1.07 mg cm^-2 and a large strain sensing range of up to 80%. As a comparison, the strain sensor based on unfragmented carbonized melamine sponges has only a GF of ∼8.0 and limited stretchability (<7%). In situ tension tests indicate that the strain-response mechanism of the sensor is mainly ascribed to the reorientation of individual FCMS at low strains (<40%), while crack propagation dominates the strain-response behavior of the sensor at strains larger than 40%. The high sensitivity and large strain sensing range of the sensor, as well as the low-cost and scalable fabrication method, enable diverse applications. It can not only detect large-strain human arthrosis movements, but it also exhibits the capability to monitor subtle human physiological activity.