Ultrasensitive and wide-range reduced graphene oxide/natural rubber foam sensors for multifunctional self-powered wireless wearable applications

Flexible wearable electronics is an emerging research field in recent years, showing the great potential in human health monitoring and motion capture, electronic skin and intelligent robots. However, it is still challenging to develop all-in-one sensors with high sensitivity, wide range, fast response, excellent reliability and mechanical durability for multiple wearable purposes. Here a hierarchical conductive structure based on reduced graphene oxide (RGO) segregated network and porous natural rubber (NR) is rationally designed via industrially-applicable synchronous foaming-reduction-vulcanization (SFRV) method. The resultant all-in-one RGO/NR foam sensors have wide detection range (0.87–223 kPa), high sensitivity (7.00 kPa−1), fast response (70 ms) and excellent durability (1000 cycles), and simultaneously exhibit differentiated responsiveness to various external stimuli such as pressure, acoustic vibration, temperature, humidity and gaseous chemicals. Besides, a smart insole consisting of 24 foam blocks as sensor array is fabricated to identify plantar pressure distribution for gait recognition, abnormal posture correcting and diseases diagnosis applications. Surprisingly, the RGO/NR foam can also harvest mechanical energy during compression cycles and deliver an open-circuit voltage of 20–30 V and current of 10 nA. This provides an opportunity to develop wireless self-powered multifunctional wearable system based on the RGO/NR foam for human health and sport monitoring.