Enhancing the sensitivity of crack-based strain sensor assembled by functionalized graphene for human motion detection

Human motion detection needs sensors with flexibility,high sensitivity and linearity.However,conventional strain sensors are rigid and not suitable for human motion detection applications.Graphene-based strain sensors can overcome the above challenges but currently are still in the infancy of their development.In this work,properties of graphene-based crack-type strain sensors are investigated and guidelines to improve the sensitivity of graphene films as sensing elements are developed.First,it is found that the pre-strains influences the crack morphology and density,which further results in different sensor sensitivities and linearity.Second,the graphene film thickness influences the crack density due to the sliding between graphene layers;namely,a thinner graphene film with more cracks exhibits higher sensitivity.Third,the substrate influences the bonding strength with the graphene film,leading to different crack formations,which results in adjusted sensitivity.The cracks on PDMS are channel cracks while those on epoxy are isolated short cracks.The channel cracks are preferred to cause high sensitivity while the isolated short cracks hardly have a blocking effect on the current transport.Finally,the optimized graphene strain sensors are used to detect various human motions and exhibit high sensitivity.