Design,Fabrication And Properties Of Graphene Based Flexible Stress/Strain Sensors

In the development process of the Internet,the electronic devices have achieved the goals of portability and miniaturization.However,the Internet of thing(IOT)has coming,which bring new chanllenge for traditional stress/strain sensors because they are lack of flexibity and wearablity.In addition,the novel stress/strain sensors are required to show high performance,new features and low cost.In this paper,many kinds of innovative stress/strain sensors based on the popular two-dimensional material graphene were developed by the micro/nano technology.The fabricated wearable electronics display excellent properties and multi-functions,which promote the development of wearable devices and expand the application of intelligent electronics.The details are summatized as follows:Low pressure chemical vapor deposition(CVD)was used to prepare few layers graphene film on copper foil substrate,and a highly transparent single-chip flexible stress/strain sensor was fabricated by combining graphene with polyethylene terephthalate(PET)substrate.Based on the principle of' linear resistance,the assembled sensors can reflect one-dimensional stress position with a high sensitivity of 23.2%·mm-1 and a fast response time of 18.1ms.The optical transmittance of the sensor was up to 80%.which promised the sensor served as a smart window that can warn of rain without sacrificing the visual functionalities.In addition,a flexible smart panel had been assembled only connect two external circuits and succeed in reappearing the touch path.To optimize the structure of the single chip device,a sandwich type double-chip flexible stress/strain sensor was successfully developed.The working principle of the device was the same as the single one.The sensors featured a high sensitivity of 14.3%·mm-1,a long lifetime of 14000 cycles,and fast response time of 0.3 ms.Furthermore,the electrical signals of the sensor were almost irrelevant to the interference signals such as bending strain.This rational design of innovative materials and devices presented a great potential for electronic devices to completely replace the unique tough sensing properties of human skin.The reduced graphene oxide(rGO)foams were prepared and dispersed in deionized water(DI),and a super elastic stress/strain sensor was obtained.The device was based on the micro contact of rGO in the liquid,and had the distinguishable response resistance for the compressive stress and tensile strain.The novel sensors showed a high sensitivity(gauge factor of 31.6 and stress sensitivity of 12.2%·kPa-1),extremely wide sensing range(0.1%?400%)and excellent stability(more than 15000 cycles).The sensing liquid of the device can be refilled when it failed,this enabled the recycling of the materials and reduces the waste rate.Therefore,it was attractive and promising for practical applications in multifunctional wearable electronics such as the detection of acoustic vibration,human vocalization and other human motions.An outstanding sensitivity stress/strain sensor was successfully fabricated by mixing the rGO and waste pulp.The conductive rGO inlaid in the fibrous network to form a 3D micro-architecture,where the electrical conductivity and mechanical elasticity of the composite can be tuned simultaneously by varying the rGO proportion.The device applied in local strain reveales more influenced by electrical property,tending to choose low rGO proportion and displaying a sensitivity of 72%·kPa-1 in a 10 kPa sensing region.On contrary,the sensor used for integral strain shows a greater dependence on mechanical property,which profer to high rGO proportion and reaching a gauge factor of 2517 in a 100%working range.The sensor exhibited fast response(14.35 ms rising time)and high stability(more than 100000 cycles).And the 3D micro-architecture were scalable,low cost,and promising in human-computer interactions(HMI),including but not limited to human health monitor and intelligent wearable keyboard.Graphene foams(GFs)obtained by atmospheric pressure CVD was used to prepare the multi-functional stress/strain sensor by combining with modified silicone rubber(MSR).The sensing principle of strain was based on the micro-fracture and healing of GFs while visualization was attributed to the thermochromic materials(TM)in MSR.The sensors demonstrated a high sensitivity(gauge factor of 1039 and stress sensitivity of 18.3%·kPa-1).an outstanding stretchability up to 100%and great stability(more than 10000 cycles).The soft and reversible strain sensor can be easily mounted on human skin as a wearable device for high accuracy detecting of electrophysiological stimuli,a wearable heater for thermotherapy or body warming and even for acoustic vibration recognition.The rationally designed sensors were scalable and promising in human-computer interactions,such as smart visual-touch panel.