Research On The Time Response Characteristics Of Graphene Flexible Strain Sensors

Graphene flexible strain sensor is mainly composed of graphene sensing layer with lamellar structure and flexible substrate.It has the advantages of good conformity,high sensitivity,low cost,simple processing and convenient application in circuit.It has become a new research object in the field of flexible sensor.Most of the research focuses on flexible wearable and electronic skin applications,with emphasis on sensitivity and other indicators.In this paper,the characteristics of time response of the graphene flexible strain sensor are studied,and the possibility of high dynamic micro-strain sensing for increasingly complex mechanical structures in the industrial field is explored.First of all,the main factors affecting the time response of graphene flexible strain sensor,including flexible substrate,sensitive layer and the interface between them,are obtained through analysis.Based on the two-dimensional grid structure design of graphene film and the stacking structure design of graphene wafer,a mechanical simulation analysis model was established.Based on the propagation formula of mechanical wave in solid medium,the propagation time of strain in flexible substrates is calculated at the order of 3?s.Therefore,it is judged that the interface and sensitive layer are the main factors affecting the response time from hundreds of microseconds to tens of milliseconds.The influence of different sensitive layer structures on response time is studied and the network structure has advantages over the layered structure in the change of propagation stress.The influence of different strength bonding interface on response time is analyzed.The lower or higher strength bonding force will not be able to effectively transfer strain,thus affecting response time.Then,according to the two key factors-sensing layer and interface bonding,two kinds of sensor with different sensitive layer structure-planar thin film structure and two-dimensional grid structure,and three kinds of sensors with different interface bonding strength-weak interface bonding strain sensor,strong interface bonding sensor and moderate interface bonding sensor are designed.With the help of spray deposition technology,graphene wafers are micro-stacked on the substrate surface to introduce more surface active sites and improve the chemical inertia of graphene layer.At the same time,a new type of interface modifier-dopamine,was introduced to design the non-covalent interface bonding.The rapid debonding and sliding between the sensitive layer and the substrate were realized eventually,and meanwhile the process design and preparation of the fast response graphene flexible strain sensor were achieved.Then,sensors with two kinds of sensitive layer structure and three kinds of sensor structures with different interface bonding strength are tested.The results show that under the same interface bonding strength,the response time of the sensor with two-dimensional mesh sensitive layer structure(260?s)is faster than that of the planar thin film structure(700?s);However,under the same sensitive layer structure(two-dimensional mesh structure),when the interface bonding strength is moderate,the minimum response time can be 200?s.According to the performance evaluation of the sensor with two-dimensional mesh structure and moderate interface strength,the results show that under 1%tensile strain,the sensitivity is over 100,the creep is only 4.54%,and the change rate of relative resistance is about 7%under 1000 tensile cycles,which means the sensor fabricated by this process not only has fast response,but also has good mechanical compliance and high sensitivity.In addition,by the conformal interface modification design on irregular complex surface,the preparation of flexible graphene strain sensor without substrate is realized.Through the real-time monitoring of 4-6?m micro-strain on irregular complex structure surface(the relative resistance change rate is about 6.64%),it is shown that this fast response flexible strain sensor also has the accurate detection of micro-strain and the strong confonnal ability on irregular structure surface.Besides,the array flexible strain sensor is successfully fabricated on the irregular sphere surface for the accurate measurement of the distributed micro-strain signal of the complex object surface.In summary,this sensor technology has great application prospects in structural component detection and biological signature detection.