Research On The Fabrication Of Flexible Strain Sensor Based On Carbonized Paper And Its Applications In Human Motion Monitoring

With the booming development of flexible electronics,sensors based on flexible substrates integrated with high-performance sensing materials have become a new research hotspot.Low cost,simple fabrication,eco-friendliness and superior performance are aims and trends of flexible sensors.Among various of methods of getting sensing materials,carbonization is a simple and green one.It converts the originally-insulated biomaterials into conductive carbon materials without complicated process,toxic chemicals and polluting gases,thus attracting many researchers'attention.To date,considerable biomaterials have been carbonized and related research has shown technical characteristics of good conductivity and high sensitivity.However,tube furnace carbonization at current time is of extremely low efficiency,and ultralong time duration required for carbonization has reduced its attraction.In addition,most flexible sensors based on carbonization strategy only have single mode function such as strain sensing or pressure sensing,especially lacking the temperature sensing,the monitoring of which is of great significance in fields of environment,electronic system and personal healthcare.Therefore,this study is focused on the carbonization of biomaterials.Low-cost,easily available paper was carbonized and then encapsulated by silicone rubber elastomer to act as a flexible multifunctional sensor.Specific work and results are as follows:(1)Rapid annealing furnace was adopted for biomaterials carbonization,and the time duration required for thermal treatment has reduced from several hours of conventional tube furnace carbonization to five minutes.This simple manufacturing process can be quickly extended to other biomaterials.Specifically,cost effective and sustainable multilayer facial tissue(MFT)was carbonized for five minutes under N2 atmosphere and then encapsulated by silicone rubber to obtain UCMFT multifunctional sensor.(2)The as-fabricated UCMFT sensor can respond to tensile strain,vertical pressure and temperature change.Moreover,it exhibits positive resistance variation to both strain and temperature,while shows negative resistance variation to pressure,which is helpful to distinguish strain and pressure signals.Specifically,UCMFT sensor shows characteristics of high strain sensing sensitivity(GF?186),wide stretching range(0-100%),low detection limit(0.04%),small hysteresis(14.08%),fast response(?80ms)and remarkable durability(7000 stretching-releasing cycles under 50%strain).At the same time,it can sense pressure of up to 44 kPa,and the maximum temperature sensitivity is one order larger than those of counterparts,reaching 4.48%?-1 in the range of 25-65?.(3)UCMFT sensor can be directly attached to human skin to monitor full-scale human motions,including intensive strain like joint movement and subtle strain such as breathing,pulse beating,eyes blinking and speaking.The output signals are strong and stable,so there is no need for extra amplification modulus,implying great application potential in personal healthcare and human-machine interactions.