Design Of Graphene Based Sensor

Graphene with a single atomic layer has unique thermal,electrical and optical properties.At the same time,because of its high specific surface area,high mechanical strength and easy functionalization,it is an ideal carrier for composite materials.In the sensing environment,the properties of graphene composite materials will change accordingly,and can be used as sensing materials to design sensors.In this thesis,a series of sensors based on graphene composites are successfully designed,mainly including the design of fluorescence measuring resistance sensor based on RGO/NaYbF₄:Yb³⁺-Er³⁺ graphene conductive composite fluorescent materials,the design of flexible capacitive pressure sensor based on porous RGO/PDMS and the design of flexible resistive stretch sensor based on RGO/NMP graphene conductive ink.The sensing mechanism,sensing performance and application prospect are studied.The specific experimental studies are as follows:In the first chapter,graphene and its preparation methods,graphene composite materials and their preparation methods,as well as the application and research status of sensor design based on graphene composites are introduced in detail.In the second chapter,graphene is successfully prepared by electrochemical stripping method and the mechanism of electrolytic stripping is explained.The principle of fluorescence measuring resistance sensing based on graphene composite RGO/NaYbF₄:Yb³⁺-Er³⁺,capacitive pressure sensing based on RGO/PDMS,and resistive stretch sensing based on RGO/NMP are introduced.In the third chapter,based on RGO/NaYbF₄:Yb³⁺-Er³⁺ graphene conductive composite fluorescent material,the fluorescence measuring resistance sensor is designed to realize non-contact variable resistance measurement.Composite fluorescent materials with Yb³⁺-Er³⁺ ions doped by up-conversion RGO/NaYF₄ and C/NaGdF₄ are successfully prepared by hydrothermal method,which has negative temperature coefficient thermistor?NTC? resistance and fluorescence characteristics.By using the Steinhart-Hart equation and Boltzmann distribution law,the relationship between the fluorescence intensity ratio?FIR?and the resistance is studied,and the sensor design for detecting the variable resistance by FIR technology is realized.The research results show that the relative sensitivity S_R of RGO/NaYbF₄:Yb³⁺-Er³⁺with graphene as the carbon source is higher and can reach 1.039×10^-3/?,the resistance error ?_R is small and the performance is stable,which is an ideal sensor design.At the same time,the sensitivity S_R of thermal coupling energy level 543 nm/658 nm is more stable than that with 543 nm/524 nm.In the fourth chapter,the elastic capacitive pressure sensor is designed based on the porous RGO/PDMS graphene composite to realize the detection of compressive stress and convert the pressure signal into the capacitive signal output.The porous three-dimensional flexible structure is prepared by dispersing electroexfoliated RGO in PDMS and adding sugar particles,which can be used as sensing material and dielectric layer of capacitor structure after curing and dissolution.The sensitivity of the pressure sensor is improved by studying the influence of factors such as sugar concentration,PDMS curing degree and the doping method of graphene on the pressure detection.The maximum sensitivity of the sensor in the small pressure range of 0 kPa-30 kPa is 0.15817 kPa^-1,and the maximum sensitivity of the sensor in the large pressure range of 50 k Pa-200 kPa is 0.02869kPa^-1.The hysteresis of the pressure sensor is small,the response is fast,and the time is less than 200ms.After 1000 times of cyclic pressure,the capacitance value can be output stably,and the cycle performance of the sensor is good and stable.The proposed design of capacitive pressure sensor based on porous RGO/PDMS composite material is environmentally friendly and can be prepared in large area,which can meet the performance requirements of compressive stress sensing and can be applied to wearable electronic devices.In the fifth chapter,based on RGO/NMP conductive ink graphene composite,a flexible resistance tensile sensor is designed to detect the tensile stress and convert the tensile strain into resistance signal output.The conductive ink was prepared by dissolving RGO in NMP,and injected into the hollow elastomer PDMS as the sensing material to prepare the flexible resistive tensile sensing structure.The influence of the stability and concentration of conductive ink on the sensitivity of the sensor is studied.The sensor can be stretched,bent and twisted,and the resistance under different bending angles can be output stably.When the ink concentration is 6 mg/ml,the sensor has higher sensitivity,less hysteresis and stable performance.The sensitivity coefficient under small strain is 0.02601.The flexible tensile sensor can be used to calibrate the stretch and bend.The resistance can still output stably after 1000 times of 45% strain,which can meet the service life and technical requirements of electronic devices.Based on the design of conductive ink RGO/NMP resistive tensile sensor,a new flexible sensor design idea based on fluidity sensing material is provided.The liquidity of the sensing layer is used to calibrate the bending and stretching.The process is simple and can be quickly prepared,which can be applied to the skin surface to detect vital signs.