Investigation Of LC Resonant Flexible Sensor Technology Based On The Graphene Heterogeneous Sensitive Material

There are widely requirements for miniaturized,integrated and curved surface conformal wireless flexible sensors in the rotation parts,human physiological state monitoring,health care,food safety and environmental monitoring.In response to above-mentioned requirements,we have proposed a variety of sensors,which contains gas,humidity and integrated multi-parameter sensors based on graphene heterojunction.The sensitivity characteristics of graphene and its heterogeneous materials were investigated,and we have clarified the sensitivity mechanism of each parameter.Electromagnetic simulation software HFSS is used to simulate and optimize the design of the sensor,and the multi-parameter decoupling system is constructed to realize the miniaturized manufacturing of the sensor.These researches provide new ideas for various parameters measurement for narrow space,sealed,curved surfaces and high-speed rotation environment.Aiming at the mentioned challenges,we have carried out research on high performance sensors,including the design,fabrication,sensitivity mechanism and application for gas sensors,humidity sensors,and integrated multi-parameter sensors.The main research content includes the following aspects:（1）The passive equivalent circuit model of LC wireless sensor is constructed and the influence for each sensitive element on the resonant frequency of the sensor is also analyzed.The sensitivity mechanisms of capacitive and resistive LC wireless passive sensors are investigated,and equivalent models are constructed,respectively.The equivalent circuit model of LC wireless passive multi-parameter sensor is also investigated,the induced voltage and current of each circuit are analyzed,and the characteristic parameters of the sensor are obtained by input impedance.（2）Different graphene heterogeneous nanomaterials preparation method has been proposed.Such as chemical reduction,lithium ion intercalated method,ultrasonic method,respectively,developed silver nanoparticles modified reduced graphene oxide（Ag-RGO）,silver nanoparticles modified molybdenum disulfide（Ag-MoS₂）and reduced graphene oxide-tungsten disulfide（RGO-WS₂）heterojunction nanomaterials.The sensitive materials were characterized by SEM,TEM,Raman spectroscopy,XPS and XRD to obtain high-performance graphene-based heterojunction nanomaterials.（3）According to different demands for various parameters in different environment,the strain,gas and humidity sensors of graphene-based heterojunction sensitive materials were investigated.The reduced graphene oxide（RGO）modified by silver nanoparticles（Ag NPs）as the strain sensing material,and polydimethylsiloxane（PDMS）is used as the base material and packaging material to form a sandwich structure.The Ag NPs attached to the RGO surface greatly enhances the connection on the RGO surface,which improves the conductivity of the RGO layer,and enables the preparation of high strain sensitivity sensors.The sensor has the characteristics of high sensitivity,wide range,ultra-fast response time and time.At the same time,a wireless NFC labeled ammonia gas sensor was developed,which realized wireless real-time monitoring of ammonia gas（NH₃）with a concentration of 5-100 ppm finally.There are two wireless label ammonia gas sensors were developed,and the wireless real-time monitoring of ammonia gas（NH₃）with concentration of 1-100 ppm was finally realized.On this basis,a fast response,Ag-MoS₂ wireless gas tag sensor is further studied,due to it’s accurately monitoring and low cost.The sensor has a sensitivity of 0.097 ppm^-1,the detection limit of the wireless gas sensor is 1 ppm,and it has fast response,short recovery time and good repeatability at room temperature.In addition,when NH₃ concentration is 0-100 ppm,the sensor has good linearity.In the end,the wireless label sensor was applied to the working conditions of meat spoilage and large breeding bases.A humidity sensor based on RGO and tungsten disulfide（WS₂）two-dimensional heterojunction nanomaterials is proposed.The wireless humidity sensor has fast response time（0.56 s）and recovery time（2.26 s）.The sensor operates in a humidity range of 5%to 95%RH with a sensitivity of 14 k Hz/%RH（5-35%RH）,150 k Hz/%RH（35-65%RH）and 110 k Hz/%RH（65-95%RH）,respectively.Based on the above excellent performance,the sensor can be used to detect weak signals such as human voice and respiration,and it can also be used to monitor skin humidity and evaluate human metabolism.（4）To satisfy the demands for the simultaneous monitoring of multiple parameters in complex environments,such as mechanical rotation,an integrated multi-parameter wireless passive sensor with multi-resonance multiplexing is proposed to achieve the design and manufacturing of 3D integrated of wireless sensors with three parameters of temperature,pressure and humidity,which is based on the research of LC wireless passive single-parameter sensors.The research and testing of temperature,humidity and pressure parameters have been carried out respectively.The temperature test range is 25℃-120℃,the humidity test range is5% RH-95% RH,and the pressure range is 0 kPa-300 kPa.The decoupling analysis of multi-parameter sensor test results is carried out,and it is constructed a multi-parameter decoupling model.In order to obtain the influence coefficient of the temperature parameter on the pressure parameter,and to realize the accurate extraction of the pressure parameter,it is used to fit the test results with the flat plate fitting method under the temperature and pressure compound environment.