The Study About Flexible Wearable Strain Sensor Based On Graphene Composites

A wearable or attachable health monitoring intelligence system is supposed to be the next generation of personal portable devices for telemedicine practice.Intelligent and flexible sensing electronics are key factors that enable health monitoring systems to track and monitor physiological signals in real time.These signals are closely related to physical conditions such as heart rate,wrist pulse,body temperature,blood/intraocular pressure,and blood/sweat.Monitoring these physiological signals has provided a convenient and non-invasive method to diagnose and assess health.Graphene-based wearable sensing has recently received widespread attention.Because of the excellent mechanical properties of graphene and the 25% Young's modulus in the stretched state,it is very suitable for flexible and stretchable electronic equipment.In addition to its excellent mechanical properties,graphene also has unique electrical properties such as high carrier mobility and good piezoresistive sensitivity.In addition,graphene is an ideal two-dimensional structural material that enables large-scale device fabrication through a top-down approach and is accessible with existing manufacturing techniques.This thesis is based on graphene itself and the construction of a composite of graphene and other materials to realize the design and construction of flexible sensor parts,and further introduces capacitive structure and variable color visual sensing to perfect the graphenebased wearable sensor,which is aim to achieve monitoring of a variety of physiological signals in the human body.The specific research contents are as follows:1.Wearable sensors for monitoring human motion simultaneously with the color of colloidal crystals and electrical signals of graphene films are realized by preparingn on-close packed colloidal crystal films of silica in PEGPEA as substrates and lamellar r GO as conductive layers.The simultaneous detection of multiple human motions,such as some large-scale motions,in terms of finger bending or wrist bending,is realized by using two kinds of signal changes.In addition,the resistance change of graphene film can also be used to detect many kinds of small movements of human body,such as throat movement,breathing and pulse,etc.2.The tensile and conductive r GO/TPU composites were prepared by combining graphene with TPU elastomer.Based on the resistance change of the composite at different temperatures,we can monitor the temperature of human body and external environment.In addition,a stretchable capacitance sensor is fabricated by using r GO/TPU composite as the electrode plate and Ecoflex as the elastic medium in the middle,which can be used to detect physiological signals of human body,such as joint movement,breathing,external pressure,muscle movement and so on.And the main applied force can be distinguished through the direction of the sensor's electrical signal response: when the main applied force is pressure,the capacitance of the sensor increases;when the main applied force is tension,the capacitance of the sensor decreases.3.Large-scale free-standing graphene films with good electrical conductivity were prepared by improved dropping coating method,and flexible inverse opal films(IAOA)were introduced as substrates to enhance the sensitivity of the sensor with its porous structure.Graphene resistance changes can be used to monitor a variety of human movements,such as finger bending,different direction of wrist bending and throat-based small movements,such as drinking,breathing and coughing.When sweat enters the porous inverse opal film substrate,the refractive index of the inverse opal film can be altered by changing the medium in the hole,which results in a significant change in its color.The simultaneous detection of sweat in motion is realized by using the color change of the inverse opal substrate.