Preparation Of Fiber Strain Sensor And Design Of Monitoring System

At present,flexible conductive fiber membrane has been widely used in integrated circuits and electromagnetic shielding clothing industries due to its excellent flexibility and electrical conductivity,and it has a wide application prospect in wearable devices in medical and human motion monitoring fields.The preparation methods are mainly embodied in physical coating or coating conductive materials,but there are still some problems such as low sensitivity and poor actual monitoring effect when the strain sensor is prepared.Therefore,a variety of flexible conductive fiber membranes are obtained by electrostatic spinning method,and strain sensors placed in different parts of the body are prepared by these fiber membranes for sensing heartbeat,respiration,pulse movement,etc.And the acquisition and transmission of signals and threshold judgment are achieved by using small programs to control Zig Bee.According to different application requirements,the formulation and preparation methods of conductive fiber membrane were optimized to improve the sensor performance.The relationship between the composition and microstructure of the material and the sensor performance was preliminarily studied.The specific research contents of this project are as follows:（1）Polyvinyl pyrrolidone（PVP）,polyvinylidene fluoride（PVDF）and PAN were prepared by electrostatic spinning,and PAN was selected as the main fiber-based material according to the sensing mechanism of the piezoresistive strain sensor,and different concentrations of PAN were explored.And the influence of the propelling speed of the syringe pump on the PAN fiber,and compared the effect of the flat collector and the rotating collector on the orientation of the fiber,and finally found that the rotating collector can improve the orientation of the fiber.The PAN fiber membrane was immersed in ANI aqueous solution by in-situ polymerization,and then the fiber membrane was immersed in ammonium persulfate aqueous solution under acidic conditions,and finally PANI/PAN fiber membrane was obtained by reaction at low temperature.Meanwhile,the effects of ANI monomer concentration,ammonium persulfate concentration,HCl concentration and reaction time on PANI/PAN fiber membrane were investigated.And the prepared PANI/PAN fiber film was encapsulated with polydimethylsiloxane（PDMS）as a strain sensor,and the effect of different tensile rates on the resistivity of the sensor was tested.（2）Ag NWs were prepared by polyol method.The mass ratio of PVP K25 with Na Cl concentration to Silver nitrate（Ag NO₃）was investigated Effects of volume ratio of ethylene glycol to diethylene glycol(C₄H₁₀O₃)and temperature on Ag NWs Ag NWs were also added into the spinning precursor containing PAN and dimethylformamide（DMF）.It was found that the length of Ag NWs in the fiber film was less than 5μm,and the silver wires with longer length were blocked in the syringe due to irregular arrangement.To spinning orientational precursor fluid in micro/nano silver wire,explores the use of magnetic and electric fields of spinning liquid precursor of Ag NWs directional arrangement In terms of the electric field,Ag NWs aqueous solution with the increase of voltage,electrolysis of water phenomenon produced by a large number of bubbles,causes of Ag NWs electric field force is far less than the surface tension of solution,not as directional arrangement as expected;In terms of magnetic field,Fe₃O₄ was prepared by coprecipitation method and attached to the surface of Ag NWs.Magnetic Fe₃O₄@Ag NWs was prepared and mixed into the spinning precursor solution,and magnetic field was applied to the precursor solution;For the sensor prepared with Ag NWs/PANI/PAN fiber membrane with an average length of 4-5μm Ag NWs,the heart rate signal can be more accurately recognized than PANI/PAN fiber strain sensor,and the resistivity change is increased by 31.5%compared with PANI/PAN fiber strain sensor,and GF is increased to 35 The Ag NWs/PANI/PAN fiber strain sensor can monitor the detection of human throat,knuckle,wrist,leg and other parts.In addition,The PAN fiber membrane was immersed in GO aqueous solution,and the GO was promoted to penetrate into the PAN fiber membrane by ultrasound.After three times of ultrasound,the PAN fiber membrane was removed and then reduced with hydrazine hydrate.The r GO/PAN fiber strain sensor was prepared by electrostatic spinning.The sensor was stretched 500 times a day and its initial resistance was recorded.The initial resistance was 27.158 kΩ,after 15 days of stretching,the resistance is 28.799 kΩ,and the performance is relatively stable.（3）The sensor prepared is applied to the development of the Internet of Things.The star network structure composed of one Zig Bee host and two Zig Bee slave is used to send and receive data,and the Zig Bee host device and esp8266 module are connected with the combination of Zig Bee technology and WIFI technology.When the esp8266 is connected to the Internet,the device number is searched and input through wechat mini program,and different instructions are sent in310 ms period to obtain the sensor data of the corresponding machine.In addition,the host device is set to determine the threshold value,and the value can be set according to the needs of different parts.When the sensor strain occurs,when the value of the execution result of the small program exceeds the threshold value,the host buzzer will start to alarm,and when the value falls back to the threshold value,the alarm will be relieved.（4）In view of the fact that the sensors will contact the outer surface of the human body,we studied the electromagnetic shielding characteristics and bactericidal bacteriostasis of the fiber membrane.In terms of electromagnetic shielding,PANI/PAN fiber film can play a shielding effect in the decimeter and centimeter wave range.This is because when the electromagnetic wave propagates to the surface of PANI/PAN fiber film,it will produce reflection attenuation,absorption attenuation,multiple reflection attenuation and multiple absorption loss.Finally,the transmitted wave through PANI/PAN fiber film is part of the original electromagnetic wave,so as to reduce the interference of electromagnetic wave.In bactericidal and bacteriostatic aspect,PANI/PAN fiber membrane has good bacteriostatic and bacterioidal performance to Escherichia coli.This is due to the presence of benzene and quinone rings in PANI molecular chain,most of the main chain is in a positive potential state,while the cell wall of EScherichia coli has a negative charge.Under the action of Kuwara force,the cell wall of EScherichia coli is absorbed by PANI/PAN fiber membrane and destroyed,thus losing activity.