Study On Electromechanical Properties And Model Of Conductive Coated Fabric Sensor

Compared with traditional hard sensors,smart sensors based on flexible fabric have attracted much attention in the field of smart wearable in recent years because of their advantages such as softer and more comfortable,stretchability,good elasticity and wide range of work.Fabric strain sensors fabricated by coating method perform poorly during large mechanical deformation,but large strain range and high sensitivity are often not combined.Some researchers have improved the performance of the sensor from the material selection and preparation method,but the research on the sensing mechanism affecting the sensing behavior has not yet formed a mature system,and there is a lack of effective electrical model to clarify the strain sensing mechanism of coated sensors in the stressed state.Based on this,this project design and prepare a flexible sensor can withstand large strain and has good sensor performance,from the microscopic perspective of the coating of the coating surface of the observation and analysis,resistance change,further exploration of the conductive coating of fabric sensor mechanism will provide a basis for the application and improvement of such sensors.The main work contents and conclusions of this paper are summarized as follows:(1)Preparation and performance test of conductive coated fabric sensor.According to the large deformation,high resilience,good conductivity and flexible requirements,choose the nylon and spandex knitting as the base material,composite polymer material composed of carbon nanoparticles/silicone rubber/silicone oil as conductive coating material,through screen printing,sewing conductive wire and conductive silver paste conductive coating fabric sensor.Through the electron microscope,it is found that the coating is not uniform on the microscopic level,and the surface of the fabric presents a small square appearance.This is because the height of the coil column is higher than the height at the intersection position of the two coil columns.In the process of screen printing,the coating in the raised area is easy to be printed,and the coating in the concave area is difficult to transfer.The transverse density of knitting is 97/5cm and 211/5cm;the thickness of conductive coating is about 11μm and the gram weight of conductive coating fabric is 82.5g/m~2.The mechanical lag rate of sensor is 11.82%,flat knitwear is 8.97%,and the Young’s modulus of conductive coated fabric is 0.186MPa,which is much smaller than the modulus of human skin.(2)Strain sensing test of conductive coated fabric sensors,mainly including cyclic tensile test,strain sensing test at different elongation rates,and strain sensing test at different tensile speeds.At the speed of 10mm/min and 10 cycles of 60%strain,the sensor can respond positively and periodically;but the resistance will drift with the cycle loading,the sensitivity of the sensor within 0-60%strain is approximately 3.11;the relationship between resistance and elongation is more in line with the secondary polynomial,and the fitted R~2 reaches 0.99954;the sensor performance stabilizes after the sixth stretch,and the sensor is good.In the strain sensing test under different elongation,with the increase of elongation,the sensor electrical lag gradually decreases and gradually stabilizes;when the strain exceeds 1.5%,the output-input characteristic curve has good linear relationship,the strain sensitivity coefficient GF can be approximated as constant,and GF decreases with the increase of elongation;with the increase of the constant elongation,the time required to achieve equilibrium gradually becomes smaller,and the electric hysteresis characteristic parameterΔR is basically unchanged.At the tensile velocity of12mm/min,60mm/min and 120mm/min,the time of resistance relaxation becomes shorter with increasing the tensile velocity,the sensitivity of the sensor becomes higher,the mechanical hysteresis gradually decreases,and the electrical hysteresis increases first and then slightly decreases,which is inconsistent with the mechanical hysteresis phenomenon.The derivative slope of the fitted quadratic term equation for the sensor at 120mm/min is 4.569,and the minimum k at 12mm/min is 3.73475,and the difference between the two is 0.83425.At a loading speed of 2400mm/min,the sensor could respond transiently with a response time of 800ms,and showed nearly identical response behavior under repeated loading-hold-unloading cycles.(3)Qualitative description and quantitative analysis of the resistance change behavior from the micro perspective.Under different tensile strain,the uneven strain distribution of knitted fabric in a single cell makes the coating at the unit edge receive greater force,making the conductive coating more prone to tear and crack,and the crack shape is distributed along the edge part of the unit"W"shape;the morphological change of the surface of the conductive coating fabric determines the connected state of the conductive pathway,which is the main cause of the change of strain sensing behavior.The crack characteristic parameters under different strains are extracted,and the functions of crack number,average crack length and average crack width change with strain are obtained.For the small structural units in the selected area,the resistance of the whole selected area can be regarded as the resistance rate of resistance and the crack parameters under different strains.Through the theoretical deduction,the crack parameters are analyzed by the control variable method,and the crack number has a positive influence on the sensitivity of the sensor.