Research On The Flexible Piezoresistive Sensor Of Micro-nano Carbon Materials And Its Application In Smart Clothing

Intelligent wearable health monitoring system can effectively reduce the mortality of patients and improve the life quality of the elderly.Flexible piezoresistive sensor is the key component to obtain human biological information and is the basic technology of wearable health monitoring system.The research of high performance flexible piezoresistive sensor is of great significance for the development of smart clothing.In order to study the performance of different types of flexible piezoresistive sensors and clarify their sensing mechanism,three types of sensors were prepared:1.Modified graphit/polyurethane flexible piezoresistive sensor,2.Modified multi-walled carbon nanotubes/polyurethane flexible piezoresistive sensor,3.Surface micron structure multi-walled carbon nanotubes and silver nanowire/polyurethane flexible piezoresistive sensors.First,the surface modified graphite and multi walled carbon nanotubes were doped into the polyurethane resin to obtain two kinds of conductive films with good elasticity,and the sandwich-structure modified graphite/polyurethane flexible piezoresistive sensor and multi-wall carbon nanotube/polyurethane flexible piezoresistive sensor were prepared.Based on SEM,TEM,FTIR spectrum,Raman spectrum,Dielectric spectrum and self-developed mechanics-electricity performance tester,the structure,mechanical properties and electrical properties of the conductive film and its sensors are systematically studied.The results show that the particle size ratio of modified graphite and multi-walled carbon nanotube is 16.7%and 36%lower than those of unmodified,indicating that the dispersibility of the modified micro nano particles in the polyurethane matrix is obviously improved;the modified graphite/polyurethane and the multi-wall carbon nanotube/polyurethane conductive film with low dopant mass ratio have capacitive effect under the high frequency excitation signal.Based on this experimental phenomenon,a new conductive channel model is constructed.There is a two power function relationship between the resistance relative change and the pressure of the conductive film.The relationship of sensitivity and pressure of the sensor can be obtained by the derivation of function,which provides a new method for calculating and predicting the sensitivity of the flexible piezoresistive sensor.The piezoresistive sensitivity of 30wt%modified graphite/polyurethane conductive film reaches the highest value of 6.38kPa-1,and its hysteresis and repeatability errors are respectively±12.3%and ±20%;The sensitivity of 1wt%modified multi-walled carbon nanotube/polyurethane conductive film is 4.208 kPa-1,and the hysteresis and repeatability errors are ±8.2%and ±6.63%respectively.In order to further improve the sensitivity and simplify the structure of the flexible piezoresistive sensor,a multi-walled carbon nanotube-silver nanowires/polyurethane conductive film with surface microstrip structure is prepared by template method.The micro structure surface of the conductive film and the interactive single surface electrode are combined to prepare the micro structure conductive film/single side electrode flexible piezoresistive sensor.Within the pressure range of 0-2kPa,the sensitivity of the sensor is as high as 46.93kPa-1.The hysteresis and repeatability errors of the flexible piezoresistive sensor doped with multi-walled carbon nanotubes and silver nanowires are ±4.15%and ±1.56%respectively.The finite element simulation results show that the micro structure of the conductive film and the contact area of the single electrode have negative correlation with the piezoresistive sensitivity of the composite conductive film.The prepared flexible piezoresistive sensor is used for human body physiological signal monitoring,and a mechanical model of the flexible piezoresistive sensor when measuring the pulse frequency or respiratory frequency of the human body is established and its working principle is studied.It provides theoretical support for expanding and optimizing the application of flexible sensors in smart clothing.Finally,the three kinds of sensors are used to prepare smart clothings such as pressure distributionmeasurement insole,respiratory frequency measurement pressure measurement vest and glove.The experimental results show that the smart clothing can accurately detect the foot pressure distribution in the human body,the respiratory frequency and fingertip pressure of the human body.Flexible piezoresistive sensors have very broad application prospects in smart clothing and intelligent home products.