Research On Self-Powered Fiber-based Flexible Strain Sensor

With the development of intelligent textiles,the fiber flexible strain sensor made by combining textile materials and electronic materials has attracted attention due to its advantages such as soft,light weight,volume control,good bending and tensile performance,and unique fiber structure.It can meet the deformation requirements of wearable electronic devices and is easy to be combined with other kinds of flexible devices to form multi-functional integrated wearable electronic products.It has a great development prospect in the field of flexible electronics.In this study,the piezoresistive fiber flexible strain sensor,capacitive fiber flexible strain sensor and combined fiber flexible strain sensor were prepared by using three-dimensional polyester vertical netting nonwoven material with excellent compression recovery as fiber substrate,and the sensing performance and application were explored.First,the surfactant sodium dodecylbenzene sulfonate(SDBS)and carboxylated multi-walled carbon nanotubes(MWNTS-COOH)were dispersed and dissolved in deionized water.After ultrasonic treatment for 4 hours in warm water at 50?and ultrasonic frequency at 50Hz,the active material of carbon nanotubes dispersion was prepared.The results show that the self-made carbon nanotube dispersion has no obvious precipitation after standing for 24 hours,and the particle size distribution of the dispersion presents a standard normal distribution,with an average particle size of 68 nm and a concentration of 5.0 mg/m L carbon nanotube dispersion keeps its resistance at about 5 k?after repeated impregnation and drying on nonwoven materials for three times.The sample of piezoresistive fiber flexible strain sensor was prepared by impregnation and adsorption of the carbon nanotube dispersion onto the polyester vertical mesh nonwoven matrix material.Scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and volt-ampere characteristic curve analysis showed that the carbon nanotubes were successfully adsorbed on the surface of the polyester fiber,forming a stable conductive network inside the three-dimensional framework of the polyester nonwoven material.The sensing characteristics of the sensor under compression and bending deformation were explored,and the response time was 400 ms,the small pressure of 100 Pa could be recognized,the detection range was 100-800 Pa,and the sensor had good responsiveness and sensitivity.The active material of carbon nanotubes was adsorbed to the upper and lower surfaces of the polyester vertical mesh nonwoven material matrix by the method of drop coating,which was used as the upper and lower plates of the capacitive sensor,and the middle part was the dielectric layer to make the capacitive fiber flexible strain sensor.The electrochemical characteristics of the capacitive sensor were investigated,and it was found that the measured CV curve of the capacitor was approximately an isosceles triangle,and the charging and discharging times were basically the same.The maximum volume capacitance was 13.82 mF/cm~3 at the scanning rate of 5 mV/s.And after 1000 times of continuous charging and discharging,the efficiency of the capacitor is still stable at 98%,the capacitance loss can be ignored,showing an ideal electrochemical behavior.The response time of the sensor is 200 ms,and it can identify small pressure strain of 100 Pa.The detection range is 0.5-2 kPa.Under 5%compression strain,the capacitance change rate is 100%,while under 20%compression strain,capacitance change rate is 320%.It has good electrochemical performance and sensing characteristics.Based on piezoresistive fiber flexible strain sensor and capacitive fiber flexible strain sensor,a composite fiber flexible strain sensor,which combines piezoresistive fiber flexible strain sensor and fiber flexible strain capacitor,is fabricated.This highly compressible system has an absolute resistance change rate of 5%at 100 Pa and 12%at 500 Pa.When the bending Angle is 30°,the absolute value of the resistance change rate is 3%,and when the bending Angle is 120°,the absolute value of the resistance change rate is 16%.At bending Angle of 60°,it can be repeated 6000 times,and at 10%compression,it can be repeated 4500 times.The combined fiber strain sensor gives full play to the three-dimensional advantages of nonwoven materials,combines the functions of piezoresistive fiber strain sensor and capacitive fiber strain sensor,and has a promising application prospect in human motion change detection and self-powered sensor.