Study On The Sensing Properties And Sensing Mechanism Of The Flexible Capacitive Pressure Sensor

Because of their avantages,flexible sensors have attracted extensive attention in many important areas such as wearable electronic devices,human-computer interaction,intelligent skin,which exhibit a huge application prospect.However,although the related research is in-depth,the flexible sensors are still not mature on the whole.There are still some problems such as complex preparation process,high cost,low sensitivity;in addition,the application of flexible sensor in aerodynamic pressure measurement of aircraft structure has not been reported yet.The main methods of aerodynamic pressure confirmation on aircraft structure are pressure hole method,pressure-sensitive paint method and computational fluid dynamics method;but these methods still have the problems of complex installation,low accuracy and large calculation amount.The rapid development of flexible sensors brings new opportunities to the aerodynamic pressure measurement of aircraft structure surface.In view of the existing problems of low sensitivity,low liner range and complex fabrication process of the flexible capacitive sensor,this thesis explored the sensing mechanism and the sensing performance of the flexible capacitive sensor based on electrical double layer capacitors and interface polarization effect from chemical and physical aspects.The study focuses on the sensing materials,theoretical model,fabrication process,structure design and aerodynamic pressure sensing characteristics.The main contents of this thesis are as follows:(1)A flexible capacitive sensor based on the ionic membrane had been proposed.The sensitivity of the sensors had been improved by introducing the electrical double layer capacitors.The electrospun,solution mixing and mould method were used to fabricate the FP/IL,PU/IL,PVDF/IL,PVA/H3PO4 and PVA/KOH ionic membrane.The effects of the process parameters,different contents of ionic liquid and metal salts additions on the surface morphology and microstructures of the ionic membrane had been studied.(2)The sensing performance of the capacitive sensors based on the FP/IL,PU/IL,PVDF/IL,PVA/H3PO4 and PVA/KOH ionic dielectric layer had been studied.The experimental results show that the sensors have a high linear response in the pressure range of 0 kPa to 36.2 kPa,the sensitivity up to 26.2/kPa and the response time is 14 ms.In addition,the sensing performance are stable under more than 1000 cycles test.Comparing to the traditional capacitive sensors,these sensors have the both high sensitivity and wide linear range.(3)A flexible capacitive sensor based on interface polarization effect had been developed,which could improve the sensitivity and durability of the sensor effectively.The PVDF/CNTs composite nanofiber membrane and the PDMS/GO composite membrane were fabricated by the electrospun and solution mixing methods.The influence of CNT content and porosity to the mirosture and surface morphology of the PVDF/CNTs nanofiber membrane and PDMS/GO composite membrane.The experimental results show that the surface of PVDF/CNTs composite nanofiber was smooth and uniform with 0.5 wt%CNT addition and the PDMS/GO composite membrane was uniform and high porosity with 3 wt%ZnO particle addition.(4)The PVDF/CNTs composite nanofiber membrane and the PDMS/GO composite membrane were used for the dielectric layer of the capacitive sensor.The two sensors were high sensitivity,and the sensing performance were studied.The experimental results show that the sensors have a high linear response in the pressure range of 0 kPa-15.0 kPa,the sensitivity is as high as 0.99/kPa and the response time is 14 ms.In addition,the sensors are stable under more than 1000 cyclic loading.(5)A simple and efficient fabrication method of surface microstructure dielectric layer for the highly sensitive flexible capacitive sensor had been developed.A PDMS membrane with a hemispherical microstructure was prepared by mixing PVC foaming agent with PDMS solution.The effect of PVC content to the surface morphology of PDMS membrane was studied.The PDMS membrane with a hemispherical microstructure was used for the dielectric layer of the capacitive sensor,and the sensing performance was studied.The experimental results show that the sensors have a high linear response in the pressure range of 0 kPa-11.5 kPa,the sensitivity is as high as 0.31/kPa.In addition,the sensors were stable under more than 1000 cyclic loading.(6)According to the engineering application,the influence of the thickness of dielectric layer,bending rate,temperature,humidity and other factors on the sensing performance of the flexible capacitance sensor had been studied.The experimental results show that the sensor has good stability.Based on the above analysis results,the capacitive sensor based on PVA/KOH ionic membrane was selected from the aspects of deformation ability,sensitivity and stability,and the corresponding sensor network is designed for aerodynamic pressure measurement.The experimental results show that the sensor and the sensor network can measure the magnitude and spatial distribution of the aerodynamic pressure accurately.