Investigation Of The Design,fabrication And Sensing Performence Of Flexible Capacitive Pressure Sensor

The rapid development of bionic technology,display technology and the Internet of Things industry has promoted people's demand for high-performance,advanced electronic skin sensors.Capacitive pressure sensors have become a hot area of research at home and abroad in recent years due to their skin-like behaviors such as fast response speed,good stability,and non-contact sensing characteristic.However,the traditional capacitive pressure sensor usually adopts a planar structure,and the block-shaped dielectric material has a great elastic resistance,which limits the compressibility of the device and affects the overall performance of the sensor.In order to solve this problem,researchers have conducted a lot of explorations on the design strategies of the device.Currently,there are three main types of strategies used to improve the performance of capacitive pressure sensors:the first is to select materials with low modulus and good dielectric properties as the dielectric layer of the sensor,the second is to pattern the structure of the sensor dielectric layer or electrode,the third is to dope a small amount of conductive material into the dielectric material,so that the dielectric constant of the dielectric layer changes when the dielectric layer is compressed.Since there are many technical processes with complicated and high cost operations such as photolithography and electrospinning in the existing structured solutions,in order to reduce energy consumption and achieve the goals of economy,efficiency,convenience and environmental protection,the preparation process of the sensor still has a lot of exploration space.In this thesis,a simple and low-cost method is used to prepare a capacitive pressure sensor that uses polydimethylsiloxane microbeads to modify the dielectric layer structure.The performance of the device is systematically tested,and its application potential as a wearable device has been verified according to the actual application scenarios.The main contents of this paper are as follows:(1)By dispersing and curing polydimethylsiloxane droplets in a sodium lauryl sulfate solution,polydimethylsiloxane microbeads were obtained,and then a capacitive pressure sensor containing polydimethylsiloxane microbeads in the dielectric layer was prepared.Through characterization and mechanical simulation analysis,the mechanism of the microbead structure improving the sensor performance was summarized.The performance test results of the sensor shows that the microbeads structure effectively improvs the sensitivity of the sensor(the sensitivity from 1 k Pa to 10 k Pa is 0.0479 k Pa^-1,which is 9 times that of the planar structure device),and the sensor also shows greater pressure detection range(1-100 k Pa),lower detection limit(0.2 k Pa),faster response and recovery speed(120 ms and 110 ms),and good performance stability(the response and the baseline does not change significantly under 1000 load cycles at 20 k Pa).The prepared device was used to complete the joint motion detection of the human upper limbs(including fingers,wrists and elbows),the detection of respiratory frequency and the functional verification of the gesture recognition.(2)Different concentrations of silver nanowires were incorporated into Ecoflex as the sensor dielectric material,and the effect of the doping process on the performance of capacitive pressure sensors was studied.The characterization results and theoretical formulas were used to analyze and predicted that doping conductive fillers in dielectric materials would improve the sensitivity of the sensor.Comparing the force-sensitive characteristics of devices with different doping concentrations,the results showed that the sensitivity of the sensor first increases and then decreases with the increase of doping concentration.In this experiment,when the doping concentration of silver nanowires was0.06wt%,the sensitivity of the sensor reached the best effect(the sensitivity from 1 k Pa to 10 k Pa is 0.0968 k Pa^-1,which is twice that of undoped devices).Based on the excellent force-sensitive performance of the sensor,a more in-depth exploration of its application as a wearable device had been carried out.By analyzing the causes of common joint disease"primary metatarsalgia",the sensor was installed on the insole to distinguish the pressure changes exerted by the thumb in different walking positions,so as to provide early warning and correction of walking positions that are at risk of disease.Finally,an array device with 9 sensing units was prepared to complete the shape detection of simple objects.