Flexible Pressure Sensor Based On Porous Composite Polyurethane Dielectric Layer

As an important part of the sensing field,flexible electronic technology is developing wearable,intelligent and portable.Capacitive flexible pressure sensors are widely concerned because they are easier to integrate into flexible equipment.The main challenge of flexible sensors is the sensitivity.Improving the dielectric properties of the dielectric layer is the most important to the fabrication of capacitive flexible sensors with high sensitivity.The micro-structure can increase the change of effective permittivity in the compression process of the sensor,and the composite active material can improve the permittivity of the dielectric layer.Therefore,the microstructure treatment of the dielectric layer and composite active materials become the research hotspot of flexible sensing.Firstly,the research background and status of flexible pressure sensor were introduced,and the purpose and significance of this paper were described.The basic principle of micro-structure treatment and composite active material preparation of dielectric layer to enhance the sensitivity of capacitive flexible sensor was introduced.Polyurethane(PU)porous sponge was selected as the flexible substrate,and titanium dioxide(TiO₂)and multi-walled carbon nanotubes(MWCNT)were used as the active materials to prepare the flexible sensor.Secondly,the composite porous dielectric layer was prepared with combining PU porous sponge and TiO₂through 3-aminopropyltriethoxysilane(APTES)by dip-coating method to improve the dielectric properties of the dielectric layer.And the results showed that it can improve the sensitivity of the sensor.When the concentration of TiO₂aqueous solution was 1 mg/m L,the sensitivity of the sensor reached 0.93 k Pa^-1.The dielectric constant measurement results showed that the composite of high dielectric material TiO₂and PU can improve the dielectric properties of the composite,so they can enhance the sensing sensitivity.Thirdly,based on the percolation principle,MWCNT and PU composite dielectric layers with different contents were prepared by dip coating method.The sensitivity of the sensor was tested and the results showed that the sensitivity of the sensor reached 1.07k Pa^-1when the mass ratio of MWCNT to PU is 1:5.The influence of percolation threshold on the dielectric properties of the composite was discussed.Finally,the TiO₂/MWCNT@PU dielectric layers with different content ratio were prepared according to the composite doping mode of dielectric material/conductive material.When the ratio of TiO₂:MWCNT is 5:2,the sensor sensitivity reached 1.8 k Pa^-1,which was better than the sensor of TiO₂@PU and MWCNT@PU.It showed that the synergistic effect of dielectric/conductive composite doping can greatly improve the overall performance of the sensor.The above three sensors had low detection limits(1.4 Pa,1.25 Pa,0.75 Pa)and repeatability.And they have been successfully applied to the actual operation measurement of object grasping,analog code information transmission,human joint bending and so on.