Study On The Linearization Of The Pressure Sensors Made Of CNT/polymer Composite

Composites consisting of carbon nanotubes(CNTs)and polymers have been attracting more and more attention since they possess the advantages of both components.CNTs with high aspect ratio exhibit excellent electrical conductivity.Therefore,CNT/polymer nanocomposites with high electrical conductivity can be fabricated by dispersing little amount of CNTs into insulating polymers.The composites made of CNTs and epoxy resin(EP)are piezoresistive materials,which means the resistances of CNT/EP composites vary with external strain.Such a characteristic can be used to design highly sensitive pressure sensors.However,the resistance-strain relationship of this type of composites is usually nonlinear.On the other hand,sensitivity and linearity are two important indexes used to assess the performance of sensors.Hence,it is meaningful to improve the linearity of CNT/EP composite pressure sensors while maintaining their high sensitivity.In this study,finite element method(FEM)was used to analyze the strain of CNT/EP composite films subjected to out-of-plane pressure.The pressure-strain curves of the films were optimized by choosing proper film shapes.On this basis,CNT/EP composite pressure sensors with linear resistance-strain relationship were designed.First,the FEM models of CNT/EP composite films with different shapes were established using ABAQUS.Numerical simulation show that the CNT/EP films under fixed boundary and lateral pressure are endued with nonlinear dependence relationship between stain and pressure.Second,based on the nonlinear relationship between resistance and strain of the CNT/EP composite films,this study analysed five kinds of CNT/EP composite films with various geometrical shapes including rhomb,rectangle,ellipse,square and circle using FEM.Different pressure-strain curves were obtained and incorporated into the resistance-strain relationship of the CNT/EP composites,so that the resistance-pressure curves of the films were carried out.The result indicate that the film with rhomb shape will result in the best linearity as compared with rectangle,ellipse,square and circle films.Further,prototypes of a specifically designed CNT/EP composite pressure sensor were fabricated and tested.The experimental results are consistent with the simulation ones.It is also found that the CNT/EP composite pressure sensors have good linearity when the pressure is within the range of 20~80kPa.