Theoretical Analysis, Electrical Properties And Application Research Of Three-dimensional Poisson Senso

Flexible electronic sensor is a signal conversion device which can be freely stretched and deformed.Compared with traditional silicon-based sensors,sensors made by MEMS technology,field effect tubes prepared by CMOS technology,etc.,as a wearable electronic device,it can be fitted and compatible with surfaces with complex structures,and can even be implanted into the human body for postoperative rehabilitation monitoring,and automatically decomposed in the body at a later stage.With the rapid development of social civilization,flexible sensors in human health detection,action recognition,industrial production,smart home,soft robots and other fields of increasing demand,and gradually tend to be integrated,miniaturization,such as the rapid rise of OLED.The flexible electronic strain sensor is a kind of detection device to detect the behavior of mechanical deformation of the sensor.Its function is mainly to convert the mechanical signals formed directly or indirectly into electrical signals,which can be used for tensile stress,shear stress,pressure detection,etc.Sensitivity,durability,robustness,signal-to-noise ratio and hysteresis are all important evaluation indexes of flexible sensors.With the in-depth cross-development of science and technology in various fields,sensitivity plays an increasingly prominent role in various indexes of flexible sensors.Flexible sensors with low sensitivity can no longer meet the needs of the development of The Times.In reality,most materials have the Poisson effect,that is,when the material is stretched axially,it will cause radial compression.The problem brought by this phenomenon to the field of flexible sensing is that,when the positive strain occurs in one direction of the flexible sensor,the conductive material will be squeezed perpendicular to this direction,which makes the conductive material more closely contact with each other,resulting in the decrease of the total resistance,which to some extent cancels out the resistance change caused by the separation of the conductive material along the positive strain direction.Thus limiting the improvement of sensor sensitivity.This phenomenon is noticed for the first time in this paper,and it is proposed that the residual resistivityρ_ris a function of the resistivityρ_rxrelated to radial defect and the resistivityρ_ryrelated to axial defect.Under the guidance of this theory,further mathematical derivation and electrical simulation are carried out.Poisson effect is an important factor limiting the sensitivity improvement of flexible strain sensors,and it is also an important challenge for sensors to solve the sensitivity bottleneck in a certain system.In addition,the concept and definition of independent response dimension of flexible sensors are proposed for the first time.Under this definition,most flexible sensors are one-dimensional/two-dimensional flexible sensors.The flexible sensor designed in this paper not only solves the limitation of Poisson effect on sensing sensitivity,but also becomes a three-dimensional flexible sensor because of the folding crack/Poisson crack bidirectional crack.It has three independent response dimensions and has good and different response ability in three directions,so it is suitable for application in the field of multidimensional detection.To overcome the sensitivity bottleneck caused by Poisson effect in the field of flexible sensing.Based on theoretical calculation,circuit simulation,physical and chemical properties of sensitive materials and finite element simulation of special structures,a novel three-dimensional flexible electronic strain sensor with a Poisson crack guided by a spine array structure is proposed in this paper,which is called a Poisson sensor.Due to the existence of a Poisson crack array,the sensor can effectively avoid the radial extrusion of conductive layer caused by the Poisson effect during axial stretching,and the gradual extrusion of conductive material caused by the Poisson effect is converted into the crack array tends to close,so as to improve the sensing sensitivity within a certain stretch range.Poisson sensors are prepared by UV mask photolithography,micro and nano embossing,pre-stretch spraying and other processes.The sensitivity of each stretch interval can also be adjusted by adjusting the pre-stretch value and the base structure to adapt to different application scenarios.Poisson sensors are also suitable for all kinds of three-dimensional microstrain sensing and integrated circuit design.Through the electron microscopic morphology of Poisson sensor and ingenious experimental design,the complex sensing mechanism of Poisson sensor is explained,which helps to prove the feasibility of the proposed method.Compared with the general uniformly coated planar sensor,its sensitivity is indeed improved,and it meets the basic requirements of some sensors such as stable performance.In addition,the Poisson sensor can be controlled by photolithography of different structural substrates and changing the pretension value.In the end,the paper also shows the applications of Poisson sensor,such as human movement monitoring,physical quantity detection of substances,real-time signal monitoring and wireless transmission.The main contents of this paper include:（1）Put forward the Wyeth current bridge electrical model corresponding to the Poisson sensor,carried out in-depth theoretical calculation of the circuit,searched for the mechanism of action between various parts of the circuit,and found out the idea of solving the Poisson effect problem.After classification and discussion,it was found that when the radial resistance met certain conditions,by reducing its decline rate during axial tensile,The limitation of axial resistance change caused by radial Poisson effect squeezing of flexible sensors can be reduced.Based on certain conditions,Proteus circuit simulation was used to further confirm the feasibility of reducing the radial resistance decline rate to improve the sensitivity.（2）By analyzing the physicochemical properties,electronic properties and mechanical properties of the conductive material MXene/CNTs and the coupling agent APTES,the interaction between them and the internal mechanism of sensing were revealed.It can be seen that MXene after etching with MAX phase material has oxygen-containing group sealing and good conductivity at the same time.CNTs had a Young’s modulus of up to 1TPa as a reinforcing material for MXene.The mixed conductive layer of the two will form a rich topology conductive network,reduce the initial resistance and broaden the detection range.The bridge between the conductive layer and the PDMS substrate is bonded by the coupling agent APTES,which can realize self-catalytic hydrolysis of amino group,so as to avoid the introduction of impurities.The tensile strength of MXene/MWCNTs thin films was tested,and the finite element mechanical simulation of the spinal array was carried out by COMSOL to obtain the stress distribution of the spinal array with different structures.It is found that the stress concentration generated by the sensor is greater than the tensile strength of MXene/MWXNTs films（1.92MPa）under certain conditions,which is sufficient to form a regular Poisson crack array after the sensor conductive layer Poisson rebound.（3）According to the conclusion of finite element analysis,the groove array SU-8template was prepared by UV mask photolithography,and the spine array substrate was fabricated by PDMS spin coating.The conductive material was sprayed by Lay-by-Lay under a certain axial pretension.The PDMS were released after solvent evaporation,and Poisson sensors with regular Poisson cracks were obtained.（4）The radial resistance test of the Poisson sensor is designed and it is found that the change rate of the radial resistance of the Poisson sensor is greater than that of the general uniformly coated planar sensor.Combined with scanning electron microscopy surface morphology,it can be seen that the fold crack of the Poisson sensor has begun to expand when the axial strain reaches the₂¹of pre-drawing value.Combined with the above conclusions,it can be proved through mathematical derivation that the Poisson sensor prepared in this paper can indeed reduce the decline rate of radial resistanceρ_Gduring axial tension.By comparing the axial and radial sensing performance of the Poisson sensor and the general uniformly coated plane sensor,it is found that the sensitivity of the Poisson sensor is greater in both directions than that of the general uniformly coated plane sensor.Finally,the principle of regulating Poisson sensor is proposed to meet different application requirements.（5）The basic electrical performance of the prepared Poisson sensor is compared.It is found that the sensor has a millisecond response time（360ms）and recovery time（340ms）,which can quickly recognize the detected signal.At the same time,the cyclic stability of the Poisson sensor in the x/y direction was tested,and it can be seen that it still maintains stable waveform after 1000 cycles of stretching release.At the same time,the detection limit of Poisson sensor is tested,and it is found that it can sense the stress below 10Pa,and the lower detection limit is conducive to the identification of micro-strain.（6）The Poisson sensor is applied to human pulse monitoring to output clear pulse waveform,including shock wave（P）,tidal wave（T）and relaxation wave（D）.When applied to droplet quality detection,different peaks and equilibrium values of droplet with different qualities are output,and there is certain positive correlation.The 555 oscillator and single-chip microcomputer detection system are introduced to monitor the tension perceived by the Poisson sensor.The value is output on the LCD screen and sent to the mobile phone in real time through the Bluetooth module.The potentiometer on the multipurpose board can also be fine-tuned for calibration.