Research On Sensitivity Enhancement And Applications Of Flexible Pressure Devices Based On Structured Micro-Cavity

Flexible capacitive pressure sensors have been widely used in many fields,such as robot tactile perception,aircraft smart skins etc.,due to the advantages of softness,light weight,simple structure,and large-area compatibility.High performances of pressure sensors are desired for these applications,e.g.positive and negative pressure measuring,high sensitivities,and system-level multi-functional integration on curved surfaces.For the above challenges,this dissertation focuses on the structural design of microcavities,expounds their merits in the performance improvement of pressure sensors,provides detailed mechanical analyses and modeling,and finally demonstrates system-level applications via electronic skin.The main research contents and innovations are as follows:(1)An ultra-thin flexible sensor array for positive and negative pressure measurement is developed by the structural design of air cavities and microchannels.The electromechanical model of capacitance changes relative to pressures of the sensor is established when the sensing film of the pressure sensor with clamped edges is under large deformation.The effects of the structural and material parameters on sensing sensitivities and capacitance changes are discussed,which provide the guidance for the sensor design and the development of acquisition circuits.When attached to curved surfaces,the effects of surface curvature on sensing performances are further analyzed.Benefitting from the design of airflow microchannels,the in-situ calibration method is proposed to completely eliminate the errors caused by the surface curvature.(2)The elastic support design based on microscale hollow structures is proposed for sensitivity improving of flexible pressure senosrs.The solvent-evaporation-assisted casting method is innovatively proposed to fabricate hollow microstructures(HMs).Two main factors of solution volumes and evaporation-driven flow are studied to regulate the microstructure morphologies from the solid to the hollow.The geometric expression of the inner profiles of the hollow micro pyramid is determined completely.The relationships between the compressive stiffness of HMs and their structural/material parameters are given,which provide a guidance for the performance design of pressure sensors and point out the importance of HMs and plasticizing modification of films in sensitivity enhancement.The test results indicate that the pressure sensor based on the HM shows nearly 10 times improving in sensitivity than the solid microstructure-based pressure sensor under the same structural dimensions and material elastic modulus.(3)The integration applications of flexible electronic skin with a full coverage on curved surfaces based on pressure sensors are explored from two levels of multi-array units and multifunctional sensing.The application of surface airflow sensing around a typical airfoil is presented for negative pressure measuring.A series of wind tunnel tests with varying angles of attack(Ao A)and wind velocities,are conducted to verify the advantages of high sensitivity(recognizing a small pressure change caused by the changes of the Ao A of 1° or 0.5 m/s wind velocity),and high accuracy(only about 1% difference from the results of the commercial pressure tap).Furthermore,the airflow separation phenomenon of the airfoil is revealed,and the stall Ao A is determined.The application of robot tactile perception is presented for positive pressure measurement.A 3D-shaped electronic skin adapted to the non-developable and time-dynamic surface of the bionic hand is developed.The closed-loop feedback system from devices sensing to robot actions is established,and the multi-sensory perception of based on vision and tactile is developed to achieve multi-functional tactile feedbacks and fully automatic pulse-diagnosis by a robot.