Dynamic/Static Mechanics Information Detection Of Piezoelectric/Piezoresistive Dual-mode Flexible Pressure Sensor

With the development of electronic devices towards intelligent wearability,flexible electronic devices have attracted wide attention.Among them,flexible pressure sensor has become a research hotspot in recent years because of its broad application prospects in intelligent medical,health monitoring,human-computer interaction,intelligent robots and other fields.Many flexible pressure sensors with superior performance have been successfully developed by researchers at home and abroad based on different sensing materials and sensing principles through reasonable structure design.However,piezoelectric sensors still have the disadvantage of sensing static force and deformation,and piezoresistive sensors still have the disadvantage of long response time.In this thesis,the sensing mechanism and characteristics of piezoelectric sensor and piezoresistive sensor are analyzed and experimentally studied in detail.Finally,through reasonable material selection and structural design,a new flexible dual-mode pressure sensor which can simultaneously detect dynamic and static mechanical information is developed.The main research contents include the following four aspects:?1?Firstly,the relationship between the output voltage and the pressure of the planar piezoelectric film sensor is established by combining the piezoelectric equation of the piezoelectric film with the theory of electrical measurement.The influence of internal resistance,pressure and frequency of voltmeter on the test voltage of piezoelectric sensor is discussed.The theoretical basis of measuring mechanical signal and loading rate by piezoelectric sensor is established.Then the above theory is extended to piezoelectric thin film sensors with pyramid microstructures.The influence of pyramid microstructures on the sensing performance is analyzed and compared with the finite element simulation results.The results show that the introduction of microstructures can effectively improve the accuracy of piezoelectric sensors.?2?h-BTO/P?VDF-TrFE?composite piezoelectric thin films with high piezoelectric coefficients were prepared by adjusting the content of BaTiO₃?h-BTO?modified by hydrogen peroxide in the composites.On this basis,planar thin film structures and flexible piezoelectric sensors with pyramidal microstructures were fabricated,and the influence of pyramidal microstructures on the sensing performance was studied.Through the study of piezoelectric sensor's performance of pressure sensing and bending strain sensing,it is proved that piezoelectric sensor can effectively realize the theoretical prediction of loading force and loading rate at high frequency,and the insufficiency of its measurement under quasi-static loading is also analyzed.?3?Through the reasonable design of piezoresistive sensor structure and the study of sensing mechanism,a flexible pressure sensor with double pyramid microstructures was prepared based on graphene?rGO?material.The pressure sensing and bending strain sensing properties of piezoresistive pressure sensor are also studied.The experimental results show that piezoresistive sensors can effectively monitor quasi-static force or deformation,which is expected to make up for the shortcomings of piezoelectric sensors.?4?Design,fabrication,working principle and application of piezoelectric and piezoresistive dual-mode sensor:piezoelectric/piezoresistive dual-mode sensor was successfully fabricated by combining h-BTO/P?VDF-TrFE?piezoelectric sensor with rGO piezoresistive sensor.The two-mode sensor adopts layered structure design,which avoids the interference between piezoresistive signal and piezoelectric signal.In addition,compared with single mode sensor,dual mode pressure sensor has larger pressure detection range and wider frequency detection range.In a certain range,dual-mode sensors can detect pressure information from static to dynamic,from low frequency to high frequency.Dual-mode sensors can detect the magnitude,velocity and direction of pressure or deformation in complex loading process.Finally,the dual-mode sensor is applied to the measurement of bending deformation of human joints and the bending of manipulators,which solves the disadvantage of piezoresistive sensor that can not distinguish bending direction and bending rate,realizes the accurate measurement of bending angle,bending direction and bending rate,and widens the application scope of flexible pressure sensor.In this thesis,the working principle and measurement method of piezoelectric/piezoresistive dual-mode sensor for simultaneously detecting the magnitude,speed and direction of loading force or deformation are given through theoretical,finite element analysis and experimental research,and applied to human motion detection and manipulator motion detection.It provides theoretical and experimental guidance for the future flexible pressure sensor in measuring force or deformation under complex loading process and its application.