The Design And Application Of Porous Flexible Resistive Force Sensor

With the development of the Internet of Things technology,flexible wearable force sensors have been widely used in human-computer interaction,health monitoring,robot control,electronic skin.The diverse application scenarios pose an increasingly urgent demand for high-performance sensors.The porous structure can effectively improve the sensitivity of devices because of its small elastic modulus,high porosity,and large specific surface area,who is an ideal structure for designing flexible sensors.However,the design and research of most flexible resistive force sensors based on porous structures still rely on trial and error methods,which require tedious comparative experiments for device design and optimization.In response to the above issues,the following research work was carried out in this thesis:1.Based on the percolation theory and the microelement equivalent circuit method,the theoretical models applicable to porous flexible resistive strain sensors and porous flexible resistive pressure sensors were established separately.These models reveal the constraint relationship between device sensitivity and material and structural parameters,which can be used to guide the optimization design of devices and predict their sensing performance.2.Through the dip coating process,carbon nanotubes（CNTs）and two-dimensional transition metal carbides（MXene）were deposited on porous polyurethane（PU）sponge as sensitive layer,and a strain/pressure dual mode porous sensor based on this CNTs/MXene@PU sponge was fabricated.The theoretical model was used to predict the relationship between material ratio and device performance,and the theoretical prediction results are consistent with the experimental results.The proposed porous sensor exhibits the ability to detect both strain and pressure stimuli（strain:0-60%;pressure:0-15 k Pa）,high sensitivity,and good stability in 5000 cycles durability testing.The proposed sensor also presents great performance in detecting subtle expressions,sound vibrations,human joint movements.3.Through the vacuum filtration and high-temperature thermal reduction process,the porous structure was introduced into reduced graphite oxide（r GO）and MXene composite films as the sensitive layer,and an ultra-thin and highly sensitive porous pressure sensor based on this composite film was prepared.The theoretical model was used to predict the relationship between material ratio and thermal reduction time and device performance,and the theoretical prediction results were consistent with the experimental results.The proposed sensor presents high sensitivity(0.918 k Pa^-1,0-0.9 k Pa)and fast response/recovery time,and exhibits good performance in static/dynamic testing,5000-cycle durability,and stability tests.The sensor exhibits excellent performance in real-time detection of weak pressure signals（such as human pulses and speech）.At the same time,combining machine learning can achieve speech recognition with a recognition accuracy of 100%.4.The pressure sensing units based on porous composite film were printed on-demand on the hand shaped polyimide substrate by replacing the vacuum suction filtration with the microelectronic inkjet printing,and an integrated electronic skin that can realize shape and texture recognition was fabricated.Benefiting from the porous structure introduced by the high-temperature reduction,each single-unit exhibits high sensitivity(0.934 k Pa^-1,0-0.6 k Pa),wide detection range（0-50 k Pa）,high consistency,and good stability during 5000 cycles durability testing.By combining machine learning and scalable micro pyramid modules,it is possible to achieve recognition accuracy of 100%for 8shapes and 99.7%for 10 textures.In summary,this thesis established theoretical models for porous flexible resistive strain sensors and pressure sensors,respectively.Under the guidance of theoretical models,the constraint relationship between device sensitivity and porous structure and materials was explored,different structures were designed,process parameters were optimized,and three porous flexible resistive force sensors were fabricated and tested,verifying the feasibility of using theoretical models to guide device optimization.Finally,the potential application value of the proposed porous flexible resistive force sensor in health monitoring,human motion detection,and electronic skin was demonstrated.