3D Printing And Performance Of Flexible Pressure Sensor Based On Gallium-based Liquid Metal

The flexibility of electronic devices has become the development direction of future electronic devices.Flexible force-sensitive sensors are a typical type of flexible electronic devices,which have a wide range of applications in human motion detection.However,due to the limitations of materials and production processes,the circuits and functional areas of flexible force-sensitive sensors have the problems of difficult design,high cost,and complicated processes in the process of flexibility.In this paper,the preparation of flexible wires and flexible functional materials in flexible force-sensitive devices was studied.Then,the force-sensitive devices were manufactured rapidly by 3D printing by the as-prepared flexible wires and flexible functional materials.Finally,the performance of the force-sensitive device was tested and verified.The GaInSn alloy as the conductor of flexible wires was prepared by atmosphere-protected smelting.The melting point,electrical conductivity,density,and matrix adhesion of the Ga InSn alloy were tested,and the flexible wire was prepared by using 3D printed flexible microchannels injected Ga InSn alloy.The resistance stability and fatigue resistance of flexible conductors with different sizes under deformation and stress were studied.Finally,print an analog circuit to observe the working conditions of the flexible conductor under deformed conditions.As a result,it was found that the melting point of GaInSn alloy is 9°C,the electrical conductivity is 0.303×107 S·cm^-1,and the density is 6.124 g·cm^-3.GaInSn alloy can rely on its oxide film to adhere to the TPU substrate and maintain the pathway.In addition,flexible conductors based on GaIn Sn alloys can be used to produce complex circuits through 3D printing.Among them,flexible wires with a size of 0.5×0.5 mm² have better resistance to stress and deformation.Finally,it is verified that the flexible circuit with LEDs produced by 3D printing can work stably under actual bending,twisting and kneading.For the preparation of flexible conductive 3D printing materials,multi-walled carbon nanotubes（MWNTs）,mesophase carbon microspheres（MCMB）and thermoplastic polyurethane（TPU）were used as raw materials.The effects of the amount of conductive filler and the size of MCMB on the electrical and mechanical properties of the material were studied.The results show that the electrical conductivity of the material increase with the increasing the MWNTs and MCMB,while the tensile strength and elongation reduce.The amount of MWNTs added has a greater impact on the conductivity and mechanical properties of the material.The conductivity of the material prepared by adding 5μm MCMB is higher at the condition of the same amount of MWNTs.With low MWNTs addition,the mechanical properties of the material are weaken more serious with 15μm MCMB.In order to explore the functionality of the material,the I-U characteristic lines of the flexible conductive 3D printing material added with 5μm MCMB was tested by giving different tensile and compressive forces,and the cyclic fatigue test was performed under dynamic pressure.The results show that the material is sensitive to both tension and pressure.As the tension increases,the material resistance increases,and as the pressure increases,the material resistance decreases,but the material is more sensitive to pressure.Under dynamic cyclic pressure,the resistance change rate of the material can be changed periodically within a stable range,showing a good pressure-sensitive resistance effect and repeatability.And increasing the content of conductive filler appropriately can increase the material's sensitivity to force obviously.Based on the electrical conductivity and mechanical properties analysis in the chapter 2,the flexible conductive composite containing 9%MWNTs and 6%5μm MCMB can be used for subsequent manufacture of flexible pressure sensors.In order to realize the rapid manufacturing of flexible pressure sensors,the GaInSn alloy flexible wires and flexible conductive 3D printing materials were combines to quickly design and manufacture flexible pressure sensors through 3D printing.And the response of actual pressure of the sensor was discussed.It was found that the flexible pressure sensor manufactured by 3D printing has a sensitive response to the actual pressure and can feedback different signal changes according to the pressure.By connecting the flexible pressure sensor and the Arduino microcontroller,the sensing signal can be output to the computer,and the on and off of LED can be controlled to realize the visualization of the sensing signal.