Research On Flexible Mechanical Sensor Based On Laser-induced Graphene

Graphene,is a flat film with a hexagonal honeycomb structure composed of carbon atoms and sp2 hybrid orbitals.It is a two-dimensional material with the thickness of only one carbon atom,and its optical,electrical,and physical and chemical properties make the material has a very broad application prospect.Laser-induced graphene（LIG）is a simple,environmentally friendly and economical way to produce graphene in large quantities under natural environments.In this paper,LIG materials are prepared using this technology,and conductive solvents are obtained by mixing LIG with Ag NWs and PEDOT:PSS respectively,finally a series of flexible mechanical sensors based on LIG composite materials have been successfully prepared,such as Bondi flexible pressure sensor based on LIG/Ag NWs,flexible strain sensor based on LIG/PEDOT:PSS conductive ink,flexible RC circuit pressure-frequency sensor based on LIG.We have studied the influence of different factors on the performance of flexible devices and the details are as follows:The first chapter introduces the formation mechanism of laser-induced graphene and the preparation method of composite materials in detail.Summarized the research status and development prospects of flexible sensors based on laser-induced graphene and described the preparation methods of LIG composites materials.In Chapter 2,we directly selected the band-aid center with natural cotton fiber as the material of the sensor,and obtained the conductive path by immersing in Ag NWs,prepared the flexible Bondi pressure sensor based on LIG/Ag NWs composites material which realized the monitoring of the pressure signal.The sensing principle of the flexible Bondi pressure sensor based on LIG/Ag NWs composite material is described,the influence of different factors on the performance is deeply studied.The range of pressure monitoring threshold of the sensor is 0-180N,the time relaxation is about 300ms,and the pressure is applied and removed continuously for 100 times.Performance can remain stable after compression.The dynamic tracking test shows that the sensor can be used to monitor and recognize different dynamic postures such as bending fingers and high-five actions.In Chapter 3,in order to further increase the linear range of the flexible strain sensor and increase its strain value,we prepared a PDMS film using a homogenizer,and prepared a PEDOT:PSS/LIG material based on PEDOT:PSS/LIG by doping laser-induced graphene by blending Conductive ink,and inject the conductive ink into the hollow tube shaped by PDMS to make a flexible strain sensor based on LIG/PEDOT:PSS material.The sensing principle of the flexible strain sensor based on LIG/PEDOT:PSS material is described,and the influence of PEDOT:PSS doping volume and LIG concentration on the electrical properties and deformation of the sensor is studied.In addition,studies have found that the elastic strain of the sensor can be increased to 300%under this technical condition,and the highest sensitivity in the range of 0-100KPa can reach0.94568k Pa^-1.It is sensitive to the bending angle of 0-180°,and it is fully stretched after 200 times.Its sensing performance can still remain stable.In addition,continue to lengthen the length of the PDMS hollow tube and wind it with a starting point at one end to obtain a new type of disk-type flexible pressure sensor,and test its performance.In Chapter 4 simulates the photothermal process of laser engraving through COMSOL three-dimensional modeling,analyzes the heat distribution in the laser engraving process,and combines experiments to study the influence of laser power and engraving time on the electrical properties of LIG.With the continuous deepening of research on flexible mechanics sensors,we link mechanics with functional circuits and develop flexible mechanics-frequency sensors that display pressure characteristics with frequency.By engraving the LIG pattern into finger-crossing microcapacitors,combined with a first-order RC circuit,the mutual conversion between pressure and cut-off frequency is realized,and a flexible RC pressure-frequency sensor based on LIG material is fabricated.The sensing principle of the pressure-frequency sensor of the flexible RC circuit is described.The time domain and frequency domain characteristics,transient response characteristics,and filtering characteristics of the RC circuit itself are analyzed.The transformation relationship between the force and the cut-off frequency under different pressures is tested.Stability under different bending angles and different temperature changes.The instantaneous response of the sensor under 500k Hz input signal is 0.5us,and the change trend of its amplitude-frequency characteristic curve and phase-frequency characteristic curve is in good agreement with the theoretical calculation value.The environmental adaptability is good.Its performance can be kept stable under the test conditions of 5000 cycles of bending（0-180°）and different ambient temperature（0-100°C）,and it has good environmental adaptability.