Flexible Temperature Sensors Based On Carbon Based Composites

In recent years,with people’s attention to intelligent life and the development of wearable technology,wearable sensors have gradually become the research hotspot of scientific researchers,and temperature is one of the important parameters reflecting human health,so in health detection,the research of flexible temperature sensors is particularly important.Flexible temperature sensor is different from rigid temperature sensor,it has the characteristics of good flexibility,small volume,light weight.In particular,it can be naturally attached to complex curved surface without affecting the performance of the product,and it is expected to become an important member of wearable electronic products.According to the principle of temperature measurement,flexible temperature sensors can be divided into thermocouple and thermal resistance.The two hot electrodes of the flexible thermocouple are made of two different materials.The materials for preparing the electrodes need to have high conductivity and high flexibility,and the relationship between the thermoelectric potential generated during temperature measurement and the temperature difference is linear or approximately linear.The flexible thermal resistance temperature sensor only needs one kind of temperature-sensitive material to prepare the temperature-sensitive element,and the temperature-sensitive material has a large rate of change in the temperature-sensitive resistance,and the resistance temperature-sensitive characteristic has a linear relationship.In addition,both types of flexible temperature sensors need to have excellent stability,flexibility and mechanical properties,and the manufacturing process is simple and convenient.Based on the above requirements for materials of flexible temperature sensors,this paper studies low-dimensional nanomaterials with high flexibility,high conductivity,and good linearization of thermistors,mainly discussing two types of flexible temperature sensors,studies the stability and repeatability of the temperature sensor and its application in the wearable field.The specific research work is as follows:Bismuth telluride（Bi₂Te₃）nanoflakes were synthesized by hydrothermal method.A single layer of mxene nanoflakes was successfully prepared by etching a element in MAX phase with hydrofluoric acid（HF）.Two kinds of nanocomposites were compounded with commercial one-dimensional carbon nanotubes（CNTs）,and two kinds of flexible composite films were obtained by vacuum filtration.Bi₂Te₃/CNTs composite films were sintered in N₂ atmosphere to obtain high-performance thermoelectric materials.Two kinds of flexible composite films are used as the two electrodes of the sensor and combined with the flexible substrate to design and prepare the flexible thermocouple type temperature sensor.The stability and repeatability of the temperature sensor at room temperature are studied.It is found that the temperature sensor has a good linear relationship in the horizontal test.The fitting value obtained by least squares fitting was0.99994.In the bending state,the linear fit is 0.99997,the temperature sensor still has a good linear relationship,and after repeated heating and cooling experiments,the temperature difference and output potential have the same linear relationship,which shows that the flexible thermocouple temperature sensor has good stability and repeatability.The chemically reduced graphene is compounded with commercially available carbon nanotubes to obtain a flexible temperature-sensitive material,and a flexible heat-sensitive temperature sensor device is prepared.The specific research contents are as follows:a graphene oxide（GO）-carbon nanotube flexible composite thin film with a three-dimensional network structure was prepared by vacuum suction filtration,and a flexible thermosensitive material was obtained by reduction with hydroiodic acid（HI）.Self-designed and assembled a flexible thermal resistance temperature sensor with a thermosensitive film,the resistance temperature characteristics of the flexible thermal temperature sensor were studied,and the linear fitting degree is 0.993 by least squares fitting,and showed linear relationship,sensitivity TCR=-0.32%;after repeated heating and cooling cycle tests,it was found that the sensor has the same resistance change under the same temperature difference,which shows that the prepared flexible thermal resistance type temperature sensor has Good stability and repeatability.Based on the good resistance temperature characteristics,stability and repeatability of the thermal resistance type temperature sensor,it is integrated into the cotton fabric together with the conductive yarn prepared by the conjugate spinning method.The newly developed flexible STM32Ltype polyimide circuit board is used to collect the temperature-sensitive response signal of the integrated fabric,which shows the temperature sensing fabric’s function of monitoring temperature.