Study On Mechanism And Performance Of Flexible Touch Sensor Based On Carbon Fiber Beams

Electronic skins(E-skins)require to integrate multiple-sensing functions to sense stimuli from the outside environment(such as pressure,temperature,and humidity),and to distinguish the signals from the different stimuli.Because the flexible structure of Eskins can fit well on the various curved surfaces,so that they have broad application prospects in the fields of environmental monitoring,health monitoring and bionic robots.In this master's dissertation,we first review the progresses in the E-skins field which were performed by the relevant researchers,and then discuss the mechanisms and performances of the flexible pressure sensor and temperature sensor in detail.And then,the dominating scientific questions have been concluded in the aspect of integrations of the flexible structures and the sensing functions.This dissertation starts with these scientific questions,we propose a feasibility to use the carbon fiber beams as flexible sensing materials,and carry out the relevant works which include the establishment of sensing mechanism models and their formula derivations,the fabrication and characterization of pressure sensors and temperature sensors,and an effective way to detect and distinguish the multi-signal in their integrated sensors.Main work and achievements of the dissertation can be summarized as follows.1.In order to solve the problem about the integration of flexible structures,a conductive carbon fiber beam with a self-supporting structure was proposed as the sensing material,and this way can solve effectively the dependence of the flexible sensor on the flexible substrate and flexible electrodes.Secondly,based on quantum tunneling effect and impurity scattering mechanism,we designed a sensing model to use only one single carbon fiber beam(CFB)to simultaneously detect pressure and temperature changes from the outside environment,and the signals from pressure and temperature stimuli can be distinguished through its transverse piezoresistance and longitudinal thermal resistance respectively.Moreover,we inferred the mathematical relationship between two kinds of resistance and its corresponding stimuli respectively.2.A flexible pressure sensor and a temperature sensor were fabricated by using the carbon fiber beams,and their sensing performances were characterized in situ to confirm the feasibility of the sensing mechanism and the mathematical relationship.And then,these results were further applied in the calibration algorithm of these sensor.3.In the study of the temperature drift problem in the pressure sensor,we found that the pressure signals can eliminate the ambient temperature drift by using the resistance change rate to characterize the external force size.This method was further applied to the cooperative work of temperature sensor and pressure sensor.At last,integrating the temperature sensor and pressure sensor above to form the flexible touch sensor,which can detect and distinguish the magnitude of the force from being touched and the temperature of the touched object in real timeThe main contribution of this thesis is that only one carbon fiber beam which has a self-supporting structure is used as the "building block unit",and various sensing functions can be achieved by selecting different carbon fiber structures,and these sensing signals can be effectively distinguished through its transverse piezoresistance and longitudinal thermal resistance respectively.This work is expected to break the inertial thinking that a sensing material is only specialized in a specific sensing function in the field of sensors.