Research On Cement-based Material Strain Sensor Based On Planar Transmission Line

The building structure will be challenged by various environmental factors such as load and temperature during the construction process and later use,which will cause damage to the surface or inside of the structure.These damages are hidden structural hazards.Failure to discover in time will cause damage to the people and property in the building.In the field of structural health monitoring,there are various methods for monitoring the strain caused by external loads or temperature changes in the structure,such as electrical measurement,piezoelectric method,and ultrasonic method.The application of these traditional methods often has poor anti-interference ability,complicated wiring,and cost.It can not meet the special environment or small size strain monitoring requirements.Strain sensors designed using the principle of antennas have been research hotspots in recent years due to their low cost,high sensitivity,simple fabrication,and small size,providing new ideas for structural health monitoring.This paper designs two strain sensors based on the principle of the plane transmission line,and proposes two kinds of strain sensors according to the different structural forms of the plane transmission line,and applies them to the strain measurement of the surface of the cement mortar test block.It is verified by theoretical analysis,simulation and experimental measurement.Its strain monitoring performance.The main research contents are as follows:(1)Deriving the relationship between reflection coefficient(S11)phase parameters and strain of transmission line sensor according to the planar transmission line theory.Studying the difference between the two-port open-circuit microstrip transmission line and the one-port microstrip transmission line applied to the strain sensor.Analyzing the influence of the structure of the zigzag microstrip transmission line on the planar transmission line strain sensor.Moreover,a new "composite microstrip-coplanar waveguide transmission line" structure is proposed.The transmission characteristics are studied theoretically,applied to the strain sensor of cement mortar material and the relationship between S11 phase and strain was explored.Analyzing the effect on miniaturizing the strain sensor,reducing the edge effect and coupling effect of the plane transmission line.Furthermore,the feasibility of applying the two structures to the surface strain sensing of cement mortar was analyzed.(2)Using HFSS simulation software to test the theory of planar transmission line strain sensors.The strain sensor model of the zigzag line and composite microstrip-coplanar waveguide microstrip transmission line are established.The strain is simulated to the surface of the cement mortar test block according to the designed strain and Poisson effect,and the test was measured.The complex dielectric constant of cement mortar is input into the software material library in order to optimize the simulation model.Then the response of sensor S11 phase parameters with strain were investigated.(3)Producing strain sensor and cement mortar test block,building test platform,measuring the actual working effect of strain sensor,calculating the strain transfer ratio of the strain sensor attached to the cement mortar and testing the change of S11 phase of the two sensors under strains.The theoretical results,simulation results and measurement results were compared to obtain the main conclusions of the application of the planar transmission line strain sensor in the field of concrete structure SHM.Different application conclusions of two kinds of planar transmission-line strain sensors were obtained.The above research content proves the feasibility of the planar transmission-line strain sensor used for the SHM of cement mortar structures from theory,simulation and experiment,and quantitatively explains the sensing characteristics of the two types of strain sensors,and analyzes the application suitable for two kinds of strain sensors.The results give new ideas and new targets for the field of strain sensors.