Performance And Application Research Of The Coaxial Cable Fabry-perot Sensor

In the process of long-term service,structures affected by environmental corrosion,material aging and long-term effect of load,will accumulate damage,even occur catastrophic accidents in extreme cases.So it is of great significance to do real-time monitoring and diagnosis of major engineering structures.But strain sensors really applicable to engineering should have high sensitivity and resolution under normal load,as well as enough measurement range in case of overload to monitor changes of structures.Coaxial cable comes into the research field because of its strong material properties,resistance to electromagnetic interference,low cost,large elongation and many other advantages,especially the similar theory of electromagnetic field with the optical fiber which makes it possible to develop coaxial cable sensors.This paper focuses on the electromagnetic theory and deformation sensing mechanism of the coaxial cable Fabry-Perot interferometer(CCFPI)sensor,type selection and performance test of coaxial cables,the simulation of sensor design parameters and improvement of manufacturing method,fabrication and performance test of the smart bar and the smart steel strand,strain monitoring of the reinforced concrete beam using CCFPI sensors.The main research contents are as follows:Firstly,influence factors of characteristic impedance of the coaxial cable are analysed basing on transmission line theory.Methods of making impedance discontinuities are described.The sensing mechanism of CCFPI sensor is studied according to the double wave interference theory.The relationship between resonant frequency shift of the interference spectrum and the cable strain is formulated.Secondly,9 types of coaxial cables are selected to make CCFPI sensors using clamping method,and then the sensing properties are tested to obtain the basic performance indexes of various types of sensors.The design parameters of SF141 type CCFPI sensor are optimized by HFSS software simulation.The validity of the CCFPI sensor in strain measurement is verified experimentally.Thirdly,the SF047 type CCFPI sensor is packaged in the glass fiber reinforced plastic(GFRP)to make GFRP-CCFPI smart bar,and then the mechanical properties and sensing properties are studied experimentally.The intermediate wire of the steel strand is replaced by the smart bar to make CCFPI smart steel strand.The feasibility of using CCFPI smart steel strand to realize structure self-sensing is discussed in experiments.Finally,CCFPI sensors are embedded in a reinforced concrete beam.Working performances of CCFPI sensors are analysed by comparing with the traditional sensors,and the effectiveness of CCFPI sensors in monitoring strain of steel bars and concrete is verified.