The Study On Crack Propagation Monitoring Method Of Steel Structure Based On Microstrip Antenna Sensor Array

Microstrip antenna sensor has the advantages of simple structure,low cost,ultra-thin and light weight,monitoring the strain and crack passively and wirelessly of the structure to be tested,and thus has great potential in SHM.Although domestic and foreign scholars have done a lot of research on the structure monitoring method of microstrip antenna sensors,there are few studies on the structure monitoring methods based on microstrip antenna sensor array.In this paper,a crack monitoring method based on microstrip antenna sensor array is proposed for large-area monitoring of cracks,and verified by finite element simulation and experiment.The main research contents and results of this paper are as follows:(1)The design method and the impedance matching of microstrip antenna sensor were analyzed according to the "transmission line theory".Based on the "cavity model",the internal field and current distribution of the microstrip antenna sensor were solved.The mutual coupling between the microstrip antenna sensor array elements were discussed based on the mutual impedance method and the scattering parameter method.Finally,the crack monitoring principle of the microstrip antenna sensor array was analyzed.(2)First,the microstrip antenna sensor was designed and the impedance matching was optimized.Then,the effects of the crack on the resonant frequency and current distribution of microstrip antenna sensors were analyzed by simulation.Finally,the effects of different patch sizes on crack monitoring were discussed.The results show that as the crack length increases,the resonant frequency of the sensor decreases parabolically,and the current path and current density of the sensor vary with the crack propagation.The smaller the size of the patch is,the greater the crack monitoring sensitivity and the "effective monitoring range" are.(3)Based on the above analysis of single sensor crack monitoring,the crack monitoring method based on microstrip antenna sensor array was studied.The results show that as the distance of the array elements increases,the coupling between the elements decreases.Although the coupling between the elements does not affect the crack monitoring,it will affect the parameters such as the gain of the sensor array.When propagating under the sensor array,the crack will affect the resonant frequency of the array element in turns.Although the change trend of the resonant frequency of the first element is the same as that of the single sensor,the change trend of the resonant frequency of the subsequent element will gradually become linear.(4)The microstrip antenna sensor crack monitoring test platform was built.The sensor specimens were fabricated by etching process.The effects of cracks on the resonant frequency of the microstrip antenna sensor and sensor array were measured and compared with the simulation results to verify the effectiveness.The research results in this paper verify the feasibility of crack propagation monitoring based on microstrip antenna sensor array,and have important reference value for the practical application of microstrip antenna sensor.