Mechanisms And Methods Of SRR Metamaterials Based Wireless Sensors For Concrete Structural Health Monitoring

Concrete is widely used in the construction of buildings,bridges,water resources and other public facilities because of its excellent properties such as impact resistance,ease of pouring,and economical price.Concrete materials show excellent durability;however,concrete structures can be damaged due to exposure to harsh conditions related to the environment,loading,erosion,frost,overloading,etc.Therefore,monitoring the deterioration of concrete structures and taking timely protective measures such as repairs and modifications can prolong the service life of the structure and reduce the potential damage.However,the monitoring methods currently used have various problems,such as short life span,complex structure,high cost,low sensitivity and accuracy,etc.To address the bottlenecks and challenges of the current concrete structural health monitoring（SHM）technology,this thesis proposes a wireless sensor for structural health monitoring based on electromagnetic metamaterials,which is sensitive to changes in the dielectric constant of the surrounding environment.This is because electromagnetic metamaterials are very sensitive to changes in the dielectric constant of the surrounding environment,and this electromagnetic property can be used to monitor the samples.The research focuses on the structural design,sensing mechanism and performance optimization mechanism of the microwave electromagnetic metamaterial wireless sensor,which provides an important theoretical basis and technical support for the realization of a new concrete structure health monitoring technology with high sensitivity,high stability as well as high reliability.At the same time,it provides theoretical basis and technical route to broaden the application scope of metamaterials.The main research contents of this thesis are as follows:（1）A swastika-like open resonant ring（SRR）structure is designed and numerically simulated in the X-band（8-12 GHz）using CST microwave studio.The Q value of the sensor is maximized at the resonant frequency f₀=8.724 GHz when the sensor side length l=10.4 mm and split spacing g=1.4 mm,indicating that the sensor has the best sensing performance at this structure size.The equivalent parameter extraction method based on the CST software yields a negative value of the dielectric constant when resonance occurs in this metamaterial sensor,so the resonance type of this metamaterial sensor can be judged as electrical resonance.The average sensitivity of the sensor was calculated to be 304 MHz/RIU and the FOM value was about 3.527.By simulating the effect of the SRR metamaterial sensor deformation on the resonant frequency,it was found that the metamaterial sensor has a good ability to monitor the deformation.Therefore,it is shown that the sensor has good sensing performance.（2）The coaxially fed patch antenna is designed as the feed signal source for the sensor to obtain the wireless sensor,the structure is simulated by high frequency electromagnetic simulation software HFSS,and the size and feed point location of the best performance antenna are obtained using the parameter scanning and structure optimization functions of the software.The calculation shows that the optimized patch antenna S11 return loss bandwidth is increased by 1.32%and the resonant amplitude is reduced to below-30 d B.Finally,by analyzing the antenna electromagnetic characteristic parameters and radiation gain directional diagram,it is concluded that the VSWR of the antenna is less than 2 in the range of 8.57 GHz-8.97 GHz,the antenna gain is greater than 4.5 d Bi inside the studied frequency band,and it has good directional radiation in z-axis,the simulation results show that the antenna is theoretically feasible as the feed signal source of the sensor.（3）Finally,the designed SRR metamaterial sensor and patch antennas were manufactured and tested experimentally.Firstly,the prepared SRR metamaterial sensor device was demonstrated to have the ability to detect the thickness,chloride ion mass fraction and humidity variation of the sample by using cement net slurry slices under different conditions instead of concrete under actual environment as the test sample.The performance of this wireless sensor was tested using a vector network analyzer,and the S₁₁curve of the patch antenna was tested to contain the resonant frequency of the metamaterial sensor in the frequency range below-10 d B,and its VSWR was less than 2 in the range of 8.48 GHz-8.84 GHz,indicating a good impedance match between the feed line and the antenna and high radiation efficiency.Putting the metamaterial sensor piece into the middle of transmitting antenna and receiving antenna,the measured S₂₁ operating frequency of the antenna wireless sensing and the S₂₁ frequency error of the waveguide test sensor is only 0.2%,which indicates that the designed patch antenna can be used as the wireless feed source of the SRR sensor.