Study Of High-performance Antenna Sensor Based On Local-field Enhancement

Infrastructure such as transmission pipelines,dams,railways and bridges,etc.,are subject to extreme weather and frequent stress for a long time,the cracks and defects may occur,and structural damage is prone to occur during their life cycle.Therefore,there is an urgent need for Structural Health Monitoring(SHM)to ensure the safe and reliable operation of infrastructure.The antenna sensor has the advantages of high sensing sensitivity,low manufacturing and maintenance costs,and simple structure,which is conducive to the condition-based maintenance of large-scale infrastructure.At present,antenna sensors are widely used in Ultra High Frequency(UHF)Radio Frequency Identification(RFID),but there is still a trade-off between sensing and communication that has not been resolved.In addition,due to the weak detection field of current common antenna sensors,the resolution of crack detection is difficult to reach the sub-millimeter level,and practical installation issues such as conformity with the metal to be tested are less considered.Based on the topic selection of scientific research projects,this dissertation aims to improve the performance of the antenna sensor and takes the local-field enhancement as the starting point to study the operating principles and design methods of Electromagnetically Induced Transparency-like(EIT-like)and frequency-selective Spoof Surface Plasmon Polaritons(SSPPs).The main research work is as follows:1.Aiming at the trade-off between sensing and communication,a wireless passive sensor based on EIT-like is designed to realize the separation of sensing and communication in the UHF RFID band.The trade-off between sensing and communication is essentially the result of competition between energy used for sensing and communication functions,so a reasonable allocation of limited energy is required.The EIT-like structure is composed of bright and dark modes.The bright mode can be directly coupled with incident electromagnetic waves,with obvious radiation loss and a low-Q factor.The dark mode generates a bound field through the inductive coupling of the bright mode,which has high-Q and local-field enhancement characteristics.The bright mode is used for communication,and the dark mode is used for sensing,realizing energy redistribution,achieving the effect of high gain and high sensitivity.In the design of the structure,choose the ceramics with a high dielectric constant as the substrate to enhance the radiation efficiency.The split-ring resonator(SRR)loaded with the chip is designed as a bright mode,and the U-shaped symmetric resonator is designed as a dark mode.The characteristics of EIT-like effects are verified by electromagnetic analysis,and the peak realized gain in the UHF RFID band is up to 3.77 d Bi.The RFID system test verifies the feasibility of the sensor for detecting cracks,and the sensitivity of detecting crack depth and crack width is-2.73 MHz/mm~2 and-2.75 MHz/mm~2,respectively.2.Aiming at the weak detection field of the antenna sensor and less consideration of actual installation issues such as conformal to the metal to be tested,a smart coating based on frequency-selective SSPPs is designed to realize the detection of sub-millimeter cracks and flexible conformal.High-sensitivity antenna sensors puts a high demand on the confinement ability of the field.SSPPs can confine the near-field energy to the sub-wavelength region,and the toroidal dipole can generate a trapped mode through coupling excitation,and further concentrate the near-field to the area to be measured,with local-field enhancement characteristics.In the design of the structure,the low-profile flexible Rogers Duroid 5880material is selected as the substrate,which is easy to conform to the metal under test.The periodic H-shaped strip and the rectangular ring at the center of the waveguide structure form an SSPPs waveguide,which achieves high transmission efficiency in Ultra Wide Band(UWB).The two back-sited U-shaped rings inside the rectangular ring are used as a toroidal magnetic dipole,and the frequency selective effect is generated by strong coupling with the rectangular ring.The characteristics of SSPPs and trapped waves are verified by electromagnetic analysis.Use the frequency of trapped mode to characterize the crack depth and crack width,and the detection sensitivities are-866.7 MHz/mm~2 and-1050 MHz/mm~2 respectively.