Research On Tag Antenna For Passive RFID Structural Defect Detection

With the rapid development of sensor technology and wireless communication technology,domestic infrastructure construction and modern intelligent construction are advancing by leaps and bounds.At present,metal has became a major mainstream material for domestic infrastructure construction.Modern intelligent construction put forward higher requirements for the healthy service life cycle of metal components.Metal components serve in a bare environment,which are prone to surface structural defects and corrosive defects under the condition of long-term heavy load stress.Therefore,it is necessary to detect the extent to which the structural defects generated on the metal surface expand during service in order to determine whether a metal component is healthy.The small defect can provide the health inspection department with the change characteristics in the metal component load-bearing capacity as an early warning function.Under the long-term load stress condition,a small defect will gradually expand to form a large-scale defect gradually.Then the large-scale defect may lead to structural bearing capacity failure.Therefore,small defects expansion degreed detection can provide a data reference for the inspection department to determine whether the components are in healthy service.Meanwhile,they can provide an important basis for the normal service life cycle evaluation of infrastructure buildings.In structural health defect detection,frequently-used techniques include ultrasonic defect detection,magnetic particle defect detection,penetration defect detection,pulse eddy current defect detection,and fiber optic defect detection,etc.In order to solve the above problems in the defecting techniques such as equipment volume,cable layout,harsh environment,detection density,and manual inspection limitations.This paper starts with tag antenna that works in the ultra-high frequency band(UHF)in the radio frequency identification(RFID)system,improved a three-dimensional defect detection tag antenna designed by the predecessors.At the same time,this paper researched and designed two anti-metal tag antennas.Namely symmetrical butterfly type defect detection tag antenna and miniaturized hourglass type defect detection tag antenna,that's based on the antennas structure and slotting technology,the metal surface feature changes are introduced into the tag ground plane,two tag antennas for defect detection are designed.First of all,the size of three-dimensional bending microstrip defect detection tag antenna is 22mm*16mm*16mm,simulated resonance frequency of 914.7MHz and return loss of-43.6d B.It can detect the lateral defect depth and width unidirectional expansion of the metal.The two anti-metal tag antennas measurements are 34mm*34mm*1.6mm and 29mm*29mm*1.6mm respectively.Their simulated and measured resonance frequencies are both in the UHF frequency band,and the return loss are lower than-26.1d B,which have good anti-metal properties.Compared with the threedimensional microstrip model tag antenna,the symmetrical butterfly type defect detection tag antenna and the miniaturized hourglass type defect detection tag antenna have higher defect detection accuracy,and they can detect the result of defect expansion caused by the unidirectional expansion or simultaneous expansion of lateral defects on metal structure surface.It satisfies the application scenarios of actual defect expansion,and also has the advantages of size and easy processing.This article provides a method of tag antenna design for wireless passive defect nondestructive testing for SHM,which has significance for wireless sensor networks,fault diagnosis and prediction.