| Wave-transparent materials are a very important and versatile media material and are used in a variety of applications,such as shaft joint filling media,base stations,microwave heating containers and many more.Structures made from wave-transparent materials are inevitably flawed in use,posing a significant threat to the safety of the structure and interfering with the performance of the equipment.Compared to low frequency microwaves,V-band has better detection capability,smaller device size and is easily accessible to transceivers due to the maturity of civil radar in this frequency band.Defective 2D detection techniques are important for the optimal design of wavetransparent materials,control of the preparation process,quality control of finished products and characterisation of material properties,and research into detection techniques for the V-band also provides the basis for the development of portable detection systems.The purpose of this paper is to investigate the interaction mechanism between defects and microwaves,including the effect of shaped materials on defect detection and the effect of defect depth and aperture on the detection of V-band.The specific research content is:1.Theoretically,this paper uses the antenna reflection method to test the sample and characterise its internal defects according to the reflectance distribution obtained by scanning the sample with the antenna.For the detection of defects in shaped materials,the electromagnetic propagation theory is used to model and analyse wavetransparent materials with three different surfaces:flat,abrupt thickness and gradual thickness,respectively.The accuracy of the surface reflectance calculation is verified by model approximation and finally using simulation software.2.In terms of system design,this paper designs and builds a two-dimensional scanning test system,including test antennas and various microwave transition structures,and designs the corresponding fixtures for the fixed connections between the various parts;to realise the automatic control of the system,a motor control module is added and software is written for adjusting the motor position,vector 3.In the test method,the theoretical value of the reflectivity distribution when the antenna beam scans the defect-free sample is approximated by the analysis of the interaction process between the three shaped samples and the microwave,using the local plane wave model.The results can be used to attenuate the influence of the sample surface as well as the edges,thus enabling accurate defect localisation.In addition,it was found that the scanning results of samples with gradual thickness changes were affected by bright and dark streaks,so a multi-frequency point test method was proposed to locate defects by image comparison.Finally,this paper uses the system to detect flat materials with defects of different aperture sizes and depths,and is used to investigate the effects of defect depth and aperture size on defect detection.The experimental results show that by scanning and calibrating the defective samples with the system built in this paper,the internal defects of the three shaped materials can be effectively tested.In particular,for planar materials,the system enables the detection of defects with pore diameters greater than 2 mm and depths greater than 2 mm with a test resolution of half a wavelength(λ=4.5 mm). |
