Miniaturized Imaging Chamber Based On An Inhomogeneous Matched Absorbing Surface

Microwave imaging based on the inverse scattering problem is one of the most important applications in the field of practical engineering.Based on the inverse scattering microwave imaging,the position,permittivity,profile,refraction parameter and other spatial or material information of the imaged object illuminated by a single-frequency continuous wave can be obtained in a non-contact manner.Therefore,it has attracted many interests in scientific research and engineering applications.The classical theory of inverse scattering microwave imaging is derived under ideal infinite space or non-scattering boundary conditions.In microwave enginnnering,the above-mentioned environment can be approximately realized in electrically large anechoic chambers.This is the reason why the early used microwave imging experiments were mainly carried out in microwave anechoic chamber,but it is obviously not suitable for most practical application scenarios.Based on the characteristics of the inverse scattering microwave imaging system working in a single-frequency continuous wave,in order to promote the practical applications of microwave imaging,an inhomogeneous,ultra-thin,dual-angle absorbing surface was implemented to simultaneously absorb incident and scattered fields based on the concept of an artificial perfect matched layer.Moreover,a compact microwave imager integrated with a board-integrated,multi-port vector network analyzer,a miniaturized cylindrical anechoic chamber and a step motor-driven turn table was implemented.This microwave imager worked at 5.98 GHz and its diameter is only 6.9?.Experimental imaging verified its effectiveness.The main innovative work of this dissertation includes:At the theoretical level,based on the parameter-simplified perfect matched layer model,the inhomogeneous artificial surface and the effective medium equivalence,this article successively derived the models of effective constitutive parameters aiming at absorbing the single-frequency electromagnetic waves incident from single-angle and dual-angle directions respectively.Moreover,this article theoretically proves the feasibility of realizing the miniaturized inverse scattering microwave imging chamber based on a single-frequency continuous wave,and provides clear method and target data for the design,simulation and realization of the inhomogeneous matched absorbing surface.At the realization level,there are two steps.Aiming at the fixed position of the transmitting and receiving antennas,the inhomogeneous matched absorbing surface working at single-angle and dual-angle incidence are successively realized through lots of simulations and optimizations.On this basis,two semi-closed cylindrical miniaturized chamber were constructed,its diameter are 6? and 6.9?,respectively.The distribution of the voltage standing wave ratios inside the chamber was experimentally measured based on the perturbation method.The measurement results comply with the theoretical expectations and full-wave simulations.At the system integration level,this article further implemented a full-featured,highly integrated miniaturized inverse scattering microwave anechoic chamber integrated with the antenna,the feed system,PCB integrated multi-port vector network analyzer and electric motor-based turntable.Through the microwave imging of the actual smaples,the effectiveness and accuracy of the obtained imaging chamber are verified.The above innovative work is of great significance to advance the practical application of inverse scattering microwave imaging.