Design Of Perfect Absorber Based On Equivalent Circuit And Impedance Matching

Metamaterials are a type of composite materials,which are obtained by reasonable artificial design from existing natural substances.Therefore,metamaterials have some excellent characteristics that are different from natural materials.The absorber based on metamaterials can obtain the required dielectric constant and permeability by selecting materials and optimizing structural parameters.When the structural dielectric constant is close to its permeability,the structural impedance matches the impedance of the free space,that is,the perfect absorption of electromagnetic waves is achieved.In recent years,the perfect absorption characteristics of absorbers based on metamaterial make it have broad application prospects in many fields,for example,solar energy capture,stealth,and thermal emission.As a result,wide-band metamaterial absorbers have become one of the hot research directions.At present,with the increase of absorber absorptivity,there may be problems such as not wide working band,using precious metal materials or single design method.Therefore,for the above existing problems,combined with the equivalent circuit method and impedance matching theory,a wide band perfect absorber with two stacked structures is designed in this paper,as well as the performance,structural parameters and intrinsic mechanism of the absorber are analyzed by the finite difference time domain method.The main research work of the thesis is as follows:We propose a multilayered perfect absorber based on equivalent circuit method.Firstly,based on the dipole equivalent circuit method,the absorption mechanism of the monolayer model is analyzed.In order to further broaden the absorption band,multiple resonant absorption peaks are superimposed to form a broadband perfect absorber with multilayered structure.Numerical analysis shows that under normal incidence,the absorber has an average absorption rate of more than 96% at 300～3000nm,and the wavelength covers the ultraviolet to mid-infrared region;the average absorption level is over 91% of the absorber at a wide angle of ±70°,and it has any polarization independence.By calculating and analyzing the electromagnetic energy distribution of the absorber,it is found that its excellent absorption performance is excited by slow wave effect,local surface plasma and propagating surface plasma resonance.In addition,because iron is prone to oxidation,we use metallic chromium to replace part of the iron layer to improve the metallic materials in the structure.Both of these absorbers can achieve impedance matching to achieve wide-band perfect absorption.In order to reduce the complexity of structural processing and further improve the absorption performance,based on the above-mentioned laminated structure,a metamaterial perfect absorber with a simple laminated structure is designed in combination with impedance matching theory.The absorber is composed of two metal-semiconductor film-semiconductor pairs of different sizes,which is easy to excite a variety of resonant modes to achieve ultra-broadband perfect absorption.The finite-difference time-domain method was used to study and analysis the main parameters and the electromagnetic field energy distribution of the absorber,as well as the influence of the polarization angle and incident angle on absorption performance.The results show that the average absorption rate of the absorber in the visible-mid-infrared range is higher than 97% and it is still higher than 90% at a wide incident angle of 60°;in addition,the absorber has the independence for arbitrary polarization angle;the characteristics of broadband perfect absorption are caused by the gap-surface plasmon polaritons,the propagation surface plasmon polaritons,and the Fabray-Perot resonance.Therefore,the designed absorber has the advantages of high absorption,wide working band,and easy processing.The two perfect absorbers with laminated structure designed in this paper have good absorption performance in a wide band,and the selection of non-precious metal materials saves production costs,which provides the possibility for large-scale manufacturing and application of absorbers.Moreover,we combined the equivalent dipole circuit theory and impedance matching theory to assist in the design of the absorber,which provides method guidance for further research on the perfect absorber.The proposed ultra-wideband,strong absorption,polarization independent absorber provides a reference for applications in solar energy collection,magnetic recording and other fields.