Design And Research Of Microwave Broadband Metamaterial Absorbers

Metamaterial absorber is a new type of artificial absorbing material,which can absorb the electromagnetic wave energy in a specific frequency band efficiently,but the reflection and transmission are very small.Compared with the traditional absorbing materials,it has the advantages of thin thickness,lightweight,strong absorption,customizable design and so on.It has important application values in the fields of the antenna system,sensor,electromagnetic stealth and so on.It is widely concerned by researchers all over the world,and it is one of the research hotspots in the academic field.Starting from the research background and significance of the metamaterial absorbers and the research status at home and abroad,based on the full understanding of the theory of the metamaterial absorber,this paper focuses on the design and research of the microwave broadband metamaterial absorbers.(1)Aiming at the problem of the narrow absorption bandwidth of current metamaterial absorbers,an ultra-wideband metamaterial absorber with wide incident angle stability and absorption band covering the X and Ku bands is designed.It consists of an elongated copper patch rotated 45 ° at the top,a lossy FR-4 dielectric substrate in the middle,and a copper cladding at the bottom.The simulation results show that the transverse electric wave(TE)and the transverse magnetic wave(TM)reach the absorptivity more than 90% in the X and Ku bands(8 GHz-18 GHz)at normal incidence.Moreover,the structure can be scaled to change the operating frequency band without changing the waveform,and the relationship between the overall structure scale factor and the absorption frequency band is given.In order to explore the mechanism of absorption,the distribution of electric field and surface current density were analyzed.The impedance matching principle and the constitutive electromagnetic parameters obtained by inversion were used to explain the physical phenomenon of ultra-wideband high-intensity absorption of electromagnetic wave.The absorbing structure designed in this paper is particularly simple,which is convenient for processing and application.Without involving the use of new materials or loading lumped components,the absolute and relative bandwidths are reach up to 10 GHz and 76.92% respectively,compared with the reported absorption structure has been improved by at least 2.71 GHz and 10.25%,respectively.(2)Aiming at the problem of a certain reflection of electromagnetic waves in the absorption band,a microwave broadband metamaterial absorber with polarization insensitivity and stable characteristics of wide incident angle,and with stable absorption band is designed.The top is a resonant unit composed of four rings and a cross-shape loaded with lumped resistors,the middle is a lossy FR-4 dielectric substrate,and the bottom is a metal cladding.Based on the analysis of its equivalent circuit model,the structural parameters were simulated and optimized.The mechanism of broadband smooth and strong absorption is deeply analyzed through the distributions of electric field and surface current density and the equivalent input impedance.Then the polarization and wide incidence angle,as well as the absorbing characteristics of each layer structure are studied.The simulation results show that the absorptivity is more than 90% in the frequency range of 5 GHz-9.2 GHz under normal incidence of TE and TM polarizations achieve,especially in the broadband range of 5.9 GHz-8 GHz,the perfect absorption of electromagnetic waves(the absorptivity is more than 99%,then the reflectivity is less than 1%)is achieved.The average absorption rate is as high as 97.71% in the entire working frequency band,which is 3.11% higher than the absorption structure reported in the literature.Moreover,by changing the relative permittivity of the intermediate dielectric substrate,the working frequency band can be adjusted under the condition that the waveform is basically unchanged,and the fitting expression of the relationship between the relative permittivity and the absorption band is given.The two kinds of metamaterial absorbers designed in this paper can be applied to higher or lower frequency band,which have good portability.They and can be used in the antenna system,electromagnetic stealth and improve electromagnetic compatibility of devices.