The Design Of Metamaterial Absorber And Its Absorption Characteristics

Electromagnetic metamaterial(EM MM),a novel artificial structure after transformation of conventional material,has been attracting considerable attention in international scientific fields due to its ability to possess extraordinary physical properties,such as reversed Doppler shift,reversed Cerenkov radiation,perfect lens,etc..In this thesis,based on the relevant research methods of the metamaterial absorber(MA),we construct two absorbers based on resistive film with different patterns and a multi-band absorber,all which are polarization-insensitive and wide-angle.Firstly,we present a broadband,polarization-insensitive and wide-angle MA in the microwave regime by using crossed-rectangular-ring-shaped resistive film.Simulation results indicate that the absorber obtains wide absorption from about 4.75 GHz to 17.57 GHz with absorptivity over 90% at normal incidence and the relative bandwidth goes up to 115%.The distribution of power loss density is involved to interpret absorption mechanism of the MA and it is concluded that the crossed-rectangular-ring resistive film mainly supplies the broadband absorption due to the ohmic loss.Then introduce the multi-reflection interference theory to explain the structure's absorption.By analyzing the absorption rates under oblique incidence,it can be reached that the electric polariton that causes the resonant broadband absorption in the composite structure can be effectively excited by the electric field.The magnetic field contributes a little to the excitation of the electric polariton.Secondly,we construct a broadband,polarization-insensitive and wide-angle microwave absorber based on cross-ring-shaped resistive film.Simulation results indicate that the absorber obtains wide absorption from 5.54 GHz to 20.3 GHz with absorptivity above 90% at normal incidence and the relative bandwidth is 114%.The distributions of surface current densities and normal electric fields on the metallic layer and resistive layer are involved to research the intrinsic absorption mechanism.By analyzing the absorption spectra under oblique incidence,the results can be reached that the electric polariton that causes the broadband and high absorption in the composite structure can be effectively excited by the electric field and the magnetic field contributes a little to the excitation of the electric polariton,which coincide with the analysis to the distributions of surface current densities and normal electric fields.At last,based on the transmission theory introduce the equivalent circuit model to calculate the structure's absorptivity.The calculated absorption rates agree fairly well with the simulated results,which indicates that introducing the equivalent circuit model to calculate absorption rates of the absorber is feasible.Thirdly,we design a multi-band microwave MA to obtain the multi-band and high absorption of the incident electromagnetic wave based on nested split square ring and crossed-rectangular ring.The multi-band MA has four distinctive absorption peaks from the simulation results at 5.22 GHz,7.10 GHz,9.67 GHz and 13.73 GHz with the absorptivity 99.4%,97.7%,99.6% and 99.5%,respectively.Then determine the influences of metallic split square ring and crossed-rectangular ring on the MA's absorption.And the distributions of power loss density at four resonant frequencies are monitored to explain the absorption mechanism.The results of analysis to distributions of power loss density agree well with the influences of metallic split square ring and crossed-rectangular ring on the MA's absorption.The changes of absorption spectra with the incident angles increasing under oblique incidence have the opposite trend compared with the changes of the first two structures' absorption rates.The magnetic polariton that causes the multi-band and high absorption in the composite structure can be effectively excited by the magnetic field and the electric field contributes a little to the excitation of the magnetic polariton.Additionally,we discuss the loss contributions of each part of the multi-band MA to the absorption.