| With the rapid development of technology,the wide application of electromagnetic waves has brought great convenience to people's lives.However,excessive electromagnetic radiation can affect people's health and pollute the current ecological environment.Therefore,how to effectively absorb electromagnetic waves and solve the problem of electromagnetic radiation has become the research focus of relevant personnel.Absorbing materials refer to materials that can effectively absorb lossy electromagnetic waves.They were first used in the field of military safety,and are mainly divided into traditional absorbing materials and metamaterials.The research object of this paper is metamaterial,which refers to the artificial composite material that has been modified and designed to have many special physical properties.In 2008,Landy et al.proposed a perfect absorber based on the structure of a periodic resonant unit.The absorption at the peak is close to 100%,which has attracted wide attention of researchers.After that,a variety of absorber structures have been proposed,mostly by a metal film of a certain pattern attached to the dielectric substrate to form an electrical resonator and a magnetic resonator structure.These absorbing structures are light in weight and have a strong absorption capacity in a particular frequency band,but generally the absorption band is too narrow.Aiming at the low-frequency end application of broadband absorbing materials,this paper designs a new 3D metamaterial absorbing structure based on the truncated cone structure.In order to obtain a wider absorbing band and better absorbing effect,a spacer layer with magnetic absorbing properties was used in combination,and the lower limit of the absorbing frequency that can be achieved by such a material structure was also studied.In this paper,the optimization of one kind of ultra-broadband metamaterial microwave absorber have been carried out by electromagnetic field simulation and theoretical analysis,combining 3D metamaterial absorbing structure with traditional magnetic material.Making full use of the electromagnetic wave absorption of the magnetic material and the frequency designability of the periodic metamaterial structure,and taking account of the impedance matching,multiple reflection and absorption of the electromagnetic field of the 3D gradient unit,a periodic absorbing structure which consists of frustums of a cone is designed.Each frustum consists of 20 layers of metal resonant sheets with the size linearly enlarged and 20 layers of magnetic complex filled with carbonyl iron powder.The two kinds of layers are stacked one another.The electromagnetic simulation software CST Microwave Studio is used to design the structure,calculate the absorbing effect and analyze the distribution of electromagnetic field of the absorbing structure.After the optimization of the relevant parameters,the final simulation results show that the structure has an effective absorption in the frequency range of 4.5-18 GHz,and the absorption rate of normal incidence is more than 90%.The analysis and simulation results also show that when the thickness of absorbing material is not more than 5mm,the lower limit of absorbing frequency can be achieved by combining magnetic material with metamaterial,which is about 4 GHz.The research results of this paper have certain guiding significance for the future research and design of metamaterial absorbing structures. |
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