Design And Numerical Simulation Of Terahertz Metamaterial For The Perfect Absorbers

Despite of the considerable scientific interest since the 1920s,the Terahertz frequency range remains one of the least utilized areas of the electromagnetic spectrum.Due to its special physical properties,such as higher frequency,broad-band,small divergence angle and strong penetrability,the terahertz electromagnetic wave can penetrate many non-conductive substances,earning widely potential applications.Metamaterials have concentrated considerable attention since the 1990s due to their exotic electromagnetic properties.With the longtime research over twenty years,the field of Metamaterials has developed a rich variety of structural and functional types,which includes the metamaterial perfect absorbers.In this paper,based on the classic metal-media-metal configuration,we proposed and explored a broad-band terahertz perfect absorber.The main contents and results of this paper are as follows:In the first chapter,first we introduced the concept of metamaterials,then briefly summarized the research process of metamaterials and the electromagnetic response of metamaterials.At the end of this chapter,the latest developments in the field of metamaterials are reviewed.In the second chapter,several theories of metamaterial research are introduced in detail including the equivalent medium theory and the S-parameter extraction method of equivalent electromagnetic parameters.In the end,the impedance-matching theory and its more accurate equivalent circuit model of transmission line are presented.In the third chapter,the concept and properties of surface plasmons are firstly introduced,then the propagation mode,energy characteristics as well as penetration depth of surface plasmons are described in detail.Secondly,the localized surface plasmon mode as the second excitation mode of plasmas is introduced.Finally,we have a discussion about the coupling between localized surface plasmons.In the fourth chapter,a broadband perfect absorber which can work in terahertz band is studied via the finite difference time domain method.It's discovered that the proposed metamaterial absorber could achieve perfect absorption of over 99%in 1.25 THz-1.75 THz and over 90%in 1.13 THz-2.25 THz.The Commercial software FDTD Solutions was used to simulate the designed structure.And the internal absorption mechanism was analyzed by changing the size of the device,the polarization angle and incident angle of the incident electromagnetic wave.Through the analysis of geometric parameters of the structure model and the distribution of electromagnetic field inside it,we found that the coupling effect of the inner and outer rings of chromium with low conductivity causes that the incident electromagnetic energy dissipates in the metal layer because of the ohm loss.The simulation results provide an important reference for the study and application of the metamaterials perfect absorptions of metal plasma with low conductivity.At last,the research of the full text is summarized and prospected.