Design And Investigation Of Terahertz Metamaterial Absorption Devices

The design of terahertz(THz)functional devices is a research hotspot that has attracted much attention recently,and has shown extraordinary application value in the fields of absorption,modulation,and slow light.Based on the traditional sandwich structure and the intelligent functional requirements as the starting point,this work studies the single-tunable,dual-tunable and reconfigurable metamaterial functional absorbers for THz waves.Combining active controllable materials such as graphene and VO₂ with traditional structures,a series of THz metamaterial functional devices have been designed according to different communication scenarios.The impedance matching theory,transmission line theory and interference theory are used to deeply analyze and understand the working mechanism and functional characteristics of the designed meta-device.The main contents of this paper are as follows:(1)Triple-band and broadband THz metamaterial absorbers based on graphene with a single amplitude tunable are designed,respectively.Its structure follows the classic three-layer metamaterials structure,by adjusting the Fermi energy of graphene,to enable the absorber to switch freely between the absorption and reflection states in the target THz region.And the switching intensity in the target frequency region can reach more than 80%,which can be widely applied in the field of THz communication.In addition,the above two unit cells use coupled structured graphene,which improves the absorption efficiency and reduces the complexity of the unit cell.(2)THz tunable broadband absorbers based on a dual-parameter control system are designed respectively.Graphene and VO₂ are introduced into the unit cell structure,and they are not sensitive to changes in polarization and incident angle.Among them,the broadband dual-amplitude adjustable absorber is made up of three layers,by reasonably controlling of the parameterized graphene Fermi level and VO₂ conductivity,the THz device can have different attributes:broadband absorption and high modulation.The structural unit of the broadband amplitude/frequency dual adjustable THz absorber consists of a four-layer structure.When the Fermi level of graphene is changed alone,the position of the broadband absorption spectrum will be blue-shifted.When the conductivity of vanadium dioxide is changed alone,the amplitude of the broadband absorption spectrum can be dynamically adjusted.Therefore,the device can achieve active adjustability of resonance frequency and absorption amplitude at the same time.(3)Two bi-functional THz metamaterial absorbers with reconfigurable properties in the THz band is designed.The unit cell of the devices adopts a stacked structure of multi-layer metamaterials,and a VO₂ switching layer is placed in the middle of the unit cell.By changing the VO₂ conductivity to simulate the phase transition process,a switchable characteristic of the designed meta-structures is realized.Simply put,when VO₂ is in the metallic state,the designed reconfigurable devices all behave as tunable broadband THz absorbers.By adjusting the VO₂conductivity,the magnitude of the absorption spectra in the broadband range can be dynamically changed.When VO₂ behaves as an insulator,the THz device with switchable broadband/dual-band absorption properties will act as a dual-band perfect absorption spectra in the target range,and the working state of the dual absorption band can be switched by controlling the graphene Fermi energy.And THz functional device with absorption/slow-light switchable characteristics features a broadband THz induced transparency(EIT)window,and the bandwidth of its transmission spectrum exceeds 0.42 THz.Moreover,the properties of the EIT window can be controlled by the characteristic parameters of the Fermi level.In addition,the designed functional structure can also maintain a good control effect on the incident wave when the incident is obliquely incident.