Research On Absorption Characteristics Of Terahertz Metamaterial Structure

Terahertz waves,electromagnetic waves with frequencies between 0.1 THz and 10 THz,have attracted widespread attention because of their penetrating and coherent properties.However,the development and application of terahertz technology is limited by the lack of natural materials that produce a strong response to terahertz waves.Metamaterials are expected to break this situation,and the strong response of structures to terahertz waves can be achieved through the unique design of metamaterials,which in turn can effectively modulate terahertz waves.In general,the electromagnetic properties of metamaterials prepared based on noble metals will not be able to be changed.New tunable terahertz metamaterials have been developed to achieve active modulation of the absorption properties of terahertz metamaterials are of great value for the application of terahertz waves.Meanwhile,similar to the electromagnetically induced transparency effect in atomic systems,plasmons supported by metamaterials can also produce electromagnetically induced transparency effect,forming resonant modes with high Q-value,high transparency,and strong dispersion,which is not limited by conditions such as low-temperature strongly pumped light.These properties make plasmon induced transparency promising for a wide range of applications in devices such as slow-light devices,optical memories,high-resolution sensors,and nonlinear switches.The main work of this paper is as follows:1.The absorption characteristics of a multi-band terahertz metamaterial based on a metallic circular structure are studied and designed by a time-domain finite difference method.Two absorption peaks with absorption rates of 0.83 and 0.61 are obtained at 1.15 THz and 2.51 THz,respectively,for this metamaterial structure.By simulating the electromagnetic field distribution properties of the structure,it is determined that the first absorption peak is formed due to the local surface plasmon resonance of the metal nanocircle,while the second peak is generated by the mutual coupling between the electric dipole resonance of the metal nanocircle and the periodic array structure.The structure parameters were tuned so that the structure formed three absorption peaks of 0.99,0.98,and0.71 at 0.915 THz,2.444 THz,and 2.595 THz,respectively.Tunable materials are added to the above structure to study the absorption characteristics of the structure under different graphene Fermi levels.The absorption bandwidth and frequency could be tuned by adjusting the Fermi levels.2.A multi-band plasmon-induced transparency metamaterial(PIT)structure based on metal ring is designed and studied.The structure is simulated to produce two transmission windows with transmittance greater than 90% at 3.81 THz and 4.43 THz,respectively.Based on the electromagnetic field distribution model,multipole decomposition theory and near-field coupling theory,it is determined that the first transmission peak is formed by the destructive interference between two bright modes,and the second transmission peak is formed by the mutual coupling between magnetic dipole and electric quadrupole and excitation of the multipole mode together.Due to the symmetrical design of the structure,it has polarization insensitive properties.The dynamic modulation of the transparent window peak is achieved by changing the conductivity of vanadium dioxide in the structural material.In addition,the sensing properties of the metamaterial and the slow-light properties are also investigated.The sensing sensitivity of the PIT window of the structure can reach up to 160 GHz/RIU,and the group delay of the terahertz metamaterial is 37.9ps,which proves that the structure has good sensing properties and "slow-light" properties.