Research On Metamaterial Terahertz Absorber Based On Lumped Element

Terahertz is a frontier cross-field,with low quantum radiation energy,and a high spectrum signal-to-noise ratio.A metamaterial is a specific artificial material with unique physical properties.Metamaterial structures are typically arranged by the design of subwavelength metal units.Metamaterials can achieve different regulations of electromagnetic waves by changing the resonator units in the structural period.A metamaterial absorber is a kind of electromagnetic device which converts the incident electromagnetic wave into molecular potential energy,heat energy and other energy forms by using various loss mechanisms inside the device.Compared with traditional absorbers,metamaterial absorbers have numerous advantages,such as high absorption performance,small size and thin thickness.By loading lumped elements in the device,the design of the absorber can be more diversified.According to the above characteristics,lumped elements are applied to a terahertz metamaterial absorber to achieve broadband absorption spectrum and tunability.The main research contents of this thesis are as follows:1.A terahertz metamaterial absorber with a single ring structure based on lumped resistance is proposed.The absorber can realise over 90% absorption in the frequency band range of 10.2 THz-18.1 THz and 69% relative bandwidth,achieving broadband absorption.The resistance equivalent to the given resistance value can be attained qualitatively and quantitatively using the doped silicon model.The current and electric field distribution of a single ring structure metamaterial absorber based on lumped resistance loading is simulated.The absorption mechanism is analyzed using an equivalent circuit model.The effect of structural parameters on the absorption spectrum was analyzed using an equivalent formula.2.By adding the same resonant unit within one period,which is one of the commonly adopted methods to expand the absorption band of the absorber,a terahertz metamaterial absorber with a double ring structure based on lumped resistance is proposed.The broadband absorption of the absorber is more than 90% in the band range of 8.2 THz-16.9 THz,and the relative bandwidth is 73%.The current and electric field distribution of the double ring structure absorber loaded with lumped resistance is simulated by using the doped silicon model to achieve equivalence of the high-frequency resistor.The absorption mechanism is analyzed using the equivalent circuit model,and the influence of the structure parameters on the absorption spectrum is analyzed using the equivalent formula.3.A terahertz metamaterial absorber with a double ring structure based on lumped resistance and graphene loading is proposed.The absorber can achieve more than 90%broadband absorption in the range of 6.1 THz to 18.5 THz,and its relative bandwidth is99.2%,further broadening the absorption bandwidth.The current and electric field distribution of the terahertz metamaterial absorber loaded with lumped resistance and graphene is simulated using the doped silicon model to obtain equivalence of the high frequency resistance.The absorption mechanism is analyzed using the equivalent circuit model,and the influence of structural parameters on the absorption spectrum is analyzed using the equivalent formula.4.A terahertz metamaterial absorber based on a switching diode is proposed to realize the tuning of absorber absorption characteristics.When the diode is on,the absorber has the maximun absorption at 7.7 THz,while when the diode is off,the peak can be tuned to 3.2 THz.The current and electric field distribution of the terahertz metamaterial absorber based on the switched diode is simulated.The absorption mechanism is analyzed by an equivalent circuit model,and the effect of structural parameters on the absorption spectrum is analyzed by the equivalent formula.Furthermore,by applying the switching diodeto the above-mentioned double structure wideband terahertz metamaterial absorber,a switchable wideband metamaterial absorber based on a switching diode can be designed accordingly.When the diode is on,the absorber can achieve over 90% absorption in the frequency band range of 6.3 THz-8.3THz,and the relative bandwidth is 28.6%.In the off state,the absorber absorbs more than90% of the frequency band from 3.4 THz to 6.2 THz,and the relative bandwidth is 40%,realizing the switch of absorption bandwidth.The bandwidth switching mechanism is analyzed using equivalent circuit model.5.A varactor diode is applied to the terahertz metamaterial absorber,with the change of its capacitance value through the altered applied voltage,the absorption frequency of the absorber can be tuned simultaneously.The current distribution of the metamaterial absorber based on the varactor diode is simulated and the absorption mechanism is analyzed using the equivalent circuit model.The effect of adjustable absorption frequency and structural parameters on absorption spectrum is analyzed using the equivalent formula.Furthermore,based on the findings of resonance frequency points in different phase changes,a super surface phase gradient is bulit,and the reflection of the electric field figure is obtained,The abnormal reflection angle of about 30 ° is calculated by the Snell reflection formula,almost consistent with the phase amplitude figure of the simulation results,indicating the diversified applications of the variable-capacitance loaded diode metamaterial structure.