| Metasurfaces are two-dimensional surface structures composed of periodically arranged subwavelength resonant units with extraordinary electromagnetic properties.By rationally designing the geometric structure and material parameters of metasurface units,the frequency,amplitude and phase of incident electromagnetic waves can be flexibly controlled,and many novel functional devices will appear,which has attracted extensive attention.Metasurface absorbers are typical representatives of metasurface functional devices,which can achieve almost complete absorption of electromagnetic waves in an extremely thin thickness.In the past,the metasurface absorbers of metal structures provided electrical resonance and magnetic resonance in the same position,which complicated the optimization process of dimensional parameters to achieve perfect absorption.This paper proposes the idea of separating the electric resonator from the magnetic resonator,based on the degenerate critical coupling theory,through the rational design and optimization of the geometry of the resonator and the parameters of the constituent materials,not only can achieve near-perfect absorption at the operating frequency,but also has polarization insensitivity and double-sided wave absorption.Due to the design method of the separation resonator,the regulation of the resonant frequency and its absorption rate has great advantages over the traditional method.This paper first briefly introduces the concept,research progress and application of metasurface absorbers,then analyzes the absorption mechanism of metasurface absorbers,and finally designs two different types of metasurface absorbers: electromagnetic resonance separation metasurface absorbers and electromagnetic resonance separation metasurface absorbers with polarization insensitive properties.The main contents of this paper were as follows:(1)The effects of loss and size parameters on the absorption performance of the electric and magnetic resonators in the designed metasurface absorber are systematically studied.The results show that the absorptivity of the electric resonator and the magnetic resonator in the metasurface absorber first increases and then decreases with the increase of the loss,and the maximum absorptivity will not exceed 0.5.The resonant frequency of the electric resonator and the magnetic resonator in the metasurface absorber has little effect on the absorption rate.(2)Based on the separation resonance idea and degenerate critical coupling theory,a metasurface absorber structure is designed.The full-wave electromagnetic simulation results show that the structure can achieve an absorption rate of 99.3%.By changing the structure size of the absorber,the absorption frequency can be moved arbitrarily between 7 GHz and13 GHz,so it also has very good tunability.If the dielectric material in the wave absorber has a suitable loss tangent,the wave absorber also has the function of double-sided wave absorption.In addition,the absorption mechanism is analyzed,and the results show that the nearly complete absorption of the metasurface absorber originates from the electrical resonance and the magnetic resonance,and the energy loss mainly occurs in the dielectric layer.The metasurface absorber structure samples are fabricated by PCB(Printed Circuit Board)process and tested.The test results are basically in line with expectations.The deviation from the theory are mainly caused by the small loss of the substrate dielectric material.(3)By changing the unit structure and arrangement of the electric resonator and the magnetic resonator and the electromagnetic parameters of the substrate dielectric material,a polarization-insensitive metasurface absorber is designed.The numerical calculation results show that the absorber has an absorption rate of 99.5%,and the absorption frequency can be shifted arbitrarily between 7 GHz and 11 GHz.If a suitable loss tangent is selected for the dielectric material,double-sided wave absorption can also be achieved. |
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