The emergence of metamaterials, a new type of artificial materials exhibiting characteristics that are not available in nature, had a profound impact on the advances in terahertz (THz) science and technology by realizing appropriate electromagnetic responses in the THz frequency. Despite the recent efforts, the still existing needs for the more efficient manipulation of THz waves fuels the development of metamaterial based THz active and passive devices such as filters, polarizers, and modulators.
In this work, we present a dual-band THz filter based on self-complementary metasurfaces that are two-dimensional arrays of the unit-cells consisting of an artificial resonator and its complementary counterpart. The unit cell of the self-complementary metamaterial utilized to realize the dual-band filter is based on a combination of a Jerusalem cross and its complementary structure designed to resonate in the THz regime. This structure functions as a selective band-stop filter (BSF) or band-pass filter (BPF) depending on the polarization states of the incident wave. It is also observed that the transmission phases of the two orthogonally polarized waves exhibit 90° phase difference in broad frequency range. It implies that it can be utilized as a quarter wave plate manipulating the polarization of the incident THz waves.
The use of self-complementary structures enables the design of a 2-in-1 THz filter device whose function can be chosen between BPF and BSF by changing its orientation.
The operating principles and design guidelines of the self-complementary metasurfaces will also be presented by using electromagnetic simulation and equivalent circuit method.
We analyze and design the reflection phase characteristics in metasurface based asymmetric Fabry-Perot cavities, consisting of a metallic metasurface backed by a ground metal plane. The metamaterial cavity is modeled using transmission line theory and effective surface admittance approach, where the free space and substrate are described by equivalent transmission lines. The individual metasurface is modeled by an equivalent surface admittance connected at the junction of the transmission lines. Analysis using the above model reveals that the effective metasurface susceptence and cavity thickness govern the resonance frequency of the cavity structure. While, the effective metasurface conductance at that frequency determines whether the overall cavity resonator is in under coupled, critically coupled or over coupled regimes. Therefore by appropriately controlling the metasurface effective conductance and the cavity thickness, the metasurface cavity can be designed to have desired resonant regime. In under and critically coupled regimes, the cavity resonator exhibits a reflection phase variation limited between 90° and 270°. While in over coupled regime, reflection phase variation from 0° to 360° is exhibited. We demonstrate and verify the above results using full wave EM simulations. Using an example metasurface consisting of cross shaped resonators, we demonstrate controlling effective metasurface conductance to realize any desired reflection amplitude and phase. The presented results provide important guidelines for realizing phase control devices such as lenses or beam deflectors. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science, ICT and Future Planning) (No. 2017R1A2B3004049).
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