Two-dimensional Metasurface Research Articles

Novel ultra-compact two-dimensional waveguide-based metasurface for electromagnetic coupling reduction of microstrip antenna array

A novel ultracompact two-dimensional (2D) waveguide-based metasurface is proposed herein and applied for the first time to reduce mutual coupling in antenna array for multiple-input multiple-output applications. The unit cell of the proposed 2D waveguide-based metasurface is ultracompact (8.6 mm × 4.8 mm, equal to λ0/14.2 × λ0/25.5) mainly due to the symmetrical spiral lines etched on the ground. The metasurface exhibits a bandgap with two transmission zeros attributing to the negative permeability in the vicinity of magnetic resonance and the negative permittivity in the vicinity of electric resonance. Taking advantage of these two features, a microstrip antenna array is then designed, fabricated, and measured by embedding an 8 × 1 array of the well-engineered 2D waveguide-based metasurface elements between two closely spaced (9.2 mm, equal to λ0/13.3) H-plane coupled rectangular patches. There is good agreement between the simulated and measured results, indicating that the metasurface effectively reduces antenna mutual coupling by more than 11.18 dB and improves forward gain. The proposed compact structure has one of the highest reported decoupling efficiencies among similar periodic structures with comparable dimensions. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:789–794, 2015.

Two-dimensional fractal metasurface and its application to low profile circularly polarized antennas

Two-dimensional (2D) Wunderlich-shaped fractal reactive impedance surface (WRIS) is designed and extensively investigated to reduce the dielectric substrate thickness without deteriorating the electromagnetic characteristic. Slot resonators, Hilbert-shaped complementary single ring resonator (HCSRR), and the complementary three-turns spiral resonator have been used to achieve antenna miniaturization and also to render the circularly polarized (CP) wave. For demonstration, WRIS-inspired HCSRR- and TCSR-loaded CP antennas are optimized, fabricated, and measured. Numerical and experimental results indicate that both antennas owe compact size smaller than 0.18λ0 × 0.25λ0 × 0.017λ0, exhibit comparable impedance, and axial ratio (AR) bandwidth better than 1.60% and pure CP performances. Furthermore, the antennas are free of metallic via holes and easy of fabrication, indicating promising applications in wireless communication systems.

Fano collective resonance as complex mode in a two-dimensional planar metasurface of plasmonic nanoparticles

Fano resonances are features in transmissivity/reflectivity/absorption that owe their origin to the interaction between a broad bright resonance and a dark (i.e., sub-radiant) narrower one. They may emerge in the optical properties of planar two-dimensional (2D) periodic arrays (metasurfaces) of plasmonic nanoparticles. In this letter, we provide a thorough assessment of their nature for the general case of normal and oblique plane wave incidence, highlighting when a Fano resonance is affected by the mutual coupling in an array and its capability to support free modal solutions. We analyze the representative case of a metasurface of plasmonic nanoshells at ultraviolet frequencies and compute its absorption under TE- and TM-polarized, oblique plane-wave incidence. In particular, we find that plasmonic metasurfaces display two distinct types of resonances observable as absorption peaks: one is related to the Mie electric dipolar resonance of each nanoparticle and the other is due to the forced excitation of free modes with small attenuation constant, usually found at oblique incidence. The latter is thus an array-induced collective Fano resonance. This realization opens up to manifold flexible designs at optical frequencies mixing individual and collective resonances. We explain the physical origin of such Fano resonances using the modal analysis through which we calculate the free modes with complex wavenumber supported by the metasurface. We define equivalent array dipolar polarizabilities that are directly related to the absorption physics at oblique incidence and show a direct dependence between array modal phase and attenuation constants and Fano resonances. We thus provide a more complete picture of Fano resonances that may lead to the design of filters, energy-harvesting devices, photodetectors, and sensors at ultraviolet frequencies. Similar resonances may be also extended to the visible range with an appropriate choice of geometries and materials.

Highly anisotropic metasurface: a polarized beam splitter and hologram.

Two-dimensional metasurface structures have recently been proposed to reduce the challenges of fabrication of traditional plasmonic metamaterials. However, complex designs and sophisticated fabrication procedures are still required. Here, we present a unique one-dimensional (1-D) metasurface based on bilayered metallic nanowire gratings, which behaves as an ideal polarized beam splitter, producing strong negative reflection for transverse-magnetic (TM) light and efficient reflection for transverse-electric (TE) light. The large anisotropy resulting from this TE-metal-like/TM-dielectric-like feature can be explained by the dispersion curve based on the Bloch theory of periodic metal-insulator-metal waveguides. The results indicate that this photon manipulation mechanism is fundamentally different from those previously proposed for 2-D or 3-D metastructures. Based on this new material platform, a novel form of metasurface holography is proposed and demonstrated, in which an image can only be reconstructed by using a TM light beam. By reducing the metamaterial structures to 1-D, our metasurface beam splitter exhibits the qualities of cost-efficient fabrication, robust performance, and high tunability, in addition to its applicability over a wide range of working wavelengths and incident angles. This development paves a foundation for metasurface structure designs towards practical metamaterial applications.