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A Facile Film-Nanoctahedron Assembly Route to Plasmonic Metamaterial Absorbers at Visible Frequencies
摘要： Plasmonic metamaterial absorbers (MAs) with broadband and near-perfect absorption properties in the visible region were successfully fabricated via a facile film-colloidal nanoparticle (NP) assembly method. In this approach, colloidal octahedral Au NPs were employed as the surface meta-atoms of MAs, while the nanoscale-thick SiO2 and Al films were used as the dielectric spacer and reflector respectively. It is worth noting that the Au nanoctahedron were randomly assembled onto the Al-SiO2 films, and no effort was made to precisely control their spatial arrangements. The optical characterization showed that the as-prepared MAs exhibited broadband high absorption (average absorptivity above 85%) within the whole visible spectrum for a broad range of incident angles (0°–60°). In particular, two polarization-independent near-perfect absorption peaks (absorptance above 99%) were recorded near 540 nm and 727 nm respectively. Moreover, the absorption properties of the MAs can be effectively controlled and tailored by varying the geometry (the thickness of the dielectric spacer and the surface coverages of the Au nanoctahedron). Electromagnetic simulations further demonstrated that enhanced Mie resonances and strong plasmonic coupling effects were critical for the designed MAs. This work here may provide an efficient and alternative route for the design of scalable visible light absorbers for applications such as solar cells, photothermalvoltaics, and biochemical sensors.
关键词： metamaterial absorbers,broadband and near-perfect absorption,aperiodic nanostructures,optical impedance matching,self-assembly
更新于2025-10-22 19:40:53
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Metamaterial emitter for thermophotovoltaics stable up to 1400?°C
摘要： High temperature stable selective emitters can significantly increase efficiency and radiative power in thermophotovoltaic (TPV) systems. However, optical properties of structured emitters reported so far degrade at temperatures approaching 1200 °C due to various degradation mechanisms. We have realized a 1D structured emitter based on a sputtered W-HfO2 layered metamaterial and demonstrated desired band edge spectral properties at 1400 °C. To the best of our knowledge the temperature of 1400 °C is the highest reported for a structured emitter, so far. The spatial confinement and absence of edges stabilizes the W-HfO2 multilayer system to temperatures unprecedented for other nanoscaled W-structures. Only when this confinement is broken W starts to show the well-known self-diffusion behavior transforming to spherical shaped W-islands. We further show that the oxidation of W by atmospheric oxygen could be prevented by reducing the vacuum pressure below 10?5 mbar. When oxidation is mitigated we observe that the 20 nm spatially confined W films survive temperatures up to 1400 °C. The demonstrated thermal stability is limited by grain growth in HfO2, which leads to a rupture of the W-layers, thus, to a degradation of the multilayer system at 1450 °C.
关键词： W-HfO2 layered structure,selective emitters,metamaterial emitter,high temperature stability,thermophotovoltaics
更新于2025-10-22 19:40:53
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A symmetrical dual-beam bowtie antenna with gain enhancement using metamaterial for 5G MIMO applications
摘要： A symmertrical dual-beam end-?re bowtie antenna with gain enhancement is achieved by intergating three pairs of metamaterial (MTM) arrays for 5G MIMO applications. The ?rst pair of MTM array with high refractive index (HRI) are deployed to form a wide beam antenna. The second pair of HRI MTM array are arranged along the end-?re direction (x-direction) in front of the radiators in order to split the single wide beam into dual beam. Besides, the third pair of anisotropic MTM array with HRI along x-direction and near zero refractive along y-direction are incorporated in front of the second pair of MTM array to improve the gain performance. The proposed technique is veri?ed by both the full-wave electromagnetic simulation and experiment, and the simulated and measured results agree very well with each other. Moreover, the measured results reveal that the main beam directions of the proposed antenna point to ±30? with respect to the end-?re direction (0?) over 24.25-27.5 GHz, with a maximum gain of 7.4 dBi at 26GHz and a 4.2 dB gain improvement compared to the wide beam antenna.
关键词： zero index metamaterial,high refractive index,Metamaterial,5G MIMO communications,dual beam
更新于2025-09-23 15:23:52
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Bandwidth enhancing method using tri-ring resonator metamaterial for small devices
摘要： Metamaterials are composite structures of the specific behavior for electromagnetic properties of permittivity, permeability, and refraction, which are not commonly found in regular materials. Metamaterial structure, which has negative value of permittivity and permeability that shows passband response in transmission line, where as if any of these two properties has opposite polarity then it shows stopband response. These behaviors of metamaterial are frequency dependent and have resonance for particular frequencies. At frequency resonance, the traditional metamaterials have narrow band response and to improve its frequency bandwidth, a method using tri-ring resonator is proposed with increasing number of order of resonator. The proposed metamaterial structure is simulated in full-wave simulator and MATLAB tool is used to analyze the properties of metamaterial structure from simulated S-parameter. Proposed technique gives flexibility to use the design for multiple application like, rejection filter for Bluetooth 2.4 GHz, Wi-Fi (2.4 and 5 GHz), WiMAX (2.5 and 3.4 GHz), and 5G (3.4-3.8 GHz).
关键词： SRR,band rejection,split ring resonator,metamaterial,broadband
更新于2025-09-23 15:23:52
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Metamaterial-Based Radiative Cooling: Towards Energy-Free All-Day Cooling
摘要： In the light of the ever increasing dangers of global warming, the efforts to reduce energy consumption by radiative cooling techniques have been designed, but are inefficient under strong sunlight during the daytime. With the advent of metamaterials and their selective control over optical properties, radiative cooling under direct sunlight is now possible. The key principles of metamaterial-based radiative cooling are: almost perfect reflection in the visible and near-infrared spectrum (0.3–3 μm) and high thermal emission in the infrared atmospheric window region (8–13 μm). Based on these two basic principles, studies have been conducted using various materials and structures to find the most efficient radiative cooling system. In this review, we analyze the materials and structures being used for radiative cooling, and suggest the future perspectives as a substitute in the current cooling industry.
关键词： daytime radiative cooling,infrared atmospheric window,metamaterial,selective reflection,selective emission
更新于2025-09-23 15:23:52
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On the Double Nano-Coned Graphite Metasurface-Based Multiband CIC Absorber
摘要： Spectral characteristics of nano-engineered absorber comprised of nano-cone-shaped multi-layered (or cascaded) graphene metasurface (that results in graphite medium) were investigated under different chemical potentials and incidence conditions. The configuration of the proposed absorber is of the conductor-insulator-conductor (CIC) kind, wherein the top and bottom metasurfaces are identical in a pattern having the array of graphite-cones. Such three-layer CIC absorber hosts relatively thick dielectric substrate sandwiched between graphite nano-cone-based metasurfaces, in order to trap incidence electromagnetic fields. The results in respect of absorbance revealed usefulness of the proposed structure in spectral filtering in the visible and far-infrared regimes. Also, the tuning feature of absorber through altering the chemical potential of metasurfaces was highlighted.
关键词： Nano-engineered mediums,Complex mediums,Metamaterial absorbers,Graphene structures
更新于2025-09-23 15:23:52
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Application of metasurfaces in the design of performance-enhanced low-profile antennas
摘要： This paper presents a review of metasurface-based antennas conducted at the Microwave Communication Laboratory (MCL) of Ajou University in the Republic of Korea. In this paper, pro?le miniaturization, bandwidth enhancement, multiband operation, and radiation pattern control of metasurface-based antennas are considered. The paper ?rst presents metasurface-based antennas implemented by placing various radiators on top of the metasurface. It then presents antennas implemented by placing the radiators below the metasurface with and without the ground plane. Metasurface-based antennas are not only able to achieve high ef?ciency with a low pro?le but they are also able to generate extra resonances from the metasurface structures, which signi?cantly enhances the overall performance of the antennas. These additional resonances were utilized in multiband and/or wideband operations. In addition, the design of a planar compact wide-gain-bandwidth metasurface-based antenna and its radiation characteristics are presented at a terahertz (THz) frequency range. The THz antennas were designed with metasurfaces and a planar leaky-wave feeding structure. Finally, the outlook on future research at the MCL for antenna-related work and their applications using metasurfaces is provided.
关键词： surface wave resonance,sequential rotation,crossed dipole,arti?cial magnetic conductor,metamaterial,wideband,circular polarization,leaky-wave,Antenna,array,metasurface
更新于2025-09-23 15:23:52
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Reduced order derivation of the two-dimensional band structure of a mixed-mode resonator array
摘要： In this paper, the 2D band structure of a mixed-mode metamaterial resonator array for in-plane waves is investigated. The band structure in the interior and on the boundary of the irreducible Brillouin zone and 1D dispersion diagrams for different propagation angles are calculated numerically and presented. Additionally, a reduced order analytical method is established to compare and approximate the band structure. The studied metamaterial, with a T-shaped cantilever beam as the resonator in its square array repeating unit cells, exhibits branches with mixed P and SV waves except at exactly one angle of propagation. This paper also reports on the occurrence of avoided level crossings, which are related to the existence of exceptional points in the complex domain. A reduced order analytical approach is used that can generate partial (low branches) band structure with relatively little computational effort. The reduced order model agrees well with the numerical results for these low branches and can provide support in mode identification and band sorting. With proper adjustments in parameters, this analytical method will be applicable to other metamaterials that have a similar unit cell structure.
关键词： band structure,reduced order model,resonator array,metamaterial,avoided level crossings,mixed-mode waves
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE Asia-Pacific Conference on Antennas and Propagation (APCAP) - Auckland (2018.8.5-2018.8.8)] 2018 IEEE Asia-Pacific Conference on Antennas and Propagation (APCAP) - MIMO Antenna Array Decoupling Based on a Metamaterial Structure
摘要： A metamaterial decoupling structure is designed and used to enhance the isolations in the MIMO antenna array consisting of two patch antenna elements which operate at 5.3 GHz. The distance from edge to edge between the two microstrip patch antennas is 11 mm which is about 0.19λ corresponding to the center resonance frequency. The designed metamaterial structure constructed with three modified split-resonator rings is periodically set in the middle of the devised MIMO array so as to reduce the effect of the surface wave propagation between the two microstrip antennas. The simulation results obtained from the calculations show that the isolation is enhanced about 12.5 dB without sacrificing the bandwidth and good radiation pattern characteristics.
关键词： metamaterial,decoupling,MIMO antenna array
更新于2025-09-23 15:23:52
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Numerical study of a wide-angle and polarization-insensitive ultrabroadband metamaterial absorber in visible and near-infrared region
摘要： An ultrabroadband metamaterial absorber structure based on a periodic array of metallic-dielectric multilayered conical frustums is numerically investigated and proposed. The metamaterial absorber indicated an absorptivity of higher than 90%, which covered the visible and near-infrared region at 480-1480 nm, and a relative absorption bandwidth of 102%. The high absorptivity can be maintained with large incident angles up to 60° under both transverse electric and transverse magnetic polarizations. Furthermore, the proposed absorber exhibits polarization insensitivity owing to its rotational symmetry structure. Compared with the previously reported ultrabroadband metamaterial absorbers, the design in this work indicates high practical feasibility in terms of compact structure for large bandwidth, wide incident angle and polarization insensitivity, thereby suggesting its promising application, for example, in solar cells and thermal emitters.
关键词： Metamaterial,Absorber,Visible,Ultrabroadband,Near-Infrared
更新于2025-09-23 15:23:52