Multi-band Absorber Research Articles

Electromagnetic simulations of polarization-insensitive and wide-angle multiband metamaterial absorber by incorporating double asterisk resonator

A novel multiband metamaterial absorber (MTMA) is proposed which is capable of well presenting a polarization-insensitive and wide incident angle stability in the microwave frequency range. The proposed MTMA comprising two vertically stacked asterisk-based copper resonators separated by dielectric layer of flame retardant type four and backed with a thin copper film. High-frequency structure simulator was used to simulate the absorber and to depict surface current distribution. The results showed that the absorber is operated at three narrow bands with high absorptivity of about 92, 100 and 100% at frequencies of 2.75, 4.3 and 9.5 GHz, respectively. The position of the resonant peaks can be effectively tuned by adjusting the geometry parameters of the structure, thereby achieving a multiband, polarization-independent and wide-angle absorber. The designed structure is important for the application of sensors, thermal images and in constructing broad multiband signals for electromagnetic compatibility/interference.

Silicon Antennas Metasurface Based Light Absorber With Quantitatively Adjustable Operating Frequency and Intensity

Metallic perfect absorbers have been widely studied due to the potential applications. Nevertheless, it is rather difficult to quantitatively adjust the absorption properties. Here, we propose a new multi-band absorber platform, which is with the capability to be quantitatively manipulated the resonant frequency and intensity. In this work, a metasurface consisting of silicon resonators is used to act as the optical coupling component, which can produce strong electromagnetic resonances. The maximal absorptance ∼100% is achieved in the four-band absorber. More importantly, the operation wavelengths show linear relationship to the resonator's height. Furthermore, the absorption efficiencies can be quantitatively controlled by the polarization angle of the incident light. These findings pave a new way for the precise-design absorbers and hold applications in artificially adjustable optoelectronic devices.

Tunable multi-band terahertz absorber using a single-layer square graphene ring structure with T-shaped graphene strips.

We numerically demonstrate a tunable dual-band terahertz metamaterial absorber (MA) with near-unity absorption using single-layer square graphene ring structure with T-shaped graphene strips. By periodically loading four T-shaped graphene strips to the square graphene ring periodic array without additionally increasing the size of MA device, the pre-existing resonant frequency will have a red shift and simultaneously a new resonance will be generated at higher frequency for achieving a dual-band MA. The two absorption peaks can be tuned to the resonant frequencies of interest by varying the parameters of the square graphene ring and T-shaped graphene strips. The operating frequency of the absorption spectrum can be also manipulated by adjusting the chemical potential of graphene, without changing their geometric parameters. Additionally, numerical results show that the proposed MA possesses polarization-independent and incident-angle-insensitive properties. To further extend the proposed structure's application with more absorption peaks, a tri-band MA is investigated through adding four more T-shaped graphene strips based on the dual-band absorber configuration. Therefore, our research work will be a good candidate for the design of various graphene-based tunable multi-band absorbers at different frequency regions with potential applications in optoelectronic devices and systems.

Manipulation of the near-field coupling in metamaterial for multi-band absorber

In this work, a metamaterial perfect absorber (MPA) in the microwave region is numerically and experimentally demonstrated based on the near-field coupling of resonators. By decreasing the distance between split-ring resonators (SRRs), the coupling of SRRs is enhanced. Consequently, the original resonance of SRRs splits, leading to a multi-band perfect absorption. In addition, the proposed multi-band MPA is polarization-insensitive and can maintain the high absorption in a wide range of incident angle. Our work is expected to provide a different way to create the potential devices by using the multi-band and the broadband MPAs.

A Perfect Absorber Based on Similar Fabry-Perot Four-Band in the Visible Range.

A simple metamaterial absorber is proposed to achieve near-perfect absorption in visible and near-infrared wavelengths. The absorber is composed of metal-dielectric-metal (MIM) three-layer structure. The materials of these three-layer structures are Au, SiO2, and Au. The top metal structure of the absorber is composed of hollow three-dimensional metal rings regularly arranged periodically. The results show that the high absorption efficiency at a specific wavelength is mainly due to the resonance of the Fabry–Perot effect (FP) in the intermediate layer of the dielectric medium, resulting in the resonance light being trapped in the middle layer, thus improving the absorption efficiency. The almost perfect multiband absorption, which is independent of polarization angle and insensitivity of incident angle, lends the absorber great application prospects for filtering and optoelectronics.

Wideband perfect absorption based on metamaterial in near-infrared range

A new design for expanding the absorption band of absorber in near-infrared range is theoretically proposed. This design is achieved by a layered cascade metamaterial structure that consists of four metamaterial slabs. A single metamaterial slab is made of a periodic array of tilted metal layers. The results show that the layered cascade structures obviously broaden the widths of the absorption bands. The transfer matrix is derived according to the special properties of the structure designed in the paper, and the absorption of the design is numerically simulated using the transfer matrix method. The influence of structural parameters on the absorption properties of metamaterial layer is analyzed: the locations of the absorption peaks are red-shifted with the increase of the inclination angles of the metal layers and the distance between the metal layers. The positions of the absorption peaks are blue-shifted with the increase of the thicknesses of the metal layers. The widths of the absorption bands increase while the centers of absorption peaks remain the same with the increase of the thicknesses of the metamaterial slabs. According to the above results, the metamaterial slabs which contain similar structural parameters are selected to constitute a layered cascade structure. The absorption of the layered cascade structures is numerically simulated and theoretically analyzed. The simulation results show that the absorption bands are obviously widened and the multi-band absorption peaks are found in the near-infrared region with the superposition of different suitable materials.

Experimental verification of multi-band metamaterial absorber with double structured layers

Microwave absorbers have been attracted much more attentions in both military and civil fields nowadays. In this paper, we present a multi-band metamaterial absorber with the excellent performances of wide-angle incidence and polarization insensitivity. The designed absorber is composed of two distinct metallic layers separated by a dielectric substrate. The simulated absorptions of the absorber are 92.9%, 92.5% and 98.5% at 5.92 GHz, 6.12 GHz and 8.54 GHz, respectively. The microwave experiments are performed to verify the simulations, and the measured results are in agreement with the simulations. Surface current distribution is illustrated to investigate the physics of absorption. We believe that the designed absorber has numerous potential applications in stealth, sensing, electromagnetic absorption and thermal detectors.

Absorbing properties of metamaterial dihedral corner reflector

In this paper, the absorbing property of metal-cross shaped metamaterial dihedral (MCMD) and cross-cross shaped metamaterial dihedral (CCMD) with the same parameters are investigated. In TE mode, the absorptivities are 91.1% at 9.17 GHz for MCMD and 99.7% at 9.20 GHz for CCMD. For MCMD and CCMD, the absorptivities are 90.5% and 99.8% at 9.2 and 9.17 GHz respectively for the TM polarized incident wave. The results of simulation and measurement show that CCMD has better multi-band absorption performance and lower radar cross-section than MCMD. Experiments have demonstrated the reflection coefficient can be utilized to analyze the electromagnetic characteristics of dihedral corner as well. The study of dihedral corner reflector is of great importance as it is used in modeling many areas such as stealth technology, electromagnetic compatibility and target recognition.

A Near-Infrared Multi-Band Perfect Absorber Based on 1D Gold Grating Fabry-Perot Structure

In recent years, multi-band perfect absorbers have great advantages in spectroscopy, infrared detection and other fields. Here we propose and use the finite-difference time-domain (FDTD) method to numerically calculate the multi-band absorber based on 1D gold grating Fabry-Perot (FP) structure. The full-wave simulation results show that under normal incident conditions, four different absorption peaks can be obtained in the near-infrared band and the absorption is all close to 1. These resonance peaks are derived from the third-, fourth-, fifth-, and sixth-order resonances of mode coupling in the FP cavity, respectively. The narrowest absorption bandwidth is 24 nm and the quality factor is 37.6. By adjusting the structural parameters of the grating, its spectrum can be adjusted and selected, and its working angle tolerance can reach 50°. In addition, numerical results show that the absorber can detect slight changes in the environment when used as a sensor. Therefore, our absorber has potential applications in the field of sensor detection.

Study on Temperature Adjustable Terahertz Metamaterial Absorber Based on Vanadium Dioxide

In the study of modern optics, the work of terahertz metamaterial absorbers is mostly multi-band perfect absorbers and ultra-wideband perfect absorbers. In contrast, in practical applications, metamaterial absorbers with adjustable resonance frequency or amplitude play an essential role in many forms. Here, we firstly designed an ultra-wideband terahertz metamaterial perfect absorber, achieving over 99% perfect absorption in the 6.6-8.9 THz range. Secondly, based on the absorber, phase change material VO2 was added to improve the structure, and three tunable terahertz metamaterial absorbers based on VO2 were designed, respectively realizing broadband movement and conversion between broadband and multi-band. Also, the terahertz absorber with dynamic tuning characteristics can flexibly control the absorption performance, providing an excellent platform for the realization of terahertz filtering, modulation, and so on.

基于光子晶体异质结构的磁可调石墨烯多带吸收

基于光子晶体异质结构的磁可调石墨烯多带吸收

Multi-band and broadband metamaterial perfect absorber based on conductive polymer and near-field coupling

We present a simple method for enhancing the bandwidth and absorptivity of metamaterial perfect absorber (MPA)-formed disk resonators. Utilizing low-conductivity polymer and near-field coupling of multi-band resonances, a 6.8 GHz broadband MPA is achieved with absorption over 90%. The proposed MPA also shows polarization-independent absorption behavior. Furthermore, the structural design is useful for making broadband MPA and can be applied to higher frequencies with a simple configuration.

Graphene-embedded broadband tunable metamaterial absorber in terahertz band

Numerous studies have been conducted to design terahertz broadband metamaterial absorbers for various applications, such as electromagnetic stealth, photodetection, and broadband communications. It remains a hot research topic to design metamaterial absorbers (MAs) to achieve broadband absorption while maintaining a wide range of tunability. Here, we present a novel design of graphene-embedded metamaterial functioning as a broadband tunable absorber based on the field reinforcement effect and plasmon resonance of graphene. With a stacked configuration, the absorptivity of the MA proposed in this paper can be as high as 90% in a wide range of 1.2 THz. By comparative analysis, we exhibit that the MA shows a relatively wider absorption bandwidth than the one without the embedded graphene, which discloses the significance of integrating graphene layer in our design. The detailed numerical calculations of the surface currents and electric field distributions are presented in this paper to better uncover the physical mechanisms of the broadband and multi-band absorption. Moreover, further numerical calculations show that the designed MA also demonstrates several other excellent properties, such as tunability, polarization insensitivity, incident angle insensitivity and outstanding structural parameters tolerance. The proposed graphene-embedded MA can be used in various promising applications, like smart sensors, broadband absorber and imaging devices.

Realizing the Multiband Absorption in the Visible Region via the Collaboration of Fabry–Pérot, Propagating Surface Plasmons, and Void Plasmons Resonance Effects

Herein, a novel method is proposed to achieve multiband absorption in the visible region. Different from the conventional metal–insulator–metal (MIM) based multiband absorbers which absorb normally incident plane waves at different frequencies based on the impedance matching effect, the multiband absorption proposed here is achieved through the coupling effects of Fabry–Pérot (FP), propagating surface plasmons (PSPs), and void plasmons (VPs) resonance. A clear physical image is unveiled by means of numerical simulations through the geometric parameters corresponding to various resonance modes. The absorption features can be easily controlled by tuning the period of square lattice, porosity of unit cell in the top silver layer, and the film thickness of the middle layer. The presented study on the physical mechanism of the multiband absorption is believed to be beneficial for designing new‐generation absorbers for suitable novel applications.

Fundamental properties of delafossite CuFeO2 as photocatalyst for solar energy conversion

Photocatalysis technology can meet the two global issues of energy shortage and environmental pollution at the same time. Due to the unique layered quasi-two-dimensional superlattice structure, and the specific functions of structural motifs, delafossite compounds have become a popular candidate family for photoelectric conversion applications. In this article, 3R-delafossite CuFeO2 microcrystals with complete stoichiometry, high crystallinity and purity, uniform composition, cubic size of ∼1.47 μm, single crystal phase were obtain by the optimized hydrothermal process. Combined with optical measurement and density functional theory calculation, the electron transition mechanism of CuFeO2 was analyzed in depth and systematically. CuFeO2 has obvious multi-band spectral absorption characteristics, which are helpful to clarify the controversy about band gap values of CuFeO2. CuFeO2 microcrystals exhibit potential hydrogen production from photocatalytic water-splitting to and photocatalytic degradation of pollutants. Tetracycline hydrochloride degradation testing was adopted to further verify the potential of CuFeO2 microcrystals for wastewater purification. CuFeO2 microcrystals not only exhibit excellent photocatalytic degradation performance, but also present Fenton reaction activity in dark conditions after adding H2O2. It is particularly important that the removal rate of tetracycline hydrochloride was significantly enhanced by the coupling of photocatalytic reaction and Fenton reaction, suggesting that CuFeO2 emerges excellent Photo-Fenton reaction activity. Finally, this article not only provides the fundamental physical chemical properties of CuFeO2 for solar energy conversion, but also points out the development direction of further improving the efficiency.

Coordinated multi-band angle insensitive selection absorber based on graphene metamaterials.

In this paper, we propose a tunable, multi-band, selective absorber composed of multiple layers. Each layer consisted of SiO2/graphene/SiC, and a layer of silver was used as the ground plane of the entire structure. Simulation results show that we can passively and actively coordinate the resonant frequency of the perfect absorption peak by changing the geometric parameters of the array and the Fermi level of the graphene. The absorber is not sensitive to the angle of incidence and the direction of polarization. We propose a theoretical basis for the formation of multiple absorption peaks. The theoretical calculations are in good agreement with the simulation results. In addition, we simulated the three- and four-layer structures. The results show that in the terahertz (THz) band, composite structures of three and four layers can obtain three and four perfect absorption peaks, respectively. Our results provide new insights into the THz band of harmonizable multi-band absorbers that can be applied to THz imaging to coordinate sensors and other optoelectronic devices.

High-Order Resonance in a Multiband Metamaterial Absorber

The typical metamaterial absorber includes a single absorption band, based on a single resonator. We note that four or more absorption peaks are formed by only a single meta-atom, that is, a widely used cut-wire (CW) structure. Through a differential equivalent-circuit approach, the absorption mechanism of odd-order magnetic resonance and electric resonance in CW was elucidated by one unique circuit. With electrical interaction between adjacent meta-atoms taken into consideration, the absorption properties of a CW structure are proved as a function of the geometric parameters, and are verified through numerical and experimental results. By obtaining the experimental results of disk-structured meta-atoms showing higher than third-order magnetic resonance absorption bands, the existence and absorption properties of higher-order magnetic resonances for meta-atoms in a non-CW metamaterial are shown to be coherent with those of a CW structure. This presence of multiple absorption peaks opens the possibility for multiband metamaterial absorbers not only in the GHz but also in the visible range.

Super compact ultrathin quad‐band with wide angle stability polarization independent metamaterial absorber

AbstractIn this article, a compact ultrathin polarization‐insensitive wide‐angle metamaterial‐based microwave absorber with quad‐band characteristics is presented. The designed microwave absorber provides simulated peak absorption of 99.16%, 98.21%, 98.32%, and 99.76% at 3.7 GHz, 6.4 GHz, 10.7 GHz, and 14.3 GHz, respectively. The absorption frequency lies in microwave frequency bands of S, C, X, and Ku. The unit cell of the proposed microwave absorber consists of two diagonally connected closed ring resonator (CRR) along with one metallic patch enclosed by the inner CRR. Each side of the enclosed patch is connected with inner CRR at the center of length. The unit cell of the proposed 0.0197λlowest (wavelength at lowest frequency) thick multiband absorber fits in a volume of 8 × 8 × 1.6 mm3. The proposed metamaterial‐based microwave absorber exhibits identical absorption characteristics for both transverse‐electric and transverse‐magnetic polarized radiations and also provides well peak absorption for an oblique incidence up to 75°. Finally, the absorber is fabricated and experimental result validates simulated one.

Effect of slit width on surface plasmon resonance

In this paper, a hybrid resonator composed of an all-metal grating made of copper and a dielectric cavity filled with SiO2 between slits is simulated and calculated by the finite-difference time-domain method (FDTD). We study the effect of slit width on surface plasmon resonance by changing the size of the dielectric cavity. In the case of parallel light incident vertically, the resonator can achieve multi-band absorption and have a perfect absorption peak. The dielectric cavity can not only localize the incident light wave, but also enhance the effect of surface plasmon of metal structure. Our results can be widely used in the field of surface plasmon, which is beneficial to the development of surface plasmon resonators in sensing and detection.

Near-infrared multi-narrowband absorber based on plasmonic nanopillar metamaterial

A multi-narrowband absorber composed of gold nanopillar metamaterial is numerically designed and investigated in this paper. Full-wave simulations indicate that five distinctive narrow-band absorption peaks with the maximum absorption rate up to 99.3% and the lowest above 80% can be achieved in the near-infrared regime at normal incidence. Polarization dependence over a incident angular range of ± 30°is also researched. We demonstrate the spectroscopic tunability of our absorber by adjusting the structural parameters of the gold nanopillar array. Physical mechanism of the multi-narrowband absorption is construed as the vertical Fabry–Perot-like gap plasmonic resonances induced by electric and magnetic dipolar polaritons. Compared to the previous researches on multi-band absorbers, we realize no less than five near-infrared narrow absorption bands by utilizing just simple configuration with single pattern, which makes considerable application potential in the fields of absorption filtering and spectroscopic sensing.