In this paper, the idea of square fractal geometry has been utilized to introduce a tunable wideband graphene-based perfect plasmonic absorber in the near-infrared region. It consists of a MgF2 layer and an array of gold squares fractal loaded on a graphene layer. In the designed absorber a single layer of graphene has been used instead of multilayered graphene structures. The structure is polarization-insensitive under normal incidence due to the geometric symmetry. The absorption and bandwidth of the structure are almost insensitive to the incident angle up to 15° and 45° for TE and TM polarizations, respectively. Moreover, by choosing appropriate structural parameters, the resonance wavelength of the desired plasmonic absorber can be controlled. The absorption of the introduced structure can be tuned by changing the chemical potential of the graphene. Therefore, the proposed fractal absorber can act as switch and inverter at λ = 1995 nm. Furthermore, the equivalent circuit model of the absorber has been derived to confirm the validity of the simulation results. The superiorities of our fractal absorber are wide full-width at half-maximum of 406 nm, multi-applicant, perfect absorption, and fabrication feasibility due to the simple structure with the maximum absorption tolerance error of 5.12%.
相似文献In this article, we demonstrate a tunable ultra-broadband metamaterial absorber (TUMA) in terahertz (THz) band which is based on the multilayered structure composed of an Au reflective layer, polyimide dielectric layers, and vanadium dioxide (VO2) periodic structures, respectively. We gain the tunable absorption spectra because of the room temperature phased-changed character of VO2. The relative bandwidth reaches to 81.2% and the absorption rate is over 90% at the frequency range of 1.63–3.86 THz when the temperature (t1) is 350 K, but when t1 = 300 K, the presented absorber is acted as a reflector whose absorption is small besides the frequency points of 9.75 THz and 9.81 THz. For the sake of comprehending the physical mechanism in-depth, the electric field (E-field) diagrams, the surface current distributions and the power loss density (PLD) of the TUMA are investigated. The influences of structural arguments and incident angle (θ) on the absorption are also analyzed. The emulated consequences show that the absorption spectrum can be regulated by changing structural parameters and incident angle and the tunable absorption regions can be obtained by altering the external temperature.
相似文献In this paper, a graphene-based tunable multi-band terahertz absorber is proposed and numerically investigated. The proposed absorber can achieve perfect absorption within both sharp and ultra-broadband absorption spectra. This wide range of absorption is gathered through a unique combination of periodically cross- and square-shaped dielectrics sandwiched between two graphene sheets; the latter enables it to offer more absorption in comparison with the traditional single-layer graphene structures. The aforementioned top layer is mounted on a gold plate separated by a Topas layer with zero volume loss. Furthermore, in our proposed approach, we investigated the possibility of changing the shapes and sizes of the dielectric layers instead of the geometry of the graphene layers to alleviate the edge effects and manufacturing complications. In numerical simulations, parameters, such as graphene Fermi energy and the dimensions of the proposed dielectric layout, have been optimally tuned to reach perfect absorption. We have verified that the performance of our dielectric layout called fishnet, with two widely investigated dielectric layouts in the literature (namely, cross-shaped and frame-and-square). Our results demonstrate two absorption bands with near-unity absorbance at frequencies of 1.6–2.3 and 4.2–4.9 THz, with absorption efficiency of 98% in 1.96 and 4.62 THz, respectively. Moreover, a broadband absorption in the 7.77–9.78 THz is observed with an absorption efficiency of 99.6% that was attained in 8.44–9.11 THz. Finally, the versatility provided by the tunability of three operation bands of the absorber makes it a great candidate for integration into terahertz optoelectronic devices.
相似文献In this paper, we demonstrate a dual-band metamaterial perfect absorber based on a Ag-dielectric-Ag multilayer nanostructure. The structure of top metal film covers nanoring grooves array. A dielectric layer has a function of confining electromagnetic fields. Theoretical analysis shows that two absorption peaks (1059 nm and 1304 nm) with the absorption of 99.2% and 99.9% have been achieved, respectively. The physical origin of perfect absorption peaks are related to the Fabry-Perot resonance effect and localized surface plasmon resonance (LSPR) of the nanoring grooves. Its perfect absorption and resonance wavelength can be well regulated by adjusting the relevant structural parameters. Additionally, the absorber demonstrates good operation angle-polarization-tolerance at wide incident angles (0–60°). We believe that our design has a promising application in plasmon-enhanced photovoltaic, optical absorption switching, and modulator optical communications in the infrared regime.
相似文献Ensuring a good trade-off between high-quality factor (Q-factor) and polarization independency is a key challenge for designing practicable terahertz metamaterial devices. We propose a symmetric composite aluminum-structured metamaterial absorber to achieve high Q-factor beyond 80 and near-unity absorbance of arbitrary polarization waves in the terahertz regime. Ultrahigh Q-factor reaches 84, and polarization-independent absorption is as high as 99% for resonant frequency tuning from 7.58 to 8.97 THz, covering 14% of the standard THz gap. The geometric effect of the symmetric sublattice on resonant frequency tuning is analyzed. The large Q-factor and strong absorption by oblique incidence is discussed. Designed high-Q metamaterial perfect absorber has various applications, including terahertz hyperspectral imaging, filtering, and sensing.
相似文献We present a multi-band terahertz absorber formed by periodic square metallic ribbon with T-shaped gap and a metallic ground plane separated by a dielectric layer. It is demonstrated that absorption spectra of the proposed structure consist of four absorption peaks located at 1.12, 2.49, 3.45, and 3.91 THz with high absorption coefficients of 98.0, 98.9, 98.7, and 99.6%, respectively. It is demonstrated that the proposed absorber has the tunability from single-band to broadband by changing the length of square metallic ribbon and we can also select or tune the frequencies which we want to use by changing polarization angles. Importantly, the quality factor Q at 3.91 THz is 30.1, which is 5.6 times higher than that of 1.12 THz. These results indicate that the proposed absorber has a promising potential for devices, such as detection, sensing, and imaging.
相似文献The need for an easy to fabricate perfect and narrowband light absorber in the visible range of electromagnetic (EM) spectrum has always been in demand for many scientific and device applications. Here, we propose a metal-dielectric-metal (MDM) 1-D grating plasmonic structure as a perfect narrow band light absorber in the visible and its application in glucose detection. The proposed structure consists of a 1- D grating of gold on the top of a dielectric layer on a gold film. Optimization for dielectric grating index (n), grating thickness (t), grating width (W), and grating period (P) has been done to improve the performance of plasmonic structure by calculating its quality factor and figure-of-merit (FOM). The optimized plasmonic structure behaves as a perfect narrowband light absorber. The flexibility to work at a specific wavelength is also offered by the proposed structure through an appropriate selection of the geometrical parameters and refractive index of the dielectric grating. The equivalent RC model is used to understand different components of the proposed structure on the optical response. The absorption response of the structure is invariant to the incident angle. Moreover, the calculated absorbance of the proposed plasmonic structure is ~ 100% with a narrow full-width half maxima (FWHM) of ~ 2.8 nm. We have numerically demonstrated a potential application of the proposed MDM absorber as a plasmonic glucose sensor in the visible range with detection sensitivity in the range of 140 to 195 nm/RIU.
相似文献A tunable multi-band metamaterial perfect absorber is designed in this paper. The absorber made of a composite array of gold elliptical and circular disks on a thick metallic substrate, separated by a thin dielectric spacer. The absorptivity and the field enhancement of proposed structures are numerically investigated by the finite difference time domain method. Three absorption peaks (1.15, 1.55, and 2.05 μm) with the maximal absorption of 99.2, 99.7, and 97.3% have been achieved, respectively. By altering the dimensions of associated geometric parameters in the structure, three resonance wavelengths can be tuned individually. Physical mechanism of the multi-band absorption is construed as the resonance of magnetic polaritons. And the absorber exhibits the characteristics that are insensitive to the polarization angle due to its symmetry. The research results can have access to selective control of thermal radiation and the design of multi-band photodetectors.
相似文献In this article, a terahertz absorber tuned by temperature field with a newfangled structure is presented, which comprises the mercury resonators. In this scheme, temperature (T) build-up will lead the mercury stored in the bottom slot to expand through the columniform hole and be full of the upper central cross container, which can transform the absorption bands of such an absorber. The simulated results manifest that when T is increased from 0 to 25 °C, the dual-frequency absorption points (2.59 THz, 3.03 THz) and a narrow absorption region over 90% (6.54–7.10 THz), whose relative bandwidth (RB) is 7.9%, will be tailored to a single-frequency point absorption (3.12 THz) and a broadband absorption area (6.00–7.21 THz, and RB = 18.3%). For figuring out the property of the absorber mentioned above, the impacts of incident and polarization angles along with some relevant parameters of the structure on the absorption property are investigated. In addition, for plainly expounding the physical mechanism of absorption, the distributions of the surface current diagrams of the presented absorber are calculated, as well as the electric field diagrams, the magnetic field diagrams, the power loss density diagrams, and the power flow density diagrams. The proffered scheme in this article may offer a novel idea for realizing the reconfigurable absorbers.
相似文献In this research, a perfect absorber based on an Au-ZnO-Al structure was studied numerically. The wavelength-selective and angle-independent characteristics of the device were demonstrated by simulation. The roles of the top metallic layer and the middle dielectric layer in producing a wavelength-selective perfect absorber with a high quality factor were investigated. The direction for further improving the quality factor is also pointed out in this paper. The research will be helpful for understanding the origination of perfect absorption in these types of metal-insulator-metal structures and producing a color filter with a high quality factor.
相似文献In this study, we present a high-performance tunable plasmonic absorber based on metal-insulator-metal nanostructures. High absorption is supported over a wide range of wavelengths, which is retained well at a very wide range of incident angles too. The coupling process occurs with high absorption efficiency of ∼ 99% by tuning the thickness of the dielectric layer. In addition, a complex trapezoidal nanostructure based on simple metal-insulator-metal structures by stacking different widths of Cu strip-nanostructures in the vertical direction has been put forward to enhance light absorption based on selective absorption. A trapezoidal sample has been designed with a solar absorption as high as 95% at wavelengths ranging from 300 nm to 2000 nm for different operating temperatures. Furthermore, the optical absorber has a very simple geometric structure and is easy to integrate into complex photonic devices. Perfect absorption and easy fabrication of the metal-insulator-metal structure make it an attractive device in numerous photonic applications.
相似文献A three-dimensional cross-shaped fractal metamaterial absorber with ultra-wide wavelength band, polarization-independence and wide-angle, is numerically investigated by the finite-difference time-domain method. In this absorber, the solar energy is trapped by the cross-shaped fractal of the upper layer, and the Si-ring filled with iron in the middle layer and the wavelength band can be broadened by the self-similarity of fractal structure. The absorber exhibits absorptivity higher than 91% for the wavelengths from 400 to 2000 nm and an absorption bandwidth of about 133%. Furthermore, the proposed absorber realizes polarization independence, and the maximum incident angle is 76°. However, as the iron material applied in the nano-metamaterial absorber (NMA) can be easily oxidized and rusted, it is replaced by nickel with characteristics such as corrosion resistance and high-temperature resistance; thus, an improved NMA is obtained. The improved absorber not only eliminates the corrosion-prone defects of the above proposed structure but also maintains polarization independence and high absorption and widens the angle of incidence up to 79° and thereby can be applied in many areas, such as solar energy harvesting.
相似文献In this paper, a non-structured graphene sheet loaded with a sinusoidal-patterned dielectric is introduced as an ultra-wideband metamaterial absorber in terahertz regime. Regardless of conventional structures with multilayered-graphene, a single layer sheet of non-structured graphene is used whereas the proposed structure benefits from dielectric width modulation and cavity method in order to excite continuous graphene plasmon resonances. The structure comprises four layers that two Fabry-Perot cavity mirrors are constructed by upper sinusoidal-patterned dielectric and a gold film. Full wave simulation results demonstrate that a broadband over 90% absorption with absolute bandwidth of 6.58 THz and central frequency of 3.97 THz is achieved under normal TE/TM incident plane wave. The designed structure yields 166% relative bandwidth. According to the symmetric configuration, the absorption spectra of mentioned polarizations are thoroughly close to each other resulting to a polarization insensitive structure. The stability of bandwidth and absorbance of the structure versus angle of incidence, θ, up to 35°/65° for TM/TE polarizations, respectively, and azimuth angle, φ, shows an interesting capability for utilization as detectors and sensors. The simple geometry of utilized graphene layer results in easy fabrication. The designed structure has wideband absorption in THz regime. Moreover, it is more compact than conventional broadband THz absorbers.
相似文献This paper presents a simple multi-band metamaterial absorber for terahertz applications. The unit cell of the proposed structure consists of a single square ring having gaps at the centers on three of its sides. The proposed absorber produces three absorption bands for all polarizations and hence the design can be considered as insensitive to polarization variation. It provides an average absorption of 96.92% for the TE polarization with a peak absorption of 99.44% at 3.87 THz and for the TM polarization, it provides an average absorption of 98.4% with a peak absorption of 99.86% at 3.87 THz. An additional absorption peak is observed for the TE polarization at 1.055 THz that gradually diminishes with the increase in polarization angle and completely vanishes for the TM polarization. Thus, the structure displays a hybrid polarization response with polarization insensitivity in three bands and polarization sensitivity in one band. Parametric analysis has been carried out validating the optimal selection of the design parameters. The simplicity of the design and its combined polarization sensitive and polarization insensitive absorption characteristics can find tremendous applications in the field of terahertz imaging and sensing.
相似文献The objective of this study is to enhance the efficiency of copper indium gallium selenide (CIGS) solar cells. To accomplish that, composition grading of absorber layer was carried out by using SILVACO’s technology aided computer design (TCAD) ATLAS program. Results showed a meaningful improvement of output parameters including open-circuit voltage (Voc), short-circuit current (Isc), fill factor (FF), and power conversion efficiency (η). For further performance improvement of the cell, Au plasmonic scattering nanoparticles were loaded on the top of the ZnO window layer. Plasmonic nanoparticles can restrict, absorb, navigate, or scatter the incident light. By using the spherical Au nanoparticles, a very good increase in the light absorption in the cell over the reference planar CIGS solar cell was observed. The highest η = 19.01% was achieved for the designed ultra-thin bandgap-graded CIGS solar cell decorated by Au nanoparticles.
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