In this paper, a tri-layer metamaterial composed of a split-disk structure array sandwiched with two layers of twisted sub-wavelength metal grating is proposed and investigated numerically in terahertz region. The numerical results exhibit that linear polarization conversion via diode-like asymmetric transmission for terahertz waves within ultra-broadband frequency range is achieved due to Fabry-Perot-like resonance. In our design, the conversion polarization transmission coefficient for normal incidence is greater than 90 % in the range of 0.23–1.17 THz, equivalent to 134.3 % relative bandwidth. The physical mechanism of the broadband linear polarization conversion effect is further illustrated by simulated electrical field distributions.
相似文献We design and numerically demonstrate a novel metamaterial structure consisting of a dielectric layer sandwiched between two silver films and is perforated with two kinds of square-shaped holes at different angles, which is a dual-band double-negative (each band possesses simultaneously negative permittivity and permeability) metamaterial with broad NRI bands in mid-infrared region(3–30 μm). The broadband of NRI contributed to the strong magnetic resonance caused by the excitation of surface plasmon polaritons. The influence of the number of square-shaped holes on the properties of the designed structures are also investigated by analyzing and comparing the transmission, permeability, permittivity, refractive index, and figure of merit. Then, by optimizing the structural parameters, the proposed structure exhibits a negative band with a figure of merit of 3.3, which is to our knowledge larger than previously reported plasmonic metamaterial in mid-infrared region(M-IR). The value of negative refractive index(NRI) reaches −6 and the bandwidth of NRI can reach up to 4.2 THz in the low-frequency band of M-IR region, which is the widest NRI band in M-IR spectrum at present as far as we know. Moreover, the metamaterial structure is simple and easy to be manufactured with standard fabrication techniques. This work will be very meaningful in designing dual-band negative-index material with broad NRI band and low loss. Finally, the proposed metamaterial has huge potential applications in multiband or broadband devices.
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Toroidal resonance of planar structure is feasible and interesting for many appealing applications. We numerically and experimentally investigated the toroidal resonances in a planar metamaterial comprising core-shell structures and its constituent core and shell components at THz frequencies. The investigated structure demonstrated sharp toroidal and hybrid toroidal resonance modes in 0.2–0.3 THz range. Our analysis showed that these modes could be explained by the interaction of resonance toroidal modes of the shell and core components. The response of the investigated planar core-shell toroidal metasurface is notably geometry dependent and can be easily tuned by tailoring the device geometry. Presented work can be used for advanced THz photonics applications, including precise bio-sensing, narrow-band filters, fast-switching, and modulation.
相似文献In this article, the design of a frequency reconfigurable broadband THz antenna based on vanadium dioxide (VO2) is investigated. Instead of being fed by the microstrip line directly, a windmill-shaped feeding structure is designed to provide a proximity-coupled feeding method. Many modes with contiguous resonant frequencies can be excited to obtain the wideband performance. The proposed antenna combines gold with metamaterial VO2. Thanks to insulator-metal phase transition characteristic of VO2 at phase transition temperature (68 °C), we can change the length of the resonant branches to realize frequency reconfiguration by changing the external temperature (T). The simulated results illustrate that when T = 50 °C (State I), such an antenna has a bandwidth of 35.2% (7.01–10 THz) with S11 below − 10 dB, and a maximum gain of 6.62 dBic. When T = 80 °C (State II), it has a bandwidth of 21.8% (5.77–7.18 THz) with S11 below − 10 dB, and a maximum gain of 4.49 dBic. Thus, we realize a design of a proximity-coupled antenna with reconfigurable wideband over the THz band.
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, 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A dielectric metamaterial absorber has been proposed, which consists of fractal-like structure and conductive sheet. The fractal-like structure is made by the high permittivity dielectric and also is covered by the conductive sheet. Absorptivity of such a dielectric metamaterial absorber is 99.1%, which can be found at 10.196 GHz; meanwhile, the absorber is polarization insensitive. To enhance the bandwidth of absorber, a novel absorber also is proposed, whose bandwidth is 0.566 GHz, which ranges from 9.752 to 10.318 GHz, and relative bandwidth is 5.64%. The maximum absorptivity can reach to 99.8%, and the proposed absorber also is polarization insensitive. In the meantime, the absorber shows excellent performance which is incident angle insensitive; when the incident angle is increased to 70°, the absorptivity is larger than 75%.
相似文献Three layers of periodic artificial metamaterial sensing structure (including the upper metal particles, intermediate dielectric layer, and the lower reflective layer) with ultra-narrow band absorption were designed. The resonance characteristics and sensing properties were analyzed by the finite difference time domain (FDTD) method. The effect of localized surface plasmon resonance (LSPR) was obviously observed at the resonance wavelength of 911 nm, and it achieves nearly perfect absorption of exceeding 98% with a full width at half maximum (FWHM) of 3.5 nm. In addition, a wavelength sensitivity of 542 nm/RIU with a figure of merit (FOM) of 155 was obtained in the refractive index (RI) range from 1.00 to 1.35, which has a wide range of applications. The results show that the proposed structure has high absorption and RI sensitivity, which is suitable for bioengineering and medical detection.
相似文献A five-band polarization-insensitive perfect metamaterial absorber (PMA) is reported in this paper for THz detection and sensing applications. The proposed absorber is constructed using interconnected circular ring elements enclosed by a square loop. The ring elements are interconnected using short strip lines which increases the electrical length to offer resonance at the lower frequencies of the THz regime without increasing the electrical length. The proposed absorber has a footprint of 0.12 λeff?×?0.12 λeff where λeff is the effective wavelength calculated at the lowest operating frequency. The absorber provides 92%, 84%, 90%, 100%, and 100% absorption at 0.24, 0.56, 0.65, 0.82, and 0.95 THz, respectively. The proposed structure offers structural symmetry, and hence, it is polarization-insensitive. The proposed five-band absorber has good angular stability consistent with many research works reported in the literature and has a small frequency ratio of 1:2.3:2.7:3.4:3.9. The proposed absorber can be used as a permittivity sensor and its sensitivity is estimated to vary from 5.8 GHz/permittivity unit (PU) to 23.56 GHz/PU.
相似文献A metal nanowire placed in a dielectric hole is proposed to guide THz modified surface plasmon polaritons (MSPPs). In theory, the MSPP waveguide can guide THz wave with nano-scale mode width (570 nm) and simultaneously ultra-long propagation distance (2.4 m). Compared with conventional surface plasmon polaritons (SPPs) on a bare metal nanowire, the MSPPs’ mode nanoconfinement can be maintained by keeping a part of the mode field nearly unchanged. On the other hand, by modifying the rest of the mode field, the THz power inside the metal nanowire can be significantly reduced for MSPPs, which dramatically decreases the propagation loss (3 orders of magnitude).
相似文献Due to the advantage of improving the sensing performance, narrow-band metamaterial perfect absorbers (MPAs) have attracted much attention in the sensor field. Here, we propose an ultra-narrow-band infrared absorber (UNBIRA) based on localized surface plasmon resonance. The peak absorption of the UNBIRA exceeds 99% with the full width at half maximum (FWHM) of 1.94 nm and 6.32 nm for transverse electric (TE) wave and transverse magnetic (TM) wave in 1.5–1.8 μm. The corresponding Q-factors for TE wave and TM wave are 817 and 266, respectively. When used as an infrared refractive index sensor, the sensitivity of UNBIRA is as high as 1632.5 nm/RIU for TE wave and 1647.5 nm/RIU for TM wave. Accordingly, the figure of merits (FOMs) of 816.2/RIU for TE wave and 260.7/RIU for TM wave are achieved. This UNBIRA possesses a simple geometry structure and an excellent sensing performance, implying a great potential for application of ultra-narrow infrared sensing or detecting.
相似文献Terahertz metamaterial absorbers (MMA) have found wide scope of research prospective, remarkably in the development of multiband absorbers. Considerable applications are established using these multiband absorbers in THz imaging, wireless communication and bolometric detectors. The MMA was built on a GaAs substrate of 30 µm thickness and the hexagonal metallic pattern was etched out on a gold layer of 0.4 µm thickness on the top surface. The underlying ground layer is metallic backed. This design realizes the multiband (9-bands) of absorption in the spectral region from 0.56 to 0.92 THz. The multiband absorption mechanism of the absorber was examined by electric field dispersion analysis and impedance matching concept. From the established results, the absorber exhibits nine bands within a narrow frequency range and secures promising applications in hyperspectral imaging, clinical sensing and detection.
相似文献A novel three-dimensional terahertz metamaterial by integrating planar and standup resonators on a sapphire substrate is proposed. This structure shows the capability of dynamic-shifting single- and double-negative refractive index bands under temperature control. When the temperature rises from 160 K to 290 K, the single- and double-negative bands of the metamaterials exhibit blue-shift, which is attributed by the simultaneously tuning of the electromagnetic resonance frequencies of the resonators. If the temperature rises to 300 K, the bianisotropy of the metamaterials increases rapidly, while it performs stable between 160 K and 290 K.
相似文献In this paper, on the basis of metamaterial, a simply single-layer and tunable reflective polarization converter has been numerically investigated, which is composed of vanadium dioxide film (VO2) component combined with two-corner-cut square patch cut by a slit and reflective ground layer. Calculated results obtained by the CST Microwave Studio show that in the frequency of 2.22–5.42 THz, high polarization conversion efficiency (polarization conversion ratio (PCR) above 90%) can be normally achieved at the temperature about 25 °C for both the linearly and circularly polarized wave incidence. At the same time, the cross-polarization converter can be analyzed and obtained from the view on qualitative variable of polarization azimuth angle (θ) and ellipticity (η). Moreover, a tunable polarization conversion property can be realized by the designed device with vanadium dioxide utilizing changing different conductivities. Even so, to be demonstrated, the physical mechanism of the merits of controllability and uniqueness has been discussed by the distributions of current densities and E-field map, respectively. According to the prior results, the designed metamaterial could be applied in the area of temperature-controlled sensing, THz wireless communication, tunable polarized devices.
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The polarization characteristics of high-birefringence photonic crystal fiber (HB-PCF) selectively coated with silver layers are numerically investigated using the full-vector finite element method (FEM). The fundamental mode coupling properties and polarization splitting effect are discussed in detail. Results show that the resonance wavelength, resonance strength, and splitting distance between two polarized modes can be adjusted significantly by changing the fiber structure, the diameter of silver rings, and the thickness of silver layers. A single-polarization filter at 1310 nm bands is proposed with the corresponding loss 500 dB/cm and full width half maximum (FWHM) only 23 nm. This work is very helpful for further studies in polarization-dependent wavelength-selective applications or other fiber-based plasmonic devices.
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