Showing papers on "Metamaterial absorber published in 2020"

Design of a dual-band terahertz metamaterial absorber using two identical square patches for sensing application

Abstract: A dual-band terahertz metamaterial absorber composed of two identical square metallic patches and an insulating medium layer on top of a continuous metallic ground is demonstrated. Two resonance peaks (labeled A and B) with near 100% absorbance are obtained, of which peak A derived from the localized resonance of the two square patches has a line-width of 0.2571 THz and quality factor of 6.9156, while peak B which resulted from the hybrid coupling of the localized resonance of the two square patches and surface lattice resonance of the device has a very narrow line-width of 0.0083 THz and large quality factor of 296.2771. Narrow line-width and large quality factor have important prospects in sensing application. Based on this, the sensing performance of the device is explored; it is revealed that peak B exhibits highly sensitive sensing ability (including a sensing sensitivity of 1.9010 THz per RIU and figure of merit of 229.04) in terms of the surrounding index. In addition, the influence of structural parameters on the absorption performance is discussed to further verify the formation mechanism of these two absorption peaks.

A Broadband Tunable Terahertz Metamaterial Absorber Based on Single-Layer Complementary Gammadion-Shaped Graphene.

Abstract: We present a simple design of a broadband tunable metamaterial absorber (MMA) in the terahertz (THz) region, which consists of a single layer complementary gammadion-shaped (CGS) graphene sheet and a polydimethylsiloxane (PDMS) dielectric substrate placed on a continuous metal film. The Fermi energy level (Ef) of the graphene can be modulated dynamically by the applied DC bias voltage, which enables us to electrically control the absorption performance of the proposed MMA flexibly. When Ef = 0.8 eV, the relative bandwidth of the proposed MMA, which represents the frequency region of absorption beyond 90%, can reaches its maximal value of 72.1%. Simulated electric field distributions reveal that the broadband absorption mainly originates from the excitation of surface plasmon polaritons (SPPs) on the CGS graphene sheet. Furthermore, the proposed MMA is polarization-insensitive and has wide angles for both transverse-electric (TE) and transverse-magnetic (TM) waves in the broadband frequency range. The broadband absorption capacity of the designed MMA can be effectively adjusted by varying the Fermi energy level of graphene. Lastly, the absorbance of the MMA can be adjusted from 42% to 99.1% by changing the Ef from 0 eV to 0.8 eV, which is in agreement with the theoretical calculation by using the interference 41theory. Due to its simple structure and flexible tunability, the proposed MMA has potential application prospects in tunable filtering, modulators, sensing, and other multispectral devices.

A dual-band metamaterial absorber for graphene surface plasmon resonance at terahertz frequency

Abstract: In this paper, we present a dual-band metamaterial absorber for graphene surface plasmon resonance at terahertz frequency. We use the finite difference time domain (FDTD) method to study the absorption characteristics of the homocentric graphene ring and disk nanostructure. These simulation results show that the change of the geometrical parameters and the substrate thickness of the nanostructure can change the absorption characteristics and the emergence of dual-band absorption peaks. Moreover, we study the field distribution of nanodisks with different radius in detail. By changing the Fermi level of graphene, the wavelength of their absorption peaks can be adjusted flexibly. In addition, the proposed dual-band absorber also shows a good angle tolerance for both TE and TM polarizations. By calculation the surface-filled water (n = 1.332) and 25% aqueous glucose solution (n = 1.372) for the metamaterial absorber, the sensitivities of mode I and mode II are 5.0 μm/RIU and 15.0 μm/RIU. These research results will have broad application prospects for sensing and spatial light modulators.

Dual-controlled switchable broadband terahertz absorber based on a graphene-vanadium dioxide metamaterial

Abstract: We propose a dual-controlled switchable broadband terahertz (THz) metamaterial absorber based on a hybrid of vanadium dioxide (VO2) and graphene that demonstrates strong polarization-independent characteristics and works well at a wide range of incidence angles. The peak absorptance of the proposed absorber can be tuned from 26 to 99.2% by changing the Fermi energy of the graphene; the absorptance can be dynamically tuned from 9 to 99.2% by adjusting the conductivity of the vanadium dioxide because of its unique insulator-to-metal transition characteristic. Using these two independent controls in tandem, we found that the state of the proposed absorber can be switched from absorption (>96%) to reflection (>73.5%), and the transmittance can be tuned from 0% to 65% while maintaining broad bandwidth (1.05-1.6 THz), resulting in a better-performing switchable broadband terahertz absorber. Furthermore, we have provided a discussion of the interference theory in which the physical mechanism of the absorption is explained from an optical point of view. The absorber achieves dual-controlled absorptance switching via two independently controllable pathways, offering a new method for switching and modulation of broadband THz radiation.

Triple-band perfect metamaterial absorber with good operating angle polarization tolerance based on split ring arrays

Abstract: In this paper, a triple-band perfect metamaterial absorber based on Cu-dielectric-Cu triple-layer nanostructure is reported. The top metal film structure consists of a ring and four pairs of capacitor plates, which has a frequency selection effect, allowing the absorber to resonate in the near infrared range. Theoretical study shows that the absorption of the three absorption peaks (872.54 nm, 1008.69 nm and 1138.62 nm) are 87.1%, 99.9% and 99.6%, respectively. The average absorption is 95.53%, including two perfect absorption peaks. Changing the structural parameters can affect its absorption peaks and resonant wavelengths. At the same time, due to the high symmetry of the absorber, it is not sensitive to the polarization angle and incident angle. Whether in the TE mode or the TM mode, the absorber at a wide incident angle (0-60°) also exhibits good operating angle polarization tolerance. Therefore, the perfect metamaterial absorber we designed can be widely used in sensing.

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

Abstract: 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.

Study on Temperature Adjustable Terahertz Metamaterial Absorber Based on Vanadium Dioxide

Abstract: 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.

A Tunable Triple-Band Near-Infrared Metamaterial Absorber Based on Au Nano-Cuboids Array.

Abstract: In this article, we present a design for a triple-band tunable metamaterial absorber with an Au nano-cuboids array, and undertake numerical research about its optical properties and local electromagnetic field enhancement. The proposed structure is investigated by the finite-difference time domain (FDTD) method, and we find that it has triple-band tunable perfect absorption peaks in the near infrared band (1000-2500 nm). We investigate some of structure parameters that influence the fields of surface plasmons (SP) resonances of the nano array structure. By adjusting the relevant structural parameters, we can accomplish the regulation of the surface plasmons resonance (SPR) peaks. In addition, the triple-band resonant wavelength of the absorber has good operational angle-polarization-tolerance. We believe that the excellent properties of our designed absorber have promising applications in plasma-enhanced photovoltaic, optical absorption switching and infrared modulator optical communication.

Isolation Improvement of MIMO Antenna Using a Novel Flower Shaped Metamaterial Absorber at 5.5 GHz WiMAX Band

Abstract: This brief demonstrates the use of metamaterial absorber (MA) to achieve high isolation between two patch antennas in a 2-element multiple-input–multiple-output (MIMO) system operating at 5.5 GHz resonant frequency useful for WiMAX application. The proposed flower shaped MA, designed on a $9\times 9$ mm2 FR-4 substrate with 1 mm thickness, exhibits near unity normalized impedance at 5.5 GHz with an absorptivity of 98.7%. A four element array of the MA is arranged in the form of a line in the middle of the two radiating patches in order to suppress the propagation of surface current between them at the operating frequency. Using the proposed flower shaped MA, an isolation of nearly 35 dB is achieved. The MIMO structure is studied in terms of return loss, isolation, overall gain, radiation pattern, envelope correlation coefficient (ECC), diversity gain (DG), total active reflection co-efficient (TARC), etc. The structure is finally fabricated and measured to show good agreement with the simulated results.

Large-scale, low-cost, broadband and tunable perfect optical absorber based on phase-change material.

Abstract: Metamaterial-based electromagnetic absorbers have attracted much attention recently, but most previous realizations suffer from issues of narrow bandwidth, time-consuming and high-cost fabrication methods, and/or fixed functionalities, and so are unfavorable for practical applications. Here, we demonstrate experimentally a large-scale, broadband, polarization-independent, and tunable metamaterial absorber, which works for both visible and near-infrared light. A lithography-free and low-cost method was utilized to fabricate a centimeter-sized metamaterial sample in a metal-insulator-metal (MIM) configuration with nano-scale precision, in which a phase-change material, Ge2Sb2Te5 (GST), was adopted as the insulating spacer of the MIM structure. With two different resonance mechanisms working together, the proposed device was shown to exhibit high absorptivity (>80%) within a broad wavelength band (480-1020 nm). By thermally tuning the phase state of the GST layer, we can dramatically enlarge the working bandwidth of the metamaterial absorber by shifting one absorption peak by about 470 nm. These findings may stimulate many potential applications in, for example, solar cells, energy harvesting, smart sensing/imaging, and color printing.

A tunable terahertz metamaterial absorber composed of elliptical ring graphene arrays with refractive index sensing application

Abstract: In this paper, we demonstrate a tunable absorber composed of periodically patterned elliptical ring graphene metamaterial arrays. An absorption peak at 53.6 μ m with the maximum absorption of 49.2% of pure graphene layer has been realized. The effects of different parameters are studied by the Finite Difference Time Domain (FDTD) method. Besides, we simulate the spectra as the surrounding refractive index changes to better evaluate the sensing performance of the structure, producing a structure with the sensitivity up to 14110 nm/RIU. Finally, this paper also analyzes the absorption characteristics of bilayer graphene structure, and has a tunable dual-band selective absorption effect with a maximum absorption of 49.6%. Based on the research, it is more convenient to design the graphene-based optoelectronic devices, biosensor and environmental monitor.

Elliptical metallic rings-shaped fractal metamaterial absorber in the visible regime

Abstract: Achieving the broadband response of metamaterial absorbers has been quite challenging due to the inherent bandwidth limitations. Herein, the investigation was made of a unique kind of visible light metamaterial absorber comprising elliptical rings-shaped fractal metasurface using tungsten metal. It was found that the proposed absorber exhibits average absorption of over 90% in the visible wavelength span of 400–750 nm. The features of perfect absorption could be observed because of the localized surface plasmon resonance that causes impedance matching. Moreover, in the context of optoelectronic applications, the absorber yields absorbance up to ~ 70% even with the incidence obliquity in the range of 0°–60° for transverse electric polarization. The theory of multiple reflections was employed to further verify the performance of the absorber. The obtained theoretical results were found to be in close agreement with the simulation results. In order to optimize the results, the performance was analyzed in terms of the figure of merit and operating bandwidth. Significant amount of absorption in the entire visible span, wide-angle stability, and utilization of low-cost metal make the proposed absorber suitable in varieties of photonics applications, in particular photovoltaics, thermal emitters and sensors.

Compact and low-frequency broadband microwave metamaterial absorber based on meander wire structure loaded resistors

Abstract: In this paper, a compact and low-frequency broadband microwave metamaterial absorber (MMA) based on meander wire structure loaded with lumped resistor has been proposed and investigated numerically and experimentally. Compared with the single meander wire structure, the bandwidth and absorption level of the proposed MMA loaded with lumped resistors can be improved extremely. The retrieved equivalent constitutive parameters and simulated electric and magnetic fields distributions have been demonstrated to illustrate the mechanism underlying observed absorption. The simulated results exhibit that the proposed MMA can keep a good stability in a wide angular range for both transverse electric (TE) and transverse magnetic (TM) waves under normal and oblique incidence. Further simulated results indicate that the performance of the MMA can be adjusted by changing parameters of unit-cell structure and lumped resistors. Finally, we have fabricated a modified MMA sample practically, composing of meander wire structure loaded with lumped resistors, FR-4(loss), foam and continuous metal film. The modified MMA yields absorbance of over 85% from 1.84 GHz to 5.96 GHz in the experiment, and the relative bandwidth is about 105.6%, which is agreement reasonable with simulation.

Switchable and tunable terahertz metamaterial absorber with broadband and multi-band absorption

Abstract: In this paper, we propose and demonstrate a switchable terahertz metamaterial absorber with broadband and multi-band absorption based on a simple configuration of graphene and vanadium dioxide (VO2). The switchable functional characteristics of the absorber can be achieved by changing the phase transition property of VO2. When VO2 is insulating, the device acts as a broadband absorber with absorbance greater than 90% under normal incidence from 1.06 THz to 2.58 THz. The broadband absorber exhibits excellent absorption performance under a wide range of incident and polarization angles for TE and TM polarizations. Moreover, the absorption bandwidth and intensity of the absorber can be dynamically adjusted by changing the Fermi energy level of graphene. When VO2 is in the conducting state, the designed metamaterial device acts as a multi-band absorber with absorption frequencies at 1 THz, 2.45 THz, and 2.82 THz. The multi-band absorption is achieved owing to the fundamental resonant modes of the graphene ring sheet, VO2 hollow ring patch, and coupling interaction between them. Moreover, the multi-band absorber is insensitive to polarization and incident angles for TE and TM polarizations, and the three resonance frequencies can be reconfigured by changing the Fermi energy level of graphene. Our designed device exhibits the merits of bi-functionality and a simple configuration, which is very attractive for potential terahertz applications such as intelligent attenuators, reflectors, and spatial modulators.

An ultra-broadband terahertz metamaterial coherent absorber using multilayer electric ring resonator structures based on anti-reflection coating

Abstract: We propose a method for achieving THz ultra-broadband coherent absorption using the anti-reflection theory of metamaterials. The metamaterial absorber consists of a periodic array of electric ring resonators with a multilayered structure which form the desired refractive index dispersion and provide continuous anti-reflection over a wide frequency range. The destructive interference mechanism and resonance absorption of the absorber are determined by simulation analysis and numerical simulation. Simulation results show that the absorption bandwidth is almost 8.02 THz (absorption rate >90%) over the entire terahertz band (0.1 THz–10 THz). This design provides an effective and viable method for constructing broadband absorbers for stealth technology and the construction of enhanced transmittance devices.

Design of a wideband terahertz metamaterial absorber based on Pythagorean-tree fractal geometry

Abstract: Broadband absorption in the terahertz regime is a challenge and onerous to realize with a single layer metasurface. Self-similarity in fractal structures are exploiting metamaterial characteristics that offer a promising platform to design wideband microwave and optical devices. This paper presents a metamaterial absorber that consists of fractal geometry of Pythagorean-tree. The proposed metamaterial absorber demonstrates the wideband absorptivity in a terahertz spectrum ranging from 7.5–10 THz. Both transverse electric (TE)–and transverse magnetic(TM)–mode are taken up under different obliquity incidence angles to deeply study the angular dependence on absorption features of the Pythagorean-tree fractal meta-absorber (PTFMA). A numerical approach of interference theory is employed to verify the simulation results of the designed PTFMA. Further, the performance of the PTFMA was analyzed in terms of the figure of merit (FOM) and operational bandwidth (OBW) for different geometric parameters. Furthermore, surface electric field patterns and current distributions were studied to understand the absorption mechanism of the suggested PTFMA. The designed absorber would be a promising contender for bolometers, THz detection, and communication.

Numerical analysis of an ultra-wideband metamaterial absorber with high absorptivity from visible light to near-infrared

Abstract: In this study, we designed a novel ultra-wideband (UWB) absorber and numerically analyzed it to demonstrate that its light absorptivity was greater than 90% in the wavelength range of visible light and near-infrared (405-1505 nm). The structure of proposed novel UWB absorber consisted of four layers of films, including silica, titanium, magnesium fluoride, and aluminium, and the upper silica and titanium layers had rectangular cubes in them. For that, the excitations of propagating surface plasmon resonance (PSPR), local surface plasmon resonance (LSPR), and the resonance of Fabry-Perot (FP) cavity were generated at the same time and combined to reach the effect of perfect absorption and ultra-wideband. The proposed absorber had an average absorptivity of 95.14% in the wavelength range of 405 ∼ 1505 nm when the light was under normal incidence. In addition, the UWB absorber was large incident angle insensitive and polarization-independent. The absorber proposed in the paper had great prospects in the fields of thermal electronic equipment, solar power generation, and perfect cloaking.

Wide-angle metamaterial absorber with highly insensitive absorption for TE and TM modes.

Abstract: Being incident and polarization angle insensitive are crucial characteristics of metamaterial perfect absorbers due to the variety of incident signals. In the case of incident angles insensitivity, facing transverse electric (TE) and transverse magnetic (TM) waves affect the absorption ratio significantly. In this scientific report, a crescent shape resonator has been introduced that provides over 99% absorption ratio for all polarization angles, as well as 70% and 93% efficiencies for different incident angles up to [Formula: see text] for TE and TM polarized waves, respectively. Moreover, the insensitivity for TE and TM modes can be adjusted due to the semi-symmetric structure. By adjusting the structure parameters, the absorption ratio for TE and TM waves at [Formula: see text] has been increased to 83% and 97%, respectively. This structure has been designed to operate at 5 GHz spectrum to absorb undesired signals generated due to the growing adoption of Wi-Fi networks. Finally, the proposed absorber has been fabricated in a [Formula: see text] array structure on FR-4 substrate. Strong correlation between measurement and simulation results validates the design procedure.

Ultra-narrowband dielectric metamaterial absorber with ultra-sparse nanowire grids for sensing applications.

Abstract: Due to their low losses, dielectric metamaterials provide an ideal resolution to construct ultra-narrowband absorbers. To improve the sensing performance, we present numerically a near-infrared ultra-narrowband absorber by putting ultra-sparse dielectric nanowire grids on metal substrate in this paper. The simulation results show that the absorber has an absorption rate larger than 0.99 with full width at half-maximum (FWHM) of 0.38 nm. The simulation field distribution also indicates that the ultra-narrowband absorption is originated from the low loss in the guided-mode resonance. Thanks to the ultra-narrow absorption bandwidths and the electric field mainly distributed out of the ultra-sparse dielectric nanowire grids, our absorber has a high sensitivity S of 1052 nm/RIU and a large figure of merit (FOM) of 2768 which mean that this ultra-narrowband absorber can be applied as a high-performance refractive index sensor.

Sensitive detection of chlorpyrifos pesticide using an all-dielectric broadband terahertz metamaterial absorber

Abstract: Metamaterial absorbers consisting of metal, metal-dielectric, or dielectric materials display properties that make them feasible for use as signal enhancement tools to quantitatively detect traces amounts of samples. We propose an all-dielectric broadband terahertz absorber on a highly-doped silicon-based sensing chip. This semiconductor metamaterial absorber exhibits an experimental absorption of ∼99 % at 1.33 THz and a broad bandwidth (absorption of ≥90 %) that covers 600 GHz of the center frequency. The measurement agreed well with the simulations and calculations and the wide tuning ability of the absorber was verified by optical excitation. Furthermore, we demonstrated that this metamaterial absorber, as a highly stable THz sensor to temperature, humidity and time, shows promise in detecting trace pesticides. Regression coefficients between chlorpyrifos concentrations (0.1, 1, 10, 50 and 100 m g L - 1 ) and the corresponding spectral peak intensities and the frequency shifts near 0.93 THz were 0.9943 and 0.9750, respectively. The detection limit of chlorpyrifos reached a level of 0.1 m g L - 1 , and the frequency response of the absorber to 10 m g L - 1 chlorpyrifos solution was 4.6 GHz. These results indicate that the combination of THz spectroscopy and metamaterials can be used in the detection of chemical and biological materials with high sensitivity and stability, providing a new strategy for future applications in the fields of food and agriculture.

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

Abstract: 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.

Transparent ultrawideband absorber based on simple patterned resistive metasurface with three resonant modes

Abstract: A transparent low-profile polarization-insensitive metamaterial absorber with ultrawideband microwave absorption is presented. A fractional bandwidth of 125.2% (4.3–18.7 GHz, absorptance > 90%) is achieved using a simple patterned resistive metasurface. The thickness of the absorber is only ∼0.086 times the upper-cutoff wavelength. The experimental results agree with full-wave simulation results. A Cu-metal-mesh ground plane enhances the shielding efficiency and visible transparency. Radar cross-sections (RCS) are reduced across all reflection angles, over frequencies spanning the C, X, and Ku bands. With its visible-wavelength transparency, low profile, polarization insensitivity, excellent absorption, and wideband RCS reduction, the proposed absorber has wide applicability.

An Ultrathin and Ultrawideband Metamaterial Absorber and an Equivalent-Circuit Parameter Retrieval Method

Abstract: In this article, we propose an ultrathin and ultrawideband metamaterial (MTM) absorber based on periodically arranged metallic square spirals. The design, characterization, and measurement of the proposal are presented as its equivalent circuit. The lumped elements of the equivalent circuit are extracted using a proposed algorithm based on the least-square method, which presents a straightforward and promising approach and shows a good matching with the electromagnetic simulation. The unit cell of the proposed structure has the square spiral mounted on an FR-4 substrate in front of a conductive plate. The simulated results show an absorptivity of more than 90% from 11.4 to 20.0 GHz, covering the $Ku$ -band for transverse magnetic (TM) and transverse electric (TE) polarizations, and this broadband feature is confirmed by the experimental measurement. Furthermore, the proposed MTM absorber is $\lambda /16.4$ in thickness at the lowest frequency of absorption. The proposed MTM has proper response under oblique incidence from 0° to 50° and shows great performance with regard to the absorbers previously presented in the literature.

Design and parametric analysis of a wide-angle polarization-insensitive metamaterial absorber with a star shape resonator for optical wavelength applications

Abstract: Optical wavelengths considered as the key source of electromagnetic waves from the sun, and metamaterial absorber (MMA) enables various applications for this region like real invisible cloaks, color imaging, magnetic resonance imaging, light trapping, plasmonic sensor, light detector, and thermal imaging applications. Contemplated those applications, a new wide-angle, polarization-insensitive MMA is presented in this study. The absorber was formatted with three layers that consisted of a sandwiched metal-dielectric-metal structure. This formation of metamaterial absorber showed a good impedance match with plasmonic resonance characteristics. The structure was simulated using the FIT and validated with the FEM. A variety of parametric studies were performed with the design to gain best physical dimension. The mechanism of absorption also explained immensely by various significant analysis. The design had average 96.77% absorption from wavelengths of 389.34 nm to 697.19 nm and a near-perfect absorption of 99.99% at a wavelength of 545.73 nm for TEM mode. For an ultra-wide bandwidth of 102 nm, the design exhibited above 99% absorbance. The proposed is wide-angle independent up to 60° for both TE and TM mode, which is useful for solar energy harvesting, solar cell, and solar thermophotovoltaics (STPV). This MMA can be used for an optical sensor or as a light detector. Moreover, this proposed design can be employed in some applications mentioned above.

Numerical study of a broadband metamaterial absorber using a single split circle ring and lumped resistors for X-band applications

Abstract: We report a numerical study on the design of a broadband metamaterial absorber (MMA) with a single layer of metal–dielectric–metal based on an FR-4 substrate for X-band applications. The MMA structure consists of a periodic array of a split circle ring and lumped resistors coupled within split segments. The MMA structure achieves a broadband absorption response in the frequency range of 7.8–12.6 GHz with an absorptivity of above 90% under normal incidence for all polarization angles. The absorptivity remains above 70% in the frequency range of 6.8–11.8 GHz at wide incident angles from 0° to 30° for both transverse electric and transverse magnetic polarizations. The physical mechanism of the absorber is explained by the electric and the surface current distributions that, in turn, are significantly affected by magnetic resonance.

Ultra-narrow-band terahertz perfect metamaterial absorber for refractive index sensing application

Abstract: We numerically propose and demonstrate an ultra-narrow perfect metamaterial absorber (PMA) for refractive index sensing applications in the terahertz region. The designed PMA is only composed of a gallium arsenide (GaAs) cross-shaped resonator array on an opaque copper/silicon substrate. Simulated results show that the proposed PMA can achieve a near-perfect absorption peak with an absorptivity of 99.49% and a high quality factor value of 637 at 2.44THz. The physical mechanism of the narrow absorption is explained by the electric field, magnetic field and Poynting vector distributions. As a refractive index sensor, its sensitivity and figure of merit reach up to 1.94THz/refractive index unit (RIU) and 506RIU−1, respectively. These results make the proposed PMA to have great potential in detecting, imaging and sensing applications.

Quad band metamaterial absorber based on asymmetric circular split ring resonator for multiband microwave applications

Abstract: This article presents a metamaterial based on a modified asymmetric circular split ring resonator for absorber applications in the microwave regime. This metamaterial absorber (MMA) exhibits four absorption peaks to cover C, X, and Ku band applications. The MMA unit cell is formed on a low-cost FR4 substrate with electrical dimensions of 0.106 λ0 × 0.106 λ0, for which wavelength, λ0 is calculated at 4.1 GHz. The resonator of the unit cell is structured with three concentric intercoupled circular split rings with dimensions modified to obtain maximum absorption peaks of 97.9%, 99.1%, 99.5%, and 99.95% at 4.1, 6.86, 11.3, and 13.45 GHz, respectively. Metamaterial and absorber properties are investigated in the analysis of the surface current, electric, and magnetic fields. The unit cell exhibits single negative metamaterial properties with an effective medium ratio (EMR) of 9.15 and quality factor (Q factor) greater than 20. Beyond that, the equivalent circuit of the MMA unit cell is modeled and validated by comparing S11 obtained from Advanced Design System (ADS) and CST software. The MMA array’s absorption properties are also examined in the simulations. Measured results of the unit cell and array correspond well with the result of simulation in terms of absorption at intended frequencies. Given its good EMR, superior quality factor, and high maximum absorption, the MMA can be a good candidate for a multiband absorber in microwave applications like sensing, detecting, notch filtering and to decrease the indirect reverberation and reflections caused by the metallic part of the radar and satellite antennas.

Graphene-based tunable multi-band metamaterial polarization-insensitive absorber for terahertz applications

Abstract: This paper presents a graphene-based tunable polarization-insensitive metamaterial absorber (MMA) at terahertz (THz) frequencies. The absorber consists of top patterned gold (Au) layer followed by single layer of graphene, dielectric spacer, and Au layer at bottom. The proposed MMA demonstrates multi-band absorption with the characteristics of both broad- and dual-band absorption by optimizing dimensions (parametric analysis). Broad-band absorption reaches over 90% for the range of 4.57–6.45 THz with the relative absorption bandwidth of 34%, and the absorption peak at 6.86 and 7.20 THz having 98.9 and 95.2% absorption. The normalized impedance and constitutive electromagnetic parameters of the MMA are calculated using the Nicolson–Ross–Weir (NRW) method to validate the absorption rate. Furthermore, proposed absorber is polarization-insensitive upto 90° for transverse electric wave. The tunable characteristic of MMA is achieved by tuning the Fermi energy of graphene with the application of bias voltage. Accordingly, the proposed multi- and broad-band absorbers find its potential applications in spectroscopy detection, imaging, and sensing.