Showing papers on "Metamaterial absorber published in 2019"

Highly Sensitive Terahertz Metamaterial Sensor

Abstract: A novel design of nearly perfect metamaterial absorber is proposed and analyzed for terahertz sensing applications. The full vectorial finite element method is used to simulate and analyze the reported design. The suggested structure is based on increasing the confinement of both electric and magnetic fields simultaneously at the resonance frequency. Therefore, an absorptivity of 0.99 is achieved at 2.249 THz with a narrow resonant peak and a $Q$ -factor of 22.05. The resonance frequency is sensitive to the surrounding medium refractive index at fixed analyte thickness. Consequently, the reported metamaterial design can be used as a refractive index (RI) sensor with the high sensitivity of 300 GHz/RIU and the figure of merit (FoM) of 2.94 through an RI range from 1.0 to 1.39 at the analyte thickness of $1.0~ \mu \text{m}$ . Furthermore, the proposed sensor has a sensitivity of 23.7 GHz/ $\mu \text{m}$ for the detection of the sensing layer thickness variation at the fixed analyte RI of 1.35. It is worth noting that most of the biomedical samples have a refractive index range from 1.3 to 1.39. Therefore, the reported sensor can be used for biomedical applications with high sensitivity.

Vanadium dioxide-assisted broadband tunable terahertz metamaterial absorber.

Abstract: Tunable terahertz (THz) functional devices have exhibited superior performances due to the use of active materials, such as liquid crystals, graphene, and semiconductors. However, the tunable range of constitutive parameters of materials is still limited, which leads to the low modulation depth of THz devices. Here, we demonstrate a broadband tunable THz absorber based on hybrid vanadium dioxide (VO2) metamaterials. Unlike other phase change materials, VO2 exhibits an insulator-to-metal transition characteristic and the conductivity can be increased by 4–5 orders of magnitude under external stimulus including electric fields, optical, and thermal pumps. Based on the unique transition character of VO2, the maximum tunable range of the proposed absorber can be realized from 5% to 100% by an external thermal excitation. Meanwhile, an absorption greater than 80% in a continuous range with a bandwidth about 2.0 THz can be obtained when VO2 is in its metal phase at high temperature. Furthermore, the absorber is insensitive to the incident angle up to 50° and such a broadband THz absorber can be used in applications including imaging, modulating, cloaking, and so on.

Low-frequency sound absorption of hybrid absorber based on micro-perforated panel and coiled-up channels

Abstract: We propose a hybrid acoustic metamaterial as a super absorber for a relatively broadband low-frequency sound based on a simple construction with deep-subwavelength thickness (5 cm). The hybrid metamaterial absorber is carefully designed and constructed based on a microperforated panel (MPP) and coiled-up Fabry–Perot channels. It is demonstrated analytically, numerically, and experimentally that over 99% of acoustic absorption could be achieved at a resonance frequency (<500 Hz) with the working wavelength about 30 times larger than its total thickness. It is revealed that the superior absorption is mainly caused by the friction losses of acoustic wave energy in the MPP. The frequency of the absorption peak could be tuned by adjusting the geometry parameters of the MPP and the channel folding numbers. The relative absorption bandwidth could also be tuned flexibly (up to 82%) with a fixed deep-subwavelength thickness (5 cm). The absorber has wide potential applications in noise control engineering due to its deep-subwavelength thickness, relatively broad bandwidth, and easy fabrication.

Polarization-Independent Perfect Optical Metamaterial Absorber as a Glucose Sensor in Food Industry Applications

Abstract: Perfect optical metamaterial absorbers (POMMA) utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. In all the reported absorbers, the absorption occurs only at a single wavelength or dual/multi-band wavelengths where plasmon resonances are ex-cited in the nanostructure. Here we not only show a single-band perfect absorber but also demonstrate that our proposed design has the ability to be multi-band absorber at the same structure. Furthermore, we numerically demonstrate the proposed POMMA can be utilized as a glucose sensor for refractive index sensing which has more than 225 nm/RIU sensitivity at the infrared frequency regime which is good value. Its polarization-independent absorbance is about 100% at normal incidence for both TE and TM polarization modes. The proposed optical glucose sensor offers great potential to maintain the performance of localized surface plasmon (LSP) sensors in nanostructures in food industry applications.

Theoretical design of a triple-band perfect metamaterial absorber in the THz frequency range

Abstract: A triple-band perfect metamaterial absorber based on periodically arranged graphene split ring resonator (SRR) is proposed in this study. The calculation results by the FDTD method indicate that the SRR structure has three absorption peaks at frequencies 3.56 THz, 10.38 THz and 12.96 THz with absorption efficiency 99.57%, 99.98%, and 99.76%, respectively. By changing the chemical potential or relaxation time, the absorption characteristics of the split ring resonator structure can be flexibly tuned. Furthermore, we also examine the sensing performance of the proposed metamaterial absorber, the sensing performance of the high-frequency band is significantly higher than the low-frequency band. We believe that our results will pave the ways for the development of applications using metamaterials with high efficiency and multi-band spectral selectivity in biochemical sensing, optical switching, and modulating.

Near-infrared absorption-induced switching effect via guided mode resonances in a graphene-based metamaterial

Abstract: Optical switches based on dielectric nanostructures are highly desired at present. To enhance the wavelength-selective light absorption, and achieve an absorption-induced switching effect, here we propose a graphene-based metamaterial absorber that consists of a dielectric grating, a graphene monolayer, and a photonic crystal. Numerical results reveal that the dual-band absorption with an ultranarrow spectrum of the system is enhanced greatly due to the critical coupling, which is enabled by the combined effects of guided mode resonances and photonic band gap. The quality factor of the absorber can achieve a high value (>500), which is basically consistent with the coupled mode theory. Slow light emerges within the absorption window. In addition, electrostatic gating of graphene in the proposed structure provides dynamic control of the absorption due to the change of the chemical potential of the graphene, resulting in an optional multichannel switching effect. Unlike other one-dimensional devices, these effects can be applied to another polarization without changing the structure parameters, and the quality factor is significantly enhanced (>1000). The tunable light absorption offered by the simple structure with an all-dielectric configuration will provide potential applications for graphene-based optoelectronic devices in the near-infrared range, such as narrowband selective filters, detectors, optical switches, modulators, slow optical devices, etc.

A broadband and polarization-independent metamaterial perfect absorber with monolayer Cr and Ti elliptical disks array

Abstract: We design a broadband perfect metamaterial absorber from visible to near infrared regime consisting of monolayer Cr and Ti elliptical disks array located on the SiO2-Au layer. The bandwidth for the absorption above 90% reaches about 1140 nm and above 99% reaches about 584 nm. The high absorption and broadband obtained mainly come from the mode of the plasma excitation. The broadband perfect absorber we demonstrate here, is insensitive to the incident polarizations, which shows great potential value in high-temperature photonic applications, such as solar energy harvesting, light trapping.

Tunable and scalable broadband metamaterial absorber involving VO 2 -based phase transition

Abstract: Optical absorbers with dynamic tuning features are able to flexibly control the absorption performance, which offers a good platform for realizing optical switching, filtering, modulating, etc. Here, we propose a thermally tunable broadband absorber applying a patterned plasmonic metasurface with thermo-chromic vanadium dioxide (VO2) spacers. An actively tunable absorption bandwidth and peak resonant wavelength in the region from the near- to mid-infrared (NMIR) are simultaneously achieved with the insulating–metallic phase transition of VO2. Moreover, the scalable unit cell, which is composed of multi-width sub-cells, provides a new freedom to further manipulate (i.e., broaden or narrow) the absorption bandwidth while maintaining a high relative absorption bandwidth and efficient absorbance at the same time. For both transverse-electric and transverse-magnetic polarizations, the proposed nanostructure exhibits a high absorption over a wide angular range up to 60°. This method holds a promising potential for versatile utilizations in optical integrated devices, NMIR photodetection, thermal emitters, smart temperature control systems, and so forth.

Tunable Graphene-based Plasmonic Perfect Metamaterial Absorber in the THz Region.

Abstract: The optical performance of a periodically tunable plasma perfect metamaterial absorber based on a square-square-circle array we propose in the terahertz region is analyzed in this work by the finite difference time domain (FDTD) method. We not only discuss the impact of various parameters such as period a, length L, radius R, and incident angle θ under transverse magnetic (TM)- and transverse electric (TE)-polarization on the absorption spectra of the absorber but also study the effect of the Fermi energy EF and relaxation time τ. Finally, we simulate the spectra as the surrounding refractive index n changes to better evaluate the sensing performance of the structure, producing a sensitivity S of the structure of up to 15006 nm/RIU. On account of this research, we find that the absorber is beneficial to sensors and detectors in the terahertz region.

Truly All-Dielectric Ultrabroadband Metamaterial Absorber: Water-Based and Ground-Free

Abstract: A truly all-dielectric metamaterial absorber, made of subwavelength water-based resonators and free of metallic ground, is designed, fabricated, and characterized. We demonstrate theoretically and experimentally that our metamaterial features a highly uniform perfect absorption for frequencies between 7.74 and 23.56 GHz, perfect thermal stability for temperatures from 0 to 100 $^\circ$ C, and excellent absorption performance for large angles of oblique incidence. The proposed metamaterial absorber can be fabricated at low cost, is environment friendly, and may find potential applications in broadband scattering reduction and electromagnetic energy harvesting.

Solar energy harvesting with ultra-broadband metamaterial absorber

Abstract: In this study, a novel metamaterial absorber (MA) is designed and numerically demonstrated for solar energy harvesting. The structure is composed of three layers with different thicknesses. The int...

Numerical Study of a Wide-Angle and Polarization-Insensitive Ultrabroadband Metamaterial Absorber in Visible and Near-Infrared Region

Abstract: An ultrabroadband metamaterial absorber structure based on a periodic array of metallic-dielectric multilayered conical frustums is numerically investigated and proposed. The metamaterial absorber indicated an absorptivity of higher than 90%, which covered the visible and near-infrared region at 480–1480 nm, and a relative absorption bandwidth of 102%. The high absorptivity can be maintained with large incident angles up to 60° under both transverse electric and transverse magnetic polarizations. Furthermore, the proposed absorber exhibits polarization insensitivity owing to its rotational symmetry structure. Compared with the previously reported ultrabroadband metamaterial absorbers, the design in this work indicates high practical feasibility in terms of a compact structure for a large bandwidth, a wide incident angle, and polarization insensitivity, thereby suggesting its promising application, for example, in solar cells and thermal emitters.

Optically transparent and flexible broadband microwave metamaterial absorber with sandwich structure

Abstract: With the aim to design broadband microwave absorbers with optically transparent, flexible and stable performances in 8–18 GHz, a sandwich structure is designed and fabricated by sandwiching the periodic arrayed ITO film into two transparent and flexible polyvinyl chloride layers. With the induced metamaterial structure to tailor the effective input impedance, the proposed sandwich absorber can realize more than 90% absorption in 8–18 GHz for both TE and TM polarization when the incident angle is less than 30°. Meanwhile, the optical transmittance of the designed absorber reaches more than 80% transmittance with the wavelength larger than 532 nm, and the average optical transmittance for the visible light (400–800 nm) is 80.2%. The proposed absorber shows broadband microwave absorption in both X and Ku band with simultaneously high transmittance in visible frequencies, indicating that the proposed sandwich metamaterial absorber has great potentials for developing optical transparent absorbing devices.

Metamaterial absorber sensor design by incorporating swastika shaped resonator to determination of the liquid chemicals depending on electrical characteristics

Abstract: In this work, sensor abilities of the metamaterial absorber based on swastika shaped resonator are developed both theoretically and experimentally at X-band frequency range. The structure is consisted of a swastika shaped resonator on the top of dielectric layer and have an air gap to fill chemicals liquids between the copper plate and backside resonator. In this study, a full-wave EM solver CST Microwave Studio (Computer Simulation Technology) based on finite integrate technique has been used to simulate and investigate the absorption of the metamaterial structure with chemicals liquids depending on the electrical properties. A vector network analyzer 85070E probe kit has been used to measure the relative dielectric constants and loss tangent of some chemical liquids (ethanol content, methanol content, acetone, methanol, ethanol, Polyethylene Glycol 300, water) in the related frequency range. Absorption value of the sensor structure for selected chemicals placed in the air gaphas been investigated. It is obtained that there is a significant difference in absorption ratios between each chemicals and overall resonance frequency shifts have been observed which provides information to accurately estimate density rate of the sensed liquids. The absorption mechanisms of the metamaterial has been explained by using electric field, magnetic field and surface current distributions. Furthermore, the resonance absorption properties of the metamaterial based absorber sensor can be modified and adjusted easily by varying the dimensions of the resonator. Experimental and simulated results demonstrate that the resonance frequency of the swastika metamaterial based sensor is linearly related to the permittivity of selected chemicals which creates an appropriate approach for multipurpose sensor devise and electrochemical sensor.

Compact Ultra-Thin Seven-Band Microwave Metamaterial Absorber Based on a Single Resonator Structure

Abstract: In this paper, we present the design, simulation, measurement and characterization of a seven-band polarization-insensitive and wide-angle metamaterial absorber (MMA) in the microwave frequency region. The unit-cell structure of the designed MMA is composed of a single closed-meander-wire resonator structure placed over a metal ground plane by a dielectric substrate. The simulated results exhibit that the proposed MMA has high-level absorption of over 90% at seven distinct resonance frequencies, which agree reasonably with experiment. Simulated electric field distributions reveal that the observed high-level absorption mainly originates from higher-order electric resonance response. Simulated absorbance under different angles of polarization and oblique incidence indicate that the high absorption of this MMA can be kept stable for both transverse electric and transverse magnetic waves. Furthermore, the influences of geometric parameters of the unit-cell structure on absorption properties of the MMA were also studied numerically. In addition, this proposed MMA has good performances of thinner thickness, polarization-insensitive and wide-angle properties, which has many potential applications such as detection, imaging and sensing.

Dual-band switchable terahertz metamaterial absorber based on metal nanostructure

Abstract: In this paper, a tunable terahertz metamaterial absorber with two bands is proposed. It is composed of Au reflector, dielectric layer and periodic array of Au. By adjusting different materials and optimizing parameters, it can achieve the characteristics of both broadband and single peak absorption. In the range of 3.5–4.1 terahertz, the broadband absorption rate can reach over 90%, the relative bandwidth ratio is 17%, and the absorption peak at 7.15 THz can reach 98.9%. The coupling mechanism of broadband and unimodal absorption is studied by coupled mode theory. In addition, the designed absorber has broad application prospects in terahertz imaging and sensing due to its broadband and tunable characteristics.

Design and analysis of polarization independent conformal wideband metamaterial absorber using resistor loaded sector shaped resonators

Abstract: A polarization independent conformal wideband metamaterial absorber has been proposed in this study. The proposed absorber unit cell consists of a circle and a slotted sector, loaded with four lumped resistors between them to improve the absorption bandwidth. Measured and simulated results exhibit more than 90% absorption in the frequency band from 3.90 GHz to 10.5 GHz under the normal incidence angle, and the fractional bandwidth is 91.6%. The proposed absorber is polarization independent due to the symmetrical nature. The absorber unit cell is compact in configuration with a unit cell size of 0.16 λo × 0.16 λo, where λo is the wavelength at 3.9 GHz and the substrate thickness is 0.098 λo. Once the proposed absorber is wrapped on the cylindrical surface, it shows good absorptivity in the absorption frequency band. The effects of many designed parameters have been studied to understand the performance of the wideband absorber. To recognize the absorption phenomenon of the absorber, normalized impedance, electric field distribution, and surface current density have been demonstrated. Finally, the proposed conformal absorber fabricated and measured the absorption for flat and curved surfaces, which exhibits good agreement between the simulated and the experimental results.

Numerical Study of an Efficient Broadband Metamaterial Absorber in Visible Light Region

Abstract: We report a numerical study of a broadband metamaterial absorber in visible light region by utilizing a single layer of metal–dielectric–metal configuration. The absorption bandwidth and absorption performances are tailored by varying the resonator shapes and metal materials. The absorption bandwidth of the proposed metamaterial absorber (MA) structure is enhanced significantly with decreasing the order of rotational symmetry of the resonator shape. Using gold configuration, the twofold symmetry MA structure based on the double-sized axe shaped resonator exhibits the broadband absorption response over the entire visible light and apart of infrared spectrum range from 320 to 982 nm with absorptivity above 90% for both transverse electric and transverse magnetic polarizations. The physical mechanism of broadband absorption is explained by the current, electric, and magnetic distributions, significantly affected by the propagating surface and localized surface plasmon resonances. Furthermore, the high absorber performances of the twofold symmetry MA structure can be obtained over entire visible light region (400–700 nm) for both noble metal of gold and low-cost metal of nickel configurations, indicating the proposed absorber is a promising candidate for low-cost and large-scale fabricate device operated in visible light region.

Vanadium dioxide based broadband THz metamaterial absorbers with high tunability: Simulation study

Abstract: With their unprecedented flexibility in manipulating electromagnetic waves, metamaterials provide a pathway to structural materials that can fill the so-called "THz gap". It has been reported that vanadium dioxide (VO2) experiences a three orders of magnitude increase in THz electrical conductivity when it undergoes an insulator-to-metal transition. Here, we propose a VO2 based THz metamaterial absorber exhibiting broadband absorptivity that arises from the multiple resonances supported by a delicately balanced doubly periodic array of VO2 structures and numerically demonstrate that the corresponding absorption behavior is highly dependent on the VO2's THz electrical properties. Considering the phase transition induced dramatic change in VO2's material property, the proposed metamaterial absorbers have the potential for strong modulation and switching of broadband THz radiation.

Facile design of an ultra-thin broadband metamaterial absorber for C-band applications.

Abstract: We report a facile design of an ultra-thin broadband metamaterial absorber (MA) for C-band applications by utilizing a single layer of a metal-dielectric-metal structure of FR-4 substrate. The absorption performances are characterized using a numerical method. The proposed MA exhibits the broadband absorption response over the entire C-band spectrum range from 4.0 GHz to 8.0 GHz with absorptivity above 90% and the high absorptivity is remained over 80% for a large incident angle up to 40° under both transverse electric (TE) and transverse magnetic (TM) polarizations over the band. The origin of absorption mechanism is explained by the electric and surface current distributions, which is also supported by the retrieved constitutive electromagnetic parameters, significantly affected by magnetic resonance. In addition, compared with the previous reports, the proposed MA presents a greater practical feasibility in term of low-profile and wide incident angle insensitivity, suggesting that the proposed absorber is a promising candidate for C-band applications.

Cascaded Graphene Frequency Selective Surface Integrated Tunable Broadband Terahertz Metamaterial Absorber

Abstract: The quest of novel materials and structures to design an efficient absorber for realizing wave trapping and absorption at terahertz (THz) frequencies is an open topic. But the design of a thin, wideband, and tunable THz absorber is still an arduous job. Hence, in this paper, a hybrid THz metamaterial absorber integrated with a cascaded graphene frequency selective surface (FSS), with ultra-high absorbance over a wide frequency range is designed using an analytical equivalent circuit model. Such an approach provides a feasible way to optimize the device by interrelating the effective electromagnetic and circuit parameters with the unit cell dimensions of FSS. A systematic study and critical analysis over a wide range of device parameters including graphene chemical potential and FSS design variables is demonstrated. A peak dip in reflection coefficient of -30.27 dB is observed at 2.94 THz for an optimal device with a chemical potential (μ c ) of 0.38 eV (μ c1 ), and 0.25 eV (μ c2 ) in the range of 0.1-4.0 THz. The cascaded FSS configuration results in the unique anti-reflection-based absorption phenomena, which is responsible for the achievement of -10 dB absorption bandwidth of 2.34 THz (0.85-3.19 THz). In addition, the frequency-dependent effective permittivity, permeability, and impedance is extracted using reflection data, in order to understand the device physics. Such ultra-thin and broadband absorbing device architecture may confer potential application perspectives in THz sensing, imaging, and detection.

Graphene-based tunable triple-band plasmonic perfect metamaterial absorber with good angle-polarization-tolerance

Abstract: In this paper, a new graphene-based tunable triple-band plasmonic perfect metamaterial absorber which is composed of two groups of graphene elliptical ring resonators and a gold plate separated by a dielectric layer is presented. The two sets of graphene elliptical ring resonators are connected to each other, so their internal parameters can be easily adjusted by voltage, which can dynamically control the absorptive characteristics of graphene metamaterials. In addition, the proposed absorber shows a very good angle-polarization-tolerance because of the high symmetry of the structure configuration. The results show that this kind of symmetrical double ellipse structure can produce three highly effective absorption peaks which are respectively at around 38.7 μm, 20.2 μm and 12.8 μm and the value of peaks can even reach more than 99%. Moreover, due to the strong tunability, our absorber has a great potential in infrared and terahertz detection.

A broadband terahertz metamaterial absorber enabled by the simple design of a rectangular-shaped resonator with an elongated slot

Abstract: Broadband metamaterial absorbers are of critical importance in practical applications, but their obtainment approaches are quite complex at present. We demonstrate here that a fairly simple structure design formed by a rectangular-shaped resonator having an elongated slot can be utilized to achieve a broadband absorption response at terahertz frequencies. More than 50% absorption in a continuous frequency range of 1.62 THz (with a central frequency of 2.05 THz) can be gained, and its relative absorption bandwidth is 79.02%, which is superior to that of previous broadband absorption devices. The basic principle of the broadband absorption originates from the superposition of four different but narrowly separated resonance peaks that resulted from different response positions of the suggested resonator. Results further reveal that the broadband terahertz absorption performance (or its four resonance peaks) can be controlled by the resonator dimensions. The suggested method can provide a new type of design strategy to realize broadband integrated terahertz absorption devices.

Experimental Validation of a Frequency-Selective Surface-Loaded Hybrid Metamaterial Absorber With Wide Bandwidth

Abstract: The achievement of wide absorption bandwidth for a single-layer metamaterial absorber remains a challenge. In this letter, a frequency-selective surface (FSS), single-substrate layer, broadband metamaterial absorber is investigated theoretically, experimentally, and by simulation in the frequency range of 2–18 GHz. Simulations of the reflection coefficient of the absorber with different substrate dielectric thicknesses, FSS thicknesses, and FSS dimensions indicate that there exist optimal values for the absorber design. The measured results from a fabricated prototype are in close agreement with the simulations, suggesting the effectiveness of the structure for actual electromagnetic applications. The fabricated absorber with thickness 2.0 mm has a minimum reflection coefficient of −29.0 dB at 12.2 GHz. The −10 dB absorption bandwidth is 7.5 GHz in the range of 8.5–16 GHz. Effective complex electromagnetic parameters are extracted to quantitatively understand the absorption. A miniaturized structure, single-substrate layer, simple geometry, and wide bandwidth are some of the key features of the proposed metamaterial absorber.