Multi-band Absorber Research Articles

Broadband infrared plasmonic metamaterial absorber with multipronged absorption mechanisms.

A broadband plasmonic metamaterial absorber with near perfect multiband absorption in the infrared region is designed using a metal-insulator-metal configuration and fabricated using photolithography. The metal-insulator-metal configuration consists of a Ti microdisk array, a SiO2 insulator spacer, and an Al bottom layer. The multiband absorption occurs with near perfect absorption at 4.8-7.5 µm and 9.7-10.5 µm. Ultra-broadband absorption in the mid-IR wavelength range between 3-14 µm is realized by adding a rough photoresist layer on top of the periodic microdisk structures. The multiband absorption is achieved through the combined mechanisms including plasmonic surface lattice resonance, gap plasmon resonance, Fabry-Perot cavity resonance, and the intrinsic phonon-polariton absorption of SiO2.

Infrared five-band polarization insensitive absorber with high absorptivity based on single complex resonator

In general, a single-resonator absorber can exhibit only a single absorption band under fundamental mode resonance while a multiband absorber can be achieved by combining resonators of different sizes. However, because of disturbances between adjacent resonators, it is difficult to obtain a multiband absorber containing more than four absorption bands within a certain frequency range in which all absorption peaks simultaneously exhibit an absorptivity greater than 90%. In this work, based on a metal/insulator/metal structure, we design a single complex resonator absorber to provide five absorption bands with absorptivities greater than 90%. A large-perimeter metallic structure combined with small strips is the key factor of this design. The former allows the excitation of high-order mode resonances, whereas the latter provide high absorptivity. Our investigations could not only extend the design ideas for multiband absorbers but also offer useful design clues for devices based on multimode resonances.

A multi-band binary radar absorbing metamaterial based on a 3D low-permittivity all-dielectric structure

A new binary-structured metamaterial absorber (MA), consisting of a 3D cross-shaped dielectric (CSD) periodic array and a metal back plane, is proposed and fabricated. This structure realized six resonant absorption peaks below −10dB in the range of 8–18 GHz. Both simulated and experimental results demonstrate the effectiveness of this design in generating multiband and low frequency absorption, which is difficult to achieve in previous 2D dielectric absorbers. The electromagnetic(EM) field and energy loss density distributions of absorption peaks were investigated as well as effects of structural parameters on the reflection loss spectra. It indicated that multimode resonance is generated by standing waves in the 3D dielectric structure. Moreover, since the structure is made of a low-permittivity dielectric resin, the fabrication is relatively easy and low-cost. The design of a three-dimensional low-permittivity all-dielectric structure described in this work has potential applications in the EM energy capture and stealth fields.

An Octaband Polarization Insensitive Terahertz Metamaterial Absorber Using Orthogonal Elliptical Ring Resonators

Terahertz metamaterial absorbers are the latest developments that have tremendous applications in terahertz spectroscopy and terahertz imaging. Especially, the research progressed in the direction of designing multiband absorbers. In this work, a polarization-insensitive metamaterial absorber capable of offering absorption in eight bands is proposed. The unit cell of the absorber consists of two orthogonal elliptical ring resonators (ERRs) that are optimally designed to offer maximum absorption in eight bands. The absorption percentage provided by the structure are 89.46% at 0.63 THz, 99.22% at 1.55 THz, 78.02% at 1.89 THz, 99.27% at 2.33 THz, 99.67% at 2.65 THz, 98.67% at 2.91 THz, 99.64% at 3.22 THz, and 88.02% at 3.42 THz. The absorption characteristics were independent of the polarization angle and thus, the structure is insensitive to variations in polarization angle. This is the first work that reports the design of an octaband terahertz absorber and can find significant use in practical devices.

Development of frequency-tunable multiple-band terahertz absorber based on control of polarization angles.

Controlling and tuning the spectral absorption response of metamaterial absorbers fabricated by arranging a set of resonators in a regular array is challenging. Polarization tunable multi-band terahertz resonant absorbers were developed using anisotropic microstructure arrays. The unit cell consisted of four pairs of H-shaped resonators of different sizes and a metallic ground plane separated by a dielectric layer. Discrete operating frequency shifts and dynamic amplitude tuning were observed by changing the polarization angle. The effect of the polarization angle on the absorption amplitude was evaluated. This work provides a concise approach to realize tunable absorption characteristics, which can be applied in sensors, detectors, and switches.

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

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.

A broad dual-band switchable graphene-based terahertz metamaterial absorber

A switchable graphene-based terahertz metamaterial absorber is proposed by using nonstructured graphene loaded with simple dielectric resonators, which can achieve both the broad and dual-band absorption with polarization-independent and wide-angle characteristics. The relative bandwidth of the two bands above 80% absorption reaches 97.8% and 31% in the frequency range of 0.473–1.407 THz and 2.273–3.112 THz, respectively. By changing the chemical potential of graphene, the state of the absorber can be switched from absorption (>80%) to reflection (>91%) over the two broad bands. Physical mechanisms of the broad dual-band switchable absorber are investigated by the impedance matching theory and the coupled-mode theory. The dual bands are caused by the Fabry-Perot resonance of dielectric substrate, the broad and high absorption originates from the appropriate impedance match between the absorber and free space. As the absorber is based on a monolayer nonstructured graphene loaded with simple dielectric resonators, the processing difficulty will be reduced greatly and it is easy to tune it through the bias voltage. This structure provides a new perspective to design broad multi-band absorbers and would have promising applications in multiple amplitude modulators, imaging and sensing.

Polarization-Controlled Nanogap Cavity with Dual-Band and Spatially Overlapped Resonances

Metasurfaces are ultrathin, two-dimensional arrays of subwavelength resonators, which can possess optical properties unobtainable naturally. One such desirable property is dual-band absorption occurring at the same spatial location, which could enable the enhancement of multiple processes simultaneously. However, demonstrations of multiband absorption to date have been limited to the mid-infrared and microwave regimes. Here, metasurfaces are demonstrated to have spatially overlapped, dual-band absorption in the visible to near-infrared using arrays of plasmonic nanogap cavities that consist of a sub-10 nm dielectric layer sandwiched between gold rectangles and a gold film. The relative strength of the two modes is tuned dynamically by varying the incident polarization, and the period between elements is used to tune the spectral bandwidth. Additionally, these near-perfect absorber structures fabricated by electron beam lithography (EBL) are compared to similar nanogap geometries fabricated using colloidally synthesized nanoparticles. This comparison reveals that EBL nanogap structures can achieve similar absorption performance to colloidal nanoparticles while enabling a much greater control of the nanoparticle shape, size, and relative position. These widely tunable, dual-band metasurfaces may find applications in spectrally multiplexed photodetectors and for enhancement of optical processes, such as nonlinear generation and Stokes-shifted absorption and emission processes.

MULTI-BAND PERFECT ABSORPTION INDUCED BY BREAKING THE SYMMETRY OF METAMATERIAL STRUCTURE

In this work, a multi-band metamaterial perfect absorber is demonstrated numerically and experimentally in the microwave region based on the breaking symmetry of geometrical structure. Initially, when the structure, which is designed in the X shape, is in the symmetric geometry, only one absorption peak is observed. By breaking the symmetry of structure, new absorption peaks emerge, leading to the multi-band perfect absorption. In addition, the separations of absorption peaks are proportional to the degree of geometrical asymmetry. Our work presents a simple and efficient approach to create multi-band metamaterial perfect absorbers.

Iron-incorporated chalcopyrite of an intermediate band for improving solar wide-spectrum absorption

The high efficiency chalcopyrite tandem cell with two solar absorbers of CuGaS2 and CuInSe2 remains difficult to be fabricated, but intermediate band chalcopyrite is practical to be developed. Herein, the Fe incorporation into the Ga site of chalcopyrite is successful to induce obvious solar multiband absorption. Three intermediate bands are evidenced by the UV–Vis–NIR absorption spectra, which is confirmed by first principle density functional theory (DFT) calculations. These intermediates bands improve solar energy conversion by absorbing more photons in several solar energy ranges including 2.21–1.48 eV, 1.48–0.73 eV, and around 0.57 eV to enhance solar thermal collection and photocatalytic degradation. The consistent nature of the intermediate bands suggested by theoretical analyses mainly are composed of the nondegenerate the eg and t2g states of Fe-3d orbitals.

Polarization‐independent multiband metamaterials absorber by fundamental cavity mode of multilayer microstructure

AbstractWe propose a multiband metamaterial absorber consisting of silicon brick array on metal substrate in infrared range. Using the regular hexagon array of silicon bricks, the absorption rate can reach to 90% over the bandwidth of 100 nm, and four absorption peaks with the absorption rate of more than 98% can be obtained. The absorber is independent on polarization angle. The multiband absorption performance can be attributed to primary cavity mode and Mie resonance in silicon bricks. Importantly, when the all‐dielectric silicon bricks are replaced by metal‐dielectric‐metal sandwich structure, the absorption rate above 75% with the bandwidth of more than 200 nm in the absorber can be realized, and it is polarization‐insensitive. The absorption peaks are increased to obtain broadband absorption. Our designed sandwich microstructure can generate the resonance effect of magnetic dipole among coupled layers, leading to the characteristics of broadband absorption.

Multi Band Metamaterials Absorber for Stealth Applications

Purpose – This paper presents a simulation study using CST microwave studio computer software.
 Methodology/approach/design – A simple structure based on metamaterial are used to construct a perfect metamaterial absorber. It is made of just one uncompleted square patch copper placed on top of dielectric layer to separate it from a copper ground plate.
 Findings – This design provides four perfect absorption regions with absorption peaks of an average of 93%. The characteristic study of parameters such as copper dimensions and dielectric properties led to an expected result in the synthesis of resonant frequency.
 Practical implications – The multi-band absorption can be used in energy harvesting applications, protection from the effects of electromagnetic waves, radar stealth technology and thermal imaging. Moreover, the experimental results show good agreement with CST simulation.

Nanoribbon-ring cross perfect metamaterial graphene multi-band absorber in THz range and the sensing application

In this paper, we propose a graphene nanoribbon-ring cross structure. A multi-band absorber is obtained by a simple combination of graphene nanoribbons and and graphene ring. We obtain that the theoretical absorption of three resonance wavelengths are 99.8%, 98.4% and 65.7%, respectively. We carefully analyzed each resonance wavelength, and the compact structure makes that small changes in the position of graphene nanoribbons and graphene ring have a great influence on the number of resonance wavelength. Meanwhile, the small changes in the chemical potential of graphene can tune the position of resonance wavelengths in the spectrum. At last, we discuss the sensing properties of this structure. The FoM (figure of merit) values of the three resonance wavelengths are high, and the FoM of the three peaks can reach 4.1, 3.679 and 12.66. The absorbers have great adjustability and great application potential in sensing.

Tunable multi-band terahertz absorber based on graphene nano-ribbon metamaterial

The tunable multi-band selective absorption effect with graphene nano-ribbon metamaterial is investigated. It is achieved by depositing a set of graphene nano-ribbons on a dielectric spacer backed with a metallic mirror. A dual-band and tri-band absorbers are designed to illustrate such multi-band selective absorption behavior. The designed graphene absorbers exhibit near-unity absorption at multiple resonance frequencies, which is attributed to the plasmonic resonance of graphene nano-ribbons with different widths. Moreover, the multiple resonance wavelengths can be tuned in a wide frequency range by changing the Fermi energy and the absorbers possess large angle insensitivity. Last, a Fabry-Perot model is employed to give a physical understanding of such multi-band selective absorption effect. It is believed that the conclusions may be useful for designing of next-generation graphene-based optoelectronic devices.

Creating Multiband and Broadband Metamaterial Absorber by Multiporous Square Layer Structure

Since the metamaterial perfect absorber (MPA) is composed of electromagnetic resonance structures, the main operational mechanism of the MPA is electromagnetic resonance. In this work, we use Finite Integration Technique (FIT)–based simulation to study a metamaterial absorber based on multi-layer resonance structures then the result is verified by experiment. We find that increasing the number of layers gives rise to an increase in the absorption energy and induces a large number of the absorption peak up to 9, thus forming a broad and multiband metamaterial in the frequency range from 5 to 8.9 GHz. In addition, the tunability of structural parameters in the four-layer structure allows optimizing the absorption peaks with an intensity of over 90%, which is in good agreement with the experimental result. These findings could play an important role in the design of radar shield or military devices.

MXene/Co3O4 composite material: Stable synthesis and its enhanced broadband microwave absorption

Abstract Microwave absorbers serve the purpose to ensure the transmission efficiency and accuracy in 5G telecommunications. Two-dimensional MXene has great potential in absorbing microwave. In this study, MXene(Ti3C2Tx)/Co3O4 composites are successfully fabricated by a facile and stable hydrothermal treatment in concentrated strong base and Argon environment, followed by a one-step annealing process. Phase composition, chemical state of elements, morphology and structure of the new composite materials are studied by systematical characterization. It is revealed that adsorbed Na+ ions and terminations, which are generated at the interface during hydrothermal treatment in concentrated NaOH solution, can protect the Ti3C2Tx from being decomposed. The synthesis mechanism is also proposed for stable fabrication of other MXene-based composite materials. The MXene/Co3O4 composite is able to perform single-band absorption, multiband absorption and even broadband absorption in 2–18 GHz band by tuning its composition and thickness. Particularly, better than 90% absorption in a wide range of 10.8–17 GHz can be achieved with a thickness of just 2 mm. Enhanced wideband absorption originates from the multilayer structure, the surface defects, the conductivity of Ti3C2Tx and the capacitance structure of Co3O4. Ultrathin and broadband high absorption features make the material a promising candidate for future application.

Multiband terahertz absorber and selective sensing performance.

Multiband terahertz absorbers are essential photonic components for responding to, manipulating, and modulating terahertz waves. In this work, improved electric split resonant ring arrays are used to demonstrate multiband terahertz wave absorption. The proposed design strategy is simple, practical, and significant. Experiments and simulations reveal perfect absorption at 0.918 THz and 1.575 THz for the transverse magnetic (TM) polarization and at 0.581, 1.294, and 1.556 THz for the transverse electric (TE) polarization. In addition, the weak resonant peaks that occurred in the experiments in both polarization states have been verified by the simulations. Furthermore, five concentration gradients of 2, 4-dichlorophenoxyacetic acid solutions and six concentration gradients of chlorpyrifos have been detected using the absorber. The lowest detectable concentration that could be monitored was 0.1 ppm. The absorption, intensity, and frequency shift values for the different solution concentrations at the resonant peaks were analyzed. The highest linear regression coefficients were 0.9862 and 0.9565 for the TE and TM polarizations, respectively. This multi-band absorber was demonstrated to be highly efficient in detecting pesticides for food safety applications.

Hybrid Metal-Semiconductor Meta-Surface Based Photo-Electronic Perfect Absorber

Metal films and semiconductor materials have been utilized for numerous optoelectronic devices due to the impressive electrical features. Nevertheless, the feasible way for achieving light anti-reflection or perfect absorption from opaque metal films and high-index semiconductors has not been established yet. In this work, we numerically propose and demonstrate a new functional metal–semiconductor slab, which can produce perfect light absorption in the optical range. High-index semiconductor resonators have been used to provide strong optical field coupling with the incident light. For the Ag–Si resonant slab consisting of a silicon rings array in the Ag slab, dual-band light absorption with the absorption efficiency above 99% is achieved due to the hybridized coupling of photonic and plasmonic modes for the Si and Ag resonators. Additionally, tri-band light absorption can be obtained when a paired silicon rings array is used. Moreover, these absorption properties can be spectrally manipulated via tuning the structural parameters. Furthermore, the absorber scheme is observed to be realizable by other metals and semiconductors. These optical and structural features can not only provide alternative ways for multi-band light absorption but also suggest new insight on the functional optoelectronics such as the infrared photo-detectors, hot-electron excitation, and nonlinear optics.

Independently controllable dual-band terahertz metamaterial absorber exploiting graphene

In this paper, we demonstrate the design and characterization of a controllable dual-band terahertz metamaterial absorber formed by cascading a Salisbury-screen-like structure based on patterned graphene and a gold-graphene hybrid frequency selective surface. By electrostatically changing the chemical potentials of the graphene layers, absorptivity and operating frequency of the metamaterial absorber can be tuned independently without interference. Simulations indicate the absorptivity of the first absorbing peak can be varied from 35% to greater than 99% at 1.45 THz while the position of the second one can be tuned from 2.85 THz to 3.6 THz continuously with absorptivity of 90%. It provides a new perspective on the design of multiband tunable absorbers, thus promoting the realization of terahertz sensors and detectors for practical applications.

Composite graphene-metal microstructures for enhanced multiband absorption covering the entire terahertz range

We numerically demonstrate a novel route to effectively enhancing multi-band terahertz absorption enabled by a variety of tunable polarization-insensitive multiband terahertz absorbers based on composite graphene and metal microstructures. In these devices, the multiband plasmon resonance absorption in graphene, resulted from the Fabry–Pérot cavity between the continuous graphene and the underneath metal reflector, can be effectively enhanced by the designed metal microstructures. As a demonstration, we simulate several multiband absorbers based on composite graphene and several patterned metal microstructures (spiral, ring, disk, square). It is interesting to find that the number of absorption bands can be arbitrarily manipulated by the dielectric spacer hight. By setting the same spacer height of 60 μm, all absorbers exhibit identical absorption properties with six near-unity absorption bands in the whole terahertz region ranging from 0.1 to 10.0 THz under normal incidence regardless of the shapes of microstructures. These absorption bands also show clear independence of polarization under normal incidence and the absorbance peaks can be flexibly adjusted by changing the graphene chemical potential. Our work opens up a new avenue for the development of various multiband graphene absorbers, which may have enormous potential applications in terahertz photoelectric detectors, sensors, modulators, and switches.