Multi-band Absorber Research Articles

Mechanically tunable multi-band terahertz absorber based on overlapping graphene nanoribbon arrays

With promising applications in broadband communication, terahertz (THz) imaging, biochemical sensing, nondestructive testing and other fields, THz absorbers have become a hot research topic in recent years. Although a number of graphene-based multi-band THz absorbers with tunable performances have been reported, the tuning methods are mostly limited to electrical tuning. Here, we report a mechanically tunable multi-band THz absorber, which is based on overlapping graphene nanoribbon arrays. By adjusting the horizontal position of the upper cover plate with graphene nanoribbon array, the frequencies of the absorption peaks can be tuned in a wide range. In addition to the absorption peaks originating from even-order lateral Fabry-Pérot resonance (LFPR) modes, there are also absorption peaks originating from inductor-capacitor (LC) oscillations. An equivalent LC circuit model is developed and theoretical results match well with simulated values. The proposed mechanically tunable THz absorber may provide a reference for tunable THz absorbers that can be applied in various fields.

Tunable, polarization-dependent multi-band perfect metamaterial absorber based on single layer mickey-like patterned graphene

This paper proposes and investigates a polarization-dependent multi-band perfect absorber composed of mickey-like patterned graphene. Simulation results demonstrate three perfect absorption peaks at 24.62 μm, 31.16 μm, and 65.12 μm with maximal absorbance of 96.6%, 98.8%, and 99.1% respectively, for instance, when an incident y-polarized wave is taken. A hybrid combination of the two ear and face structures effectively enhances and improves the absorption performance. This is evidenced by a step-by-step spectrum analysis of each decomposed and synthesized component, as well as an analysis of electric field coupling and impedance matching theory. Further investigation of the device's performance reveals that it is largely insensitive to incident angles (up to 30°), but is significantly affected by polarization angles due to the characteristic asymmetric properties of the structure along the x axis. The absorption peaks can be dynamically tuned by adjusting the effective parameters of graphene, the permittivity of the dielectric material, and the refractive index of its surroundings. Based on polarization related modulation mechanism, such graphene surface plasmon resonance (GSPR) induced device has potential applications in polarized light filtering, differentiation of dielectric materials, and sensing of surrounding refractive indices.

Tri-band metasurface absorber based on square rotational symmetry

In this paper, a multi-band metasurface absorber is designed, measured and investigated. There are four centrosymmetric two-tangent copper trapezoids that make up its unit cell. The parameters of the unit cell have great influence on the frequency of absorption peaks, with optimized parameters leading to absorptivity of 99.4%, 93.9% and 99.7% at 4.80GHz, 8.68GHz and 10.92GHz, respectively. The physical mechanism of absorption is further analyzed based on the distributions of surface current, electric and magnetic field, as well as the impedance matching. Furthermore, the absorber exhibits characteristics of polarization insensitivity and incident sensitivity, which are demonstrated through experiment. In addition, the proposed absorber is able to monitor different environments that the sensitivities are 0.15 GHz/PIU, 0.50 GHz/PIU and 1.53 GHz/PIU at three absorption peaks. In addition, the FOM of the proposed sensors at corresponding resonant frequencies are 0.68, 1.61 and 4.78, respectively. The result reflects that the proposed metasurface shows effective sensing abilities. The designed metasurface absorber has potential applications in both military and civil fields.

Optimization and modulation of a multiband multimode metamaterial absorber and its application in healthy hotel indoor gas sensing

Here, a multiple modes metamaterial absorber with four peaks was proposed and verified. All absorption peaks were excited by the multiple modes coupling between adjacent unit cells. By increasing the structural parameter D, absorption peaks were strengthened and shifteded to the low-frequency region. When the lattice constant P was increased, these peaks were decreased and shifteded to the high-frequency region. Similarly, when the dielectric layer thickness t 3 was gradually increased, these absorption peaks were weakened. Temperature was gradually increased, these absorption peaks were gradually reduced and shifteded to the high-frequency region. The multi-mode coupling effetct between unit cells was important to the performance of the metamaterial absorber.

Simultaneous optimization of conduction and polarization losses in CNT@NiCo compounds for superior electromagnetic wave absorption

Polarization and conduction losses are the two most crucial dielectric loss mechanisms for carbon-based composites, but their synergistic effects in different frequency bands need to be further revealed. More importantly, for polarization and conduction losses, the strengthening of one party always comes at the expense of the other, which inevitably limits the overall performance of the absorbers. Herein, we have developed a composite of CNT and NiCo hybrid particles via a scalable wet chemical process and annealing method. Through the adjustment of the precursor and the annealing temperature, the conduction and polarization losses of the composite are optimized simultaneously. The optimized samples achieved the full absorption of the X and Ku bands under conditions of low filling rate and thin thickness. Further theoretical and experimental studies have revealed conduction loss and polarization loss laws at different frequency ranges. The synergistic effect of conductive loss and magnetic loss in the low-frequency region ensures that the sample exhibits high microwave dissipation performance. However, in the medium and high-frequency part, the magnetic loss can be almost ignored and the timely replenishment of polarization loss keeps the wave-absorbing performance at a high level. The excellent multi-band absorption characteristics make the as-obtained absorbers meet the needs of future applications.

Multi-functional graphene periodic patterns

By describing an idea based on binary matrices, a meta-surface design methodology has been introduced in the THz spectrum window. Independence of the numerical values of the geometrical parameters, the shape of graphene patterns, as well as the mode of the bias network for the patterns, have been investigated. The possibility of describing meta-surfaces by circuit equivalents has made it possible to predict the behavior of meta-surfaces at least in the THz band with acceptable accuracy by exploiting the idea of impedance matching. Considering the significant effect of changing graphene patterns and applying multiple biases, this work tries to optimize the pattern's shapes and external bias application. In this regard, two simple binary matrices are introduced which present pattern types and corresponding biasing schemes. Leveraging developed equivalent circuit models for known periodic graphene patterns, a systematic procedure is suggested to consider pattern diversity and simultaneous multiple biases for single layers. Exploiting patterns of graphene disks, rings, and ribbons besides a back reflector and polymer substrate, a reconfigurable and adjustable wave absorber is suggested. Two sets of external stimulations via chemical potentials force the device to show wide-band and multi-band absorption while appealing tuning capability is achieved for multi-band mode. Considering both operational modes, it seems that the proposed absorber can cover almost all of the THz spectrum with excellent shifting possibilities. The validity of impedance matching description is verified by full-wave simulations while ample analysis is shown to investigate reliability against oblique radiation.

Compact single-band and multiband terahertz plasmonic absorbers using hybrid graphene-metal resonators with switching and modulation capability

THz thermal and single-pixel imaging need compact tunable absorbers with features like high modulation depth and multi bandwidth in the case of multispectral imaging. Here we are going to propose compact switchable absorbers based on a hybrid graphene-metal resonator that is designed through a genetic algorithm and numerical method. The proposed absorbers have a thickness as small as λmax/120 and can acquire perfect modulation depth. The special shape of the proposed resonator helps to gather 6 resonance bands in a very compact unit-cell. A theoretical formula is proposed to predict the resonance frequencies of the absorber based on Fabry-Perot concepts and graphene-metal plasmons. The role of local and propagating surface plasmon and their hybridization in the absorption mechanism is clarified. The modulation capabilities and tunability of the absorbers are analyzed. The absorbers work very well in a wide range of incident angles. Based on numerical analysis the hybrid resonators were capable of suppressing parasitic resonance modes making the designed absorbers ideal for emitter applications. The proposed absorbers have applications in THz thermal imaging, modulators, and emitters.

Multiband polarization insensitive metamaterial absorber for radar cross-section reduction

In this paper, a polarization-insensitive, metamaterial absorber with more than 91 % absorptivity is investigated numerically and experimentally for radar cross-section reduction at X, Ku, and K bands. The unit cell structure of the absorber is comprised of a symmetrically arranged defective L-shaped patch made of copper metal, which is imprinted on a metal-backed FR-4 lossy dielectric substrate. The proposed absorber yields multiband absorption response at distinct absorption peaks at 11.1, 15.5, and 16.3 GHz along with the broadband response of 4.8 GHz from 18.6 to 23.4 GHz (absorption peaks at 18.9, 20, 21.9, and 23 GHz) in the absorption spectra. The Characteristic mode analysis has been carried out and presented to verify the modes and resonance in the structure. The physical absorption phenomenon is clarified by presenting the induced electric field, top and bottom surface current distribution, and various retrieved constitutive electromagnetic parameters. The structure is studied for various polarization angles for both transverse electric (TE) and transverse magnetic (TM) waves at normal incidence which shows strict insensitivity to the direction of arrival of electromagnetic(EM) signal. The structure is also investigated under oblique incidence for both TE and TM waves where the response holds good up to 50° incident angles in both cases. The novelty of the proposed absorber lies in its multiband response at X, Ku, and K bands through a unique metallic pattern on a thin FR-4 substrate along with characteristics of broadband, polarization insensitiveness, wide incidence angle independence, and compactness incorporated in a single and simple design without using external components. A prototype of the absorber has been fabricated and simulated results are validated with measured results. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction and energy harvesting applications at X, Ku, and K bands.

Inverse Design of Dual‐Band Optically Transparent Metasurface Absorbers with Neural‐Adjoint Method

AbstractMassive applications of microwave technology have led to a large amount of electromagnetic pollution, which seriously interferes with the normal operation of communication systems in people's daily life. Optically transparent metasurface absorber is emerging as a promising candidate for solving this problem in some specific scenarios. When designing multiband metasurface absorbers, the coupling within the cell structure generally prevents the independent modulation of the absorption effect in each band. The rapid development of deep learning provides a new way for designing high‐performance metasurface. Here, a forward network model is built to predict the absorption spectrum of the metasurface absorber. In the network model, 1D (one‐dimensional) inverse convolution is used as the upsampling layer, which enables the network model to have a good prediction on small data sets while avoiding overfitting on large data sets. Based on the network model, a dual‐band optically transparent metasurface absorber is also designed by employing the neural‐adjoint (NA) method. The results taking advantage of deep learning method for high‐efficiency design of metasurface absorbers without considering the coupling effect, have shown great capability to optimize the absorption efficiency of different frequency bands independently, which may provide an alternative way to design other multiband microwave devices.

Triple-Band Surface Plasmon Resonance Metamaterial Absorber Based on Open-Ended Prohibited Sign Type Monolayer Graphene.

This paper introduces a novel metamaterial absorber based on surface plasmon resonance (SPR). The absorber is capable of triple-mode perfect absorption, polarization independence, incident angle insensitivity, tunability, high sensitivity, and a high figure of merit (FOM). The structure of the absorber consists of a sandwiched stack: a top layer of single-layer graphene array with an open-ended prohibited sign type (OPST) pattern, a middle layer of thicker SiO2, and a bottom layer of the gold metal mirror (Au). The simulation of COMSOL software suggests it achieves perfect absorption at frequencies of fI = 4.04 THz, fII = 6.76 THz, and fIII = 9.40 THz, with absorption peaks of 99.404%, 99.353%, and 99.146%, respectively. These three resonant frequencies and corresponding absorption rates can be regulated by controlling the patterned graphene's geometric parameters or just adjusting the Fermi level (EF). Additionally, when the incident angle changes between 0~50°, the absorption peaks still reach 99% regardless of the kind of polarization. Finally, to test its refractive index sensing performance, this paper calculates the results of the structure under different environments which demonstrate maximum sensitivities in three modes: SI = 0.875 THz/RIU, SII = 1.250 THz/RIU, and SIII = 2.000 THz/RIU. The FOM can reach FOMI = 3.74 RIU-1, FOMII = 6.08 RIU-1, and FOMIII = 9.58 RIU-1. In conclusion, we provide a new approach for designing a tunable multi-band SPR metamaterial absorber with potential applications in photodetectors, active optoelectronic devices, and chemical sensors.

Metamaterial beam with dual-action absorbers for tunable and multi-band vibration absorption

This paper presents a new class of metamaterial beams of tunable and multi-band vibration absorption. The metamaterial beam is composed of uniform and periodic beam cells with locally resonant substructure called dual-action vibration absorber, DA. A DA vibration absorber comprising of three locally resonant subsystems, 3-DOF spring-mass-damper subsystems, is utilized to generate frequency stopbands to stop elastic wave propagation. The governing equations of motion for a periodic beam cell are derived. Several distinct mass and stiffness configurations for the metamaterial beam with DA vibration absorber are proposed. The dispersion relations and presence of three frequency stopbands are studied. A finite element method based on Timoshenko beam theory is used to model and analyze the introduced metamaterial beam with DA vibration absorber. The frequency response simulations agree well with the projected stopbands of the developed dispersion relations of the mass and stiffness configurations. The concept of the presented metamaterial beam with tunable and multi-stopbands is promising for wave propagation attenuation and control applications.

Synthesis of hollow ZnFe2O4/residual carbon from coal gasification fine slag composites for multiband electromagnetic wave absorption

Electromagnetic wave (EMW) absorbers play an essential role in equipment anti-interference and human health protection. Herein, hollow ZnFe2O4/residual carbon (RC) composites were prepared using a simple hydrothermal method. The absorbing properties of the hollow ZnFe2O4/RC composites can be tuned by adjusting the RC amount. The composites show an apparent double-peak EMW absorption capability in S, C, and Ku bands. The minimum reflection loss (RL) is − 38.99 dB with 4.0 mm thickness, and the effective absorption bandwidth (RL ≤ −10 dB) is 3.20 GHz with 4.1 mm thickness. The hollow ZnFe2O4/RC composites are anticipated to be promising EMW absorbers due to their strong magnetic loss, good impedance match, optimized electrical properties, and efficient microstructure. This work demonstrates the viability of creating highly effective microwave absorbing materials with multiband EMW absorption capacity, which can be utilized to create future EMW absorbers.

Multiscale structure and interface engineering of Fe/Fe3C in situ encapsulated in nitrogen-doped carbon for stable and efficient multi-band electromagnetic wave absorption

Most reported electromagnetic wave absorption (EWA) materials show significant effective absorption in a certain frequency range, but their performances deteriorate dramatically as the frequency changes. As the range of working frequencies for electronic devices is gradually widening, it is of great interest to explore frequency-insensitive EWA materials that can achieve efficient absorption in every waveband by simply changing the absorption thickness. To this end, a multi-scale absorber (Fe/Fe3C@NC) is rationally synthesized by chemical foaming and in-situ growth strategy. By controlling the growth of carbon nanotubes, the Fe/Fe3C@NC-2 exhibits a well-constructed 3D multi-scale architecture. Thanks to dipole polarization, interface polarization and magnetic-dielectric energy conversion, the Fe/Fe3C@NC-2 overcomes the frequency dispersion behavior and keeps a stable dielectric attenuation capability across the entire frequency range. Consequently, it delivers a superb full-band absorption of -50.1, -59.83, -55.87 and -51.91 dB in the S, C, X and Ku bands, respectively. The maximum radar cross-sectional reduction reaches 35.44 dB m−2 when the incident θ is 20°, testifying its impressive performance. Surprisingly, this EWA material also shows a remarkable resistance to oxidation and corrosion derived from the tightly coated carbon layers. This work provides new insight into the design of multi-band and stable EWA materials for practical application.

Penrose tiling-inspired graphene-covered multiband terahertz metamaterial absorbers.

In this work, we propose two different graphene-covered nanostructured metamaterial absorbers inspired by Penrose tiling. These absorbers allow spectrally tunable absorption within the terahertz spectrum corresponding to 0.2-20 THz. We have conducted finite-difference time-domain analyses to determine the tunability of these metamaterial absorbers. The proposed structures, Penrose models 1 and 2, perform differently from each other due to their design characteristics. Penrose model 2 reaches a perfect absorption at 8.58 THz. In addition, the relative absorption bandwidth calculated at full-wave at half-maximum in Penrose model 2 varies between 5.2% and 9.4%, which characterizes the metamaterial absorber as a wideband absorber. Also, we can observe that as we increase the Fermi level of graphene from 0.1 to 1 eV, the absorption bandwidth and relative absorption bandwidth both increase. Our findings show the high tunability of both models through varying graphene's Fermi level, the graphene's thickness, the substrate's refractive index, and the proposed structures' polarization. We can further observe multiple tunable absorption profiles that may find applications in designer infrared absorbers, optoelectronic devices, and THz sensors.

Coupled Tamm Phonon and Plasmon Polaritons for Designer Planar Multiresonance Absorbers.

Wavelength-selective absorbers (WS-absorbers) are of interest for various applications, including chemical sensing and light sources. Lithography-free fabrication of WS-absorbers can be realized via Tamm plasmon polaritons (TPPs) supported by distributed Bragg reflectors (DBRs) on plasmonic materials. While multifrequency and nearly arbitrary spectra can be realized with TPPs via inverse design algorithms, demanding and thick DBRs are required for high quality-factors (Q-factors) and/or multiband TPP-absorbers, increasing the cost and reducing fabrication error tolerance. Here, high Q-factor multiband absorption with limited DBR layers (3 layers) is experimentally demonstrated by Tamm hybrid polaritons (THPs) formed by coupling TPPs and Tamm phonon polaritons when modal frequencies are overlapped. Compared to the TPP component, the Q-factors of THPs are improved twofold, and the angular broadening is also reduced twofold, facilitating applications where narrow-band and nondispersive WS-absorbers are needed. Moreover, an open-source algorithm is developed to inversely design THP-absorbers consisting of anisotropic media and exemplify that the modal frequencies can be assigned to desirable positions. Furthermore, it is demonstrated that inversely designed THP-absorbers can realize same spectral resonances with fewer DBR layers than a TPP-absorber, thus reducing the fabrication complexity and enabling more cost-effective, lithography-free, wafer-scale WS-absorberss for applications such as free-space communications and gas sensing.

Reconfigurable optoelectronic absorber based on nested nano disk-ribbon graphene Pattern in THz range

A two-layers, multi-band super absorber with the capability of being tuned is proposed in this paper. The idea behind the design is to realize periodic arrays of graphene disks via graphene ribbons with different lengths. Then circuit modeling is developed to be used alongside the impedance matching concept to achieve more than ten absorption peaks. The exploited spacer is a lossless polymer in the THz frequency range while the bottom of the device is occupied by a relatively thick golden plate. The developed circuit model description is verified by full-wave simulation. According to the simulation results, the proposed absorber shows more than ten peaks with absorption over 90%. The peak frequencies are interestingly able to be shifted via exploited single chemical potential variations. Additionally, deviations of absorber response against graphene electron relaxation time and device geometry are shown to be marginal which makes the presented meta-absorber, a reliable optical device.

Porous carbon-loaded hollow FeNi alloy particles for highly efficient electromagnetic wave absorbing materials

In order to develop an easy-to-use and highly efficient microwave absorbing material (MAM) that can reduce the burden of electromagnetic wave (EW) pollution on people's lives, we used a simple co-precipitation method to prepare a highly efficient MAM with porous carbon loaded hollow FeNi alloy particles. And the resulting FeNi/C composites achieve multiple scattering by exploiting the structural properties of porosity and hollowness, while benefiting from good magnetic and dielectric loss properties, and exhibit multi-band absorption performance and excellent EW attenuation capability. The sample HS FNC11 has the minimum reflection loss (RLmin) value of − 49.90 dB at 14.48 GHz and an effective absorption bandwidth (EAB) of 7.23 GHz at a thickness of 1.5 mm, which provides a new strategy for investigating efficient MAM.

Focusing on the Development and Current Status of Metamaterial Absorber by Bibliometric Analysis.

In this paper, a total of 4770 effective documents about metamaterial absorbers were retrieved from the Web of Science Core Collection database. We scientifically analyzed the co-occurrence network of co-citation analysis by author, country/region, institutional, document, keywords co-occurrence, and the timeline of the clusters in the field of metamaterial absorber. Landy N. I.'s, with his cooperator et al., first experiment demonstrated a perfect metamaterial absorber microwave to absorb all incidents of radiation. From then on, a single-band absorber, dual-band absorber, triple-band absorber, multi-band absorber and broad-band absorber have been proposed and investigated widely. By integrating graphene and vanadium dioxide to the metamaterial absorber, the frequency-agile functionality can be realized. Tunable absorption will be very important in the future, especially metamaterial absorbers based on all-silicon. This paper provides a new research method to study and evaluate the performance of metamaterial absorbers. It can also help new researchers in the field of metamaterial absorbers to achieve the development of research content and to understand the recent progress.

Simulated Studies of Polarization-Selectivity Multi-Band Perfect Absorber Based on Elliptical Metamaterial with Filtering and Sensing Effect

In this work, the Ag-SiO2-Ag metamaterial with elliptical nano-slits was proposed to investigate the multi-band polarization-dependent perfect absorber. It was found that multi-band perfect absorptions can be induced under TE and TM-polarized illuminations. Simulation results showed that the absorption peaks for TE-polarized wave appeared at 337.6 THz and 360.0 THz with 98.5% and 97.6% absorbance, respectively. Conversely, the absorption peaks for TM-polarized wave appeared at 325.7 THz and 366.1 THz with 96.3% and 97.9% absorbance, respectively. As a result, the elliptical metamaterial presented polarization-selectivity property for perfect absorption, and so, the metamaterial can filter out different frequencies of TE- and TM-reflected waves, i.e., the elliptical metamaterial can be used as a reflecting filter. In addition, this work studied the sensing performance of the elliptical metamaterial and showed that the dual-band sensing performances were different at low and high frequencies. The sensitivities (S) to the refractive index reached up to 151.1 THz/RIU and 120.8 THz/RIU for the TE and TM-polarized waves around 337.6 THz and 325.7 THz, which provide promising potential in near-infrared photoelectric sensor and detector. However, both the absorption frequency and intensity of TM-polarized wave were insensitive to the refractive index of the medium around 366.1 THz, and so, the study provides a theoretical basis for infrared stealth of different media.

Constrained multi-objective optimization problem model to design multi-band terahertz metamaterial absorbers

The multi-band metamaterial absorbers studied today offer optimal sensing performance by maximizing the absorption at resonance frequencies. A constrained multi-objective optimization problem (CMOP) model is proposed to intelligently obtain the optimized geometrical parameters of the designed MA for optimal multi-band absorption. The proposed multi-band terahertz metamaterial absorber is formed by a patterned metallic patches (symmetric snowflake-shaped resonators) layer and a continuous metallic layer separated by a dielectric layer. The simulation results show that there are three discrete narrow resonance peaks with the absorption of 99.1%, 90.0%, and 99.9% in the range of 0.5–2 THz after being optimized by the proposed CMOP model. The reflection loss of all resonance modes is improved significantly compared with the conventional brute-force approach. Specifically, reflection loss at the highest resonance frequency is suppressed from -6.76 dB to -28.17 dB. Consequently, the reported MA design can be used as a refractive index sensor with the highest sensitivity of 495 GHz/RIU and the figure of merit (FoM) of 8.9 RIU−1 through a refractive index ranging from 1.0 to 1.6 at the analyte thickness of 18.5 μm. It is worth noting that most of the liquid samples have a refractive index ranging from 1.0 to 1.6. Therefore, the reported sensor can be used for liquid detection with high sensitivity.