Broadband Metamaterial Absorber Research Articles

Ultra-broadband metamaterial perfect solar absorber with polarization-independent and large incident angle-insensitive

Broadband metamaterial perfect absorbers have attracted a great attention to the people who study its use in solar energy harvesting. However, it is an extremely challenge to integrate such properties as ultra-broadband, perfect absorption, polarization-independent, angle-insensitive to a large incident angle and so on into a simple absorber structure. In this paper, we use FDTD to design a simple ultra-broadband metamaterial perfect absorber, consisting of x-cavity titanium nano-disk array based on a Silicon nitride-Titanium-Silicon nitride-Titanium four-layer structure. The optimized results indicate that the absorber broadband absorption spectra range from 400 nm to 2500 nm with 97.6% average absorption at normal incidence. The interactions among SPR, MR and CR lead to a high absorption. Moreover, the absorber is both polarization-independent and large incident angle-insensitive for both TE and TM-polarized waves. In addition, the absorber has an extremely high tolerance to fabrication errors, which is of great significance for practical production and application.

A broadband metamaterial absorber with flexible low infrared radiation

In this paper, based on split resonant ring (SRR) and NaCl solution (NS), a conformal and low thermal infrared radiation (LTIR) broadband metamaterial absorber (MA) with double SRRs and NS resonant cavity is proposed. Through simulation and measurement, it is proved that the proposed absorber has electromagnetic (EM) wave absorptivity of more than 90% under different polarization angles and different conformal conditions at 9.58–24.42 GHz. By introducing microfluidic channels, coupled electromagnetic thermal and coupled heat transfer simulations demonstrate that the design MA can maintain the thermal stability and LTIR characteristics under different power EM waves irradiation with low flow velocity (0.05 m s−1). Based on its good absorption performance and LTIR performance, it can be predicted that the proposed MA will have great application value in non-planar surface EM wave stealth and infrared stealth.

A vanadium dioxide-based metamaterial with quatrefoil and circle loaded structure on flexible polyamide substrate for terahertz applications

In this study, a novel broadband metamaterial (MTM) absorber is proposed, which is based on vanadium dioxide (VO2) resonators coated onto a flexible polyamide substrate. The VO2 resonator is in the form of a quatrefoil and circle-loaded complementary square split ring resonator (CSSRR), which is fine tuned to operate in the terahertz range. The MTM design and simulation were carried out using Computer Simulation Technology (CST) software, by which different layouts were investigated to achieve the optimum structure. The results showed the presence of two pronounced peaks for the proposed MTM structure at 0.88 and 1.42 THz. The absorption peaks were found to be insensitive to the wave polarization and incident angle from 0° to 90°. The absorption mechanism of the MTM was investigated considering the insulating and metallic states of VO2. The results were in a good agreement with those calculated using high frequency simulated structure (HFSS) software. The flexible nature of the proposed MTM design makes it a viable candidate for non-planar and conformal geometry applications in stealth technology, and terahertz imaging.

Design of a Broadband Perfect Solar Absorber Based on a Four-Layer Structure with a Cross-Shaped Resonator and Triangular Array

As solar energy is a low-cost and clean energy source, there has been a great deal of interest in how to harvest it. To absorb solar energy efficiently, we designed a broadband metamaterial absorber based on the principle of Fabry–Pérot (FP) cavities and surface plasmon resonance (SPR). We propose a broadband perfect absorber consisting of a four-layer structure of silica–tungsten–silica–titanium (SiO2–W–SiO2–Ti) for the incident light wavelength range of 300–2500 nm. The structure achieves perfect absorption of incident light in the wavelength range of 351.8–2465.0 nm (absorption > 90%), with an average absorption of 96.3%. The advantage of our proposed structure is that it combines the characteristics of both high and broadband absorption, and has high overall absorption efficiency for solar radiation. It is also independent of polarization and insensitive to incident angle. We investigated how absorption was affected by different structures, materials, geometric parameters, and refractive indices for different dielectric materials, and we explored the reasons for high absorption. This structure is refractory and ultrathin, and it offers a good tradeoff between bandwidth and absorption. It therefore has premium application prospects and value.

Ultra-thin optically transparent broadband microwave metamaterial absorber based on indium tin oxide

Broadband metamaterial absorber (MMA) with optically transparent property is essential for solving the electromagnetic pollution problem at gigahertz. In this work, we designed and prepared a sandwich MMA consisting of high-transmittance substrate polymethyl methacrylate (PMMA), a periodically arranged indium tin oxide (ITO) film, and a low resistivity ITO reflective layer. The microwave absorbance over 90% can be achieved in the frequency range of 6–17.8 GHz. Wide-angular stability, good polarization insensitivity and optical transmittance to visible light (400–800 nm) are realized. The microwave attenuation mechanisms of the proposed MMA were investigated by surface current distribution and power loss density. The excellent microwave absorption and optical transmittance properties indicate the strong potential and feasibility of the designed MMA for the development of optically transparent microwave absorbing windows and devices.

Broadband metamaterial absorber in the visible region using a petal-shaped resonator for solar cell applications

We present an efficient broadband metamaterial (MM) solar spectrum absorber with a wide incident angle and polarization-insensitive absorption. Proposed absorber is a three layers absorber in the form of a metal-dielectric-metal (resonator) structure. We use a single dielectric layer of silicon dioxide (SiO 2 ) between the metasurface (petal-shaped) and the lower layers of tungsten (W) metal. We obtained around 99% average absorption from 400 nm to 750 nm and a near-unity absorption at 572.23 nm wavelength. The unit cell structure shows 99% absorption from wavelengths from 456.62 nm to 677.73 nm and has an ultra-wide bandwidth (221.11 nm). For both the transverse magnetic (TM) and transverse electric (TE) modes, this design demonstrates the wide-angle absorption up to 60°. These properties can be used for thermo-photovoltaics, solar cells, and energy harvesting devices. In addition, geometrical studies are also carried out to obtain the optimized physical dimensions of the proposed absorber. We also analyze the weighted absorption under AM1.5 solar luminosity by changing the thickness parameter of the SiO 2 layer. Short circuit current density ( J sc = 26.41 mA/cm 2 ), open-circuit voltage ( V oc ), fill factor, and conversion efficiency are also observed for the proposed absorber. These results reveal their utility for solar cell applications. • Proposing metamaterial structure for thin-film solar cells. • Proposed absorber exhibits nearly perfect absorption in the visible region. • Absorber shows polarization-insensitive and incident angle independent absorption. • Absorption properties can be tuned by geometric parameters. • Proposed absorber exhibits a significant short-circuit current density.

Fussy Inverse Design of Metamaterial Absorbers Assisted by a Generative Adversarial Network

The increasing demands for metasurfaces have led researchers to seek effective inverse design methods, which are counting on the developments in the optimization theory and deep learning techniques. Early approaches of the inverse design based on deep learning established a unique mapping between the device’s geometry parameters and its designated EM characteristics. However, the generated solution based on the traditional inverse design method may not be applicable due to practical fabrication conditions. The designers sometimes want to choose the most practical one from multiple schemes which can all meet the requirements of the given EM indicators. A fuzzy inverse design method is quite in demand. In this study, we proposed a fuzzy inverse design method for metamaterial absorbers based on the generative adversarial network (GAN). As a data-driven method, self-built data sets are constructed and trained by the GAN, which contain the absorber’s design parameters and their corresponding spectral response. After the training process is finished, it can generate multiple possible schemes which can satisfy the customized absorptivity and frequency bands for absorbers. The parameters generated by this model include structure sizes and impedance values, which indicates that it has the ability to learn a variety of features. The effectiveness and robustness of the proposed method have been verified by several examples for the design of both narrowband and broadband metamaterial absorbers. Our work proves the feasibility of using deep learning methods to break the limits of one-to-one mapping for the traditional inverse design method. This method may have profound usage for more complex EM device design problems in the future.

Ultra‐Broadband Wide‐Angle Polarization‐Independent Enhanced Absorber with Ultraviolet to Far‐Infrared Absorption Performance

Ultra‐thin broadband metamaterial absorbers exhibit high absorptivity and broad bandwidths. Herein, an ultra‐broadband wide‐angle polarization‐independent enhanced absorber with a metal–insulator–metal (MIM) structure is proposed and simulated. The enhanced absorber exhibits ultra‐wideband characteristics from ultraviolet to far‐infrared range (0.35–10 μm), where it achieves an average absorption > 96%. It is insensitive to variations in the polarization state, exhibits a wide‐angle absorption because of a high degree of geometric symmetry, and shows a satisfactory absorption performance for a combination of different materials. Thus, the distinct structural characteristics of the device play a pivotal role in absorption. These advantages improve the flexibility of material selection in the design and manufacturing process of ultra‐broadband enhanced absorbers, thereby broadening their application potential in solar energy harvesting, infrared detectors, and thermal imaging.

Bismuth-based broadband metamaterial absorber

A numerical simulation of a metamaterial broadband absorber is performed using the finite-difference time-domain method. The absorber adopts a four-layer structure with titanium dioxide (TiO2) rectangular pairs, a bismuth (Bi) layer, a silicon dioxide (SiO2) layer, and a titanium nitride (TiN) layer from top to bottom, respectively, and the TiO2 rectangular pairs are periodically and symmetrically arranged in a rectangular array. The optimization results show that the average absorption of the designed absorber is 97.6% in the wavelength range of 500 to 3500 nm and the average absorption can reach 99% in the wavelength range of 811 to 3162 nm (2351 nm). The coupling of local surface plasmon resonance and propagating plasmon resonance and the good absorption and broadband absorption properties exhibited by metallic Bi were further found by analyzing the distribution of electromagnetic fields. The designed absorber has polarization and temperature-insensitive properties and a simple structure and is easily fabricated.

Nanoparticle-on-Mirror Metamaterials for Full-Spectrum Selective Solar Energy Harvesting.

Most broadband metamaterial absorbers are realized by patterning periodic arrays of plasmonic nanoparticles (>100 nm) on dielectric/metallic substrates to enable both electric and magnetic resonances. These metamaterials, however, require costly nanolithographic top-down techniques for fabrication. Here, we demonstrate new-concept nanoparticle-on-mirror (NoM) metamaterial absorbers by densely packing plasmonic nanoparticles of much smaller size (∼30 nm) on metal films directly. Such a simple but rational design enables the use of all-solution-based bottom-up processes. Because of the decoupling of electric and magnetic polarizations in these ultrasmall nanoparticles, excellent impedance match and near-perfect light absorption can be achieved in a broad band over the solar spectrum with weak thermal emission. Proof-of-concept large-area NoM metamaterial absorbers that offer a solar absorptance of 94% but a low IR emittance of 2% are experimentally demonstrated. The outstanding performance, bottom-up process, and great compatibility render the design promising for efficient and large-scale solar energy harvesting.

Broadband-absorption mechanism in a water-based metamaterial absorber

Bulky water has been used to construct broadband metamaterial absorbers (MAs). Herein, a broadband MA using sheet of water instead of bulky water is proposed for terahertz domain. The proposed structure has excellent stability to wide incident angles. Most important, the proposed structure surpasses those based on bulky water in terms of absorption performance. The distributions of field and power loss are investigated, which reveal that power loss is mostly contributed by magnetic resonance occurring at the borders of water and PDMS and thus broadband absorption is dependent on the contact area of water and its surrounding dielectric. Therefore, the designed absorber based on sheet of water is superior due to larger contact area. This provides an enlightenment that maximizing contact area between water and its surrounding dielectric such as using sheet of water can enhance absorption performance in the design of water-based MAs, which can facilitate the design. The results of this work may be directive and helpful for designing water-based broadband absorbers.

Broadband and ultra-low reflection metamaterial absorber embedded with magnetic materials

In this study, we design, prepare and characterize a broadband, ultra-low reflectivity and incidence angle-insensitive metamaterial absorber. The design of this absorber not only provides a novel idea for the design of broadband absorbers, but also enhances the application prospects of metamaterial absorbers. By introducing FeSiAlp/epoxy magnetic composite and optimizing the structural parameters, the absorption performance of the metamaterial absorber has been significantly improved. The effective absorption bandwidth (bandwidth with reflectivity less than −10dB) is increased by 3.4 times from 2.19 GHz to 7.49 GHz, and the RLmin (minimum reflection loss) value reaches −38.31 dB at 17.83 GHz, that is the absorption rate reaches 99.99%. Meanwhile, the experimental results also verify the simulation design results. Therefore, the absorber not only plays the characteristics of strong absorption of metamaterial, but also absorbs the advantages of broadband of magnetic material.

Broadband terahertz metamaterial absorber and modulator based on hybrid graphene-gold pattern

We have numerically demonstrated a tunable broadband metamaterial absorber (MA) by introducing a graphene pattern and a gold disk, of which the bandwidth is up to 3.4 THz. When the chemical potential of graphene changes from 0 eV to 0.5 eV, the proposed MA structure can also be used as a modulator with the minimum and maximum modulate depth being about 69.5% and 92.5%, respectively. By tuning the relaxation time of the graphene from 0.1 ps to 0.5 ps, several obvious absorption peaks will occur in the broad and flat absorption band , which will deteriorate the broadband absorption characteristics and make it show a trend of multi-band absorption characteristics. To further increase the absorption bandwidth, a new graphene pattern and an additional gold disk are added into the proposed MA structure to form a new type of MA structure. Simulation result shows that the newly designed MA structure can achieve a wider absorption bandwidth of more than 4.0 THz. Meanwhile, it still has the performance of excellent modulation characteristic, polarization insensitive and wide tolerance of incident angles. All these optimal characteristics of the proposed MA structures will undoubtedly benefit the use of metamaterial absorber, high speed communication, terahertz detection devices, optoelectronic devices and so on. • Both graphene and gold patterns are used in the design of proposed metamaterial absorber. • The proposed structure can achieve broadband absorption with a bandwidth of 3.4 THz. • It has the characteristics of both polarization insensitivity and wide incident angles. • By adjusting the chemical potential of the graphene, dynamic tunability of the absorption performances can be achieved.

All-nitride broadband metamaterial absorbers

Perfect absorber is an important kind of electromagnetic metamaterials. In this study, all-nitride perfect broadband metamaterial absorbers were theoretically designed and studied. Nitride is used as both conducive and insulating layer materials in the absorbers. A three-layer absorber achieve a absorption performance above 90% within 640–1500 nm. A four-layer absorber, in which an additional nitride insulating layer are applied, gives a perfect absorption bandwidth between 260 and 1510 nm. In addition, the nitride absorber exhibits polarization independence at normal incidence and keeps a high absorption at large incidence angle. The results show that the all-nitride absorbers provide high absorption performance comparable to noble metal peers, and are promising alternatives in the related applications.

Design of 2.5D Miniaturized Broadband Absorber for Ultrahigh-Frequency Band

A broadband metamaterial absorber (MA) structure for Ultrahigh-Frequency (UHF) band was proposed, and the miniaturization of the unit was realized by combining the method of bending metal wires and loading metal vias. The size of the unit cell is 0.040 λL × 0.040 λL × 0.075 λL (λL is the wavelength corresponding to the lowest frequency of 0.5 GHz). The simulation results show that the bandwidth of the MA is from 0.50 GHz to 1.33 GHz, and the relative bandwidth is 90.7%. Polarization insensitivity of the MA was realized through assembling a 2 × 2 orthogonal array. TE and TM polarizations maintain more than 80% of the absorptance in the range of 40° at oblique incidence. The consistency of full-wave simulation, circuit simulation and measured results is high, which verifies the broadband absorption characteristics of the proposed MA.

Realization of broadband terahertz metamaterial absorber using an anti-symmetric resonator consisting of two mutually perpendicular metallic strips

This paper presents a scheme to achieve a broadband metamaterial absorber in the terahertz region, which is consisted of an anti-symmetric T-shaped resonator (formed by two mutually perpendicular metallic strips) on top of a metallic back layer separated by an insulator dielectric layer. The anti-symmetric T-shaped resonator can have a strong electromagnetic interaction with the incident beam, resulting in four different absorption peaks having adjacent frequencies, and the superposition effect of these adjacent peaks produces a broadband absorption. The resonance bandwidth of greater than 80% absorption can have 0.58 THz ranging from 1.54 to 2.12 THz, and its relative resonance bandwidth is 31.69%. The resonance bandwidth and relative resonance bandwidth can be scaled by controlling the parameters of two mutually perpendicular metallic strips in the anti-symmetric T-shaped resonator. Moreover, the parameter optimization of the anti-symmetric T-shaped resonator can realize five discrete absorption peaks with adjacent frequencies, and their combined effect can obtain not only broadband absorption but also a greater absorption bandwidth compared with the case of broadband absorption having four absorption peaks.

Tunable terahertz absorption modulation in graphene nanoribbon-assisted dielectric metamaterial

Designing metamaterial absorbers with tunable and broadband response with high modulation depth is crucial for application in switches, polarization sensitive devices, and optical filters. In this article, we report a tunable broadband metamaterial absorber in terahertz regime. The design comprises frustum shaped dielectric (SiO2) metamaterial structures on top of a one-dimensional period array of graphene nanoribbons (GNRs) deposited over the ultrathin metal-backed dielectric. For TM polarization, our design offers a near-perfect absorption in the range of 0.72 THz to 0.9 THz with 72.7 fractional bandwidth. On the contrary, we get a negligible absorption for the TE polarization of the incident light, thereby giving an absorption contrast ratio up to 20.5 dB. The excitation of plasmons in GNRs combined with resonance induced by the graphene-dielectric-metal cavity leads to nearly perfect broadband absorption for the TM polarized radiation. Further, modulation of the absorption spectrum has been achieved by changing graphene conductivity with the help of its Fermi energy. A theoretical model based on effective medium theory and transfer matrix method has been presented to validate absorption response for various Fermi energy values of the graphene. The figure of merit of our design can outperform some of the recently reported tunable metamaterial absorbers.

Perfect metamaterial absorber for solar energy utilization

A polarization insensitive, broadband and wide-angle perfect metamaterial absorber for nearly full solar spectrum harvesting is designed and studied. The structure is a periodic dielectric square array coated with an iron film separated from a bottom iron film by a silica planar and a phase change material cavity. Above 93% absorbance over the spectral range of 400–2000 nm along with 98% average absorption are achieved. The underlying physical mechanism is interpreted by illustrating the electric field intensity distributions at several resonant peaks. In addition, such high and wideband absorption properties remain excellent in a very wide incident angle ranges and the designed absorber possesses large fabrication tolerance, both of which are very attractive for practical application. Furthermore, the absorption spectra are commendably consistent with the AM1.5 spectrum, and the integrated absorption for nearly full solar spectrum is robust against the angle of incidence. These results indicate that the proposed scheme can be applied in solar energy harvesting as well as broadband thermal emission.

Multidimensional manipulation of broadband absorption with dual-controlled terahertz metamaterial absorbers

In this paper, we develop a dual-controlled graphene plasmon-based broadband metamaterial absorber (BMMA) integrating the photosensitive silicon. The designed device can implement active frequency, intensity, and bandwidth modulations of broadband absorption by electrically doping graphene and optically pumping silicon individually or simultaneously, featuring terahertz devices with multidimensional manipulation. To interpret the modulation mechanism of the broadband absorption, an equivalent circuit model based on the transmission line theory is constructed, and theorical results agree well with the simulated ones. In addition, the absorption characteristics depending on polarization angles, incident angles, and structural parameters are also systematically investigated. Therefore, the proposed broadband metamaterial absorber with multidimensional tunability endowed by dual-controlled mode could have potential applications on the design of active and multifunctional terahertz metadevices, such attenuators, modulators, selectors, and detectors.

Broadband polarization insensitive and tunable terahertz metamaterial perfect absorber based on the graphene disk and square ribbon

Designing broadband absorbers with only one metamaterial layer operating in the terahertz band is a relatively difficult challenge. In this paper, we proposed and investigate a broadband metamaterial perfect absorber (MPA) based on the graphene disk and square ribbon. The conductive substrate of this structure is made of gold and the middle dielectric layer of this structure is made of Rogers RT5880LZ, which acts as a spacer layer between the gold and graphene layers. This structure, while having only one metamaterial layer, also has the advantage of easy implementation because the graphene embedded on the dielectric surface does not have a complex design. The simulation results show that the proposed absorber can provide absorption above 90% with a bandwidth of 2.173 ​THz (1.482–3.655 ​THz). The fractional bandwidth ratio of the proposed structure is 85% for absorption greater than 90%. The absorption mechanism of this structure based on electric fields has been investigated. Since the design of the proposed broadband MPA is symmetrical, this structure is not sensitive to polarization and has a good bearing angle in the range of 0–30°. The proposed structure is tunable because we can shift the absorption frequency by changing the Fermi level of graphene (μc). The proposed absorber with these properties is suitable and flexible for applications such as sensing, imaging, and spectroscopy.