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Open AccessArticle

Broadband Polarization-Insensitive Tunable Terahertz Metamaterial Absorber Based on an Asymmetric Graphene Structure

by Ahmed Ali, Sulaiman Al-Sowayan, Waleed Shihzad, Asrafali Barkathulla, Zaid Ahmed Shamsan, Majeed A. S. Alkanhal and Yosef T. Aladadi

Nanomaterials 2026, 16(9), 502; https://doi.org/10.3390/nano16090502 - 22 Apr 2026

Viewed by 821

Abstract

A graphene-based tunable broad-band terahertz (THz) metamaterial absorber is presented, exhibiting strong and stable absorption across a wide frequency range. The device employs an ultra-thin three-layer structure consisting of a metallic reflector, a dielectric spacer, and a patterned graphene metasurface with an asymmetric [...] Read more.

A graphene-based tunable broad-band terahertz (THz) metamaterial absorber is presented, exhibiting strong and stable absorption across a wide frequency range. The device employs an ultra-thin three-layer structure consisting of a metallic reflector, a dielectric spacer, and a patterned graphene metasurface with an asymmetric geometry. Through optimized structural parameters, the absorber achieves broad-band absorption exceeding 90% between 2.45 THz and 6.11 THz with a bandwidth of 3.66 THz, featuring three distinct resonant frequencies at 2.764 THz, 3.534 THz, and 5.41 THz, corresponding to peak absorption efficiencies of 97.26%, 96.96%, and 99.90%, respectively. Impedance matching and electric field analyses confirm that the enhanced absorption arises from the strong coupling of electric and magnetic resonances within the multilayer structure. Moreover, the absorber exhibits polarization-insensitive behavior under varying polarization angles and maintains high absorption stability for both TE and TM modes up to an incident angle of 60°, as verified by simulation results, and allows dynamic tunability through Fermi-level modulation. These characteristics highlight the absorber’s potential for advanced THz imaging, sensing, and stealth applications. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Microwave Absorption and Electromagnetic Interference Shielding)

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12 pages, 3642 KB

Open AccessArticle

A Flexible and Polarization-Insensitive Metasurface Harvester Featuring a Dual-Ring Unit with a T-Shaped-Gap Outer Ring for Microwave Power Transfer

by Zhonglin Li, Tianxin Ma, Qian Yu, Yu Zhao, Zhuozheng Wang, Xu Liu and Tao Chen

Micromachines 2026, 17(3), 319; https://doi.org/10.3390/mi17030319 - 4 Mar 2026

Viewed by 704

Abstract

This paper proposes a flexible and polarization-insensitive metasurface (MS) operating at the 5.8 GHz band for electromagnetic energy harvesting. The proposed MS unit features a top-layer dual-ring resonator with a T-shaped gap and a bottom cross-shaped coplanar waveguide (CPW), fabricated on a flexible [...] Read more.

This paper proposes a flexible and polarization-insensitive metasurface (MS) operating at the 5.8 GHz band for electromagnetic energy harvesting. The proposed MS unit features a top-layer dual-ring resonator with a T-shaped gap and a bottom cross-shaped coplanar waveguide (CPW), fabricated on a flexible polyimide substrate. To elucidate the physical mechanism of energy capture, an equivalent circuit model is established based on transmission line theory. Expressions for the total input impedance are derived, revealing the quantitative relationship between the structural parameters and the impedance-matching condition. The simulation results validate this theoretical model and show that the structure achieves an absorption efficiency of 97.5% and a harvesting efficiency (HE) of 86.6% at 5.72 GHz. The conversion efficiency remains above 50% over a wide range of incident angles, and the HE exhibits minimal variation within a polarization angle range of 0–90°. Experimental results indicate that the MS reaches a maximum HE of 73.2%, maintains over 40% efficiency under large-angle incidence, and achieves more than 65% HE across various curved surfaces. With its mechanical flexibility, polarization insensitivity, and simplified manufacturing, this MS harvester provides a reliable and scalable power solution for wireless power transfer applications. Full article

(This article belongs to the Topic Advanced Energy Harvesting Technology, 2nd Edition)

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17 pages, 3068 KB

Open AccessArticle

Magnetoresponsive Fiber-Reinforced Periodic Impedance-Gradient Absorber: Design and Microwave Absorption Performance

by Yuan Liang, Wei Chen, Shude Gu, Xu Ding and Yuping Duan

Nanomaterials 2026, 16(1), 42; https://doi.org/10.3390/nano16010042 - 29 Dec 2025

Viewed by 869

Abstract

In recent years, achieving ultra-wideband electromagnetic absorption has emerged as a critical challenge in confronting advanced broadband electromagnetic detection technologies. This capability is essential for effectively countering sophisticated radar systems. In this study, we present a novel multilayer metamaterial absorber that integrates an [...] Read more.

In recent years, achieving ultra-wideband electromagnetic absorption has emerged as a critical challenge in confronting advanced broadband electromagnetic detection technologies. This capability is essential for effectively countering sophisticated radar systems. In this study, we present a novel multilayer metamaterial absorber that integrates an FR4 transmission layer, a periodic gradient dielectric structure designed for resonant impedance matching, and a magnetic skin layer for enhanced energy dissipation. By employing asymptotic gradients in both structure and composition, this design achieves dual-gradient electromagnetic parameter modulation, enabling efficient absorption across the X, Ku, and K bands (8.6–26.4 GHz) with a total thickness of 3.5 mm (effective thickness: 2 mm) and a density that is one-third that of conventional magnetic metamaterials. The proposed absorber demonstrates polarization insensitivity, stability across wide incident angles (up to 60°), and an absorption efficiency of 94%, as confirmed by full-wave simulations and experimental validation. Moreover, the fiber-reinforced hierarchical structure addresses the traditional trade-off between broadband absorption performance and mechanical load-bearing capacity. Full article

(This article belongs to the Special Issue Enhanced Electromagnetic Wave Absorption: Nanomaterials and Nanotechnology)

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16 pages, 14453 KB

Open AccessArticle

A Broadband and Wide-Scanning Dual-Polarized Dipole Array with Low Profile

by Yunfan Peng and Chang Liu

Electronics 2024, 13(24), 4976; https://doi.org/10.3390/electronics13244976 - 18 Dec 2024

Viewed by 2076

Abstract

This study presents a novel methodology for designing a planar broadband wide-scanning dual-polarized array using tightly-coupled dipoles and wide-angle impedance matching. By etching the S-shaped gaps between the dipoles and incorporating shorting vias with defected ground structures, we demonstrated that all radiation elements [...] Read more.

This study presents a novel methodology for designing a planar broadband wide-scanning dual-polarized array using tightly-coupled dipoles and wide-angle impedance matching. By etching the S-shaped gaps between the dipoles and incorporating shorting vias with defected ground structures, we demonstrated that all radiation elements can be arranged on a single-layer substrate. Additionally, we introduced a thin printed circuit board (PCB) layer with two-dimensional periodic structures for impedance matching at wide scan angles. Leveraging high permittivity and constrained electromagnetic waves, we realized zero-scan blindness within this band. The aperture consisted of only two PCB layers, with a total profile of approximately 0.091λ_low, where λ_low represented the free-space wavelength at 6 GHz. A 3 × 4 dual-polarized array was fabricated and measured to validate the proposed approach. The measured active voltage standing wave ratio for one embedded array element surpassed 2.2 over 6–18 GHz. By enabling the orthogonal dipoles at the edge of the array to be mutually coupled using an additional metal patch, the active S₁₁ for the edge cells exceeded −8.8 dB over 6.9–18 GHz. The measured patterns were in good agreement with simulations over 6–18 GHz, with the array exhibiting good radiation performance over ±60° in the E- and H-planes. Full article

(This article belongs to the Section Microwave and Wireless Communications)

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12 pages, 2395 KB

Open AccessArticle

Absorption and Reflection of Switchable Multifunctional Metamaterial Absorber Based on Vanadium Dioxide

by Enbo Liu, Taiguo Lv and Minghong Wang

Appl. Sci. 2024, 14(14), 6004; https://doi.org/10.3390/app14146004 - 10 Jul 2024

Cited by 5 | Viewed by 2063

Abstract

A dynamically tunable terahertz broadband absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The absorber consists of two patterned VO₂ layers and a metal bottom layer separated by two polytetrafluoroethylene (PTFE) dielectric layers. Simulation [...] Read more.

A dynamically tunable terahertz broadband absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The absorber consists of two patterned VO₂ layers and a metal bottom layer separated by two polytetrafluoroethylene (PTFE) dielectric layers. Simulation results show that the absorption exceeds 90% in the frequency range of 2.4–11 THz with a relative bandwidth of 128.4% under normal incidence. When VO₂ is in the metal phase, the designed absorber functions as an ideal absorber. The absorption rate can be flexibly adjusted from 2% to 99% as vanadium dioxide transitions from the insulator phase to the metal phase. Therefore, the newly developed broad structure has the capability to seamlessly transition between functioning as an absorber or reflector through modifications in the conductivity of VO₂ from the insulator phase to the metal phase. Moreover, further insight into the underlying physical processes can be gained by studying the insensitivity of the proposed absorber to the polarization of incident light and its ability to achieve high absorption across a wide range of incident angles. Impedance matching theory and electric field distribution of the absorber are investigated. The THz absorber has many potential applications in fields such as THz sensors, modulation, and switches. Full article

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12 pages, 4755 KB

Open AccessArticle

Five-Band Tunable Terahertz Metamaterial Absorber Using Two Sets of Different-Sized Graphene-Based Copper-Coin-like Resonators

by Jieru Wang, Xuefeng Qin, Qian Zhao, Guiyuan Duan and Ben-Xin Wang

Photonics 2024, 11(3), 225; https://doi.org/10.3390/photonics11030225 - 29 Feb 2024

Cited by 7 | Viewed by 3349

Abstract

In this paper, a five-band metamaterial absorber with a tunable function in a terahertz band is proposed, which consists of a gold grounding layer, a polyimide dielectric layer, and a periodic patterned graphene layer. The patterned graphene layer is constructed from two sets [...] Read more.

In this paper, a five-band metamaterial absorber with a tunable function in a terahertz band is proposed, which consists of a gold grounding layer, a polyimide dielectric layer, and a periodic patterned graphene layer. The patterned graphene layer is constructed from two sets of copper-coin-shaped structures of different sizes. The designed absorber achieves absorptions of 96.4%, 99.4%, 99.8%, 98.4%, and 99.9% at 4.62 THz, 7.29 THz, 7.70 THz, 8.19 THz, and 8.93 THz, respectively, with an average absorption intensity of 98.78%. The physical mechanism of this five-band absorber was explained by the impedance matching principle and electric field distribution. The absorption performance of the five-band absorber can be effectively tuned by changing the geometry of the patterned graphene array and the thickness of the dielectric layer. Given that the resonant frequency of the absorber varies in proportion to the Fermi level, by varying the Fermi level of the graphene hypersurface, we can achieve the continuous tuning of the absorption performance over a wide frequency range. The five-band absorber has a stable absorption performance over a wide incidence angle of 0–65°, and by combining the merits of high absorption, dynamic adjustability, and a large number of absorption peaks, the given absorber could have great potential for applications in nondestructive testing, imaging, communication, sensing, and detectors. Full article

(This article belongs to the Special Issue Recent Advances in Optical Metamaterials and Metasurfaces)

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14 pages, 6332 KB

Open AccessArticle

A Theoretical Proposal for an Actively Controlled Ultra-Wideband Absorber Based on Vanadium Dioxide Hybrid Metamaterials

by Ubaid Ur Rahman Qureshi, Muhammad Ismail Khan and Bin Hu

Appl. Sci. 2022, 12(19), 10164; https://doi.org/10.3390/app121910164 - 10 Oct 2022

Cited by 22 | Viewed by 2917

Abstract

In this study, an ultra-wideband actively tunable terahertz absorber composed of four identical arc-shaped structures made of phase transition material vanadium dioxide (VO₂) is presented. A metal ground plane is placed at the bottom and an insulating spacer (quartz) as the [...] Read more.

In this study, an ultra-wideband actively tunable terahertz absorber composed of four identical arc-shaped structures made of phase transition material vanadium dioxide (VO₂) is presented. A metal ground plane is placed at the bottom and an insulating spacer (quartz) as the middle dielectric layer. Simulation results demonstrate 90% absorption with a broad bandwidth spanning 3 THz (2.7 THz–5.7 THz) under normal incidence. The proposed structure transforms from a reflector to an absorber by changing the conductivity from 200 S/m to 2 × 10⁵ S/m; the absorbance at peak frequencies can be consistently tuned from 4% to 100%. Absorption spectra demonstrate that the polarization angle does not affect the response of the proposed structure. Power loss density (PLD) and impedance-matching theory are further analyzed to learn more about the physical origin of ultra-wide absorption. The ultra-wide operating bandwidth, high absorption efficiency, active tunability, and independence of polarization make the proposed structure an excellent candidate for integration into profound THz applications such as sensors, modulators, and optic-electro switches. Full article

(This article belongs to the Section Nanotechnology and Applied Nanosciences)

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11 pages, 4166 KB

Open AccessArticle

Methodology for Improving Scanning Performance Loading an Array Element with a 3D All-Metal WAIM

by Diego Bermúdez-Martín, Raphaël Gillard, Carlos Molero, Hervé Legay and María García-Vigueras

Electronics 2022, 11(18), 2848; https://doi.org/10.3390/electronics11182848 - 9 Sep 2022

Cited by 6 | Viewed by 3029

Abstract

All-metal 3D printing technologies are allowing the conception of new structures for different applications. This publication explores the potential of employing for the first time an all-metal 3D unit-cell topology to perform wide-angle impedance matching layers. A new equivalent circuit is derived for [...] Read more.

All-metal 3D printing technologies are allowing the conception of new structures for different applications. This publication explores the potential of employing for the first time an all-metal 3D unit-cell topology to perform wide-angle impedance matching layers. A new equivalent circuit is derived for the oblique incidence, providing a good estimation of the cell response for the scanning range (

θ = [0 °, 55 °]

) in the main scanning planes for a linearly polarized radiated field. This analytical model is later used to develop a wide-angle impedance matching design methodology for a generic antenna. This methodology is tested in practice to match a phased array made of metallic horns at 18 GHz. An improvement of 5 dB is obtained in the simulations for angles

θ > 35 °

for the H-plane. Full article

(This article belongs to the Special Issue Metastructures and Antennas with Enhanced Properties for Modern Microwave and Millimeter-Wave Applications)

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16 pages, 3471 KB

Open AccessArticle

Perfect Absorption of Fan-Shaped Graphene Absorbers with Good Adjustability in the Mid-Infrared

by Hongyu Ren, Qianyi Shangguan, Zijun Song, Yong Zhao, Zao Yi, Guolu Ma, Jianguo Zhang, Hua Yang, Shifa Wang and Pinghui Wu

Coatings 2022, 12(7), 990; https://doi.org/10.3390/coatings12070990 - 14 Jul 2022

Cited by 5 | Viewed by 2898

Abstract

This paper presents a graphene metamaterial absorber based on impedance matching. A finite difference in time domain (FDTD) method is used to achieve a theoretically perfect absorption in the mid-infrared band. A basis is created for the multiband stable high absorption of graphene [...] Read more.

This paper presents a graphene metamaterial absorber based on impedance matching. A finite difference in time domain (FDTD) method is used to achieve a theoretically perfect absorption in the mid-infrared band. A basis is created for the multiband stable high absorption of graphene in the mid-infrared. The designed graphene absorber is composed of graphene, a dielectric layer, a gold plane, and a silicon substrate, separately. The incident source of mid-infrared can be utilized to stimulate multiband resonance absorption peaks from 2.55 to 4.15 μm. The simulation results show that the absorber has three perfect resonance peaks exceeding 99% at λ₁ = 2.67 μm, λ₂ = 2.87 μm, and λ₃ = 3.68 μm, which achieve an absorption efficiency of 99.67%, 99.61%, and 99.40%, respectively. Furthermore, the absorber maintains an excellent performance with a wide incident angle range of 0°–45°, and it also keeps the insensitive characteristic to transverse electric wave (TE) and transverse magnetic wave (TM). The results above indicate that our perfect graphene absorber, with its tunability and wide adaptability, has many potential applications in the fields of biosensing, photodetection, and photocell. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

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9 pages, 2579 KB

Open AccessEditor’s ChoiceArticle

A Simple Structure for an Independently Tunable Infrared Absorber Based on a Non-Concentric Graphene Nanodisk

by Kun Yu, Peng Shen, Wei Zhang, Xicheng Xiong, Jun Zhang and Yufang Liu

Materials 2022, 15(6), 2296; https://doi.org/10.3390/ma15062296 - 20 Mar 2022

Cited by 8 | Viewed by 2822

Abstract

Due to its unique electronic and optical properties, graphene has been used to design tunable optical absorbers. In this paper, we propose a plasmonic absorber consisting of non-concentric graphene nanodisk arrays, which is designed to operate in the mid-infrared spectral range and is [...] Read more.

Due to its unique electronic and optical properties, graphene has been used to design tunable optical absorbers. In this paper, we propose a plasmonic absorber consisting of non-concentric graphene nanodisk arrays, which is designed to operate in the mid-infrared spectral range and is capable of achieving nearly perfect absorption. Two perfect absorption peaks are produced due to the impedance of the structure, which matches that of the free space. The influences of the thicknesses of the dielectric layer, the size of graphene nanodisk, and the incident conditions on the absorption are studied. Moreover, the absorption intensity can be independently tuned by varying the Fermi levels of two graphene nanodisks. Furthermore, the polarization-independent absorbance of the absorber exceeds 95% under oblique incidence, and remains very high over a wide angle. This proposed absorber has potential applications in optical detectors, tunable sensors, and band-pass filters. Full article

(This article belongs to the Special Issue Nano and Advanced Material Engineering)

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9 pages, 1981 KB

Open AccessArticle

Tunable Dual Broadband Terahertz Metamaterial Absorber Based on Vanadium Dioxide

by Xiao-Fei Jiao, Zi-Heng Zhang, Tong Li, Yun Xu and Guo-Feng Song

Appl. Sci. 2020, 10(20), 7259; https://doi.org/10.3390/app10207259 - 17 Oct 2020

Cited by 56 | Viewed by 5248

Abstract

With the rapid development of terahertz technology, tunable high-efficiency broadband functional devices have become a research trend. In this research, a dynamically tunable dual broadband terahertz absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The [...] Read more.

With the rapid development of terahertz technology, tunable high-efficiency broadband functional devices have become a research trend. In this research, a dynamically tunable dual broadband terahertz absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The metamaterial is composed of patterned VO₂ on the top layer, gold on the bottom layer and silicon dioxide (SiO₂) as the middle dielectric layer. Simulation results show that two bandwidths of 90% absorption reach as wide as 2.32 THz from 1.87 to 4.19 THz and 2.03 THz from 8.70 to 10.73 THz under normal incidence. By changing the conductivity of VO₂, the absorptance dynamically tuned from 2% to 94%. Moreover, it is verified that absorptance is insensitive to the polarization angle. The physical origin of this absorber is revealed through interference theory and matching impedance theory. We further investigate the physical mechanism of dual broadband absorption through electric field analysis. This design has potential applications in imaging, modulation and stealth technology. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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13 pages, 5295 KB

Open AccessArticle

Wide-Angle Polarization-Independent Ultra-Broadband Absorber from Visible to Infrared

by Jing Liu, Wei Chen, Jia-Chun Zheng, Yu-Shan Chen and Cheng-Fu Yang

Nanomaterials 2020, 10(1), 27; https://doi.org/10.3390/nano10010027 - 20 Dec 2019

Cited by 73 | Viewed by 4249

Abstract

We theoretically proposed and numerically analyzed a polarization-independent, wide-angle, and ultra-broadband absorber based on a multi-layer metasurface. The numerical simulation results showed that the average absorption rates were more than 97.2% covering the broad wavelength of 400~6000 nm (from visible light to mid-infrared [...] Read more.

We theoretically proposed and numerically analyzed a polarization-independent, wide-angle, and ultra-broadband absorber based on a multi-layer metasurface. The numerical simulation results showed that the average absorption rates were more than 97.2% covering the broad wavelength of 400~6000 nm (from visible light to mid-infrared light) and an absorption peak was 99.99%, whatever the polarization angle was changed from 0° to 90°. Also, as the incidence angle was swept from 0° to 55°, the absorption performance had no apparent change over the wavelength ranges of 400 to 6000 nm. We proved that the proposed metasurface structure was obviously advantageous to achieve impedance matching between the absorber and the free space as compared with conventionally continuous planar-film structures. The broadband and high absorption resulted from the strong localized surface plasmon resonance and superposition of resonant frequencies. As expectable the proposed absorber structure will hold great potential in plasmonic light harvesting, photodetector applications, thermal emitters and infrared cloaking. Full article

(This article belongs to the Section Nanophotonics Materials and Devices)

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9 pages, 2203 KB

Open AccessArticle

Ultra-Wideband and Wide-Angle Microwave Metamaterial Absorber

by Xavier Begaud, Anne Claire Lepage, Stefan Varault, Michel Soiron and André Barka

Materials 2018, 11(10), 2045; https://doi.org/10.3390/ma11102045 - 20 Oct 2018

Cited by 62 | Viewed by 8812

Abstract

In order to extend the performance of radar absorbing materials, it is necessary to design new structures with wideband properties and large angles of incidence which are also as thin as possible. The objective of this work, realized within the framework of the [...] Read more.

In order to extend the performance of radar absorbing materials, it is necessary to design new structures with wideband properties and large angles of incidence which are also as thin as possible. The objective of this work, realized within the framework of the SAFAS project (self-complementary surface with low signature) is, then, the development of an ultra-wideband microwave absorber of low thickness. The design of such material requires a multilayered structure composed with dielectric layers, metasurfaces, and wide-angle impedance matching layers. This solution has been realized with on-the-shelf materials, and measured to validate the concept. At normal incidence, the bandwidth ratio, defined for a magnitude of the reflection coefficient below −10 dB, is 4.7:1 for an absorber with a total thickness of 11.5 mm, which corresponds to λ/7 at the lowest operating frequency. For an incidence of 60°, this bandwidth ratio is reduced to 3.8:1, but the device remains ultra-wideband. Full article

(This article belongs to the Special Issue Electromagnetic Wave Absorbing Structures)

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