Metasurface Absorber Research Articles

Design and theoretical analysis of a tunable bifunctional metasurface absorber based on vanadium dioxide and photoconductive silicon.

A tunable bifunctional metasurface absorber based on vanadium dioxide (VO2) and photoconductive silicon (PSi) is proposed in a terahertz (THz) band. When the conductivities of VO2 (σvo2) and PSi (σPSi) are 10 S m-1 and 1 × 105 S m-1, the designed absorber has a function of dual-broadband absorption. The absorptivity rate of over 90% is in the dual-broadband of 2.47-3.71 THz and 8.90-10.62 THz, corresponding to relative bandwidths (RBs) of 40.13% and 17.62%, respectively. When σvo2 and σPSi are equal to 2 × 105 S m-1 and 1 × 105 S m-1, the proposed design has a function of single-broadband absorption. More than 90% absorptivity is achieved in 4.69-7.72 THz (RB = 48.83%). Furthermore, the absorptivity under the dual- and single-broadbands is manipulated by changing σPSi. An impedance matching theory, equivalent transmission-line (TL) model and electric field distribution are used to reveal the tunable bifunctional absorption mechanism. The influences of structure parameters, polarization mode and incidence angle on the dual- and single-broadband absorption are investigated. The dual- and single-broadband absorption performances are maintained within the incident angles of 55° and 60°, which also possess polarization insensitivity. The proposed absorber has a potential application value in multifunctional devices such as modulation, sensing and electromagnetic (EM) stealth.

Metasurface inverse designed by deep learning for quasi-entire terahertz wave absorption.

Ultra-broadband and efficient terahertz (THz) absorption is of paramount importance for the development of high-performance detectors. These detectors find applications in next-generation wireless communications, military radar systems, security detection, medical imaging, and various other domains. In this study, we present an ultra-wideband THz wave metasurface absorber (UTWMA) featuring a composite surface microstructure and a multilayer absorbing material (graphene). This UTWMA demonstrates remarkable capabilities by achieving highly efficient absorption levels, reaching 96.33%, within the 0.5-10 THz frequency range. To enhance the efficiency and precision of the design process, we have incorporated artificial neural networks, which enable rapid and accurate parameter selection. Moreover, we have conducted a comprehensive analysis of the absorption mechanism exhibited by the UTWMA at different frequencies. This analysis combines insights from the electric field distribution and effective medium theory. The findings presented in this paper are expected to catalyze further research in the domain of broadband THz technology, particularly in the context of metasurfaces and related fields. Additionally, this work paves the way for the development of compact, supercontinuous THz photovoltaic or photothermal electrical devices.

An elliptical nanoantenna array plasmonic metasurface for efficient solar energy harvesting.

Plasmonic metasurfaces with subwavelength nanoantenna arrays have attracted much attention for their ability to control and manage optical properties. Solar absorbers are potential candidates for effectively converting photons into heat and electricity. This study introduces a novel ultrathin metasurface solar absorber employing elliptical-shaped nanoantenna arrays. We theoretically and numerically demonstrate a near-perfect broadband absorber with over 90% absorption efficiency in a wide range of wavelengths of 300-2500 nm, using finite element (FEM) and finite-difference time-domain (FDTD) methods. The proposed nanostructure configuration enhances light absorption by exciting localized surface plasmon resonances (LSPRs) between elliptical-shaped nanoantenna gaps at many wavelengths, maintaining stability at wide incident angles and insensitivity to light polarization. Compared to other state-of-the-art absorbers with a thickness of less than 300 nm, the designed nanostructure with 260 nm thickness achieves over 90% optical absorption across a broad range of wavelengths of 300-1116 nm in air (or vacuum) environments and performs effectively under water conditions for solar energy harvesting in a range of wavelengths of 300-1436 nm, and therefore can serve as a solar evaporator. Combining refractory plasmonic titanium nitride (TiN) and semiconductor gallium nitride (GaN) nanostructures holds great potential for efficient optoelectronic and photocatalytic applications, especially in harsh and high-temperature environments like thermophotovoltaic systems. The TiN-based metasurface absorber, with its ultrathin nanostructure and suitable spectral absorption in ultraviolet-visible-infrared spectra, offers scalability and cost-effectiveness. The findings in this work will deepen our understanding of LSPRs and pave a novel path for efficient solar energy conversion.

A Spiral Wire_coil Wideband Metasurface Absorber with Ultrathin and Flexible Feature for Microwave Applications

A Spiral Wire_coil Wideband Metasurface Absorber with Ultrathin and Flexible Feature for Microwave Applications

Customizable multifunctional metasurface absorber based on bidirectional deep neural networks covering the quasi-entire terahertz band

Customizable multifunctional metasurface absorber based on bidirectional deep neural networks covering the quasi-entire terahertz band

An Ultrathin Multiband Chiral Metasurface for Transmission and Asymmetric Absorption of Electromagnetic Waves

This article presents an ultrathin chiral metasurface which can exhibit multiband asymmetric absorption as well as symmetric transmission in a specific frequency band outside the absorption regions. Unlike most electromagnetic metasurface absorbers, the proposed structure does not have a continuous conducting sheet at the bottom which also allows it to act as a bandpass spatial filter. The metasurface has a substrate thickness of only λhigh/62.5 and λlow/34 at the highest and lowest operational free‐space wavelengths, respectively. The transmission band is centered at 5.5 GHz, and the asymmetric absorption bands are centered at 3, 3.33, and 4.5 GHz, respectively. The operational bands can be tuned as per user requirements. The metasurface has an angular stability of 45° for both TE and TM incidence. It can be used for radar cross‐section (RCS) reduction, electromagnetic shielding, and as a spatial bandpass filter.

Investigations on a Triple-Band Metasurface Absorber as THz-Biomedical Sensor

Investigations on a Triple-Band Metasurface Absorber as THz-Biomedical Sensor

Dual-band terahertz chiral metasurface absorber with enhanced circular dichroism based on temperature-tunable InSb for sensing applications.

Circular dichroism (CD) in terahertz (THz) regions has been widely used in biomonitoring, analytical chemistry, communication sensing, and other fields. Herein, we present a simple design for a dual-band THz chiral metasurface absorber (CMA) with a stronger CD effect based on temperature-tunable InSb for enhanced sensing applications. The proposed dual-band CMA consisted of a periodic array of the evolved C-shaped InSb adhered to a copper substrate. The designed CMA at 305 K achieved a right-handed circular polarization (RCP)-selective absorbance of 98.86% and 97.43% at 1.65 THz and 1.89 THz, respectively, and left-handed circular polarization (LCP) absorbance of 9.98% and 22.46%, respectively, and exhibited stronger CD values of 0.89 and 0.75. In addition, the CD properties of the designed CMA can be adjusted by changing the geometrical parameters of the unit-cell structure. The simulated electric field and power follow distributions indicate that this dual-band chiral-selective absorption of the designed CMA is due to the different plasma resonance mode excitations for the incident circular polarization (CP) wave. In addition, the CD properties of the designed CMA can be adjusted by changing the geometrical parameters of the unit-cell structure. Furthermore, CD spectra can be dynamically adjusted by varying the outside temperature and refraction index (RI) of the filled analytes. The designed dual-band CMA can function as a high-performance temperature sensor with sensitivities of 4.68 GHz K-1 and 5.52 GHz K-1 and also as an RI sensor with sensitivities of 1080 GHz RIU-1 and 860 GHz RIU-1, respectively. Our proposed tunable dual-band CMA with its exquisite performance has the potential to be widely applied in diverse areas such as detection, sensing, and other related optoelectronic fields.

Design and analysis of a dual-broadband microwave metasurface absorber with flexibility and transparency

Design and analysis of a dual-broadband microwave metasurface absorber with flexibility and transparency

Grid composite meta-surface absorber with thermal isolation structure for terahertz detection.

This paper specifically focuses on the absorber, the critical component responsible for the detector's response performance. The meta-surface absorber combines two resonant structures and achieves over 80% absorptance around 210 GHz, resulting in a broad operating frequency range. FR-4 is selected as the dielectric layer to be compatible with standard printed circuit board (PCB) technology, which reduces the overall fabrication time and cost. The absorbing unit and array layout are symmetrically designed, providing stable absorptance performance even under incident waves of different polarization angles. The polarization-insensitive absorptance characteristic further enhances the compatibility between the absorber and the detector in the application scenario. Furthermore, the thermal insulation performance of the absorber is ensured by introducing thermal insulation gaps. After completing fabrication through PCB technology, testing revealed that the absorber maintained excellent absorptance performance within its primary operating frequency range. This performance consistency closely matched the simulation results.

Global rigorous coupled wave analysis for design of multilayer metasurface absorbers.

In this work, a novel Global NV-ETM RCWA method is proposed to accelerate the optimization of the periodic stepped radar absorbing structure. This method is based on the rigorous coupled-wave analysis (RCWA) utilizing the normal vector field (NV) and enhanced transmittance matrix (ETM) approach. The NV field dramatically improves the convergence rate for both dielectric and magnetic metasurfaces. The Global NV-ETM RCWA algorithm is developed to further accelerate the complete search calculations. Using the proposed method, the periodic stepped radar absorbing structures are efficiently optimized to realize the entire band absorption in 2-18 GHz. The optimization results demonstrate the Global NV-ETM RCWA method significantly increase the computational efficiency, with a 38-fold improvement over direct NV-ETM RCWA calculations when the truncation order N=3. This method provides a powerful tool for designing metasurface absorbers with various desired functionalities.

Dual-band waveform-selective metasurfaces for reflection suppression

In this study, we present a design method to realize waveform-selective metasurface absorbers operating in more than one frequency band, which is validated both numerically and experimentally. The waveform-selective metasurface absorbers could preferentially absorb target electromagnetic waves of the same frequency in accordance with the incident waveform, more specifically, the pulse width. Although such waveform selectivity is expected to offer additional selectivity at a fixed frequency, thus far, its operation has been limited to a single frequency band. Our design method enables waveform-selective metasurface absorbers to suppress reflection depending on the incident pulse width at two independent frequencies. Importantly, the dual-band approach is enhanced by varying the spatial ratio of unit cells assigned to the two frequencies. Thus, our study opens up possibilities for the utilization of waveform-selective metasurfaces in diverse frequency bands, providing a valuable and versatile solution to address challenges spanning various applications, such as wireless communications, sensing, and electromagnetic shielding.

Plane-Wave Spectrum Analysis of Spherical Wave Absorption and Reflection by Metasurface Absorber

Plane-Wave Spectrum Analysis of Spherical Wave Absorption and Reflection by Metasurface Absorber

Waveform-Selective Metasurface Absorber With a Single-Patch Structure and Lumped Nonlinear Circuit for a Higher-Order Mode

Waveform-Selective Metasurface Absorber With a Single-Patch Structure and Lumped Nonlinear Circuit for a Higher-Order Mode

Dual Band Metasurface Absorber with Insensitive Polarization and Incidence Angle for S and C Band Applications

Dual Band Metasurface Absorber with Insensitive Polarization and Incidence Angle for S and C Band Applications

Multi-polarization selective absorber based on terahertz metasurface

Tunable absorbers attract much attention due to their wide applications, such as integrated optical sensors, multiplexing far-field imaging and so on. In this paper, we design a multi-polarization selective absorber based on terahertz metasurface, whose geometric symmetry is tunable to satisfy the requirements of linear and circular polarization selective absorbers. At the ON state, the metasurface selectively absorbs y-polarized wave at 1.0 THz, with the linear dichroism of 0.84. At the OFF state, the metasurface selectively absorbs left circularly polarized wave at 1.16 THz, with the circular dichroism of 0.81. The physical mechanism of the metasurface is explained by the Jones calculus and the electromagnetic field distributions. In addition, the multi-polarization selective behavior is insensitive to the incident angle. Finally, we design a sample to verify the potential application of the metasurface absorber, which displays multiplexing imaging of ‘C’, ‘mirrored C’, ‘O’ and blurred images under different polarized incidences at different states. Such a metasurface, switching between linear polarization selective absorber and circular polarization selective absorber, may achieve stable applications in multifunction integrated absorbers, detectors, and image encryptions.

Genetic algorithm-enhanced design of ultra-broadband tunable terahertz metasurface absorber

In this paper, we demonstrate an ultra-broadband tunable metasurface absorber and investigate the automation of its design process, avoiding the traditional manual trial-and-error process. Here, automation is achieved by controlling the random coding structure of the VO2 layer by genetic algorithm. Subsequently, the bandwidth of the metasurface absorber is enlarged by a structural design forming a Fabry-Perot cavity. The genetic algorithm-enhanced metasurface absorber absorption bandwidth ranges from 1.84 to 8.36 THz, with a relative bandwidth of up to 127.8 %. The maximum absorption can be tuned from 4 % to 100 % by controlling the conductivity of VO2 through temperature. Our results may provide guidance for the automated design studies of ultra-broadband tunable terahertz metasurface absorbers.

Metasurface Absorbers with Film-Coupled Au Nanoclusters to Achieve Broadband and Polarization-Independent Absorption of UV-Vis Light.

Metasurface absorbers (MAs) have attracted widespread interest in the recent study of subwavelength artificial optical metasurfaces, although most reported MAs suffer from the actualities of costly and time-consuming fabrications, narrow working bandwidth, polarization-dependent responses, etc., somewhat limiting their practical applications. Herein, we introduce a facile and low-cost method to fabricate MAs with excellent absorption performances via the self-assembly of synthesized Au nanoclusters (NCs) on a Au film spaced by a nanoscale-thick dielectric SiO2. Interestingly, the proposed MAs with well-designed Au film-coupled Au NCs (i.e., an appropriate surface coverage of Au NCs and the compatible thickness of the SiO2 spacer) exhibited a measured average absorbance above 90% within a broad UV-vis wavelength band (200-800 nm). In addition, owing to the MAs' topological symmetry, their UV-vis absorption behaviors presented polarization insensitivity with the incident light angles ranging from 20 to 50°. It has been demonstrated that the excited different surface plasmon resonance modes between Au NCs and the adjacent Au film were vital; in addition, the light-trapping effects from "V"-shaped structures of Au NCs were favorable for the designed MAs with enhanced light absorption. We believe that such MAs and the potential self-assembly fabrication strategy may facilitate scalable optical applications such as photothermalvoltaics, ultraviolet protection, optical storage, and sensing.

Dual-band chirality-selective absorbing by plasmonic metasurfaces with breaking mirror and rotational symmetry.

In this work, we proposed a state-of-the-art metasurface model that breaks the mirror symmetry and rotation symmetry of the structure. It consists of two-layer rotating gold split rings, and has the capability of chirality-selective absorption for circularly polarized light (CPL) in two bands. The absorption peaks for left- and right- circularly polarized (LCP&RCP) light appeared at 989 nm and 1404 nm, respectively, with the maximum absorptivity of 98.5% and 96.3%, respectively. By changing the rotation angle of the two-layer gold split rings, it could also be designed as a single-band chiral metasurface absorber, which only absorbed RCP light but not LCP light, and the absorptivity of RCP light could be up to 97.4%. Furthermore, we found our designed absorbers had the characteristics of great circular dichroism (CD) and symmetric absorption. The physical mechanism of the selective absorption of CPL by the absorbers may be explained by the current vector analysis. In addition, the absorption peak could be tuned with the changing of the geometrical parameters of the structure. The proposed chirality-selective metasurface absorbers could be used in CD spectral detection, optical communication, optical filtering, and other fields.

Tunable ultra-wideband graphene metasurface absorber: A mode merger design approach for terahertz applications

This paper presents a systematic approach for designing an ultra-wideband (UWB) absorber for terahertz (THz) applications. The metasurface consists of top patterned graphene (Gpat) and bottom continuous graphene (Gcont), each having a thickness of 0.335 nm and separated by a 3 μm thick silicon dioxide (SiO2) dielectric. Multiple absorbing modes have been generated by engraving rectangular, star-shaped, and circular ring slots on the top Gpat resonating at 3.22, 4.52, and 0.32 THz, respectively. A circular ring slot works as a coupling controller and helps to combine different slot resonances. The mode merger technique, along with the high plasmonic coupling between Gpat and Gcont controlled by Gcont help to attain an absorption bandwidth (BW) of 5.9 THz (193.44%) with absorptivity ≥ 90% ranging from 0.1 to 6 THz. The periodicity and thickness of the proposed polarization-insensitive metasurface are found to be λ0/300 and λ0/996.68, respectively, where λ0 is free space wavelength computed at 0.1 THz. Absorptivity ≥ 80% for incidence angle up to 60∘ under both transverse electric (TE) and transverse magnetic (TM) polarization has also been achieved. The absorber provides excellent frequency tunable characteristics over a UWB band and shows blue-shift with increased chemical potential (μc).