Ultra-wideband Absorber Research Articles

Direction‐Dependent Janus Metasurface Supported by Waveguide Structure with Spoof Surface Plasmon Polariton Modes

AbstractIn this work, a novel direction‐dependent Janus metasurface (DDJM) supported by waveguide structure (WGS) with surface plasmon polariton (SSPP) modes is proposed. In −z‐direction, linear‐to‐linear (LTL) polarization conversion (PC) can be implemented at the low frequencies by the reflection characteristics of the WGS. And in the +z‐direction, the ultrawideband absorption takes shape due to the SSPP modes, in which strongly localized oscillation of free electrons are confined to the metal–dielectric interface assisted by the WGS. The combination of the WGS and the PC structure finally enables the low‐frequency LTL PC with the high polarization conversion ratio (over 0.9) at 0.87–1.35 THz in −z‐direction, corresponding to the relative bandwidth of 43.24%, as well as the absorption in +z‐direction with an efficiency of over 0.9 in the frequency range of 0.8–1.2 THz. Also the fixed direction‐independent transparent window brought by WGS runs from 1.57 to 1.90 THz when the co‐polarized transmission coefficient exceeds 0.85, occupying a staggered band compared to that of PC or absorption. The favorable properties of the DDJM promise a potential practical application in full‐space electromagnetic wave control and radar stealth technology fields.

Carbon-encapsulated Co7Fe3 nanocomposites with high intensity and ultra-wideband microwave absorption

Composites composed of ferromagnetic alloy/dielectric material have been widely studied and applied. The alloying of the two metals endows these composites with escalated magnetic loss capacity, but they are usually micro-sized, which is not conducive to further improving the absorption performance. Herein, we develop an efficient approach to synthesize Co7Fe3@C nanocomposites with particle sizes ranging from 32 to 42 nm based on the in-situ carbon coating on the FeCo2O4 precursor and subsequent carbothermal reduction procedure. The thickness of carbon coating can be effectively tailored by controlling the reaction conditions. The minimum reflection loss (RL) value of the Co7Fe3@C nanocomposite with a carbon coating of 2.5 nm goes up to −100.8 dB at only 1.7 mm thickness, and the effective absorption bandwidth (EAB) also reaches 9.9 GHz (8.1–18 GHz) at 2.0 mm. Moreover, as the carbon coating increases to 4.2 nm, the bandwidth escalates to 11.5 GHz (6.5–18 GHz) at 2.0 mm, which covers the whole X and Ku bands and half of the C band. The remarkable performance originates from the strong magnetic loss capability of the nano-sized Co7Fe3 core as well as the good impedance matching brought by appropriate carbon coating. Accordingly, the Co7Fe3@C nanocomposite is convinced to be a competent candidate among absorbers with high absorption intensity and ultra-wide broadband.

Ultra-broadband dual-square ring metamaterial absorbers from visible to far-infrared region

This study proposes an ultra-wideband (UWB) metamaterial absorber based on dual-square ring (DSR) microstructures from the visible to the far-infrared region. The simulation results indicated that the absorber achieved more than 90% absorption in the wavelength range of 1200 nm to 11,000 nm. In addition, the absorption rate is greater than 80% in the wavelength range of 500–13,000 nm, achieving an ultra-broadband absorption with a bandwidth of over 12,000 nm. The designed UWB absorber has promising applications in thermal photovoltaic power generation, infrared imaging, photoelectric detection.

Backend-Balanced-Impedance Concept for Reverse Design of Ultra-Wideband Absorber

Wider absorption bandwidth is usually accompanied by more complex and difficult designs and more computational costs, which have become an important challenge in the field of electromagnetic scattering. In this communication, the backend-balanced-impedance (BBI) new design concept is put forward for the first time which considers the backplane as an impedance that can be designed to compensate for the impedance of a known absorber for expanding the absorption bandwidth. Based on the design concept, an ultra-wideband absorber derived from the known absorber is proposed simply and efficiently. The matched BBI for the known absorber is obtained and developed using reverse calculation. To explain the operating principle, a simple equivalent circuit (EC) model of the ultra-wideband absorber from the BBI is established. Furthermore, the electric field and surface loss distribution are systematically analyzed to demonstrate physical pictures of the BBI. The simulated and measured results show that the designed ultra-wideband absorber from the BBI can get an absorption band in the 0.87–9.28 GHz range (165.8%) for at least 10 dB of reflection reduction at the normal incidence with a thickness of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.0858\lambda _{L} $ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{L} $ </tex-math></inline-formula> denotes the wavelength at the lowest operating frequency.

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

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.

A graphene-based compatible flexible film with ultra-wideband microwave absorption and low infrared emissivity

Excessive electromagnetic radiation affected equipment and human health. Therefore, it is urgent to eliminate hazardous electromagnetic waves. In this work, a green synthesis technology was adopted to obtain a novel protective composite. Combining CuS/ZnS (CZS) and graphene oxide (GO), the prepared composites can absorb more than 99% electromagnetic waves. CZS nanoparticles are evenly distributed on the surface and inside of reduced graphene oxide that can form abundant interfacial polarization to enhance electromagnetic attenuation ability. The composite film has an extensive effective absorption bandwidth (fe), up to 10.14 GHz under the filling ratio of 12%, covering the X-band and Ku-band. More importantly, the absorption bandwidth could reach 6.38 GHz with the ultra-low filling rate is 6%. In addition, the composite film also has a relatively low infrared emissivity of 0.577, which can meet the requirements of low infrared radiation. These results are of great significance for designing and synthesizing high-performance materials for microwave infrared compatible pollution protection.

Dual-band/ultra-broadband switchable terahertz metamaterial absorber based on vanadium dioxide and graphene

A dual-band/ultra-broadband switchable terahertz absorber based on vanadium dioxide (VO2) and graphene is proposed in this article. By controlling the properties of VO2 and graphene, the operation mode of the absorber can be switched between dual-band and ultra-wideband absorption. The simulation results show that the absorber works in the dual-band absorption mode when VO2 is in the insulating state and the Fermi energy level of graphene is 1.5 eV. The absorptivity are 99.4% and 99.8% at 1.08 and 3.52 THz, respectively. The frequency position of the absorption peaks can be switched by regulating the Fermi energy level of graphene. While the VO2 is transitioned to the metallic state and the Fermi energy level of graphene is 0.05 eV, the absorber operates in the ultra-broadband absorption mode with the absorptivity over 90% in the range 0.94–4.31 THz, and the relative absorption bandwidth reaches 128%. In addition, the working principle of the proposed absorber is analyzed by impedance matching theory and electric field distribution. Based on these characteristics, the proposed metamaterial absorber is expected to be used in the terahertz bio-detection and imaging fields.

Strong absorption in ultra-wide band by surface nano engineering of metallic glass

Broadband light absorption is important for applications such as infrared detectors, solar energy collectors, and photothermal conversion. We propose a facile and common strategy to fabricate light absorbers with strong ultra-wideband absorption. Due to their excellent thermoplastic forming ability, metallic glasses could be patterned into finely arranged nanowire arrays, which show extremely low reflectivity (∼0.6%) in the visible and near-infrared regimes, and a low reflectivity (∼15%) in the mid-infrared regime as caused by multiscale nano spacing, multiple reflections, and plasmonic behavior. The strong absorption at surfaces with nanowires provides excellent photothermal conversion properties. The photothermal properties show that a surface with nanowires can be rapidly heated up to ∼160 °C at a rate of 28.75 °C/s, which is 30 times higher than smooth surfaces. Meanwhile, a surface with nanowires shows a high photothermal conversion efficiency (ηPT = 56.36%). The fabricated metallic glass absorbers exhibit adaptability as they can be easily formed into various complex shapes and meet the requirements under harsh conditions. The outcomes of our research open the door to manufacturing high-performance absorbers for applications in photothermal electric power generation, desalination, and photodetectors.

A novel ultra-broadband absorber based on carbon-coated honeycomb panels combined with metamaterials

In this paper, a radar absorber with composite structure of metasurface/honeycomb is proposed. Carbon coating is used as a loss material, and honeycomb sandwich structure is used as a support layer to enhance mechanical strength. Introducing impedance matching layer in the top layer of honeycomb absorber can significantly improve the low-frequency absorption performance. The simulation results show that the absorption efficiency of the combined structure absorber can reach more than 90% in the frequency range of 3.65–17.3 GHz. We verified the simulation results through experiments. This method provides an idea for the design of ultra-wideband absorber and has a potential application prospect in stealth material design.

A Compact Ultrawideband Frequency Selective Rasorber With Hybrid 2-D and 3-D Structure

A compact ultra-wideband frequency selective rasorber (CUWFSR) with hybrid two-dimensional (2-D) and 3-D structure is proposed in this letter. The wide absorption band is obtained by the multiple resonances excited by two dipole resonators and the hybrid structure. By inserting split-ring resonator into the short dipole to bypassing the losses in the passband, an FSR with an internal transmission window and ultrawideband absorption performance is finally realized. The proposed rasorber shows a fractional bandwidth of 140.8% with a transparent window from 14.2–15.8 GHz. Then an improved design which involves two approaches of bypassing the losses of the lossy layer is also provided. Finally, an FSR with a middle passband at 15 GHz and a fractional bandwidth of 137.3% for the absorption rate better than 90% is achieved. The prototype of the improved CUWFSR is fabricated and measured for validation.

Achieving Ultra-Wideband and Elevated Temperature Electromagnetic Wave Absorption via Constructing Lightweight Porous Rigid Structure

HighlightsConstructing a porous carbon fiber/polymethacrylimide (CP) structure for acquiring promising electromagnetic absorption performance and withstanding both elevated temperature and high strength in a low density.The absorption bandwidth of CP composite can reach ultra-wideband absorption of 14 GHz at room temperature and even cover the whole X-band at 473 K.The lightweight of the CP composite with a density of only 110 mg cm−3 coupled with high compressive strength of 1.05 MPa even at 453 K.

An ultra-wideband origami microwave absorber

Microwave absorbers have been used to mitigate signal interference, and to shield electromagnetic systems. Two different types of absorbers have been presented: (a) low-cost narrowband absorbers that are simple to manufacture, and (b) expensive wideband microwave absorbers that are based on complex designs. In fact, as designers try to increase the bandwidth of absorbers, they typically increase their complexity with the introduction of several electromagnetic components (e.g., introduction of multi-layer designs, introduction of multiple electromagnetic resonators, etc.,), thereby increasing their fabrication cost. Therefore, it has been a challenge to design wideband absorbers with low cost of fabrication. To address this challenge, we propose a novel design approach that combines origami math with electromagnetics to develop a simple to manufacture ultra-wideband absorber with minimal fabrication and assembly cost. Specifically, we utilize a Tachi–Miura origami pattern in a honeycomb configuration to create the first absorber that can maintain an absorptivity above 90% in a 24.6:1 bandwidth. To explain the ultra-wideband behavior of our absorber, we develop analytical models based on the transmission-reflection theory of electromagnetic waves through a series of inhomogeneous media. The ultra-wideband performance of our absorber is validated and characterized using simulations and measurements.

Wide-angle energy steering and magnetic information detection-coding of stacked ferrite-based elements in the gradient magnetic domain

By stacking ferrite-based elements (FBEs) with three kinds of magnetic fields, a tunable optical multifunctional device with wide-angle energy steering and magnetic information detection-coding is designed. For the transverse electric (TE) wave, the effective refractive index and properties of FBEs in a constant magnetic field are investigated theoretically. Based on this, we analyze the abilities of FBEs to control the energy of the electromagnetic (EM) wave in a gradient magnetic domain systematically. The computed results show that the ultra-wideband absorption and the transmission window in the absorption band are realized within the incident angle of 0−60° for the forward propagation. Reciprocal energy coexistence of absorption and transmission can be also available by expanding the applied magnetic field into the pairwise symmetric distribution. In addition, the transmission window is utilized to achieve magnetic intensity detection and the detection results (with or without absorption peak) are coded with logical values “0” and “1”. Finally, a logic gate is formed in which continuous random magnetic information can be encoded. Those calculated results can apply for wide-angle reciprocal energy steering, multipurpose magnetic detection, and coding.

Inverse design a patternless solar energy absorber for maximizing absorption

The recognition of broadband and high-absorption solar energy has increased interest in the application of solar energy. In the present study, we use the particle swarm optimization and the finite-difference time-domain (PSO/FDTD) algorithm to design an optimal patternless solar absorber. This absorber contains a multilayer common metal‒dielectric flat film that enables perfect absorption within the broadband solar energy spectrum. The average absorption rate of the solar energy absorber associates with the proposed inverse design method for the wavelength range of 300–2500 nm is 98.2%. The performance of the absorber is stable within the incidence angle range of 0–40°, irrespective of whether the polarization mode is transverse electric or transverse magnetic, and the absorption performance remains high at a high incidence angle of 60°. The proposed 2-inch diameter solar energy absorber can be heated to 86 °C within 100 s, indicating a heating power of 950 W m−2. The proposed absorber has a simple structure, low manufacturing cost, perfect ultra-wideband absorption that is independent of polarization, high thermal conversion performance, and substantial potential for solar energy applications.

Design of an ultra-wideband solar energy absorber with wide-angle and polarization independent characteristics

An extremely effective solar energy absorber has been devised in the study. In order to achieve an almost-perfect ultra-wideband absorption spectrum under solar radiation, this structure is constructed with a silver metal-based phi-shaped resonator (PSR), SiO2 substrate, and silver metal ground layer. In the span of ultraviolet to the mid-infrared range, we attain an average absorption of 94.42%, achieving ultra-wideband properties. In addition, the absorption rate above 90% and 95% is observed for the bandwidth of 2680 nm and 1310 nm has an average absorption of 96.17% and 98.13%, respectively, according to our results eight near-perfect absorption peaks are also observed in this range. The optimized design is found by investigating how various design parameters affect the absorption spectrum. The polarization-insensitive and broad-angle absorption characteristics of the suggested solar absorber are 0°–60° wide, which makes it ideal for absorbing solar radiation that can be employed for solar energy conversion applications.

Metamaterial Solar Absorber Based on Refractory Metal Titanium and Its Compound

Metamaterials refers to a class of artificial materials with special properties. Through its unique geometry and the small size of each unit, the material can acquire unique electromagnetic field properties that conventional materials do not have. Based on these factors, we put forward a kind of high absorption near-ultraviolet to near-infrared electromagnetic wave absorber of the solar energy. The surface structure of the designed absorber is composed of TiN-TiO2-Al2O3 with rectangles and disks, and the substrate is Ti-Al2O3-Ti layer. In the study band range (0.1–3.0 μm), the solar absorber’s average absorption is up to 96.32%, and the designed absorber absorbs more than 90% of the electromagnetic wave with a wavelength width of 2.577 μm (0.413–2.990 μm). Meanwhile, the designed solar absorber has good performance under different angles of oblique incident light. Ultra-wideband solar absorbers have great potential in light absorption related applicaitions because of their wide spectrum high absorption properites.

Origami-Based Metamaterials for Dynamic Control of Wide-Angle Absorption in a Reconfigurable Manner

Achieving ultrawide-angle absorption is urgently required in stealth technology. In this article, we propose a promising scheme to push the development of this issue and achieve wide-angle electromagnetic (EM) absorption in a dynamically controllable manner via a reconfigurable origami-based metamaterial. For this purpose, the Miura-ori sheet is applied to load the meta-atoms with cross-shaped resistive films. Accordingly, the wide-angle absorption characteristics of the origami absorber change drastically by adjusting the folded states. In contrast with the conventional 2-D and 3-D absorbers, the 3-D origami absorber state has four normal vectors. Thus, it provides an excellent approach to prevent the deterioration of absorption in a wide-angle range. When the folding angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta =35$ </tex-math></inline-formula> °, the origami absorber exhibits an ultrawideband absorption of 1.44–40 GHz and wide-angle absorption up to 70°. As a proof-of-concept, a prototype that can shift the folding angle from 0° to 90° was fabricated. The absorption performances in the two folding states of fixed folding angles are numerically simulated and experimentally verified in the microwave regime. We believe that the better coverage incident-angle characteristics of the proposed reconfigurable origami-based absorber at specific folding state broaden its applications in various fields, such as EM pollution, radar technology, and EM invisibility.

Optimization of Metamaterial‐Based Solar Energy Absorber for Enhancing Solar Thermal Energy Conversion Using Artificial Intelligence

AbstractA highly efficient psi‐shaped solar energy absorber in the paper is developed. This structure is designed using titanium‐based psi shaped resonator, SiO2 based substrate, and Tungsten metal‐based base layer to achieve a near‐perfect ultrawideband absorption spectrum under solar radiation. The average absorption of 97.04% is achieved in the observed range including the ultraviolet to mid‐infrared regimes and the ultrawideband characteristics are also achieved. It is also noted that for the bandwidth of 3730 and 2500 nm, above 90% and 95% absorption rate are achieved, respectively. The effect of several design parameters on the spectrum of absorption is explored and accordingly, optimized design is identified. Furthermore, the absorption response of the developed solar energy absorber is polarization‐insensitive and wide‐angle from 0° to 50°. Experiments are meant to identify the optimal parameter values for solar absorber design by employing a random restart hill climbing optimization approach. According to the experimental data, this strategy can reduce the computing power and time requirements of the simulation process by 97.57%.

Graphene-based ultra-wideband absorber for terahertz applications using hexagonal split ring resonators

In this paper, a hexagonal split ring ultra-wideband absorber is proposed at THz frequency. The proposed structure consists of four graphene based hexagonal split rings, a dielectric substrate and graphene layer at the bottom. The proposed absorber achieves an ultra-wideband absorption characteristics from 0.95 THz to 2.96 THz with percentage bandwidth of 102.8% and bandwidth of 2.1THz with absorptivity beyond 90%. Also, 100% absorption is achieved from 2.07 to 2.33 THz making this unique feature for THz applications. Ultra-wideband response is mainly resulted because of overlapping of strong Electromagnetic (EM) resonance of the four split rings. The modes generated within the graphene split rings are merged for achieving ultra wide band response. Furthermore, the proposed absorber is polarization insensitive because of symmetry geometry and also exhibits absorption greater than 90% for incidence angle up to 75° for both TE and TM waves. In addition, tunability is achieved by varying the graphene chemical potential. These features make the proposed metal free absorber useful for terahertz applications and future nanoscale systems. The proposed absorber shows narrow absorption characteristics for higher graphene chemical potential values which can also be utilized for sensor applications.

Equivalent-circuit-intervened deep learning metasurface

Recently, some advanced computer algorithms, including the inverse design method based on deep learning, have been widely applied to design versatile electromagnetic devices, featuring fast design and high efficiency especially in the global optimization problem. However, enormous amount of data generated from blind preliminary and computationally expensive simulations to predict the optical responses is required. Herein, to overcome this shortcoming of traditional deep-learning-based inverse design method, a fast, highly efficient, and sufficiently accurate synergetic strategy for devising photonic applications is presented, which integrates an explicit equivalent-circuit-intervened model as the guide in the implicit deep learning method to avoid blind calculations. As a case study of the proposed synergetic paradigm, the absorbers with customized and challenging spectral patterns are explored. For verification, three proof-of-concept designs were characterized: single-layer notched-band absorption, dual-layer trap absorption, and triple-layer ultra-wideband absorption. Our approach solves the knotty issues of batch designs, as well as the complex and time-consuming processes, suffered in traditional approaches. Moreover, our demonstrated equivalent-circuit-intervened intelligent strategy can be directly extended to various other photonic architectures, advancing a significant step toward real-world applications.