Ultra-broadband Absorption Research Articles

An Ultra-Broadband and Highly-Efficient Metamaterial Absorber with Stand-Up Gradient Impedance Graphene Films

Metamaterial absorbers (MMAs) that absorb electromagnetic waves among an ultra-broad frequency band have attracted great attention in military and civilian applications. In this paper, an ultra-broadband and highly-efficient MMA is presented. The unit cell of the proposed MMA was constructed with two cross-placed stand-up gradient impedance graphene films, which play a key role in improving impedance matching. Considering the trade-off between absorbing performance and processing complexity, in our design, we adopted the stand-up graphene films that have a gradient with three orders of magnitude in total. The simulated results of the proposed absorber show an ultra-broadband absorption (absorptivity > 90%) from 1.8 GHz to 66.7 GHz and a highly-efficient absorption (absorptivity > 97%) in the range of 2-21.7 GHz and 39.6-57 GHz. The field analysis was adopted to explain the mechanism of the proposed absorber. To validate this design, a prototype of 20 × 20 units was processed and assembled. The graphene films were processed with graphene conductive ink using screen print technology. The measured results are in good agreement with the simulated ones. The proposed absorber may find potential applications in the field of stealth technologies and electromagnetic interference.

Dynamically switchable multifunctional terahertz absorber based on graphene and vanadium dioxide hybrid metamaterials

A multifunctional terahertz absorber based on a hybrid configuration of vanadium dioxide ( V O 2 ) and graphene is proposed, which is enabled to dynamically switch between ultrabroadband and double-narrowband absorption characteristics using the phase-shifting property of V O 2 . When V O 2 is in the metallic phase and the Fermi energy level of graphene is 0.01 eV, ultrabroadband absorption from 3.04 THz to 8.78 THz can be achieved. The absorption can be continuously adjusted from 0.7% to 99.9% by changing the conductivity of the V O 2 through temperature. When V O 2 is in the insulating phase and Fermi energy level of graphene is 0.4 eV, the proposed absorber exhibits a double-narrowband absorption characteristic, achieving 99.8% and 97.3% absorption at 1.79 THz and 4.62 THz, respectively. Since graphene is an electronically controlled material, it is able to dynamically modulate the resonant frequency and absorption intensity by changing the Fermi energy level of graphene. In addition, the physical mechanism of the multifunctional absorber is revealed using electric field distribution and the impedance-matching theory. The proposed absorber has potential applications in optical switching, image processing, and stealth technology.

Ultra-broadband sound absorption of a multiple-cavity metastructure with gradient thickness

In order to achieve ultra-broadband perfect sound absorption at low and middle frequencies, a novel acoustic metastructure composed of a multiple-cavity coupled resonator and melamine foam (MF) is proposed. Firstly, the metastructure termed as MPP-AG consisting of microperforated panel (MPP) and multiple annular groove cavities (AG) is investigated. Analytical research and finite element simulation are conducted, and the sound absorption characteristics are verified through the impedance-tube test. The effects of the MPP and backing cavity parameters on the sound absorption and coupling performance of the AG are studied. In Particular, MPP-AG with gradient depth shifts the initial frequency with a sound absorption coefficient greater than 0.5 to a lower 315 Hz at the deepest depth of 95 mm. The MPP-AG is optimized with the Genetic Algorithm and the absorption lower band with an absorption coefficient greater than 0.5 is shifted towards 278 Hz. Furthermore, through filling melamine foam into the MPP-AG, the improved metastructure MPP-AG-MF is established to broaden the absorption bandwidth. A perfect absorption (α>0.8) between 255 and 1600 Hz can be obtained at a depth of 70 mm by the optimization of the MPP-AG-MF with the Genetic Algorithm. This study can provide significant guidance for noise attenuation and sound absorber design, which is promising to be used in aerospace, transportation, construction and mechanical design, etc.

Multi-Scale Design of Ultra-Broadband Microwave Metamaterial Absorber Based on Hollow Carbon/MXene/Mo2 C Microtube.

Developing various nanocomposite microwave absorbers is a crucial means to address the issue of electromagnetic pollution, but remains a challenge in satisfying broadband absorption at low thickness with dielectric loss materials. Herein, an ultra-broadband microwave metamaterial absorber (MMA) based on hollow carbon/MXene/Mo2 C (HCMM) is fabricated by a multi-scale design strategy. The microscopic 1D hierarchical microtube structure of HCMM contributes to break through the limit of thickness, exhibiting a strong reflection loss of -66.30dB (99.99997 wave absorption) at the thinnest matching thickness of 1.0mm. Meanwhile, the strongest reflection loss of -87.28dB is reached at 1.4mm, superior to most MXene-based and Mo2 C-based microwave absorbers. Then, the macroscopic 3D structural metasurface based on the HCMM is simulated, optimized, and finally manufactured. The as-prepared flexible HCMM-based MMA realizes an ultra-broadband effective absorption in the range of 3.7-40.0GHz at a thickness of 5.0mm, revealing its potential for practical application in the electromagnetic compatibility field.

Ultra-broadband microwave absorption of honeycomb-like three-dimensional carbon foams embedded with zero-dimensional magnetic quantum dots

The magnetic response behavior of microwave absorbing materials (MAMs) is beneficial to the expansion of the effective bandwidth in the high-frequency electromagnetic fields. However, the high density of magnetic components does not match with the lightweight requirement of MAMs. In response to this contradiction, the metal-organic framework (MOF) ZIF-67 material and melamine foam were used in the present work as the magnetic component and self-sacrificial template, respectively. A three-dimensional honeycomb carbon foam with zero-dimensional magnetic Co quantum dots (Co-QDs/CF) was prepared by a simple two-step method. The unique honeycomb structure significantly improved impedance matching and carrier mobility, providing more scattering paths for the electromagnetic wave conduction while reducing the overall density. In turn, the uniformly embedded magnetic Co-QDs endowed the 3D carbon foam with excellent high-frequency magnetic response while ensuring light weight. The ultra-small size (<10 nm) enhanced the exchange coupling between magnetic particles while suppressing the eddy current effect, and the magnetic loss capability was greatly improved. Interestingly, Co-QDs acting as numerous micro-resistors formed a large three-dimensional conductive network with the carbon skeleton, which demonstrated outstanding electron transport ability, so that the conductance loss was significantly enhanced. Surprisingly, the effective absorption bandwidth of Co-QDs/CF in the 2–18 GHz band was as high as 8.74 GHz with a matching thickness of 2.5 mm, while the corresponding filling rate was only 20 wt%. Thus, the proposed ingenious strategy to construct three-dimensional conductive networks using ultra-small magnetic quantum dots opens up new prospects for the development of lightweight broadband MAMs.

Broadband plasmon-induced transparency to an anapole mode induced absorption conversion Janus metastructure by a waveguide structure in the terahertz region.

A Janus metastructure (MS) assisted by a waveguide structure (WGS) resting on anapole modes and exhibiting direction-dependent behavior has been developed in the terahertz (THz) region. Ultra-broadband absorption is formed by the destructive interference through the anapole as well as Janus trait and is shaped by nested WGS. In this design, vanadium dioxide (VO2) is expected to attain functional transformation from plasmon-induced transparency (PIT) to absorption. The insulating nature of the VO2 results in the creation of the PIT, which is characterized by a wide and high transmission window ranging from 1.944 THz to 2.284 THz, corresponding to the relative bandwidth of 7.4% above 0.9. However, when the VO2 reaches the metallic state, a high absorptivity of 0.921 at 2.154 THz can be implemented in the -z-direction owing to the excitement of the toroidal dipole and electric dipole moments in the near-infrared region. And in the +z-direction, the broadband absorption above 0.9 in the 1.448-2.497 THz range takes shape in virtue of surface plasmon polariton modes, in which intensely localized oscillation of free electrons is confined to the metal-dielectric interface supported by the WGS. Noting that the MS is equipped with a favorable sensitivity to the incidence angle, we develop an ultra-broadband backward absorption in the TM mode from 0.7-10 THz nearly all above 0.9 when the incidence angle changes from 30°-70°. Moreover, owing to the highly symmetrical structure, the MS exhibits exotic polarization angular stability. All the awesome properties make this MS a good candidate for various applications such as in electromagnetic wave steering, spectral analysis, and sensors.

An ultra-broadband solar absorber based on α-GST/Fe metamaterials from visible light to mid-infrared.

In this paper, we proposed an ultra-broadband and high absorption rate absorber based on Fe materials. The proposed absorber consists of a rectangle pillar, two rings, a SiO2 film, a Ge2Sb2Te5(GST) planar cavity, an Fe mirror, and a SiO2 substrate. The average absorption reaches 98.45% in the range of 400-4597 nm. We investigate and analyze the electric field distributions. The analysis of the physical mechanism behind the broadband absorption effect reveals that it is driven by excited surface plasmons. Furthermore, the absorber can maintain high absorption efficiency under a large incident angle. The geometrical symmetric structure possesses polarization insensitivity properties. The proposed structure allows for certain manufacturing errors, which improves the feasibility of the actual manufacture. Then, we investigate the effect of different materials on absorption. Finally, we study the matching degree between the energy absorption spectrum and the standard solar spectrum under AM 1.5. The results reveal that the energy absorption spectrum matches well with the standard solar spectrum under AM 1.5 over the full range of 400 to 6000 nm. In contrast, energy loss can be negligible. The absorber possesses ultra-broadband perfect absorption, a high absorption rate, and a simple structure which is easy to manufacture. It has tremendous application potential in many areas, such as solar energy capture, thermal photovoltaics, terminal imaging, and other optoelectronic devices.

Tunable composite lattice structure for low-frequency and ultra-broadband underwater sound absorption.

The underwater sound absorption technique in low-frequency and broadband has far-reaching prospects since it is essential for noise reduction of deep-sea operation requirements and evading advanced underwater target detection. Here, we propose an underwater sound-absorbing composite lattice with low-frequency and ultra-broadband characteristics. The composite lattice is constructed by regular spatially stacking cells with different sizes of metallic core spheres. All the core spheres are coated with silicon rubbers, and cells are embedded in the rubber matrix. In the composite lattice stereostructure, the lattice cells convert incident longitudinal waves into transverse waves through multiple local resonance coupling and multiple scattering. The energy is localized and dissipated in the composite lattice. We analyze the relationship among the corresponding absorption spectrums, the displacement clouds, and the resonance modes of lattice cells. Then, we construct a composite lattice and realize low-frequency broadband absorption from 693 to 1106 Hz with absorptance above 0.8. Further, our investigation demonstrates that the absorption bandwidth can be extended to ultra-broadband from 1077 to 10 000 Hz, where the thickness of the composite lattice is λ/17.05. The proposed composite lattice provides a practical approach to designing ultrathin low-frequency and ultra-broadband acoustic absorption coating for underwater noise suppression.

Ultra-broadband and tunable infrared absorber based on VO2 hybrid multi-layer nanostructure

We propose an ultra-broadband near- to mid-infrared (NMIR) tunable absorber based on VO2 hybrid multi-layer nanostructure by hybrid integration of the upper and the lower parts. The upper part is composed of VO2 nanocylinder arrays prepared on the front illuminated surface of quartz substrate, and VO2 square films and VO2/SiO2/VO2 square nanopillar arrays prepared on the back surface. The lower part is an array of SiO2/Ti/VO2 nanopillars on Ti substrate. The effects of different structural parameters and temperature on the absorption spectra were analyzed by the finite-difference time-domain method. An average absorption rate of up to 94.7% and an ultra-wide bandwidth of 6.5 μm were achieved in NMIR 1.5–8 μm. Neither vertical incident light with different polarization angles nor large inclination incident light has a significant effect on the absorption performance of the absorber. The ultra-broadband high absorption performance of this absorber will be widely used in NMIR photodetectors and other new optoelectronic devices.

Establishing a unified paradigm of microwave absorption inspired by the merging of traditional microwave absorbing materials and metamaterials.

The merging of traditional microwave absorbing materials with metamaterials holds significant potential for enhancing microwave absorber performance. To unlock this potential, a unified paradigm is urgently required. We have successfully established such a paradigm, focusing on regulating effective electromagnetic parameters and interfacial forms across microscopic, mesoscopic, and macroscopic scales. Building upon this foundation, we introduce an active co-design methodology for jointly optimizing full-scale structures and the concept of "full-scale microwave absorbers" (FSMAs). Under this guidance, performance improvements can be achieved efficiently, leading to crucial breakthroughs. For demonstration, we present a case study designing ultra-thin miniaturized FSMAs capable of ultra-broadband and low-frequency absorption. Simulation results show absorptivity exceeding 90% in the 2-28 GHz range, with absorptivity surpassing 85% and 74% in the 1.5-2 GHz and 1-1.5 GHz ranges, respectively. Additionally, the total thickness and macro period are only 5 mm, roughly equivalent to 0.033 wavelengths of the lowest operating frequency. Most importantly, we have broken the Rozanov limit, with experimental results further validating this design. This work significantly enhances our understanding of microwave absorption and offers a shortcut for pursuing improved performances and breakthroughs.

Wide-temperature-range multispectral camouflage enabled by orientation-gradient co-optimized microwave blackbody metastructure coupled with conformal MXene coating.

Cloaking against electromagnetic detection is a well-researched topic; yet achieving multispectral camouflage over a wide temperature range remains challenging. Herein, an orientation-gradient co-optimized graded Gyroid-shellular (GGS) SiOC-based metastructure with a conformal MXene coating (M@SiOC) is proposed to achieve wide-temperature-range microwave/infrared/visible-light-compatible camouflage. Firstly, the combination of coordinate transformation and genetic algorithm endows the GGS architecture with optimal orientation and gradient, allowing superior microwave blackbody-like behavior. Secondly, a microwave-transparent, low-infrared-emissivity MXene metasurface is constructed in situ to permit wide-temperature-range infrared camouflage. Finally, the outstanding spectral selectivity of MXene enables camouflage against 1.06 μm-lidar and visible-light detection. As a result, the as-fabricated [110]-oriented GGS M@SiOC metamaterials exhibit outstanding wide-temperature-range multispectral camouflage: (i) ultrabroadband microwave absorption exceeding 80% in the X-Ku band from room temperature (RT) to 500 °C with absorption above 86.0% (91.4% on average) at 500 °C; (ii) excellent long-wavelength infrared camouflage for object temperatures from RT to 450 °C, reaching an infrared signal intensity of 78.5% for objects at 450 °C; and (iii) camouflage against both 1.06 μm-lidar and dark environment. Compared with traditional hierarchical metamaterials necessitating complex micro/nano-fabrication processes, this work provides a novel pathway toward the realization of structurally integrated multispectral stealth components by combining flexible metastructure design and high-fidelity additive manufacturing.

Multi-scale integrated design and fabrication of ultra-broadband electromagnetic absorption utilizing multi-walled carbon nanotubes-based hierarchical metamaterial

Ultra-broadband electromagnetic absorption has become a critical issue competing with advanced broadband electromagnetic detection systems. In this study, an innovative strategy for the broadband absorption is proposed via combining periodic patterns and the hierarchical structure with gradient electromagnetic performance, which introduces an abnormal electromagnetic response for improved maneuverability in impedance matching and multiple electromagnetic loss mechanisms. The electromagnetic parameters for each layer were determined by the fixing content of multi-walled carbon nanotubes (MWCNTs) in gypsum, and the periodic stepped meta-structure was optimized via the finite element simulation. The optimized hierarchical MWCNTs/gypsum metamaterial with a thickness of 8.0 mm realized an average absorption intensity of −21.6 dB (>99.3% absorption) in the frequency band of 4–40 GHz. Particularly, broadband EM absorption for reflection loss less than −10 dB and −15 dB was achieved in the ranges of 4.2–40 GHz and 5.6–40 GHz, respectively. The ultra-broadband and strong electromagnetic absorption properties of the proposed metamaterial should be the synergic result of the excellent impedance matching and the multiple EM wave loss caused by the multi-scale integrated structure. Therefore, the proposed MWCNTs/gypsum metamaterial with the innovative strategy of combining the hierarchical structure and periodic patterns, could provide an insight for achieving high-performance absorption materials.

Bifunctional metasurface for cross-polarization conversion and ultra-broadband absorption in terahertz range

A bifunctional terahertz (THz) metasurface based on vanadium dioxide (VO2) was proposed, which can achieve near-perfect cross-polarization conversion (CPC) and ultra-broadband absorption. When VO2 is in insulator state, the metasurface acts as a cross-polarization converter, converting linearly polarized (LP) and circularly polarized (CP) waves into the corresponding cross-polarized waves. The polarization conversion ratio (PCR) exceeds 99.5% in the frequency range of 4.1∼6.7 THz at normal incidence, and can be maintained more than 98.3% even at an incident angle of 20°. When VO2 is in metal state, the metasurface becomes a THz broadband absorber with absorption efficiency above 90% in a wide frequency range of 2.9 THz∼8.4 THz. The absorption efficiency is almost unchanged when the incident angle increases from 0° to 15° for TE wave. In addition, the absorption efficiency can maintain above 90% at 4.0∼7.1 THz when the incident angle is up to 60° for TM wave. Moreover, the interference theory model was utilized for verifying theoretically the validity of the numerical simulation results of our proposed metasurface, and the theoretical calculation results are in good agreement with the simulation results. We believe that this proposed metasurface has potential applications in many fields, such as sensing, imaging, non-destructive detectors, super lenses, and telecommunications.

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.

Metamaterial solar absorber based on titanium resonators for operation in the ultraviolet to near-infrared region

In this work, we design an ultra-broadband metamaterial solar absorber with near-unity absorption. The absorber’s structure is optimized by using the particle swarm optimization algorithm. A unit cell of the absorber consists of three T i / T i O 2 / T i square disks enclosed by a Ti square ring resonator, all superimposed on a thin stack of T i O 2 / T i films. The optimized structure shows high average absorption of 96.92% over the full wavelength range of 200–3200 nm. The over 90% absorption bandwidth is 3000 nm, which covers the ultraviolet, visible, and near-infrared regions. The solar absorption of the structure is 95.5% in the range of 280–3200 nm. The absorber is polarization independent and insensitive to incident angle changes. The absorption remains higher than 80% and 75% for TM and TE polarizations, respectively, even under oblique incidence radiation up to 55°. The structure possesses high thermal and chemical stability owing to the use of Ti and T i O 2 materials. Due to its outstanding features, the absorber has high potential to be used in solar energy harvesting, thermo-photovoltaics, and thermal emitting applications.

Highly efficient, perfect, large angular and ultrawideband solar energy absorber for UV to MIR range

Although different materials and designs have been tried in search of the ideal as well as ultra-wideband light absorber, achieving ultra-broadband and robust unpolarized light absorption over a wide angular range has proven to be a major issue. Light-field regulation capabilities provided by optical metamaterials are a potential new technique for perfect absorbers. It is our goal to design and demonstrate an ultra-wideband solar absorber for the ultraviolet to a mid-infrared region that has an absorptivity of TE/TM light of 96.2% on average. In the visible, NIR, and MIR bands of the solar spectrum, the absorbed energy is determined to be over 97.9%, above 96.1%, and over 95%, respectively under solar radiation according to the Air Mass Index 1.5 (AM1.5) spectrum investigation. In order to achieve this wideband absorption, the TiN material ground layer is followed by the SiO2 layer, and on top of that, a Cr layer with patterned Ti-based resonators of circular and rectangular multiple patterns. More applications in integrated optoelectronic devices could benefit from the ideal solar absorber's strong absorption, large angular responses, and scalable construction.

Tunable wideband-narrowband switchable absorber based on vanadium dioxide and graphene.

A functionally tunable and absorption-tunable terahertz (THz) metamaterial absorber based on vanadium dioxide (VO2) and graphene is proposed and verified numerically. Based on phase transition properties of VO2 and tunability of graphene, the switching performance between ultra-broadband and narrow-band near-perfect absorption can be achieved. We simulate and analyze the characteristics of the constructed model by finite element analysis. Theoretical calculations show that when VO2 is in the metallic state and the graphene Fermi energy is 0 eV, the designed absorber can perform ultra-broadband absorption. The absorber achieves greater than 95% absorption in the 2.85 - 10THz range. When VO2 is in the insulating state and the graphene Fermi energy is 0.7 eV, more than 99.5% absorption can be achieved at 2.3 THz. The absorption rate can be tuned by changing the conductivity of VO2 and the Fermi energy of graphene. Moreover, the proposed absorber displays good polarization insensitivity and wide incident angle stability. The design may have potential applications in terahertz imaging, sensing, electromagnetic shielding and so on.

Stereolithographically 3D Printed SiC Metastructure for Ultrabroadband and High Temperature Microwave Absorption

AbstractBroadband microwave absorption is essential on the realms of electromagnetic compatibility and protection in civil application scenarios. However, coordination of material and structure is difficult without proper iterative design between material and structure resulting in insurmountable drawbacks of traditional microwave absorption medium operating under high temperature erosion. Herein, SiC metastructure is manufactured in bulk by stereolithographic 3D printing. The dielectric loss tangent of SiC sintered body is over 0.5 and up to 1.5 at most showing good electromagnetic energy dissipation properties. The optimized SiC metastructure with complicated suspended features achieves −10 dB broadband microwave absorption from 6.96 to 40 GHz at room temperature (RT) across total frequency range of 33.04 GHz. The proposed SiC metastructure is able to endure in situ 1000 °C and ex situ 1600 °C erosion in air atmosphere maintaining −10 dB effective bandwidth in 4.54–40 and 10.89–39.67 GHz, respectively. Broadband microwave absorption under oblique incidence from 0° to 60° is also achieved in a wide temperature range from RT to 1600 °C. The densification of SiC results in a high mechanical strength of 217.36 MPa for structural load bearing applications. The intrinsic electromagnetic variation of SiC under different temperature is relaxed and adapted to the metastructure design. The functions of broadband microwave absorption and high temperature protection are integrated into one metastructure.

Design of an optically-transparent ultra-broadband microwave absorber

The optical window of low-observable platform needs to be compatible with ultra-broadband absorption, hence an optically-transparent absorber with ultra-broadband absorption is designed and analyzed in this paper. The transparent materials indium-tin-oxide (ITO) film and polymethylmethacrylate (PMMA) are selected as the lossy layer and the supporting dielectric layer, respectively. The optically-transparent ultra-broadband absorber (OT-UBA) is composed of three layers of ITO square patterns, three layers of PMMA dielectric and a uniform ITO plane. The ITO square patterns can realize arbitrary equivalent series of RC (resistor and capacitor) circuit, so that three layers of ITO square patterns together with the ITO plane can achieve ultra-broadband absorption based on the equivalent circuit optimization. Measured results shows that the 90%-absorption bandwidth covers 2–17 GHz while the light transmittance achieves 59.6% with a total thickness of only 12.9 mm.

Brewster metasurfaces for ultrabroadband reflectionless absorption at grazing incidence

Previous reflectionless metasurfaces based on balanced electric and magnetic responses in engineered resonant meta-atoms become ineffective at oblique incident angles and usually have strong reflection at grazing incidence, where the impedance becomes near-zero or divergent. Here, by introducing the concept of anomalous generalized Brewster effect to metasurfaces, we demonstrate an exceptional resonance-free Brewster metasurface that exhibits ultrabroadband zero reflection at grazing incidence. The anomalous generalized Brewster effect is obtained via combining the mechanisms of the generalized Brewster effect and the anomalous Brewster effect, which are both resonance-free and thus enable ultrabroadband functionalities. As a practical application, Brewster metasurfaces exhibiting ultrabroadband reflectionless perfect absorption at grazing incident angles are constructed and demonstrated by full-wave simulations and microwave experiments. Our work could enable reflectionless wave manipulation at grazing incidence with an ultrawide working bandwidth.