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[Display omitted] The compound eyes of the dragonfly, Pantala flavescens Fabricius, are covered by micro-scaled ocelli capable of sensing polarized light, an attractive property for radar stealth and counterreconnaissance. In this work, we fabricated biomimetic electromagnetic wave absorption materials (EAMs) by analyzing the covert information identifications of biological systems and focusing on the design of metastructures and microstructures. Several bionic metasurfaces with anisotropic double-V meta atoms made up of (FeCoNiSi 8.9 Al 8.9)C 0.2 high-entropy-alloy (HEA) ribbons for multiple-degrees-of-freedom recognition and broadband absorption are presented. The covert phase, amplitude, and angular momentum of electromagnetic waves were controlled and recognized as information by manipulating the rotation angle θ of meta atoms. A vortex wave with a topological charge of 1 was generated to recognize linearly polarization and left- and right-handed circular polarization. In addition, the polarization conversion enhanced absorption. The hierarchical nanostructures of HEA ribbons give rise to suitable electromagnetic loss and a superior impedance match. Finally, inspired by the structure of compound eyes, the designed multilayer metamaterials realized effective absorption (reflection loss (RL) ≤ − 10 dB) within the 4.5–18 GHz regime under 2.8 mm thickness. These materials provide evidence for a new way for integrated EAMs and metamaterials. [ABSTRACT FROM AUTHOR]

In view of the practical demands and mechanistic conflicts between microwave absorption and heat shielding compatibility, a double‐layer composite coating based on moth‐eyed hexagonal anti‐reflective structure is prepared by combining the advantages of metamaterials and coatings. The hexagonal periodic sequential configuration of the upper infrared shield layer (IRSL) can break the continuity of the electric field, induce a networked concentration of the surface current and internal electric field of the microwave absorption layer, thus optimizing the impedance matching and counteract the attenuated absorption performance due to the high dielectric IRSL. In addition, the emissivity of IRSL can be tuned artificially by changing the filler composition and particle size. The structural double‐layer composite coatings have a maximum effective absorption (reflection loss←10 dB) bandwidth of 7.4 GHz in the SKu bands at deep subwavelength thickness, while the infrared emissivity is 0.292. This work provides a novel approach for multispectral modulation in the field of advanced compatible protection systems. [ABSTRACT FROM AUTHOR]

Highlights: Nanocrystalline high-entropy alloy powders (HEAs) with the unprecedented combination of superior manufacturability, large aspect ratios, and thin intergranular amorphous layers are constructed via a multistage mechanical alloying strategy. FeCoNiCr0.4Cu0.2 HEAs for 20 h of dry milling and 5 h of wet milling (D20) exhibit excellent corrosion resistance, high Curie temperature, and temperature-stable broadband megahertz electromagnetic wave absorption.Developing megahertz (MHz) electromagnetic wave (EMW) absorption materials with broadband absorption, multi-temperature adaptability, and facile preparation method remains a challenge. Herein, nanocrystalline FeCoNiCr0.4Cu0.2 high-entropy alloy powders (HEAs) with both large aspect ratios and thin intergranular amorphous layers are constructed by a multistage mechanical alloying strategy, aiming to achieve excellent and temperature-stable permeability and EMW absorption. A single-phase face-centered cubic structure with good ductility and high crystallinity is obtained as wet milling precursors, via precisely controlling dry milling time. Then, HEAs are flattened to improve aspect ratios by synergistically regulating wet milling time. FeCoNiCr0.4Cu0.2 HEAs with dry milling 20 h and wet milling 5 h (D20) exhibit higher and more stable permeability because of larger aspect ratios and thinner intergranular amorphous layers. The maximum reflection loss (RL) of D20/SiO2 composites is greater than − 7 dB with 5 mm thickness, and EMW absorption bandwidth (RL < − 7 dB) can maintain between 523 and 600 MHz from − 50 to 150 °C. Furthermore, relying on the “cocktail effect” of HEAs, D20 sample also exhibits excellent corrosion resistance and high Curie temperature. This work provides a facile and tunable strategy to design MHz electromagnetic absorbers with temperature stability, broadband, and resistance to harsh environments. [ABSTRACT FROM AUTHOR]

Derived from the increasing demand for radar and infrared camouflage integration, a two‐layer hierarchical structure that combines coating and a square patch‐based metasurface is designed. Under deep subwavelength thickness, the infrared stealth layer (IRSL) can markedly reinforce microwave absorption layer (MAL) performance. More than 90% of the electromagnetic wave energy in the 3.7–5.1 GHz and 12.8–18 GHz bands can be absorbed. The hierarchical structure expands the effective absorption bandwidth of the exposed coatings from 0 to 6.6 GHz, and the maximum reflection loss increases from −8 to −40 dB. Moreover, the emissivity in the midinfrared range is maintained at an extremely low value of 0.281. The delay of magnetic resonance is found in the simulation model, indicating that strong magnetic resonance is formed in coatings after covering the IRSL. Meanwhile, the absorption peaks of the coatings are controlled by low‐pass filter metasurfaces. These two factors contribute to the enhancement effect of IRSL on MAL and break the boundary between radar and infrared stealth. Herein, an original solution for tuning multispectral electromagnetic (EM) waves is provided and it has broad application prospects in advanced compatible camouflage material. [ABSTRACT FROM AUTHOR]

Chiral wave-absorbing metamaterials can enhance microwave attenuation performance by converting linearly polarized waves into circularly polarized waves. However, the mechanism for transforming incident waves into vortex waves to overcome the angular momentum mismatch to satisfy broadband stealth is unclear. This work proposes a chiral-assisted geometrically phase (CAGP) metasurfaces that utilizes the Pancharatnam-Berry (PB) phase concept to convert incident plane waves into reflected vortex waves. Such metamaterials demonstrate adaptive transformation capabilities under the incidence of electromagnetic (EM) waves with multi-polarization modes, providing an effective absorption bandwidth (≥90 % absorptivity, reflection loss ≤ −10 dB) reaches 6.92 GHz (9.16–16.08 GHz) at a thickness of 2.48 mm. Based on an orbital angular momentum (OAM) phase and amplitude analysis, the mode purity of the generated vortex waves is discussed in detail, and the mechanisms are analyzed and verified by simulation models to confirm their effectiveness and practicability. Additionally, the metamaterials exhibit excellent radar cross-section (RCS) reduction properties and stable polarization insensitivity properties. In short, this work presents a tailorable metasurface to manipulate the OAM spectrum and achieve broadband microwave attenuation, which holds great potential for various applications in chiral wave-absorbing metamaterials. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon-coated Cu nanocapsules (Cu@C NCs) with controllable graphite-like shells were designed and synthesized for applications in wireless communication, military stealth or electronic devices. A modified arc plasma method was employed to prepare the NCs, where a solid carbon source was used to provide a carbon-saturated atmosphere, resulting in the constitution of core–shell nanostructures with thickness-controllable carbon shells. Formation mechanisms were involved in the nucleation and growth, adsorption–diffusion or secondary growth process. The Cu@C NCs with thicker graphite-like shells demonstrated the enhanced oxidation resistance, thermal stability and excellent electromagnetic absorption performance ranging between 2 and 18 GHz. A mass of hetero-interfaces and defects inside them strengthened dielectric polarizations and achieved impedance matching. The Cu@C NCs exhibited a minimum reflection loss of − 38.4 dB at 4.88 GHz. Benefiting from the structurally controllable core–shell nanostructure, the Cu@C NCs would become a potential candidate material for electromagnetic wave absorption applications. [ABSTRACT FROM AUTHOR]

The microscopic morphology of the composites has a great influence on their microwave absorbing (MA) performances. However, it remains a challenge to achieve morphology control through a facile way when preparing composites of carbon nanotubes and zinc oxide. In this work, a simple and room-temperature approach is proposed to synthesize zinc oxide/carbon nanotubes (CNT/ZnO) nanocomposites with different microstructures. Changing the type of solvent can lead to different microstructures of CNT/ZnO nanocomposites. This is mainly because of the different ion molar ratio to Zn2+ and OH- in the reaction solution. Besides by adjusting the content of CNT, the microwave absorbing properties of the obtained CNT/ZnO nanocomposites can be controlled. When the CNT content is 10% mass fraction, the minimum reflection loss (RL) of CNT/ZnO-E nanocomposite can reach − 55.42 dB at a thickness of 3 mm. With the increasing weight ratio of CNT, the degree of disorder in the material and the number of the defects increase, 3D conductive networks are easier to form, resulting in the enhanced polarization loss and conductive loss. However, excessive CNTs will cause excessive current induced which is not conducive to electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

Electromagnetic wave loss caused by rotating polarization of chiral structures has long been considered as a disadvantage in transmission, detection, etc., however, it can be turned to benefit in microwave absorbing materials to enhance absorption. Herein, inspired by the chiral structure of jeweled beetles, gyrotropic metamaterials (MMs) are designed and prepared, and experimentally demonstrate the enhanced microwave absorption by rotating polarization; the bandwidth of absorptivity greater than 80% (reflection loss, RL ≤ −7 dB) covers the entire 4–18 GHz frequency range under an ultralow surface density of 1.45 kg m−2; the mechanism analyzed and verified by simulation models demonstrates this a universal method. A new paradigm of MMs fabricated by high entropy alloy (HEA) is offered in this work, which increases the freedom of MM design and promotes the integration of material science and physics. Multifarious wave adaptability and multifunctionality achieved by integrated HEA unit cell and foamed polyurethane realize ultrasonic and water wave absorption, as well as impact and corrosion resistance. These designs hold great promise for facilitating functionally integrated materials for stealth technology, antiterrorist, encryption, sensing, and photon detection. [ABSTRACT FROM AUTHOR]

Flaky carbonyl iron particles/nano silicon dioxide/Polyurethane (FCIP/SiO2/PU) composites coatings were fabricated. And FCIP were fabricated from sphere carbonyl iron particles (SCIP) by ball milling. The electromagnetic parameters of absorbers (SCIP, FCIP and SiO2) and the reflection loss (RL) of coatings were measured in the frequency range of 2–18 GHz. The results showed that the complex permeability and absorbing properties of FCIP are significantly enhanced compared with SCIP because of its smaller thickness and easy magnetization plane. In addition, as a low dielectric material, SiO2 can build more wave-transmission channels and optimize the impedance matching, making more electromagnetic wave transmitting into the coatings and being attenuated. Due to the addition of SiO2, the absorbing properties and effective absorption bandwidth of coatings are further enhanced. The reflection loss values exceeding − 10 dB can be obtained in the frequency range of 8.5–18 GHz with a thickness of 1 mm. [ABSTRACT FROM AUTHOR]

Optimizing impedance matching is crucial to achieve high-efficiency electromagnetic wave (EMW) absorption performance. In this work, Hollow CoSe 2 @N-doped Carbon/Carbon Nanotube-x (HCSC/CNTs-x) with unique three-dimensional conduction network was synthesized by using protection etching and high-temperature selenization strategies. The conductivity of HCSC/CNTs-x was regulated by varying the content of CNTs, and the extended three-dimensional electron transport pathway resulted in enhanced conduction and multiple reflection loss, while also optimizing impedance matching. Hollow CoSe 2 @N-doped carbon (HCSC) further facilitates the optimization of impedance matching. The abundant heterogeneous interfaces and defects induce strong interface polarization and dipole polarization, and the multiple loss mechanisms work in concert to confer excellent EMW absorption performance to HCSC/CNTs-x. The RL min of HCSC/CNTs-30 reaches −41.68 dB, and the EAB max is 4.92 GHz at only 2.0 mm. The design strategy of three-dimensional conduction network of HCSC/CNTs-x provides an effective way to achieve the impedance matching optimization of CoSe 2 -based EMW absorption materials. The unique three-dimensional conduction network of HCSC/CNTs-x was successfully synthesized by protected etching and high-temperature selenization. The extended three-dimensional electron transport path not only enhances the conduction loss and multiple reflection loss, but also optimizes the impedance matching to achieve the harmony between impedance matching and electromagnetic loss capability. Attributed to the synergistic effect of multiple loss mechanisms, HCSC/CNTs-30 has excellent electromagnetic wave absorption performance with the RL min up to −41.68 dB and the EAB max is 4.92 GHz only 2.0 mm. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Polyaniline (PANI)/graphene oxide (GO) sandwich-like composite was synthesized for achieving higher microwave absorption performance using a one-step intercalation polymerization of aniline under acidic condition in the presence of GO layers with ammonium persulfate as an oxidant at various GO contents. Long-time mechanical stirring was adopted to obtain perfect sandwich-like structure. The samples were characterized by Scanning electron microscopy, Transition electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, 4-point probes resistivity measurements system and vector network analysis. The results revealed that the PANI-GO-PANI sandwich-like microstructures were successfully synthesized. The electromagnetic absorption properties were enhanced versus pristine PANI. The maximum reflection loss (RL) value reached −41.29 dB at 6.8 GHz with a thickness of 5 mm. The bandwidth (RL < −10 dB) attained an amazing 13.1 GHz from 4.9 to 18 GHz with suitable thickness. By controlling the content of GO, the average conjugation length of PANI nanorods on GO layers can be modulated, resulting in controllable wave-absorbing properties and various frequency bands. Graphical abstract By controlling the content of GO, the average conjugation length of PANI nanorods on GO layers can be modulated, resulting in controllable wave-absorbing properties and various frequency bands. Image 1 Highlights • Synthesize sandwich-like structured PANI/GO composite through mechanical stirring for enough long time. • Content of GO modulated the average conjugation length of PANI in sandwich-like composite. • Average conjugation length of PANI modulated conductive and microwave properties of sandwich-like composite. • Sandwich-like PANI/GO achieved promising EM wave absorption properties combined dielectric loss and impedance matching. [ABSTRACT FROM AUTHOR]

Flake FeSiAl (FFSA) powders were used as absorbent in absorption coatings with a thickness of 1 mm. Two types of SiO2 powders (DNS-2, RNS-A) were added to the coatings in order to improve the impedance matching and the absorption properties. The electromagnetic parameters of FFSA and two types of SiO2 powders were measured by transmission/reflection technology, and the reflection loss of coatings was measured by the arch method in the frequency range of 2-18 GHz. The effect of FFSA content on the microwave absorbing properties was analyzed. And as the content increases, the effective absorption bandwidth (RL ≤ − 10 dB) firstly increases and then decreases and the absorbing peak shifts to lower frequency ranges. Then the absorbing properties of the FFSA/SiO2 coatings were investigated. The results show that the microwave absorption performance was improved significantly when the appropriate amount of SiO2 powder was added to the coating. The minimum reflection loss decreased by 10 dB (DNS-2) and 24.3 dB (RNS-A), respectively. The effective absorption bandwidth (RL ≤ − 10 dB) increased by 2 GHz and 1.8 GHz. The interface polarization and SiO2-channel models were built to analyse the enhanced microwave absorption mechanism of the coatings. [ABSTRACT FROM AUTHOR]

The new paradigm was introduced for achieving excellent electromagnetic (EM) waves absorption through multi-layer superimposed quasiperiodic-metamaterials, which were generated in rotary high entropy alloys ribbon. With the help of asymmetry, the designed anisotropic metamaterials with excellent absorption (Reflection Loss ≤ − 10 dB) covered from 3.8 GHz to 18 GHz on the scale of sub-wavelength. High entropy alloys ribbon increased soft magnetic properties that design cascaded configuration metamaterials displayed distinct phase differences with increased rotation angle, which significantly focus on microwave attenuation. Meanwhile, the direction of the wave vector accompanied by rotation can realize polarized conversion, from linear polarizer to circular polarizer which is demonstrated in simulation, highly desirable in controlling EM waves and shrinking the size of traditional absorbing coating. Our study provides a fresh perspective to developing high-performance absorbers by combining soft magnetic and irregular phase patterns as possible as need for complex EM waves manipulations, arbitrary phase encoding, and vortex field. [Display omitted] • Quasiperiodic structure, without translation symmetry but possess rotation symmetries, can regard as a novelty paradigm for achieving excellent electromagnetic wave absorption. • Based on alloying elements, the electromagnetic parameters of high entropy alloys ribbon used to design cascaded configuration metamaterials for rotating wavefront. • With the help of asymmetry, the effective absorption bandwidth (Reflection Loss ≤ − 10 dB) covered from 3.8 GHz to 18 GHz on the scale of sub-wavelength. • The high entropy alloy ribbons can realize polarized conversion, from linear polarizer to circular polarizer in simulation, and adjust the position of absorption peak when combined with traditional wave absorbing coating. [ABSTRACT FROM AUTHOR]

[Display omitted] • Complex spinel ferrimagnets (CSFMs) are constructed in situ in multi-elemental alloy powders (MEAs) by annealing treatment. • The microstructure and composition of the CSFMs are regulated to modulate the natural resonance frequency and improve permeability via adjusting the annealing temperature. • The MEAs/CSFMs composites not only exhibit efficient broadband megahertz electromagnetic wave absorption, but also have multi-temperature adaptability, oxidation and corrosion resistance. The contradiction between the demand for highly efficient low-frequency electromagnetic wave (EMW) absorption materials and the relatively poor permeability of existing absorbers has become increasingly prominent. However, the intrinsic natural resonance in magnetic material hinders the modulation and enhancement of permeability. Herein, (FeCoNiCu) x Cr 3−x O 4 complex spinel ferrimagnets (CSFMs) are constructed in situ in multi-elemental alloy powders (MEAs) for the first time, via annealing treatment. The microstructure and composition of the CSFMs are regulated by adjusting the annealing temperature, aiming to modulate the natural resonance frequency and achieve highly efficient megahertz (MHz) electromagnetic absorption. Simultaneously, annealing treatment improves the crystal integrity, which is conducive to enhancing intergranular magnetic coupling to elevate permeability temperature stability and the Curie temperature. The minimum reflection loss value of the MEAs/CSFMs composites is less than −7 dB at 3 mm and the effective EMW absorption bandwidth maintains between 425 and 470 MHz at 5 mm from −50 to 150 °C. In addition, the MEAs/CSFMs composites also exhibit excellent oxidation resistance and corrosion resistance due to the oxide layer on the surface. This work offers a new and tunable strategy toward modulating the natural resonance frequency for efficient temperature-stable broadband EMW absorption at specific frequency bands. [ABSTRACT FROM AUTHOR]

[Display omitted] • T-ZnO w can enable FCIPs to show the vertically oriented distribution. • The vertical distribution can significantly improve impedance matching. • The effective bandwidth of T-ZnO w /FCIPs covers the entire X-band over 30–350 °C. Currently, most magnetic high-temperature microwave absorbing materials (MAMs) suffer from the problem of impedance mismatch caused by sudden increase in conductivity along with the changing temperature. Herein, the tetra-needle zinc oxide whisker (T-ZnO w) is used as a structural template to manage the spatial distribution of flake carbonyl iron powders (FCIPs), achieving temperature-stable broadband microwave absorption in the range of 30–350 °C. By adjusting the filling content of T-ZnO w makes FCIPs change from random distribution to a vertically oriented distribution. This distribution provides more stable conductive paths and facilitates low temperature-sensitivity conductance loss. At the same time it provides more transmission channels for the incidence of electromagnetic waves (EMW) and achieves excellent impedance matching. Compatibility of conductance loss and impedance matching is thus achieved. The effective absorption bandwidth (reflection loss (RL) < −10 dB) of T-ZnO w /FCIPs in the range of 30–350 °C could cover entire X-band (8.2–12.4 GHz). This work proposes a simple method to adjust the spatial distribution of absorbers and provides a valuable inspiration for the preparation of temperature-stable broadband MAMs. [ABSTRACT FROM AUTHOR]

The structural destructive resonance caused by the single resonant thickness of flat microwave absorbers results in narrow absorption, hindering the progress of stealth materials. Multi-scale optimization and metastructure design are effective in the improvement of multiple resonance thickness as well as wavefront transmission, allowing for greater freedom in the realization of broadband. Herein, hierarchical metamaterials constructed from pyramid metastructure composites and Huygens' metasurface on the basis of Fibonacci spiral element are reported here, with effective absorption bandwidth (reflection loss ≤ −10 dB) ranging from 4.8 to 18 GHz in terms of subwavelength thickness. The hybrid absorber also exhibits robustness with incident angle across 0°–50° for transverse magnetic polarization. The gradient impedance model based on pyramid composites comprising spherical carbonyl iron particles and graphene sheets will serve as a driver for the enhancement of the electromagnetic wave transmission and the booster of impedance matching. Huygens' resonance of HMS induces the magnetic field convergence effect due to the simultaneous balance of effective surface current and magnetic current, which facilitates the absorption of lossy composites for further broadening absorption bandwidth. This integrated design could be widely applied to other absorbent materials of choice. [Display omitted] • In the case of the electrical and magnetic response are properly balanced, the field excited by the meta-atom composed of centrosymmetric Fibonacci spirals shows similar dispersion of electric and magnetic polarizabilities, resulting in a negligible reflection of the proposed Huygens' metasurface in the frequency range of 2–18 GHz. • A comprehensive design of hierarchical metamaterials from four perspectives: microscale, mesoscale, macroscale and metamaterials, which provides a rigorous and scientific route for the broadband directional design of microwave absorbing materials. • The effective absorption bandwidth of proposed hierarchical metamaterial ranges from 4.8 to 18 GHz across C, X and Ku-band in terms of subwavelength thickness (0.096 λ 0) which merely 7% over theoretical minimum thickness dictated by the causality limit, and exhibits robustness with incident angle across 0°–50° for transverse magnetic polarization. [ABSTRACT FROM AUTHOR]

Although various absorbers have been developed for electromagnetic-wave absorption materials (EAMs), the uniform composition and microstructure limit the design freedom of the soft magnetic properties, thus resulting in a ceiling of the absorption properties. Herein, we propose a revolutionary concept of C-doped FeCoNiSiAl high-entropy-alloy (HEA) ribbons with hierarchical nanostructures composed of ultrafine grains (400 nm), B2 nanoprecipitates (80 nm), and C@FeNi core–shell nanoparticles (15 nm) to induce superior soft magnetization and absorption. The hierarchical nanostructures resulted in a low coercivity (H C , 589.04 A/m) and a low conductivity (294.1 S/cm) to support the loss effect and impedance matching, and 87% of the saturation magnetization (M S , 135.13 emu/g) was maintained, even at the high temperature of 973 K, corresponding to ultra-stable magnetization. Furthermore, the Curie-temperature was greater than 1000 K. The B2 nanoprecipitates and corresponding interfaces created strong stray magnetic flux lines and magnetic domain vortices, and thus, the metasurfaces innovatively fabricated with HEA ribbons induced a strong absorption peak (−50.88 dB) and effective broadband absorption (reflection loss (RL) ≤ −10 dB within 5.86–18 GHz) due to the strong magnetic coupling. The hierarchical nanostructure is a promising strategy to tailor magnetic HEAs with a new degree of freedom for advanced EAMs. [Display omitted] [ABSTRACT FROM AUTHOR]

• Fe/MnO 2 @C composites with unique Schottky heterojunction have been designed by a simple modified arc-discharge method. • Compared to binary composite, ternary Fe/MnO 2 @C composite show attractive advantages in microwave absorption performs. • A maximum reflection loss of − 53.6 dB is observed at 2 mm thickness. And the effective bandwidth reaches 6.35 GHz. The ubiquitous and further deterioration of electromagnetic environment has put forward higher demand for microwave absorption materials with the rapid advancement of 5 G communication and artificial intelligence. Rational manipulation of materials with unique heterojunctions and adjustable electromagnetic properties as lightweight and high-efficiency microwave absorption is the focus and difficulty of research at home and abroad. Schottky junction is designed and fabricated via implanting Fe/MnO 2 nanocrystal confined in carbon matrix, wherein core nanoclusters are tailored. Manganese oxide coupling magnetic metallic iron lamellar nanocrystal benefits the improvement of static magnetization and tuning graphitization degree. The fascinating heterojunction by modifying a Schottky junction can not only enable balance among loss capacity and impedance matching, but also can accelerate the carrier migration and promote abundant interfaces. The efficient microwave absorption is optimized yielding maximum reflection loss of − 53.60 dB and broadening the effective bandwidth of 6.35 GHz. Furthermore, tailoring the morphology of implanted core nanoclusters successfully realizes selective-frequency of microwave absorption. The ternary Fe/MnO 2 @C composite formed by the self-assembly of Fe/MnO 2 nanocrystal core and carbon shell show superior advantages compared to binary composite (e.g., Fe@C, Fe@MnO 2 , MnO 2 @C) in microwave absorption performance. Thus, the performances of appropriately tailored nanoclusters with unique architecture endow optimal synergistic effects between magnetic and dielectric loss. [ABSTRACT FROM AUTHOR]

Quasicrystals can enhance wave transmission and boost nonlinear phenomena due to rotational symmetry forbidden in conventional periodic crystals. As a projection of higher-dimensional quasicrystal lattice, quasiperiodic structures represent a novel platform that exhibits robust microwave-absorbing capacity in thin thickness and digs out the influence of structural configurations on electromagnetic wave absorption from local and global aspects. Due to the synergy effect of composites and structure, quasiperiodic metamaterials with Penrose tiling achieve 12.2 GHz in effective absorption bandwidth (reflection loss < −10 dB), from 5.78 GHz to 18.00 GHz with 2 mm thickness. It has obvious advantages in absorbing electromagnetic wave compared with corresponding periodic absorbers according to the characteristic of local anisotropy and higher order translational symmetry in Brillouin zone. By enhancing multiple scattering and nonlinear coupling effects, Penrose tiling provides new insights to design absorbers with outstanding electromagnetic performance and higher flexibility and tunability. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical 2D N-doped graphene@amorphous carbon are designed. • Phase mutation, group delay and resonance response are certified. • Almost perfect impedance-matching (SWR approaching 1) is achieved. • An alternative route for polymers and graphene as promising MAMs is provided. Two dimensional (2D) nitrogen-doped graphene@amorphous carbon was constructed by in-situ polymerization of sandwich-like structured polyaniline/graphene oxide composites then carbonization at 650 °C in vacuum. The results revealed that the as-prepared 2D N-doped graphene@amorphous carbon and N-doped amorphous carbon nanorods have almost the same decomposition degree and crystal structure. However larger defective degree and more polar bonds are conducive to enhance the polarization loss capacity, and larger dielectric constant can contribute to prominent conductive loss potential. The standing-wave ratio at 13.325 GHz of 2D N-doped graphene@amorphous carbon is 1.08426 approaching to 1, almost perfect impedance-matching level achieving. HFSS simulations certify phase mutation, group delay and the resonance response between N-doped graphene@amorphous carbon and testing microwave, as well as the stronger microwave loss capacity and better impedance matching. Both of the above make 2D N-doped graphene@amorphous carbon a promising microwave absorbing material. The minimum reflection loss (RL) of nitrogen-doped graphene@amorphous carbon can reach −29.5 dB and the effective absorbing bandwidth (EAB, RL < −10 dB) can reach 5.355 GHz ranging from 12.56 to 17.915 GHz only at a thickness of 2.25 mm. [ABSTRACT FROM AUTHOR]

• FeCoNiCr 0.4 Cu Χ HEAs with large aspect ratio are successfully prepared by mechanical alloying method. • Relying on the "cocktail effect" of HEAs, the addition of appropriate Cu element can increase the aspect ratio of the particles. • It has been proven that the large aspect ratio is beneficial to enhance permeability in the megahertz frequency range. • The sample has stable electromagnetic wave absorption performance and superior oxidation resistance with increasing temperature. Electromagnetic wave absorption materials for megahertz (MHz) frequency range remains a key core issue that the poor effective attenuation performance and impedance mismatch. Based on previous research and theoretical analysis, an effective solution is to improve the real and imaginary parts of the complex permeability. In addition, the absorbents are also required to have excellent temperature stability and oxidation resistance due to exposure to harsh environments such as air and high temperature. Herein, the FeCoNiCr 0.4 Cu X high entropy alloys powders (HEAs) with planar anisotropy are prepared by mechanical alloying method. Relying on the "cocktail effect" of HEAs, the addition of appropriate Cu element can increase the aspect ratio of the particles and the shape-dependent anisotropy field to further improve the permeability. Experimentally, the real part of the permeability for the FeCoNiCr 0.4 Cu 0.2 HEAs ranges from 2.7 to 7.5 and the imaginary part of the permeability can reach 2.7 in the MHz frequency range. The maximum reflection loss can reach −33.6 dB at 484 MHz and the effective absorption bandwidth (reflection loss<−10 dB) can almost cover the entire MHz frequency range. Furthermore, the FeCoNiCr 0.4 Cu 0.2 HEAs have stable electromagnetic wave absorption performance and superior oxidation resistance with increasing temperature. This research exploits the characteristics of HEAs to further break the inherent magnetic limit by adjusting the morphology and provides a new pathway for solving the matter of MHz electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

Building core@shell nanostructures and doping ions are two important strategies to optimize the performance for the microwave impedance matching and attenuation. In this research, the Ag-doped α-MnO 2 @δ-MnO 2 was successfully synthesized by combining hydrothermal reaction and chemical deposition reaction. Driven by the lowest surface energy principle, all the δ-MnO 2 nanosheets nucleate on the surface of α-MnO 2 nanowires. During this process, the edge of nanosheets attach on the α-MnO 2 nanowire with low lattice mismatch of δ (201)//α (211) (nearly 0) and vertically grow on the nanowires surfaces, then the assembled core-shell composites can be prepared. The core-shell composites exhibit synergistic effect and improved the impedance matching, so that the absorbing performance has been obtained. The composite shows the minimum reflection loss (RL) of −53.67 dB at 13.28 GHz for 1.8 mm thickness, and the broadest effective absorbing bandwidth (RL < −10 dB) is 5.44 GHz as the thickness was 1.9 mm. The excellent performance is come from the preferable impedance matching, the large heterogeneous existence of the interfaces and the numerous transmission paths for microwave. Image 1 [ABSTRACT FROM AUTHOR]

Difficulty of multicomponent regulation and nanostructure design make it challenging to fabricate high-performance electromagnetic wave (EMW) absorption materials. Herein, pomegranate-like Fe 3 C@graphitic carbon embedded in amorphous carbon matrix (Fe 3 C@GC/AC) is successfully prepared through a viable heating induced self-assembly strategy. By adjusting carbonization temperature, controllable electromagnetic parameters and impedance matching characteristics of Fe 3 C@GC/AC nanocomposites could be acquired. Besides, dielectric loss and magnetic loss are offered by GC and Fe 3 C, while the amorphous carbon not only disperse Fe 3 C@GC nanoparticles well, but also strengthens interface polarization. The detailed analysis show that Fe 3 C@GC/AC nanocomposites exhibit excellent EMW absorption performance under the combined function of unique pomegranate-like nanostructure and various loss mechanisms of multi-components. Moreover, the strongest reflection loss value of optimal sample (RCF-700) is up to −96.3 dB (loss of EMW above 99.99999%) with a matching thickness of 2.08 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covers 6.38 GHz (11.62–18.0 GHz, covering Ku-band). In addition, the EAB can reach 14.08 GHz with the simulated thickness varies from 1.0 to 5.0 mm, covering 88% of the measured frequency range. The deep exploration of the bio-inspired structure of multi-component system provides a creative and effective way for high-performance EMW absorbers. [ABSTRACT FROM AUTHOR]

This study reports a carbonyl iron/glass fiber cloth composites for radar-infrared compatible stealth in a wide temperature range. All-in-one design strategy breaks the multi-layer design limitation of traditional multi-spectrum stealth materials, which not only obtains better electromagnetic stealth effect with thinner thickness but also shows excellent flexibility and tensile strength simultaneously. [Display omitted] • All-in-one design is proposed to achieve radar-infrared compatible stealth for FCI/GF cloth in a wide temperature range. • Orientation distribution structure achieves synergistic optimization of microwave loss and impedance characteristics. • FCI/GF cloth demonstrates effective bandwidth of 5.82 GHz and excellent infrared stealth properties at high temperature. Multispectral camouflage in a wide temperature range is still a challenging issue owing to the incompatibility of stealth mechanisms corresponding to different spectra. Herein, we develop a flexible flaky carbonyl iron (FCI)/glass fiber (GF) cloth, using all-in-one design of microwave absorption and infrared (IR) stealth to eliminate the above contradictions. Due to micron-scale gaps and height differences on the surface of GF cloth modified with Fe 3 O 4 , FCI gains a special vertical structure, which not only induces multiple eddy centers in FCI to enhance magnetic loss but also reduces the microwave reflection area, achieving a synergistic improvement in attenuation and impedance characteristics. Therefore, FCI/GF cloth with a thickness of 2.0 mm obtains a maximum effective absorbing bandwidth of 5.82 GHz in a range of 25–400 °C. On the other hand, combination of FCI and GF cloth decreases IR emissivity while maintaining wonderful heat insulation performance, allowing objects over 250 °C to obtain promising thermal IR camouflage. The all-in-one design successfully breaks barriers faced by traditional hierarchical radar-IR compatible stealth materials such as strong reflection, great thickness, loss and impedance mismatch. [ABSTRACT FROM AUTHOR]

• Microspheres composed of MnO 2 nanofibers are synthesized via a facile one-step method. • Nickel doping introduces defects in the MnO 2 , which enhanced microwave absorption. • The microspheres show tunable microwave absorption in the X and Ku bands. • A maximum reflection loss of −40 dB is observed at 8.31 GHz. Pure dielectric absorbers with a tunable wide-band response and strong attenuation capability for electromagnetic wave (EMW) absorption are challenging to synthesize. Herein, a series of hierarchical MnO 2 microspheres composed of MnO 2 nanofibers are synthesized via a simple one-step hydrothermal method. By varying the hydrothermal synthesis conditions, the surface architectures of the MnO 2 microspheres could be adjusted, thereby tuning their EMW absorption performance. In addition, nickel doping causes defects in the MnO 2 nanofibers, which further boosts microwave absorption performance. Compared to 2D MnO 2 nanorods, the hierarchical microspheres formed by the self-assembly of MnO 2 nanofibers offer tunable microwave absorption in the X and Ku bands. The Ni-doped microspheres with the optimized morphology show a maximum reflection loss of −40 dB is observed at 8.31 GHz, and an effective absorption bandwidth of 6.1 GHz at 2 mm thickness. [ABSTRACT FROM AUTHOR]

Electromagnetic absorbents with peculiarities of light-weight, beneficial structure, broadband, adequate corrosion resistance, and facile synthesis route are always highly practical in the telecom and stealth fields. In this regard, a new type hybird material (SiC/Fe)@C nanowires (NWs) has been effectively synthesized through an in-situ vapor-liquid-solid growth confined at arc-plasma region. A (SiC/Fe)@C NW is composed of a dielectric SiC NW with a magnetic Fe nanoparticle at it tip, both tightly encapsulated by conductive graphene-like carbon nanolayers at the surfaces. Such carbon-coated NWs form a randomly interconnected network, endowing a proper impedance matching to microwave and an anti-corrosion ability. It is found that the composite of (SiC/Fe)@C NWs and paraffin with a 25 wt% loading has shown the lowest reflection loss (RL) of −63.44 dB at 12.4 GHz, with a wide effective absorption band (RL ≤ −10 dB) of 7 GHz in thickness of 1.95 mm. This superb RL is attributed to the synergic outcomes from the balanced dielectric/magnetic losses with an appropriate impedance matching, resulted from the intrinsic physical properties and special structures of the (SiC/Fe)@C NWs. Pseudo percolation threshold, near 30 wt% loading of (SiC/Fe)@C NWs in the electromagnetically transparent matrix, implies the significant efficacy of concentration/distribution of absorbent on RL performances. Image 1 • (SiC/Fe)@C NWs have been fabricated by arc-discharge plasma; formation mechanism well explained by VLS growth. • (SiC/Fe)@C NWs found oxidation resistant up to ∼500 °C, allowing the microwave absorber adaptive in an atrocious condition. • 1D geometry of (SiC/Fe)@C NW synergistically contribute to microwave absorption. • The (SiC/Fe)@C NWs/paraffin composite reveals RL min. of -63.44 dB at 12.4 GHz in 1.95 mm thickness, and EAB of 7 GHz. [ABSTRACT FROM AUTHOR]

• Fe 80.7 Si 4 B 13 Cu 2.3 powders has a bcc-Fe nanocrystalline/amorphous composite structure. • The powders possess high M s , high μ and matchable ε in high frequency. • The powders exhibit superior electromagnetic wave absorption properties in X-band. Fe 80.7 Si 4 B 13 Cu 2.3 nanocrystalline soft magnetic alloy powders with outstanding electromagnetic wave absorption properties in X-band (8–12 GHz) have been successfully synthesized by a ball-milling method. As milling time increases from 40 to 160 h, the mean particle size of the near spherical powders with a bcc-Fe nanocrystalline/amorphous composite structure decreases from 9 to 6 μm, while the average nanocrystalline grain size stabilizes at around 10 nm. The alloy powders possess high saturation magnetization of 178.2–183.4 emu/g. The alloy powders/paraffin (3:1 in mass ratio) composites exhibit real permeability and permittivity of 2.18–2.42 and 7.3–9.7 at 2 GHz, respectively, and imaginary permeability of 0.68–0.77 at resonance frequencies of around 12.5 GHz. The composites with thicknesses of 2.1–2.3 mm exhibit large reflection losses (RL) of −39.1 to −50.5 dB with effective absorption bandwidths (RL < −10 dB) of 4.5–5.0 GHz covering the X-band. The excellent absorption properties are benefited from the high permeability and matchable permittivity of the nanocrystalline alloy powders in GHz range. [ABSTRACT FROM AUTHOR]

Abundant resources, light weight as well as stable physicochemical properties enable carbon nanomaterials promising candidates toward microwave absorption. However, it is still a great challenge for carbon-based absorbers to achieve broad frequency bandwidth and strong absorption, which fundamentally ascribes to the poor impedance matching resulted by their comparatively high electrical conductivities. Herein, a feasible and high-yield method has been employed to the in-situ synthesis of N-doped graphene nanoflakes which can effectively address interfacial impedance mismatching, and realize the majority of microwaves penetration into the interior of absorber. The incorporation of substitutional N atoms into graphene lattices markedly weaken crystallization degree and introduce masses of defects, directly leading to the decline of electric conductivity, meanwhile benefiting the improvement of static magnetization. Our findings indicate that compared with pure graphene nanoflakes, the counterpart containing 4.6 at.% of nitrogen exhibits an excellent absorption capability, in which more than 99% of microwave energy can be quantitatively attenuated at 5–18 GHz. Experimental results coupled with theory calculations further elucidate that such high performance essentially originates from the proper impedance matching constructed in the N-doped graphene nanoflakes. Image 1091 [ABSTRACT FROM AUTHOR]

Dielectric ceramics composites are potential high-temperature microwave absorption materials (MAMs), and the critical challenge is to achieve high-efficiency and temperature insensitive absorption characteristics suitable for wide temperature and frequency range. Herein, the electromagnetic attenuation properties of TiN/Fe 2 Ni 2 N/SiO 2 composites are studied in detail. The magnetic ceramic composites proposed exhibited stable attenuation behaviors at a wide temperature range (293–873 K). Notably, the optimal reflection loss (RL) value had reached −32.4 dB with a thickness of 2.8 mm at 373 K, and the effective absorption bandwidth (EAB) covered 3.89 GHz at 873 K. The excellent high-temperature attenuation capacity is attributed to the balancing strategy of dielectric and magnetic losses, as well as multiple polarization loss behaviors. The results showed that introducing magnetic components to form magnetic ceramic composites might shed light on the development of the TiN ceramic family for promising MAMs at a wide temperature range. [Display omitted] • Magnetic TiN/Fe 2 Ni 2 N nanocomposites were fabricated via an in-situ ammonia calcination process. • The introduction of Fe 2 Ni 2 N can compensate for the issue of impedance mismatch at elevated temperatures. • The magnetic-dielectric balance strategy achieves stable and efficient high-temperature microwave attenuation behavior. [ABSTRACT FROM AUTHOR]

[Display omitted] • The prominent soft magnetic properties are ascribed to their special coherent microstructure. • A short-time ball-milling does not change the coherent BCC/ L2 1 structure of MEA powders. • The prominent soft magnetic and high resistivity, which contributes to the excellent electromagnetic wave-absorbing properties. • Al 1.5 Co 3.5 Fe 3.5 flake powders possess the maximum effective bandwidth of 7.01 GHz with a sample thickness of 1.7 mm. Magnetic alloy powders show a great superiority in the balance of permittivity and permeability for electromagnetic (EM) wave-absorption. However, it is necessary to enhance their effective absorption bandwidth (Δf) and impedance matching due to their insufficient soft-magnetic properties and low resistivity, which would be solved by high/medium-entropy alloys (HEAs/MEAs). In this report, we designed Al 1.5 Co 3.5 Fe 3.5 and Al 1.5 Co 3 Fe 3 Cr MEAs with prominent soft-magnetic property and high resistivity. It is contributed to the special coherent microstructure with ultrafine magnetic body-centered-cubic nanoprecipitates uniformly-distributed into the L2 1 matrix, which could not be changed by ball-milling. Thus, alloy powders possess excellent EM properties, as evidenced by the minimum reflection loss of −42.2 dB at 14.52 GHz and the largest Δf = 7.01 GHz in 5 h-milled Al 1.5 Co 3.5 Fe 3.5 , better than existing alloy powders. The wave-absorbing behavior of MEA powders was discussed from both permittivity and permeability. The current findings offer a useful design strategy for developing high-performance absorbers. [ABSTRACT FROM AUTHOR]

• Novel Cr 3 C 2 @C hexgonal-shaped nanoplatelets were fabricated by arc-discharge plasma. • Anti-oxidation stability up to 350 °C is found in Cr 3 C 2 @C nanoplatelets. • Dielectric and magnetic losses operated synergistically in Cr 3 C 2 @C nanoplatelets. • Cr 3 C 2 @C nanoplatelets exhibited a minimum reflection loss of −36.9 dB at1.6 mm thickness. Core-shell nanomaterials have been considered excellent microwave absorbents due to their unique morphologies and designs. Here, hexagonal-shaped Cr 3 C 2 nanoplatelets coated with carbon shells (Cr 3 C 2 @C) were fabricated by an arc discharge plasma process. In as-synthesized Cr 3 C 2 @C nanoplatelets a weak ferromagnetism is found with an observable coercivity of 38 Oe, a saturation magnetization of 4 × 10−1 emu/g, and along with a suitable conductivity of 9.56 × 102 Ω−1cm−1. The observed suitable electrical conductivity and inductive magnetism of Cr 3 C 2 @C nanoplatelets played a vital role as a magnetic and conductive losses. Intrinsic defect-rich Cr 3 C 2 cores and amorphous carbon shells acted as dielectric polarization centers, wherein the incident electromagnetic wave dissipated through polarization and interfacial losses. The Cr 3 C 2 @C nanoplatelets with 30 wt% loadings in the paraffin matrix exhibited a minimum reflection loss of −36.9 dB at the thickness of 1.6 mm. The excellent refelection loss performance of Cr 3 C 2 @C nanoplatelets was certified to be a result from the synergetic effects of dielectric/magnetic losses and impedance matching. Furthermore, the Cr 3 C 2 @C nanoplatelets exhibited oxidation resistivity at 350 °C endorsing their application in harsh atmospheres. [ABSTRACT FROM AUTHOR]