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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]

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]

[Display omitted] • Transparent basalt is covered with Co/CoNi sequential configurations. • CoNi nanolayers have a net-like morphology at the higher Co ratio. • The effective absorption bandwidth reaches 4.665 GHz at 1.47 mm. • Sequential nanolayers boost the charge transfer and magnetic coupling. The typical design for electromagnetic wave absorbing materials is the composites made of high dielectric components and magnetic materials, which is a single type. This article presents a unique paradigm for high microwave absorption (MA), whereby the transparent basalt substrates are evenly covered by the sequential configurations formed by the entangled Co/CoNi nano-units. The sequential nanostructure consistently displays a net-like morphology at a 5/10 min reaction for the higher Co content in CoNi, exhibiting the regular variety for complex permittivity. On the other hand, it is constructed by the spherical nano-units with a higher Ni ratio in CoNi. After 5 min of reaction, the nanospheres are arranged with the nanogaps, or they are continuously arranged on basalt after 10 min. Correspondingly, the basalt/CoNi composites exhibit unfavorable 'mutation' characteristics with the too-small or too-large complex permittivity, detrimental for optimized MA. As expected, with the specific Co/Ni ratio, the net-like basalt/CoNi obtained at 5 min displays outstanding MA due to appropriate dielectric loss and strong magnetic coupling (−61.98 dB at 2.03 mm, 4.665 GHz at only 1.47 mm). Especially, the nano-scale magnetic coupling is confirmed by micromagnetic simulation. This work breaks the limitations of traditional absorbers and provides new design ideas about magnetic-dielectric components. [ABSTRACT FROM AUTHOR]

Dielectric composites based on polybasic components with hierarchical structures have promising potentials for electromagnetic absorber. However, strategy to strengthen coupling of transition metal oxides still demands to be optimized to enhance electromagnetic loss. Herein, inspired by the hierarchical structure of balsam pear, ultrafine ZnO is uniformly distributed and tightly capped in MnO2 by self‐assembly hydrothermal method. The unique hierarchical structure provides abundant polarization centers with large specific surface area. The compositions promote attenuation performance of electromagnetic waves, enhance relative permittivity and satisfy impedance matching as compared with that of pure ZnO or MnO2. The effective bandwidth (RL< −10 dB) reaches 5.93 GHz obtained with thin thickness of 1.8 mm. The effective bandwidth reaches 15 GHz via regulating their thickness. The fabricated MnO2/ZnO composites can achieve great adaptability in microwave. MnO2/ZnO composites keep stability even heated 700 °C in air. The phase and weight remain unchanged. The proposed interfacial modulation strategy can provide new opportunities for the design of efficient electromagnetic absorber with thermal stability. [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]

The inability of existing electromagnetic wave absorbing materials (EAMs) to manipulate electromagnetic waves in multiple dimensions leads to the failure to satisfy the demands placed on electromagnetic (EM) defense technology by the current complex EM environment. To break this dilemma, this study focuses on the impedance properties of EAMs, conferring additional ability to disperse and deflect reflected waves by encoding EAMs with opposite phase responses in different impedance mismatch modes. Due to the synergy of both absorption and scattering mechanisms, the developed scattering metamaterial absorber exhibits excellent anti-reflection performance, with reflectivity below 0.1 in the 7.8–16.7 GHz at 2 mm thickness. Furthermore, a genetic algorithm is employed to tailor the desired scattering field to meet the stealth requirements of specific environments, allowing for the directional transmission of EM energy in the one-dimensional or homogeneous distribution in the three-dimensional. The proposed scattering metamaterial absorber constructed by coded EAMs exhibited excellent anti-reflection properties and environmental stealth adaptability, opening up new possibilities for the development of advanced EM defense technology. [ABSTRACT FROM AUTHOR]

The cement-based composites made from graphene nano-platelets (GN) and hollow glass microspheres (HGM) were prepared and its electromagnetic waves absorbing properties were researched in this work. Results show that the absorbing properties were improved after the combination of GN and HGM. As the filling ratio of glass microspheres increases, the value of absorption peak and the bandwidth below −5 dB increases at first and decreases afterwards. In addition, several sharp peaks were obtained and the values tend to appear at high frequency. With further increase of GN, the value at absorbing peak decreases and the curves become relatively flatter. When GN is 0.2%, HGM is 40% (vol/vol) and the thickness is 20 mm, materials have the excellent absorbing properties with the average reflectivity loss being −8.2 dB in the range of 2–18 GHz and the bandwidth was 4.4 GHz below −5 dB. The thickness of sample has a significant influence on the absorbing properties. The optimal thickness is 20–30 mm with 40% (vol/vol) HGM and 0.2% (wt/vol) GN combine together. [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]

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]

In order to improve the absorbing properties of the electromagnetic wave absorbing plate, double-layer wave absorbing materials, which are composed of a matching layer and an absorbing layer, were devised. The matching layer is a surface layer of the wave absorbing sample, from which most of the incident waves easily enter the sample, and the absorbing layer is a second layer under the matching layer, which plays an important role in incident wave attenuation. The total thickness of the double-layer composites is the sum of the thicknesses of the matching layer and the absorbing layer. In this paper, a-manganese dioxide and carbon black (CB) were used as absorbents in the matching layer and the absorbing layer respectively. Meanwhile, the structure of the a-manganese dioxide and the CB particles were analysed by x-ray diffraction and transmission electron microscopy, and the dielectric property and absorbing mechanics were also studied. The results showed that, in the case of the mass fraction of CB in the absorbing layer being 30% and the thickness of the absorbing layer being 3 mm, the effectual absorption band (below [?]10 dB) of the double-layer wave absorbing materials reaches 8.6 GHz and 7.6 GHz in the testing frequency range between 8 GHz and 18 GHz, respectively, when the mass fraction of a-MnO2 in the matching layer was 10% and the thicknesses of the matching layer were 2 mm and 1 mm, respectively, and the effectual absorption band (below [?]10 dB) reaches 8.7 GHz in 8-18 GHz when the mass fraction of a-MnO2 in the matching layer was 20% and the thickness of the matching layer was 2 mm. [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]

The increasing prevalence of electromagnetic wave technology has raised concerns regarding electromagnetic pollution and its potential hazards. Microwave absorbing materials (MAMs) have emerged as an effective solution for capturing and dissipating electromagnetic waves. This study presents a novel approach for developing flexible microwave absorbers by dispersing carbon-coated FeNi alloy nanoparticles (FeNi@C NPs) into a polydimethylsiloxane (PDMS) matrix. The unique contributions lie in the mass production of (FeNi)@C NPs through the arc plasma and controlled making of (FeNi)@C/PDMS nanocomposites for practical electromagnetic wave (EMW) absorption/shielding application. Simultaneously, the formation mechanism of (FeNi)@C NPs is illustrated in detail by real-time optical emission spectroscopy. The obtained (FeNi)@C/PDMS nanocomposites show multifunctionality such as hydrophobicity and mechanical performance, rendering them suitable for applications in lightweight flexible electronics, wearable devices, and stealth technology. Through adjustments in the contents of (FeNi)@C fillers, the (FeNi)@C/PDMS nanocomposites exhibit excellent microwave absorption capacity. At a mass ratio of 15% of (FeNi)@C NPs, the minimum reflection loss is −33.51 dB at a thickness of 2.3 mm with an effective absorption band of 4.96 GHz. This enhanced performance is attributed to the synergistic effects of magnetic and dielectric loss, multiple reflection/scattering, conduction loss, and suitable impedance matching. Furthermore, the (FeNi)@C/PDMS nanocomposites demonstrate remarkable corrosion resistance, exhibiting a positive shift in corrosion potential to −0.18 V compared to bare aluminum (−0.83 V), along with a corresponding protection efficiency of 98.78%. In conclusion, this study provides a validated strategy for the fabrication of EMW absorption nanocomposites consisting of magnetic nanoparticle fillers and polymer matrix, highlighting their potential for application in intricate environments. • The optical emission spectroscopy was employed to analyze the growth of FeNi@C NPs. • A large-sized, flexible FeNi@C/PDMS nanocomposites were obtained by mechanical mixing. • The minimum RL of FeNi@C/PDMS nanocomposites was −33.51 dB with an EAB of 4.96 GHz. • The FeNi@C/PDMS nanocomposites exhibited good mechanical properties, corrosion resistance, and hydrophobicity. [ABSTRACT FROM AUTHOR]

Abstract: Due to the electromagnetic transparency of expanded polystyrene (EPS), the cement-based composites filled with EPS beads can be regarded as a type of “porous” material. The electromagnetic reflection loss of this porous composite material in the frequency range from 8 to 18GHz was studied experimentally in this paper. Findings show that the filling of EPS beads can improve the reflection loss of plain cement material greatly and the EPS filling ratio, EPS bead size and sample thickness all have remarkable effects on the electromagnetic wave reflection loss of this porous composite material. With a EPS filling volume concentration of 60% and EPS size of 1mm, the reflection loss is all higher than −8dB in 8–18GHz and the bandwidth for −10dB reaches 6.2GHz for a sample with the thickness of 20mm. This composite material still has a relatively low bulk density and can be handled easily. [Copyright &y& Elsevier]

• 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]