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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]

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]

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]

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]

The earliest microwave absorbing materials (MAMs) are fabricated in the early 20th century for military purpose to inhibit radar detection. Currently, the application of MAMs has been existing in every part of human's life to prevent radiation and interference. The microwave absorbant and microwave absorbing coatings classified by composition including alloys, metal oxides, conductive polymers, carbon materials, ceramic materials both in traditional and innovative forms are introduced in this work. Considering the harsh and complex application environment, MAMs with high temperature resistance and infrared-compatible stealth performance are involved. Metamaterials, showing excellent electromagnetic properties which are far beyond that of the materials can achieve, including perfect absorber, digitally coded control metamaterials, bionic structural materials, and adjustable smart metamaterials, are also introduced specifically in this work. In addition, to investigate electromagnetic response of absorbant, the first-principles calculations works are overviewed. The electromagnetic properties, loss mechanisms, structure, fabrication method, regulation approaches, designing principles, current applications, and future prospects of MAMs are involved in this work. This work gives a comprehensively overview over the MAMs for their theoretical and experimental advances in recent years including the military radar (frequency range of 2–18 GHz) stealth materials, relevant infrared compatible (infrared-visible, infrared-radar, infrared-laser) stealth materials, and other stealth materials with multifrequency adaptability. [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]