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Chirality, in which electromagnetic characteristic promotes asymmetric polarization, is expected to realize broadband absorption for microwave absorption materials (MAMs). Herein, inspired by the microstructure of nepenthes, a scalable approach is reported for fabricating hierarchical‐chiral helical carbon fibers with broadband microwave absorption as well as multispectral chiral manipulation. The chiral potential barriers are established by applying helically distributed stress to the fiber, which induce helical electric dipoles via positive and negative charges accumulated at the potential barriers. The states of polarization loss by Debye relaxation are 2, 3, and 4 in the samples with achirality, single‐chirality, and dual‐chirality, respectively; the polar vector of achiral electric dipoles is transformed into pseudovectors through chiral potential barriers to improve the synergistically magnetic loss, and the grade of chirality is quantified based on symmetry breaking theory. The single‐chiral fibers reach strongest absorption peak value of −30.67 dB at 2.96 GHz (carbon content is 50 wt%), and the dual‐chiral fibers achieve effective absorption bandwidth (RL ≤ −10 dB) of 8.8–18 GHz. In addition to microwaves, the chiral photonic manipulation plays a role in near‐ultraviolet and visible spectra. The present discovery points to a pathway for using chiral model to open up new microwave absorption mechanism and integrated application. [ABSTRACT FROM AUTHOR]

Microwave absorbing materials with stable-wide effective absorbing bandwidth (EAB) are regarded as desirable candidates for eliminating electromagnetic interference at high temperatures. However, it still remains a challenge to simultaneously regulate the dielectric and magnetic losses in wide temperature ranges for the above excellent microwave absorption performance. Herein, a novel magnetic-dielectric composite of carbonyl iron (CI)/carbon foam (CF) with three-dimensional (3D) reticulated structure is fabricated for the first time by carbonization and vacuum impregnation. 3D reticulated structure not only provides well-defined conductive paths and controlled electrical conductivity-temperature characteristics for optimizing dielectric loss, but also induces structural magnetic loss through induced currents to retard the attenuation of magnetic loss at high temperatures. Benefiting from the synergistic regulation of dielectric and magnetic losses, CI/CF composites show the ultra-stable wide EABs at a thickness of only 1 mm, maximum EAB of 8.48 GHz and minimum EAB of 8.32 GHz in the temperature range of 298–573 K. This work provides inspirations for construction of high-temperature microwave absorbing materials with tunable magnetic and dielectric losses. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: A multifunctional microwave modulator is developed for electromagnetic protection, infrared stealth and operating temperature monitoring over wide temperature ranges for the first time. Microwave modulator achieves the integration of two electromagnetic protection mechanisms, microwave absorption and radiation deflection. Microwave modulator demonstrates the maximum effective bandwidth of 5.2 GHz with a thickness of only 1.5 mm in the temperature range 298–673 K. High-temperature electromagnetic (EM) protection materials integrated of multiple EM protection mechanisms and functions are regarded as desirable candidates for solving EM interference over a wide temperature range. In this work, a novel microwave modulator is fabricated by introducing carbonyl iron particles (CIP)/resin into channels of carbonized wood (C-wood). Innovatively, the spaced arrangement of two microwave absorbents not only achieves a synergistic enhancement of magnetic and dielectric losses, but also breaks the translational invariance of EM characteristics in the horizontal direction to obtain multiple phase discontinuities in the frequency range of 8.2–18.0 GHz achieving modulation of reflected wave radiation direction. Accordingly, CIP/C-wood microwave modulator demonstrates the maximum effective bandwidth of 5.2 GHz and the maximum EM protection efficiency over 97% with a thickness of only 1.5 mm in the temperature range 298–673 K. Besides, CIP/C-wood microwave modulator shows stable and low thermal conductivities, as well as monotonic electrical conductivity-temperature characteristics, therefore it can also achieve thermal infrared stealth and working temperature monitoring in wide temperature ranges. This work provides an inspiration for the design of high-temperature EM protection materials with multiple EM protection mechanisms and functions. [ABSTRACT FROM AUTHOR]

Noting that the dielectric properties of manganese oxide make it a promising microwave-absorbing material, a low-temperature method to deposit crystalline MnO2 over carbon nanotubes (CNTs) is developed. Adjusting the pH of the precursor solution allows control over the phases and morphologies of the synthesized manganese oxides MnO2 and Mn3O4 that have minimum reflection losses of − 11 dB and − 6 dB, respectively. The synthesized CNT-MnO2 and CNT-Mn3O4 nanocomposites are superior microwave absorbers than simpler physical mixtures of CNTs and manganese oxides, with reflection losses as high as − 19 dB at 9.5 GHz and − 34 dB at 4 GHz, and have wider absorption bands than pure manganese oxides. Coating CNTs with manganese oxide not only increases dielectric and magnetic losses, but also improves the impedance match between free space and the absorber. The addition of CNTs to pure MnO2 and Mn3O4 improves impedance matching by enhancing the relaxation polarization and conductivity losses, magnetic loss, including contributions form eddy current and natural resonance. This facile, low-cost, scalable, high-yield method produces an enhanced microwave-absorbing nanocomposite. [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]

Hydrothermal synthesis between (NH )S O and MnSO was carried out to investigate the structure, morphology, and electromagnetic properties of Ni-doped MnO with different doping amounts. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and vector network analysis. The analysis results revealed that all the final products were α-MnO and few amounts of γ-MnO , and the morphology changed obviously with the increase of the Ni doping amount. The doping of Ni had a certain effect on the electromagnetic properties, and some other properties derived from electromagnetic performances were also investigated, such as dielectric and magnetic loss tangent and microwave-absorbing properties. All the reflection loss (RL) peaks of the final products were moving toward lower frequency with increasing thickness, and with the thickness of 2 mm, the final products all had the maximum effective absorption bandwidth (RL < −10 dB), and the Ni-doped MnO had better reflection loss performance than the undoped MnO in the range of high frequency. [ABSTRACT FROM AUTHOR]

Highlights: The crystalline Fe/MnO@C core–shell nanocapsules embedded in porous amorphous carbon matrix (FMCA) was prepared by a novel confinement strategy of modified arc-discharge method. The heterogeneous crystalline–amorphous nanocrystals disperse evenly and exhibit improvement of static magnetization and excellent electromagnetic absorption properties. The adding MnO2 confines degree of graphitization and contributes to form amorphous carbon. Dielectric loss and microwave absorption are achieved adjustable. Crystalline Fe/MnO@C core–shell nanocapsules inlaid in porous amorphous carbon matrix (FMCA) was synthesized successfully with a novel confinement strategy. The heterogeneous Fe/MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2–18 GHz. The addition of MnO2 confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon. The heterogeneous materials composed of crystalline–amorphous structures disperse evenly and its density is significantly reduced on account of porous properties. Meanwhile, adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network. The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption. The optimal reflection loss (RL) is up to − 45 dB, and the effective bandwidth (RL < − 10 dB) is 5.0 GHz with 2.0 mm thickness. The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber, but also offers a general duty synthesis method for heterogeneous crystalline–amorphous composites with tunable composition in other fields. [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]

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]

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]

• 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]