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Recently, high‐entropy alloy (HEA) microwave‐absorbing materials have attracted extensive attention. Herein, a double‐layer structure consists of a low‐infrared emission metasurface and a FeCoNiMn0.5Si0.5Al0.5 HEA coating with enhanced microwave absorption performance is designed. The upper metasurface consisting of periodic hexagonal aluminum structural unit has excellent low‐infrared emission properties, while enabling selective transmission and absorption enhancement of radar waves. The emissivity of the low‐infrared emitting layer is lower than 0.2, and the metastructure on its surface affects more on the high‐frequency absorption performance. The bottom layer made of HEA coating with 1 mm hexagonal etching structure has an effective absorption bandwidth of 2.8 GHz, and its reflection loss (RL) can reach −42 dB. There is a certain fit relationship between the unit size of the periodic structure and the absorption performance of the underlying coating. For the coatings with high‐frequency RL peaks, a larger unit size of the periodic structure will lead to an obvious improvement on the absorption performance. A broad application prospect for multiband compatibility stealth is provided. [ABSTRACT FROM AUTHOR]

In order to break through the bottleneck of narrow effective absorption bandwidth (reflection loss RL ≤ −10 dB) of microwave absorbing materials, herein, we fabricate the metamaterials with carbon fiber (CF) and FeSi alloy (FSA) ribbon metastructure which is distributed in the carbonyl iron powders (CIP)/polyurethane (PU) matrix. The experimental results show that the microwave absorption capacity of the matrix can be significantly enhanced by CF. Compared with the pure matrix, the effective absorption bandwidth increases from 9.4–13.44 GHz to 11–16.8 GHz when the CF is parallel to the electric field vector and the spacing between adjacent CF is 20 mm. Furthermore, the CF and FSA ribbons are arranged in the matrix as an orthogonal arrangement, and the best absorption bandwidth cover 9.76–14.46 GHz when the electric field is parallel and 9.96–14.1GHz when the electric field is vertical when the spacing is 30 mm. The electromagnetic simulation of the metamaterials is calculated, it is proved that the increase of effective absorption bandwidth is due to the strengthening of carbon fiber and its coupling with FSA ribbon. This paper provides a new research path for improving the absorption properties of thin layer microwave absorbing materials. [ABSTRACT FROM AUTHOR]

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]

Despite great efforts in material design and modification, there are still obstacles to improve the effective microwave absorption, which hinders the development of stealth materials. By introducing a magnetically induced Huygens' metasurface with Fibonacci spiral meta‐atom, a hierarchical absorber with carbonyl iron particle coating is designed and prepared, of which the total effective absorption bandwidth (EAB, reflection loss ≤−10 dB) amazingly reaches 9.41 GHz, exceeding 199% of the original coatings', and the absorption peak value declines from −15.91 to −32.12 dB. The overall thickness of the absorber is 7 mm, only 0.17 over the minimum thickness dictated by the causality limit. A conceptual basis for the proposed design is provided, that is, the balance of effective surface current and magnetic current induced simultaneously will enhance the electromagnetic (EM) wave transmission, which contributes to broadening the absorption bandwidth with promising impedance matching. The system is validated numerically and experimentally, suggesting a novel route to obtain high‐performance microwave absorption materials for the EM stealth technology. [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]

Highlights • The carbonyl iron/graphene sheets/polyurethane ternary coatings were prepared. • The graphene sheets can tune microwave absorption frequencies and enhance the absorption properties of composites coating. • The effect bandwidth (RL<−10 dB) is in the frequency range of 10.9 −18 GHz with a thickness of 1 mm. • The minimum reflection loss is −30.1 dB at 15.6 GHz. Abstract Waterborne polyurethane matrix coatings using the carbonyl iron particles (CIP) and graphene sheets (GNs) as electromagnetic wave absorbing fillers were fabricated. The electromagnetic parameters of CIP and GNs were measured in 2–18 GHz by transmission/reflection technology. The reflection loss (RL) of the coatings was measured by the arch method. The electromagnetic loss mechanisms and the effect of GNs addition on absorption properties and of composites were discussed. And the morphology of fillers and the micrographs of coatings fracture surface were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that, the unique electromagnetic properties of GNs can make up the shortage of CIP, and the synergistic effects of dielectric/magnetic composites can improve the electromagnetic wave attenuation. In addition, the electromagnetic wave absorption properties can be adjusted by simply changing the content of GNs and CIP particles to obtain the broadband microwave absorption coatings with small thickness. When the mass ratio is CIP:PU:GNs = 2.5:1:0.01, reflection loss values exceeding -10 dB can be obtained in the frequency range of 10.9−18 GHz with a thickness of 1 mm. The models of equivalent circuit and synergistic effect among CIP/GNs/PU composite coating were built to analyze the improvement mechanisms of absorption properties. [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]

[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]

We fabricated flaky FeSiAl (FFSA) absorption coatings and flaky FeSiAl (FFSA)/carbon black (CB) composite absorption coatings, and studied the effects of a discrete structure on the absorption performance of both coatings. The electromagnetic parameters of FFSA and CB were measured in the frequency range of 2–18 GHz using transmission/reflection technology. We also investigated the electromagnetic loss mechanisms of FFSA and CB. The microwave absorption properties of the coatings were determined by measuring the reflection loss (RL) using the arch method. We then analyzed the effects of the contents and the discrete structure on absorption properties. The results showed that, for the FFSA coatings, discrete structures markedly improved absorption properties. When the discrete unit sizes decreased, the absorption properties increased. The addition of CB further improved the absorption performance of the FFSA absorption coating. And when FFSA/CB composite coatings were cut into discrete structures, the absorption peak values decreased and the absorption peak frequencies shifted toward higher frequency ranges, which were consistent with those of the FFSA coating. Because of the conductivity differences between FFSA and CB, the FFSA/CB composite coatings with discrete structures had significant improvements in absorption. The improved absorption weakened when the CB content achieved a certain value. The equivalent circuit models were built to analyze the improvement mechanisms of absorption properties when the coating was cut into a discrete structure. [ABSTRACT FROM AUTHOR]

A method of improving the electromagnetic (EM) absorption property of conventional microwave absorber (CMA) is proposed here. The structural design process was mainly concerned with systematic analysis and research into the impedance matching characteristic and induced current. By processing a CMA-carbonyl-iron powder (CIP) coating into many isolated regions, the discrete-structure microwave absorber (DMA) had a much better absorption property than the corresponding CMA. When the thickness was only 2.0 mm and the component content was 33 wt%, the loss of reflection was less than −10 dB shifted from 6–7 GHz to 7–13 GHz and the loss of minimum reflection decreased from 12.5 dB lost to 32 dB lost through a discrete-structure process. The microwave absorption properties of coatings with different component contents and thicknesses were investigated. The minimum reflection peaks tended to shift towards the lower frequency region as CIP content or coating thickness increased. By adjusting these three factors, a high-performance broadband absorber was produced. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) with nanoscale crystal structure have supposed to be good microwave absorbers due to their excellent soft magnetic properties. Annealing is typically employed to optimize microwave absorption, however, grain coarsening motivated by temperature will lead to serious deterioration of soft magnetic properties. Herein, we introduce the rare earth (RE) element Gd into FeCoCrAlGd x (x = 0, 0.1, 0.2, 0.3) HEAs, which is expecting to inhibit the nanograin coarsening through dispersing Gd 2 O 3. The incorporation of Gd results in a low coercivity (H c), high saturation magnetization (M s), and high complex permeability (μ′ and μ″) of the HEAs. Especially, the H c for as-annealed FeCoCrAlGd 0.2 (114 Oe) is only 60.6 % of that for as-annealed FeCoCrAl (188 Oe). Owing to the remarkable magnetic properties, all Gd-doped HEAs have a larger effective absorption bandwidth at lower thicknesses. The reflection loss (RL) of as-annealed FeCoCrAlGd 0.1 reaches a maximum absorption of −45 dB and an effective absorption bandwidth of 5 GHz (thickness is 1.5 mm). In addition, DFT (density functional theory) calculations are performed to analyze the energies and magnetic moments of the systems. This article provides guidance for design of high performance soft magnetic microwave absorbers. • Coarsening behavior of nanograins during annealing is suppressed by dispersed Gd 2 O 3 particles. • Gd-doped high-entropy alloys have significantly lower coercivity and higher saturation magnetization. • Static magnetic properties induce higher complex permeability and excellent microwave absorption. • The energies and magnetic moments of the systems were calculated by density functional theory (DFT) calculations. [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]

[Display omitted] • Basalt coated by NiO is synthesized by water bath method followed by sintering process. • The enhanced microwave absorption for basalt@NiO heterostructure has been achieved when sintered at 300 °C. • An amount of vacancies defects and large heterogeneous interface in basalt@NiO-300 °C improve the dielectric loss. • Basalt@NiO heterostructure also has low density, high temperature resistance and excellent anticorrosion. The heterostructure has attracted widespread attention in improving microwave absorption due to the unique composition and structure. Herein, a novel two-dimensional (2D) plate@shell basalt@NiO heterostructure is synthesized through a sequential process of water bath method followed by a sintered operation. The sintering temperature helps regulate the microwave absorption performance by controlling the heterogeneous interface and vacancy defects of basalt@NiO to optimize the dielectric loss. The RL of the prepared basalt@NiO with the sintering temperature of 300 °C reaches up to −15.93 dB at 16.13 GHz, which is attributed to the polarization loss enhanced by vacancy defects (O, Ni vacancies) introduced by low-temperature sintering and large heterogeneous contacts constructed by basalt and NiO. Meanwhile, the high concentration of vacancy defects also leads to a large electrical conductivity that positively contributes to dielectric loss. Furthermore, the basalt@NiO composite possesses relatively low density, high thermal stability and anticorrosion. This finding provides a way for designing the light microwave absorption materials with excellent environmental stability. [ABSTRACT FROM AUTHOR]

Abstract: Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO2 was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18GHz. With increasing SiO2 content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18GHz. When the coating with the optimized SiO2 and CI weight concentration (SiO2:CI:ER) of 2:5:1, the optimal RL got to −17.3dB and the effective absorption band (RL better than −4dB) reached 5.7GHz. In comparison, the minimum RL value was only −5.9dB and the bandwidth (RL better than −4dB) was just 4.1GHz for the SiO2-free composite coating. [Copyright &y& Elsevier]

Abstract: To prevent serious electromagnetic interference, a single-layer wave-absorbing coating employing complex absorbents composed of carbonyl-iron powder (CIP) and carbon black (CB) with epoxy resin as matrix was prepared. The morphologies of CIP and CB were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The electromagnetic parameters of CIP and CB were measured in the frequency range of 2–18GHz by transmission/reflection technology, and the electromagnetic loss mechanisms of the two particles were discussed, respectively. The microwave absorption properties of the coatings were investigated by measuring reflection loss (RL) using arch method. The effects of CIP ratio, CB content and thickness on the microwave absorption properties were discussed, respectively. The results showed that the higher thickness, CIP or CB content could make the absorption band shift towards the lower frequency range. Significantly, the wave-absorbing coating could be applied in different frequency ranges according to actual demand by controlling the content of CIP or CB in composites. [Copyright &y& Elsevier]

Abstract: To solve more and more serious electromagnetic interference problem, one thin microwave absorbing sheet employing carbonyl-iron powder (CIP) and chlorinated polyethylene (CPE) was prepared. The pattern, static magnetic properties and phase of CIP were characterized by scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and X-ray diffraction (XRD), respectively. The electromagnetic parameters of CIP were measured in the frequency range of 2–18GHz, and the electromagnetic loss mechanisms of the powder were discussed. The microwave absorption properties of composite sheets with different thicknesses and CIP ratios in matrix were investigated by measuring reflection loss (RL) in 2–18GHz frequency range using the arch method. The results showed that appropriate CIP content and thickness could greatly improve microwave absorption properties in lower frequency range. For the sample with the weight ratio (CIP:CPE) of 16:1 and 1.5mm thickness, the bandwidth (RL below −10dB) achieved 1.1GHz (2–3.1GHz), and the minimum reflection loss value was obtained −13.2dB at 2.2GHz. This suggested that CIP/CPE composites could be applied as thin microwave absorbers in S-band (2–4GHz). [Copyright &y& Elsevier]

Perfect stealth has attracted humanity for decades owing to the advent of metamaterials, however, despite long-standing efforts in design and fabrication, it has been challenging to achieve ultra-broadband absorption under deep-subwavelength thickness, the fundamental hurdle is Plank-Rozanov limit, which hindering the development of stealth materials. Herein, inspired by the absorption model of Pachliopta aristolochiae, present works demonstrate an approach with composition concept to ideal stealth, through the synergy of microwave melanin and bionic metastructure, the fabricated biomimetic metamaterials exhibit effective absorption over 2–18 GHz range under 0.04 λ max thickness for radar stealth, which breakthrough the Plank-Rozanov limit by utilizing the enhanced resonance of bionic metastructure in absorption, corresponding mechanisms are demonstrated by simulation models. The metamaterials also robustness for arrangement and polarizations, compatible infrared emissivity is reduced to 0.43, as well as flexibility and impact resistance during minus temperature. The principle behind here is universal and can be extended to many metamaterials and a broad range of absorption. Image 1 [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]

The microwave absorbers developed so far encounter a bottleneck for the constraint of absorption by deep sub-wavelength thickness. In this work, we report enhanced and tunable structural composite metamaterials, which were fabricated by parallel and orthogonal arrayed Fe-Si alloy ribbons sandwiched between two layers of carbonyl iron powder/polyurethane matrix. It demonstrated a minimum resonance peak value −66.90 dB under deep sub-wavelength thickness (1.25 mm), an extraordinary result that indicated almost complete absorption. The absorption of 90% (reflection loss (RL) < −10 dB) bandwidth covered 10.2 to 18 GHz, almost the entire band of test. The absorbing mechanisms were explored by the simulation models that verified the coupling in the ribbons and the matrix. The composite metamaterials have adaptability during various bending, curling and impact conditions, and the radar-infrared compatible stealth property could also be reached. These results demonstrated that the composite metastructure provides new possibilities for the manufacture of high-performance microwave absorbing materials. [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]

Abstract: Nanocrystalline carbon black/barium titanate compound particle (CP) was synthesized by sol–gel method. The phase structure and morphology of compound particle were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM) and Raman spectrum measurements, the electroconductivity was test by trielectrode arrangement and the precursor powder was followed by differential scanning calorimetric measurements (DSC) and thermal gravimetric analysis (TGA). In addition, the complex relative permittivity and permeability of compound particle were investigated by reflection method. The compound particle/epoxide resin composite (CP/EP) with different contents of CP were measured. The results show barium titanate crystal is tetragonal phase and its grain is oval shape with 80–100nm which was coated by carbon black film. As electromagnetic (EM) complex permittivity, permeability and reflection loss (RL) shown that the compound particle is mainly a kind of electric and dielectric lossy materials and exhibits excellent microwave absorption performance in the X- and Ku-bands. [Copyright &y& Elsevier]

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]

Influences of the arrayed carbon fibers (CFs) and gradiently dispersed Fe nanoparticles (NPs) inside epoxy resin (ER) matrix on the microwave absorption and mechanical properties were investigated. As a microwave absorbent, the Fe NPs were synthesized by an arc discharge plasma method and subsequently surface-modified by using of silane coupling agent (KH-550) to improve their dispersion in organic ER matrix. To measure the naturalistic electromagnetic and mechanical properties of such nanocomposite plates, a series of square plates (20 × 20 cm 2 ) were fabricated by filling the modified Fe NPs (30 wt.%) with/without orientated CFs at different mass percentages (0, 1.38 wt.%, 2.76 wt.% and 5.52 wt.%) into the ER matrix. The excellent microwave absorption of nanocomposite plate occurred as the direction of CFs was vertical to that of incident microwave, in such case the multi-reflections of microwave were caused by CFs and favors to create a great absorption probability to Fe NPs. A well matched input impedance of the plate to air is necessary for the effective entrance of incident microwave and to be attenuated by the structural resonance and electromagnetic losses. The input impedance of nanocomposite plate is mainly determined by the content of absorbent (Fe NPs with a gradient dispersion), CFs (with orientations to incident microwave, i . e . vertical, parallel or perpendicularly cross-linked to each other) and the geometric configuration (sizes of the plate, distribution of each components, etc.). It was figured out that the nanocomposite plate (30 wt.% of Fe NPs, 5.52 wt.% of CFs vertical to incident microwave) exhibits a higher reflection loss (RL) of −26.8 dB at 4.9 GHz, in which the structural resonances, appropriate conductivity, dielectric polarization and impedance matching were involved. The effects of gradiently dispersed Fe NPs and the arrayed CFs with orientations on the electromagnetic and mechanical properties were emphasized and investigated. [ABSTRACT FROM AUTHOR]