Search

There is an urgent need to develop microwave absorbing materials with ultra‐broadband absorption and multiband stealth compatibility, but this is difficult to achieve due to the difficulty of perfect electromagnetic impedance matching. Therefore, inspired by the anti‐reflection moth eye model, this article prepares carbonyl iron (CIP)/polyurethane (PU) absorbing materials into three biomimetic structures of cylinder, circular cone, and semi‐ellipsoid structures to optimize the absorption performance, which realizes the effective absorption of 5.13–18 GHz. The simulation models proved that the biomimetic structures can improve the anti‐reflection performance by building gradient impedance inside the materials. Finally, under the synergistic action of multiple reflection and gradient impedance mechanisms, the effective absorption bandwidth (EAB) of the semi‐ellipsoid moth eye biomimetic structure material with a total thickness of 3 mm can reach 6.94 GHz. The material can still achieve the EAB of 6.84 GHz with a low infrared emissivity of 0.242 by constructing the double‐layer structure. This work effectively solves the problem that the EAB of traditional microwave absorbing materials is difficult to be broadened due to impedance mismatch, and puts forward a new idea for optimizing the performance of microwave absorbing materials and compatible stealth. [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]

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]

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]

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]

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]

[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]

• 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]

• FeCoNiMn x Al 1−x HEAs with similar proportion dual phase structure(FCC and BCC) are prepared by mechanical alloying. • The induction effect of Al promotes the ferromagnetic transformation of Mn and then improve the magnetism of HEAs. • A compensation mechanism is proposed to explain the magnetism changes of HEAs with different Mn contents. • A method for predicting magnetism and high frequency permeability of HEAs by first principles calculation is provided. Fe-Co-Ni-Al high entropy alloys (HEAs) with lower coercivity (H c) and high permeability are considered as a new generation of candidates for microwave absorbing materials. Expecting to obtain higher saturation magnetization (M s) and high frequency permeability, we designed a series of FeCoNiMn x Al 1−x (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) HEAs, and first principles calculations were used to explore the spin state and magnetic changes of Mn with different Al content under the ferromagnetic transition of Mn. Firstly, the face-centered-cubic (FCC) and body-centered-cubic (BCC) phases with almost equal content were determined by experiments. The atomic models of HEAs were successfully established using the obtained crystal structure information and the spin states and magnetic moments of elements in HEAs with different Mn content were calculated. Due to the magnetic moments of ferromagnetic elements and the anti-ferromagnetic to ferromagnetic transformation of Mn elements, when Mn content is 0.2, the average magnetic moment reached 0.85/atom. The experimental results authenticate that FeCoNiMn 0.2 Al 0.8 has the highest M s of 95.0 emu/g. Higher M s is favorable for HEAs to exhibit favorable high frequency magnetic properties, the maximum value of μ′ is 2.341, and that of μ″ is 0.823 in GHz frequency. This work illustrates the importance of the ferromagnetic transformation of Mn in HEAs for regulating high frequency magnetic properties and shows the guiding significance for predicting the magnetic properties of absorbing materials via using first principles calculations. [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]

[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]

As the increasing requirements on microwave absorber resulting from the complex application environment, composites consisting of multiple components have obvious superiority to the pure materials. In order to achieve excellent absorption performance for composites, both composition and microstructure should be properly designed. In this work, a three-phase composite consisting of conductive CNT, magnetic ZnFe 2 O 4 and dielectric ZnO with coating structure is designed to enhance the microwave absorbing performance. The three-phase CNT@ZnFe 2 O 4 @ZnO composites are prepared by a two-step coprecipitation method. The as-prepared composite shows good impedance matching and high attenuation. When the content of ZnFe 2 O 4 is 3 mmol, the composite has a reflection loss of −33.5 dB at 4.4 GHz. The huge interfaces area attributed to both the multi-phase component and multi-layer structure helps to improve the interface polarization, dipole polarization, multiple reflection and scattering. Besides, the synergy of the different loss mechanisms coming from the different materials can also effectively promote the absorption. [Display omitted] • A three-phase CNT@ZnFe 2 O 4 @ZnO composite with coating structure is designed to enhance microwave absorbing performance. • ZnFe 2 O 4 microspheres grow on CNT skeleton over which the ZnO nanoparticle of ~10–20 nm covers uniformly. • The influence of ZnFe 2 O 4 content on the electromagnetic properties of CNT@ZnFe 2 O 4 @ZnO is discussed. • A maximum reflection loss of −33.5 dB at 4.4 GHz is obtained for prepared composite. [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]

The FeCoNiCu x Al (x = 0.2–0.7) high-entropy alloy powders were synthesized by ball milling and then the prepared FeCoNiCu 0.5 Al powders were annealed at different temperatures (673K, 773K and 873K). The characteristics of powders were discussed, including microstructure, morphology, particle sizes, magnetic and electromagnetic properties. The crystal structures of powders are simple FCC and BCC phases with flaky microscopic morphologies. The FeCoNiCu x Al alloys with various Cu contents are soft magnetic materials, which possess high saturation magnetization and low coercivity. High conductivity and improved surface polarization with large aspect ratio of flaky powders can enhance permittivity. High saturation magnetization of soft magnetic materials can reinforce permeability. These can promote the microwave absorbing capacity of FeCoNiCu x Al alloy powders, the reflection loss (RL) of FeCoNiCu x Al alloy powders all can reach −10dB or less and the minimum RL value is −28.04 dB at Cu x=0.5. Meanwhile, phases, morphology, conductivity and saturation magnetization are changed during different temperatures annealing treatment, which makes the RL values improved differently, and the minimum RL value is −40.05 dB at 673K annealing. These studies have shown that high-entropy alloys have great potential to become promising absorbers. • The content of Cu in FeCoNiCu x Al can adjust the ratio of FCC and BCC phase. • Annealing treatment can improve the microwave absorption performance of high entropy alloys. • The minimum RL value can achieve −40.05 dB. [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]

In this paper, polyaniline/graphene oxide composites were prepared by a one-step intercalation polymerization of aniline in the presence of GO layers under different mechanical agitation duration period, and the formation mechanism and microwave absorbing mechanism were investigated for an entire hierarchical sandwich-like structured polyaniline/graphene oxide composites. The morphology and structure were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) nitrogen sorption-desorption measurement and vector network analysis (VNA). The results revealed that mechanical agitation duration promoted the heterogeneous nucleation of aniline on graphene oxide layers and induced the formation of PANI-GO-PANI sandwich-like microstructure. The minimum reflection loss of entire sandwich-like structure reaches −28.12 dB at 5.675 GHz and an ultra-wide effective absorbing bandwidth (RL < −10 dB) over 13.175 GHz from 4.825 GHz to 18 GHz with the thickness varies from 2 mm to 5.5 mm, performing much better than pristine PANI and mixtures of PANI nanorods and sandwich-like structure. This paper reveals that constructing a hierarchical microstructure can be a promising method for developing novel microwave absorbing materials. [ABSTRACT FROM AUTHOR]

• Co-doped MnO 2 nanowires exhibit excellent electromagnetic absorption performance with the minimal reflection loss is −51.03 dB and effective absorbing bandwidth can reach 7.04 GHz. • The bonds length decreases and bonds energy increase caused by Co doping result in the enhancement of attenuation ability and the impedance matching. • Thinner nanowires supply more surface and interface and improve the multiple polarizations loss. The essence of designing ideal absorption materials is to control the electromagnetic parameters. In this work, doping strategy was adopted to regulate electromagnetic parameters. According to the experimental results and density functional theory calculations, the introduction of Co can make the charge redistribute, distortion increase, bonds length decrease, and bonds energy enhance, which can lead to the reducing of dielectric storage and raising of dielectric loss. Meanwhile, the superfine long nanowires of Co-doped MnO 2 can bring abundant surface and interfaces, which improve the polarization relaxations. These changes result in the enhancement of attenuation and improvement of impedance matching feature at the same time. Therefore, the Co-doped MnO 2 exhibits excellent microwave absorption performance, the minimal reflection loss is -51.03 dB and effective absorbing bandwidth can reach 7.04 GHz. This work offers an effective approach for the design of high-performance microwave absorption materials, which has been validated through experimental and theoretical evidence. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNT) coated with magnetic nanoparticles are promising microwave absorbing materials with high performance. Despite several previous investigations, the relationship between intrinsic composition and preparation conditions of this composite material to its microwave loss mechanisms and absorbing properties have not yet been fully understood. We present a convenient and cost-effective hydrothermal method to deposit crystalline manganese iron oxide (MnFe 2 O 4) over CNT. Adjusting the hydrothermal reaction time and CNT content allows control over the microstructure of the resulting CNT-MnFe 2 O 4 nanocomposite and its microwave absorbing properties, resulting in a better microwave absorber than pure MnFe 2 O 4. Composites synthesized at 150 °C for 10 h with 10 wt% CNT reveal a reflection loss as high as −38 dB at 5.7 GHz for an absorber thickness of 5 mm and frequency bandwidth (RL < −10 dB) up to 3.59 GHz. As the hydrothermal reaction time is reduced to 1 h, the minimum reflection loss increases significantly to −41 dB at 11.8 GHz for a 2 mm coating thickness. Defects and functional groups on the surfaces of CNT act as nucleation sites for MnFe 2 O 4 and help reduce agglomeration, which decreases overall particle size. Microwave absorbing mechanisms are also discussed. Coating CNTs with manganese iron oxide increases microwave dissipation by enhancing conduction loss, interface polarization, relaxation polarization, and magnetic loss, including the contributions of eddy current and natural resonance, which are all related to the reaction time and CNT content. Consequently, the synthesis-property relationship could potentially be used to design CNT-based nanomaterials that have more effective microwave absorption. Unlabelled Image • A convenient and cost-effective method to deposit crystalline MnFe 2 O 4 over CNT • The minimum reflection loss obtained is −41 dB at 11.8 GHz. • Absorption bandwith of ~3.7 GHz with RL < −10 dB is observed at multiple frequencies. • The synthesis-property relationship of CNT-based nanomaterials is discussed. [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]

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]