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Excellent thermostable performance is the basis for the further development of microwave absorbing materials in the field of military stealth. Herein, a high‐temperature metamaterial absorber (HMA) with high impedance patterns (multi‐octagonal‐rings), two quartz (SiO2) layers, and a metallic ground film is designed and simulated. The optimal structural parameters are obtained by optimizing the circuit parameters and the size of HMA. The interaction of electric and magnetic resonance in multioctagonal rings results in a wide absorption bandwidth and excellent absorption performance. The experimental results show that the structure has good impedance matching performance, and the effective absorption bandwidth (−10 dB) (EAB) of the structure can reach 10.6 GHz from room temperature to 700 °C under the combined effect of resonance loss and ohmic loss. [ABSTRACT FROM AUTHOR]

The bandwidth adaptation factor (BAF), which is calculated as BW • (λ L - λ H): (d • f r), is a crucial evaluation parameter for designing ultrathin broadband absorbers. In this paper, a high BAF absorber is designed by utilizing an impedance frequency selective surface (FSS), which includes a six pinnacles FSS, a La-doped mullite ceramic dielectric layer and a metal backplane. The optimal numbers of pinnacled FSS is determined through comparison and optimization, and the power monitor results indicate that the main loss modes are electrical and ohmic loss. Subsequently, the impedance analysis reveals that the favourable absorption performance is attributed to good impedance matching and high loss coefficient. Furthermore, the observation of the current distribution on the surface confirms that the primary loss appears at the pinnacles. The proposed absorber has below −10 dB reflectivity in 12.26–18.00 GHz. Meanwhile, the BAF is 3.36 and the thickness is only 0.061 λ L (1.5 mm). The measured results are in good agreement with the simulation results, demonstrating an excellent BAF characteristic. [ABSTRACT FROM AUTHOR]

The fabrication of a shell on the surfaces of ferromagnetic particles has been proved to be an efficient approach to tailoring and improving the electromicrowave (EM) absorption. In this study, core–shell composites (FeCo@SiO 2 /TiO 2 , FeCo@SiO 2 @TiO 2) were designed and fabricated by facile hydrolysis reactions. In these novel composites, the combined effects of the characteristics of each component result in excellent properties. The FeCo core exhibits strong magnetic loss, and the SiO 2 /TiO 2 shell not only acts as an impedance matching medium, but also exhibits excellent dielectric loss. Moreover, the SiO 2 and TiO 2 can efficiently limit direct contact between FeCo particles and protect the FeCo core from oxidation at high temperature. The FeCo@SiO 2 , FeCo@TiO 2 , and FeCo@SiO 2 @TiO 2 absorbers exhibit enhanced EM absorption, with maximum reflection losses (RL max) of −38.49, −36.53, and −33.72 dB at thicknesses d of 2, 5, and 3 mm, respectively, compared to −19.23 dB for FeCo single particles (d = 5 mm). The improvement is due mainly to the improved impedance matching and multiple interfacial polarization. In particular, after annealing at 500 °C, the RL max values of the FeCo@SiO 2 , FeCo@TiO 2 , and FeCo@SiO 2 @TiO 2 absorbers are −25.41, −24, and −32.38 dB at thicknesses of 3, 3, and 5 mm, respectively, which are much higher than that of uncoated FeCo (−1.39 dB, d = 5 mm). These findings demonstrate that the fabricated FeCo-based core–shell structures can be good candidates for use as room- and high-temperature EM absorbers. [ABSTRACT FROM AUTHOR]

To achieve strong electromagnetic wave absorbing properties, it is important to have good impedance matching, moderate electrical conductivity, and high polarization loss, particularly at low frequency. However, meeting these requirements for polymer-derived ceramics remains challenging. This paper proposes a simple approach to addressing this challenge by adjusting the crystallinity and defects of SiBCN ceramics. The addition of Sm as a catalyst and tailored heating temperatures were used to create SiBCN ceramics with adjustable crystallinities and defective nanograins. The controlled crystallinity provided good impedance matching, while the tailored defective nanograins offered high polarization loss. The combination of these factors results in high-performance electromagnetic wave absorption, with the SiBCN ceramics achieving a minimum reflection loss of −59.13 dB at 3.6 GHz and an effective attenuation bandwidth of 6.87 GHz with a thickness of 2.22 mm. This study provides an effective strategy for the design and fabrication of strong EMW absorbing materials. [ABSTRACT FROM AUTHOR]

One-dimensional La3+-doped mullite of diameter 20–30 nm and length 2–3 μm was prepared by a molten salt method. The electrical properties of La (x) Al (6- x) Si 2 O 13 (x = 0, 0.5%, 1.0%, 2.0%) can be effectively adjusted by the La3+ doping content. The electrical conductivity increased from 1.18 × 10−8 (x = 0) to 2.09 × 10−6 S cm−1 (x = 2.0%). The real part of permittivity was improved from 2.5 (x = 0) to 3.2 (x = 2.0%) in the frequency range 2–18 GHz. The presence of La3+ increased the dielectric loss types and improved the characteristic impedance matching, leading to excellent electromagnetic wave absorption with a minimum reflection loss of −18 dB. First-principles calculations revealed that La doping can decrease the band gap of mullite from 3.677 to 3.541 eV and induce the formation of local dipole moments, which can ultimately improve both the electrical conductivity and the dielectric polarization. [ABSTRACT FROM AUTHOR]

Flexible manipulations of morphology and composition have been considered as an art to achieve excellent microwave absorption performance for absorbers derived from metal-organic frameworks (MOFs). In this work, a strategy combining ligand-exchange induced hollow engineering and high-temperature one-step sulfuration has been proposed to fabricate the Co 9 S 8 /Co@N, S dual-doped carbon-based absorbers with tailored solid, yolk-shelled and entirely hollow polyhedral morphologies. The progressive hollow engineering not only enables composition control in the sulfuration process, but also endows the proposed absorbers with superior microwave absorption capacity due to the enhanced conductivity loss and Maxwell-Wagner polarization as well as optimized impedance matching. The yolk-shelled Co 9 S 8 /Co@N, S dual-doped carbon-based composite achieves a broad effective absorption bandwidth of 5.13 GHz at 1.88 mm with 20 wt% loading and realizes a minimum microwave loss of − 51.78 dB @ 11.63 GHz with 2.37 mm. This work reveals that the joint strategy of ligand-exchange induced hollow engineering and gas-solid reactive thermal process is an effective path to construct high-efficient lightweight multi-interfacial microwave absorbers for addressing the electromagnetic pollutions. [Display omitted] • Ligand-exchange etching facilitates tailored cavity structure in MOF-derived MAMs. • Progressive hollow engineering enables composition control in sulfuration process. • Proposed yolk-shelled absorber achieves an EAB of 5.13 GHz with 20 wt% filling. • Synergy of attenuation and impedance matching realizes superior EM absorption. [ABSTRACT FROM AUTHOR]

Prussian blue analogues (PBAs) derivatives have emerged as microwave absorbing materials to address electromagnetic pollution in recent years. In this work, bimetallic NiFe-PBA derived multi-interface N-doped carbon (NC) encapsulated NiFe alloys/Ni phosphide composites (NFPC) were prepared by thermal treatment and phosphating process. The PBAs samples with different chemical compositions and particle sizes were synthesized by manipulating the proportions of raw materials. The particle sizes of PBAs significantly impact the morphology, phosphating degree and electromagnetic properties of the NFPC composites. The results indicated that the NFPC composites exhibit excellent microwave absorption performance, with a minimum reflection loss of −41.4 dB at 1.36 mm and the effective absorption bandwidth of 4.4 GHz at 1.34 mm. The corresponding microwave attenuation mechanisms of NFPC composites were further investigated. This study not only presents a comprehensive investigation into the controlled growth of PBAs, but also provides innovative design strategies and valuable insights on utilizing multiple interfacial magnetic alloys/phosphides@NC composites as efficient microwave absorbing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Electromagnetic pollution resulting from the electronic communication can be mitigated by using microwave absorbers. The magnetic N-doped carbon foams with diverse surface morphologies as absorbers were synthesized via alkalization treatment, hydrothermal reaction, and carbothermic reduction reaction. The microstructure, electromagnetic parameters, and microwave absorption properties can be tailored by adjusting thermal treatment temperatures. The results indicated that the composites exhibit exceptional microwave absorption properties, with a minimum reflection loss of −44.15 dB at 11.18 GHz and an effective absorption bandwidth of 5.3 GHz at a thickness of 1.53 mm. The exceptional microwave absorption properties can be attributed to the synergistic effect of superior impedance matching, robust dielectric loss, and magnetic loss. The far-field radar cross section (RCS) is also reduced, achieving a maximum RCS reduction value of 14.6 dBm2. The present study presents a novel concept for the fabrication of lightweight and broadband microwave absorbing materials. • The magnetic foams with diverse surface morphologies were synthesized. • The composite exhibits high-performance microwave absorption. • Electromagnetic properties and absorption mechanisms were investigated in detail. • An effective absorption bandwidth of 5.3 GHz can be achieved. [ABSTRACT FROM AUTHOR]

Exploring high-performance electromagnetic wave (EMW) absorbers remains a formidable challenge in the face of severe EMW radiation and interference. The incorporation of manganese oxide into carbon matrix magnetic composites is proposed to enhance the EMW absorption properties in this work. Multiple interfacial ternary-component Fe 3 C/MnO/Nitrogen-doped carbon (NC) absorbers were synthesized through facile hydrothermal, oxidative polymerization and carbothermal reduction processes. The results indicated that the composites designed exhibit excellent EMW absorption properties, with an effective absorption bandwidth of 4.88 GHz (13.12–18 GHz) at a mere thickness of 1.5 mm. The outstanding performance of EMW absorption can be attributed to the effective modulation of electromagnetic parameters through a large number of heterogeneous interfaces, defects, and magnetic loss. Meanwhile, adjusting the filling ratios of the composites in the absorber also can significantly adjust the electromagnetic parameters of the samples. This work presents effective approach for the preparation of high-performance EMW absorbers with ternary components, as well as a strategy for developing novel broadband absorbers that are lightweight and have thin thickness. • Multi-interface core-shell Fe 3 C/MnO/NC composites were successfully prepared. • The phase compositions and defects can be regulated by the thermal treatment temperature. • Electromagnetic properties and absorption mechanisms were investigated in detail. • The effective absorption bandwidth is 4.88 GHz with a thickness of only 1.5 mm. [ABSTRACT FROM AUTHOR]

Microwave absorbing materials (MAMs) have been used to address electromagnetic pollution for both civil and military applications, and MAMs with broadband microwave absorption still remain a challenge. The microwave absorption performance of Ti 3 CNT x MXene is poor due to impedance mismatch. Modification of Ti 3 CNT x with magnetic materials is an effective way to improve the impedance matching and increase the effective absorption bandwidth (EAB). Here, 2D Ti 3 CNT x based magnetic composites were successfully prepared by an electrostatic self-assembly method. The microwave absorption properties of the composites were investigated by varying the loading of Ti 3 CNT x in the composites and the filling ratio of the composites in the absorber. The EAB can reach 4.75 GHz with an absorber thickness of only 1.32 mm. Integrated with a macroscale multilayer periodic gradient design, the FCM (Fe@NC/Ti 3 CNT x) composites based metastructure exhibits broadband microwave absorption with an EAB of 12.5 GHz ranging from 5.5 GHz to 18 GHz at a total thickness of 4.5 mm. The microwave attenuation mechanisms were studied by dielectric loss, magnetic loss and impedance matching. The multi-scale development of MXene-based magnetic composites makes them possible to applied to broadband microwave absorption. • Multiple interfacial 2D hexagonal Fe@NC/Ti 3 CNT x composites were successfully fabricated. • The metastructure based on FCM composites was designed. • Microwave absorption mechanisms were investigated from multiscale perspective. • The EAB of FCM metastructure is 12.5 GHz at a total thickness of 4.5 mm. [ABSTRACT FROM AUTHOR]

• Metal-polyphenol network facilitates magnetic MAMs derived from non-magnetic MOFs. • Temperature-induced composition modulation and controlled growth of MWCNTs. • At ultrathin thickness of 1.38 mm, the effective absorption band reaches 4.6 GHz. • Magnetic-dielectric synergistic effect realizes the superior microwave absorption. Magnetic carbon-based microwave absorption materials (MAMs) derived from metal-organic frameworks (MOFs) have been regarded as promising candidates for addressing the electromagnetic pollution. The construction of magnetic carbon-based MAMs derived from MOFs with ferromagnetic centers (Fe, Co, Ni etc.) and their composites has become a mainstream in recent years. However, MOFs with non-magnetic centers have received less attentions due to the challenges in achieving magnetic-dielectric synergistic effect and proper impedance matching in their derivatives. In this work, a facile metal-polyphenol network coating strategy has been proposed to facilitate the construction of magnetic MWCNTs decorated TiN 0.9 /NC absorber derived from non-magnetic MIL-125(Ti). The regulation effect of carbothermal temperature on magnetism, defect density, graphitization degree as well as electromagnetic parameters of absorbers have been systematically investigated. The obtained composites exhibit outstanding microwave absorption performance due to the magnetic-dielectric synergistic effect and improved impedance matching. The minimum reflection loss reaches −42.55 dB at 1.91 mm and the effective absorption bandwidth reaches as wide as 4.6 GHz with an ultra-thin thickness of only 1.38 mm. It is believed that this study provides a new way to construct efficient magnetic carbon-based MAMs with non-magnetic metal-based MOFs and a meaningful exploration for the preparation of ultra-thin absorbers. [ABSTRACT FROM AUTHOR]