Search

So far, developed microwave absorbers exhibit significant changes in absorption with temperature, which hinder their operation within a wide temperature range. In this paper, a microwave absorber based on SiBCN ceramics was prepared. Due to the excellent high‐temperature stability of SiBCN ceramics, its permittivity changes less with temperature, avoiding the issue of performance deterioration or even failure that traditional refractory absorbers face at high temperatures. The experiment proves the absorption bandwidth for –15 dB of the SiBCN metamaterials absorber (SMA) is 12 GHz at 800°C, with a maximum absorptivity of 99.99%. According to the computed data, the resonance loss contributes 81.9 to 94.5% of the microwave absorption of SMA. This work demonstrates significant potential for applications in radar stealth under harsh conditions. [ABSTRACT FROM AUTHOR]

A broadband metamaterial absorber (MA) with high‐temperature resistance is designed and fabricated using a regular octagonal ring‐cross structure as a frequency‐selective surface (FSS). A high‐temperature conductive paste and SiO2 are used as the FSS raw materials and middle layer, respectively. Simulation and experimental results show that the absorber reaches a reflection loss below −5 dB at the 5.17–18 GHz range with normal incidence at room temperature. The measured values are in good agreement with the simulation results. At 800 °C, the absorption bandwidth expands to 13.3 GHz (4.72–18 GHz). The equivalent impedance of the absorber is obtained using an inversion method to qualitatively explain its working mechanism. The electric energy density, magnetic energy density, and surface current at the resonance frequency provide an intuitive understanding of the power loss of the structure. Comprehensive analysis illustrates that the main absorption mechanisms of the high‐temperature broadband MA (HBMA) are ohmic and resonance losses. [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]

Iron-containing siliconboron carbonitride (SiBCN) ceramics with multiple heterogeneous interfaces were fabricated using the microstructural design and polymer-derived ceramics (PDC) approach. The characterization results revealed the in - situ generation of nanocrystals, including graphite, belt-like silicon nitride (Si 3 N 4), and silicon carbide (SiC) whiskers, in amorphous SiBCN matrix after annealing. At the same time, these dielectric lossy phases successfully constructed multiple heterogeneous interfaces and three-dimensional network structures. Consequently, the conductivity of the ceramics increased from 4.49 × 10−9 (annealed at 800 °C) to 0.67 × 10−4 S cm−1 (annealed at 1600 °C). The real part of permittivity improved from 4.57–3.36 (annealed at 800 °C) to 10.90–8.38 (annealed at 1600 °C) in the frequency range of 2–18 GHz. The formation of multiple heterogeneous interfaces caused interfacial polarization and increased the multiple relaxations, which ultimately led to a superior microwave absorption property with a minimum reflection loss (RL min) of −34.28 dB and an effective absorption bandwidth (EAB) of 3.76 GHz (8.64–12.4 GHz). [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]

Designing nanocomposite with multi-level interfaces is an effective approach to improving the microwave absorbing capability of materials. In this study, the urchin-like multiple core-shelled Co/CoS 2 @NC@MoS 2 composites (CCM) are designed and fabricated by high-temperature pyrolysis and solvothermal process, where the structure and phase composition are affected by the migration of Co. Abundant interfaces in the multiple core-shelled structures favor the polarization relaxation loss, defects of MoS 2 and nitrogen doping carbon (NC) matrix induce the dipole orientation polarization loss. The CCM composite exhibits excellent microwave absorption with the strongest reflection loss (RL) of − 43.9 dB. Meanwhile, the broadest effective absorption bandwidth (EAB, RL<−10 dB) is 4.4 GHz with a thickness of 1.5 mm. Besides, with the thickness of 1.0–3.5 mm, all peaks of RL min < −20 dB (99 % absorptivity). It is believed that this work can provide an effective strategy for the design of tunable multi-interface nanostructures to regulate microwave absorption. • The urchin-like multiple core-shelled Co/CoS 2 @NC@MoS 2 composites (CCM) are fabricated. • The reactivity of Co under the pyrolysis temperature could affect the structure and phase composition. • The intrinsic loss of CCM is dominated by the polarization relaxation loss. • The effective absorption bandwidth is 4.4 GHz with a thickness of 1.5 mm. [ABSTRACT FROM AUTHOR]