Search Results (496)

Electromagnetic wave absorption ability and mechanical strength are critical performance metrics for cement-based microwave-absorbing materials. Enhancing electromagnetic wave absorption efficiency typically involves the incorporation of functional phases and optimization of pore structures. However, these modifications often introduce challenges, such as interfacial incompatibility between the functional phase and cement matrix, and reduced material density, which can compromise mechanical integrity. This study presents a structurally engineered, high-performance cement-based microwave-absorbing material fabricated from solid waste materials. By leveraging the poor interfacial compatibility between rubber powder and cement paste, the material achieves increased porosity, thereby improving impedance matching. Additionally, the presence of abundant dielectric and magnetic components in slag significantly enhances electromagnetic wave dissipation. Through the synergistic tuning of impedance matching and dissipation capacity, the cement-based microwave-absorbing material demonstrates a substantial improvement in electromagnetic wave absorption, with the absolute value of its reflection loss increasing by 2.8 times after CO₂ curing. Furthermore, the application of CO₂ curing technology facilitates the transformation of alkaline compounds such as Ca(OH)₂ into CaCO₃, resulting in notable gains in mechanical performance—compressive strength and flexural strength are elevated by 38% and 23%, respectively. This work not only achieves a balanced optimization of electromagnetic wave absorption and mechanical robustness in cement-based materials but also offers a sustainable pathway for the high-value utilization of industrial solid waste. Full article

A low-profile tri-band metamaterial absorber is developed for microwave attenuation and electromagnetic shielding applications within the S-, C-, and X-band regions. The absorber employs a compact resonant topology comprising a square metallic ring and two nested decagonal resonators, fabricated on an FR-4 dielectric layer with a metallic backing. Numerical optimization results in three highly efficient absorption bands located at 3.6 GHz, 7.4 GHz, and 11 GHz, where the absorptivity exceeds 99%. The physical origin of the absorption response is examined through field localization, induced current distributions, constitutive parameter extraction, and impedance characteristics. The analysis demonstrates that the resonant modes generated by the coupled metallic elements promote strong confinement of electromagnetic energy within the structure, leading to dissipation of the incident power. The geometrical unit-cell symmetry further enables a nearly identical response for different polarization states, while maintaining stable operation for incoming angles up to 60° under both TE and TM excitations. To verify the simulation results, an array prototype was manufactured and tested using a free-space characterization technique. The measured absorption characteristics closely follow the simulated response, showing the effectiveness of the design methodology. Owing to its compact dimensions, near-unity absorption, angular stability, and strong shielding capability, the developed absorber offers significant potential for electromagnetic compatibility enhancement, microwave shielding, and radar-related applications. Full article

(Fe/C)/ABS resin electromagnetic metamaterials were fabricated via 3D printing, and the effect of iron salt loading (0, 1, 2, and 3 g) in the Fe/C filler on the microwave absorption performance of the resulting composites was systematically investigated. The results demonstrate that, with increasing iron salt content, the microwave absorption bandwidth of the samples exhibits a trend of initial significant broadening followed by saturation. At an iron salt loading of 1 g, the (Fe/C)/ABS resin composite achieves an effective absorption bandwidth (EAB) of 6.2 GHz at a matching thickness of 10 mm, representing an approximately 48% enhancement over that of the pure C/ABS resin composite (4.2 GHz). The incorporation of iron salts not only endows the material with magnetic loss capability but also promotes the formation of an sp²-hybridized carbon framework within the carbon matrix during Fe/C composite preparation, concurrently introducing abundant defect sites that augment the dielectric loss capacity. Under the synergistic magneto-dielectric loss mechanism, the microwave attenuation coefficient of the material is markedly enhanced, and the effective absorption bandwidth is substantially broadened, all at a filler loading of merely 2.5 wt%. This study elucidates the influence of iron salt loading on the microwave absorption performance of (Fe/C)/ABS resin composites, while the 3D printing-based fabrication approach employed herein offers a promising technical pathway for the development of novel microwave-absorbing materials. Full article

The skin is the largest organ of the human body and, due to its direct contact with the external environment, is one of the most vulnerable tissues. Traditional medical bandages and gauze exhibit limited efficacy in wound management, often neglecting the control of wound inflammation and the promotion of skin regeneration. Hydrogels, as an emerging material, possess appropriate swelling capacity, oxygen permeability, and the ability to absorb wound exudates, thereby facilitating wound healing, making them an ideal choice for functional applications in skin tissue engineering. In this study, dual-treated balsa wood (BWSM) was used as the hydrogel substrate, with polyvinyl alcohol (PVA), chitosan (CS), and zinc gluconate (ZnG) used as the primary raw materials. The BWSM/PVA/CS/ZnG hydrogel was prepared via gamma-ray irradiation. Balsa wood treated with alkaline solutions, hydrogen peroxide solutions, and microwave treatment processing exhibited enhanced transparency, increased porosity, improved thermal stability and swelling rates, while retaining adequate mechanical strength. Gamma-ray irradiation of the BWSM/PVA/CS/ZnG hydrogel wound dressing demonstrated sustained drug release and antibacterial efficacy through release and antimicrobial tests. Animal experiments showed that the BWSM/PVA/CS/ZnG composite hydrogel promoted wound healing in mice and effectively prevented scar formation. The aforementioned results demonstrate that the PVA/CS/ZnG composite hydrogel loaded with balsa wood exhibits durable antibacterial properties and high mechanical strength and promotes wound healing, making it suitable for applications in biomedical materials such as wound dressings. Full article

Gel-based materials are emerging as lightweight, mechanically compliant, and electromagnetically tunable platforms for next-generation antennas, electromagnetic interference (EMI) shields, microwave absorbers, and radomes. This review summarizes recent progress in hydrogel-, aerogel-, ionogel-, organohydrogel-, and xerogel-based electromagnetic materials, with emphasis on how network structure, pore architecture, solvent phase, and functional fillers regulate permittivity, conductivity, impedance matching, and attenuation. The device-level roles of gels are discussed in miniaturized and reconfigurable antennas, absorption-dominated shielding systems, broadband microwave absorbers, high-temperature wave-transparent radomes, and metamaterial, energy-harvesting, and bioelectronic systems. Particular attention is paid to the mechanisms of dipolar relaxation, ionic conduction, interfacial polarization, conduction loss, magnetic loss, and multiple scattering. Finally, key challenges are identified, including hydrogel dehydration and freezing, aerogel fragility, ionogel cost and leakage, limited long-term reliability, and the lack of standardized performance metrics. Future directions toward durable, scalable, multifunctional, and device-integrated gel-based electromagnetic materials are proposed. Full article

With the rapid development of communication technologies, electromagnetic pollution has become increasingly serious, driving the urgent demand for high-performance low-frequency microwave absorbers. This work focuses on Nd-Fe-C powders prepared by high-energy ball milling, aiming to explore low-cost, mass-producible absorbing materials with excellent low-frequency microwave absorption performance. The Nd_10.2Fe_84.6C_5.2 alloy was synthesized via arc melting, and its powders were subsequently fabricated by high-energy ball milling for different milling durations. X-ray diffraction, scanning electron microscopy, and vector network analysis were employed to investigate the effect of high-energy ball milling on the microwave absorption properties of the Nd_10.2Fe_84.6C_5.2 alloy. As the ball milling time increased, the particle size decreased, and the minimum reflection loss shifted to a lower frequency. Additionally, increasing the thickness of the absorbing coating also moved the minimum reflection loss toward the low-frequency region. The Nd_10.2Fe_84.6C_5.2 alloy after 12 h of ball milling had good performance in the C (4.0–8.0 GHz) band when the coating thickness was in the range from 1.4 to 2.2 mm. A minimum reflection loss of −19.2 dB was achieved at 5.2 GHz, and the effective absorption bandwidth (RL < −10 dB, corresponding to a microwave absorption efficiency of 90%) reached 1.8 GHz at a matching thickness of 2.2 mm. Full article

Spinel NiCo₂O₄ has emerged as a promising microwave absorption material due to its unique crystal structure and abundant defect sites. Nevertheless, its low intrinsic electrical conductivity leads to insufficient conductive loss and unsatisfactory high-frequency impedance matching, severely limiting the simultaneous realization of strong electromagnetic attenuation and broad absorption bandwidth. Fe³⁺ doping is an effective modification strategy for NiCo₂O₄ by virtue of its matched ionic radius and dual modulation capability for dielectric and magnetic properties. Herein, pristine and Fe-doped NiCo₂O₄ absorbers with different doping contents (4%, 6%, 8%) were fabricated via a hydrothermal–calcination route, and the correlation between Fe doping concentration, microstructure, electronic structure, electromagnetic properties, and microwave absorption performance was systematically investigated. Benefiting from moderate 6% Fe doping, the optimized F6 sample exhibits a refined porous nano-agglomerate structure, which provides abundant heterogeneous interfaces and pore channels for electromagnetic wave scattering and attenuation. The introduced oxygen vacancies and balanced Ni²⁺/Ni³⁺, Co²⁺/Co³⁺, and Fe²⁺/Fe³⁺ mixed-valence states effectively strengthen interfacial and dipole polarization, while the optimized electrical conductivity and magnetic properties synergistically boost conductive and magnetic losses. Owing to the dual-loss synergism and superior impedance matching (58% proportion of Δ < 0.4), the F6 sample achieves an excellent minimum reflection loss of −62.7 dB at 2.2 mm and a wide effective absorption bandwidth of 4.6 GHz. This work clarifies the intrinsic structure–performance mechanism of Fe-doped NiCo₂O₄, providing a reliable and feasible strategy for the design and preparation of high-performance spinel-type microwave-absorbing materials. Full article

As a novel low-carbon material, alkali-activated materials (AAMs) can effectively mitigate the environmental burden caused by the cement industry, and their functional development can further enhance their additional commercial benefits. This study employed alkali-activated blast-furnace slag (AAS) as a matrix and incorporated steel slag (SS) as a functional component, and the compressive strength, workability, shrinkage characteristics, microstructure, and microwave-absorbing properties of SS-containing AAS were systematically investigated. The results show that although the low reactivity of SS impairs the compressive strength of AAS, it effectively reduces the setting rate of AAS. At an SS dosage of 50% (sample B-S50), the 28-day drying shrinkage of AAS reached a minimum value of 778 με. The dissolution and hydration of SS provide additional Ca²⁺ and OH⁻ for AAS, thereby effectively promoting the hydration of blast-furnace slag and facilitating the formation of C–(A)–S–H and N–A–S–H gels. Moreover, SS acts as a conductive functional component, enhancing the conductivity of AAS and enabling a minimum reflection loss of −29.47 dB with 0.53 GHz effective bandwidth at 20 mm thickness. After further modification with steel fibers, the thickness-dependence of the microwave-absorbing properties of AAS was reduced, allowing effective absorption across multiple thicknesses (5 mm, 15 mm, and 25 mm). This study offers new insights into the high-value utilization of low-reactivity industrial solid waste and offers design methods for its functional development. Full article

With the advancement of electronics and communication technologies, there is growing interest in high-performance microwave-absorbing materials. The material composition and structural design are critical factors influencing the electromagnetic wave (EMW) absorption capabilities. X-type barium ferrite (Ba₂Co₂Fe₂₈O₄₆) exhibits advantages in enhancing high-frequency magnetic loss and interface polarization through its unique hexagonal crystal structure and morphological design, while also optimizing impedance matching to a certain extent. However, the effective absorption bandwidth (EAB) of single-phase barium ferrite is often restricted. Therefore, doping with other elements is necessary to broaden the EAB. In this study, La³⁺-substituted X-type hexagonal ferrites Ba₂Co₂Fe_28−xLa_xO₄₆ (x = 0.00, 0.05, 0.10, 0.15, and 0.20) were successfully synthesized via a high-temperature solid-state reaction method, and the effects of different La³⁺ doping concentrations on the electromagnetic parameters and wave-absorbing performance of Ba₂Co₂Fe₂₈O₄₆ were investigated. After doping, the materials demonstrated excellent electromagnetic absorption performance: when x = 0.15, RL_min = −48.36 dB; when x = 0.10, EAB = 9.03 GHz (RL ≤ −5 dB). Full article

Superparamagnetic materials have attracted increasing attention for high-frequency microwave absorption because superparamagnetic relaxation can partially overcome the high-frequency limitations of conventional magnetic absorbers. Herein, Fe₃O₄/rGO composite powders were prepared by electrostatic self-assembly and subsequently incorporated into an epoxy matrix, and magnetic-field-induced alignment was introduced during curing. Owing to the synergistic effects of interfacial polarization, magnetic dissipation, and improved impedance matching, the optimized composites exhibited markedly enhanced microwave absorption performance. In particular, when the rGO content was 10 wt% and an external magnetic field was applied, the composite achieved effective absorption across the entire X-band (8–12 GHz) within a thickness range of 1–3 mm, together with a minimum reflection loss of −40.3 dB. The enhanced performance is attributed to the combined contributions of abundant heterogeneous interfaces, superparamagnetic relaxation, and field-induced orientation of Fe₃O₄-decorated rGO sheets. This work provides a simple physical strategy for the microstructural regulation of magnetic–dielectric composites toward high-performance microwave absorption. Full article

In this study, Fe₇₀Ni₃₀ metal was deposited onto continuous glass fiber composites via magnetron sputtering, followed by surface coating with SiO₂. The effects of key process parameters-including Fe₇₀Ni₃₀ sputtering duration (2, 5, 10, 20, and 30 min) and SiO₂ surface coating-on the electromagnetic properties and microwave absorption performance of the materials were systematically investigated. Scanning electron microscopy (SEM) characterization revealed that as sputtering time increased, the metal coating evolved from discrete small particles into a continuous film. Cross-sectional SEM analysis further demonstrated the formation of a bilayer structure after SiO₂ introduction. X-ray diffraction (XRD) patterns confirmed the presence of diffraction peaks corresponding to the Fe₇₀Ni₃₀ alloy solid solution. Electromagnetic parameter measurements indicated that the influence of sputtering time on electromagnetic properties was primarily pronounced during the metal layer growth stage; once a continuous film was formed, the variation in electromagnetic parameters diminished. Concurrently, the SiO₂ coating exhibited a significant regulatory effect on dielectric parameters. Reflection coefficient calculations showed that the optimal absorption thickness for the single-layer material ranged from 2.5 to 3.0 mm, with the absorption peak shifting toward lower frequencies as thickness increased. However, the effective absorption bandwidth (EAB) was only 3–5 GHz, failing to meet wideband requirements. In contrast, the three-layer composite structure (total thickness: 3.8 mm) optimized via genetic algorithm achieved impedance gradient and loss synergy, expanding the EBW (R < −10 dB) from 4.8 GHz (single layer) to 10 GHz (8–18.0 GHz)-a substantial improvement over the single-layer configuration. This work provides experimental evidence and technical support for the structural design and process optimization of lightweight, high-efficiency, wideband microwave-absorbing materials. Full article

Metasurface absorbers play a critical role in microwave electromagnetic control, yet conventional designs suffer from fixed performance and strong cross-coupling between tunable parameters, limiting their adaptability in dynamic environments. Here, we propose a dual-band reconfigurable metasurface absorber with independent modulation of absorption intensity and frequency. The absorber adopts a double-layer metallic structure integrated with PIN diodes and varactors, realizing independent regulation of absorption intensity and frequency. In the lower band (4.1–7.7 GHz, S₁₁ < −10 dB), the absorption intensity is continuously tunable via the PIN diode bias without frequency shift, while in the upper band (13.4–14.4 GHz), the absorption frequency is continuously tunable via the varactor bias without intensity variation. Quantitative cross-sensitivity analysis yields a frequency shift of less than 1.5% during intensity tuning and an intensity variation of less than 0.8 dB during frequency tuning. The absorber exhibits polarization insensitivity and stable performance under oblique incidence up to 45°. An equivalent circuit model is developed and validated against full-wave simulations. Numerical analyses of fabrication tolerance for the active components confirm that the highly decoupled behavior is robust, with absorption peak shifts below 0.15 GHz and intensity variations below ±1.2 dB. Our conceptual design highlights the potential towards independent multi-parametric control in reconfigurable metasurface absorbers for adaptive electromagnetic shielding, smart radomes, and frequency-agile sensing. Full article

Biomass-derived carbon-based electromagnetic wave (EMW) absorbers have attracted significant attention for their abundant availability and environmentally friendly characteristics. A novel strategy combining biomass templates with a ZIF-67-assisted approach was developed to fabricate Co₃O₄@C composites via pyrolysis. This work demonstrates that the intrinsic structure of biomass templates can be effectively leveraged to regulate both the microstructure and the electromagnetic properties of the resulting composites, enabling tunable microwave absorption performance. Among the prepared samples, M3 exhibits the lowest reflection loss (RL) of −54.79 dB at a thickness of 4.61 mm, and achieves an effective absorption bandwidth (EAB) of 3.43 GHz at 2.82 mm. This superior performance originates from the synergistic optimization of impedance matching and the coupling of dielectric and magnetic loss mechanisms. The porous biomass-derived carbon framework not only enhances multiple scattering and impedance matching but also provides abundant interfaces to induce strong interfacial and dipole polarization. Meanwhile, the uniform in situ growth of ZIF-67-derived Co₃O₄ nanoparticles introduces enhanced magnetic loss through exchange resonance, while structural defects further promote multiple dielectric relaxation processes. This study presents a novel waste-to-value strategy for the rational design of hierarchical composite absorbers, offering high-performance EMW absorption while demonstrating a low-cost, environmentally friendly, and scalable route for converting natural wood waste into functional materials. This work not only provides new insights into constructing high-performance, lightweight, and cost-effective EMW-absorbing materials but also aligns with the principles of sustainable development, resource efficiency, and green chemistry. Full article

Millions of tons of lignin waste are generated annually by the pulp and paper industries and by biofuel production. Current strategies for lignin valorization, biochars and hydrogels, often rely on time-costly and pollutant-generating processes and therefore fail to meet sustainability requirements nor are economically efficient. In this work, we address the challenge of transforming lignin into a valued-added material. We propose using microwave processing to convert lignin into a functional material that is carbon-rich, structured, hydrophilic, and highly porous. Unlike conventional methods, this process is rapid, occurring in approximately 30 s under normal conditions. It induces graphitization and up to a sixfold volumetric expansion of the lignin precursor sample, leading to the formation of a stable carbon material with high porosity in the form of capsules. The resulting material exhibits strong hydrophilicity, absorbing up to 90% of its volume in water within minutes while enabling controlled release over periods of up to 24 h. This unique combination of ultrafast processing, high water uptake capacity, and controlled-release performance positions the material as a promising alternative to the valorization of lignin. Its properties make it particularly suitable for water management applications in agriculture and urban environments. Full article

The development of cost-effective and resource-rich materials is crucial for the practical application of microwave absorbers. This study demonstrates the successful fabrication of core-shell Fe and TiC nanoparticles encapsulated within carbon shells using the arc discharge method. The samples are designated as Fe3Ti1 and Fe1Ti3, where the numbers indicate the Fe-to-Ti mass ratio in the precursor (e.g., Fe1Ti3 = 1:3 by mass). In the arc discharge synthesis mechanism, the mass ratio of Fe to Ti in the raw material was adjusted from 3:1 to 1:3 to optimize the Fe/TiC/C interfaces under a CH₄ forming gas atmosphere. TEM analysis reveals spherical and polyhedral nanoparticles with diameters of 30–50 nm and a uniform carbon shell thickness of 3–4 nm. Raman spectroscopy shows that the Fe1Ti3 sample has a higher defect density (I_D/I_G = 1.13) compared to Fe3Ti1 (0.87), indicating a more disordered carbon structure. Magnetic measurements yield saturation magnetization values of 87 emu/g for Fe3Ti1 and 50 emu/g for Fe1Ti3, with coercivities of 190.72 Oe and 203.65 Oe, respectively. When composited with paraffin at 50 wt% loading, the Fe1Ti3 sample exhibits superior microwave absorption performance, achieving a minimum reflection loss (RL) of −25.22 dB at 8.23 GHz and an effective absorption bandwidth (RL ≤ −10 dB) of 4 GHz (6.5–10.5 GHz) at a thickness of 2.5 mm. This enhanced performance is attributed to the synergistic effect of multiple loss mechanisms, including conduction loss within the three-dimensional core-shell architecture, interfacial polarization at the heterojunctions between the core and the carbon shell, and magnetic loss induced by ferromagnetic behavior associated with defects in both the shell and carbon atomic layers. The magnetic loss in the (Fe/TiC)@C nanocomposites primarily arises from the natural resonance (at ~6.5 GHz) and exchange resonance (at ~12 GHz) of the Fe cores. The dielectric loss is primarily attributed to dipole, interfacial, and space charge polarization from TiC and the carbon shell, as well as multiple scattering effects between nanoparticles. Furthermore, far-field radar cross-section simulations substantiate that the Fe/TiC@C nanocomposite demonstrates excellent radar wave attenuation capability. Further, first principles simulations reveal that introducing Fe at the C/TiC interface induces strong charge redistribution and orbital hybridization, transforming a localized dielectric interface into a highly conductive and electronically coupled C/Fe/TiC system. This interfacial modulation enhances both dielectric loss (via charge transport and polarization) and magnetic loss (via Fe-induced magnetic interactions), thereby enabling optimized dielectric-magnetic synergy for broadband microwave absorption in (Fe/TiC)@C nanocomposites. Full article