Search Results (464)

In recent years, achieving ultra-wideband electromagnetic absorption has emerged as a critical challenge in confronting advanced broadband electromagnetic detection technologies. This capability is essential for effectively countering sophisticated radar systems. In this study, we present a novel multilayer metamaterial absorber that integrates an FR4 transmission layer, a periodic gradient dielectric structure designed for resonant impedance matching, and a magnetic skin layer for enhanced energy dissipation. By employing asymptotic gradients in both structure and composition, this design achieves dual-gradient electromagnetic parameter modulation, enabling efficient absorption across the X, Ku, and K bands (8.6–26.4 GHz) with a total thickness of 3.5 mm (effective thickness: 2 mm) and a density that is one-third that of conventional magnetic metamaterials. The proposed absorber demonstrates polarization insensitivity, stability across wide incident angles (up to 60°), and an absorption efficiency of 94%, as confirmed by full-wave simulations and experimental validation. Moreover, the fiber-reinforced hierarchical structure addresses the traditional trade-off between broadband absorption performance and mechanical load-bearing capacity. Full article

Microwave radiation is a potential alternative to conventional disinfection of acrylic resin, but exposure time must be minimized, e.g., by combining it with chemical agents, due to its effects on material properties. This study aimed to microbiologically evaluate the antifungal activity of microwave disinfection performed in distilled water, sodium hypochlorite (NaOCl), chlorhexidine (CHX), hydrogen peroxide (H₂O₂), or without immersion. Thermally polymerized PMMA samples colonized with Candida albicans ATCC 14053 were exposed to microwaves for 1 or 3 min in an unmodified microwave oven. Disinfection effectiveness was assessed by colony counting after 48 h of culture and absorbance after crystal violet staining. All microwave treatments significantly reduced fungal counts compared with the control (5360.00 ± 1663.09 CFU/mL). Complete inhibition of colony growth occurred only after 3 min exposure in distilled water, NaOCl, or CHX. One-minute exposure in these liquids reduced but did not eliminate fungi. The least effective method was disinfection without immersion, yielding 1040.00 ± 169.71 CFU/mL after 1 min and 560.00 ± 108.32 CFU/mL after 3 min. None of the tested conditions fully removed biofilms, although microwaves combined with NaOCl produced the best results. Overall, it was found that the presence of a liquid itself, rather than the type of chemical used, was the key factor in effective microwave-assisted disinfection. Microwave disinfection without the addition of chemicals does not remove biofilms. Full article

With the rapid advancement of detection technologies, traditional static electromagnetic absorbers increasingly struggle to meet controllable stealth requirements across diverse dynamic environments. To achieve active and controllable modulation of electromagnetic reflection characteristics, this paper proposes a transparent reconfigurable metamaterial absorber based on an origami structure. By adjusting the folding angles of the indium tin oxide (ITO)-polyethylene terephthalate (PET) film, the structure achieves reversible deformation from the vertical state to the horizontal state. This enables continuous modulation of the reflectance from below −10 dB (absorbing state) to nearly 0 dB (reflecting state) within the 4–18.9 GHz frequency range, with a relative bandwidth exceeding 130% and excellent angular stability. The energy loss and current distribution under different states are analyzed, revealing the mechanisms behind broadband absorption and deep modulation. Experimental measurements of the fabricated metamaterial align well with simulation results. Leveraging its flexible structure, reversible modulation capability, and angular stability, this origami-inspired reconfigurable metamaterial demonstrates promising application potential in the fields of adaptive electromagnetic camouflage and stealth protection. Full article

This article presents a review of current research on the use of molybdenum disulfide (MoS₂) and its composites as promising materials for energy storage systems and functional coatings. Various MoS₂ morphologies, including nanoflowers, nanoplatelets, and nanorods, are considered, as well as their effects on electrochemical properties and specific capacity. Particular attention is paid to strategies for modifying MoS₂ using carbon nanomaterials (graphene, carbon nanotubes, porous carbon) and conductive polymers, which improve electrical conductivity, structural stability, and durability of electrodes. The important role of chemical vapor deposition (CVD), which allows the formation of uniform coatings with high purity, controlled thickness, and improved performance characteristics, is noted. A comparative analysis of advances in the application of MoS₂ in sodium-ion batteries, supercapacitors, and microwave absorbers is provided. It has been shown that the synergy of MoS₂ with carbon and polymer components, as well as the use of advanced deposition technologies, including CVD, opens new prospects for the development of low-cost, stable, and highly efficient energy storage devices. Full article

In this paper, the dependence of the microstructure and properties on Spark Plasma Sintering modes of an AlN-35 β-SiC (wt.%) composite is investigated. It was found that the use of a heating rate of 100 °C/min during the sintering process of the AlN-35 β-SiC (wt.%) composite leads to the formation of a solid solution (AlN)_x–(SiC)_x−1 at 1900 °C during 5 min, and under a pressure of 50 MPa. It was observed that, at a heating rate of 50 °C/min and a pressure of 25 MPa, yttrium oxide used as a sintering additive impedes the diffusion of SiC into AlN. This impedes the formation of a solid solution (AlN)_x–(SiC)_x−1 and helps preserve SiC grains, which act as the main absorbing phase in the obtained composites. It is shown that the use of sintering additives and SPS technology allows obtaining samples with a density of 3.26 g/cm³, which coincides with the theoretical value of the composite. The dielectric characteristics and absorbing properties of sintered materials are determined in the frequency bands from 5.6 to 26 GHz. It has been discovered that the reflection, transmission, and absorption coefficients can be regulated depending on the thickness of the sample. In addition, it is shown that composites containing solid solutions and silicon carbide grains in their structures have the best absorbing properties. On the other hand, the material containing only solid solutions is a promising material that can be used as microwave filters. Full article

Salisbury screen-type radar absorption structures (RASs) consisting of a resistance sheet, a spacer, and a conductive base provide an efficient method for microwave absorption. An impedance-matched resistance sheet allows microwaves to enter, whereas superior microwave absorbers enhance their performance further. In the present work, an impedance matching composite film was prepared by using polymer/iron/iron nanowires. By varying the polymer, poly (methyl methacrylate) (PMMA), poly (vinylidene fluoride) (PVDF), and poly (vinyl alcohol) (PVA), to iron powder ratios (1:1, 2:1, and 4:1), composite films were synthesized and examined by scanning electron microscopy, X-ray diffraction, and the four-point probe method to determine the materials’ characteristics. An impedance-matched composite film was prepared based on the selected composition with 1–10 wt.% iron nanowire additions. Experimental results showed that the polymeric composite film prepared by a ratio of iron-PVA of 4:1 exhibited a sheet resistance of 49 ± 9.7 Ω/sq due to well dispersion of iron powder in PVA. With 1 wt.% Fe nanowire addition, the optimal composite sheet resistance was 329.7 ± 45.3 Ω/sq, which corresponded to an impedance matching degree (i.e., |Z_in/Z₀| value) of 0.88 ± 0.12 and can be used as a resistance sheet for a Salisbury screen-type absorber in RAS applications. Full article

Graphene can effectively enhance the impedance matching and dielectric loss capability in dielectric loss/magnetic loss dual-mechanism absorbers, and influences the overall magnetic loss capability of the material through various mechanisms. In this study, carbonyl iron/graphene composite absorbers with different graphene contents were prepared using the solution blending method. An absorbing honeycomb structure was fabricated using aramid honeycomb as the substrate via an impregnation process. The complex permittivity and complex permeability of the materials were tested within the 2–18 GHz frequency band. The absorption capability and mechanism were comprehensively analyzed alongside the reflection loss curves. Furthermore, the influence of graphene on the magnetic loss capability of the dual-mechanism absorbing material was investigated through VSM tests. Research indicates that the content and distribution of graphene can enhance the dispersion of CIP. In addition to a significant improvement in dielectric loss, it also exerts an influence on magnetic loss through a synergistic mechanism. Full article

The manufacturing techniques, structural features, and optical attributes of titanium dioxide (TiO₂) nanoparticles are highlighted in this study. These nanoparticles are notable for their remarkable photocatalytic activity, cheap cost, chemical stability, and biocompatibility. TiO₂ consists of three polymorph structures: anatase, rutile, and brookite. Because of its electrical characteristics and large surface area, anatase is the most efficient for photocatalysis when exposed to UV light. The crystallinity, size, and shape of titania nanoparticles (NPs) are influenced by diverse production techniques. Sol-gel, hydrothermal, solvothermal, microwave-assisted, and green synthesis with plant extracts are examples of common methods. Different degrees of control over morphology and surface properties are possible with each approach, and these factors ultimately affect functioning. For example, microwave synthesis provides quick reaction rates, whereas sol-gel enables the creation of homogeneous nanoparticles. XRD and SEM structural investigations validate nanostructures with crystallite sizes between 15 and 70 nm. Particle size, synthesis technique, and annealing temperature all affect optical characteristics such as bandgap (3.0–3.3 eV), fluorescence emission, and UV-visible absorbance. Generally speaking, anatase has a smaller crystallite size and a greater bandgap than rutile. TiO₂ nanoparticles are used in gas sensing, food packaging, biomedical coatings, dye-sensitized solar cells (DSSCs), photocatalysis for wastewater treatment, and agriculture. Researchers are actively exploring methods like adding metals or non-metals, making new composite materials, and changing the surface to improve how well they absorb visible light. Full article

Microwave heating is a method with a uniform heating effect and environmental friendliness in in-place hot recycling, but the microwave absorption capacity of traditional asphalt mixtures is still insufficient. As an excellent microwave-absorbing material, magnetite powder has the characteristics of high temperature resistance, corrosion resistance, and good thermodynamic stability. This study selects it as the microwave-absorbing material, prepares AC (Asphalt Concrete) type and SMA (Stone Mastic Asphalt) type microwave asphalt mixtures by adjusting its content, and investigates its influence on the microwave-heating characteristics and pavement performance of the mixtures. Simulations of the microwave-heating process of AC-type mixtures using COMSOL software (COMSOL Multiphysics 6.2) show that magnetite powder achieves optimal performance in terms of heating effect and economic efficiency when its content is 0.5%. Subsequently, laboratory tests are conducted to study the wave absorption and temperature rise performance of AC and SMA microwave asphalt mixtures; combined with economic factors, the optimal contents of magnetite powder for the two types of mixtures are determined to be 0.5% and 1%, respectively, and at the same time, these results are explained based on multiple physical theories. Furthermore, pavement performance is investigated through laboratory tests, including high-temperature rutting tests, low-temperature bending tests, immersed Marshall tests, and freeze–thaw cycle durability tests, and the results indicate that the high-temperature performance, low-temperature performance, and water stability of the microwave asphalt mixtures all meet the specification requirements for pavement performance. Subsequently, after 15 freeze–thaw cycles, the splitting tensile strength retention rate and stiffness modulus of the two types of mixtures show minimal differences from those of ordinary mixtures, and there is no durability degradation caused by the incorporation of magnetite powder. Finally, outdoor environment verification is carried out, and the results show that under complex conditions such as environmental factors, the wave absorption and temperature rise rates of AC and SMA mixtures at optimal contents are 52.2% and 14.6% higher than those of ordinary AC and SMA asphalt mixtures, respectively. In addition, these microwave asphalt mixtures have the advantages of both sustainability and reduced carbon emissions. By combining simulation methods and experimental verification, this study finally prepared two types of microwave asphalt mixtures with excellent performance, not only improving the microwave absorption and heating performance of asphalt mixtures, but also reducing environmental pollution and energy consumption, which conforms to the development of green transportation. Full article

In this study, the microwave heating efficiency of a water body is investigated with different shape factors. In particular, the same water volume was deposited in cylindrical containers with different diameters. Here, “shape factor” refers to the ratio between the surface fluid layer, which strongly absorbs microwave energy, and the inner layer, which is heated largely via conduction. For a liquid in a cylindrical container, the shape factor is characterised as the ratio between the depth and diameter of the air/water surface area. The heating efficiency is characterised by relating the energy absorbed in the outer fluid layer with the energy gained in the bulk and monitoring the temperature in the fluid bulk at the point that the outer layer commences boiling. A correlation equation for the uniformity of the sample heating (with stirring) provided a simple link between the physical factors and microwave (MW) parameters. It was found that a depth/diameter ratio approaching 1:1 provided the most uniform heating. The correlations between the fitting parameters and physical conditions provide a simple yet effective method to characterise the thermal homogeneity of microwave heating that can assist with practical parameterisation of the design of microwave reactors. Full article

There is a need to address the limitations of wheat straw (WS) as a raw biomass fuel, promote its valorisation into a high-quality renewable solid fuel, and enable this fuel to replace fossil fuels in applications such as power plants and industrial boilers. This study focused on optimizing microwave torrefaction parameters to enhance key fuel properties. Optimal conditions were determined via the Box–Behnken design (BBD) within Response Surface Methodology (RSM) as 422.32 W of microwave power, 14.95 min of irradiation time, and a 15 g microwave absorber, resulting in a 69.12% mass yield, an 18.44 MJ/kg higher heating value (HHV) surpassing lignite at 16.76 MJ/kg, and a 25.50% Energy-Mass Co-efficiency Index (EMCI). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis/derivative thermogravimetric analysis (TG/DTG) were conducted to gain insights about chemical composition and thermal stability variations due to torrefaction. LCA showed that electricity produced from 1 ton of torrefied WS reduces CO₂ emissions by 259.26 kg CO₂eq compared to electricity generated from bituminous coal. From an economic perspective, the usage of torrefied WS for power generation lead to a net profit of CNY 435.19/ton. This scalable technology, by valorising agricultural waste for fuel production, delivers dual environmental and economic benefits, laying the groundwork for industrial deployment. Full article

We present the design of an optically transparent, flexible, and tunable microwave absorber covering the X and Ku frequency bands. The absorber is based on a metasurface composed of a periodic array of graphene spiral resonators (GSRs) attached to an ultrathin PET film placed over an ITO-backed dielectric spacer. An equivalent circuit model (ECM), described by closed-form equations, is proposed to optimize the structure for maximum absorption within the target frequency range. The optimized absorber achieves a peak absorbance of 99.7% for normally incident waves while maintaining over 90% absorption at various incident angles in the frequency range from 8.5 GHz to 17.4 GHz. In addition, a double-layer graphene spiral resonator (DGSR) metasurface is proposed to extend the absorber’s operational bandwidth, demonstrating a bandwidth enhancement of approximately 3 GHz and a relative bandwidth of 90% without compromising miniaturization or incident angle stability. Given their remarkable attributes, both GSR and DGSR configurations show great potential for applications in radar stealth technology and transparent electromagnetic compatibility. Full article

Sustainable ultraviolet (UV) filters that couple photoprotection with antioxidant activity are needed. Carbon dots (CDots) derived from agro-industrial waste have emerged as promising candidates. CDots were prepared from Coffea canephora (coffee leaf) residues by a one-pot microwave route and characterized by UV–Vis, FTIR, and TEM. Antioxidant capacity was determined by CUPRAC and DPPH-EPR. The photoprotective efficacy was assessed in vitro by diffuse reflectance spectrophotometry before and after solar-simulator exposure. Nearly spherical CDots (3.3 ± 0.7 nm) displayed a 4.16 eV optical bandgap and broad absorption from 200 to 400 nm. At 10 μg mL⁻¹, CDots exhibited 24.62 ± 0.19% antioxidant activity relative to Trolox by CUPRAC, while by DPPH-EPR, they showed 99.9 ± 12.5% of radical quenching at 240 µg mL⁻¹. Addition of 4.5% w/w (dry basis) CDots to the sunscreen system increased the in vitro SPF from 26 ± 13 to 161 ± 8 (p < 0.05) while maintaining the critical wavelength at 380 ± 0.64 nm. After 30 min of irradiation, the SPF dropped only 10%, versus 44% for the CDots-free sample (control), indicating superior photostability. Coffee leaf CDots acted as an efficient broadband UV absorber and antioxidant that markedly enhanced and stabilized a conventional sunscreen formulation. The work positions waste-derived CDots as an eco-friendly, next-generation multifunctional ingredient, aligning with circular economy principles. Full article

In order to establish a general design methodology for water-based electromagnetic metamaterial absorber microstructures, a topology optimization method for water-based metamaterial absorber microstructures design was proposed in this paper. According to Mie resonance and impedance matching theory, the realization mechanism and physical model of the broadband water-based metamaterial absorber were constructed. The highest average in-band absorption rate was taken as the design object; the topological optimization model for water-based metamaterial absorber design was established. A metamaterial absorber microstructure with 16 discretized water columns inside the unit cell was designed as an example. The obtained structure exhibited a very high average in band absorption rate in the specific frequency band. The proposed method was a collaborative optimization approach that employed a single type of design variable, namely water column height, to simultaneously adjust surface impedance matching and specific resonant modes. It provided a feasible method for achieving the highest average absorption rate within a specific band. Full article

In complex electromagnetic environments, traditional static absorbers struggle to meet dynamic control requirements. Tunable absorbers based on metasurfaces have emerged as a research hotspot due to their ability to flexibly control electromagnetic wave properties. This paper provides a systematic review of research progress in tunable absorbers across the microwave, terahertz, and infrared bands, with a focus on analyzing the physical mechanisms, material systems, and performance characteristics of five dynamic control methods: electrical control, magnetic control, optical control, temperature control, and mechanical control. Electrical control achieves rapid response through materials such as graphene and varactor diodes; magnetic control utilizes ferrites and other materials for stable tuning; optical control relies on photosensitive materials for ultrafast switching; temperature control employs phase-change materials for large-range reversible regulation; and mechanical control expands tuning freedom through structural deformation. Research indicates that multi-band compatibility faces challenges due to differences in structural scale and physical mechanisms, necessitating the integration of emerging materials and synergistic control strategies. This paper summarizes the core performance metrics and typical applications of absorbers across various bands and outlines future development directions such as multi-field synergistic control and low-power design, providing theoretical references and technical pathways for the development of intelligent tunable absorber devices. Full article