Search Results (442)

This study describes a quite special and interesting atmospheric event characterized by the simultaneous presence of fresh and aged smoke layers. These peculiar conditions occurred on 16 July 2024 at the CNR-IMAA atmospheric observatory (CIAO) in Potenza (Italy), and represent an ideal case for the evaluation of the impact of aging and transport mechanisms on both the optical and microphysical properties of biomass burning aerosol. The fresh smoke was originated by a local wildfire about 2 km from the measurement site and observed about one hour after its ignition. The other smoke layer was due to a wide wildfire occurring in Canada that, according to backward trajectory analysis, traveled for about 5–6 days before reaching the observatory. Synergetic use of lidar, ceilometer, radar, and microwave radiometer measurements revealed that particles from the local wildfire, located at about 3 km a.s.l., acted as condensation nuclei for cloud formation as a result of high humidity concentrations at this altitude range. Optical characterization of the fresh smoke layer based on Raman lidar measurements provided lidar ratio (LR) values of 46 ± 4 sr and 34 ± 3 sr, at 355 and 532 nm, respectively. The particle linear depolarization ratio (PLDR) at 532 nm was 0.067 ± 0.002, while backscatter-related Ångström exponent (AEβ) values were 1.21 ± 0.03, 1.23 ± 0.03, and 1.22 ± 0.04 in the spectral ranges of 355–532 nm, 355–1064 nm and 532–1064 nm, respectively. Microphysical inversion caused by these intensive optical parameters indicates a low contribution of black carbon (BC) and, despite their small size, particles remained outside the ultrafine range. Moreover, a combined use of CIAO remote sensing and in situ instrumentation shows that the particle properties are affected by humidity variations, thus suggesting a marked particle hygroscopic behavior. In contrast, the smoke plume from the Canadian wildfire traveled at altitudes between 6 and 8 km a.s.l., remaining unaffected by local humidity. Absorption in this case was higher, and, as observed in other aged wildfires, the LR at 532 nm was larger than that at 355 nm. Specifically, the LR at 355 nm was 55 ± 2 sr, while at 532 nm it was 82 ± 3 sr. The AEβ values were 1.77 ± 0.13 and 1.41 ± 0.07 at 355–532 nm and 532–1064 nm, respectively and the PLDR at 532 nm was 0.040 ± 0.003. Microphysical analysis suggests the presence of larger, yet much more absorbent particles. This analysis indicates that both optical and microphysical properties of smoke can vary significantly depending on its origin, persistence, and transport in the atmosphere. These factors that must be carefully incorporated into future climate models, especially considering the frequent occurrences of fire events worldwide. Full article

Multilayer thin films composed of cobalt (Co), carbon (C), and chromium (Cr) possess promising electromagnetic properties, yet the combined Co–C–Cr system remains underexplored, particularly regarding its performance as a microwave absorber. Existing research has primarily focused on binary Co–C or Co–Cr compositions, leaving a critical knowledge gap in understanding how ternary multilayer architectures influence electromagnetic behavior. This study addresses this gap by investigating the structure, phase composition, and microwave absorption performance of Co–C–Cr multilayer coatings fabricated via magnetron sputtering onto porous silicon substrates. This study compares four-layer and eight-layer configurations to assess how multilayer architecture affects impedance matching, reflection coefficients, and absorption characteristics within the 8.2–12.4 GHz frequency range. Structural analyses using X-ray diffraction and transmission electron microscopy confirm the coexistence of amorphous and nanocrystalline phases, which enhance absorption through dielectric and magnetic loss mechanisms. Both experimental and simulated results show that increasing the number of layers improves impedance gradients and broadens the operational bandwidth. The eight-layer coatings demonstrate a more uniform absorption response, while four-layer structures exhibit sharper resonant minima. These findings advance the understanding of ternary multilayer systems and contribute to the development of frequency-selective surfaces and broadband microwave shielding materials. Full article

Measuring pH is a critical parameter in environmental monitoring, biomedical diagnostics, food safety, and industrial processes. Optical fiber sensors have proven highly effective for pH detection due to their exceptional sensitivity, rapid response, and resistance to electromagnetic interference, making them well suited for real-time monitoring. This review offers a comprehensive analysis of recent advances in optical fiber-based pH sensors, covering key techniques such as fluorescence-based, absorbance-based, evanescent wave, and interferometric methods. Innovations in Fiber Bragg Grating and Surface Plasmon Resonance technologies are also examined. The discussion extends to the impact of pH-sensitive coatings—ranging from nanomaterials and polymeric films to graphene-based compounds—on enhancing sensor performance. Recent advancements have also enabled automation in data analysis and improvements in remote sensing capabilities. The review further compares the economic viability of optical fiber sensors with traditional electrochemical methods, while acknowledging persistent issues such as temperature cross-sensitivity, long-term stability, and fabrication costs. Overall, recent developments have broadened the functionality and application scope of these sensors by improving efficiency, accuracy, and scalability. Future research directions are outlined, including advanced optical interrogation techniques, such as Addressed Fiber Bragg Structures (AFBSs), microwave photonic integration, and optimized material selection. These approaches aim to enhance performance, reduce costs, and enable the broader adoption of optical fiber pH sensors. Full article

The study of the effects of 2.45 GHz electromagnetic fields on the health and safety of people and organisms as a whole is essential due to their widespread use in everyday life. It is known that they can cause thermal and non-thermal effects—at the molecular, cellular and organismal level. Yeast suspensions were treated with 2.45 GHz microwave radiation in the near-field of antenna at two distances (2 and 4 cm) and two time periods (20 and 60 min)—setups resembling the use of mobile devices. The release of UV-absorbing substances from the cells was studied as an indicator of membrane permeabilization, total intracellular antioxidant activity and reduced glutathione were determined, and a comet assay for damage to the DNA was performed. A correlation between reduced antioxidants and increased membrane permeability during EMF treatment was observed at a distance of 2 cm for 20 min, suggesting the presence of oxidative stress, while a similar effect was not observed with conventional heating. Slightly increased membrane permeability was observed after irradiation for 60 min at a distance of 4 cm, but this was not related to the antioxidant status of the cells. A trend towards increased DNA damage was observed under both conditions. Full article

The nitriding process was employed to optimize the low-frequency microwave absorption properties of Y₂Fe₁₂Co₄Si/paraffin composites. The effects of nitriding temperature on the phase composition, static magnetic properties, electromagnetic parameters, and microwave absorption performance were systematically investigated. As the nitriding temperature increases, lattice expansion results in a significant increase in saturation magnetization and a higher ratio of in-plane to out-of-plane anisotropy fields. This, in turn, boosts the electromagnetic parameters of the composite material. With a further rise in temperature, an increased content of α-Fe is produced and the ratio of the in-plane to out-of-plane anisotropy field diminishes, leading to a decline in electromagnetic parameters. At 500 °C, these factors reach an optimum level, maximizing the composite’s electromagnetic parameters. The composite exhibited a minimum reflection loss (RL_min) of −55.9 dB at 5.58 GHz with a thickness of 2.46 mm. Moreover, at a thickness of 2.21 mm, the composite achieved a maximum effective absorption bandwidth (EAB_max) of 2.95 GHz (5.05–8 GHz). Compared with other low-frequency-absorbing materials, the composite exhibited stronger absorption and a wider absorption bandwidth at a lower thickness in the C band. Full article

There is great potential for the development of microwave-absorbing materials (MAMs) for structural regulation. Auxetic structures have excellent mechanical properties, which can be applied to multifunctional MAMs in various fields. Here, the microwave absorption performances of the auxetic structures were simulated using the High-Frequency Structure Simulator (HFSS), by regulating the structure, dielectric constant, layer number, and pore size. The simulation results show that increasing the dielectric constant, layer number, or decreasing pore size will lead to a decrease in the frequency of minimum reflection loss (RL_min). The main purpose of this study is to elucidate the influence of structure, dielectric constant, layer number, and pore size on the absorption performance of auxetic structures and obtain practical auxetic MAMs with a performance of RL_min < −30 dB and effective absorption bandwidth (EAB) > 3 GHz. Finally, practical auxetic MAMs between 8 and 18 GHz and MAMs optimized in dielectric constant were obtained, which were proven to have the advantages of lightweight characteristics, high absorption, and wide bandwidth. The four structures exhibit great RL_min values of −51.09, −55.52, −47.09, and −54.98 dB with wide EAB values of 3.25, 3, 4.75, and 4.5 GHz, demonstrating the strong electromagnetic wave absorption performance of auxetic structures. This work provides theoretical guidance for the study of auxetic structures in the field of microwave absorption and provides an effective approach for multi-disciplinary research on MAMs. Full article

In the past, powder-like microwave absorbers have made notable breakthroughs in performance enhancements, but complicated processes and undesirable properties have limited their practical application. Herein, a novel poly(ionic liquid) (PIL)-based ionic gel with excellent microwave absorption properties was prepared via a facile UV-initiated polymerization method. By simply adjusting the mole ratio of the polymerizable ionic liquid (IL)monomer and the IL dispersion medium, the microwave absorption properties of the obtained ionic gels can be tuned. A maximum reflection loss (RL_max) of −45.7 dB and an effective absorption bandwidth (EAB) of 8.08 GHz were achieved, which was mainly ascribed to high ionic conduction loss induced by the high content of the dispersion medium. Furthermore, it displayed recyclable, adhesive, and self-healing properties, thus providing a new candidate for developing efficient microwave absorbers for practical applications. Full article

Utilizing biomass resources to develop carbon-based microwave-absorbing materials adheres to the principles of sustainable development. Nevertheless, the single loss mechanism of pure carbon materials is limited. Additionally, the carbonization of artificially synthesized polymers has poor environmental performance and involves complex processes. These issues restrict their performance and broader applicability. In this study, cobalt-doped seaweed sludge porous carbon (Co/SSPC) with different cobalt contents was synthesized via a simple grinding–carbonization treatment. The addition of cobalt can regulate the graphitization degree of porous carbon, achieving a suitable amorphous-to-crystalline carbon ratio of 2.05. This not only enhances magnetic loss but also modifies dielectric loss and optimizes impedance matching. The construction of synergistic magnetic and dielectric loss mechanisms enables Co/SSPC to exhibit excellent microwave absorption performance. Specifically, Co/SSPC achieved a minimum reflection loss (RL_min) of −66.91 dB at a thickness of 4.79 mm and an effective absorption bandwidth (EAB) of 5.09 GHz at a thickness of 1.6 mm. This study provides a practical approach for the functional application of natural polymer waste algal sludge and highlights its potential in the low-cost production of microwave absorbing materials. Full article

Laurus nobilis L., Lauraceae, bay laurel, has been traditionally used for its various therapeutic properties, and in recent years has been gaining interest for its potential applications in skincare products. However, the biological effects of bay laurel, particularly its hydrosols, a water fraction obtained during essential oil production, remain unexplored. The objective of this study was to identify the volatile compounds in L. nobilis hydrosols (LnHYs) from different coastal regions of Croatia (north, middle, and south Adriatic) and to evaluate their potential safety and efficacy for dermatological applications. Upon isolating LnHYs using microwave-assisted extraction, LnHY volatiles were identified and quantified using gas chromatography and mass spectrometry. Oxygenated monoterpenes were the dominant compounds in all LnHYs (61.72–97.00%), with 1,8-cineole being the most abundant component (52.25–81.89%). The physical and chemical parameters of LnHYs were investigated to assess their purity and quality. Biological activity (cytotoxicity and wound-healing effect) was tested on the human keratinocyte cell line (HaCaT), selected as the experimental model due to its relevance to skin biology. Additionally, contents of polyphenolic substances, antioxidative effects using the Oxygen Radical Absorbance Capacity (ORAC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods, and the antimicrobial activity of LnHYs toward five skin microorganisms were determined. All tested hydrosols showed similar biological activity, with only minor differences. Cytotoxicity studies indicated the safety of the dermatological application of LnHYs, and the results of the wound-healing assay showed their neutral to mildly positive effect. Considering the growing use of bay laurel preparations in pharmaceutical and cosmetic applications, extensive studies on their biological activity, quality, and safety are essential to either support or regulate their use in humans. Full article

Kutno is a picturesque city in central Poland, known for extensive rose breeding worldwide. Soil samples and rose petals were collected from 13 locations in the city and characterized by diverse environments. This allowed determining the response of plants to changing cultivation conditions. Rose petals have found a wide range of applications. They are used in the food, pharmaceutical and cosmetic industries. The aim of the research was to assess the contents of Cu, Zn, Cd, Ni, Pb and Cr in soils and their accumulation in rose petals. Samples were subjected to the microwave mineralization process using a mixture of concentrated HCl and HNO₃. The metal contents in the soil and roses were determined by HR-CS-AAS and ICP-OES, respectively. Roses are usually cultivated in soils with a limited mobile fraction of heavy metals. In these unfavorable conditions, flower petals can absorb heavy metals substantially. Petals of roses cultivated for cosmetic, pharmaceutical or food purposes should be tested for heavy metal content. This study indicates that toxic metals are blocked at the root zone, and their transport to the above-ground parts is severely hampered. Nevertheless, metals related to the photo-synthesis process (Zn, Cu) are more intensively taken up by roses, while the uptake of toxic metals is partially inhibited. Full article

MOFs-derived magnetic carbon-based composites are considered to be valuable materials for the design of high-performance microwave absorbents. Regulating phase structures and introducing mixed-valence states within the composites is a promising strategy to enhance their charge transfer properties, resulting in improved microwave absorption performance. In this study, iron oxide components show a temperature-dependent phase evolution process (α-Fe₂O₃→Fe₃O₄→Fe₃O₄/FeO), during which the valence states of iron ions are regulated. The tunable phases modulate the magnetic Fe₃O₄ component, resulting in enhanced magnetic loss. The changed valence states affect the polarization relaxation by adjusting the electronic structure and tune the electron scattering by introducing defects, leading to enhanced dielectric loss. The microwave absorption properties of iron oxide@carbon composites display phase- and valence state-dependent characteristics. Especially, Fe₃O₄@C composites exhibit superior microwave absorption properties, ascribed to the improved magnetic/dielectric losses induced by good impedance matching and strong microwave attenuation capacity. The minimum reflection loss of Fe₃O₄@C composites reaches −73.14 dB at 10.35 GHz with an effective absorption bandwidth of 4.9 GHz (7.69–12.59 GHz) when the absorber thickness is 2.31 mm. This work provides new insights into the adjustment of electromagnetic parameters and microwave absorption properties by regulating the phase and valence state. Full article

This paper presents the synthesis and characterization of Ni-TiN@CN nanocomposites fabricated via arc discharge, followed by dopamine polymerization and pyrolysis. The cubic morphology of the Ni-TiN cores and uniform CN encapsulation were confirmed by structural analyses. Electromagnetic evaluations revealed that the CN shell thickness critically influenced the dielectric dispersion, polarization relaxation and conductive loss. The optimal sample (Ni-TiN@CN-3) achieved a minimum reflection loss of −42.05 dB at 4.06 GHz. The incorporation of magnetic Ni particles introduced a magnetic loss mechanism, while the multiple intrinsic defects within the heterogeneous structure synergistically generated defect dipole polarization and conductive loss. The strategic addition of Ni facilitated the construction of heterogeneous interfaces, which achieved enhanced interface polarization effects. The effective absorption bandwidth (≤−10 dB) reached 14.9 GHz, while the effective absorption bandwidth (≤−20 dB) achieved 6.5 GHz. The optimized CN layer facilitated a synergistic interplay between the dielectric loss and magnetic loss, which ensured balanced impedance matching and attenuation, as well as enhanced electromagnetic wave dissipation. This integrated optimization ultimately endowed the material with exceptional microwave absorption performance through an effective electromagnetic energy conversion. This work highlights Ni-TiN@CN nanocomposites as promising candidates for high-performance microwave absorbers in extreme environments. Full article

Composite catalysts combining absorbers and active metal hold significant potential for improving the efficiency of biomass microwave-assisted pyrolysis (MAP). Compatibility optimization of composite catalysts can be facilitated through comparative analysis for the influential mechanisms of absorbers and catalysts. Therefore, decoupling experiments about the MAP of Sargassum and calculations based on density functional theory (DFT) were conducted in this research, to investigate the influential mechanisms of absorbers and active metal. The results show the introduction of both the absorbers (SiC) and active metal (MgO) increase the yields of high-value components, such as hydrogen and hydrocarbons. However, their influential mechanisms are different. The introduction of SiC enhances the heating rate within the reaction zone, shortening the duration of MAP and inhibiting the condensation of bio-oil and the interaction between bio-oil and bio-char, and thereby increasing the bio-oil yield by 4%. The introduction of MgO lowers the energy barriers for macromolecular decomposition and gas generation, promoting the decomposition of bio-char and bio-oil, and thus leading to a 12% increase in the yield of bio-gas. This research conclusion provides a theoretical basis for the optimization and design of composite catalysts. Full article

The application of graphene nanoplatelets (GNPs) in polymer composites is a challenge due to their high tendency to agglomerate and restack during processing. In this work, alkyl phosphonium-based ionic liquid was used to assist the dispersion of GNP in an ethylene-vinyl acetate (EVA) matrix, through a melt-mixing procedure. The mechanical properties and creep resistance of the films prepared by the film extrusion process were evaluated. The results demonstrated that the noncovalent treatment of GNP with the ionic liquid (IL) enhanced the electrical conductivity and creep stability of the EVA composites. The microwave absorbing properties were studied in the X-band and Ku-band. A reflection loss (RL) of −15 dB for EVA containing 0.5 wt% of GNP and 1:1 wt% of GNP/IL was achieved. The use of a multi-layered structure containing thin film layers was efficient for enhancing the microwave absorbing performance, with a minimum RL of −24.6 dB and effective absorption bandwidth of 4.3 GHz. This result is attributed to the internal reflection and scattering of the radiation between layers. The use of simple, low-cost materials and procedures, combined with the system’s excellent mechanical and electrical properties, makes it a promising candidate for multifunctional applications as electrostatic dissipative and microwave absorbing materials for electronic packaging and other electronic devices. Full article

Carbonyl iron powder is a widely used microwave-absorbing material due to its numerous advantages. However, carbonyl iron powder is prone to corrosion in high-salt-spray environments, reducing the service life of the composite material and limiting its applications, particularly in marine environments. In this study, we prepared polystyrene-encapsulated carbonyl iron microcapsules via in-situ polymerization and investigated their structure and properties. The results show that the coating of the polystyrene shell did not affect the crystal structure of the carbonyl iron and hardly weakened its electromagnetic properties. Compared to uncoated carbonyl iron powder, polystyrene-encapsulated carbonyl iron microcapsules exhibited superior corrosion resistance in both HCl solution and salt-spray environment. This work offers a potential solution for enhancing the durability of microwave-absorbing material in corrosive environments. With this simple, effective, and low-budget procedure, the cost of microwave-absorbing coating used in marine environments would be significantly reduced. Full article