Search Results (228)

There is currently an effort to scale up sol–gel nanomaterials without compromising quality, and microwave heating can pave the way for this due to its heating efficiency, resulting in a fast and homogeneous process. In this work, the sol–gel synthesis of transition metal aerogels, specifically iron-based aerogels, is studied using a microwave-assisted sol–gel methodology in an open-system multimode device as a potential route to scale-up production. Different approaches were tested to evaluate the best way to increase yield per batch, with different vessel shapes and volumes. It is shown that the shape and size of the vessel can be determinant in the interaction with microwaves and, thus, in the heating process, influencing the sol–gel reactions and the characteristics and homogeneity of the obtained nanomaterials. It has been found that a wide vessel is preferable to a tall and narrow one since the heating process is more homogeneous in the former and the sol–gel and cross-linking reactions take place earlier, which improves the mechanical properties of the final nanomaterial. For mass production of nanomaterials, the interaction of the reagents with the microwave field must be considered, and this depends not only on their nature but also on their volume, shape, and arrangement inside the cavity. Full article

Terahertz spectroscopy (0.1~10 THz), as a new type of non-destructive testing method with both microwave and infrared characteristics, has shown remarkable potential in the field of food quality testing in recent years. Its unique penetration, high sensitivity, and low photon energy characteristics, combined with chemometrics and machine learning methods, provide an efficient solution for the qualitative and quantitative analysis of complex food ingredients. In this paper, we systematically review the principles of terahertz spectroscopy and its key applications in food testing, focusing on its research progress in pesticide residues, additives, biotoxins, and mold, adulteration identification, variety identification, and nutrient content detection. By integrating spectral data preprocessing, reconstruction algorithms, and machine learning model optimization strategies, this paper further analyzes the advantages and challenges of this technology in enhancing detection accuracy and efficiency. In addition, combined with the urgent demand for fast and nondestructive technology in the field of food detection, the future development direction of the deep integration of terahertz spectroscopy technology and artificial intelligence is envisioned, with a view to providing theoretical support and technical reference for food safety assurance and nutritional health research. Full article

Against the background of the vigorous development of materials science and the deep cross-infiltration in many fields, a new medicine food homology, carbon dots (herein combined and abbreviated as MFH-CDs), has sprung up, showing great potential. This review used ChatGPT 4.0 to collect background information related to carbon dots, focusing on the common rich medicinal and food resources such as Lycium barbarum, Chinese yam, honeysuckle, and Ganoderma lucidum. These carbon dots are synthesized by hydrothermal synthesis, microwave radiation, and pyrolysis, which have the advantages of small particle size, high quantum yield, and low cytotoxicity. Recent studies have found that MFH-CDs have great application potential in biosensors, biological imaging, and drug delivery. In this paper, the characteristics of preparing carbon dots from different medicinal and edible resources and their applications in biology in recent years are reviewed, which provides in-depth guidance for the research and application of carbon dots from medicinal and edible biomass, helps it shine in multidisciplinary fields, and opens a brand-new journey from traditional medicinal and edible culture to cutting-edge technology application. 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

Microwave sounding observations obtained from the National Oceanic and Atmospheric Administration (NOAA) and the European Meteorological Operational Satellite Program (METOP) satellites have been used for retrieving the cloud ice water path (IWP). However, the IWP algorithms developed in the past cannot be applied to the Fengyun-3F (FY-3F) microwave radiometers due to the differences in frequency of the primary channels and the fields of view. In this study, the IWP algorithm was tailored for the FY-3F satellite, and the retrieved IWP was compared with the fifth generation of reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA5) and the Meteorological Operational Satellite-C (METOP-C) products. The results indicate that the IWP distribution retrieved from FY-3F observations demonstrates strong consistency with the cloud ice distributions in ERA5 data and METOP-C products in low-latitude regions. However, discrepancies are observed among the three datasets in mid- to high-latitude regions. ERA5 data underestimate the frequency of high IWP values and overestimate the frequency of low IWP values. The IWP retrieval results from satellite datasets demonstrate a high level of consistency. Furthermore, an analysis of the IWP time series reveals that the retrieval algorithm used in this study better captures variability and seasonal characteristics of IWP compared to ERA5 data. Additionally, a comparison of FY-3F retrieval results with METOP-C products shows a high correlation and generally consistent distribution characteristics across latitude bands. These findings confirm the high accuracy of IWP retrieval from FY-3F data, which holds significant value for advancing IWP research in China. Full article

As an efficient energy storage solution, lithium-ion batteries (LIBs) play a crucial role in the electric vehicle sector, driving innovation and development in the automotive industry. One common strategy to enhance energy density is to manufacture thicker electrodes. However, the pore distribution in thicker electrodes is often suboptimal, with elongated and tortuous pathways impeding charge transport. Optimizing the pore structure in electrodes is essential for fabricating high-performance batteries. In this study, we performed microwave sintering on lithium cobalt oxide materials and observed the three-dimensional evolution of pores during the sintering process using synchrotron radiation computed tomography (SR-CT).We discovered that pore evolution exhibits directional characteristics. Further analysis revealed that the electromagnetic loss of particles is related to the direction of the electric field, which is the reason for the directional behavior of pore evolution. This research could provide a new potential approach for the fabrication of advanced electrode materials by using electric field control during the battery manufacturing process to align pores vertically, thereby improving both the energy density and charge–discharge rate of the battery. Full article

Background/Objectives: The development of effective therapies for brain disorders is highly correlated with the ability of drugs or nanosystems to cross the blood–brain barrier (BBB), which has been limited. Recently, carbon dots (CDs) have been receiving attention to be used as BBB-crossing theranostic agents due to their inherent advantages, such as low size, excellent biocompatibility, high quantum yield (QY), tunable fluorescence, high drug loading, and relatively easy synthesis at low cost. The aim of this study was to design CDs with precisely controlled fluorescence properties for advanced bioimaging and an in-depth assessment of BBB permeability. Methods: CDs were synthesized using a microwave-assisted approach, optimized through microwaves’ irradiation time, and employing citric acid, urea, and sodium fluoride as precursors. The optimized sample was labeled as NF-CD. Results: A comprehensive physicochemical, photoluminescence, and biological characterization revealed the ability of NF-CD to diffuse across a neuromimetic-BBB model, mainly due to their small size (average diameter of 4.0 ± 1.1 nm), exhibiting excitation-dependent fluorescence in the blue and green wavelengths, high biocompatibility and QY, and exceptional photostability. Conclusions: Owing to the exceptional fluorescence characteristics and biological compatibility, NF-CD presents promising opportunities in theranostic applications, particularly in brain-targeted bioimaging, nanocarrier-based drug and immunotherapy delivery, early-stage diagnostics, and personalized medicine. NF-CD’s ability to cross the BBB further underscores the relevance of pioneering nanomaterial-based strategies for neurological disorder diagnostics and precision-targeted therapeutic interventions. Overall, this research contributes to the broader field of nanotechnology-driven biomedical advancements, fostering innovations in neurological diagnostics and therapeutic delivery systems. Full article

Orbital angular momentum beams have been extensively researched due to their ability to enhance the channel capacity of microwave systems. Metasurface near-field calculations of different sizes have been completed. Near-field calculations with Gaussian noise for metasurfaces of different sizes were also completed. The presence of noise suggests that the vortex electric field generated by the small metasurface of the vortex wave may experience disturbance and be overwhelmed by strong noise. On the other hand, the large vortex wave metasurface exhibits superior anti-noise capability. Its anti-interference characteristic was verified by conducting full-wave simulations on metasurfaces of l = −3 and l = −5. Based on the OAM spectral analysis, the mode purity of the generated vortex waves was calculated in detail. Simulation results indicated that a large-scale metasurface exhibits stronger anti-interference capability, which may inspire the design and research of vortex wave metasurfaces in the future. Full article

Spectrum conversion is one of the important applications in the non-linear electromagnetic (EM) field, which is widely used in antennas, wireless communication, radar imaging, etc. However, controlling spectrum conversion with excellent retrospective characteristics at oblique incidence directions remains a major issue in microwave systems. In this paper, a time-modulated Van Atta array is proposed to manipulate the spectral distribution of the echo signal. The array prototype experiments are conducted to demonstrate the variation properties of the monostatic radar cross section (RCS) at oblique incidence directions. On this basis, the periodic modulation model of the retrospective signal is established for the time-modulated Van Atta array. Several discrete harmonic components are symmetrically distributed on both sides of the original spectra. The influence of modulation parameters on the generated harmonics is analyzed in detail. The array prototype experiment is carried out, and the variation characteristics of the monostatic RCS in the oblique incidence direction are verified. Full article

The thermal stabilization of expansive soils has emerged as a promising and sustainable alternative to conventional chemical stabilization methods, addressing the long-standing challenges associated with soil swelling and shrinkage. This review critically evaluates the mechanisms, applications, and advancements in thermal stabilization techniques, with a particular focus on both traditional approaches (e.g., kiln heating) and emerging innovations such as microwave heating. This study synthesizes recent research findings to assess how thermal treatment modifies the mineralogical, physical, and mechanical properties of expansive soils, reducing their plasticity and improving their strength characteristics. Comparative analysis highlights the advantages, limitations, and sustainability implications of different thermal methods, considering factors such as energy efficiency, scalability, and environmental impact. While thermal stabilization offers a viable alternative to chemical treatments, key challenges remain regarding cost, field implementation, and long-term performance validation. The integration of thermal treatment with complementary techniques, such as lime stabilization, is explored as a means to enhance soil stability while minimizing environmental impact. By addressing critical research gaps and providing a comprehensive perspective on the future potential of thermal stabilization, this review contributes valuable insights for researchers and engineers seeking innovative and sustainable solutions for managing expansive soils. Full article

In the context of pollution-free waste treatment, anaerobic fermentation liquid (AFL), a prominent by-product of biogas engineering, has emerged as a focal point in contemporary research. Concurrently, vitamin C, an active compound abundant in fruits and vegetables, possesses extensive application potential. The development of efficient extraction processes and the utilization of its biological activities have garnered significant attention from researchers. This study investigated the impact of AFL on the growth and vitamin C content of Bok choy through field trials of varying concentrations of AFL. The results indicated that the growth characteristics of Bok choy exhibited a concentration-dependent trend with increasing AFL dosage, with the highest yield observed in the AFL-2 group (8.43 kg/m²). Additionally, with the increase in the concentration of the AFL application, the vitamin C content in Bok choy exhibited a trend of initially increasing and then decreasing, reaching its highest value (70.83 mg/100 g) in the AFL-1 group. Furthermore, response surface methodology was employed to optimize the microwave-assisted organic solvent extraction process of vitamin C, revealing that the optimal conditions for microwave-assisted extraction using a 2% citric acid solution were as follows: a microwave power of 313 W, a microwave time of 1.3 min, and a liquid-to-solid ratio of 16.4:1 v/w, achieving a vitamin C extraction rate of 90.77%. Subsequent mechanistic studies on colitis repair demonstrated that the combination of vitamin C and allicin significantly enhanced the ability of intestinal microorganisms to ferment and degrade complex carbohydrates in colitis-afflicted mice, thereby alleviating intestinal inflammation, markedly reducing bacterial invasion signals on intestinal epithelial cells, and decreasing the risk of intestinal infection. This study provides a valuable perspective for the harmless utilization of agricultural waste, and provides a theoretical basis and technical support for the high-value utilization of natural active ingredients. Full article

This study examines the effects of thermal (1000 °C), hydrothermal (100 °C), mechanochemical (ambient T), and microwave (~100 °C) treatments on three types of Chinese vermiculites, one with lower potassium content than the others. The goal was to obtain materials with enhanced properties related to specific surface areas. The response of the vermiculites to treatments and their physicochemical properties were analyzed using X-ray diffraction (XRD), thermal analysis (TG and DTG), and textural characterization via the BET method. XRD analyses showed similar mineral composition in treated and untreated samples, but the treatments affected the intensity and width of phase reflections, altering crystallinity and structural order, as well as the proportions of vermiculite, hydrobiotite, and phlogopite. Thermogravimetric analysis revealed two mass loss stages: water desorption (from 25 °C to about 250 °C) and recrystallization or dehydroxylation (above 800 °C). The isotherms indicated mesoporous characteristics, with hydrothermally CO₂-treated samples having the highest specific surface area and adsorption capacity. The samples with vermiculite, hydrobiotite, and phlogopite generally showed moderate to high specific surface area (S_BET) values, and mechanochemical treatments significantly increase S_BET and pore volume (V_p) in the vermiculite and hydrobiotite samples. Crystallinity affects S_BET, average V_p, and average pore size, and its monitoring is crucial to achieve the desired material characteristics, as higher crystallinity can reduce S_BET but improve mechanical strength and thermal stability. This study highlights the influence of different treatments on vermiculite properties, providing valuable insights into their potential applications in various fields (such as thermal insulation in vehicles and aircraft, and the selective adsorption of gases and liquids in industrial processes, improving the strength and durability of building materials like cement and bricks). Full article

The Gravity Recovery and Climate Experiment Follow-On (GRFO) mission precisely measures the inter-satellite range between the centers of mass of its twin satellites to map the earth’s gravity field. The baseline ranging measurement is achieved using the K-band ranging (KBR) system, which is sensitive to satellite attitude variations caused by the offset between the satellite center of mass and the KBR antenna phase center. Accurate decoupling of the KBR range from attitude variations requires precise determination of the KBR’s antenna offset vectors (AOVs). To address this, GRFO conducted eight KBR calibration maneuvers on 17 and 28 September 2020. However, these maneuvers exaggerated the impact of microwave multipath noise, complicating AOV estimation. Existing studies have not fully mitigated this noise. This study introduces a new frequency-domain method to estimate AOVs by leveraging double-difference signals and analyzing their spectral characteristics, along with those of the KBR range during calibration maneuvers, to suppress multipath noise. Our recalibrated AOVs achieve good alignment between the KBR and laser ranging interferometer (LRI) ranging signals. We validate our recalibrated AOVs by comparing the residuals between the LRI and KBR ranging signals corrected using both recalibrated AOVs and documented AOVs. The results show that, for the majority (58.4%) of the analyzed period (from January 2020 to June 2023), the residuals corrected by the recalibrated AOVs are closer to the LRI ranging signal. These findings demonstrate the effectiveness of the proposed method in addressing multipath noise and improving the accuracy of KBR range measurements. This work provides a framework for future gravity missions requiring precise calibration of multipath effects in inter-satellite ranging systems. Full article

The measurement and analysis of the interaction between Bessel vortex electromagnetic (EM) and several standard targets are presented in this paper. With the aid of the angular spectrum expansion (ASE) method and physics optics (PO) theorem, scattering results on the plates (metal and dielectric) and a sphere could be derived. Furthermore, plane near-field scanning and near-far field conversion methods were implemented to compare the theoretical radar cross section (RCS). In the experiment, the quasi Bessel vortex wave was generated by a holographic metasurface antenna, and the whole measurement was performed in an anechoic chamber. The results of both the theory and measurement show that the scattered fields of the plate and sphere still had characteristics of the vortex EM wave, and the scientificity and accuracy of the measured RCS were verified. Our work involved a vortex scattering experiment in the microwave frequency band, which provides strong support for the application of vortex waves in radar detection and target recognition. Full article

Terahertz (THz) waves reside in the electromagnetic spectrum between the microwave and infrared bands. In recent decades, THz technology has demonstrated its potential for biomedical applications. With the highly unique characteristics of THz waves, such as the high sensitivity to water and optimal spatial resolution coupled with the characteristics of the human cornea, such as its high water content, THz technology has been explored as a potential modality to assess corneas and corneal diseases. This systematic review provides an overview of the characteristics of THz waves, the safety profile of THz technology in the field of ophthalmology, and its clinical applications, including the objective evaluation of the corneal hydration, tear film, dry eye disease, corneal endothelium, corneal elasticity, and scarring. The paper also presents our viewpoint on the present challenges and future directions of THz technology prior to its broader integration into clinical practice. Full article