Microwave Interaction Research Articles

On tailored microstructure in AA 2024 alloy during in-situ microwave casting

In the present study, application of microwave energy was explored for tailoring the microstructure in AA 2024 alloy through directional solidification route. Microwave transparent (alumina) and absorbing (graphite) mould materials were utilized to investigate the effect of microwave interaction (electric and magnetic field components) with AA 2024 alloy on microstructure evolution in terms of dendrite size distribution and formation of eutectic phase. Results showed more pronounced eutectic phase gradient was developed using alumina mould. On the other hand, a more uniform distribution of the eutectic phase and grain size was observed with graphite mould. The development of the eutectic phase gradient is attributed to the effective microwave interaction with the AA 2024 alloy melt during solidification. This is primarily associated with the formation of an additional flux at the solid-liquid (S/L) interface of the alloy under the effect of magnetic field and an enhancement in diffusion flux due to mass transport caused by electric field component of microwave. Formation of AlCu, Al2Cu, and Al2CuMg intermetallic phases in both alumina and graphite mould casts was confirmed. Significantly higher hardness was observed at the higher eutectic phase sites within the alumina mould cast, whereas graphite mould casts exhibited better tensile properties.

Enhancing infrastructure management with InSAR monitoring

Over the last few years, the management of multi-asset infrastructure over wide regions has experienced a significant evolution due to novel technologies or accessibility to cheaper sensors combined with the Internet of Things (IoT). Interferometric Synthetic Aperture Radar (InSAR) data has proven to be the most cost-effective technology to meet users’ requests. However, InSAR’s large volume of data presents challenges for end-users. Data aggregation and visualisation are needed to streamline operations and information transfer between teams. This proposed methodology seeks to address the challenges associated with InSAR data by integrating InSAR observations with the digital equivalent of existing structures in a repeatable and scalable manner. To achieve this, deformation profiles are generated adaptively, considering the asset’s characteristics, such as width and orientation, as well as the satellite acquisition geometry. In parallel, a two-dimensional approach is followed to associate InSAR information with each structure element and thus organise the information spatially. It should be noted that, even when using high-resolution radar data, it is sometimes challenging to associate radar returns with specific asset segments due to the complex interaction of microwaves with particular targets. Consequently, a key feature of this methodology is to classify InSAR data according to a precise geocoding of each scatterer, including an accurate estimation of its elevation. This methodology makes it possible to analyse many different types of infrastructure, which can be time-consuming for large highway or railway operators. The coverage of the InSAR results on a regional scale, and the semi-automated method gives decision-makers an overview of their structures to send maintenance teams, saving time and costs. This methodology allows for InSAR-derived product analysis, making the results more readable, accessible, and impactful. This type of infrastructure monitoring reflects a new maturity of InSAR in this field, demonstrated in real case studies.

Understanding microwave interactions with polymers to enable advanced plastic chemical recycling

The widespread adoption of plastics has led to substantial production and waste generation, raising environmental concerns. Chemical recycling offers a promising solution to enhance recycling rates, with microwave heating emerging as an attractive technology for polymer breakdown. This paper investigates the dielectric properties of various polymers and their temperature dependencies, providing insight into the effectiveness of microwave heating. Results indicate that while polymers may show low dielectric loss at room temperature, those with polar segments exhibit increasing loss at high temperatures, indicating that additional susceptors may not always necessary for effective microwave heating. Three key transitions are identified with respect to their significant impact on the dielectric properties of polymers at elevated temperatures: the glass transition temperature, the decomposition temperature, and the point where the dispersion/displacement peak exceeds the measurement frequency. Additionally, this paper introduces a new approach for utilising microwave heating for the selective, multistage recycling of mixed plastics.

Microwave re-excitation of femtosecond laser tagging for highly flexible velocimetry.

Molecular tagging velocimetry is typically species specific and limited by excited state/species lifetimes. We utilize laser-generated ionization, long-lived anions, and a time-delayed microwave pulse to monitor the tagged region up to several milliseconds. This non-resonant excitation and microwave interaction is demonstrated in a range of gas mixtures. Signal levels show up to 1000-fold improvement, and the flexibility in interrogation time allows for velocity measurements over a large dynamic range (1-100 m/s) with single-shot precision of <5%. This approach has the potential for wide application over a range of relevant gas compositions, temperatures, and pressures.

A combined theoretical, computational, and experimental investigation to evaluate performance of suitable thermocouple for microwave processing

Accurate temperature measurement during any microwave processing of material is a contentious issue. While thermocouples are routinely utilized in conventional heat furnaces, their presence in microwave cavities may cause complications such as localized distortion of electromagnetic field, heat dissipation, thermal instabilities, microwave breakdown, and significant inaccuracies in temperature measurement. Therefore, in the present investigation thermocouple effects are discussed by providing the results of temperature estimation by various thermocouples for microwave cladding systems. The present study theoretically and experimentally explored the impact of multiple thermocouples on temperature measurements during microwave heating. COMSOL simulation models were developed to explore microwave and thermocouple interaction during microwave heating. Simulation models were used to assess the effects of the microwave power intensity, thermocouple orientation, and geometry on temperature measurement. The investigation outcomes can be utilized as a guide for selecting appropriate thermocouples in the applications of microwave cladding and other microwave-based manufacturing processes.

Integrated microcavity electric field sensors using Pound-Drever-Hall detection

Discerning weak electric fields has important implications for cosmology, quantum technology, and identifying power system failures. Photonic integration of electric field sensors is highly desired for practical considerations and offers opportunities to improve performance by enhancing microwave and lightwave interactions. Here, we demonstrate a high-Q microcavity electric field sensor (MEFS) by leveraging the silicon chip-based thin film lithium niobate photonic integrated circuits. Using the Pound-Drever-Hall detection scheme, our MEFS achieves a detection sensitivity of 5.2 μV/(mHz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{{{{{{{{\\rm{Hz}}}}}}}}}$$\\end{document}), which surpasses previous lithium niobate electro-optical electric field sensors by nearly two orders of magnitude, and is comparable to atom-based quantum sensing approaches. Furthermore, our MEFS has a bandwidth that can be up to three orders of magnitude broader than quantum sensing approaches and measures fast electric field amplitude and phase variations in real-time. The ultra-sensitive MEFSs represent a significant step towards building electric field sensing networks and broaden the application spectrum of integrated microcavities.

Influence of phase diffusion on atomic grating in a three-level ladder-type system in lower-level microwave-driven scheme

In this paper, we consider a scheme for electromagnetically induced grating (EIG) in a three-level ladder-type system. A microwave field of finite bandwidth making a standing-wave pattern is applied on lower levels. In addition, we have also introduced an indirect pump in our system. A weak probe field is then applied to study the effects of phase diffusion associated with the microwave control field on EIG. It is found that phase diffusion associated with the strong microwave control field strongly affect the diffraction. We have incorporated the effect of different system parameters such as the strength of the microwave field, indirect pumping mechanism, interaction length, and detuning in the weak probe field. Interestingly, the stronger microwave control field retrieves the loss in diffraction intensity caused by the phase diffusion. Our results show that the introduction of detuning in the optical probe field results in the enhancement of the phase grating effect. Furthermore, our results show that an optimized indirect pump field can slightly improve the first-order diffraction intensities both in the absence and presence of phase diffusion.

Permittivity measurements at high temperatures of selected pyrometallurgical minerals

In pyrometallurgical processes, the temperatures attained are amongst the highest of all industrial chemical processes and consequently the energy requirements are considerable. Although in the last few decades there have been significant improvements in the thermal efficiencies of these processes, some limitations are imposed by the innate characteristics of both the energy sources and the pyrometallurgical raw materials. Currently, there exist significant incentives for innovative and efficient processes that harness electricity from renewable energy sources. Furthermore, this electricity can be converted into electromagnetic radiation, such as microwaves, which can be utilized as a source of thermal energy. The fundamental properties which determine the interaction of microwaves with any given material are the real and the imaginary permittivities. This data is required for microwave process development, particularly numerical modeling. In the present research, these permittivities were determined for a number of raw materials of pyrometallurgical interest as a function of temperature and frequency by the cavity resonance perturbation technique. The materials studied were oxides, carbonates and sulphides. Also, the permittivity changes during the reduction of hematite by hydrogen were investigated. In order to interpret the permittivity variations as a function of temperature and also in the reduction process, the changes in the composition were modelled using HSC Chemistry®7.1. Some conclusions are drawn regarding the utilization of microwaves for the heating of pyrometallurgical materials.

Interaction of microwaves with nanocomposites containing Fe particles

Transmission of microwaves through a composite plate containing Fe nanoparticles in an epoxyamine matrix, as well as reflection of waves from it, has been investigated. The experiments were performed at the frequencies from 26 to 38 GHz in the magnetic fields up to 12 kOe. The ferromagnetic resonance line in the composites with the weight fraction of Fe particles from 10% to 30% has been studied. The magnetic field dependence of the microwave power dissipation has been plotted. Field dependence of the transmission and reflection coefficients have been calculated, as well as qualitative, and in some cases quantitative, agreement has been obtained. The penetration depth of microwaves into the composites has been analyzed. Spectrum of the FMR has been constructed. Results of interaction of microwaves with Fe nanoparticles are discussed taking into account magnetic properties and composite structure.

Characterization of interaction phenomena of electromagnetic waves with metamaterials via microwave near-field visualization technique

A new practical imaging technique was presented for metamaterial characterization and investigation by visualizations of the magnetic microwave near-field (H-MWNF) distributions on a metamaterial's surface using the method of thermo-elastic optical indicator microscopy (TEOIM). ITO-based transparent and ceramic-based opaque metamaterial structures were designed for magnetic near-field visualization. Depending on the incident microwave field polarization, the TEOIM system allows the characterization of the metamaterial properties and microwave interaction behavior. The working principle of the periodic structures was investigated through numerical simulations, and the obtained results exhibited strong agreement when compared with experimental observations. Moreover, the visualization of the H-MWNF revealed the potential to characterize and evaluate the absorption and transmission properties effectively.

Improvement of solubility, emulsification property and stability of potato protein by pH-shifting combined with microwave treatment and interaction with pectin

The application of potato protein (PP) in food industry has been limited due to its low water solubility, poor emulsification and stability. Herein, it was found that the pH-shifting combined with microwave heating significantly increased the solubility of PP (from 24.0% to 89.0%) and surface hydrophobicity (from 125 to 207). The particle size of PP was significantly reduced (from 249.95 ± 1.15 mm to 90.37 ± 1.03 nm). SDS-PAGE analysis indicated that the microwave treatment did not disrupt the primary structure of PP. A complex formation between modified potato protein (MPP) and pectin (PC) at the optimum mass ratio of MPP to PC of 4:1 and pH 5 was characterized by fluorescence spectroscopy, fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy, which showed that MPP and PC had electrostatic interaction. Moreover, the effect of mass ratios of MPP to PC from 5:1 to 1:2 on the phase behavior of MPP-PC soluble complexes was evaluated by the phase diagram and ζ-potential measurement. These results showed that the dispersibility, emulsification and thermal stability of the protein were improved by forming MPP-PC complexes. This study provides a valuable reference for the improvement of physicochemical and functional properties of PP which is conducive to broaden the application of the protein in food industry.

Microwave‐assisted reflux synthesis of Tungsten‐doped BiVO4 for improved photocatalytic activity

AbstractGiven its favorable physical and chemical properties, Bismuth vanadate (BiVO4) is a commonly studied metal oxide semiconductor for photocatalytic applications. However, BiVO4 shows a high recombination rate of photogenerated charges and limited charge transport capacity, which can be addressed by doping it with tungsten. To develop a highly efficient tungsten‐doped BiVO4‐based (W‐BiVO4) photocatalyst, it is necessary to control the dopant content, crystal structure, and morphology. These properties are, in turn, governed by the synthesis conditions. This work describes a pioneering method of microwave‐assisted reflux synthesis of W‐BiVO4, using ethanol as solvent and polyvinyl pyrrolidone (PVP) as a capping agent. Thus, it is possible to perform the synthesis procedure in only 30 min at 78°C, obtaining extremely regular monoclinic W‐BiVO4 nanosquares. Furthermore, the experiments showed that the most efficient photocatalyst contains 3% tungsten as the dopant. Moreover, the direct oxidation of rhodamine B by the photogenerated holes plays a crucial role in the degradation mechanism. Finally, we observed that although the addition of PVP promotes control of the morphology, it results in a poorly efficient material. This low efficiency may be related to the formation of a polymeric coating on the surface of the catalyst or to a high amount of oxygen defects. Finally, we show that the unique interaction of microwaves with the species present in the reaction media influences nanoparticle growth.

Interaction of microwave and nanomaterials for thermoresponsive drug delivery and hyperthermal cancer therapy

Interaction of microwave and nanomaterials for thermoresponsive drug delivery and hyperthermal cancer therapy

Microwave and dielectric barrier discharge atmospheric plasma interaction on guava industrial biomass for biomaterial production

AbstractThis research helps to develop a novel and economical method for improving the extraction efficiency of oil and fully valorizing guava fruit processing industrial waste into biomaterial. Dielectric barrier discharge atmospheric (DBDA) plasma is a novel non‐thermal technology that has been widely used in the food processing field of research. In this study, the synergistic effect of microwave (MW) and DBDA plasma treatment under different treatment combinations on the modification of morphological and biochemical properties of the guava pomace powder on improving the efficiency of extraction of biomaterials has been investigated. The response surface model (RSM) model was then constructed using the experimental results of Box–Behnken Design (BBD) to obtain the optimal extraction conditions. The predicted optimal extraction conditions for the microwave power level of 600 W for a treatment time of 90 s under solvent extraction at 420 min; DBDA plasma treatment as 35 kV for 15 min and solvent extraction conditions were determined as 80°C for 360 min causing an increment of the oil yield up to 16.19% when extracted using solvent extractor with ethanol as a solvent. These results indicate that the DBDA plasma treatment previous to the extraction step extraction process can contribute to reducing the duration of extraction by 120 min. The obtained data indicate that the MW and DBDA plasma pre‐treatment before the extraction can reduce the extraction duration, increase the yield, and improve the nutritional quality and functional properties.

Temperature and frequency dependencies of the permittivities of nickeliferous silicate laterite ores and reaction mixtures

The global demand for nickel metal continues to grow, while the resource base for nickel is transitioning from the nickel sulphide ores to the nickeliferous laterite oxide ores. Considerable research is being performed on developing innovative processes for extracting the nickel from the oxide ores. One potential new energy source for these processes could be microwave radiation. The interaction of microwaves with a given material is mainly determined by the permittivities. In the present research, the permittivities of a nickeliferous silicate laterite ore and both activated charcoal-ore and segregation reaction mixtures were measured as a function of both temperature and frequency using the cavity perturbation technique. In general, the ore permittivities increased slowly at low temperatures and more rapidly at higher temperatures. For the reaction mixtures, the rapid rise in the permittivities occurred at a temperature lower than for the ore and there was a characteristic peak in the permittivities. In order to understand the behaviours of the mixtures, the relevant thermodynamic literature was reviewed and also reaction simulations were performed using HSC Chemistry® 7.1. The initial rapid rise in the permittivities was attributed to the presence of the charcoal. For the activated charcoal-ore mixtures, at high temperatures the amounts of carbon and iron oxide decreased as a result of the reduction reactions and thus the permittivities decreased. Similarly, for the segregation mixture, the carbon was consumed due to the water-gas reaction and once more the iron oxide decreased. The permittivity information can be utilized to better understand the heating behaviours of the mixtures and also can be employed in numerical modelling for process development.

C and K band microwave penetration into snow on sea ice studied with off-the-shelf tank radars

AbstractSnow cover on sea ice poses a challenge for radar measurements as microwave penetration into snow is not yet fully understood. In this study, the aim is to investigate microwave penetration into snow on Arctic sea ice using commercial C (6 GHz) and K (26 GHz) band tank radars. Nadir-looking radar measurements collected at nine study locations over first-year and multiyear landfast sea ice in the Lincoln Sea in May 2018 are analysed together with detailed measurements of the physical properties of the snow cover to determine the dominant scattering horizons at both frequencies. They are evaluated for the feasibility to determine snow depth. The results show that in 39% of the measurements and only on first-year ice a major fraction of the C band radar backscatter originated closer to the snow–ice interface potentially enabling snow depth retrieval. At K band, 81% of the radar returns originated from the snow surface. Partly confirming the findings of previous studies, however, the analysis was potentially hampered by relatively warm air temperatures (up to$-0.9^\circ$C) during the study period as well as stratigraphic features and inconclusive microwave interaction with the saline basal layers found in the snow cover on first-year ice.

Temperature and frequency dependencies of the permittivities of selected pyrometallurgical reaction mixtures

High temperatures are required in pyrometallurgical processes and consequently they are extremely energy intensive. Microwaves can offer several potential thermal energy efficiency advantages such as selective and/or rapid internal heating. The fundamental parameters which determine the interaction of microwaves with any given non-magnetic material are the real and the imaginary permittivities. In the current research, the permittivities of various mixtures of several pyrometallurgical raw materials plus carbonaceous reducing agents were determined as a function of both temperature and frequency, using the cavity perturbation technique. The raw materials investigated were an oolitic iron ore, an electric furnace dust and a chromite ore. As the temperature of a mixture increased, the permittivities began to increase rapidly, at temperatures lower than for the raw material alone. Subsequently, as the temperatures increased even further, the permittivities began to decrease and consequently peaks were typically observed in both the real and the imaginary permittivities. The changes in the permittivities of the mixtures were interpreted in terms of reduction reaction information available in the literature and also the amounts of the various species present as calculated by the Equilibrium Module of HSC Chemistry® 7.1. The initial rapid rise in the permittivities of the mixtures was attributed to the presence of the carbonaceous reducing agent, while the decrease was ascribed to the consumption of the carbonaceous reducing agent and also the reduction of metal oxides to metal. The permittivity data can be utilized to better understand the heating behaviour of the mixtures and also can be employed in numerical modelling.

Development of iron-based composite materials through electromagnetic radiations in a domestic microwave oven

Microwave hybrid heating, a novel technique, is used to develop iron-based alloy (SS316), SS316+10EWAC1004 (nickel-based), and SS316+10EWAC1004+5Cr7C3 composite castings. The domestic microwave having a frequency of 2.45 × 103 MHz and a power of 0.9 kW, is used with a variable exposure time of microwave radiations. The microwave interaction procedure with the metallic powder is discussed to optimize the exposure time and temperature. A microstructure study of developed castings revealed the uniform melting of matrix and EWAC1004 with an identical dispersion of Cr7C3. The X-ray diffraction results revealed various intermetallic (Ni3Fe, Ni2Si, Cr2Ni3, MoNi4, Fe3Si, Fe2Si, CrFeNi) and hard carbides (Fe3C, Cr3C2, Cr23C6) phases. The maximum average micro-hardness is for the SS316+10EWAC1004+5Cr7C3 composite, followed by SS316+10EWAC1004. The established composite casting had a hardness of around 2 times that of the commercial SS316. The maximum density of 97% was found for Iron-based SS316-based. The grain size of microwave-processed SS316, SS316+10EWAC, and SS316+10EWAC +5Cr7C3 specimens is found to be 21 ± 4 µm, 18 ± 3 µm, and 17 ± 2 µm, respectively. It has been observed that reinforced phases hinder grain growth, and hence grain size reduces significantly. In comparison, commercial SS316 had a grain size of 31 ± 6 µm. The ASTM B-276 standard is used to determine pores that are of the order of 1.98%.

The second harmonic heating system for the NORTH tokamak

A substantial contribution in the understanding of fusion plasmas can be achieved by conducting experiments in simplified plasma devices. One of those devices is NORTH, located in Denmark. Part of the research activity on NORTH is focused on non-linear interaction of microwaves with toroidally magnetized plasmas. An additional microwave heating system was recently installed in the device. The source can deliver 800 W of 5.8 GHz microwaves, which are coupled into the plasma by a custom-made 3D printed horn antenna. The antenna design was validated by numerical modelling and experimental measurements. Here we discuss this validation, and describe the system and its commissioning. Additionally, we present a newly developed diagnostic to monitor the plasma response in the frequency range up to 6 GHz, based on a fast 12.5 GS/s digitizer. By exploiting this system, we have characterized the new source. Furthermore, we have preliminary investigated the interaction of the 5.8 GHz microwave with the plasma, and we present first observations of wave coupling in NORTH.

Insight into Enhanced Microwave Heating for Ammonia Synthesis: Effects of CNT on the Cs-Ru/CeO2 Catalyst.

Ammonia is emerging as a potential decarbonized H2 energy carrier when produced from renewable energy. The on-site production of liquid ammonia from stranded renewable energy can solve the current energy transportation challenges. The employment of microwave technology can produce the desired ammonia product at milder conditions with the supply of intermittent renewable energy sources. Our previous studies have indicated that the Cs-Ru/CeO2 catalyst is a promising catalyst for microwave-driven ammonia synthesis. In this study, the Cs-Ru/CeO2 catalyst mechanically mixed with carbon nanotubes (CNT) and chemically synthesized using coprecipitation and a hydrothermal method is investigated systematically at low temperatures and atmospheric pressure for microwave-assisted ammonia synthesis. Additionally, the combination of two Ru-based catalysts (Cs-Ru/CeO2 and Cs-Ru/CNT) is studied as well. Mechanical mixing of Cs-Ru/CeO2 with CNT exhibited superior activity as compared to the chemically synthesized Cs-Ru/CeO2-CNT catalyst. Besides the enhancement in dielectric property, the probable synergistic effect leads to increased interfacial polarization at the interface of the mechanically mixed catalyst, improving the overall heating and ammonia production rate. Moreover, the combined Ru-based catalyst also exhibited higher activity as compared to their individual activity toward ammonia synthesis. Numerous characterization techniques were performed, including thermal imaging camera and dielectric measurements, to better understand microwave interaction with the composite catalysts.