Intense Microwave Research Articles

Rapid 24 GHz microwave sintering of alumina – yttria-stabilized zirconia ceramic composites

Samples of alumina – 3 % yttria-stabilized zirconia (YSZ) composites were sintered in rapid processing regimes using 24 GHz microwave heating at rates of up to 200 °C/min and zero hold time. The final relative density was 96–99 % for the samples containing 1.5 and 7.5 wt % YSZ and 98–99 % for the samples containing 13 wt % YSZ. The microwave sintering kinetics were compared for the processes carried out by direct and susceptor-assisted microwave heating. Under direct microwave heating, the effect of an intense microwave electromagnetic field with an estimated absorbed power density of up to 130 W/cm3 resulted in a shift of the shrinkage curves by about 100 °C towards lower temperatures compared to the case of susceptor-assisted heating. The grain size of the samples sintered by direct microwave heating decreased with an increasing heating rate. The mechanical properties were slightly higher for the materials sintered under susceptor-assisted microwave heating. The samples containing 13 wt % YSZ exhibited a microhardness of about 20 GPa and a fracture toughness of about 7 MPa m1/2.

Roadmap for the increase of beam brilliance from ECRIS and Microwave Discharge Ion Sources

The requirements for future accelerator chains need to increase the injected beam brilliance significantly, still keeping high the beam quality in terms of reliability, reproducibility and stability. A roadmap for ion source development may consist of several steps: plasma simulation, multiphysics simulation of each system component, high-level control system, plasma characterization, beam characterization, data analysis and, again, plasma simulation. The cycle starts and ends with plasma simulation because it is the instrument that shows how different phenomena take part in the plasma and beam formation and because, in such a way, the accuracy grows with each cycle. Commercial multiphysics simulation tools are essential for adequately designing all ion source equipment: magnets, intense electrostatic field regions, microwave propagation and coupling, thermal dissipation and vacuum. The dependence of source performances from source parameters (magnetic field profile, gas pressure, microwave power) has been widely investigated using a high-level control system[1] able to test tens of thousands of source configurations without human interaction. This characterization technique allowed us to identify a new magnetic configuration, High Stability Microwave Discharge Ion Sources[2], that produces a beam with high stability, intensity and brilliance. The plasma simulation tool we developed discloses the role of two types of electrostatic waves in plasma formation and their correlation to stability. The simulation provides a complete view of ions and electrons energy and density distributions, the formation of the plasma meniscus and the beam extraction. The paper will present the results obtained with this development procedure on Microwave Discharge Ion Sources and how we started to apply it to the Electron Cyclotron Resonance Ion Sources development.

Integrated coplanar waveguide coil on diamond for enhanced homogeneous broadband NV magnetometry.

Nitrogen-vacancy (NV) centers in diamond have emerged as promising quantum sensors due to their highly coherent and optically addressable spin states with potential applications in high-sensitivity magnetometry. Homogeneously addressing large ensembles of NV centers offers clear benefit in terms of sensing precision as well as in fundamental studies of collective effects. Such experiments require a spatially uniform, intense, and broadband microwave field that can be difficult to generate. Previous approaches, such as copper wires, loop coils, and planar structures, have shown limitations in field homogeneity, bandwidth, and integration in compact devices. In this paper, we present a coplanar waveguide (CPW) gold coil patterned on a 3 × 3 mm 2 diamond substrate, offering full integration, enhanced stability, and broad bandwidth suitable for various NV sensing applications. Coil fabricated on diamond offers several advantages for magnetometry with NV centers ensemble, including enhanced heat dissipation, seamless integration, scalability, and miniaturization potential. We optimize critical geometrical parameters to achieve a homogeneous magnetic field with a coefficient of variation of less than 6% over an area of 0.5 mm 2 and present experimental results confirming the performance of the proposed CPW coil.

New Electromagnetic Threat Protection Systems

The issues discussed in the article refer to a new category of military operations - electronic warfare (EW). In the context of EW, the high-power microwave (HPM) technology currently enables remote disturbances of operations lasting until the circuit is reset or the electronic system is destroyed. The article examines the problem of protection and defence against using HPM pulses. The research used a compact HPM generator developed at the Polish National Centre for Nuclear Research. It has a power of 3MW, an operating frequency of 2.9 GHz and a 3 μs pulse duration, emitted with a repetition rate of 1, 50, 100 and 250 Hz. The developed HPM pulse protection systems were subjected to intense field exposure in the open space of the training ground, in its land and sea sections, and in the circuit with a reverberation chamber. The distribution of the generated field on each measurement station was tested using a high-power D-dot probe, from which the data was transferred to the recording system via an optical fibre link. In all cases, this distribution turned out to be repetitive. The field probe with a logger was used for measurements inside composite structures. Unprotected electronic systems in hobby drones, mobile phones, cameras and systems using sensors based on micro-mechanical units were exposed. An analysis was conducted to check the operation of electronic circuits, effects caused and phenomena occurring during exposures to intense microwave radiation. It was found that the developed system meets the design assumptions in conditions similar to actual exposure to HPM weapons. Screening efficiency has been determined for various spatial configurations of radiation beam incidence. The presented systems for the protection and defence against the effects of HPM weapons implemented in the technology of composite hybrid absorbers enable effective elimination of electromagnetic pulse effects.

M-PERC: A New Satellite Microwave-Based Model to Diagnose the Onset of Tropical Cyclone Eyewall Replacement Cycles

Abstract Eyewall replacement cycles (ERCs) in tropical cyclones (TCs) are generally associated with rapid changes in TC wind intensity and broadening of the TC wind field, both of which can create unique forecasting challenges. As part of the NOAA Joint Hurricane Testbed Project, a new model was developed to provide operational probabilistic guidance on ERC onset. The model is based on the time evolution of TC wind intensity and passive satellite microwave imagery and is named “M-PERC” for Microwave-Based Probability of Eyewall Replacement Cycle. The model was initially developed in the Atlantic basin but is found to be globally applicable and skillful. The development of M-PERC and its performance characteristics are described here, as well as a new intensity prediction model that extends previous work. Application of these models is expected to contribute to a reduction of TC intensity forecast error.

Enhancing broadband and intense microwave absorption properties of flaky FeSiCr powder by coating SiO2

Flaky FeSiCr@SiO2 composites with broadband and intense absorption were successfully synthesized by modified Stöber method. The phase, microstructure and morphology of flaky FeSiCr@SiO2 composites were investigated by XRD, FT-IR, SEM and TEM, confirming the successful preparation of SiO2 coating. The thermal behavior of flaky FeSiCr@SiO2 composites was analyzed by TGA/DSC. The results showed that the oxidation resistance of the coated FeSiCr powder was promoted. The electromagnetic wave absorption properties of samples with different contents of tetraethyl orthosilicate (TEOS) were systematically investigated. The sample synthetized with 10 ml TEOS possesses the optimal absorption performance, which is attributed to the synergistic effect of magnetic loss and dielectric loss. The minimum reflection loss is −65.3 dB at 4.4 GHz. And the maximum effective absorption bandwidth is 6.0 GHz with only a 1.5 mm thickness. In particular, by controlling the thickness of the absorber, the effective absorption bandwidth can reach 13.3 GHz (2.9–16.2 GHz), covering the entire C and X bands. Thus, the flaky FeSiCr@SiO2 composites can be used as high-performance microwave absorption materials.

Influence of Hydrogen Reduction Stage Conditions on the Microwave Properties of Fine Iron Powders Obtained via a Spray-Pyrolysis Technique

The relationship between the chemical purity of one-size particles and microwave properties in ferromagnetic materials is not clearly studied. Ferromagnetic nanostructured iron powders were synthesized from iron nitrate solution using ultrasonic spray-pyrolysis and then reduced in H2 flow at 350, 400, 450, and 500 °C. A rise in the concentration of solutions of a precursor from 10 to 20 wt. % led to an increase in mean particle size. The interrelationship was studied between chemical composition and the microwave dispersion of the powders obtained. An increase in the temperature of reduction changes the chemical composition and increases the amplitude of complex microwave permeability, which was studied using solid-state physics methods (XRD, STA, SEM, and VNA). It was found that annealing at 400 °C is the optimal treatment that allows the production of iron powders, consisting of about 90% of α-Fe phase, possessing a particle surface with low roughness and porosity, and demonstrating intense microwave absorption. Annealing at a higher temperature (500 °C) causes an even higher increase in permeability but leads to the destruction of nanostructured spheres into smaller particles due to grain growth. This destruction causes an abrupt increase in permittivity and therefore significantly reduces potential applications of the product. The insight into chemical–magnetic relationships of these materials enhances the data for design applications in magnetic field sensing.

Modeling of electrodynamic parameters of microwave sterilizer

For the sterilization of medical instruments, a technology for their immersion heat treatment with intense microwave radiation at the frequency of 2,45 GHz is analyzed. The advantages of this technology in comparison with traditional methods are shown. An electromagnetic model of a microwave sterilizer for surgical tools was built, taking into account the temperature dependence of the complex dielectric permittivity of the immersion medium (water). A rectangular cavity with a waveguide excitation was used as its basic unit. With the help of a numerical model on the finite element method, the values of the reflected and absorbed power, as well as the heating rate of water in the sterilizer for an operating power of 600 W, were determined. The analysis of thermal processes, performed according to a simplified method, showed a rather high efficiency of such device, which provides a high heating rate at a given frequency.

Rapid microwave sintering of functional electroceramic materials

Rapid microwave sintering processes with heating rates of up to 300 °C/min and zero isothermal hold have been implemented using a 5 kW 24 GHz gyrotron system for high-temperature microwave processing of materials. ZnO-based varistor ceramics, BaTiO3/SrTiO3 dielectric ceramics and Gd:CeO2 ceramics for solid electrolyte applications have been sintered to densities of up to 96% of the theoretical value. Using in situ optical dilatometry, correlation between the development of thermal instability under intense volumetric microwave heating and the early onset of densification has been revealed. The influence of the absorbed microwave power on densification and grain growth has been studied by comparing direct and susceptor-assisted microwave heating processes. The possibility of tailoring the microstructure and functional properties of the obtained materials by choosing optimal regimes of rapid microwave sintering is discussed.

Carbon-encapsulated Co7Fe3 nanocomposites with high intensity and ultra-wideband microwave absorption

Composites composed of ferromagnetic alloy/dielectric material have been widely studied and applied. The alloying of the two metals endows these composites with escalated magnetic loss capacity, but they are usually micro-sized, which is not conducive to further improving the absorption performance. Herein, we develop an efficient approach to synthesize Co7Fe3@C nanocomposites with particle sizes ranging from 32 to 42 nm based on the in-situ carbon coating on the FeCo2O4 precursor and subsequent carbothermal reduction procedure. The thickness of carbon coating can be effectively tailored by controlling the reaction conditions. The minimum reflection loss (RL) value of the Co7Fe3@C nanocomposite with a carbon coating of 2.5 nm goes up to −100.8 dB at only 1.7 mm thickness, and the effective absorption bandwidth (EAB) also reaches 9.9 GHz (8.1–18 GHz) at 2.0 mm. Moreover, as the carbon coating increases to 4.2 nm, the bandwidth escalates to 11.5 GHz (6.5–18 GHz) at 2.0 mm, which covers the whole X and Ku bands and half of the C band. The remarkable performance originates from the strong magnetic loss capability of the nano-sized Co7Fe3 core as well as the good impedance matching brought by appropriate carbon coating. Accordingly, the Co7Fe3@C nanocomposite is convinced to be a competent candidate among absorbers with high absorption intensity and ultra-wide broadband.

The Sun and Space Weather

The explosion of space weather research since the early 1990s has been partly fueled by the unprecedented, uniform, and extended observations of solar disturbances from space- and ground-based instruments. Coronal mass ejections (CMEs) from closed magnetic field regions and high-speed streams (HSS) from open-field regions on the Sun account for most of the disturbances relevant to space weather. The main consequences of CMEs and HSS are their ability to cause geomagnetic storms and accelerate particles. Particles accelerated by CME-driven shocks can pose danger to humans and their technological structures in space. Geomagnetic storms produced by CMEs and HSS-related stream interaction regions also result in particle energization inside the magnetosphere that can have severe impact on satellites operating in the magnetosphere. Solar flares are another aspect of solar magnetic energy release, mostly characterized by the sudden enhancement in electromagnetic emission at various wavelengths—from radio waves to gamma-rays. Flares are responsible for the sudden ionospheric disturbances and prompt perturbation of Earth’s magnetic field known as magnetic crochet. Nonthermal electrons accelerated during flares can emit intense microwave radiation that can drown spacecraft and radar signals. This review article summarizes major milestones in understanding the connection between solar variability and space weather.

Intense microwave heating at strongly polarized solid acid/water interface for energy-efficient platform chemical production

A strongly polarized solid/liquid interface is constructed to create a “micro-hydrothermal” environment under microwave and promote reaction energy efficiency. Specifically, TiO2 with open crystal structure was synthesized to maximize the density of surface-active centers and the degrees of interfacial polarization. Acidic groups were grafted on the catalyst surface, which served as catalytically active sites as well as heat-generation spots under microwave irradiation. Benefited by enhanced interfacial polarization, 10 times higher energy efficiency (6.8 mmol (kJ L)−1) than commercial TiO2 can be achieved in fructose dehydration reaction. MD simulation revealed that sulfonic group polarized surface water molecules and acted as “hot-spots” to accelerate fructose dehydration to HMF. Such alignment of site-specific heating and reaction by material design has great potential to shift the energy efficiency for a wide range of chemical reactions.

Oxidative and mutagenic effects of low intensity microwave radiation on quail embryos

Oxidative and mutagenic effects of low intensity microwave radiation on quail embryos

Перспектива использования ингибиторного барьера в селекции картофеля на устойчивость к колорадскому жуку

Abstract. The purpose of the work is the determination of the most effective method of using the inhibitory barrier in potato breeding for resistance to damage by the Colorado potato beetle. Methods. In the work, the method of setting up a field experiment was used, as well as a laboratory method for assessing the inhibition of the activity of lipases and proteinases was carried out using substrates immobilized in an agarose gel. Results. On the basis of field experiments, it was found that the level of relative resistance of potato varieties and hybrids to damage by the Colorado potato beetle, a decrease in the survival rate of insect larvae and loss of tuber yield are associated with a high activity of lipase and proteinase inhibitors and an intensive development of a hypersensitivity reaction to phytophage egg clutches. In laboratory experiments, it was established that the activity of trypsin inhibitors increased during the laying of phytophage eggs on the leaves of potato varieties Bashkirskiy. Scientific novelty. Based on the analysis of the results of world practice and our own long-term attempts to use the inhibitory barrier in breeding potatoes for resistance to the pest, a new approach has been proposed to involve genes encoding the synthesis and accumulation of protease and lipase inhibitors in tissues when creating potato resistance to damage by the Colorado potato beetle. In this case, the methodological approach should be based on the registration of the modification of the inhibitory activity of hydrolases in hybrids with an intense microwave reaction of the leaf tissue to the clutches of the Colorado potato beetle, which will significantly reduce the volume of laboratory assessment of the material. Genotypes that do not respond to egg clutches with a microwave reaction with a high degree of probability will also not modify the activity of hydrolase inhibitors. Genotypes with local short-term accumulation of inhibitors of the lipoproteinase complex in the zone of hatching of the pest offspring create the greatest depressing biological effect for the survival of 1-2 instar larvae. The creation of such genotypes is likely to be a promising model for highly resistant varieties of the Colorado potato beetle.

Low Intensity Microwave Fields and Radiation and Their Interaction with the Human Body

Sources of low-intensity microwave signals formation, which affect the metabolism processes when they interact with human body, are considered in the article. It’s noticed that increasing intensity level of the technogenic signals in environment significantly exceeds natural electromagnetic fields and radiation (EMR). The peculiarities of the registration and measurement of low-intensity signals parameters of the microwave range are considered. The processes of the interaction of the microwave signals and human organism are analyzed. Formation mechanisms of the positive and negative microwave flows of the electromagnetic radiation are revealed. Particularly, possible formation mechanism of the microwave EMR fluxes of implants in the human body. The results of the experimental study of the EMR signals levels of the objects contacting with human body, partly materials for bone defects replacement and soft tissues regeneration so as materials for physiotherapy, are given. The use of the term “electromagnetic compatibility” for materials which contacting the human body, is proposed. The expediency of its use is proven. Microwave properties of materials for clothes, minerals and building materials, which can affect the human body and environment, have been also studied.

Theoretical investigation of the temperature effects on the performance of fiber Sagnac interferometer-based optical intensity modulator and microwave photonic mixer

In this paper, analytical research has been done on the temperature-dependent performance of the fiber Sagnac interferometer (SI)-based microwave photonic (MWP) structures containing polarization-maintaining fibers (PMFs) and phase modulators (PMs). PMFs are one of the critical components used in conventional SI-based fiber-optic sensors and MWP communication structures. SI-based MWP structures use the property of the polarization-maintaining feature of the PMF to maintain the state of polarization (SOP) of the emitted light to the SI and combine the counter-propagating lights coherently at the output of the SI. On the other hand, the temperature fluctuations cause a phase difference between the counter-propagating lights inside the SI, which is used in fiber-optic temperature sensors to measure and monitor the environment temperature changes. In contrast, the temperature change effects on SI-based MWP communication structures' performance have not been described yet. In this paper, the impact of the temperature changes on the SI-based MWP structures' performance containing PMFs and PMs are investigated theoretically. In particular, the mentioned effect is analyzed in detail on the performance of two SI-based devices containing PMFs and PMs, i.e., an intensity modulator and an MWP mixer. It is shown that the performance of these structures is altered by temperature changes which must be considered in the analysis and design of the MWP structures based on SI, PMs, and PMFs.

Carbon-Encapsulated Co7fe3 Nanocomposites with High Intensity and Ultra-Wideband Microwave Absorption

Carbon-Encapsulated Co7fe3 Nanocomposites with High Intensity and Ultra-Wideband Microwave Absorption

Lignin-Derived Syringol and Acetosyringone from Palm Bunch Using Heterogeneous Oxidative Depolymerization over Mixed Metal Oxide Catalysts under Microwave Heating.

Biomass valorization to building block chemicals in food and pharmaceutical industries has tremendously gained attention. To produce monophenolic compounds from palm empty fruit bunch (EFB), EFB was subjected to alkaline hydrothermal extraction using NaOH or K2CO3 as a promotor. Subsequently, EFB-derived lignin was subjected to an oxidative depolymerization using Cu(II) and Fe(III) mixed metal oxides catalyst supported on γ-Al2O3 or SiO2 as the catalyst in the presence of hydrogen peroxide. The highest percentage of total phenolic compounds of 63.87 wt% was obtained from microwave-induced oxidative degradation of K2CO3 extracted lignin catalyzed by Cu-Fe/SiO2 catalyst. Main products from the aforementioned condition included 27.29 wt% of 2,4-di-tert-butylphenol, 19.21 wt% of syringol, 9.36 wt% of acetosyringone, 3.69 wt% of acetovanillone, 2.16 wt% of syringaldehyde, and 2.16 wt% of vanillin. Although the total phenolic compound from Cu-Fe/Al2O3 catalyst was lower (49.52 wt%) compared with that from Cu-Fe/SiO2 catalyst (63.87 wt%), Cu-Fe/Al2O3 catalyst provided the greater selectivity of main two value-added products, syringol and acetosyrigone, at 54.64% and 23.65%, respectively (78.29% total selectivity of two products) from the NaOH extracted lignin. The findings suggested a promising method for syringol and acetosyringone production from the oxidative heterogeneous lignin depolymerization under low power intensity microwave heating within a short reaction time of 30 min.

Experimental Study on Microwave Generation due to Merged Instability in F-Band Surface Wave Oscillator

A surface wave oscillator (SWO) is driven by an electron beam to generate intense microwaves. The electron beam possesses slow space-charge (SSC) and slow cyclotron (SC) modes that interact with the surface wave leading to microwave generation. The beam current and external magnetic field affect the relationship between SSC and SC modes. The SSC mode gradually approaches the SC mode when the beam current increases. Meanwhile the SC mode gradually approaches the SSC mode when the magnetic field decreases. The two modes merge in a low magnetic field and high beam current. In this work, we experimentally examine the operation of an F-band SWO in the low magnetic field region. The output power decreases with low beam current when magnetic field decreases. Meanwhile, the SWO maintains its power level with high beam current even though the magnetic field decreases to around 0.4 T. The merged instability enables a sustained power level in the low magnetic field region.

Ac magnetoresistance and microwave absorption in Sr2FeMoO6

This work investigates the microwave absorption property of the ferrimagnetic double perovskite, Sr2FeMoO6 (SFMO) using two different methods: magnetoimpedance (MI) and lock-in based broadband magnetic resonance detection. In the MI method, radio frequency (rf) current (f = 0.001 to 2.8 GHz) is injected into the sample. When dc magnetic field is swept, rf resistance exhibits a single sharp peak centred at H = 0 for f < 0.1 MHz. As f increases, the peak at H = 0 transforms into a dip accompanied by symmetrical double peaks at H = ±HP, which we attribute to the ferromagnetic resonance within the grains. HP increases with increasing frequency of the current. In the lock-in based broadband method the sample, placed on top of a coplanar waveguide, experiences an intense microwave magnetic field from the waveguide, and the field derivative of microwave power absorption is measured as the dc magnetic field is swept. Correlation between MI and microwave power absorption is shown. Landé g factors obtained from both the measurements are close, equal to 2.085, which implies the presence of Fe3+ cations. Large ac magnetoresistance in SFMO compared to its dc value, dominated by the dynamics of transverse permeability and ferromagnetic resonance within grains could be exploited for high-frequency device applications.