Absorption Of Microwave Radiation Research Articles

Model-Based PID Tuning Method for a Reactor for Microwave-Assisted Chemistry

This paper presents a model-based PID tuning method for a reactor used in microwave-assisted chemistry. The reactor is equipped with a solid-state source of microwaves and a PID controller capable of increasing or decreasing the delivered microwave power to maintain the reacting substances at the desired temperature. The model has the form of an algorithm applied in numerical simulations of two simultaneous processes: heating a substance by absorbing microwave radiation and cooling it by dissipating heat to the surroundings. It has proven its suitability for tuning the PID controller in a time-efficient manner. Despite some noticeable inaccuracies, the presented approach easily finds PID coefficients that result in stable and repeatable controller operation. In this way, significant time savings can be achieved, as well as minimizing the risks associated with, for example, boiling liquid spills. The article demonstrates that a carefully designed, but still relatively simple, model can yield significant benefits in tuning PID controllers.

Adjusting microwave sensing frequency through aspect ratio variation and bending repetitions in Permalloy ellipses

The Ferromagnetic Resonance (FMR) phenomenon, marked by the selective absorption of microwave radiation by magnetic materials in the presence of a magnetic field, plays a pivotal role in the development of radar absorbing materials, high speed magnetic storage, and magnetic sensors. This process is integral for technologies requiring precise control over microwave absorption frequencies. We explored how variations in resonance fields can be effectively modulated by adjusting both the shape and stress anisotropies of magnetic materials on a flexible substrate. Utilizing polyethylene-naphthalate (PEN) as the substrate and Permalloy (Ni79Fe21, noted for its positive magnetostriction coefficient) as the magnetic component, we demonstrated that modifications in the aspect ratio and bending repetitions can significantly alter the resonance field. The results, consistent with Kittel’s equation and the predictions of a uniaxial magnetic anisotropy model, underscore the potential for flexible substrates in enhancing the sensitivity and versatility of RF-based magnetic devices.

Interfacial reaction of mixed pure metal powders under microwave heating

To investigate the interfacial reaction of metal powder after absorbing microwave radiation, pure metal powder composed of five elements, Fe, Co, Ni, Cr, and Mn, was microwave heated at four temperature gradients of 500, 800, 1000, and 1200 °C. At 1200 °C, the powder particles diffused to form an alloy. Mechanical alloying of the mixed metal powder was performed for 5, 10, 24, and 48 h to observe the changes of the powder. The size of the alloy particles first increased, then decreased, and then increased again. The powder mechanically alloyed for 48 h was microwave heated at 700, 800, 900, 1000, and 1200 °C. The alloy only formed at 1200 °C.

Wpływ właściwości dielektrycznych na ogrzewanie rud siarczkowych w polu elektromagnetycznym

Microwave heating is a form of high-frequency electromagnetic radiation. The heating of primary and secondary mineral raw materials in the microwave field depends primarily on their dielectric and thermal properties. The condition is the absorption of microwave radiation. Dielectric heating of materials occurs immediately after placing them in an electric high-frequency field. Knowledge of the dielectric characteristics of mineral raw materials is an important assumption for the use of electromagnetic radiation at the intensification of technological treatment methods. Most mined minerals consist of several mineral components that have different dielectric properties. Most sulphides are well heated in a microwave field. Conversely, tailings components of ores, such as quartz, are transmission materials. The study of dielectric properties involves measurements of the complex relative permittivity ε*, which consists of a real and an imaginary part. The imaginary part of permittivity “loss factor” represents the measure of dielectric losses in the material. Microwave heating of sulphide ores and concentrates such are chalcopyrite, tetrahedrite, galena depends on their chemical composition and content of impurities. The article describes the influence of dielectric properties on heating of chalcopyrite in microwave field. SEM analyses of studied samples are presented.

A Novel Low-Density-Biomass-Carbon Composite Coated with Carpet-like and Dandelion-Shaped Rare-Earth-Doped Cobalt Ferrite for Enhanced Microwave Absorption.

A novel low-density composite for the absorption of microwaves was prepared by loading La-doped spinel cobalt ferrite (La-CFO) onto biomass carbon (BC) derived from corn stalks using a hydrothermal method. This composite (La-CFO@BC) not only maintained the advantageous properties of low density and abundant porosity, but also exhibited a unique morphology, with La-CFO displaying a carpet-like structure interspersed with dandelion-shaped particles. The incorporation of La-CFO effectively tuned the electromagnetic parameters of the composite, thereby improving its impedance-matching attributes and its ability to absorb microwave radiation. At a frequency of 12.8 GHz for electromagnetic waves and with a thickness of 2.5 mm, La-CFO@BC demonstrated remarkable performance in microwave absorption, attaining a noteworthy minimum reflection (RLmin) of -53.2 dB and an effective absorption bandwidth (EAB) of 6.4 GHz. Furthermore, by varying the thickness of the La-CFO@BC within the range of 1.0 to 5.5 mm, the EAB could be broadened to 13.8 GHz, covering the entire X-band, the entire Ku-band, and a substantial portion of the C-band. This study demonstrated that La-CFO@BC was a promising alternative for electromagnetic wave attenuation, which offered superior performance in microwave absorption.

ВОЛНОВОДНО ДИЭЛЕКТРИЧЕСКИЙ МЕТОД И УСТРОЙСТВА ДЛЯ ИЗМЕРЕНИЯ КОНЦЕНТРАЦИИ ВОДНЫХ РАСТВОРОВ И ОБЛУЧЕНИЯ БИОЛОГИЧЕСКИХ ОБЪЕКТОВ

A technique for studying the absorption of microwave radiation of biological objects in a thin dielectric capillary is proposed. The results of experimental studies are presented and the mechanism of the detected effects of the biological action of microwave radiation is proposed. It was found that at a certain ratio between the dimensions of the waveguide, the diameter and thickness of the walls of the capillary, the dielectric parameters of the biological material that fills the capillary and the wavelength of microwave radiation in the waveguide, a significant increase in the absorbed power in a rather narrow frequency band (waveguide-dielectric resonance) is possible. This phenomenon must be taken into account in biotechnological experiments on the irradiation of suspensions. As a result of the work done on the study of the absorption of microwave radiation by hydrocarbon mixtures and models of biological objects in aquatic environments, new designs of measuring devices were created and a technique for hydrocarbon aquametry was developed. The created products are protected by the authors of this work by a patent for an invention.

Absorption spectrum of magnetically structured emulsions in the centimeter range

The high degree of absorption of microwave radiation by composite materials with developed morphology can be significantly improved by directly changing the geometrical parameters of the subwavelength structure, which is difficult in the case of solid-state materials. In this work, a new composite liquid material with controlled absorption properties, a magnetodielectric emulsion, is investigated. The control of microgeometry parameters is accomplished through exposure to a magnetic field. The experimental studies have shown that the formation of chain structures from spherical water droplets in the composite leads to a significant change in the absorption coefficient. Thus, for an emulsion with 10% water content, exposure to a magnetic field of 25 kA m−1 increases the absorption coefficient by 400% at a radiation frequency of 10 GHz. It is noteworthy that the efficiency of the absorption properties control depends on the volume concentration of droplets in the sample and has a non-monotonic character. To interpret the obtained results, numerical modeling of the studied system in the effective medium approximation was carried out.

PVDF/poly(3-methylthiophene)/MWCNT nanocomposites for EMI shielding in the microwave range

This work presents a new approach to enhance EMI shielding efficiency of nanocomposites of dielectric polymers, multiwalled carbon nanotubes (MWCNTs) and intrinsically conducting polymers for account of using core-shell morphology for conducting components. To realize this approach new ternary nanocomposites of poly(vinylidene fluoride) (PVDF), MWCNTs and poly(3-methylthiophene) doped by Cl− anions (P3MT) were prepared through synthesis of thermally stable core/shell nanocomposites PVDF/P3MT and MWCNT/P3MT. These binary nanocomposites were mixed with pure MWCNTs or PVDF followed by compression molding to prepare the ternary nanocomposites of different morphology to discriminate their EMI shielding properties in a wide frequency range (1–67 GHz). Values of the tangent of dielectric loss angle, the efficiency of transmission, reflection and absorption of microwave radiation, and shielding efficiency (SE) of the specified materials were found from analysis of spectral dependences of their complex dielectric constants. It was shown that while the melt mixing of the binary PVDF/P3MT nanocomposite with MWCNTs both in a pure state and in the binary nanocomposite (MWCNT/P3MT) expectedly strongly enhances SE of the former, this effect is non-linear and depends on presence/absence of the P3MT shell on the MWCNT core. The ternary nanocomposite PVDF/P3MT/MWCNT made of the binary polymer-polymer nanocomposite PVDF/P3MT and pure MWCNTs showed highest SE values at the frequencies above 4.5 GHz up to 68.4 dB at 67 GHz in the case of the 1 mm thickness sample. However, below 4.5 GHz the SE was higher in the case of the ternary nanocomposites containing core/shell MWCNT/P3MT nanocomposite instead of pure MWCNT.

Harnessing the Power of Microwave Irradiation: A Novel Approach to Bitumen Partial Upgrading

The partial upgrading of “tar-like” Canadian bitumen is an essential process to reduce its viscosity to an acceptable range that meets the required pipeline specifications. An innovative and potentially greener solution has emerged in the form of microwave irradiation. This work proposes and demonstrates the use of an electrically powered commercial microwave along with carbon-based microwave susceptors (activated carbon, biochar, coke, and graphite) to promote localized thermal cracking within bitumen at a temperature as low as 150 °C, compared to the conventional method of 400 °C. The remarkable results show that just 0.1 wt% of carbon additives can reduce the viscosity of bitumen by 96% with just 10 min of microwaving at 200 °C. A Saturates, Aromatics, Resins, and Asphaltenes (SARA) analysis reveals that the mass fractions of light components (saturates) are almost doubled and that almost one-third of heavy polar hydrocarbon constituents are cracked and decomposed into much lighter molecules, resulting in higher-quality, less viscous bitumen. Furthermore, this study highlights the key role of the surface area and porosity of the carbon microwave susceptor in absorbing microwave radiation, offering exciting new avenues for optimization. Microwave-assisted partial upgrading of bitumen is a cost-effective and eco-friendly alternative to conventional upgrading, producing upgraded bitumen that requires significantly less diluent at a lower cost prior to pipeline transportation.

Зависимость параметров локализации и рассеяния электромагнитной волны в частично поглощающей среде от геометрической конфигурации выводного тракта

The paper presents first results obtained on an experimental setup designed to study the parameters of localization, scattering and absorption of microwave radiation with a power of 1-4 mW at the 38 GHz when radiation propagates in variable-section waveguides. The parameters of localization and scattering of an electromagnetic wave in a partially absorbing medium were studied depending on the geometric configuration of the output tract. The interpretation of the obtained initial results was carried out within the framework of the (1+4)D extended space model (ESM). The extended space model is formulated in (1+4)-dimensional space time-coordinate-interval action. An additional spatial coordinate in the ESM is the interval, which in the ESM has the physical meaning of the action. In the dual (1+4)D space energy-momentum-mass, the interval (action) in the ESM corresponds to the mass. ESM considers the question of the emergence of a non-zero variable mass for a photon and its localization under the influence of an external field.

Thin La doped CaMnO3 ceramics for attenuation−impedance balance to facilitate excellent microwave absorption

The perovskite structure oxide, CaMnO3, has been extensively investigated and applied as a potential microwave absorption material due to its versatile dielectric and spontaneous polarization. However, the low conductivity of pure CaMnO3 material limits its further application. Herein, to increase dielectric loss and achieve better microwave absorption properties, lanthanum (La)-doped CaMnO3 (Ca1-xLaxMnO3) ceramics were fabricated by a high temperature solid state reaction. The results of XRD and XPS show that the La atom was efficiently doped at the Ca site in CaMnO3, which carries excess positive charges and affects the valence state of Mn ions and the concentration of oxygen vacancies. Therefore, the conductivity and imaginary permittivity of Ca1-xLaxMnO3 ceramics increased dramatically with La-doped content. Benefiting from the tunable dielectric and impedance properties, Ca1-xLaxMnO3 ceramics can be utilized in a highly efficient way to absorb microwave radiation with a thin thickness. The sample with x = 0.04 shows the best microwave absorption property, with an RLmin value of -52.63 dB (d = 1.41 mm) and effective absorption bandwidth coves full X band in the thickness range from 1.315 mm to 1.395 mm.

Unraveling the role of counter anions on optical and microwave absorption characteristics of flexible copolymers

Engineering the structural architecture of materials is critical for the transmittance of visible light and absorb microwave radiation in various stealth and electronic applications. Transparent copolymers comprising of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) were synthesized at different compositions using reversible addition-fragmentation chain transfer (RAFT) polymerization. The copolymers exhibited a high percentage of light transmittance (>90%) within the visible range owing to the majority fraction of MMA units. The amine functionalities in the synthesized copolymers were ionized at room temperature by treating with dilute acids such as hydrochloric acid (HCl), trifluoroacetic acid (TFA), nitric acid (HNO3), tetrafluoroboric acid (HBF4), and hexafluorophosphoric acid (HPF6). The quaternization of the side-chain amine groups have resulted in a series of copolymer salts with an ion-pair complex. The investigation of the counter anion effect on the conductivity of the materials has been carried out to produce the highly transparent and conductive MMA-based copolymers. The presence of partially mobile Cl⁻ counter anions in the copolymers can result in conductance as high as 0.939 mS cm−1. Moreover, the optically transparent MMA-based copolymer salts have witnessed a high microwave absorption due to multiple reflections from structural and physical anisotropies.

Microwave Radiation Absorption at a Frequency of 2.45 GHz by a Composite Based on the Dust of Electrical Arc Steel-Making Furnaces

The physicochemical transformations and electromagnetic properties of a composite based on the dust of electrical arc steel-making furnaces and a carbon-containing material (hydrolysis lignin) have been studied. The complex dielectric permittivity of the studied material was measured by the resonator method during heating to 800°C. At room temperature, the effective values of the magnetic permeability and loss of the composite mixture were calculated by solving the Bruggeman equation according to the effective medium theory. The magnetic permeability during heating was found by orthogonal regression. The numerical modelof heating a dense packing from several layers of studied material grains was constructed by the finite element method with consideration of the real properties and physicochemical transformations.

Microwave Radiation Absorption at a Frequency of 2.45 GHz by a Composite Based on the Dust of Electrical Arc Steel-Making Furnaces

Microwave Radiation Absorption at a Frequency of 2.45 GHz by a Composite Based on the Dust of Electrical Arc Steel-Making Furnaces

An improved digestion coil arrangement for high-pressure microwave-assisted flow digestion

A large heated volume (22 mL) digestion coil for high pressure flow digestion was developed. By using computer simulation of the microwave field, the coil geometry was optimized for uniform absorption of microwave radiation along the digestion coil.

Microwave radiation absorption in heat-resistant basalt-based composites

Microwave radiation absorption in heat-resistant basalt-based composites

Effect of absorbed power and dopant content on densification during rapid microwave sintering of Bi2O3‐doped ZnO

AbstractZnO samples with an addition of 0, 0.035, 0.1, and 0.35 mol.% Bi2O3were microwave sintered at heating rates 10 and 50°C/min to a maximum temperature of 1200°C with zero hold time. The densification curves obtained by optical dilatometry have been studied in their dependence on the dopant concentration and the heating rate. Direct volumetric absorption of microwave radiation resulted in a 50–60°C shift of the densification curves toward low temperatures compared to susceptor‐assisted heating. An analysis of the effect of the volumetrically absorbed microwave power on the formation of grain‐boundary phases that facilitate densification is presented.

On the Electrical Conductivity, Microwave-Radiation Absorption, and Reflection of a Composite Based on Multi-Walled Carbon Nanotubes and Butadiene–Styrene Latex

On the Electrical Conductivity, Microwave-Radiation Absorption, and Reflection of a Composite Based on Multi-Walled Carbon Nanotubes and Butadiene–Styrene Latex

Microwave-assisted reduction of Ti species in MgH2-TiO2 composite and its effect on hydrogen storage

The goal of this work is to shed light on the significant dehydrogenation behavior of MgH2-TiO2 composite exposed to microwave irradiation, and the changes in chemical state of titanium species that occur as a result. It is discovered that the reduced titanium oxide (TiO2-x) formed during ball milling can significantly absorb microwave radiation and act as “hot spots”, such that the MgH2 with 25 wt% TiO2 sample is nearly completed dehydrogenated at a constant temperature of 220 °C in a microwave field. Upon full dehydrogenation, the microwave irradiated sample significantly absorbs 1.25 wt% H2 within 600 sec and 4.25 wt% H2 within 10 h at 25 °C under 1 bar of hydrogen. Characterization results of these samples show that microwave irradiation assists the uniform dispersal of defective TiO2-x species around Mg/MgH2 particles and further promotes the reduction of Ti4+ to lower valence states, for better electron transfer between Mg2+ and H-. HRTEM images as well reveal that part of Mg grain size falls around 10 nm, which is believed to significantly enhance the hydrogen sorption as observed. Our findings show that the synergistic effects of microwave irradiation and heat may advance MgH2 further to practical applications.

One-step microwave method synthesis of Fe3O4 nanoribbon@ carbon composite for Cr (Ⅵ) removal

Cr(VI) is recognized as a non-biodegradable and toxic pollutant, resulting from manufacturing and industrialization processes, which can trigger considerable environmental problems. Herein, a novel nitrogen, sulfur co-doped carbon with Fe3O4 nanoribbons composite was synthesized by microwave method within 150 s and applied for Cr(Ⅵ) removal. The raw materials are ferrous sulfate heptahydrate, thiourea and glycerin. Among them, thiourea is served as the rich precursor of carbon nitrogen and sulfur elements and can be used to prepare carbon materials co-doped with N and S elements, while ferrous sulfate heptahydrate can provide iron element for catalyzing rapid preparation of carbon-based materials and self-generation of Fe3O4 nanoribbons. Glycerol not only can be used as a solvent but also can efficiently absorb microwave radiation to make the original quickly heated. The result shows that the addition of Fe3O4 nanoribbons would greatly improve the removal of hexavalent chromium. Meanwhile, the adsorption characteristics were investigated by analyzing by the effects of pH, adsorption kinetics and adsorption isotherms. The result indicates that Fe3O4 nanoribbons can be successfully loaded onto the carbon materials. The maximum adsorption capacity of synthesized material (nitrogen and sulfur co-modified carbon/Fe3O4 (N,S-C/Fe3O4-1) composite) for Cr(Ⅵ) can be reached at pH = 5, probably due to the protonation of functional groups. The adsorption process follows the pseudo-second-order kinetics with the maximum adsorption capacity of 134 mg/g according to Langmuir isotherm model, manifesting that the Cr(Ⅵ) adsorption process is close to monolayer chemisorption. In this work, a new nitrogen and sulfur co-doped carbon/Fe3O4 composite with high Cr(Ⅵ) removal capacity can be successfully prepared within three minutes.