Convert Microwave Energy Research Articles

A novel route of carburizing through microwave hybrid heating

Abstract Carburizing is a surface treatment process by diffusing carbon into the steel. These days, manufacturing industries demand highly efficient processes that consume low power. Microwave processing is a newly evolving process that consumes low power. This study proposes a novel route for carburizing mild steel (substrate) through experimental and simulation studies using a microwave heating. Charcoal powder was used as a susceptor to convert microwave energy into heat energy and to deposit carbon on the surface of the specimen. The mild steel specimens were exposed to the microwave power input of 900 W and 360 W for exposure time of 1500 s and 1980 s naming it as S2 and S3 respectively. The microstructural analysis of specimens S2 and S3 confirms the formation of pearlite structures at the surface. However, the amount of pearlite structure was significantly higher for the S3. The higher carbon content is confirmed through energy-dispersive x-ray spectroscopy (EDS) analysis of specimen S3. The average hardness of the S3 specimen was determined to be 220.8 HV, which shows an increase of 38.36% compared to the S1 (base metal). x-ray diffraction (XRD) results indicate the additional cementite peaks (Fe3C) and ferrite-confirming phase transformations for carburized samples. The wear analysis of S2 and S3 was conducted through pin-on-disk testing. The peak COF of 0.73 and 0.64 was observed for S2 and S3 respectively. The hard surface of S3 resists the penetration of the counter body to a greater extent due to the fine morphology of pearlite. From the FEM study, the maximum value of 7.96 × 10 3 (V/m) was determined at the center region for the electric field distribution in the microwave cavity, which is the optimum value for efficient heating. The maximum temperature of the mild steel obtained during the carburization process was 900 °C in 1800 s. The microwave carburizing process requires relatively less time than the conventional carburizing process which will save energy consumption.

High-Efficiency Microwave Wireless Power Transmission via Reflective Phase Gradient Metasurfaces and Surface Wave Aggregation.

Microwave Wireless Power Transfer (MWPT) technology is crucial for emergency power supply during natural disasters and powering off-grid equipment. Traditional antenna arrays, however, suffer from low energy capture efficiency, difficult impedance matching, complex synthetic networks, and intricate manufacturing processes. This paper introduces a microwave energy receiver design utilizing Reflective Phase Gradient Metasurfaces (R-PGMs) and surface wave energy convergence technology. The design leverages the effective plane wave-to-surface wave conversion capability of R-PGMs to transform incident microwave energy into a surface wave mode, which is then efficiently harvested using a circular energy convergence array before being output to a coupling port. By optimizing R-PGM parameters, an ideal 60° phase gradient distribution is achieved, facilitating the focus of surface wave energy via dispersion characteristics. These components are integrated into a hybrid antenna array, complemented by a matched energy output port structure. Numerical simulations show that this array can efficiently convert microwave energy from plane waves to surface waves, achieving a conversion efficiency of 85.32% and a collection efficiency of 68.26%. Experimental results corroborate these findings, with peak energy collection efficiency reaching 64.68% at 5.8 GHz and an RF-DC conversion efficiency of 42%, confirming the design's efficacy. Compared to conventional methods, this design simplifies the system by avoiding complex combining networks and significantly enhances the efficiency of microwave MWPT.

The influence of thermal radiation during microwave-assisted freeze-drying of pharmaceutical unit doses

New drying technologies for biologicals have recently been developed to accelerate the time-consuming batch freeze-drying (BFD) process. Among others, microwave-assisted freeze-drying (MFD) has been suggested as a faster and more effective drying technology. In this study, MFD cycles with the microwave radiation switched on and off were performed to assess the contribution of the microwave radiation to drying acceleration. It was found that thermal radiation emitted by the drying chamber walls was predominantly accelerating the drying of monodose placebos rather than microwave radiation. The combination of ultra-low chamber pressure, high thermal heat transfer and a short primary-to-secondary phase transition reduces drying times by more than 80 % compared to conventional BFD. In a second step, a design of experiment approach was used to assess the effect of thermal radiation versus microwave radiation and their combination, together with dosage properties such as fill volume and excipient concentration upon drying rate. The outcome showed the importance of high fill volume and high excipient concentration for an effective microwave contribution to the drying rate. Nevertheless, the drying acceleration for small pharmaceutical dosages with restricted solutes was mainly driven by thermal radiation rather than 2.45 GHz microwave radiation. The inability of ice to convert microwave energy into heat hampers the potential use of microwave freeze-drying for single-dose vaccines.

Optimizing microwave heating with slotted metal tubes for cylindrical loads

Cylindrical loads are commonly encountered in microwave heating and often suffer from uneven thermal distribution. Within certain radius and dielectric parameter ranges, cylindrical loads may exhibit central thermal focusing. This paper proposes a novel microwave heating method employing a slotted metal tube (SMT) to encase the cylindrical materials. The SMT alters the electric field distribution and enhances the coupling of microwave energy, thereby improving the heating uniformity and efficiency. We first developed a simulation model for microwave heating, analyzing how permittivity and dimensions affect the thermal focus of cylindrical materials. By optimizing the slot dimensions and positions, we overcome the thermal focusing phenomenon. Then, we conducted microwave heating experiments with mashed potatoes, showing that the use of SMT improved the temperature uniformity by 38 % and increased the microwave energy conversion efficiency by 48 %. Furthermore, we applied SMT to a more challenging scenario, involving the heating of cylindrical canned foods with metal lids, using a dual-source heating setup. The experimental results indicated that SMT remained effective in enhancing heating uniformity and efficiency. This method contributes to the development of microwave energy industrial applications, providing innovative solutions for cylindrical load heating.

“Fireworks” ignition and combustion of metal nanoparticles: Based on the rapid conversion and transmission of microwave energy by energetic ionic liquids

The metal nanoparticles (MNPs) are widely used to improve the output performance of various explosives and propellants, which ignition is an important link for the energy release of fuel. The microwaves have been recognized as a safer and smart ignition method. However, it is difficult to achieve rapid ignition of MNPs under microwave radiation due to the low heating rate. The ADN energetic ionic liquids could efficiently absorb microwaves owing to excellent polarity. This work proposes a method of fast “fireworks” ignition and combustion of MNPs under microwave radiation, by employing ADN as the “central hub” for microwave energy conversion. The dispersion of Al and Ti NPs in ADN endowed the solution with nanofluid properties and significantly improved the thermal conductivity. The solution boiled violently under microwave radiation, causing the temperature of MNPs to rise continuously. Meanwhile, the acidic components produced by ADN pyrolysis destroyed the oxide shell of MNPs, further accelerating the ignition process. The ignition phenomenon of Al and Ti NPs were different due to distinct microwave absorption properties and ignition temperature. When the expanding liquid film broken, the shock wave blew the Al NPs into the air to realize the “fireworks” ignition and combustion. The Ti NPs was ignited in the solution, which further ignited the ADN solution, allowing the system for controllable ignition and combustion. The “fireworks” ignition and combustion performance of MNPs could be modulated by the input microwave power. In summary, the new ignition and combustion method of MNPs will have a profound impact on the design of ignition sequence, the improvement of microwave energy utilization and the expansion of the application of ADN-based liquid propellants.

Microwave De-Icing Efficiency Improvement of Asphalt Mixture with Structural Layer Optimization and Heat-Resistance Design.

The application of microwave de-icing technology in road engineering is constrained by its low energy utilization rate, which can be attributed to low heat production rates and ineffective heat dissipation to the underlying pavement. In this work, asphalt mixtures are designed as an upper layer (heating layer) and a lower layer (thermal-resistance layer). Magnetite slag was selected as a microwave-sensitive source for generating heat, and expanded perlite powder was incorporated into the lower layer as a thermal resistance material. Structural layer optimization and thermal-resistance layer design of the asphalt mixture were carried out by changing the thickness of the upper and lower layers to further improve the heat production rates. The design effectiveness is comprehensively evaluated by factors such as the changing law of the average surface temperature of mixtures, ice-melting time, and cost-effectiveness analyses. The results show that EP possesses better thermal stability, lower microwave energy conversion ability and more excellent heat-resistance potential compared with mineral powder. The heat-resistance layer with EP can prevent heat from being conducted to the lower layer and promote it to concentrate on the specimen surface, which can endow the microwave heating efficiency of specimens to be further improved by up to 26.97% and the de-icing time reduced by 10%, ascribed to the heat-resistance design. Furthermore, the collaborative design of the structural layer optimization and heat-resistance layer can increase energy utilization efficiency and save microwave-absorbing materials while ensuring excellent microwave de-icing efficiency.

Fe-doped Cu-based bimetallic metal-organic frameworks as nanoscale microwave sensitizers for enhancing microwave thermal and dynamic therapy for hepatocellular carcinoma.

Microwave ablation (MWA) is recognized as a novel treatment modality that can kill tumor cells by heating the ions and polar molecules in these cells through high-speed rotation and friction. However, the size and location of the tumor affect the effective ablation range of microwave hyperthermia, resulting in residual tumor tissue and a high recurrence rate. Due to their tunable porous structure and high specific surface area, metal-organic frameworks (MOFs) can serve as microwave sensitizers, promoting microwave energy conversion owing to ion collisions in the porous structure of the MOFs. Moreover, iron-based compounds are known to possess peroxidase-like catalytic activity. Therefore, Fe-doped Cu bimetallic MOFs (FCMs) were prepared through a hydrothermal process. These FCM nanoparticles not only increased the efficiency of microwave-thermal energy conversion as microwave sensitizers but also promoted the generation of reactive oxygen species (ROS) by consuming glutathione (GSH) and promoted the Fenton reaction to enhance microwave dynamic therapy (MDT). The in vitro and in vivo results showed that the combination of MWA and MDT treatment effectively destroyed tumor tissues via microwave irradiation without inducing significant side effects on normal tissues. This study provides a new approach for the combined application of MOFs and microwave ablation, demonstrating excellent potential for future applications.

Microwave-Assisted Synthesis of Nitrogen-Doped Carbon Catalysts for Oxygen Reduction Reaction with Tunable Selectivity

The oxygen reduction reaction (ORR) is the core reaction in electrocatalysis systems such as fuel cells, metal-air batteries and hydrogen peroxide (H2O2) electro-generation. The ORR reaction mechanism has two possible pathways, namely, two-electron (2e−) or four-electron (4e−) processes that enable a reduction of oxygen into H2O2 or water (H2O), respectively. Both paths are useful where the former can provide on-site direct production of H2O2 and the latter is desired in fuel cells and batteries since it enables higher energy efficiency. Optimal ORR electrocatalyst should exhibit high activity, selectivity, stability, and low cost. Carbon materials modified with heteroatoms (e.g. nitrogen (N)) are considered potential alternatives for costly noble metal catalysts including Pt for ORR in fuel cells, and Au for the ORR to H2O2 (1,2). The typical synthesis procedure for the porous nitrogen-doped carbons (N–C) is based on the single or multiple pyrolysis steps of nitrogen-rich carbon precursor. The reactions required a pyrolysis step at the temperature range of 500-1200 °C and timing of one to tens of hours. Such processes showed a highly negative environmental impact due to high energy consumption. The production of 1 ton of activated carbon from lignocellulosic biomass feedstock requires 669.83 kWh (equivalent to an emission of 62.78 tons of CO2) (3). The synthesis of the N–C by microwave (MW) irradiation can reduce energy usage and ensure a more environmentally sustainable and economically viable approach. This procedure necessitates non-transparent materials to electromagnetic waves that can convert MW energy into heat and simultaneously enable the carbonization of the starting material.This work investigated the electrocatalytic activity towards ORR for N–C–MW catalysts derived from polyaniline (PANI) prepared in a one-step MW carbonization approach. PANI was selected due to two reasons: (i) N–C made by thermal pyrolysis of PANI showed improved electrocatalytic activity toward ORR where both the 4e− and the 2e− electron transfer pathways are feasible depending on the nature of active sides (4), (ii) PANI displayed good MW adsorption properties (5). The work aimed to identify the influence of the MW reaction condition on the resulting structure of the N–C–MW and the direction of the ORR. The N–C–MW samples were prepared under MW power of 450 and 800 W and time of 70, 140 and 210 s. The ORR activity of N–C–MW samples was investigated by cyclic voltammetry in the alkaline media (O2-saturated 0.1 M KOH). The experiment was performed in a three-electrode configuration composed of a rotating ring (Pt)–disk (glassy carbon) electrode (RRDE), a graphite rod as the counter electrode and a reversible hydrogen electrode (RHE) as the reference electrode. An influence of catalyst loading on disk electrode (0.05, 0.1 and 0.2 mg/cm2) was analyzed. All investigated MW reaction conditions resulted in the formation of porous disordered carbon structures with nitrogen and oxygen functionalities confirmed by X-ray photon-electron spectroscopy. The shorter time (70 s) and lower power (450 W) of MW treatment resulted in the formation of structures with a low carbonization rate and simultaneously a relatively poor catalytic activity for ORR (an onset potential of ∼0.65 V vs RHE). The samples carbonized under moderate (power of 450 W and 800 W, time of 140 s) and severe (power of 450 W, time of 210 s) reaction conditions showed higher selectivity to H2O2 or water H2O, respectively. The selectivity of 80 % to H2O2 was achieved for the N–C–MW-800W-140s sample at the potential of 0.6 V vs RHE at the catalyst loading of 0.05 mg/cm2. The results showcase the potential of MW carbonization in producing ORR electrocatalysts with diverse functionalization, leading to modified reaction selectivity that can be utilized in various electrocatalytic applications. Acknowledgments The research leading to these results was supported by the Johannes Amos Comenius Programme, European Structural and Investment Funds, project 'CHEMFELLS V‘ (No. CZ.02.01.01/00/22_010/0003004). References Yang, S. et al., Toward the decentralized electrochemical production of H2O2: A focus on the catalysis. ACS Catalysis, 2018.Bouleau, L. et al., Best practices for ORR performance evaluation of metal-free porous carbon electrocatalysts. Carbon, 2022.Wang, YX. et al., Quantifying environmental and economic impacts of highly porous activated carbon from lignocellulosic biomass for high-performance supercapacitors. Energies, 2022.Silva, R. et al., Efficient metal-free electrocatalysts for oxygen reduction: Polyaniline-derived N- and O-doped mesoporous carbons. Journal of the American Chemical Society, 2013.Oyharçabal, M. et al., Influence of the morphology of polyaniline on the microwave absorption properties of epoxy polyaniline composites. Composites Science and Technology, 2013. Figure 1

Research on electromagnetic energy absorption and conversion device with four-ring multi-resistance structure

A device for electromagnetic energy absorption and conversion was investigated as an electromagnetic energy harvester, which is based on a four-ring multi-resistance unit. The device can convert microwave energy to thermal energy and then to electrical energy through the Bi2Te3 thermoelectric material adhered to the load resistance. The energy harvesting efficiency, power loss distribution, and current density distribution of the harvester were analyzed. In addition, the energy harvesting efficiency of the unit under different incident angles and polarization angles was studied, and the effect of incident power on the temperature and energy conversion efficiency of the unit was analyzed. The simulation results showed that the energy harvesting efficiency of the harvester reaches 99.5% at 5.8 GHz. Each unit in the harvester can generate an output voltage of 171.8 mV under 7 W incident wave power, and the maximum output power is 9.71 mW. To verify the effectiveness of this method, a 5 × 5 unit array model was fabricated and measured, and the measurement results were consistent with the simulation results.

Decoupling research on thermal effect of microwave-induced discharge with spherical carbon-based dielectric

Microwave discharge is effective in improving microwave energy conversion efficiency due to its significant thermal effect. An in-depth analysis of the thermal effect is the key to understanding the nature of microwave discharge. However, the mechanism of thermal effect of microwave discharge is still unclear because of the deficiency of decoupling research on the thermal effect in the process of microwave discharge. Consequently, the spherical carbon-based dielectric is used for igniting microwave discharge, and the total heat generated in the discharge process is stripped into the electromagnetic conversion heat and the additional heat generated by the discharge. On this basis, a model matching microwave-induced discharge with the spherical carbon-based dielectric is established. Furthermore, the heat transfer mode of discharge additional heat source is discussed and its heat generation rate is calculated. The results show that the errors between the temperature rise curves obtained by this model and the real measured curves are kept within ±5%. The heat generation rate of discharge additional heat source is a function of the average temperature of the dielectric gaps, following a relation of qDA,i(T) = Ai + BiT + CiT2. The work is of great significance to reveal the mechanism of thermal effect in process of microwave discharge.

Prosopis juliflora valorization via microwave-assisted pyrolysis: Optimization of reaction parameters using machine learning analysis

Microwave power and pyrolysis temperature are essential parameters in optimizing the bio-oil yield and quality in microwave pyrolysis. This study focused on understanding the interactions between the microwave power/heating rate and pyrolysis temperature in microwave-assisted pyrolysis of Prosopis juliflora. For optimum bio-oil yield, a discrete set of microwave powers (280 W, 420 W, and 560 W) and pyrolysis temperatures (200 °C, 350 °C, and 500 °C) were selected. A central composite design (CCD) was adopted to analyze the effect of microwave power and the pyrolysis temperature on product yields, heating rate, microwave conversion efficiency, and heat losses in pyrolysis. Moreover, the effect of heating rate, reaction time, specific microwave power, specific microwave energy, and conductive heat loss on gas, char, and liquid yields was evaluated using statistical machine learning techniques. Moreover, a new parameter, pyrolysis index, is calculated under different conditions to understand the extent of pyrolysis intensity using pyrolysis time, heating value, feedstock mass and conversion, and microwave energy conversion. The yields of bio-oil, biochar, and gas were 25–40 wt%, 25–35 wt%, and 35–40 wt% at different experimental conditions. Bio-oil consists of a mix of organic compounds with methoxy phenols at high selectivity, and the calorific value of bio-oil was in the range of 26–28 MJ/kg. Carbon number analysis revealed higher presence of C5–C9 compounds. This study shows the role of machine learning in understanding the effect of various parameters effectively and optimizing the experimental conditions accordingly.

Dielectric anisotropy effects on the microwave-induced thermodynamic response of coal: Numerical simulations and experiments

Microwave heating technology is a promising solution in underground engineering, such as mining, coalbed methane extraction, and oil/gas production, that primarily depends on the conversion of microwave energy due to dielectric properties. However, inadequate understanding of the effects of dielectric properties on microwave irradiation limits further development of microwave techniques. In this study, based on the dielectric anisotropy of coal, an electromagnetic-thermomechanical coupled model was used to numerically investigate the thermodynamic response under microwave irradiation at 2.45 GHz and 1 kW for 180 s. We performed experimental verification via indoor test. Results show that the sensitivity of microwaves to the dielectric direction in the TE10 mode is x > z > y. In different dielectric anisotropy models, the temperature and maximum principal stress increase synchronously and linearly with increasing heating time, and the curve growth rate is positively correlated with the equivalent dielectric permittivity. There are also marked temperature and stress concentrations in the sample. The compressive stress is concentrated in the center of the sample, while the tensile stress is around the outer edge. For bedding coal, tensile fractures occur under microwave irradiation along the bedding, and shear fractures run through the bedding. With the increase of the input microwave energy, the failure mode of coal gradually expands from single fracture to fracture network.

Assessment of microwave susceptors for optimum temperature rise using parametric numerical simulation

Microwave hybrid heating or indirect microwave heating has been an important development in the processing of metals using microwave energy. In this method of heating, a “susceptor” is used to absorb and convert microwave energy into thermal energy which is utilized for materials processing. Few of these processing applications are sintering, joining, cladding, casting, and composite development. However, the precise selection of a susceptor for a given process is challenging and requires a thorough understanding of the microwave heating phenomenon. In addition, predicting temperature rise in a microwave cavity is a complex task. Numerical simulation can serve to solve these two significant problems. In this work, parametric simulation of microwave heating of three major susceptor materials; silicon carbide, alumina, and coal has been carried out using a multiphysics approach. Initially, a model was developed to validate the simulation procedure. The results were in good agreement with the available data in published literature. Thereafter, the effect of microwave power, position of susceptor block, and time of irradiation on temperature rise in these materials were investigated. On comparing these susceptor blocks after altering the parametric combinations, coal exhibited the formation of hot spots and uneven temperature field with a maximum temperature of 901°C. On the contrary, the temperature attained in silicon carbide (529°C) and alumina (616°C) were lower but distributed in a relatively uniform field across the block. Regression models have also been built to correlate maximum temperature achieved with the parametric variation of parameters. It has been found that microwave power and the time of microwave irradiation have a significant coactive effect on the maximum temperature reached by the material. While the rise in the position of the susceptor block from the base leads to an adverse effect on the temperature rise. The study demonstrates that indirect microwave heating can be harnessed using the proper selection of susceptors as per the temperature requirement of the process. The regression models can be used for the accurate prediction of temperature attainment for given power input, position, and time.

Influence of ferrimagnetic resonance on conversion of electromagnetic energy by a YIG resonator into mechanical one

Using the method of physical modeling, an algorithm for calculating the force with which a standing electromagnetic wave acts on a ferrite sphere of arbitrary diameter placed in a constant magnetic field is obtained. The value of constant magnetic field intensity provides appearance of ferrimagnetic resonance. Dependence of the magnetic field of an electromagnetic wave in the middle of a ferrite sphere on the size of its resonant radius and spherical coordinates are studied. In the center of the ferrite sphere, the resonance radius of which is 4.2634 mm, the microwave magnetic field strength is 83796 times greater than the magnetic field strength in the incident plane polarized wave. Mean-square value of the magnetic field strength over the volume of the sphere increases 4.8 times. Standing wave, formed in a free space with power flow density of 622 kW/m2 and wavelength of 3.2 cm, reflects from metallic shield placed at a distance of λo/8 + nλo/2, n = 0, 1, 2, 3… measured from the center of ferrite sphere and impacts with force of 0,12 N on ferrite sphere with resonance radius of 4,2634 mm. The results of the calculated force acting on the YIG – resonator coincide with the experimental results given in the well-known works (the power flux density is 43 kW/m2, the radius of the ferrite sphere is 1.775 mm, the force is 6 ± 0.5 μN) within the measurement error. Application of spatial resonance, standing electromagnetic wave and YIG resonator allows to increase of energy conversion factor of microwave energy conversion into mechanic one 8,6·104 times in compare to application of ferrite cylinder only in known papers. The research results can be used by the developers of converters of microwave energy into mechanical energy.

Experimental Investigation into the Optimum Position of a Ring Reflector for an Axial Virtual Cathode Oscillator

A ring reflector was experimentally investigated using an axial virtual cathode oscillator (vircator). The ring reflector was installed behind the mesh anode of the axial vircator to enhance the microwave power output by forming a resonant cavity and increasing the electron beam to microwave energy conversion efficiency. The optimum position of the ring reflector is analyzed through simulations and experiments by varying the anode to reflector distance from 6 mm to 24 mm in 3 mm steps. PIC simulations show that the ring reflector enhances the microwave power of the axial vircator up to 220%. Experiments show that the microwave power from the axial vircator without the ring reflector is 11.22 MW. The maximum average peak microwave power of the axial vircator with the ring reflector is 25.82 MW when the anode to ring reflector distance is 18 mm. From the simulations and experiments, it can be seen that the ring reflector yields decaying enhancement that is inversely proportional to the anode to ring reflector distance and there is no noticeable microwave enhancement after 24 mm. The frequency range attained from the simulations and experiments is 5.8 to 6.7 GHz and 5.16 to 5.8 GHz, respectively. The difference between the simulation and experimental results is due to the error in the anode to cathode gap distance. Although the frequency is slightly changed, the ring reflector seems to have no influence on the frequency of the generated microwave.

Long-term retrogradation behavior of lotus seed starch-chlorogenic acid mixtures after microwave treatment

The effect of microwave treatment on the long-term retrogradation behavior of lotus seed starch (LS)-chlorogenic acid (CA) binary mixtures (LS-CA) was evaluated. The dielectric properties of LS-CA enhanced its microwave energy conversion capacity and the related heating effect, compared with LS. Changes in the chain length distribution (CLD) induced by microwave treatment revealed that the cleavage of internal B2 and B3 amylopectin chains was greater in LS-CA. Low-field nuclear magnetic resonance (LF-NMR) analysis showed that CA increased the water-holding capacity and stability of starch gels. Moreover, differential scanning calorimetry (DSC) and analysis of long- and short-range ordered structures indicated that CA inhibits the alignment of disordered starch polymers during retrogradation, especially the re-formation of the helical conformation. These findings significantly increase our understanding of the mechanism by which polyphenols inhibit starch retrogradation after microwave treatment. This understanding should facilitate the development of starchy foods with tailored retrogradation rates and properties.

An improved conversion of the microwave energy into plasma in an optimized microwave plasma sheet source at 2.45 GHz designed for surface treatment

Efficient conversion of the microwave energy into an atmospheric-pressure argon plasma in a microwave plasma sheet source (MPSS) operating at 2.45 GHz in ambient air is the subject of this work. The MPSSs, capable of providing an atmospheric pressure plasma in the shape of a narrow sheet are an innovative technology for variety of surface treatments with no impact on the environment. The existing designs of the MPSS exhibit unsatisfactory efficiency of the conversion of microwave energy produced by the microwave source into the microwave plasma (about 80%), which hinders implementation of the MPSSs in the industry. In this paper, after an analytical approach based on the equivalent electrical circuit method we proposed an optimization of the design of MPSS in terms of the microwave energy conversion efficiency. The MPSS design improvement consisted in reducing the electrical impedance in the input plane of the MPSS by introducing a capacitive diaphragm into the MPSS transmission line, which compensated the inductive character of the plasma sheet. The experimental measurement of the electrodynamic characteristics of the MPSS with diaphragm showed that using the diaphragm significantly decreased the microwave power losses due to the microwave reflection from about (20–30)% to a level of several percent. This substantially increased the MPSS energy conversion efficiency up to about 97%, 93% and 87% for incident powers P I of 500 W, 750 W and 1000 W, respectively. The electrodynamic characteristics of the MPSS appeared a very convenient tool for determining the conditions of maximum efficiency of conversion of the microwave energy into the microwave plasma. The electrodynamic characteristics were measured at argon flow rate of 20 Nl min−1. The analysis of the calculated input impedances of the MPSSs with and without diaphragm, based on the equivalent electrical circuits of both MPSSs confirmed that the change of the character of the input reactance of the MPSS from inductive to capacitive after introducing the diaphragm is the cause of the increase in the MPSS energy conversion efficiency. The MPSSs having the energy conversion efficiency such high as presented in this paper appears to be attractive innovative technology for economic use in industrial applications.

NEW COMPONENTS OF ALCEA NUDIFLORA EXTRACT AFTER MICROWAVE EXTRACTION

Alcea nudiflora (Lindl.) Boiss. (Malvaceae) has a wide area of growth in Central Asia, the Altai territory and Western Siberia and has long been used in folk and traditional medicine. Availability of the resource and long-term application practice makes Alcea nudiflora a promising source of valuable biologically active natural compounds. The chemical composition of A nudiflora has been studied after effective microwave assisted extraction (MAE) performed using solvents with different ability to convert microwave energy into heat: hexane, ethyl acetate, methyl tert-butyl ether (MTBE) and ethyl alcohol (EtOH). The selected MAE conditions enabled us to reduce significantly the extraction time and obtain extracts enriched with new compounds. The chemical composition of aboveground part extracts of Alcea nudiflora (Lindl.) Boiss was studied by applying GC/MS method. 13 acids were discovered for the first time, including 6 aromatic acids and 7 unbranched monobasic acids of unsaturated and saturated series, as well as 11 new neutral compounds, including 7 naphthalene derivatives.

Absorbance and transformation of SHF electromagnetic waves in quartz-containing heterogenic materials

A study of the mechanism of uptake and conversion of microwave energy into heat energy is presented. The term ”SHF – trigger”, which activates at the atomic, electronic, and molecular scales, is introduced for the mechanism of micro cracking, destruction, and crashing of quartz-containing rocks. It has been found that the uptake and conversion of microwave energy into heat energy begins there were some criteria of the sample instability in energy consummation are satisfied. This mechanism of the energy conversion with the heating effect differs from other modes of heating by its efficiency; accordingly, a special criterion is required. The loss tangent of a dielectric, such as mineral or heterogeneous rock, could serve as a measured parameter. This parameter is attributed to slowly establishing modes of relaxation, which manifest themselves in the presence of polar molecules, complicated anion radicals, chemically bounded water, solid/liquid interfaces, borders of dielectrics and conductors. In addition, a new mechanism of conversion of microwave energy into heat energy in points of contact between water-saturated pores in model specimens was suggested.

Study of microwaves energy conversion into electric current on semiconductor material NaxCuyTiz

Converting microwaves energy into electric current has been studied through co-precipitation and sintering process on the semiconductor material. Most of the application of these methods still had a challenge of lowering the resistivity value of semiconductor material. Some researches indicated by adding molten salt into semiconductor material can reduce the resistivity value. In this study, the synthesis process by combining the co-precipitation and sintering method of transition metal (titanium and copper) and alkali metal (Sodium) shown an improvement in lowering resistivity problems. Composition ratio, temperature, and distance of radiation were the variable of measurement in this research. Three semiconductor materials NaxCuyTiz were synthesized by using 60 ml of hydrochloric acid (HCl) and 80 ml of ammonium hydroxide (NH4OH) as a reagent in co-precipitation method and sintering at temperature 500°C. An Olympus microscope was used to analyze the microstructures of all three materials. Fractions x, y, and z in the materials were determined by analysis of X-ray spectrograph model 2501. The resistivity values of three materials, namely as Na0.52Cu0.37Ti0.11, Na0.26Cu0.39Ti0.35, and Na0.26Cu0.67Ti0.07 were obtained by varying the temperature of measurement. The microwave radiation was measured by observing the output voltage and current along with the radiation at a variable distance (60, 90, 10, 150, 180, and 210 cm) through the semiconductor material. The experiment showed that material Na0.52Cu0.37Ti0.11 had low resistivity and small bandgap energy as 0.875 eV and able to convert microwave energy from 1.624 × 10−24 Watt to 9.137 Watt at 60 cm of microwaves radiation distance.