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The plasma emission spectrum and polycrystalline diamond growth within 4 inches was studied by using a microwave plasma chemical vapor deposition (MPCVD) equipment with a microwave frequency of 2.45 GHz and a power of 10 kW, a 4-inch free-standing diamond thick film was prepared, and the growth uniformity, crystal quality at different positions, room temperature thermal conductivity, ultraviolet-visible-near infrared spectral transmittance and dielectric properties of diamond film were characterized. The results show that the freestanding diamond films are prepared with good uniformity and crystallinity at 10 kW power with high concentration and chemical activity of carbon and hydrogen active particles within the plasma diameter of about 100 mm. The thermal conductivity at room temperature reaches more than 1894 W/m·K, the infrared transmittance reaches more than 70%, the dielectric constant is 5.5, and the dielectric loss is 5.9 × 10−5. This study provides a theoretical possibility for the preparation of large-area high-quality diamond films in low-power MPCVD equipment.

Oil fuels derived from fossils are non-renewable, so over time, they will run out and have a negative impact on air pollution. To overcome this, there is a need for environmentally friendly alternative fuels from renewable sources such as biodiesel. This research used microwave heating with a CaO catalyst. NaOH-impregnated snail shells and active carbon support. This research aims to determine the effect of power on the conversion of candlenut seed oil into biodiesel using the NaOH/CaO/CA catalyst both in terms of compliance with the SNI 7182-2015 standard and analysis using GC-MS (Gas Chromatography-Mass Spectrometry). The synthesis of the NaOH/CaO/CA catalyst was carried out through wet impregnation and calcination at a temperature of 500°C and analyzed using gas sorption analysis (GSA). Then proceed to the transesterification process, where the power for microwave heating was varied to 300, 450, and 600 watts with a mole ratio of esterified oil and methanol, namely 1:10 for 3 minutes. The analysis results of the NaOH/CaO/CA catalyst using the GSA instrument have a surface area of 9.306 m2/g, pore volume of 0.033 cc/g, and pore diameter of 14.043 nm. Meanwhile, the results of the biodiesel analysis showed that the optimum biodiesel yield was 85.625% at 600 watts of power and had a kinematic density and viscosity that met the SNI 7182-2015 biodiesel standards. Analysis of biodiesel characteristics using GC-MS showed that the three most optimum biodiesel components were hexadecanoic acid, methyl ester (22.664%), 9,12-Octadedecadienoic acid (Z,Z)-, methyl ester (30.176%) and 9-Octadecenoic acid (Z)-, methyl ester (38.656%).

In the world of industrial drying processes, foam mat microwave drying is a significant and valuable approach. Its advantages include increased drying effectiveness, preservation of product quality, energy and cost savings, flexibility in application, and improved safety. Development of Nagpur mandarin juice powder is tedious and time-consuming due to its bitter test and less total soluble solid, therefore the present research carried out with the process parameters for microwave drying include microwave power levels (180, 360, 540, 720, and 900 W) and drying bed thicknesses (2, 4, and 6 mm). Foamed juice is produced using soy protein isolate (2.10 %), GMS (2.75 %), CMC (1.75 %), and sugar (5.10 %), with whipping times of 8 min. Additional foaming agents include guar gum (0.45 %), soy protein isolate (3.30 %), and sugar (10 %) with whipping times of 6 min. The optimal conditions for drying Nagpur mandarin juice were determined through analysis using Design-Expert 11.0.4.1 software. These conditions include 540 W of microwave power, a drying bed thickness of 3 mm, and the use of a foaming agent comprising 2.10 % soy protein isolate, 2.75 % GMS, 1.75 % CMC, and 5.10 % sugar, with an 8-min whipping period. Under these optimized conditions, the resulting powder exhibited the following characteristics: color b value of 19.59, ΔE (change in color) of 6.24, acidity of 0.40 %, ascorbic acid content of 36.64 mg/100 g, water activity of 0.26, drying time (in minutes), and overall acceptability rating of 7.77. These findings highlight the effectiveness of the optimized process parameters in achieving desirable quality attributes for Nagpur mandarin juice powder production.

This study investigates the optimization of microwave-assisted extraction (MAE) condition for phenolic antioxidants from Gossampinus malabarica flowers by response surface methodology (RSM) using a central composite design (CCD). The best combinations of microwave power (MP), solid to liquid (S-L) ratio, ethanol concentration and time were identified through MAE using RSM from G. malabarica flowers. The manipulation of process variables significantly influenced the extraction of bioactive compounds (BCs), with the MP and S-L ratio demonstrating high significance in the extraction of BCs. The optimized extraction conditions consisted of an MP of 1,000 W, a S-L ratio of 1:100, an ethanol concentration of 20 % (w/v), and an extraction time of 20 s, resulting in the highest extraction yield, extractable phenolic compounds, DPPH antioxidant activity and total flavonoid content. The actual experimental results are closely associated with the predicted values, affirming the efficacy of RSM in optimizing the phenolic extraction process from G. malabarica flowers.

Power sensor nonlinearity contributes significantly to the increase of the microwave power measurement uncertainty. Current methods for sensor calibration do not provide correction of the results, due to the sensor nonlinearity. The paper describes an improved method and an automated measuring system based on it for power sensor calibration that enables the correction of the results, taking into account amplitude and frequency dependent nonlinearity. The novel calibration method is based on the application of high-linearity thermistor power transfer standard. The power sensor calibration process is fully automated and improved by applying the automated measuring system, PC and VEEpro software. Performed calculation of the calibration measurement uncertainty and the analysis of power measurement uncertainty budget indicate that the new calibration method allows the correction of sensor nonlinearity and contributes to significant reduction of the microwave power measurement uncertainty, ranging from 15,8% to 40,5%. Experimental results and validation confirm the applicability of the improved calibration method and prove the existence of significant dependence of sensor nonlinearity on the power level, but also on the frequency of the measured microwave power.

The aim of this study is to use the response surface methodology (RSM) to mathematically model the response parameters and emission of greenhouse gases (GHG) and optimize the drying variables for a carrot dried with the microwave method using various pretreatments. To this end, the influence of the drying parameters (independent), such as microwave power and slice thickness dried by two pretreatments of ultrasonication at 30 °C for 10 min and blanching at 70 ℃ for 2 min, was explored on the dependent (response) parameters including the thermal properties (drying time, effective moisture diffusion coefficient (Deff), specific energy consumption, energy efficiency, quality features (color changes and shrinkage), and GHG emission (including CO2 and NOx). It should be mentioned that the emission of GHG was determined based on the energy consumption of various types of power plants such as the gas turbine steam power turbine, and combined cycle turbines using various fuels such as natural gas, heavy oil, and gas oil. The results indicated that the ultrasonication and blanching pretreatments can decrement the drying time (linearly), energy consumption (linearly or quadratically), shrinkage(quadratically), and color changes(quadratically) and enhance the Deff (linearly) and energy efficiency (linearly or quadratically) in all samples with R2 > 0.86. Moreover, the shortest drying time (42 min), lowest SEC (9.51 MJ/kg), and GHG emission ((4279.74 g CO2 in the combined cycle turbines plant, and 18.16 g NOX in the gas turbine plant) with natural gas for both plants) were recorded for the samples pretreated with blanching while the lowest color changes (13.69) and shrinkage (21.29) were observed in the ultrasonicated samples. Based on the optimization results, a microwave power of 300 W and steam power turbine of 2 mm were the best variables with a desirability of about 80% which resulted in the highest-quality products at the lowest GHG emission.

Biomass is a promising resource for the production of renewable energy, liquid fuels, and chemicals. Microwave pyrolysis is one of the directions of multifunctional conversion of raw materials. In the present work, the effect of microwave power on the characteristics of sawdust pyrolysis is studied. With an increase in power, the maximum yield of combustible gases increased, and a large proportion of the total pyrolysis time included the useful time for the release of gases. An increase in power affected the yield of individual gases non-linearly and on a different scale. The average yield of CO and CO2 remained practically unchanged when the microwave power was increased from 840 to 1760 W. However, with a further increase in power to 2200 W, there was a significant increase in the average yield of CO and CO2 (2.5 and 1.4 times, respectively). An increase in power by 2.6 times contributed to an increase in the average yield of CH4 by 5 times and H2 by 3.8 times. The increased power of microwaves contributed to the degassing of wood and intensification of secondary pyrolysis reactions, which resulted in a decrease in the mass of the solid residue by 5.3 times and a decrease in the liquid product yield by 2.7 times. A comprehensive analysis using MCDA showed that an increase in energy costs with an increase in microwave power is integrally compensated by an improvement in pyrolysis performance. So, when the power was varied from 840 W to 2200 W, the pyrolysis efficiency indicator increased by 1.3–2.2 times, considering the growth in energy consumption.

The study investigated the effects of different microwave vacuum freeze-drying powers (100–500 W) on the emulsifying properties and structural characteristics of egg white protein, which is of great significance in enhancing the added value of EWP and promoting its application. Emulsification analysis revealed that the emulsification performance was significantly influenced by microwave power and reached its maximum at 300 W. Fourier-transform infrared spectroscopy (FT-IR) and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) analyses showed that microwave vacuum freeze-drying treatment altered the secondary structure of EWP without changing its peptide structure. Fluorescence measurements indicated that the maximum fluorescence emission intensity decreased, and the maximum emission wavelength shifted towards blue as the power increased. Particle size, zeta potential, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses showed that the average particle size of EWP reached the minimum value of 1203.66 nm, the absolute value of zeta potential reached the maximum value of 41.35 mV, and the thermal stability was strongest, with a more uniform and loose structure observed at 300 W. Texture profile analysis (TPA) showed that appropriate power treatment significantly enhanced the chewiness and viscoelasticity of egg white protein. Therefore, appropriate power treatment could effectively improve the emulsifying properties and stability.

To reduce thermal processing hazards (TPHs), microwave baking has been extensively used in food thermal processing. In this study, the influence of microwave power and microwave time on the formation of TPHs and their precursors was explored in microwave-baked biscuits. The results indicated that the content of acrylamide, 5-hydroxymethylfurfural, methylglyoxal, and 3-deoxyglucosone increased linearly with the extension of microwave time (2, 2.5, and 3 min) and microwave power (440, 480, and 520 W). There was a significant correlation between the four TPHs. 3-Deoxyglucosone may directly or indirectly participate in the formation of the other three TPHs. The relationship between TPH levels with some heat-induced sensory characteristics was analyzed. The correlation between the sensory characteristics and the content of TPHs is L* > a* > hardness > Water activity (AW). The correlation coefficients between L* value and the four TPHs are −0.950, −0.891, −0.803, and −0.985. Furthermore, the content of TPHs produced by traditional baking and microwave baking under the same texture level was compared. Compared with traditional baking (190°C, 7 min), microwave baking at 440 W for 3 min successfully decrease methylglyoxal, 3-Deoxyglucosone, acrylamide, and 5-hydroxymethylfurfural content by 60.75, 30.19, 30.87, and 61.28%, respectively. Traditionally baked biscuits, which had a more obvious color, as characterized by lower L* value, larger a* and b* values, are more susceptible to the formation of TPHs. Therefore, microwave baking can reduce the generation of TPHs.

Microwave curing technology has been widely used in resin and its composite materials. In order to study its effect for curing unsaturated polyester resin (UPR) composites containing calcium carbonate (CaCO3) filler, this paper first investigated the influence of microwave power and microwave irradiation time on the curing characteristics of UPR. Then, CaCO3 particles were added to the UPR to investigate the microwave curing effect of the UPR composites containing the CaCO3. The results showed that microwave irradiation could heat the UPR sample evenly, and rapidly cause the chain growth reaction, thus greatly shortening the curing time. The curing degree and products of the samples after microwave curing were consistent with that of the thermal curing. The addition of CaCO3 particles could increase the heating rate of the UPR composites, which would accelerate the curing rate of the UPR. However, higher microwave power could lead to pore defects inside the UPR composites with higher CaCO3 content, resulting in a lower strength. Thus, the compactness of the samples should be improved by reducing the microwave power and prolonging the microwave treatment time.

Bi-metallic nanoparticles (NPs) have appeared to be more efficient as antimicrobials than mono-metallic NPs. The fungus Aspergillus terreus-mediated synthesis of bi-metallic Ag-Cu NPs was optimized using response surface methodology (RSM) to reach the maximum yield of NPs. The optimal conditions were validated using ANOVA. The optimal conditions were 1.5 mM total metal (Ag + Cu) concentration, 1.25 mg fungal biomass, 350 W microwave power, and 15 min reaction time. The structure and shape of the synthesized NPs (mostly 20–30 nm) were characterized using several analytical tools. The biological activities of the synthesized NPs were assessed by studying their antioxidant, antibacterial, and cytotoxic activity in different NP concentrations. A dose-dependent response was observed in each test. Bi-metallic Ag-Cu NPs inhibited three clinically relevant human pathogens: Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa. Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus were inhibited less. The DPPH and hydrogen peroxide scavenging activities of the NPs were high, reaching 90% scavenging. Ag-Cu NPs could be studied as antimicrobials in different applications. The optimization procedure using statistical analyses was successful in improving the yield of nanoparticles.

For homogeneous microwave heating in a microwave cavity with multiple 2.45 GHz microwave generators, power‐controlled phase‐shifting mode is proposed in this Letter. The proposed microwave heating system consists of a multimode microwave cavity in which dielectric materials are placed to be heated, four phase‐shifting WR‐340 waveguides for different phase excitation, four 1 kW magnetrons that produce microwave power at 2.45 GHz, and a power supply with a system controller for the magnetron output power controls. Using the proposed power‐controlled phase‐shifting mode, uniform heating distribution is achieved by reducing the hot and cold spots in the microwave cavity. The proposed experiments demonstrated that in comparison to a conventional mode with simultaneous multiple inputs, the proposed mode can achieve an improved heating uniformity of ∼64.4%.

The objective of this work was to study the dehydration of skim cheese through different methods, in particular by hot air, microwave and freeze-drying, in order to assess which of these methods would be more suitable for the development of a new product (cheese snack). For the three processes of dehydration, several temperatures, powers and times were used, respectively. The drying time was optimized to allow the water activity of the final product to be between 0.3 and 0.4. The color and texture of the product obtained by the three processes were evaluated, and the nutritional analysis (protein, lipids, ash) of the product dried by hot air at 52 ºC and by microwave at 750 W and 850 W was performed. The sensory analysis of the microwave dehydrated products was also carried out. The results obtained revealed that the temperature played a relevant role in the drying time and the hardness of the product. In the dehydration by microwave, the power of 850 W resulted in a lower drying time and a better color preservation, but in a high hardness of the samples. Among the three processes studied, the microwave drying was the fastest for the water removal from the cheese.

Electron Spin Resonance (ESR) is a dating technique using the accumulated irradiation energy in minerals under geological environments as the target. The quartz used for isotopic dating is widely distributed, and has an excellent time starting point to record fault deformation. This implies that ESR will become a valuable supplement to isotopic dating. ESR signal intensity is the key factor affecting the accuracy of ESR age, but the influence pattern and degree of different parameters on ESR signal intensity remains unknown. A paramagnetic E' center in quartz from fault zones was taken as the main investigation object. By single factor repeated experimental method, the relationship between 5 parameters of ESR dating and ESR signal intensity was analyzed. The results indicate that microwave power, field modulation amplitude, and scan width are the most important factors affecting ESR signal intensity, however the inserted direction and diameter of the sample tube had a slight influence on measuring the data. The microwave power from 0.02 mW to 0.1 mW (in Fig.1), and the field modulation amplitude from 0.25 Gs to 0.4 Gs can be used as a universal parameter range to precisely measure E' center in fault clay quartz (in Fig.3). Improper scan width was unsuitable for ESR measuring. Before the fine scanning, the pre-scan should be performed under wider scan width and then the proper scan width can be identified. Calculating the average value based on repeated measuring data can help to decrease measurement error effectively. When the proposed parameter range and measuring method are used to measure the E' center signal intensity of fault clay quartz, the ESR measurement precision can be improved remarkably.

At present, the proposed microwave power detection systems cannot provide a high dynamic detection range and measurement sensitivity at the same time. Additionally, the frequency band of these detection systems cannot cover the 5G-communication frequency band. In this work, a novel microwave power detection system is proposed to measure the power of the 5G-communication frequency band. The detection system is composed of a signal receiving module, a power detection module and a data processing module. Experiments show that the detection frequency band of this system ranges from 1.4 GHz to 5.3 GHz, the dynamic measurement range is 70 dB, the minimum detection power is −68 dBm, and the sensitivity is 22.3 mV/dBm. Compared with other detection systems, the performance of this detection system in the 5G-communication frequency band is significantly improved. Therefore, this microwave power detection system has certain reference significance and application value in the microwave signal detection of 5G communication systems.

The purpose of this study was to investigate the effects of microwave power and additives on the microwave-assisted pyrolysis of cotton stalk. Pyrolysis temperature profiles, product yields, and bio-oil components were analyzed. The results indicated that as the microwave power increased, so did the final temperature and heating rate. When microwave power increased from 800 to 1200 W, the yield of the solid residue decreased and gas yield increased, but the maximum bio-oil yield of 26.7% was achieved under a microwave power of 1000 W. All three of the additives (NaOH, Na2CO3, and H3PO4) increased the yields of solid residue and gas, while the yield of the bio-oil decreased. Gas chromatography-mass spectrometry (GC-MS) analysis indicated that the main components of bio-oil from microwave-assisted pyrolysis of pure sample were acetol, furfural, 2-methoxy-phenol, and 4-methyl-2-methoxy-phenol. Sodium hydroxide and sodium carbonate (NaOH and Na2CO3) greatly favor the formation of acetol. Phosphoric acid (H3PO4) remarkably promoted the formation of furfural and 4-methyl-2-methoxy-phenol, while H3PO4 inhibited the formation of acetol.

The aim of this study was to investigate the effects of process conditions as well as ultrasound and microwave pretreatments on shrinkage of potato strips during deep-fat frying process. Ultrasound pretreatment was performed at frequencies of 28 and 40 kHz and microwave pretreatment was conducted at powers of 3 and 6 W/g on the potato slices. Then, the frying process was done at 150, 170 and 190°C for 1, 2, 3 and 4 min. According to the results, ultrasound pretreatment significantly reduced the shrinkage of potato strips. However, microwave pretreatment resulted in a significant increase in the samples shrinkage. In addition, frying time as an important process factor had a significant effect on shrinkage; such that by increasing time, shrinkage was increased. Moreover, the results showed that temperature effect on shrinkage is not significant. Furthermore, six models were presented in order to predict shrinkage considering the process conditions and for the models constants, multivariate models were obtained based on multivariate regression analysis as a function of process conditions (ultrasound frequency, microwave power and process temperature).

The present study investigated the influence of microwave power on the drying kinetics, energy consumption and drying efficiency of green pepper during microwave drying at 180, 240, 300, 360, 420, 480 and 540 W. Seven mathematical models for describing the thin-layer drying behaviour of pepper samples were investigated. The models were compared based on their R2, RMSE and χ2 values between experimental and predicted moisture ratios. By increasing the microwave output powers (180–540 W), the drying time decreased from 9 to 2.5 min. The drying process took place in the falling rate period. The results show that the Midilli model is the most appropriate model for drying behaviour of thin layer pepper samples. A third order polynomial relationship was found to correlate the effective moisture diffusivity with moisture content. The effective moisture diffusivity increased with decrease in moisture content of pepper samples. The average effective diffusivity varied from 8.315 × 10−8 to 2.363 × 10−7 m2/s, over the microwave power range studied, with an energy activation of 14.19 W/g. Energy efficiency increased with increase in microwave power and moisture content. The least specific energy consumption (4.99 MJ/kg water) was at the microwave power of 240 W and the highest (6.80 MJ/kg water) was at 180 W.

When constructing the fast-acting two-channel microwave switch, it is difficult to use p–i–n-diodes due to inertia of processes in such structures at change of control voltage polarity for providing of deep modulation. Under the practical realization of the microwave switches on p—i—n-diodes, the requirements to the operating speed of the output signal and to the frequency range are in conflict with each other. The optimum decision may be to use the bulk (without p—n-junctions) two-electrode semiconductor structures based on the effect of intervalley transfer of electrons (TEDs) and chalcogenide-glass-semiconductors (CGS-diodes) with high operating speed and stability at considerable power levels in the wide frequency band. The paper presents the construction of the two-channel microwave switch in the three-centimeter range of wave lengths based on bulk semiconductor structures having negative differential conductivity (NDC) of N- and S-type, and realizing the functions of peak power modulator on a TED-diode and the switch on a CGS-diode respectively.

U ovom radu opisana je komparacija grupe sekundarnih etalona mikrotalasne snage kao način za održavanje metrološke sledljivosti u nedostatku primarnog etalona mikrotalasne snage. Obavljene su dve komparacije i to sa termopretvaračkim glavama, 2000. godine, a 2002. godine prošireno i na termistorske glave u opsegu frekvencija 18 do 26,5 GHz. / In absence of primary standards for microwave power, a group of microwave power secondary standards was compared as a method of sustaining metrological traceability. The comparison included thermoelectric and thermistor mounts in the frequency range from 18 to 26,5 GHz.

The microwave power is a parameter greatly influencing the rate of heating. Several authors reported on certain differences between the rated power output as a parameter used by oven manufacturers in the labelling of ovens, and the power actually delivered to the heated product. A review of the respective information is given in this article together with the results of own experiments following the influence of the oven type and the heated substance parameters on the power actually absorbed in the substance volume during its heating. As the heated substance, water and solutions of NaCl and sucrose of different concentrations were used. For the heating, four types of domestic microwave ovens and glass and plastic containers, were used. The decreasing of the efficiency of heating with the decreasing volume of the heated substance and a certain relation between the rate of this decrease and the types of oven and of substance was estimated. With the small cavity ovens, a lower rate of the decrease of the absorbed microwave power with the decreasing volume of the substance was found as compared to the large cavity oven. A certain influence of other technical oven parameters is shown in the comparison of the tests results with the ovens of the same rated power and the cavity volume. In addition to the substance volume, also its dielectric properties probably influence the microwave power absorbed in small samples during the heating. No simple dependence can be seen on the basis of the tests results between the type of container used in the tests and the power absorbed in the heated substance.