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The mechanism of biological effects of environmental electromagnetic radiation is still not completely clear. The chelation of biological small molecule peptides with metal ions plays a very important role in human metabolism. In this paper, a special experimental system was designed to measure the conductivity of carnosine and zinc chloride mixed aqueous solutions under different concentration ratios, microwave powers, and temperatures. The experimental results show that, first, different concentration ratios can alter the conductivity change rate of the mixed aqueous solution. The conductivity of the solution always increases under microwave irradiation at a concentration ratio of 1:1. However, the conductivity is reduced by −0.04% with a 1:5 concentration ratio and 6 W microwave power at 10 °C. Second, temperature can alter the conductivity change rate of the aqueous mixture. The higher the temperature, the smaller the conductivity change rate. Third, different microwave powers can alter the conductivity change rate of the mixed aqueous solution. In general, the conductivity change rate increases with an increase in microwave power. Experimentally observed reduction of the conductivity change rate in carnosine and zinc chloride aqueous solution under low microwave power and low temperature indicates that microwaves do affect the chelation of carnosine with zinc chloride. This work provides a new perspective for the mechanism of explanation of microwave biological effects.

This article introduces a polarization-insensitive rectifying surface for 2.4 GHz WLAN band RF energy harvesting. The unit cell of the rectifying surface is formed by combining an interdigital structure with a square ring structure, optimized for high RF harvest efficiency over a wide band. For optimal performance, our design employs a direct matching of the Schottky diodes to the rectifying surface, minimizing signal loss and enhancing rectification effectiveness. To demonstrate the concept, a $4\times 4$ element rectifying surface array was fabricated and measured, yielding a total efficiency of 21% at an incident power density of $2.62~\mu $ W/cm2. The measured total efficiency remains higher than 18.9% over the 2.4–2.57 GHz range, covering the 2.4 GHz WLAN band. Furthermore, the total efficiency remains constant despite variations in the polarization angle of the incident wave. Our design demonstrates a highly efficient rectifying surface for harvesting low-power energy within the 2.4 GHz WLAN band, offering a promising solution for powering wireless devices.

In our previous study, the incoherent combined microwave sources possess a higher water heating rate than a single microwave source. This novel discovery may blaze a new trail in the pursuit of energy conservation. In this paper, a particular orthogonal microwave field device was designed to quantitatively study the effect of incoherent combined microwave heating on 17 solvents. Experimental results indicate that the solvents irradiated with incoherent combined microwaves absorb more microwave energy and experience a faster temperature rise. The multiphysics simulations of water with different microwaves show that the higher heating rate is not caused by the improvement of heating uniformity. In this regard, molecular dynamics simulations of ethanol under the irradiation of incoherent microwave electric fields with perpendicular polarization directions were carried out. The molecular dynamics simulations demonstrate that the main reason for this effect is the higher collision frequency of molecules with incoherent microwave electric fields. This study demonstrates a novel effect of incoherent combined microwave heating and contributes to the development of efficient microwave heating for industrial applications.

Microwave heating is a promising technology widely used to enhance chemical processes in multiphase catalytic reactions. The design of the microwave reactor is crucial for microwave-assisted multiphase catalysis. However, assessing the reactor design’s impact on catalytic performance is often based on experiments and experience. In this study, we propose a method based on multiphysics simulation to evaluate and guide the design and scale-up of microwave cavities. First, we conduct multiphysics calculations by establishing an enlarged microwave reactor model to obtain the heating situation and gas flow stats on the catalyst support. Subsequently, by integrating parameters such as flow rate, temperature, and effectiveness, we construct the effective flow coefficient (EFC) to characterize and guide the reactor’s design quantitatively. Based on this method, we calculated four reactor models with different internal structures and obtained EFC values of 0.17, 0.19, 0.1, and 0.69, respectively. The results show that this method can quantitatively guide and optimize the reactor design from aspects such as the reactor structure, catalyst support structure, reactant feed configuration, and microwave feed configuration. This study contributes to the promotion of scale-up in microwave-assisted gas–solid catalytic reactors.

Energy efficiency has always been an inherent problem of microwave heating. In this work, the higher heating efficiency of the elliptically polarized microwave electric field is investigated via MD simulations, aiming to examine the multidirectional polarization effect during microwave heating. The MD results show that the heating efficiency growth rates of EtOH, AcOH, DMSO, H2O, and DMF are 3.17%, 3.92%, 4.14%, 5.00%, and 27.06% sequentially larger with the elliptically polarized microwave electric field (EF) than those with the linearly polarized microwave EF. Energy analyses indicate that the utilization rate of microwave energy would be increased of the elliptically polarized microwave EF with the same electric field intensities. The higher decay speed of the rotation autocorrelation function curves of elliptically polarized EF presents that the sample molecules do have a more frequent rotational motion to align with the varying polarization directions. Additionally, dielectric properties analysis gave the relation between the heating efficiency growth rate and the loss tangent of the samples. This microwave heating method is expected to be a new route to improve the microwave heating efficiency.

In a multiphysics simulation model based on the finite-element method (FEM), the large spatial scale difference will produce a large number of grids, which makes the simulation impossible. A rapid computing method for multiscale simulation based on transformation optics is proposed to solve this problem. The fine element in the object was expanded to reduce the spatial scale difference in the object by the transformation optics, and the number of grids and the computation time can be reduced. First, we deduce the expansion method for electromagnetic–thermal coupling in stacked objects in free space and the compensation method in the enclosed space. Second, a multilayer microstrip antenna comprising different thickness substrates is used to verify the method. The number of grids and computing time can be reduced to about 60% and 30%, respectively. The simulation results agree well with the experimental results. Finally, we simulate the waveguide filter with fine dielectric rods using the proposed method. The computing time can be reduced to about 40%. The proposed rapid computing method can be used to solve computational problems caused by large spatial scale differences inside the simulation objects.

A novel self-excited atmospheric pressure microwave plasma jet (APMPJ) based on a coaxial line is successfully proposed for the medical treatment. The finite-element method (FEM) is applied to obtain the optimal size of the APMPJ. The plasma parameters, such as electron density and electron temperature, are calculated within 0.1 ms. When the plasma reaches a stable state, the electron density is closed to 1022 m−3, and the electron temperature is calculated to be 1.3 eV. According to the experimental results, the argon plasma jet can be self-excited at an incident power of 20 W, and the gas temperature of the plasma jet is closed to 318 K at an incident power of 15 W. In addition, the air plasma jet can be self-excited at an incident power of 110 W. Finally, the change in the density ratio of hydroxyl (OH) radical to other particles when water vapor is added to the APMPJ at different flow rates is analyzed. It is found that a small amount of water vapor can greatly increase the relative content of OH which is tested by spectrometer.

AbstractThis work aims to improve the uniformity and efficiency of microwave heating. A dual-port simulation model based on the finite element method was built, and two pins were applied to the heating cavity. The impact of dual frequency and pins on the coefficient of variation (COV) and heating efficiency were investigated. The results demonstrated that the uniformity of dual-frequency heating can be improved by 15.4%. Moreover dual-frequency with double pins can maximally increase heating efficiency to 166.7% and the COVvalue can be reduced to 60.2%, compared with single-frequency heating. The heating effect of other materials was also analyzed. The uniform and efficient microwave heating were realized at dual frequency with pins.

Purpose: The purpose of this paper is to present the temporal reflection of electromagnetic waves (EMWs) in simple polar-molecule reactions whose polarization changes with the proceeding of the reactions. Design/methodology/approach: At a temporal boundary, based on the continuity of the electric displacement and magnetic induction, the reflected condition of EMWs is obtained, and the expression of the transmission and reflection coefficients in the reactions is derived. Subsequently, a one-dimensional model is used to validate the reflected condition and expression. Findings: If the time scale of the component concentration variation is greater than the wave period, the polarization of the reactions at a temporal boundary is continuous. The reflection does not happen. On the other hand, when the time scale of the component concentration variation is smaller than the wave period, the polarization is not continuous at a temporal boundary. The impedance of the reactions at the temporal boundary changes and the reflection occurs. Originality/value: The results may be helpful in disclosing the non-uniform distribution of EMWs in chemical reactions. [ABSTRACT FROM AUTHOR]

In this paper, the electromagnetic environment (EME) characteristics on Wangjiang campus of Sichuan University, a typical densely populated urban area, are measured and analyzed. According to the people's daily routine, the EME measurements are performed during daytime, nighttime, weekday, and weekend, respectively. By measuring the electric field (E‐field) values along the main roads on the campus, the maps of E‐field spatial distribution are obtained. Results indicate that the EME on the campus is relatively stable. The probability density functions of three orthogonal components of E‐field are all lognormal distribution and very similar to each other due to depolarization phenomenon and polarization rotation of multipath propagation. Moreover, the total E‐field is also lognormal distribution because of the high linear correlation between the components. In addition, E‐field were also measured over time on three different sites, playground, laboratory, and student dormitory, in order to get time‐varying characteristics of the EME. Results suggest how the people's activities influence on EME. All measurements on Wangjiang campus show that the maximum E‐field value is far below the regulatory exposure limits proposed by the International Commission on Non‐Ionizing Radiation Protection. Electromagnetic environment characteristics on Wangjiang campus of Sichuan UniversityMeasurement of E‐field spatial and temporal distributionThree orthogonal components of E‐field obey lognormal distribution

The ternary transitional metal oxide NiCo2O4is a promising anode material for sodium ion batteries due to its high theoretical capacity and superior electrical conductivity. However, its sodium storage capability is severely limited by the sluggish sodiation/desodiation reaction kinetics. Herein, NiCo2O4double-shelled hollow spheres were synthesized via a microwave-assisted, fast solvothermal synthetic procedure in a mixture of isopropanol and glycerol, followed by annealing. Isopropanol played a vital role in the precipitation of nickel and cobalt, and the shrinkage of the glycerol quasi-emulsion under heat treatment was responsible for the formation of the double-shelled nanostructure. The as-synthesized product was tested as an anode material in a sodium ion battery, was found to exhibit a high reversible specific capacity of 511 mAh g−1at 100 mA g−1, and deliver high capacity retention after 100 cycles.

Environmental pollution and waste of resources caused by the massive accumulation and landfill of plastic waste has been prompting the research considering its reclamation. In this work, a microwave-carbon fiber cloth (CFC) co-ignited cracking strategy is proposed for highly-efficient conversion of polyethylene to hydrogen and high-quality carbon nanotubes conducted in a simple multimode microwave reactor. When FeAlOx@C is used as the catalyst, a hydrogen yield of 64.5 mmol g−1plasticis achieved while biochar powder as the ignitor only give yield to 30.6 mmol H2g−1plastic, demonstrating the superiority of the CFC strategy where the carbon ignitor has little contact with the reactants. Further, FeAlOx@C treated by air plasma with rich oxygen vacancies is used as the catalyst. The yield is enhanced significantly, especially at low microwave power, resulting in a hydrogen yield of 67.3 mmol g−1plasticat a microwave power of 900 W, which was the highest as far as we know in the literature under direct catalytic cracking processes. Notably, the integrity of the CFC piece is maintained well, and is highly recyclable. Numerical simulation suggests that the position of CFC plays a key role in initiating the enhanced catalytic cracking process enabled by direct microwave heating.

ABSTRACTTo improve the drying efficiency of intermittent radio frequency (RF-13.56 MHz) heating porous media with a coaxial cell, a multi-physics model was built to simulate two cases and analyze the influence of power and sample height on the heating effects. Good agreement was found between experimental data and predicted values. However, a transformation was found when the temperature of sample reaches about 70–74 ºC in the experiments, therefore, the proposed theoretical model is not valid after this point. Sensitivity analysis to various parameters was also performed to identify the critical ones aimed to provide some guidelines for further improving the efficiency of electromagnetic wave heating porous media.

Continuous-flow microwave reactors find widespread application in chemical production. However, dynamic changes in the dielectric constant of reactants result in a low microwave energy efficiency. This paper reveals a circular waveguide developed using a meta-surface unidirectional propagation of microwaves. This waveguide was integrated into a continuous-flow heating system that efficiently heats materials with varying dielectric constants. A multiphysics model incorporating electromagnetic, fluid heat transfer, and chemical engineering has been built to analyze the microwave heating performance under different loads. Based on simulation and experimental findings, the meta-surface can achieve an energy efficiency of over 90% for loads with dielectric constants from 10 to 80. Moreover, a continuous-flow heating experiment conducted for biodiesel production indicated that meta-surfaces can enhance the heating efficiency by over a quarter. This research presents a promising approach toward efficient continuous-flow microwave heating, which can potentially revolutionize large-scale chemical production in industry.

The molecular mechanism of the microwave nonthermal effect is still not clear. This work investigated the spatial orientation and kinetic energy of active site collision of carnosine, a natural bioactive dipeptide, under the weak microwave irradiation using the molecular dynamics simulation. Our results showed the influences of the temperature, microwave intensity, microwave frequency, and microwave polarization mode (linear polarization and circular polarization) on the spatial orientation and kinetic energy of active site collision of carnosine. First, under the constant intensity and frequency of linear polarization microwave irradiation, the increment of the collision probability between the 6N atom of carnosine and the 28H atom of the other carnosine at effective space angle decreases from 85.0% to 3.5% with increasing temperature. Second, with the increase of microwave intensity, the change of spatial orientation and kinetic energy becomes more and more significant. However, the change of circular polarization microwaves on the spatial orientation and kinetic energy of collision is weaker than that of linear polarization. Third, under the constant intensity of linear polarization microwave irradiation, the collision probability between the 6N atom and the 28H atom at effective space angle decreases from 70.2% to 14.7% with increasing frequency. Finally, under the microwave polarization, the spatial orientation and kinetic energy of molecular collision are changed, which is summarized as the microwave postpolarization effect (MWPPE). The dependence of MWPPE on temperature, microwave intensity, microwave frequency, and polarization mode is very complicated. In the end, this effect can provide a new insight into the molecular mechanism of the microwave nonthermal effect.

Microwave nonthermal effect in chemical reactions is still an uncertain problem. In this work, we have studied the spatial orientation and kinetic energy of reactive site collision between benzyl chloride and piperidine molecules in substitution reaction under microwave irradiation using the molecular dynamics simulation. Our results showed that microwave polarization can change the spatial orientation of reactive site collision. Collision probability between the Cl atom of the C–Cl group of benzyl chloride and the H atom of the N–H group of piperidine increased by up to 33.5% at an effective spatial solid angle (θ, φ) of (100∼110°, 170∼190°) under microwave irradiation. Also, collision probability between the C atom of the C–Cl group of benzyl chloride and the N atom of the N–H group of piperidine also increased by up to 25.6% at an effective spatial solid angle (θ, φ) of (85∼95°, 170∼190°). Moreover, the kinetic energy of collision under microwave irradiation was also changed, that is, for the collision between the Cl atom of the C–Cl group and the H atom of the N–H group, the fraction of high-energy collision greater than 6.39 × 10–19J increased by 45.9 times under microwave irradiation, and for the collision between the C atom of the C–Cl group and the N atom of the N–H group, the fraction of high-energy collision greater than 6.39 × 10–19J also increased by 29.2 times. Through simulation, the reaction rate increased by 34.4∼50.3 times under microwave irradiation, which is close to the experimental increase of 46.3 times. In the end, spatial orientation and kinetic energy of molecular collision changed by microwave polarization are summarized as the microwave postpolarization effect. This effect provides a new insight into the physical mechanism of the microwave nonthermal effect.

This paper presents a novel technique for determining the mode content in a multimode waveguide from the radiation pattern measurements. The technique employs the Genetic Algorithm (GA) for determining the mode content in the waveguide from the measured pattern and a numerical method for simulating radiation patterns for the modes propagating in the waveguide. By numerical experiments, we validate the feasibility and effectiveness of the proposed technique, and illustrate its sensitivity to the number of observation points and random noise in the measurement.

In a microwave field, the dielectric properties, molecular structures, and hydrogen bonding dynamics of glycerol in its mixtures with water were determined by the molecular dynamics simulation method. The dipole–dipole correlation of glycerol is linked to the field intensity of microwaves. The results show that as the field intensity is increased, even glycerol in the second coordination shell can become correlated with each other. The structures of up to 35 glycerol molecules are observed. More than that, it was observed that lifetimes of glycerol–glycerol hydrogen bonds were prolonged, while the average hydrogen bond number was also increased. Besides, the structures in a strong microwave field mimic the weak C–H⋯O hydrogen bonds seen in high-glycerol concentration mixtures, yet the concentration is lower. These results indicate that with the assistance of the microwave field, glycerol molecules become concentrated and are more likely to establish stable interactions with others. As a consequence, the spherical clusters composed by glycerol molecules in our nanosheet synthesis experiment are easier to form.

Some measurable solution properties related to the reactant concentration, such as light density, conductivity, electromotive force, and pressure, are usually used to measure the rate constant of a chemical reacton. In this paper, the effective permittivity of a solution, where the acetone iodation reaction is carried out, has been measured and proposed to be used to calculate the rate constant of reaction. The rate constant is compared with the result calculated by using the conductivity. Both of them are in satisfactory agreement and approach the theoretical values.