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A K-band (18-26.5 GHz) lens antenna that scans two-dimensionally is introduced. The novelties lie in three aspects: (a) The two-dimensional beam scannability is achieved by deploying the feed in a focal-shifted manner. (b) Feed of nonuniform aperture is applied to compensate the gain loss due to aperture tapering from the lens. (c) It takes the form of a fully 3D printed lens antenna, in which the metallic and dielectric 3D printing technologies are used for the lens and feed fabrication respectively. The antenna features high gain, good matching and two-dimensional beamscanability.

A novel microwave heating method with rotary radiation structure has been proposed to improve heating uniformity. Through time division of the whole heating process, static heating assumption of each time step and temperature inheritance between time steps, a simulation model has been built and computed based on the finite element method combined with programming. A quantitative validation of simulation results has been performed with physical experiments. Heating uniformity and heating efficiency of the proposed method has been compared with those of two traditional methods, by which a potato slice is heated with a turntable and heated statically. The results show that the rotary radiation structure has an obvious superiority. What is more, influences of positions of the waveguide that feeds microwave and its placing directions of the proposed method have also been discussed.

A compact circularly polarized (CP) rectenna based on wide-slot antenna is designed at 5.8 GHz. The feedback wide-slot antenna is used for its broad band, easy-to-integrate circuitry, simple structure, and low sidelobes. The designed receiving antenna has a bandwidth of 31.8%. In order to minimize the profile of the rectenna, the rectifier is integrated on the back side of the substrate with a matching circuit and a dc-pass filter. It features stable conversion efficiency on three azimuthal planes. The maximum efficiency of 66.2% and an output dc voltage of 6.33 V have been measured with a 900 Ω load at the power density of 11.4 mW/cm2. A 5 × 5 rectenna array is built for large physical aperture and increased output power. The maximum conversion efficiency of 62% is observed with the array. Taking the advantage of immunity to misalignment of the CP antenna, the proposed rectenna and array are suitable to be used in mobile applications for wireless power transfer.

This paper proposes an S-band microwave transmitting system based on four-way master–slave injection-locked magnetrons, which has the advantages of low cost and high efficiency. The transmitting system consists of a microwave generator and an antenna array. The microwave generator provides four-way excitations with equal phases and amplitudes to the antenna array, where a radial divider is applied to produce and control the four-way injected signals to lock the slave magnetrons. The antenna array includes four pyramid horns and two layers of artificial materials with 2-D periodic corner-truncated square slots, which are arranged to enhance the gain and suppress sidelobes. The transmitting system is fabricated and measured. Experimental results show that the microwave generator is able to produce four-way excitations with the phase differences less than 12° and the amplitude errors less than 3%. The antenna array provides a gain of 27.2 dB, sidelobe levels less than −10 dB, and reflection coefficients less than −15 dB. The whole system operates stably at 2.46 GHz with a transmitting power of 3.5 kW.

A high power gain magnetron amplifier with output phase control based on load–pull characterization has been developed. The equivalent resonant cavity method was first introduced to facilitate the proposed magnetron amplifier system as a basic injection model, and the system behavior was qualitatively evaluated based on Alder’s equation. It is the first time that a magnetron has been locked at a 58-dB gain. The magnetron amplifier shows an enhanced power-added efficiency of 72.0%, wide output phase control range, and 18.5-MHz bandwidth at a ratio of the output to the input power of 45 dB. This is the first time a successful magnetron output phase control based on load–pull at a power gain of 45 dB has been demonstrated. The magnetron output spectra were fully synchronized with a reference signal and the phase noise of the magnetron amplifier reached −106.3 dBc/Hz at an offset of 1 kHz. An output amplitude stability of 0.01 dB (peak to peak), a phase stability of 0.5° (peak to peak), and a high-efficiency dual 1-kW magnetron amplifier coherent-power combination based on the load–pull characterization was achieved. To the best of the authors’ knowledge, this is one of the highest power gains and phase noise performances ever reported for an S-band injection-locked magnetron with a power output of over 1 kW.

A compact circularly polarized rectenna with harmonic suppression for wireless power transmission at 5.8 GHz is proposed in this letter. The substrate integrated waveguide structure is adopted for enhanced gain, unidirectional patterns, and surface wave suppression. A rectifier, which consists of a matching network, a diode, and a dc-pass filter, is integrated with the antenna at the back side. The proposed rectenna is fabricated and measured. It features 6.9 dB gain, 0.67 dB axial ratio, and 30 dB return loss. The conversion efficiency is 65.87% with a 700 Ω load. A rectenna array is also built for an increased aperture. It shows 61.49% conversion efficiency with 650 Ω load in measurement. Both the rectenna and array are satisfactory choices for wireless power transfer usage.

Current microwave drying of food product models have generally neglected mass transfer physics, which have resulted in higher predicted temperatures within the food matrix. It is necessary to inclu...

This letter presents a novel dual-frequency single-slot antenna in Ka-band based on a substrate integrated waveguide (SIW). From the view of an SIW resonator, the single-slot cuts currents of the TE101 and TE102 mode in two frequencies, respectively, which leads to a dual-frequency performance. In addition, the difference between two resonance frequencies may be tuned by varying the length of the SIW, which changes the resonant frequencies of the two modes. Three antennas operating from 25.3 to 30.7 GHz with gain greater than 6 dBi are designed and fabricated. Simulated and measured results of the antennas are presented as well. The results show that the proposed antennas achieve stable tunable dual-frequency performance, which may be applied to a Ka-band communication system.

Microwave heating has been widely used in various fields during recent years. However, it also has a common problem of uneven heating. In this paper, a novel method of selected frequencies is proposed to improve the heating performance. On the basis of integral equation theory, the heating uniformity on small changes in microwave frequency is studied analytically. The results show that the heating performance depends highly on microwave frequencies. Due to the fact that some frequencies should contribute more to improving heating performance than others, the proposed method employing the selected frequencies during the heating process. The Finite Element Method (FEM) is used to simulate the heating process and assess the performance. Results show that frequency-selected method can improve heating uniformity and heating efficiency effectively, which is also verified by experiment.

For the nonlinearly phenomena on the dielectric properties of dimethyl sulfoxide (DMSO)–ethanol mixtures under a low intensity microwave field, we propose a conjecture that there exist some abnorma...

Elements in both translation and rotation such as the screw propeller are widely applied to improve microwave heating uniformity. However, it is challenging to numerically model this heating process due to the difficulties in dynamic meshing for the moving elements. Our previous transformation optics method will be also burdensome to use in this case because it is very difficult to get the permittivity and permeability tensors. In this letter, a mesh-free numerical calculation based on a smoothed particle method is proposed to solve this complicated case. The proposed method uses smoothed particles to replace the meshes. Thus, the motion of the elements can be replaced by the motion of the particles and the dynamic meshing process can be avoided. A 2-D model is computed and the results are compared with those calculated by the finite element method. Good agreements are achieved.

It is popular to use moving elements to improve heating uniformity during microwave heating under some situations. However, it is still a challenge to simulate moving elements during microwave heating due to the complexity of mathematical modeling. In this paper, a novel continuous algorithm based on implicit function and level set methods is developed to compute this heating process. By introducing the implicit function and level set methods, the moving region’s properties are set as a function of space coordinate and time, which means that the movement of the elements is represented by the variation of the parameters. In addition, with the coordinate transformation, the coupling process of electromagnetic field and heat transfer in microwave heating can be performed. A 2-D applicator model and a 3-D applicator model with a rotating turntable are used to illustrate the proposed method in detail. Experiments are also conducted to testify the validity of the proposed method. The results obtained by the proposed method are in accordance with those obtained by experiments. Moreover, compared with conventional methods, the proposed method is more accurate and efficient.

In this letter, a microwave rectifier with a wide input power range is presented by proposing a self-tuning impedance matching (STIM). The STIM consists of a varactor reversely biased by the output voltage of the rectifier to compensate the variation of the input impedance caused by the input power, so that impedance matching is obtained over a wider input power range. For validation, the proposed rectifier at 2.4 GHz was designed and implemented. The experimental results show that the RF-dc power conversion efficiency maintains over 50% and 70% within the input power ranges of 2.5–25.5 dBm and 11–24.5 dBm, respectively. Compared with the counterpart without the STIM, an improvement of 7.2 dB in terms of the input power range when the reflection coefficient is less than −10 dB was successfully demonstrated.

The nonlinear magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics subjected to a strong alternating current (ac) magnetic field is studied according to the reaction–diffusion equation. The general nonlinear response is evaluated via the perturbation theory. An analytic equation of nonlinear magnetization is derived based on Legendre function. Numerical calculations are carried out, and the results show that both the magnetization and the probability distribution decrease with the reaction process due to the consumption of the reactants. Both the probability distribution and the magnetization are affected by the anisotropy, the reaction rate and the field energy.

Making samples moving during microwave heating is popular way to improve the heating uniformity. However, the common methods, e.g. using turntable and conveyor belt, can only make samples move in one plane, resulting in limited effect on improving the heating uniformity. In order to improve the uniformity of microwave heating in both horizontal and vertical directions, a rotary lifting turntable is used to drive the sample to rotate and lift during heating in this work. To observe the improvement of heating uniformity caused by the rotary lifting motion, an algorithm based on level set methods and implicit function are used to model the process. The electromagnetic field distribution during the heating process obtained by the model is verified by the discrete locations. The transient-temperature of three points and the spatial temperature profile obtained by the model are verified by the experiments. With this model, the heating effect of samples in rotary lifting motion is compared to that of samples only in rotary or lifting motion. The results show that the heating effect of the samples in rotary lifting motion is better than that of most of the samples in static state and single motion mode. In addition, influences of rotating speed, lifting speed, sample properties, and diameter of spiral motion on the heating effect is also analyzed. Since the proposed motion mode is aimed to change the horizontal and vertical position of the sample in the electromagnetic field to make the sample absorb microwave uniformly in all directions, it can be applied to all kinds of microwave cavities regardless of geometric shapes.

As the problems of electromagnetic pollution and interference are becoming increasingly serious, the development of electromagnetic absorption materials with a high absorption capacity and broad absorption bandwidth are stringently needed. In this work, an N-doped 2D carbon/Ni complex is synthesized through direct microwave irradiation on a mixed solution of nickel nitrate, urea, and agarose under N2. The electromagnetic absorption performance can be tuned by controlling the Ni content. Specifically, minimum reflection loss values (RLmin) of −65.5 dB at 15.8 GHz with an effective absorption bandwidth (EAB) of 4.2 GHz at a sample thickness of 1.47 mm, and −55.4 dB at 11.8 GHz with an EAB of 3 GHz at a sample thickness of 1.92 mm can be obtained. The outstanding performance of electromagnetic absorption is attributed to the multiple polarization relaxation processes and the synergistic effect between 2D carbon sheets and Ni particles.

Moving objects are widely applied in microwave heating process for improving heating uniformity. In order to improve the heating effect, various moving objects with complex shapes will be used in microwave heating. However, for objects with irregular shapes, it is difficult to model the object movement due to the difficulty of characterizing the object's boundaries. In this paper, by using Arbitrary Lagrange Eulerian (ALE) method to track the object movement, the position of the object is expressed by a time-varying implicit function. The impact of the moving object on the electromagnetic field distribution is therefore represented by the change of the implicit parameter. Meanwhile, after the heat source is transformed back to the initial position by a coordinate transformation method, the calculation of the heating process of the moving object can be realized in a fixed mesh structure, thus re-meshing is avoided. A 2-D model and a 3-D model with rotating objects in irregular shapes are used to illustrate the proposed method. Experiments are conducted to testify the validity of the proposed method. Good agreements have been obtained. Moreover, the results show that, for dealing with the cases with moving objects in complex shapes, this method is much more accurate and efficient than the ALE-remeshing method.

Currently, microwave energy is utilized for many diverse industrial applications because of its various advantages including its eco-friendliness. Low-cost, high-efficiency, and high-power industrial microwave sources are in urgent demand. In this paper, we propose a low-cost quasi-coherent power-combining system based on a combination of two magnetrons. We have analyzed and built a low-loss waveguide-based applicator combined with specific phase. This system utilizes the coupling of the combiner to quasi-lock the slave magnetron. A waveguide phase shifter lies in the slave magnetron branch to adjust the phase difference between the master and slave magnetrons’ signals to achieve high resultant efficiency. Based on theory, the phase difference between the master and the injected slave magnetrons has been numerically calculated and analyzed. The phase difference changes periodically when the slave magnetron is quasi-locked to the master magnetron and the periodicity increases with the injection ratio. Experimental results show the resultant efficiency of the proposed system can reach as high as 92% when using several suitable waveguide components. The investigation also provides guidelines for further microwave power combination systems with multiple sources.

The ternary transitional metal oxide NiCo2O4 is 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, NiCo2O4 double-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−1 at 100 mA g−1, and deliver high capacity retention after 100 cycles. Electronic supplementary material The online version of this article (doi:10.1007/s40820-017-0164-2) contains supplementary material, which is available to authorized users.

To solve nonuniform heating when microwave energy is applied in a continuous-flow applicator, a microwave heating system with a screw propeller is designed. By introducing the implicit function and level set methods, the electromagnetic heat source input into the temperature field is updated with the rotation of the screw propeller. Combined with Arbitrary Lagrangian-Eulerian Formulation (ALE) machinery, the temperature distribution in the heating process is obtained. Water is taken as the sample in the experiment to verify the computational model. By using the proposed model, we also calculate the temperature distribution of two other commonly used liquids (ethylene glycol and glycerol). To analyze the effect of a screw propeller on heating uniformity, the temperature distribution of the cases with a screw propeller is quantitatively compared to that of the cases without a screw propeller.

In this study, a substrate integrated waveguide (SIW) combined with complementary split-ring resonator (CSRR) structure is proposed for high-sensitivity measurement of complex permittivity of low loss material at 2.45 GHz. The simulated results demonstrated that the small changes can be sensed through loading the CSRR structure on both sides of SIW. Then, the experiments are performed on various dielectric samples to validate the proposed structure by measuring the particulate samples with different moisture contents and solution samples in different mixed volume ratio. The measured results show that the sensitivity of the proposed SIW with CSRR structure is always higher than the structure without CSRR. Furthermore, neural network based on actual experimental scattering parameters is used for obtaining the permittivity of samples under test. The experimental values agree well with the theoretical values, and the relative errors of e ′ and e ′ ′ are

The measured permittivity of binary liquid mixture with hydrogen bonds is larger than that of any component at some proportions or at some frequencies, which is not accurately consistent with Bruggeman's formula. Mathematical analysis about this phenomenon was made and compared with experimental data, the results indicates that there is a limitation of Bruggeman's formula about liquid mixture. Furthermore, a correction term was introduced by Debye relation model about binary liquid mixture with 1 hydrogen acceptor and donator. The numerical results obtained from modified Bruggeman's formula agrees approximately with experimental results.

A 3-D particle-in-cell simulation model of a commercial industrial heating magnetron is developed as a guide for improving a fixed-output-power magnetron. After this improvement, the magnetron is transformed into a 20-kW power-adjustable phase-locked magnetron, which can then be injection-locked with tunable power output. For the first-time ever, the output power of the injection-locked magnetron is continuously tuned from 2 to 19 kW. This large-power magnetron is both phase and amplitude controlled, and is useful for the coherent power combining of multiple magnetrons. The magnetron frequency pushing effect, which affects the injection-locked frequency range of the phase-locked magnetron, is observed in both simulations and measurements. In the injection-locking experiments, the locking bandwidth varies from 11.7 to 2.4 MHz when the output power is tuned from 5 to 19.1 kW and the injection power is kept at 120 W. Moreover, the center frequency of the phase-locked magnetron increases with increasing output power.

Moving elements have been widely used to improve heating uniformity in microwave applicators, such as rotating turntables and mode stirrers. However, it remains a challenge to compute the heating process due to the difficulty of meshing the element’s dynamic locations. In this paper, we propose a novel algorithm to solve this problem accurately and efficiently. Being surrounded by moving elements with a time-varying anisotropic layer on the basis of transformation optics, the electromagnetic field inside applicators can be computed with consideration of continuous motion of moving elements. A 2-D applicator model with a rotating turntable is used to illustrate the proposed algorithm in detail. Furthermore, we also compute the heating process of a practical 3-D applicator model with a rotating turntable. Compared with the conventional method, the proposed algorithm is more efficient and accurate. The computational results are in good agreement with experiments.

To 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.

Phase-control precision is important for applications of magnetrons in the microwave source array. Here, experimental results use a 20-kW $S$ -band continuous-wave magnetron to investigate the phase deviation of large-power phase-locked magnetrons. For the first time, the phase deviation of a 20-kW magnetron controlled through an externally injected signal was studied. The phase deviation of the injection-locked magnetron output worsened gradually, the greater the difference in frequency of the injected signal (with the same injection ratio) from the center of magnetron injection-locked bandwidth was. When the injected power was maintained at 150 W and the magnetron output was at 19 kW, the maximum phase deviation was varied from approximately 1° to 6° with frequency tuning. In addition, the phase deviation of the phase-locked magnetron decreased as the injected signal power increased at a given frequency.

Microwave nondestructive testing (NDT) technology developed rapidly, but crack detection in metal surface is facing many troubles, such as hard quantitation and low sensitivity. To solve these problems, this letter proposes a two-cell array waveguide microwave NDT probe with an array of split-ring resonators which operates at 12.5 GHz. It detects quantitatively tiny crack (as low as 0.5 mm) in metal surface. Maximum difference between simulation and experimental results is just 9%. Result shows that the peak distance of $S_{21}$ has a sensitive and quantitative link with the width and depth of crack. It is shown that the probe is capable of determining the location and dimension of surface cracks of a few millimeter depths and widths.

High-temperature sodium ion batteries (SIBs) have drawn significant heed recently for large-scale energy storage. Yet, conventional SIBs are in the depths of inferior charge/discharge efficiency and cyclability at elevated temperatures. Rational structure design is highly desirable. Hence, a 3D hierarchical flower architecture self-assembled by carbon-coated Na3 V2 (PO4 )3 (NVP) nanosheets (NVP@C-NS-FL) is fabricated via a microwave-assisted glycerol-mediated hydrothermal reaction combined with a post heat-treatment. The growth mechanism of NVP@C-NS-FL is systematically investigated, by forming a microspherical glycerol/polyglycerol-NVP complex initially and then converting into flower-like architecture during the subsequent annealing at a low temperature ramping rate. Benefiting from the integrated structure, fast Na+ transportation, and highly effective heat transfer, the as-obtained NVP@C-NS-FL exhibits an excellent high-temperature SIB performance, e.g., 65 mAh g-1 (100 C) after 1000 cycles under 60 °C. When coupled with NaTi2 (PO4 )3 anode, the full cell can still display superior power capability of 1.4 kW kg-1 and long-term cyclability (2000 cycles) under 60 °C.

Conventional microwave heating has serious problems such as non-uniform heating and low efficiency. A novel magnetron microwave sweep frequency heating method is proposed to improve microwave heating uniformity. In this method, the frequency-sweeping signal is injected into the magnetron by the injection frequency-locking technique, and the microwave sweep frequency heating of the magnetron is realized. In this paper, a complicated injection frequency locking system is given and analyzed and a multiphysics calculation model based on the finite element method for electromagnetic waves and heat transfer is established. The calculation of microwave sweep frequency heating is realized by the combination of COMSOL and MATLAB. The results show that the sweep frequency heating has an obvious superiority. An experiment is carried out to verify the simulation results. The simulation results are in agreement with the experimental data. Moreover, the effect of sweep bandwidth and sweep interval on heating uniformity is discussed.

For the discharges sustained by the travelling electromagnetic waves, the wave propagation characteristics are of great importance to discharge maintenance and stability. This study aims to investigate the propagating electromagnetic modes of the travelling wave in a cylindrical discharge tube bound by a metallic enclosure based on a microwave plasma torch. In certain particular circumstances, it is found that the cylindrical discharge tube with metallic enclosure is able to change from a one-conductor circular waveguide to a two-conductor-like coaxial waveguide. Such a change allows the travelling wave to propagate in the transverse electromagnetic mode, which has rarely been noticed before. Regarding this transition, a new criterion is proposed to determine the formation of the two-conductor-like waveguide structure. Existence conditions of different propagating modes of the travelling wave are further discussed with respect to different glass tube wall thicknesses and dielectric properties. The results indicate that it is possible to control the propagating modes of the travelling wave for different purposes by choosing a proper glass tube.

A 2450-MHz microwave-induced room-temperature atmospheric-pressure plasma jet (RTAPPJ) based on a coaxial structure is proposed for applications of plasma biomedicine. This device is a simple structure with small size, low-power requirement and high controllability. It can induce an argon discharge at atmospheric pressure with as low as 15-W microwave power. The optical emission spectrum of the RTAPPJ shows various highly reactive radicals such as OH and O. The appropriate operation condition can reduce the temperature at the downstream of the flame to be around 30 °C. This portable device is designed to be suitable to manipulate different medical treatments.

With the arrival of the information age, the electromagnetic energy in space increases constantly, resulting in the influence of electromagnetic waves on the charged aerosol particles in the environment which should be taken into account. Here, a numerical coupling method based on temporal and spatial scales is proposed to solve the difficulty in obtaining the trajectory of particles under the action of high-frequency electromagnetic waves. In the temporal scale, two constant forces with linear relationship are used to equilibrate the electromagnetic field forces under different conditions, however the above-mentioned equivalent method has the space limitation; in addition, on the spatial scale, the model with larger geometry should be divided into multiple basic modules spatially, the domain division method is adopted and due to the above method it can be used well in the basic module. Verified the correctness through the comparison of the results, and compared with the traditional method, the above method greatly reduces the computational complexity. Some interesting results were obtained by calculating the modulated waves with the above method, which indicate that special forms of electromagnetic waves will significantly affect the motion of particles.

Gas flow plays an important role in determining the discharge properties in microwave plasma torches sustained by the propagating surface wave. This paper aims to investigate the gas flow effects on the plasma column length, the surface wave propagation, and the heavy species temperature in a surface wave plasma torch operated at atmospheric pressure. The steadystate discharges of pure argon gas at atmospheric pressure under different gas inflow rates in the plasma torch are characterized by an improved 2-D axisymmetric fluid model. The obtained results demonstrate that increasing the gas inflow rate is able to decrease the surface wave propagation distance, accelerating the contraction of the plasma column length. The discharge instability is found to be motivated by the disappearance of the sustaining surface wave at high gas inflow rates. Besides, a temperature drop of about 64 °C is observed at the temperature-maximum point of the glass tube with an increase in the gas inflow rate from 1 to 16 L · min -1 . Therefore, for the surface wave plasma torch operated with only the axial gas flow, increasing the gas inflow rate cannot solve the glass overheating problem.

Two-dimensional (2D) nanostructures, though promising in energy storage, suffer from aggregation and subsequent deterioration of performance in practical applications. Hence, assembly of 2D nanostructures into three-dimensional (3D) architectures is highly desirable. Here, we report a microwave-assisted approach to the controllable synthesis of 2D materials with tunable 3D structures simply by adjusting the ratio of water/ethylene glycol (H2O/EG). Novel flower-on-sheet 3D hierarchical structures of nickel cobalt double hydroxide (NiCo LDHs) are obtained at EG content of 40%, while microspheres and 2D nanosheets are obtained when the EG content is 0% and 75%, respectively. We propose that under microwave irradiation, EG molecules disperse the nuclei and facilitate the initial formation of 2D sheets. Subsequently, the dominating hydrophobicity of the assembling results in the formation of nanoflowers on the sheets. When tested as electrode materials in supercapacitors, the flower-on-sheet NiCo LDH exhibits superior capacitance (1187.2 F g−1 at 1 A g−1), good rate capability (71% retention at 30 A g−1), and high stability (only 0.3% cyclic decay per cycle with respect to the first charge capacitance), which is ascribed to that ‘sheet’ could act as buffer substrate while ‘flower’ expose more active site. Our results demonstrate an energy-saving and one-pot approach for controllable construction of 2D derived 3D nanostructure that can be applied in next-generation energy storage materials. This work was supported by the National Natural Science Foundation of China (Grant No. 61801314), National Natural Science Foundation of China (Grant No. 61731013), State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (Grant No. KF2016-26), and National Natural Science Foundation of China (Grant No. 61501311). The authors also appreciate the technical support for Materials Characterization from The Analytical & Testing Center of Sichuan University.

The slight electrical conductivity variations of sodium chloride aqueous solutions under the microwave field have been found in experiment, but the mechanism is still unclear. By applying molecular dynamics simulations, the number of water molecules in the hydration shells of sodium are examined quantitatively, we demonstrate that the outer water molecules of shell are stripped away due to the oscillations and collisions among water molecules under the microwave field, this is a microwave desolvation effect. By further study on calculating diffusion coefficient of ions, the electrical conductivity of solutions has been estimated. The result showed that as the diffusion coefficient increased by the desolvation effect, the electrical conductivity of solutions slightly enhanced. The electrical conductivity of solutions at different temperatures and concentrations agree with the measured results in the experiment.

In practical chemical applications, in order to improve the microwave heating uniformity, moving elements, such as mode stirrers, turntables and conveyor belts, have been widely used as an easy way to implement. However, different moving elements may have different shapes, modes of motion and moving speed, which makes the simulation of the heating process very difficult. In this paper, a stepping algorithm based on implicit function and level set method is proposed to simulate the microwave heating process of multi-component with unequal moving speed. The accuracy of the algorithm is verified by discrete method and experiments. Moreover, the model was used to analyze the heating process with different components at different positions and speeds. The effect of different materials of mode stirrers and shapes of heated sample on heating process were also compared. The researches show that the proposed model can effectively improve the heating uniformity and heating efficiency.

This paper investigated the influence of gas humidity (1%, 3%, 8%, 10%, and 12%) on the characteristics of a microwave-induced atmospheric plasma jet. The plasma discharge was generated by a microwave solid-state source with a H2O–Ar mixture gas flow of 8.1 L/min. The variation in energy efficiency, O and OH concentrations, rotational temperature of heavy species, shapes of plasma plumes with different humidities, and microwave input powers were recorded and analyzed. The results showed that the concentrations of O and OH increase monotonously with gas humidity at higher input powers while they fluctuate with gas humidity at lower input powers. With an increase in the H2O/Ar ratio from 1% to 12%, the energy efficiency of the plasma generator decreases, and the plasma plumes become shorter and thinner. The rotational temperature of plasma at the nozzle also showed positive correlation with increasing humidity. Adding more input power would make all the values of these parameters increase. This paper is supposed to be helpful for the research of the interaction mechanism of mix gas plasma and microwave power and for improving the effect of plasma treating biomedical materials.

To describe the anomalous dielectric relaxation of reaction in space- and time-dependent electric field, we derive the possible kinetic equations for describing the distributions of A and B particles in a simple reaction A → B based on the biased continuous time random walk, when the jumping probabilities are evaluated after or before the waiting time, respectively. Different reaction—subdiffusion equations are derived for different cases, in which the properties of A and B particles are the same or different. The reaction and subdiffusion terms can be decoupled if the past is forgotten when B particles are converted by A particles. According to the corresponding kinetic equations in the spherical coordinates, the dielectric polarization of the reaction is derived. By comparing the different expressions of the polarization, it is found that the reaction–subdiffusion equation based on the jumping probabilities, which are independent of time and evaluated before the waiting time, is more reasonable to describe the dielectric relaxation process in the chemical reaction.

The microwave non-thermal effect is still a controversial issue. Here, the influence of weak microwaves on the spatial collision and energy distribution of water molecules is studied by the molecular dynamics simulation. The results show that the polarization of microwaves makes the change of spatial collision and energy distribution. The spatial collision probability of water molecules increases obviously in the direction of electric field and the proportion of high energy molecules decreases while the proportion of intermediate energy molecules increases. This shows the constrains of microwave fields on the water molecules, and these consequences would be helpful to understanding the microwave non-thermal effect and the mechanism of microwaves accelerating chemical reactions.

Microwave power combining based on dual 15-kW continuous-wave (CW) magnetrons in S-band is presented. The injection locking on 15-kW CW magnetrons has been successfully accomplished. The phase-locking bandwidth of each magnetron reaches 5 MHz with an improved dc power supply. Meanwhile, phase jitters are measured and analyzed briefly. The injection-locked 15-kW magnetrons have stable magnitude and tunable locked phase, which are suitable for coherent power combining. A dual-magnetron microwave power combining system has been designed and developed with an automatic phase controlling mechanism. The microwave power combining efficiency is higher than 95%. It is the first time to demonstrate a successful microwave power combining of dual 15-kW S-band CW magnetrons. The system will find industrial applications in producing diamond film from microwave plasma chemical vapor deposition. Large-power and high-efficiency microwave sources based on power combining from magnetrons are good candidates for industrial applications.

As a microwave plasma excitation structure, the tapered waveguide is mostly used in some industrial applications. A novel ridged waveguide is proposed in this paper. The fluid approximation method is applied here to simulate the excitation of argon plasma within 1 s at atmospheric pressure. Some physical parameters, such as the electron density, electron temperature, gas temperature, and scattering parameter $S_{11}$ , are obtained. When the input power is set to 1500 W, and the steady state is achieved, the electron density reaches $3.05\times 10^{20}~\text{m}^{-3}$ , the electron temperature gets to 282 15 K, and the gas temperature is 5590 K. Remarkably, at the same power, the energy coupling efficiency from microwave to plasma is 17.3% higher than that in the tapered waveguide, and the electron density and gas temperature also increase by $4.5\times 10^{19}~\text{m}^{-3}$ and 346 K, respectively.