The microwave plasma torch (MPT) is an attractive plasma source in both industry and scientific research because of its advantages in electrodeless operation ability, high energy efficiency, and ...flexibility under different operational conditions. However, relatively few numerical studies have been carried out for the MPT fed by a rectangular waveguide in two or even three dimensions. Therefore, this paper presents a 2-D, axisymmetric, and stationary fluid models to characterize the MPT, with an emphasis on the mechanism of the surface wave formation and the sustentation of the plasma column. Nine partial differential equations are included in this research, coupling microwave radiation, heat transfer, plasma bulk flow, and transport of different species with each other. The obtained results reveal how the traveling surface wave occurs and elucidate the consequent influence of the surface wave formation. Furthermore, this paper demonstrates the extension of the plasma column length and the propagation of the surface wave with an increase in the total plasma-absorbed microwave power. The dependence of the plasma column length on the plasma-absorbed microwave power is found to be motivated by the surface wave propagation. The limitations of the model and the difficulties in its numerical implementation are also discussed in the paper.
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 3.05×10 20 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 × 10 19 m -3 and 346 K, respectively.
The ternary transitional metal oxide NiCo
2
O
4
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, NiCo
2
O
4
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.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Aiming at exploring the basic functional mechanism of superstrates in the resonant cavity antenna (RCA), two popular superstrates, i.e., the homogeneous dielectric superstrate and the periodic ...microstrip superstrate are investigated. Their reflection coefficients to normal and oblique plane wave incidences are studied by using mathematical derivation and simulations. Based on it, their effects on performances of the RCA are analyzed through simulations and measurements. Results show that, despite of different configurations, the superstrates can be purposely engineered to have the same reflection coefficients, which results in the same improving effect on the RCAs broadside gain, radiation patterns and, more interestingly, broadening effect on the return loss bandwidth. The research demonstrates the key role of their effective reflective characteristics in the RCA, and can inspire more advanced superstrates for RCA designs.
Microwaves have been widely used in the treatment of materials, such as heating, drying, and sterilization. However, the heating in the commonly used microwave applicators is usually uneven. In this ...paper, a novel multi-material turntable structure is creatively proposed to improve the temperature uniformity in microwave ovens. Three customized turntables consisting of polyethylene (PE) and alumina, PE and aluminum, and alumina and aluminum are, respectively, utilized in a domestic microwave oven in simulation. During the heating process, the processed material is placed on a fixed Teflon bracket which covers the constantly rotating turntable. Experiments are conducted to measure the surface and point temperatures using an infrared thermal imaging camera and optical fibers. Simulated results are compared qualitatively with the measured ones, which verifies the simulated models. Compared with the turntables consisting of a single material, a 26%-47% increase in temperature uniformity from adapting the multi-material turntable can be observed for the microwave-processed materials.
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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.
This Letter reports a high isolation diplexer using stub-loaded resonators (SLRs). Each SLR can generate one transmission pole and one transmission zero (TZ). By changing the length of the open stub, ...the frequency of the TZ can be adjusted. The upper channel filter using the capacitive coupled SLRs can have TZs above the passband, while the lower channel filter using inductive coupled SLRs can have TZs below the passband. With those TZs, the isolation of the diplexer is greatly improved. A high isolation diplexer is designed and fabricated to validate the design concept.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
► Bivariate function was originally applied to describe the effective permittivity. ► Thermal analysis based on two methods were finished by multiphysics calculation. ► Great differences of ...temperature between the new and the traditional method. ► Thermal analysis based on the new method is more close to the experiment results.
The aim of this work was firstly to do a precise thermal analysis of microwave assisted production of biodiesel. In this paper, the effective permittivity of biodiesel synthesis was updated with two methods: a traditional method and a bivariate function of temperature and concentration of one component, then the thermal analysis of the reaction process were accomplished with multi-physics calculation. The results show that there exists large distinction in temperature between these two simulation results calculated by the two methods. The two hot spots locate in the opposite side and their temperature’s difference is up to 9°C when the reaction is just carried out for 18s. But the temperature risings and distributions calculated by the new method are closer to the measured results. The thermal analysis based on the new method will be helpful for the industrial design of biodiesel production.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Microwave processing of materials has been found to deliver enormous advantages over conventional processing methods in terms of mechanical and physical properties of the materials. However, the ...non-uniform temperature distribution is the key problem of microwave processing, which is related to the structure of the cavity, and the placement and physical parameters of the material. In this paper, a new microwave cavity structure with a sliding short based on phase-shifting heating is creatively proposed to improve the temperature uniformity. An electronic mathematical model based on the Finite Element Method (FEM) is built to predict the temperature distribution. Meanwhile, a new computational approach based on the theory of transformation optics is first provided to solve the problem of the moving boundary in the model simulation. At first, the experiment is carried out to validate the model, and heating results from the experiment show good agreement with the model's prediction. Based on the verified model, materials selected among a wide range of dielectric constants are treated by stationary heating and phase-shifting heating. The coefficient of variation (COV) of the temperature and temperature difference has been compared in detail between stationary heating and phase-shifting heating. A significant improvement in heating uniformity can be seen from the temperature distribution for most of the materials. Furthermore, three other materials are also treated at high temperature and the heating uniformity is also improved. Briefly, the strategy of phase-shifting heating plays a significant role in solve the problem of non-uniform heating in microwave-based material processing. A 25%-58% increase in uniformity from adapting the phase-shifting method can be observed for the microwave-processed materials.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A novel design of a coplanar waveguide (CPW) feed antenna array with circular polarization (CP) and a high front-to-back ratio is described. The proposed CP array is achieved by using a compact ...CPW–slotline transition network etched in the ground plane. The measured results show that this kind of feeding method can improve the impedance bandwidth, as well as the axial ratio bandwidth of the CP antenna array and provide adequate gain. The proposed array can achieve a 6.08% impedance bandwidth and a 4.10% CP bandwidth. Details of the antenna design and experimental results are presented and discussed.
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