Current Issue : April-June Volume : 2024 Issue Number : 2 Articles : 5 Articles
The resonant cavity method is a commonly used method for high-temperature testing of the complex permittivity of dielectric materials. When a resonant cavity is used for high-temperature testing, the microwave surface resistance of the cavity metal material will deteriorate due to factors such as oxidation reaction and thermal fatigue, resulting in a decrease in testing accuracy and repeatability. Therefore, when designing a high-temperature resonant cavity, the temperature response characteristics of the microwave surface resistance of the cavity metal material should be obtained in advance. In this paper, a high-temperature measurement method of microwave surface resistance of metal materials based on a separate cylindrical resonator is proposed, a mathematical model of microwave surface resistance inversion based on the resonator quality factor is established, and a high-temperature measurement system of microwave surface resistance is integrated. The reliability of the proposed method and system is verified through simulation and experiment. The measurement frequency covers 7-18 GHz, and the maximum test temperature reaches 500°C. Systematic error of microwave surface resistance measurement at room temperature is less than 3%....
In this work, the effect of Ge sample bombardment by energy Ei = 1.2 MeV mono-energetic He+ ions within the fluence range of 1013–1.2 × 1015 cm−2 on the microwave reflection/transmission modification in the frequency range of 26–38 GHz is investigated. It is shown for the first time that such Ge treatment allows achieving a drastic increase in its interaction with microwaves. After the 1 μm thick undersurface area of Ge, accounting for less than 10−3 of its bulk, underwent the fluence of 1.2 × 1015 cm−2, the increase of the microwave absorption coefficient from 0.06 to 0.78 and decrease of the microwave reflection coefficient from 0.7 to 0.18 are observed. This is caused by the occurrence of dangling atomic bonds in nanoscale cavities inside the material. Most probable energy loss mechanisms of microwaves in modified Ge are suggested. Modified semiconductor structures can be used as microwave-absorbing coverings, devices employing a periodic structure of materials or a gradient of its properties....
Rock fracturing through microwave irradiation has received significant attention recently as a viable pretreatment for improving the energy efficiency of comminution processes. This study presents a numerical analysis on the effects of microwave heating on the mechanical properties of hard rock. In particular, the reduction of the uniaxial compressive and tensile strength of granite-like rock due to microwave irradiation induced damage is numerically assessed. Rock fracture is modelled by a damage-viscoplasticity model, with separate damage variables for tension and compression types of failure. A global solution strategy is developed where first the electromagnetic problem is solved in COMSOL multiphysics software, then its solution is used as an input for the thermomechanical problem, which is finally solved by means of a staggered explicit solution method. Due to the preeminence of the thermal radiation, the thermal and the mechanical parts of the problem are considered as uncoupled. The model behaviour is tested in 3D finite element simulations of three-mineral numerical rock specimens, with mesostructures explicitly defined, pretreated first in a microwave oven and then subjected to uniaxial compression and tension tests. The results show that the compressive and tensile strength of rock can be considerably reduced by the microwave irradiation pretreatment....
The purpose of this study was to propose a highly efficient, durable, and environmentally friendly method for the rapid removal of ice and snow. A microwave-absorbing functionality layer was placed between a conductive metal mesh and magnetite sand shielding layer, and ordinary cement concrete (OC). Microwave heating, mechanical strength determination, and indoor and outdoor de-icing tests were performed on the cement concrete specimens with the shielding layer. Basalt fibers were added to the absorbing functionality layer, and the formed specimens were tested for strength and durability. The microstructure was observed using SEM experiments. The results show that the temperature rise of microwave-absorbing cement concrete with a magnetite sand shielding layer (MCMS) and microwave-absorbing cement concrete with a conductive metal mesh shielding layer (MCMM) increased by approximately 17.2% and 27.1%, respectively, compared to that of microwaveabsorbing concrete (MAC). After freeze–thaw cycles, the compressive strength and flexural strength of microwave-absorbing concrete with basalt fiber (MAB) increased by 4.35% and 7.90% compared to those of MAC, respectively. The compressive strength and flexural strength of microwave-absorbing concrete with a magnetite sand shielding layer and basalt fiber (MAMB) increased by 8.07% and 6.57%, respectively, compared to those of MCMS. Compared to specimens without basalt fiber, the wear rate per unit area of MAMB decreased by 8.8%, and the wear rate of MAB decreased by 9.4%. The water absorption rate of MAMB specimens decreased by 13.1% and 12.0% under the conditions of 20 and 40 microwave freeze–thaw cycles, respectively, compared to that of MCMS. The water absorption rate of MAB specimens decreased by 9.9% and 8.3% under the conditions of 20 and 40 microwave freeze–thaw cycles, respectively, compared to that of MAC. SEM analysis showed that the addition of basalt fibers improved the compactness and stability of the cement concrete structure as a whole. This study provides valuable references for the promotion and application of microwave de-icing technology....
The paper investigates the characteristics of the formation and morphology of microstructured zirconium oxynitride (ZrON) films, taking into account structural polymorphism during the impact of atmospheric-pressure microwave nitrogen plasma with the influx of active oxygen from the surrounding atmosphere. Optical, hydrophobic, Raman-active properties of ZrON films have been studied. X-ray diffractometry (XRD), scanning electron microscopy (SEM), ellipsometry method, and Raman spectroscopy, and moisture-resistance properties are used as analytical research methods. It is shown that during the short-term impact of microwave plasma, a morphologically heterogeneous ZrON film can be formed with a set of microhills with a uniform phase composition along the surface. The phase composition of the ZrON surface corresponds to the monoclinic structure of ZrO2. In the volume of the film, a predominantly tetragonal structure of ZrO2 is observed, as well as inclusions of the monoclinic structure of ZrO2. A mechanism for the formation of a ZrON film, taking into account polymorphism and phase transitions, is proposed. The optical properties of ZrON films are determined by both the dielectric phase of ZrO2 and the inclusions of the high-conductivity phase of ZrN. A combination of such factors as the developed microrelief and monoclinic surface structure, as well as nitride phase inclusions, enhance the hydrophobic properties of the ZrON film surface. It is shown that the surface hydrophobicity and resonant effects on ZrN inclusions allow for the enhancement of the Raman spectrum intensity due to the high concentration of analyte molecules in the scanning area....
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