真空断路器真空度与灭弧室屏蔽罩上感应电位联系机理研究

屏蔽罩电位是判断真空断路器灭弧室真空度水平优劣的一种技术手段,研究人员对屏蔽罩电位信号成分及其形成机理进行了大量的研究工作,并在理论上和试验方面取得了一定成果。但对于真空屏蔽罩上电位的成因并无公认的解释,且实际应用中难以将不同型号的断路器按同一标准对待。为寻求真空度与屏蔽罩电位的内在联系机理,本文基于前人研究成果,从电介质学及气体放电的相关理论出发,将真空度劣化过程分成三个阶段分别讨论,阐述了各个阶段依据理论基础。特别针对真空度高于0.1 Pa时较难判断的屏蔽罩电位值,利用有限元分析的方法进行了3D电场计算,分析了该真空度范围下屏蔽罩电位的变化规律,研究成果提供了一种真空度判断与评估的可行方法,具有较好的应用参考价值。     

纳米金属薄膜材料电磁参数测量方法

提出了一种基于波导法的纳米薄膜材料电磁参数测量的新方法,给出了该方法的基本原理.与常规波导测量方法相比,该方法根据纳米金属薄膜材料的特点,简化了求解算法,只需测出加载薄膜波导开路与短路时的复反射系数,即可求出薄膜的介电常数与导磁率,使测量过程简单高效并具有较高的精度.     

Hand-held unit for liquid-type recognition,based on interdigital capacitor

The implementation of a unit capable to recognize liquids based on an interdigital capacitive sensor (IDC) is presented. The sensor’s structure was fabricated on standard FR-4 PCB board. Its capacitance change relies upon permittivity change of the medium above IDC electrodes, representing dielectric properties of the liquid used. Along with the microcontroller and simple interface circuit, information about the type of the liquid is presented on a 2 × 16 character display and through RS232 connection on PC. Implemented unit was tested against seven liquids (benzene, phenol, acetone, ethanol, methanol, formaldehyde and distillated water) and a steady state when unit only detected air. Results imply usage of this approach for the fabrication of cost effective, portable devices for on-field sensing applications.     

Experimental Study on Core Permittivity of Xinjiang Oilfield

This paper introduces the principles and procedures of the core permittivity measurement using a parallel capacitor with an electromagnetic shield. The cores from the Xinjiang oilfield were measured by using the frequency-swept method at different salinities and saturations. The effects of salinity, frequency, porosity and saturation on core permittivity were investigated. The relationship of core permittivity versus water saturation and the relationship of dry core permittivity versus porosity were obtained. The permittivity values of rock matrix and oil were obtained at a frequency of 47 MHz and 200 MHz, and would provide guidance for the interpretation of dual frequency dielectric logging data.     

Electrical properties of mixtures of fatty acid methyl esters from different vegetable oils

The dependence on temperature of the permittivity and conductivity of mixtures of Fatty Acid Methyl Esters (FAME) was determined between 300 K and 343 K, in the frequency range from 20 Hz to 2 MHz. Samples were made from oil of sunflower, corn, grape, chia, canola, jatropha, coconut and cottonseed.     

Synthesis and characterization of MoS2/Fe@Fe3O4 nanocomposites exhibiting enhanced microwave absorption performance at normal and oblique incidences

Herein, we attempted to prepare MoS₂/Fe@Fe₃O₄ nanocomposites capable of strongly absorbing broadband incident electromagnetic (EM) radiation and probed the effects of their composition on complex permittivity and permeability at 2–18 GHz. Calculations of normal-incidence reflection losses (RLs) based on EM parameters revealed that the Fe@Fe₃O₄ to MoS₂ mass ratio strongly influenced the absorption peak intensity and bandwidth. Specifically, an RL peak of −31.8 dB@15.3 GHz and a bandwidth (RL < − 10 dB) of 4.8 GHz (13.2–18 GHz) were achieved at a thickness of 1.52 mm and a Fe@Fe₃O₄ to MoS₂ mass ratio of 60:40. Further, RL and bandwidth were investigated for oblique incidence, in which case two kinds of EM waves (TE – electric field perpendicular to plane of incidence; TM – electric field in the plane of incidence) were considered. The absorption peaks of TE and TM waves did not exceed −20 dB when the incidence angle increased to 30°, and the bandwidth (RL < − 10 dB) reached 4.2 GHz (TE wave) and 4.0 GHz (TM wave) when this angle was further increased to 40.0° and 50.4°, respectively. Finally, the mechanism of microwave absorption was discussed in detail.     

Tuning the dielectric properties of hafnium silicate films

The influence of Si concentration in hafnium silicate dielectrics on thermal stability and dielectric permittivity was analyzed. A phase diagram was developed using GIXRD and FTIR measurement. The stabilization of the “higher-k” cubic/tetragonal phase for annealing temperatures up to 1000 °C with a steady increase in capacitance was demonstrated for Hf_0.94Si_0.06O₂ films. It was also shown that the stabilization of nano-crystalline Hf_0.80Si_0.20O₂ films can be realized for annealing temperatures up to 900 °C. The influence of TiN electrodes on the dielectric constant and the leakage current characteristic was also investigated. A permittivity increase for annealing temperatures up to 1000 °C without degradation of leakage current was shown.     

A review on MnZn ferrites: Synthesis,characterization and applications

Researchers are taking great interest in the synthesis and characterization of MnZn ferrites due to their wide range of applications in many areas. MnZn ferrites are a class of soft magnetic materials that have very good electrical, magnetic and optical properties. The properties of MnZn ferrites include high value of resistivity, permeability, permittivity, saturation magnetization, low power losses and coercivity. The above mentioned advantageous features of MnZn ferrites make them suitable for the use in various applications. In biomedical field these ferrites are used for cancer treatment and MRI. MnZn ferrites are also used in electronic applications for making transformers, transducers and inductors. These ferrites are also used in magnetic fluids, sensors and biosensors. MnZn ferrite is highly useful material for several electrical and electronic applications. It finds applications in almost every household appliances like mobile charger, LED bulb, TV, refrigerator, juicer mixer, washing machine, iron, microwave oven, mobile, laptop, desktop, printer and so on. Therefore, the present review focuses on different techniques for synthesis of MnZn ferrites in literature, their characterization tools, effect of doping on the properties of MnZn ferrite and finally we will discuss about their applications.     

Electromagnetic determination of clay water content: role of the microporosity

The electromagnetic determination of clay water content requires a good understanding of the main factors that affect the relationship between the clay relative permittivity κ and the water content θ. The first part of this paper proposes a review of the different factors affecting it: (a) a significantly high imaginary part of the relative permittivity; (b) a frequency-dependent response; (c) a high content of bound water with a relative permittivity value lower than that of free water; (d) a geometrical effect associated with “platy” units that characterize the clay texture. The next sections focus on the c and d factors related to the microporosity of clayey geomaterials; both factors are studied with two theoretical tools: the Moment Method (MoM) and the Differential Effective Medium (DEM) theory.The calculations indicate that bound water effect and geometrical effect act as competing processes: when water is added in a dry clayey material, the geometrical effect contributes to increase the clay relative permittivity compared to media with isotropic particles; a significant amount of bound water generates a decrease in the clay bulk permittivity. Consequently, the results allow to identify two types of behaviour: (1) low surface area systems, typically kaolinite geomaterials, for which the geometrical effect is predominant, and (2) high surface area systems, typically smectite clays, for which a balance between the geometrical effect and the bound water effect is expected.Moreover, the MoM simulations suggest that the derivative ∂κ/∂θ is affected by the bound water content, but slightly depends on clay content. These numerical observations that may contribute to improve in situ water content monitoring should be validated by experimental investigations.     

电容成像对未知对象的图像重建

本文探讨了电容层析成像技术用于两相流检测中对未知介电常数对象的图像重建的方法.提出采用一次仿真校验法对管内分别充满高、低介电常数介质进行仿真校验,并结合迭代算法实现对未知介电常数对象的图像重建.仿真和实验结果表明,该法能较好的重建未知介电常数对象的图像.