圆柱腔复介电常数高温测试系统

围绕微波介质材料复介电常数高温测试关键技术进行系统设计,利用圆柱腔精确场解法实现材料介电性能变温特性测试。设计了TM_(010)模圆柱谐振腔,采用快速移动平台和感应加热技术,搭建了变温测试系统,实现了915 MHz,最高1 400℃的复介电常数快速自动化测试。针对测试系统受热后对测试结果的影响,提出了实时变温校准技术,减小了夹具介电波动引入的误差。以熔融石英为例进行重复性测试并与已有文献作对比,结果表明介电常数和损耗角正切高温下测试偏差分别在2%和6%以内。     

电力负荷参数辨识的实用改进及实测结果

针对电力负荷参数辨识中出现的参数不稳定问题,对参数辨识过程作了改进:一是将负荷参数分为重点参数和次要参数,只对重点参数进行辨识,对次要参数则直接采用其典型值进行计算;二是给出了参数初始搜索范围选取的一般方法;三是对系统容量基值和感应电动机容量基值下的参数作了一些说明,在进行联网计算时,感应电动机自身容量基值下的参数要根据系统容量基值折合;四是提出了模型类别的判别指标。基于以上改进措施,对河南电网和江苏电网的实测数据进行了参数辨识,表明以上改进措施使电力负荷建模达到实用要求。     

高频板材的复介电常数测量方法研究

复介电常数是高频板材最重要的参数之一,准确测量高频板材的介电常数和损耗,对板材的实际应用十分重要。为了获得板材的损耗特性,设计了一种基于微带线的传输线电路,并对长度分别为25.4和127 mm的微带传输线进行仿真、加工和测试,得到DC-20GHz内的回波损耗S₁₁和插入损耗S₂₁,测试数据表明,S₁₁值测试结果在-15 dB以下,且在20 GHz下传输线的插入损耗为24.02 dB/m。通过加工误差分析,电路参数变化50μm时,DC-20GHz内仿真S_11max变化可达到6 dB左右。最后结合谐振环法对同一种板材进行测试,得到板材的相对介电常数和损耗角正切。结果表明该方法得到的损耗角正切精确度较高,且在2、10和20 GHz频段下误差小于10%。     

基于VC++的介质复介电常数变温测量系统软件设计

本文针对介质电参数测量自动化与精确化的需要,综述了高Q谐振腔法测量介质复介电常数的基本方法,设计了一套基于VC 的、可兼容多种矢量网络分析仪与多种形式谐振腔的介质复介电常数变温测量软件系统,并论述了具体的开发设计过程.利用不同的方法测量多组介质片对软件进行测试,测量结果表明,该方法可以提高测量效率和精度,为介质复介电常数测量提供了一种有效的手段.     

Estimation of conductivity and permittivity of water trees in PEfrom space charge distribution measurements

Using an improved pulsed electroacoustic system which is capable of measuring space charge distribution at minimum intervals of 25 μs, the charge distribution inside water-treed polyethylene (PE) was examined. From the results, the frequency dependencies of conductivity and permittivity were examined for water trees grown in PE. The conductivity of the water-treed region is found to be >10¹⁰× higher than that of non-treed regions, while the permittivity increase is only slight     

Thermal hysteresis in the permittivity and polarization of leadzirconate titanate/vinylidenefluoride-trifluoroethylene 0-3 composites

The permittivities of 70/30 vinylidene fluoride-trifluoroethylene copolymer and lead zirconate titanate/vinylidene fluoride-trifluoroethylene 0-3 composites have been measured at 1 kHz over the temperature range of 20 to 120°C. Thermal hysteresis was observed for the 0-3 composites and abrupt changes in the permittivities occurred at different temperatures upon heating and cooling. Good agreement was found between the measured permittivities and the predictions of the Bruggeman model. Implications of the thermal hysteresis behavior on the poling of 0-3 composites are also discussed     

Partial discharges in a cavity at variable applied frequency part 1: measurements

In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01 ? 100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.     

Numerical electric field analysis of capacitance and potential in space for estimation of permittivity distribution

We have been studying on measuring capacitance and potential using long‐distance electrode for estimating a permittivity distribution. The estimating method of permittivity distribution was proposed using finite element method (FEM) and genetic algorithm. However, the measurement accuracy was not reviewed. In this paper, we carried out numerical analysis using FEM in case of change of diameter, position, and permittivity of a rod of dielectric and discussed the measurement accuracy of capacitance and potential.     

双复纤维长径比对其吸波性能的影响

采用电加热和化学气相沉淀(CVD)法合成双复纤维材料,研究了双复纤维含量一定的条件下长径比对吸波性能的影响.结果表明,双复纤维长径比的增大导致复磁导率和复介电常数都有所增大,其中复介电常数的实部显著增大,而且双复纤维长径比为15∶1左右时,吸波效果较好,吸收峰为-19.1dB,11.2～1 8GHz范围反射率低于-5d...     

A capacitance measurement method for imaging permittivity distribution in a brain phantom

The purpose of our research was to image the temperature distribution inside a human head by non-invasive measurement. To achieve this goal, we investigated a method for imaging the inhomogeneous permittivity distribution by measuring capacitance and to obtain the temperature distribution from the permittivity-temperature characteristic. This paper describes the first step in estimating the inhomogeneous permittivity distribution using our proposed new capacitance measurement method. We present the results of experiments performed using this method on a homogeneous phantom containing agar-agar. We estimate that the proposed method offers a practical technique for imaging inhomogeneous permittivity distributions, although some of the problems with this measurement procedure and image reconstruction system remain to be solved. © 1998 Scripta Technica. Electr Eng Jpn, 122(3): 37–45, 1998     

Partial discharges in a cavity at variable applied frequency part 2: measurements and modeling

In this paper partial discharges (PD) in a disc-shaped cavity are measured at variable frequency (0.01 ? 100 Hz) of the applied voltage. The measured PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, changed with the varying frequency. A charge consistent model is presented and used to dynamically simulate the sequence of PDs in the cavity. The simulation results show that the properties of the cavity surface, mainly the surface conductivity and the surface emission of electrons, change with the varying applied frequency. This is interpreted as an effect of the difference in time between consecutive PDs at different applied frequencies. This is the second of two papers addressing the frequency dependence of PD in a cavity. The first paper described how the PD frequency dependence changes with the applied voltage amplitude, the cavity size and the cavity location.     

Measurement of permittivity and dielectric loss in 2,4-dimethyl substituted pyridine using microwave cavity spectrometer and time domain reflectometer

Microwave cavity spectrometer and time domain reflectometer is used to measure the permittivity and dielectric loss at different temperatures in 2,4-dimethyl substituted pyridine. The observed data of the width of resonance profile and the shift in the resonance frequency have been analyzed using Slater perturbation equations for cavity spectrometer. The dielectric parameters measured from the time domain reflectometer as a function of time at different temperatures have been transformed to frequency domain to obtain the permittivity and dielectric loss. The observed values of the permittivity and dielectric loss at 9.0 GHz are fitted in Slater's perturbation equations to obtain the form factor, which represents interactions. The relaxation time has been evaluated at different temperatures using the ratio of width and twice of frequency shift and thermodynamical parameters have been determined. This experimental study provides fruitful information about the bulk properties of 2,4-dimethyl substituted pyridine.     

The analysis of the electromagnetic characteristics of composite materials with negative effective permittivity

A new method based on the finite difference time domain (FDTD) method is presented to numerically analyze the transmission and reflection characteristic of composite materials with negative effective permittivity. The numerical results are compared with the results of the existing theoretical model and the experimental data. The feasibility of analyzing the composite materials using the FDTD method is validated. It is useful for the design and application of the composite materials. Translated from Journal of Beijing University of Posts and Telecommunications, 2006, 29(1): 9–12 [译自: 北京邮电大学学报]     

Performance of a microwave sensor for the precise measurement ofwater vapor in gases

A microwave sensor designed for the measurement of humidity in sulfur hexafluoride (SF₆) has been developed for possible in-line use in the electrical utilities industry. This technique could be used to measure efficiently the humidity level to prevent excess moisture and to keep the electrical integrity of sensitive electrical equipment. The measuring system is based on the dielectric properties of the gas mixture at atmospheric pressure and ambient temperature. The voltage difference coming from a measuring cavity resonator and a reference one is related to the amount of water vapor in SF₆. The setup is sensitive enough to detect moisture levels down to 3 ppm     

Exact sensitivity analysis for optimization of multi-coupled cavity filters

This paper describes an efficient approach to the simulation and exact sensitivity evaluation of multi-coupled cavity filters. The approach uses sensitivity formulae for such responses as input or output reflectron coefficient, return loss, insertion loss, transducer loss, gain slope and group delay, which are derived for a two-port equivalent of a general network described by its symmetrical impedance matrix. The formulae are specialized to the case of multi-coupled cavity filters, using a filter model which takes into account many non-ideal factors such as losses, frequency dependent coupling parameters and stray couplings. The formulation also treats synchronously or asynchronously tuned structures in a unified manner. Explicit tables of first- and second-order sensitivities w.r.t. all variables of interest, including frequency, are presented. Three problems of significant practical value in manufacturing of multi-cavity filters are solved with the direct application of our formulae. A 10th-order filter is considered for all three cases. The first case is simultaneous optimization of the amplitude and delay responses to obtain a self-equalized filter. The second case is accurate prediction of the responses for a lossy filter by simulating a lossless filter. The third case involves parameter identification of the filter from simulated measurements on its responses.     

非差运动学精密定轨伪距和相位加权分析

双频星载GPS非差运动学定轨法的定轨精度完全取决于观测数据的质量,单独利用伪距观测量会导致定轨精度低,单独利用载波相位观测量容易导致法方程奇异。对非差运动学精密定轨伪距和载波相位观测量加权进行了分析,在保证获取同单独采用载波相位观测量运动学定轨相当精度的条件下,提高了定轨运算的稳定性和解算速度。用GRACE(gravity recovery and climate experiment)卫星2006年1月3日实测数据作为算例验证了该加权方法的有效性。GRACE卫星实测数据的仿真结果表明:伪距和载波相位观测量加权的非差运动学精密定轨,在R、T、N方向的定轨精度分别为3.93cm、3.19cm、3.34cm,三维位置精度为6.07cm。     

一种高精度实时电力谐波分析算法的实现

提出了一种适于高精度实时电力谐波分析的自适应调整采样率的谐波分析方法。该方法在谐波分析的同时调整采样间隔,跟踪电网频率,大大地减少了频谱泄漏。针对该谐波分析方法本文提出了离散Hartely变换递推算法,该算法大大地减少了计算量,且算法简单易于硬件实现。     

照明光源的寿命特性和改进

在绿色照明工程中提高和延长照明光源的光效十分重要。该文介绍了白炽灯、荧光灯、高压放电灯的寿命特性和长寿命化的措施。延长这些照明光源的方法有改进灯丝和电极的材料与结构，蒸镀二向色性法反光镜，使用同频电子整流点灯线路等。