基于脉冲电声法的同轴塑料电缆空间电荷测量技术的研究进展

空间电荷现象严重制约着高压直流塑料电缆的发展。目前,脉冲电声法（pulse electric acoustic,PEA）是国际上常用的测量固体电介质中空间电荷分布的非破坏性的方法之一。首先从高压脉冲的注入方式出发,简述了几种基于PEA法的同轴塑料电缆空间电荷测量技术;同时,提出了一种基于高压脉冲从测量电极注入电缆试样的改进测量装置,在该装置中通过蓄电池、环氧底座以及光电转换器等将采集数据的示波器进行对地隔离,从而提高了测量系统测量信号的频带宽度;然后,介绍了同轴塑料电缆空间电荷波形的恢复方法;最后,概述了空间电荷测量技术在评估电力电缆老化程度中的应用和未来在线测量空间电荷的可行性及发展方向。     

Poly (3,4-ethylenedioxythiophene) for chronic neural stimulation.

Chronic neural stimulation using microelectrode arrays requires highly stable and biocompatible electrode materials with high charge injection capability. Conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically deposited on thin film Pt electrodes of stimulation electrode arrays to evaluate its properties for chronic stimulation. The coated electrodes demonstrated much lower impedance than thin film Pt due to the high surface area and high ion conductivity across the film. The PEDOT film also presents intrinsic redox activity which contributes to the low impedance as well as a much higher charge storage capacity. The charge injection limit of PEDOT electrode was found to be 2.3 mC/cm2, comparable to IrOx and much higher than thin film Pt. Under biphasic stimulation, the coated electrodes exhibited lower voltage and linear voltage excursion. Well-coated PEDOT electrodes were stable under chronic stimulation conditions, suggesting that PEDOT is a promising electrode material to be further developed for chronic neural stimulation applications.     

DEVELOPMENT OF SELF-SENSITIVE PIEZOELECTRIC CANTILEVER UTILIZING PZT THIN FILM DEPOSITED ON SOI WAFER

ABSTRACT

Piezoelectric micro cantilevers were applied to a resonant type mass sensor, biosensor, vapor sensor and probe for scanning force microscopes. These devices utilize impedance, phase, and charge as output signals. However, the measurement system could be greatly simplified if an output voltage were utilized. Therefore, a self-sensitive piezoelectric cantilever with separated electrode for actuation and sensing was developed. The self-sensitive piezoelectric cantilever was fabricated from a multilayer of Pt/Ti/PZT/Pt/Ti/SiO₂/SOI through MEMS bulk micromachining. The cantilever was oscillated by a sweep sine wave and the output voltage was measured as a function of the input frequency. The resonant frequency determined from the output voltage spectrum agrees well with that measured by a laser Doppler vibrometer.     

Threshold voltage instabilities in high-/spl kappa/ gate dielectric stacks

Over recent years, there has been increasing research and development efforts to replace SiO/sub 2/ with high dielectric constant (high-/spl kappa/) materials such as HfO/sub 2/, HfSiO, and Al/sub 2/O/sub 3/. An important transistor reliability issue is the threshold voltage stability under prolonged stressing. In these materials, threshold voltage is observed to shift with stressing time and conditions, thereby giving rise to threshold voltage instabilities. In this paper, we review various causes of threshold voltage instability: charge trapping under positive bias stressing, positive charge creation under negative bias stressing (NBTI), hot-carrier stressing, de-trapping and transient charge trapping effects in high-/spl kappa/ gate dielectric stacks. Experimental and modeling studies for these threshold voltage instabilities are reviewed.     

Some factors for the space charge formation in polyethylene

Information on space-charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer-insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm-thick polyethylene (PE). The following results were obtained. For measurement factors: (1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE. (2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space-charge decay. (3) The space-charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness. For insulating material factors: (1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low-density PE (base of XLPE). The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours. (2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and antioxidant).     

屏蔽套内雷电感应电压分析

为了研究直击雷的雷电流沿金属管传输时在3种不同材质屏蔽管内的金属线上产生的感应电压,笔者应用一个简单的电阻电路图,对3种不同金属屏蔽管内金属线上的感应电压进行分析、计算,得到不同的感应电压数值,并对电子设备防雷提出了建议.数值计算结果表明,影响导线上感应电压的关键因素是屏蔽管的转移阻抗,不同金属材质屏蔽管的屏蔽效果有差异.     

充电电压上限对磷酸亚铁锂电化学性能的影响

使用循环伏安、恒电流充放电、交流阻抗方法研究了充电电压上限对橄榄石型正极材料磷酸亚铁锂的电化学嵌脱锂性质行为的影响。发现在3.5～4.5V的范围内,充电电压上限对磷酸亚铁锂的放电比容量影响不大,但高电位条件下易于引发电极过程的副反应,造成电极界面电阻增长,对电极的倍率性能不利。充电电压上限控制在3.7～3.9V之间电极表现出最佳的电化学性能。     

Charge trapping and breakdown mechanism in HfAlO/TaN gate stack analyzed using carrier separation

Charge trapping and breakdown mechanism in p- and n-channel MOSFETs with an HfAl/sub x/O/sub y/ and TaN metal electrode are investigated. Using carrier separation measurement technique, it is possible to clearly distinguish two different breakdown mechanisms: a high-K bulk initiated and an interfacial layer initiated breakdown. A model of charge trapping at different spatial locations in HfAl/sub x/O/sub y/ with a TaN gate structure is proposed to explain the polarity dependence of charge trapping characteristics and breakdown mechanisms.     

基于模量网络分析的接地极线路故障定位新算法

针对直流接地极线路发生远距离、高阻接地故障时,现有故障定位算法精度低的问题,提出了一种基于模量网络分析的接地极线路故障定位新算法。基于线路的分布参数模型,建立了故障后接地极线路故障模量网络,在此基础上利用接地极线路量测端的电压、电流量计算沿线的电压、电流分布,进而得到故障点处的测量阻抗,根据故障点处测量阻抗虚部最小的特点进行故障定位。大量仿真结果表明,该算法可实现接地极线路全长范围内的准确定位,且不受故障位置和分布电容的影响,具有较高的故障定位精度。     

基于谐波测量阻抗偏差的接地极线路保护新方法

针对目前特高压直流输电系统接地极线路保护存在死区的问题,提出了一种基于谐波测量阻抗偏差的接地极线路保护新方法。在不同故障工况下推导了接地极线路的谐波测量阻抗表达式,利用阻抗表达式分析了正常运行工况与故障工况下谐波测量阻抗的偏差特性。在此基础上,提出了基于谐波测量阻抗偏差的接地极线路故障保护判据。利用PSCAD/EMTDC进行仿真验证,仿真结果表明,所提保护方法较传统保护方法可有效检测到接地极线路发生的各种故障,耐受过渡电阻能力强,且不存在保护死区。     

一种新型海洋电场传感器的研究与设计

提出一种用于测量海洋电场信号的低噪声电场传感器,传感器包含一对钽电极和一块低噪声斩波放大器.钽电极通过将钽粉压制、烧结并经过阳极氧化制成.引入电化学阻抗谱以建立钽电极与海水两相界面的等效电路模型,建立斩波放大器的等效噪声电路并分析.测试结果表明,所设计的斩波放大器的等效输入电压噪声为0.42 nV/√Hz,钽电极的自噪声为0.67 nV/√Hz,传感器总体噪声为0.83 nV/√Hz.所设计传感器可用于微弱海洋电场信号的测量.     

Who introduced the tetrapolar method for measuring resistance andimpedance?

The technique of using an outer pair of electrodes to inject current and an inner pair of electrodes to measure potential eliminates electrode/electrolyte impedance errors when measuring the resistivity of a conducting substance. A pressing problem of the late 1800s was the accurate measurement of the resistivity of an electrolyte that was placed between a pair of electrodes in a container. Kohlrausch (1897) working in Charlottenburg, Germany, solved the problem in a limited way by 1) using 1000 Hz current and 2) creating the platinum-black electrode. By using what was then a high frequency, the electrode impedance became low. By placing a velvety-like deposit of platinum on a platinum electrode, the effective surface area was increased, thereby reducing the electrode impedance. Such blackened platinum electrodes are still used in conductivity cells designed to permit measurement of electrolytic resistivity. Working in Paris, France, well before Kohlrausch, Lippmann had solved the problem of measuring electrolytic resistivity in a simple and elegant way by introducing the tetrapolar method in conjunction with his capillary electrometer, a sensitive and rapidly responding potential indicator. Lippmann (1873) had become interested in the shape of a drop of mercury in a solution of sulfuric acid. When an iron wire was placed into the sulfuric acid and then contacted the mercury, the contour of the mercury changed. The combination of the iron wire, mercury, and electrolyte caused the charge distribution on the surface of the mercury to change, thereby altering the surface tension and, hence, the contour. Lippmann used the phenomenon of electrocapillarity, as it became known, to construct a sensitive and rapidly responding electrometer     

MLNi_(4-x)MnAl_x贮氢电极的交流阻抗研究

MH电极的交流抗阴搞图谱由两个半圆组成,低频区大半圆对应于氢的吸收过程,高频区小半圆对应于电化学反应过程.对于MLNi_(4-x)MnAl_x电极,随着Al含量的增加,阻抗图谱低频半圆明显增大,而高频半圆几乎不变;此外、电极的循环次数、充放电状态等对阻抗图谱均有较大影响.     

Flashover from surface charge distribution on alumina insulators invacuum

Surface charge distributions of disk type aluminas held between a backside electrode (alumina holder) and a needle electrode to be excited by an impulse voltage (rise time 64 μs, wave tail 700 μs) were measured. The measurement of surface charge distribution on the whole surface area of alumina YSA998 and UHA99 after impulse voltage application revealed that the surface charging can be initiated either from the anode or from the cathode triple junction. The charging initiated from the anode triple junction (for positive polarity) produced positive charge at the anode region and the density is dependent on the applied voltage, while the charging initiated from the cathode triple junction region (for negative polarity) produced negative charge around the cathode region. For positive polarity, the critical values of charge density to the flashover for alumina YSA998 and UHA98 are 5.70 and 17.2 μC/m², respectively     

Electrical characterization of the platinum/YSZ interfaces in SOFCs via micro-contact impedance spectroscopy

The concept of micro-contact in electrodes was incorporated into AC two-probe impedance spectroscopy in order to clarify the electrode-related responses in solid oxide fuel cells (SOFCs). The pointed contact of one electrode was combined with the planar electrode as a counterpart in characterizing an YSZ (yttria-stabilized zirconia)/Pt interface of SOFCs. The micro-contact in electrodes induced the decrease in capacitance and the increase in impedance and amplified the bulk responses in YSZ due to the constricted electroding area. The bulk-related portions can be separated from the interfacial polarization of Pt, even though the electrolyte/electrode interface was found to be very sensitive to the measurement condition, i.e., the oscillating voltage. The resolved bulk and interfacial resistances were analyzed using a concept of “spreading resistance.’’ Furthermore, the electrode-related issues were ramified for the application of impedance spectroscopy to the solid oxide fuel cells.     

A critical approach to measure streaming current: case of fuels flowing through conductive and insulating polymer pipes

Electrostatic charge generation phenomenon in the case of hydrocarbons flowing through pipes has been studied for a long time. The charge generation depends on the nature of both the liquid and the solid. Because of the introduction of new plastic materials and due to fuel composition evolution, it became necessary to perform a comprehensive study of the subject in the particular case of an automotive environment. The streaming current measurement permits one to characterize charge generation when a fuel flows through a plastic pipe. However, this measurement must be carefully managed. In this paper, we are working on the validity and the accuracy of such measurements. The case of conductive and insulating pipes, and the double-layer development influence, are analyzed and discussed. In particular, we give a detailed methodology in order to measure reliable streaming currents and to wisely derive the space-charge density at the wall (/spl rho//sub w/). Experimental results are presented for some solid/liquid couples.     

High repetition rate PEA system for in-situ space charge measurement during breakdown tests

In order to investigate transient space charge phenomena, it is essential that the space charge profile be observed at a high repetition rate. We have developed a new space charge measurement system using the pulsed electroacoustic (PEA) method, which can measure the space charge profiles every 10 /spl mu/s. It employs the most recent digitising oscilloscope model and a semiconductor switch. The effect of prestressing on impulse breakdown voltage of a low-density polyethylene sheet was investigated by using the new system. Experimental results suggest that positive charge injection was dominant immediately before the breakdown, and charge injection during the prestressing causes distortion of the electric field near the electrode, and enhances the subsequent charge injection due to the impulse voltage.     

Influence of dc and dc/ac composite fields on the flow electrification characteristics of transformer oil

Flow electrification characteristics of transformer oil were investigated by applying dc and dc/ac composite fields to both bare and covered coaxial cylinder electrode systems. For the bare electrode system, flow electrification characteristics were almost the same between positive and negative dc voltage applications and negative charges were generated for both dc and dc/ac composite voltage applications at high dc fields. For the covered electrode system, the apparent flow electrification characteristics differed between positive and negative dc voltage applications. For the former, negative charges were generated at high dc fields for both dc and dc/ac composite voltage applications, and for the latter, positive charges were always generated for both voltage applications. However, negative charge generation for the positive voltage application was attributed to the influence of negative charge generation at the bare part of the covered electrode end; the fundamental charge generation characteristics of the covered electrode showed an increase of positive charge generation by dc voltage application, and positive charge generation was accelerated by a composite ac field. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 10‐17     

Hydrogen peroxide and ozone formation in hybrid gas-liquid electrical discharge Reactors

Ozone in the gas phase and hydrogen peroxide in the liquid phase were simultaneously formed in hybrid electrical discharge reactors, known as the hybrid-series and hybrid-parallel reactors, which utilize both gas phase nonthermal plasma formed above the water surface and direct liquid phase corona-like discharge in the water. In the series configuration the high voltage needle-point electrode is submerged and the ground electrode is placed in the gas phase above the water surface. The parallel configuration employs a high voltage electrode in the gas phase and a high voltage needle-point electrode in the liquid phase with the ground electrode placed at the gas-liquid interface. In both hybrid reactors the gas phase concentration of ozone reached a power-dependent steady state, whereas the hybrid-parallel reactor produced a substantially larger amount of ozone than the hybrid series. Hydrogen peroxide was produced in both hybrid reactors at a similar rate to that of a single-phase liquid electrical discharge reactor. The resulting concentration of H/sub 2/O/sub 2/ in the hybrid reactors, however, depended on the pH of the solution and the gas phase ozone concentration since H/sub 2/O/sub 2/ was decomposed by dissolved ozone at high pH.     

基于虚拟仪器技术的阻抗分析仪设计与开发

提出了一种基于虚拟仪器技术的阻抗分析仪设计方法,采用自动平衡电桥阻抗测量法开发了一台阻抗分析仪.该阻抗分析仪利用信号发生卡输出电压激励信号、采用高速数据采集卡进行两通道电压同步采集、以labVIEW为平台开发测控软件实现仪器板卡控制、阻抗测量以及数据分析和处理.测试结果显示:在频率20 HZ～500 kHz、阻抗1 Ω～500 kΩ范围内,该阻抗分析仪测量误差小于5％;其频率扫描点数、测量结果的显示和保存方式可通过软件进行灵活配置.基于虚拟仪器技术的阻抗分析仪通用性和扩展性强、测试范围广、操作简单便捷.根据实际的测量需求可灵活选择不同性能指标的信号发生卡、数据采集卡以及阻抗测量电路元件参数,开发成本可控且开发周期短,可广泛应用于科研和教学实验室仪器的开发.