An improved model for soil ionization around grounding system and its application to stratified soil

An improved model for taking into account the effect of the soil ionization around grounding system under lightning strike is proposed in this paper. In this model, the soil ionization region is assumed to retain 7% of its pre-ionization resistivity, which is consistent with the experimental results on soil ionization found in literature (Trans. SA Inst. Electr. Eng. (1988) 63; AIEE Trans. 61 (1942) 349; Proc. IEE 121(2) (1974) 123) and our own laboratory experiments (Time domain modelling of the response of grounding systems subjected to lightning currents, Licenciate Thesis, Uppsala University, 2003). Compared with modelling the soil ionization as an increase in the size of the ground conductor, the model presented here will not overestimate the beneficial influence of the soil ionization in reducing the ground potential rise, especially in high resistivity soil. The model is also applied to study the transient behaviour of grounding conductors in stratified soil under lightning strike including soil ionization. It shows that making the grounding conductor to penetrate the lower resistivity soil layer could help to decrease the ground potential rise at the injection point several times.     

有机场致发光中能带模型与分子理论的讨论

在有机场致发光中,能带模型及分子理论从20世纪就存在尖锐的矛盾。在分层优化方案中,经SiO₂加速后的电子能量可以到达10eV,这足以激发发光材料发光,将分层优化方案应用到有机场致发光材料中。发现了固态阴极射线发光(SSCL),经过对它的交叉证明、普适性的验证,肯定了固态阴极射线的发光确实是在发光二极管,无机及有机场致发光之外的一种完全新型的电场诱导的发光。SSCL的特征是在它的光谱中出现短波发光峰,实验证明长波发光峰的减弱是由于电场离化效应。研究了这种效应出现的电压阈值并和SSCL的短波峰出现的电压相比,发现短波峰的出现是在激子的电场离化之后,从而找出了电子处于局域态与扩展态的分水岭,解释了在有机场致发光中能带模型和分子理论并不矛盾,只是适用的条件不同。激子的离化是随电场强度而渐进的变化,因此会有一个两种过程并存的范围。     

电极电压对碳纳米管阴极电离规性能影响的数值模拟

本文基于IE514分离规结构, 建立了碳纳米管阴极电离规物理模型, 根据电离规标准方程, 利用离子光学模拟软件SIMION 8.0分别研究了电极电压对灵敏度和I_grid/I_e的影响. 结果表明, 随着阳极/门极电压比值增大(V_grid/V_gate), I_grid/I_e也将增大, 然而, 当阳极电压增大时, 会导致灵敏度降低, 进而影响真空测量下限的延伸; 该模拟结果与相关文献报道的实验结果符合性很好. 因此, 选择合适的电极电压, 将有利于提高灵敏度, 增大阳极电流, 进一步延伸真空测量下限. 本文所采用的数值模拟方法可推广应用于各种新型碳纳米管阴极极高真空电离规的研发和理论分析中, 为解决极高真空测量难题提供了有效的研究途径. 关键词： 碳纳米管阴极电离规 电极电压 灵敏度 阳极电流     

Electrical properties of dry soil under high impulse currents

To date, no publication has been made on dry soil characteristics under high impulse current conditions. This is because, no conduction current was detected in the dry soil, which may be due to high bulk resistance in the dry soil, limitations in the impulse generator and in the transducers adopted during the tests. In this study, however, for the first time, conduction current in dry soil was observed, despite the high resistivity of the dry soil and the large equivalent resistance of the test cell. It would be expected that the ionization process occurred mainly in the dry soil, since there is no water path in dry soil, and the voids are filled mainly with air. The goal of this paper is to contribute a better understanding of the ionization and thermal phenomena that occur in dry soil.     

大气压下氩原子谱线辐射诊断试验研究

大气压下介质阻挡放电应用领域具有多范畴、深广度、常态化等优势,针对同轴电极放电试验进行了系列参数诊断。采用自主研发的介质阻挡放电助燃激励器,在一个标准大气压、放电频率11.4 kHz、放电峰值电压5.4～13.4 kV(间隔1.0 kV)条件下进行了氩气电离试验。采用原子发射光谱法(AES)对氩等离子体谱线的激发、分光进行了检测分析;选用二谱线法及Boltzmann法测试了电子激励温度;根据Stark展宽效应计算了电子密度;获得了电子激励温度及电子密度随放电峰值电压增长的变化规律。结果表明,在试验电压条件下电子激励温度并不随外加电压的升高而递增,这表明通道内微放电的主要特征并不依赖于外部电压的供给,而是取决于气体组份、气体压强和放电模型,增大外加放电电压仅增加单位时间内微放电的数量,经整合电子激励温度可达3 500 K符合典型的低温等离子体特征;电子密度随外加电压的增长而趋于准线性趋势,电子密度数量级可达到108～109 cm-3,电离度偏弱。这些参数的探索对等离子体研讨有重大意义。     

Temperature dependent characteristics of a PIN avalanche photodiode (APD) in Ge,Si and GaAs

A theoretical assessment is presented based on a modification of Baraff's theory in order to compare the temperature dependence of several characteristics, including breakdown voltage, excess noise factor, effective ionization rate ratio and efficiency in Ge, Si and GaAs PIN avalanche photodiodes. The temperature coefficient of avalanche breakdown voltage in a high field region is studied. Finally the response time of a PIN APD in these materials is discussed.This paper is supported by the National Science Council, the Republic of China.     

Weak avalanche multiplication in SiGe heterojunction bipolar transistors on thin film silicon-on-insulator

In this paper, we propose an analytical avalanche multiplication model for the next generation of SiGe silicon-on-insulator (SOI) heterojunction bipolar transistors (HBTs) and consider their vertical and lateral impact ionizations for the first time. Supported by experimental data, the analytical model predicts that the avalanche multiplication governed by impact ionization shows kinks and the impact ionization effect is small compared with that of the bulk HBT, resulting in a larger base-collector breakdown voltage. The model presented in the paper is significant and has useful applications in the design and simulation of the next generation of SiGe SOI BiCMOS technology.     

正极性纳秒脉冲电压下变压器油中流注放电仿真研究

建立了二维轴对称流体模型, 仿真研究了正极性纳秒脉冲电压下变压器油中针-板电极流注放电的起始与发展过程, 得到了不同的外施电压幅值、脉冲上升沿时间与电极间隙距离下油中流注放电的形貌、 电场强度与空间电荷密度分布等. 仿真结果表明: 空间电荷加强了流注头部前方电场, 使流注通道更易于向前推进, 形成"电离波"; 随着外施电压幅值升高, 流注发展的平均速度显著变大; 较陡的脉冲上升沿形成的放电半径较大, 对应的最大电场强度值变小; 随着电极间隙距离的增加, 流注发展平均速度变快. 仿真显示纳秒脉冲下放电中油温无明显升高, 表明此类放电过程没有明显的油气化现象. 我们认为, 场致电离是油中带电粒子产生的主导机制; 空间电荷效应增强流注前方电场使得电离进一步发展, 最终导致击穿. 本研究有助于加深对变压器油中放电起始、发展直至击穿过程的认识以及对液体电介质中电离机制的理解. 关键词： 变压器油 流体模型 流注放电 空间电荷效应     

Comparison of two cold atmospheric pressure plasma jet configurations in argon

The present study compares the operation of two cold atmospheric plasma jet (CAPJ) configurations: needle-to-cylinder electrode configuration (CAPJ I) and single high-voltage cylinder electrode around the quartz tube (CAPJ II). The CAPJs were operated in argon flowing through a quartz capillary with 0.5-mm inner diameter into the ambient air, and the plasma was generated by sinusoidal kHz frequency AC power supplies. The main emphasis of the study was on the mechanism of the initiation of ionization waves for these two configurations. For both CAPJs, there appeared several ionization waves during one half-period of the applied voltage waveform, and the number of ionization waves increased at higher voltage amplitudes. However, we discovered marked differences in the initiation of the ionization waves for two different CAPJ configuration. The applied voltage controlled the initiation of consecutive ionization waves, which propagated from the grounded electrode towards the tube orifice in CAPJ I. In the case of CAPJ II, certain time had to pass for the initiation of a new ionization wave, and subsequent ionization waves within the same half-period started at the tube orifice. In addition to the differences in the initiation of the ionization waves, we observed that the CAPJ I was ignited and sustained at lower voltages, while CAPJ II produced a longer plasma jet. The observed advantages and deficiencies of investigated CAPJ configurations point out their potential in different applications.     

亚微秒脉冲下高梯度绝缘子的沿面闪络特性

介绍了一种由聚酰亚胺和不锈钢叠加而成的高梯度绝缘子的实验研究工作。该绝缘子样品的直径60 mm,厚度8 mm,在脉冲宽度120 ns(FWHM)的电压脉冲加载下最高获得了接近13 MV/m的绝缘强度。研究了测试方法以及绝缘层厚度与金属层厚度的比例对高梯度绝缘子绝缘强度的影响,并与相同尺寸的普通材料绝缘子的绝缘强度进行了对比。结果表明,高梯度绝缘子的绝缘强度明显高于仅由聚酰亚胺构成的普通绝缘子。     

Application of Electron-Beam Ionized Discharges to Switches?a Comparison of Experiment with Theory

A theoretical investigation of high-pressure discharges ionized by an external electron beam (e-beam) was conducted. Only when secondary emission from the cathode and electron-impact ionization of metastable states were included in the analysis did calculated current-voltage (I-V) characteristics for argon and methane discharges compare well with experimental data. The I-V characteristics obtained reveal a sharp rise in the current at a certain threshold voltage. This threshold voltage and the entire I-V characteristic are shifted to lower voltages when metastable ionization is significant. Below the threshold voltage and at low external ionization source strengths, a region of negative differential conductivity is obtained. In the high-current region, the I-V slope is controlled by the secondary emission coefficient. The additional cathode sheath ionization from secondary emission and ionization from metastable states significantly reduces the discharge voltage. This important effect can be used to reduce e-beam switch losses and increase lifetime through judicious gas mixture selection and proper cathode conditioning.     

Transient demonstration of exciton behaviours in solid state cathodoluminescence under different driving voltage

In the solid state cathodoluminescence (SSCL), organic materials were excited by hot electrons accelerated in silicon oxide (SiO₂) layer under alternating current (AC). In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence (exciton emission and recombination radiation), it was demonstrated that recombination radiation should benefit from the exciton ionization.     

磷化铟复合沟道高电子迁移率晶体管击穿特性研究

用密度梯度量子模型定量研究了磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的击穿特性，考虑了复合沟道内碰撞电离以及沟道量子效应，重点研究了器件击穿电压随In_0.7Ga_0.3As沟道厚度的变化关系，提出了提高击穿电压的方法，采用商用器件模拟软件Sentaurus模拟了器件的开态击穿电压，对比了实验和模拟的结果. 研究表明：适当减小In_0.7Ga_0.3As沟道层的厚度可以在保持器件饱和电流基本不变的前提下大幅度提高开态击穿电压，这对于提高InP基HEMT的功率性能具有重要意义. 关键词： 磷化铟 高电子迁移率晶体管 密度梯度模型 击穿     

Experimental observation of negative differential characteristic of corona discharge in ultraviolet spectrum

Corona discharge is a self-sustained discharge which appears at electrodes with a small radius curvature in gas insulation. An almost invisible glow occurs just above the inception voltage. Corona phenomenon is mainly used in electro-technological processes to obtain space charge for electrostatic precipitation, separation of different particles, electrostatic liquid or solid coating, neutralization of space charge, etc. All of these processes rely on a strong nonhomogeneous electric field generated by a point – plate electrode system. When the critical value of the applied voltage is reached, the ionization processes near the point electrode start and give rise to the current between two electrodes. If the pointed electrode is positive, it is possible to observe an anomaly of the current – voltage (I-U) characteristic for the point-plate space. It means that while the voltage is raising the current density decreases in a narrow voltage area (2–3 kV). The anomaly was technically named as negative differential conductivity (dI/dU < 0). Unstable current can have a negative influence on electro-technological processes. The anomaly was detected for different shapes and materials of the electrode as well as for various temperatures and distances between electrodes. An oxidation layer, which appears on the metal electrode, also influences the ionization processes near the pointed electrode and causes a decrease of a current. In this paper measuring of the discharge activity in a point – plate electrode system is presented. Ionization of gas atoms and molecules in a high electric field and the following recombination of electrons and positive ions in the corona region can give rise to high-energy photons which produce new electrons in the field of discharge. Corona discharges are detected by DayCor Corona camera which can register UV emission generated by corona in a day light. The experiment was conducted with various shapes of the pointed electrode and distances between the high voltage and the grounded electrode under applied direct voltage with positive and negative polarity.     

Electron-optical study of the initial phase of subnanosecond pulsed electric breakdown of gas-filled gaps

The glow accompanying the breakdown of gas gaps with a strong overvoltage by voltage pulses with 1-ns and shorter fronts is studied by electron optics methods. The filling of the gap with glow was accompanied by the development of ionization wave processes originating in the bulk of the gas and controlling the first stage of the breakdown. The dynamics of evolution of ionization waves in the electrode gap was analyzed in the 1D approximation. The results of calculations are in qualitative agreement with experiment. This leads to the conclusion that breakdown can be initiated from the bulk of the gas rather than from the surface of the electrodes. At this stage, the electrodes are mainly required for producing the electric field in the gap.     

One-dimensional single and multipulse simulations of the ON/OFFvoltages and the bistable margin for He, Xe, and He/Xe filled plasmadisplay pixels

A one-dimensional plasma model developed for AC plasma display pixels is used to perform multipulse and single-pulse simulations to model the maximum sustain voltages, the minimum sustain voltages, and the voltage margins for 100% helium, 100% xenon, and for 2% xenon in helium and a 400 torr pressure (p) and a gap (L) of 100 μm. The multipulse simulations describe the growth in wall voltage at the so-called ON voltage and the decay in wall voltage at the so-called OFF voltage. For square wave forms, the ON voltage is the voltage at which a pixel attains to a stable operation in which a discharge occurs in each succeeding pulse and the wall voltage equal to the applied voltage. The OFF voltage is the voltage at which a pixel that is ON goes off and no further discharges occur. Experimental data for helium show the hysteresis in the discharge current observed when the voltage is increased to turn ON pixels and then reduced to turn OFF-pixels in a panel. Simulations which match the helium data are also shown. The difference between the ON and OFF voltages defines the bistable margin. For the helium-xenon Penning mixture, the ON and OFF voltages determined by multipulse simulations are almost identical to the values obtained from the wall voltage transfer curve method. In the helium-xenon Penning mixture, the ionization rate for xenon ground state increases dramatically compared to its ionization rate in pure xenon due to the modification in the electron velocity distribution function in the mixture. This feature provides enhanced volumetric ionization in the discharge and hence a rapid growth rate of the wall voltage which is desirable for a sharp transition from OFF to ON in a pixel     

Limiting phenomena for the spreading of water on polymer films by electrowetting

This paper is about fundamental limitations in electrowetting, used as a tool for spreading water solutions on hydrophobic surfaces, like the surface of a polymer film. Up to which point can an electric voltage decrease the contact angle? The first limitation comes when using pure water, above a threshold voltage, little droplets are emitted at the perimeter of the mother drop. We present an analysis of the drop contour line stability, involving competition between electrostatic and capillary forces, which is compatible with observations. The use of salted water solutions suppresses this instability, then one faces a second limitation: the evolution of the contact angle saturates before complete wetting. We show that this saturation is caused by ionisation of the air in the vicinity of the drop edge. We analyse the luminescence induced by gas ionization and measure the related electrical discharges. We explain how air ionization suppresses the driving force for electrowetting and how it induces the formation of an hydrophillic ring around the drop.     

基于交流调制技术的弱电流放大器研制

在射线强度测量中,积分电离室输出的电流信号在10–10～10–15 A范围内,该弱电流信号需要转换和放大才可以进行采集.针对积分电离室本文设计了一种弱电流信号放大系统,采用交流调制技术将待测弱直流电流信号调制为交流电压信号,再经放大、相敏检波、滤波等电路处理后得到直流电压信号,最后进行数据采集;同时在系统中引入直流负反...     

等离子体化学气相沉积TiN中参数的研究

一、引言 等离子体化学气相沉积(PCVD)薄膜是广泛应用的新技术。它沉积温度低,可沉积薄膜种类多,包括各种作为功能材料和结构材料的无机非金属薄膜。刘大明等对PCVD的动力学过程进行过研究。PCVD设备及工艺较简单,绕镀能力强,并且利用非平衡电离     

Application of Mn nano-flower sculptured thin films produced on interdigitated pattern as cathode and anode electrodes in field ionization gas sensor

The photolitography method was used for producing interdigitated configurations for cathode and anode electrodes of a field ionization gas sensor in which Mn helical nano-flowers with 3-fold symmetry were deposited using oblique angle deposition together with rotation of the substrate about its surface normal, with each rotation divided into six sections. These sections were alternately rotated at high and low speeds. Three different distances were chosen in the design between anode and cathode electrodes, namely 40, 100 and 200 μm. Physical structure and morphology of electrodes were studied by field emission scanning electron microscope and atomic force microscope analyses.The breakdown voltage of the system was studied for nitrogen, oxygen, argon, air and carbon mono-oxide gases. Investigations with these gases at different distances between anode and cathode and different gas pressures confirmed Paschen's Law. Results showed that at low pressures, decreasing the gap between electrodes increases the breakdown voltage. With fewer gas molecules between the electrodes the number of interactions between particles is reduced and higher energies are required for ionization of gas molecules. At high pressures, the breakdown voltage is decreased because of an increased number of molecular interactions. The sensor demonstrated good selectivity between the different gases and selectivity was enhanced with increasing gas pressure. A direct relationship was found at low pressures (e.g., 0.1 mbar) between the breakdown voltage and the gas ionization energy while at high pressures (e.g., 1000 mbar) this relationship was reversed.