Efficient charge neutralization with an ac corona ionizer

This paper discusses the problem of obtaining effective charge neutralization by an ac corona ionizer with airflow. The motion of ions and the neutralization of a charged object for different discharge frequencies and airflow velocities are investigated by a computer fluid model for positive and negative ions. The results of the investigation show that, in the region of ion transport, the quasi-neutralized charge distribution self-generated by positive and negative ions during charge neutralization can effectively transport the ions themselves from an ionizer to a charged object and significantly reduce both the unwanted fluctuation and dc offset in the potential of the object at a steady state, resulting in efficient and precise charge neutralization. Since the quasi-neutralization greatly depends on the relationship between the discharge frequency and airflow velocity, the control of the relationship may lead to better neutralization with an air-blowing ac ionizer.     

毫米级栅型电场分布FEP薄膜驻极体的制备及其电荷存储性能研究

采用电晕注极和热注极技术, 在厚度为25 μm的氟化乙丙烯共聚物(FEP)表面制备了宽度为2 mm和3 mm的具有栅型电场分布的驻极体, 研究了注极温度和电极宽度对其电荷存储性能的影响. 样品注极后经150天的存储, 栅型电场分布变得清晰而有规律, 覆盖铝电极区电位已衰减至接近零, 未覆盖铝电极区仍保持高电位; 对电极宽度为2 mm和3 mm的样品, 覆盖铝电极区与未覆盖铝电极区的表面电位差分别为110 V和130 V(电场强度差分别为44 kV/cm和52 kV/cm). 表面电位跟踪测试结果表明: 电晕注极样品初始表面电位高于热注极样品; 在相同的注极方法下, 注极温度越高初始表面电位越高, 电极宽度越小初始表面电位越低. 依据电晕注极和热注极原理对实验结果的分析表明, FEP和金属铝在电荷存储性能上的差异是FEP表面蒸镀铝电极后能获得栅型电场分布的原因所在.     

Electric field and the charge distribution on the surface of an insulator in a vacuum

The free charge steady-state distribution over the insulator surface that arises in a strong electric field in a vacuum can be found by solving the boundary-value problem for the electrostatic field strength if the angle between the field vector and vacuum-insulator interface is given. A general solution to this boundary-value problem is derived for the case of an in-plane field and rectilinear interfaces. Laws of charge and field formation that follow from the solution obtained are considered. Formulas for the electric field strength and charge density in terms of elementary functions are obtained for a number of particular cases. Power-type expressions for the electric field and a critical angle between the electrode and insulator surface that describe the field behavior and charge distribution near the vacuum-insulator-electrode contact are derived.     

雷云电场作用下长地线表面正极性辉光电晕放电的仿真研究

在雷云电场的缓慢作用下, 一种无流注的正极性辉光电晕在接地物体表面起始, 向周围空间注入大量正极性空间电荷, 从而改变雷电先导对雷击目的物的选择. 本文对雷云电场作用下起始于长地线表面的正极性辉光电晕放电进行了仿真研究; 考虑了正极性离子与其他离子的附着与碰撞作用, 建立了一种精确的二维正极性辉光电晕模型; 并通过在实验室内开展高压电晕放电试验, 测量了不同背景电场下的电晕电流; 与本文所建模型的仿真结果进行对比, 对模型的正确性进行了验证. 基于上述模型, 对正极性辉光电晕在雷云感应作用下的起始发展过程与电晕特性进行了仿真模拟, 得到了该电晕的电晕电流、正离子密度分布规律以及正离子迁移规律. 发现在雷云电场作用下, 电晕放电产生的正离子在迁移初期于垂直于地线的平面内基本呈圆对称状均匀分布, 但随着离子逐渐远离地线其分布不再均匀, 呈拉长的椭圆形分布, 多数离子最终分布于地线上方区域并逐渐向雷云方向迁移; 由于正离子在地线上方迁移区聚集形成的正空间电荷背景对行进电子束具有衰减和消耗作用, 抑制了电子崩的形成, 并降低了电子崩转化为流注的概率, 阻止了新的电子崩对流注的不断注入, 同时正空间电荷背景使气体的碰撞面增大, 增加了与电子的复合概率, 引起大量电子的消耗, 最终抑制了电子崩的形成与流注的发展, 地线表面的上行先导得到抑制.     

Computational study of glow corona discharge in wind: Biased conductor

Corona discharges in flowing gas are of technological significance for a wide range of applications, ranging from plasma reactors to lightning protection systems. Numerous experimental studies of corona discharges in wind have confirmed the strong influence of wind on the corona current. Many of these studies report global electrical characteristics of the gaseous discharge but do not present details of the spatial structure of the potential field and charge distribution. Numerical simulation can help clarify the role of wind on the ion redistribution and the electric field shielding. In this work, we propose a methodology to solve numerically for the drift region of a DC glow corona using the usual approach of collapsing the ionization region to the electrode surface, but allowing for strong inhomogeneities in the electrical and flow setup. Numerical results for a grounded wire in the presence of an ambient electric field and wind are presented. The model predicts that the effect of the wind is to reduce the extension of the corona over the wire and to shift the center of the ion distribution upstream of the flow. In addition, we find that, even though the near-surface ion distribution is strongly affected by the ion injection law used, the current characteristics and the far field solution remain pretty much unaffected.     

Modelling of ions for seeding technique to electrify the atmosphere

There are number of ways in which weak electrification can affect the microphysics of clouds, with consequences for cloud lifetime, radiative properties, and precipitation efficiency. Kauffman [2011] suggested ions produced by direct current generators will add to and enhance the catalysing effects that cosmic ray ions are now known to produce in among other things, lowering nucleation barriers, stimulating charged particle growth and stability and increasing the scavenging rate in clouds. Thus to electrify the atmosphere ions can be generated artificially in abundance along with large electric field.Ions can be generated by the corona effect using Atmospheric electrifiers (a device used to generate negative ions) which makes use of corona discharge phenomenon to charge the air particles. Exact assessment of electric field and charge density distributions and the flow dynamics inside the electrifiers is essential to understand the particle behaviour inside the electrifiers.In this paper, a novel model of governing equations to evaluate the space charge density, electric field intensity and velocity of ionized airflow is suggested as a function of applied voltage. The Poisson and charge conservation equations are derived and hence can be used to estimate the electric field and charge density distributions. Navier stokes equation can be used to get the velocity of ionized airflow because of electric force on the air. Simulation is carried out to validate the proposed model and verify that velocity is function of input voltage and is proportional to it.     

Evolution of the ion velocity distribution after sudden turn-on of a periodic electric field: A charge exchange model

An analytical solution to the problem of the ion velocity distribution evolution after turn-on of a periodic electric field is derived. The solution is constructed for the case of resonance charge exchange at a constant collision frequency (charge exchange model). The specific features of the transient process at the early stage of evolution are revealed. The phase shift between the applied field and the ion current at the periodic stage of the process is analyzed. The distribution function exhibits abrupt steps propagating in the velocity space. A method is proposed to study the ion-atom interaction cross section using a periodic electric field. The method is based on analysis of the current toward the electrode with a retarding potential.     

点电荷在拓扑绝缘体和导体中感应磁单极

利用电势和磁标势的第一类零阶贝塞尔函数的公式及拓扑绝缘体材料的本构关系, 推导了点电荷在电介质、 拓扑绝缘体和接地导体三个区域的感应电势及感应磁标势. 研究表明: 点电荷 在电介质、 拓扑绝缘体和接地导体中感应了像电荷和像磁单极; 感应像电荷和感应像磁单极的大小和正负除了与场源电荷、 拓扑绝缘体材料参数等因素有关外, 还与像电荷和像磁单极所处的空间位置有关.     

水蒸汽喷嘴荷电器在烟道中应用的研究

利用传统的Laval喷嘴,采用燃煤锅炉的功余饱和蒸汽作为预荷电器的传输煤质,对高压电晕针的位置,过热蒸汽的温度、压力与有效电流之间的关系进行了研究,并将水蒸汽正、负荷电器布置于旋风水膜除尘器改造工程的烟道中,经现场测试达到静电除尘器国家环保排放标准。     

An alternative approach for charge decay measurement to assess the suitability of materials

A method of charge decay testing is proposed in which a localized electric field is applied by a fieldmeter to an area of the material to be tested. The variation of electric field is recorded as charge migrates across the surface. Arrangements are described for this method of testing and studies reported comparing results with corona and tribocharge decay measurements. Interesting differences are shown between the methods of testing.Induction charge decay testing is not proposed as a replacement for corona or tribocharge decay testing. It offers the opportunity for simpler instrumentation and measurement of faster charge decay times.     

Injection and transport of electric charge in a metal/copolymer structure

The dynamical processes of the electric charge injection and transport from a metal electrode to the copolymer are investigated by using a nonadiabatic dynamic approach. The simulations are performed within the framework of an extended version of the one-dimensional Su-Schrieffer-Heeger (SSH) tight-binding model. It is found that the electric charge can be injected into the copolymer by increasing the applied voltage. For different structures of the copolymer, the critical voltage biases are different and the motion of the injected electric charge in the copolymer varies obviously. For the copolymer with a barrier-well-barrier configuration, the injected electric charge forms a wave packet due to the strong electron-lattice interaction in the barrier, then comes into the well and will be confined in it under a weak electric field. Under a medium electric field, the electric charge can go across the interface of two homopolymers and enter into the other potential barrier. For the copolymer with a well-barrier-well configuration, only under strong enough electric field can the electric charge transfer from the potential well into the barrier and ultimately reach a dynamic balance.     

界面极化注极聚丙烯薄膜驻极体的电荷存储特性研究

本文报道一种基于双层介质界面极化机理的新型驻极体注极技术: 借助辅助层对PP薄膜进行注极. 采用表面电位测试方法考察了注极温度、注极电压对所获PP薄膜驻极体电荷存储性能的影响, 并利用热刺激放电技术研究了其高温电荷存储性能, 同时测试了PP薄膜驻极体在X和Y方向的静电场分布. 结果表明: 界面极化注极是一种比电晕注极更为优异的驻极体形成方法. 在一定温度下, 驻极体表面电位随注极电压的增加而增加, 而且两者呈线性关系, 这一结果与注极过程的电荷积聚方程的分析完全一致. 注极温度的影响研究表明, 在保持注极电压不变(注极电压范围为0.5–3.0 kV)的情况下, 温度低于75 ℃时, 温度的变化对于注极效果的影响不明显; 当注极温度大于75 ℃ 时, PP薄膜驻极体的表面电位随注极温度的增加而增加. 表面电位随时间的变化研究表明, PP薄膜驻极体具有良好的电荷存储稳定性. 对其表面电位分布的测试表明, 界面极化注极所形成的PP薄膜驻极体呈现均匀的静电场分布.     

Electric-field-induced polarization of the layer of condensed ions on cylindrical colloids

In concentrated suspensions of charged colloids, interactions between colloids can be induced by an external electric field through the polarization of charge distributions (within the diffusive double layer and the layer of condensed ions) and/or electro-osmotic flow. In case of rod-like colloids, these field-induced inter-colloidal interactions have recently been shown to lead to anomalous orientation perpendicular to the external field, and to phase/state transitions and dynamical states, depending on the field amplitude and frequency of the external field. As a first step towards a (semi-) quantitative understanding of these phenomena, we present a linear-response analysis of the frequency-dependent polarization of the layer of condensed ions on a single, long and thin cylindrical colloid. The in-phase and out-phase response functions for the charge distribution and the electric potential are calculated for arbitrary orientation of the cylindrical colloid. The frequency-dependent degree of alignment, which is proportional to the electric-field-induced birefringence, is calculated as well, and compared to experiments on dilute fd virus suspensions.     

Decrease in the static electric gas breakdown voltage in the presence of free electrons in a discharge gap

The dependence of the gas breakdown voltage U _B on the anode-cathode spacing d, pressure p, and other gas characteristics in the presence of a steady external ionizer in the discharge gap was determined within the avalanche discharge theory. The case was considered where the spatial charge created by the external ionizer did not distort the electric field in the discharge gap. In the absence of external ionizer the obtained dependence comes down to the well-known expression for the gas breakdown voltage (the Paschen law).     

Acoustics of a flanged cylindrical pipe using singular basis functions

The problem of acoustic radiation from a cylindrical pipe with an infinite flange has been discussed in a number of papers. The most common approach is to decompose the field inside the pipe over a basis of Bessel functions. A very large number of basis functions is usually required, with a large degree of ripple appearing as an artifact in the solution. In this paper it is shown that a close analysis of the velocity field near the corner yields a new family of functions, which are called "edge functions." Using this set of functions as test functions and applying the moment method on the boundary between the waveguide and free space, a solution is obtained with greatly improved convergence properties and no ripple.     

宏观电偶极子对聚丙烯铁电驻极体膜电荷储存及其动态特性的影响

利用栅控恒压电晕充电组合反极性电晕补偿充电法，研究了孔洞(单元电畴)内分布的空间电荷型宏观电偶极子的形成，及其增长对聚丙烯孔洞膜电极化期间的电流特性及电导率的影响. 借助等温表面电位衰减测量、开路和短路热刺激放电电流谱分析等，讨论了宏观电偶极子及其密度变化时的聚丙烯孔洞驻极体膜电荷储存稳定性及电荷动态特性. 实验结果说明：由电极化形成的宏观电偶极子的自身电场提高了聚丙烯孔洞驻极体膜的电导率，从而降低了驻极体膜电荷储存的稳定性. 对呈现弱极化强度的孔洞驻极体膜，以孔洞为畴结构基本单元内的宏观电偶极子，其两性空间电荷的大部分仅仅分别沉积在透镜状孔洞上下两壁的两端. 外激发脱阱电荷从脱阱位置的输运路径，主要是绕孔洞两边沿介质层迁移；而极化强度较高的样品，其两性电荷则分别分布在上下两壁的宽广区域内，脱阱电荷的大部分在驻极体电场驱动下从脱阱位置通过孔洞层间的介质层迁移并衰减.     

电荷非平衡super junction结构电场分布

建立了电荷非平衡情况下super junction(SJ)耐压结构的二维电场分布理论模型. 获得了浓度和宽度非平衡、梯形n-/p- 区和横向线性缓变掺杂三种非平衡SJ结构的电场分布. 理论分析结果与二维器件数值仿真软件MEDICI的仿真结果符合良好. 虽然给出的电场分布为三角级数形式, 但仍能从中获得很多重要信息. 特别地, 由此可求出非平衡SJ结构的峰值电场和耐压. 该结果有助于对SJ结构的深入分析. 关键词： super junction 电场分布 电荷非平衡     

Improved fictitious charge method for calculations of electric potential and field generated by point-to-plane electrodes

In the framework of standard tip-to-plane electrode geometry favorable to corona streamer discharge development at atmospheric pressure, this work is devoted to the improvement of fictitious charge method for calculations of electric potential and field repartition when the tip is powered by a DC voltage. It is in fact dedicated to implement the image charge method (generally used in plane-to-plane electrodes) in the case of a point-to-plane geometry. The numerical method is based on the solution an open system of n equations with m unknowns (n >> m) where m is the number of fictitious charges and n the number of contours at the surface of the tip electrode defining the boundary conditions. This numerical technique can accurately interpolate the shape of the electrode tip whatever its geometry and hence allows us to accurately calculate the electric potential and field even at a position very close to the electrode. It is noteworthy that the solution of such open system of equations cannot be obtained from conventional techniques (Cramer, Gauss, matrix inversion, etc.). We used the method of least squares which enables us to close the equation systems and to find the optimal solution fulfilling all the required boundary conditions. The present method is therefore based on the coupling between the conventional method of fictitious charges using image charge method and the optimization by the Least Squares Method. The results of simulation show that the punctual fictitious charges have given the most accurate results when the electrode has symmetry of revolution like the present geometry of a pen shape anode cylinder ended by a sharp tip set in front of cathode plane.     

The influence of dielectric surface charge distribution upon thepartial discharge behavior in short air gaps

A two-dimensional breakdown model based upon the continuity equations for electrons and ions and the Poisson equation is employed to examine the influence of surface charges upon the partial discharge behavior of a short metallic-dielectric plane-parallel electrode gap of 0.05 cm in an air-like mixture at atmospheric pressure. The form of charge distribution at the dielectric electrode surface is found to significantly affect a number of important discharge parameters, such as the uniformity of the electric field, the charge density and its radial distribution within the gap, as well as the discharge propagation time     

Analytical model of a corona discharge from a conical electrode under saturation

Exact partial solutions are found for the electric field distribution in the outer region of a stationary unipolar corona discharge from an ideal conical needle in the space-charge-limited current mode with allowance for the electric field dependence of the ion mobility. It is assumed that only the very tip of the cone is responsible for the discharge, i.e., that the ionization zone is a point. The solutions are obtained by joining the spherically symmetric potential distribution in the drift space and the self-similar potential distribution in the space-charge-free region. Such solutions are outside the framework of the conventional Deutsch approximation, according to which the space charge insignificantly influences the shape of equipotential surfaces and electric lines of force. The dependence is derived of the corona discharge saturation current on the apex angle of the conical electrode and applied potential difference. A simple analytical model is suggested that describes drift in the point-plane electrode geometry under saturation as a superposition of two exact solutions for the field potential. In terms of this model, the angular distribution of the current density over the massive plane electrode is derived, which agrees well with Warburg??s empirical law.