Dynamics of induction charging for multiple particle agglomerations with a thin conducting surface layer

In electrostatic applications, particles are typically stacked in an arbitrary array. In this paper, multiple particle agglomerations with a finite volume conductivity, surface conductivity and permittivity have been simulated. Upon exposure to the electric field, electric shielding can occur due to the proximity of other particles, which greatly reduces the maximum accumulated charge and affects the charging time. All results have been obtained using the COMSOL commercial software. The simulation results show that shielding the electric field from a given particle reduces its saturation charge and the rate of charge accumulation was mainly affected by the volume and surface conductivities.     

高压放电对飞灰表面特性的影响

高压放电对飞灰表面特性会产生影响从而改变飞灰颗粒的荷电特性。使用高压窄脉冲电源大幅提高静电除尘器的放电电压,通过对不同电压放电前后飞灰表面特性进行分析,得到其影响规律。随着放电电压的升高,飞灰表面受到越来越严重的破坏,从开始相对光滑完整的表面结构逐渐转变为具有蜂窝状的新结构。放电电压越高,蜂窝的孔密度越高,孔径越小。复...     

Investigation of layers’ properties using brush discharge: Mobility of charge carriers in the layer is zero

This work is mainly based on the paper “R. Rinkunas, S. Kuskevicius, A contactless method of resistance measurement, Tech. Phys., 59 (2009) 133–137”. This paper contains a proposed contact less method for measuring resistivity of various materials, as well as various ambient parameters related to resistivity, e.g., humidity, intensity of illumination, sample thickness, etc. The mentioned paper describes experimental applications of the proposed method for measuring resistances in the range from 10⁷ Ω to 10¹³ Ω.In this work, a model of the method proposed previously is presented. On the basis of that model, it has been determined that during charging of an insulating layer of a material (on whose surface the deposited ions are immobile), the charge flux becomes wider as it approaches the surface of the insulator. For example, the diameter of the charge flow region may increase from 0.2 mm (near the needle tip) up to 2 cm near the surface of the insulator. [Those numbers correspond to the distance h = 1 mm between the needle and the substrate, insulating layer thickness 40 μm and needle–substrate voltage of 4000 V. A change of those parameters would cause a change of the size of the spot on the layer surface].It has been determined experimentally that resistance of the air gap between the needle and the substrate is linearly dependent only on h, whereas the electromotive force, which is responsible for the electric current from the needle to the substrate, also depends only on h.The radial coordinate of the points where the gradient of the electric charge density is largest is equal to h/2 (a zero radial coordinate corresponds to the point that is directly below the needle).During transfer of charge carriers from the needle onto the surface of the insulating layer, the largest potential is obtained at the point corresponding to radial coordinate r = 0, but this potential is still smaller than the electromotive force that causes electric current in the circuit (i.e., the difference between the power supply voltage and the voltage on the capacitor formed by the needle and the substrate, when no charge has been deposited yet).The time dependence of charging current and of the potential difference between the needle and the substrate is not monotonic: at first the current increases, then it begins to decrease, and the potential difference at first decreases, then it begins to increase. The initial parts of those dependences can be explained by the “breakdown” of the capacitor formed by the needle and the substrate, and the subsequent time dependence is determined by the increase of the insulating layer potential due to accumulation of charge on it.     

Ab initio studies of isolated hydrogen vacancies in graphane

We present a density functional study of various hydrogen vacancies located on a single hexagonal ring of graphane (fully hydrogenated graphene) considering the effects of charge states and the position of the Fermi level. We find that uncharged vacancies that lead to a carbon sublattice balance are energetically favorable and are wide band gap systems just like pristine graphane. Vacancies that do create a sublattice imbalance introduce spin polarized states into the band gap, and exhibit a half-metallic behavior with a magnetic moment of 1.00 μ_B per vacancy. The results show the possibility of using vacancies in graphane for novel spin-based applications. When charging such vacancy configurations, the deep donor (+1/0) and deep acceptor (0/−1) transition levels within the band gap are noted. We also note a half-metallic to metallic transition and a significant reduction of the induced magnetic moment due to both negative and positive charge doping.     

Characteristics of charge and discharge of PMMA samples due to electron irradiation

In this study, using a comprehensive numerical simulation of charge and discharge processes, we investigate the formation and evolution of negative charge and discharge characteristics of a grounded PMMA film irradiated by a nonfocused electron beam. Electron scattering and transport processes in the sample are simulated with the Monte Carlo and the finite-different time-domain(FDTD) methods, respectively. The properties of charge and discharge processes are presented by the evolution of internal currents, charge quantity, surface potential, and discharge time. Internal charge accumulation in the sample may reach saturation by primary electron(PE) irradiation providing the charge duration is enough. Internal free electrons will run off to the ground in the form of leakage current due to charge diffusion and drift during the discharge process after irradiation, while trapped electrons remain. The negative surface potential determined by the charging quantity decreases to its saturation in the charge process, and then increases in the discharge process. A larger thickness of the PMMA film will result in greater charge amount and surface potential in charge saturation and in final discharge state, while the electron mobility of the material has little effects on the final discharge state. Moreover,discharge time is less for smaller thickness or larger electron mobility. The presented results can be helpful for estimating and weakening the charging of insulating samples especially under the intermittent electron beam irradiation in related surface analysis or measurement.     

Charging Quantum Batteries with a General Harmonic Driving Field

A general harmonic driving field was considered for improving the charging efficiency of the quantum battery system. Charge saturation was used to describe the charging efficiency, where the charging mode is divided into saturated and unsaturated. The relationships between the time-dependent charge saturation and parameters of the general driving field were evaluated both analytically and numerically. The Floquet theorem was used to express time-dependent charge saturation with the quasienergy and Floquet states of the system. The analytical and numerical results were used to identify the best parameter values for optimizing the charging efficiency.     

Anomalous optical constants of thin films

The explanation of anomalous optical constants in thin chemically distinct layers on substrates offered by Plumb is re-examined and extended. The model invokes the concept of the space charged boundary layer and treats the charge carrier population as a free-electron gas to derive the optical behaviour of thin surface films. The implication of the space charge means that the optical constants of a dielectric film on a metal will vary over a distance directly proportional to the dielectric constant of the film and inversly proportional to the concentration of the electrons at the metal/film interface. Similarly as the temperature increases this space charge region should extend to larger distances from the interface.     

Spacecraft charging, an update

Twenty years after the landmark SCATHA program, spacecraft charging and its associated effects continue to be major issues for Earth-orbiting spacecraft. Since the time of SCATHA, spacecraft charging investigations were focused primarily on surface effects and spacecraft external surface design issues. Today, however, a significant proportion of spacecraft anomalies are believed to be caused by internal charging effects (charging and ESD events internal to the spacecraft Faraday cage envelope). This review will, following a brief summary of the state of the art in surface charging, concentrate on the problems introduced by penetrating electrons (“internal charging”) and related processes (buried charge and deep dielectric charging). With the advent of tethered spacecraft and the deployment of the International Space Station, low altitude charging has taken on a new significance as well. These and issues tied to the dense, low altitude plasma environment and the auroral zone will also be briefly reviewed     

Millimeter-wave scattering from neutral and charged water droplets

We investigated 94 GHz millimeter-wave (MMW) scattering from neutral and charged water mist produced in the laboratory with an ultrasonic atomizer. Diffusion charging of the mist was accomplished with a negative ion generator (NIG). We observed increased forward- and backscattering of MMW from charged mist, as compared to MMW scattering from an uncharged mist. In order to interpret the experimental results, we developed a model based on classical electrodynamics theory of scattering from a dielectric sphere with diffusion-deposited mobile surface charge. In this approach, scattering and extinction cross-sections are calculated for a charged Rayleigh particle with effective dielectric constant consisting of the volume dielectric function of the neutral sphere and surface dielectric function due to the oscillation of the surface charge in the presence of applied electric field. For small droplets with radius smaller than 100 nm, this model predicts increased MMW scattering from charged mist, which is qualitatively consistent with the experimental observations. The objective of this work is to develop indirect remote sensing of radioactive gases via their charging action on atmospheric humid air.     

Low energy electron diffraction and auger electron spectroscopy studies of the structure of adsorbed gases on solid surfaces

Low energy electron diffraction (LEED) studies of the structure of adsorbed molecules on crystal surfaces revealed that ordered surface structures predominate under most conditions of the experiments. In the absence of chemical reactions with the substrate, the degree of ordering depends on the heats of adsorption, ΔH_ads, and the activation energies for surface diffusion, ΔE_D1. Since ΔH_ads is usually markedly larger than ΔE_D1, small changes of substrate temperature facilitate ordering without appreciable increase in desorption rates. The surface structures of adsorbed gases that have been reported so far have been tabulated. For molecules whose size is compatible with the interatomic distance of the substrate, rules of ordering can be proposed that permit prediction of the structure of the adsorbed layer that is likely to form. These rules indicate close packing due to attractive interactions in the adsorbed layer, and that the rotational multiplicity of the substrate is likely to be maintained by the adsorbate structure. When molecules whose dimensions are larger than the substrate interatomic distance are adsorbed, the conditions that control ordering are more complex and simple rules may not be readily applicable.The surface structures of adsorbed gases have also been studied on high Miller Index substrate surfaces. These surfaces are characterized by ordered steps separated by terraces of low index surface orientation. Many gases have different ordering characteristics on stepped surfaces than on low index crystal faces due to the stronger substrate-adsorbate interactions in these surfaces. The dissociation of diatomic molecules at steps induces the formation of new types of surface structures (frequently one-dimensional) and the dehydrogenation of hydrocarbons at steps induces the formation of ordered carbonaceous surface structures that would not nucleate on low index substrate planes.So far, mostly work function changes upon adsorption gave indication of the magnitude of charge transfer upon adsorption and on forming of new surface chemical bonds. Most recently, chemical shifts of the Auger transitions of the substrate atoms and of the adsorbed molecules upon chemisorption, have been found to provide additional information on charge redistribution during adsorption.     

Analysis of microscopic parameters of surface charging in polymer caused by defocused electron beam irradiation

The relationship between microscopic parameters and polymer charging caused by defocused electron beam irradiation is investigated using a dynamic scattering-transport model. The dynamic charging process of an irradiated polymer using a defocused 30 keV electron beam is conducted. In this study, the space charge distribution with a 30 keV non-penetrating e-beam is negative and supported by some existing experimental data. The internal potential is negative, but relatively high near the surface, and it decreases to a maximum negative value at z = 6 μm and finally tend to 0 at the bottom of film. The leakage current and the surface potential behave similarly, and the secondary electron and leakage currents follow the charging equilibrium condition. The surface potential decreases with increasing beam current density, trap concentration, capture cross section, film thickness and electron–hole recombination rate, but with decreasing electron mobility and electron energy. The total charge density increases with increasing beam current density, trap concentration, capture cross section, film thickness and electron–hole recombination rate, but with decreasing electron mobility and electron energy. This study shows a comprehensive analysis of microscopic factors of surface charging characteristics in an electron-based surface microscopy and analysis.     

Hydrogen chemisorption on Pd(100) studied with he scattering

He scattering from the clean Pd(100) surface yields extremely weak diffraction beams relative to the specular, corresponding to a very small maximum corrugation amplitude of ~ 0.04 Å. Hydrogen adsorption at a temperature of 110 K leads to the formation of a c(2 × 2) ordered phase at a coverage of 0.5 monolayers and a (1 × 1) phase at saturation coverage. The maximum corrugation amplitude of the c(2 × 2)H is ~0.13 Å; surface charge density calculations using overlapping atomic charge densities indicate a normal distance of the hydrogens to the topmost Pd layer d_n ? 0.65–0.70 Å corresponding to a H-Pd bonding distance of ~ 2.05 Å in the fourfold hollow sites. The result that the maximum corrugation amplitude of the (1 × 1) hydrogen phase, with ~ 0.025 Å, even smaller than that of the clean surface may indicate a movement of the hydrogens closer to the topmost metal layer, when the coverage is increased from 0.5 monolayers to saturation.     

Nanoparticle electrostatic loss within corona needle charger during particle-charging process

A numerical investigation has been carried out to examine the electrostatic loss of nanoparticles in a corona needle charger. Two-dimensional flow field, electric field, particle charge, and particle trajectory were simulated to obtain the electrostatic deposition loss at different conditions. Simulation of particle trajectories shows that the number of charges per particle during the charging process depends on the particle diameter, radial position from the symmetry axis, applied voltage, Reynolds number, and axial distance along the charger. The numerical results of nanoparticle electrostatic loss agreed fairly well with available experimental data. The results reveal that the electrostatic loss of nanoparticles increases with increasing applied voltage and electrical mobility of particles; and with decreasing particle diameter and Reynolds number. A regression equation closely fitted the obtained numerical results for different conditions. The equation is useful for directly calculating the electrostatic loss of nanoparticles in the corona needle charger during particle-charging process.     

Effect of ground electrode on charge injection and surface potential of corona charged polyethylene film

The surface potential decay measurement is a simple and low cost tool to assess electrical properties of insulation materials; therefore, understanding the physical mechanisms of the surface potential decay becomes necessary. With our recent space charge measurement results on corona charged samples, bipolar charge injection on corona charged samples had been observed. Based on this new fact, it is anticipated that the ground electrode should have significant effect during corona charging and subsequently decay processes. In the paper, low density polyethylene (LDPE) film with gold ground electrode was compared with LDPE film with aluminium ground to study effect of ground electrode on charge injection and surface potential decay processes. Charging current during the corona charging, surface potential decay and space charge dynamics after corona charging in the samples with either gold coated or aluminium ground electrode were measured. Differences have been observed for gold ground electrode when compared with aluminium ground electrode. Higher work function of gold electrode is responsible for the observed differences. A preliminary simulation has also attempted to show that the bipolar injection may take place in corona charged LDPE films.     

月表尘埃颗粒带电的机理及应用研究

研究月尘颗粒在电子束环境下以及紫外源辐照下的带电机理,利用数值方法模拟月尘颗粒在不同背景环境下的充电过程,以探索月表尘埃颗粒的带电机理,进而便于地面月尘环境模拟装置选择合适的月尘带电方式进行空间模拟实验.给出了尘埃在电子束环境下的充电方程,并将紫外辐射带电与具体应用相结合.通过模拟结果可知,在电子束环境下,月尘表面的电荷数随粒径尺寸增大,随电子枪辐照束斑半径减少,随电子枪流强的增加而增多;在紫外源的辐照下,月尘表面电荷数随颗粒尺寸的增大以及紫外线辐照度的增加而增多.由月尘颗粒受太阳紫外辐照带电的数值模拟结果可知,月尘需要在太阳长时间的辐照下才可以带上可观的电荷数,地面模拟该过程需增加辐照源来加速实验.通过模拟结果的分析比较并结合"空间环境模拟装置"中对月尘舱的设计要求,最终优选紫外源辐照带电方式作为月尘颗粒的带电方案.     

Comparative analysis of light-ion ranges in gaseous,liquid, and solid media

Ranges of ions from He to Ne in gaseous (hydrogen and argon), liquid (water), and solid (carbon) media are analyzed. This analysis demonstrates the different dependences of ranges on the velocities, the charges, and the masses of ions in different velocity region. In the case of small ion velocities, the ranges are directly proportional to their velocities and masses and are inversely proportional to the nuclear charge. In the intermediate velocity region corresponding to an ion energy of Е = 0.1–1 MeV/nucleon, in which processes of ion charge exchange play an important role and the average ion charge differs from the nuclear charge, the ranges become proportional to the squared ion velocities and masses and are inversely proportional to the nuclear charge. To establish the relation between the ion ranges in the regions of small and average velocities, it is convenient to use the universal function f(Z, M) = RZ/M, successfully describing the reduced ranges of ions with given velocities in gaseous, liquid, and solid media. In the case of large velocities where ions upon passing through the media lose all electrons, the ranges are directly proportional to the squared ion energies and masses and are inversely proportional to the squared nuclear charge.     

稳态装置中的尘埃等离子体状态

介绍了用于研究尘埃等离子体中波的直流放电的尘埃等离子体装置,该装置能产生长约３０ｃｍ,直径约８．４ｃｍ的尘埃等离子体柱。在等离了体中加入尘埃后,朗缪尔探针的饱和电流明显降低。尘埃所带负电量与电机转速成正比,可达到等离子体负电量的４０％。     

Influence of charge rate on the cycling degradation of LiFePO<Subscript>4</Subscript>/mesocarbon microbead batteries under low temperature

The lithium-ion batteries show extremely poor cycling performance at low temperature. The main degradation mechanism is not clear. To address the fading mechanism, the cycling degradation of commercial LiFePO₄/mesocarbon microbead (MCMB) batteries under various charge rate (1/10C, 1/3C, 1/2C, and 1C) at ?10 °C is systematically investigated using nondestructive tests combining with post-mortem analysis. The low-temperature charging under high charge rates of 1/3C, 1/2C, and 1C results in severe lithium plating, which leads to extremely serious capacity loss. In contrast, no lithium plating occurred under low charge rate of 1/10C. The lithium plating on the anode surface leads to consumption of active lithium ions and electrolyte, which causes the capacity decay and increases ohmic resistance (R _b) with cycling number under high charge rates. The lithium plating on the anode surface is partially reversible, which brings about the capacity recovery of batteries after 80 cycles at 25 °C. The above results are proved by the followed post-mortem measurements. The evolution of the surface morphologies of MCMB electrodes upon cycling shows that a layer composed of rod-like lithium is formed on the anode surface.     

Nanoparticles superficial density of charge in electric double-layered magnetic fluid: A conductimetric and potentiometric approach

We analyze potentiometric and conductimetric measurements simultaneously performed on Electric Double-Layer Magnetic Fluid based on cobalt ferrite nanoparticles, in order to obtain the pH-dependence of the particle surface charge density. We propose a mechanism for the charging of the particle surface. This model considers the ferrofluid solution as a mixture of strong and weak diprotic acids. We show how an exact analytical treatment involving proton transfer between the particle surface and the bulk solution allows the construction of a speciation diagram of the charged superficial sites. The saturation value of the superficial density of charge is found to be equal to 0.326 ± 0.065 C m^-2. Received 9 May 2001 and Received in final form 17 July 2001     

空间电子辐照聚合物的充电特性和微观机理

空间电子辐照聚合物的充电特性和微观机理是研究和防护航天器聚合物充放电特性的基础.采用蒙特卡罗方法模拟空间电子的散射过程,快二次电子模型模拟二次电子的产生,有限差分法求解电荷连续性方程、电流密度方程和泊松方程的电荷输运过程,俘获过程基于Poole-Frenkel效应来实现.基于电子散射/输运同步模型基础,结合法国国家航空航天科研局(ONERA)的地球同步轨道电子能谱分布理论公式和欧空局(SIRENE)机构的地面实验方法,建立了基于地球同步轨道电子能谱分布的空间多能电子的散射模型.通过空间电子辐照聚合物充电过程的数值模拟,获得了空间电荷密度、电位、电场和空间电位分布.阐明了空间电子辐照聚合物的充电特性和样品微观参数与表面电位的关联性.表面电位特性与实验结果相吻合,单能电子的电位强度高于多能电子的电位.充电达到稳态时,电子迁移率较小时(小于10~(–11)cm~2·V~(–1)·s~(–1)),空间电位绝对值随电子迁移率的降低明显加强;复合率较大时(大于10~(–14)cm~3·s~(–1)),空间电位绝对值随复合率的增大而增大.研究结果对于揭示空间电子辐照聚合物的充电特性和微观机理、提高航天器充放电故障机理研究水平具有重要科学意义和价值.