Electric-potential-measurement-based methodology for estimation of electric charge density at the surface of tribocharged insulating slabs

The auto-compensated electrostatic induction probe (ACEIP) is widely used for measuring the electric potential at the surface of conductive or insulating bodies. The aim of this paper is to elaborate a methodology for using this probe in view of performing the estimation of electric charge density at the surface of tribocharged insulating slabs. In such cases, the electric potential is not uniformly distributed on the surface under investigation. Metallic plates trimmed with different shapes were used to characterize the probe. Thus, a first series of experiments enabled a crude evaluation of the shape and size of the area “seen by the probe”: a 10-mm-diameter circle. Other experiments served to determine the transfer function that relates the value measured by the probe to the potential of a small area of constant electric potential located at a well-defined distance from it. By dividing the surface under investigation into a large number of small elementary areas, it was possible to use this transfer function to express the potential measured by the ACEIP as the sum of the contributions of each such element. An inverse matrix computation method enabled the estimation of the actual surface electric potential. Based on the results of a final set of experiments, the distribution of the electric charge density was estimated for slabs charged by corona-respectively triboelectric-effect.     

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.     

Behaviour of charged insulating particles in contact with a rotating roll electrode

The overall economic efficiency of standard industrial roll-type separators for granular materials can be improved by operation at higher velocities of the rotating roll electrode. The aim of this paper is to estimate how high this speed could be and still have a good separation. The answer to this question implied the calculation of the electric image force, which opposes the centrifugal force and sticks the corona-charged insulating particles to the rotating roll electrode. This force depends on the residual charge carried by the particles. By estimating the decay of this charge from surface potential measurements carried out on granular layers of insulating materials dispersed on grounded plate electrodes, it was possible to simulate the particle lift-off from the rotating roll electrode under various operating conditions. The results presented in the paper were obtained for fly-ash particles, but the numerical simulation methodology employed by the authors can be successfully applied for the optimisation of other electrostatic separation applications.     

Neutralization of charged insulating granular materials using AC corona discharge

The control of the residual electric charge carried by granular materials processed in various electrostatic installations is a prerequisite for the safe and efficient operation of the respective industrial equipment. The aim of the present work was to evaluate the neutralization efficiency of polyethylene granules exposed to an AC corona discharge from a wire-type electrode. The control variables and their domains of variations were the following: the amplitude and the frequency of the applied high voltage (16–18 kV, 20–400 Hz), the position of the corona electrode (3–7 cm above the ground plate that carries the sample) and the duration of the exposure to the corona discharge (4–10 s). The surface potential decay method was used for monitoring the charge carried by granular samples of PE before and after neutralization. Design of experiment methodology was employed to evaluate the influence of each of the above mentioned control variables and determine the optimum operation conditions. The efficiency of the neutralization was characterized by the ratio between the values of the surface potential before and after AC corona discharge exposure. The obtained results show that neutralization efficiency may be improved by increasing the frequency of the high voltage as well as by adequately correlating its amplitude with the inter-electrode spacing.     

Dielectric barrier discharge in needle-to-plane configuration: Model of surface charge relaxation

Relaxation process of surface charge owing to dielectric barrier discharge (DBD) in “needle – air gap – polyethylene terephthalate film – plane” configuration is considered. Experimental data of the surface charge relaxation (SCR) are obtained by means of the rotating capacitive probe. Taking into account Gaussian radial distribution of accumulated charge density, effective surface and volume electrical conductivities of a barrier dielectric, phenomenological model of SCR for any dielectric thickness is proposed and exact solutions are obtained. The adequacy of the model is confirmed by the numerical computation. There is a good agreement between the experimental results and the model calculations.     

Field enhancement effect of metal probe in evanescent field

Field enhancement effect of metal probe in evanescent field, induced by using a multi-layers structure for exciting surface plasmon resonance （SPR）, is analyzed numerically by utilizing two-dimensional （2D） TM- wave finite difference time-domain （FDTD） method. In this letter, we used a flmdamental mode Gaussian beam to induce evanescent field, and calculated the electric intensity. The results show that compared with the nonmetal probe, the metal probe has a larger field enhancement effect, and its scattering wave induced by field enhancement has a bigger decay coefficient. The field enhancement effect should conclude that the metal probe has an important application in nanolithography.     

气体放电等离子体特性测量I-V曲线不对称性的研究

利用气体放电双探针法研究了等离子体的I-V曲线中的电流I相对于电压V轴交点的不对称性,并提出2种可能的解释:一认为是由于两探针表面积不同引起的;二认为是由于探针所在处等离子体电位不等引起的.本文利用仪器的工艺误差和调换放电管电压的方法,对提出的2种可能原因分别进行验证,并指出第二种解释的合理性,并对其进行了理论分析.     

Use of internal probes for diagnostics of pulse plasma

The paper describes the use of internal magnetic and electric probes for determination of the plasma parameters in the rail accelerator. Suitability of the electric probe is verified by comparison of the floating potential and plasma potential. The intrinsic magnetic field in the cluster, axial component of the electric field, current density and density of electrones in the cluster were measured by these two probes. On the base of obtained results the degree of ionisation and average value of the intrinsic magnetic field were determined.     

Electric fields and surface charge in a thin-film ferroelectric-dielectric switchable structure that were determined with a spectral probe

A new method is proposed to study the macroscopic ac fields in the elements of thin-film ferroelectric-dielectric heterostructures during their electric switching. For this purpose, the local field surrounding dielectric molecules is measured. It is important that the dielectric has a characteristic very narrow molecular absorption band, which is used as an electric-field probe. The heterostructure under study consists of a glass substrate, a transparent electrode, a 170-nm-thick layer of polymer ferroelectric, a 40-nm-thick dielectric layer, and a semitransparent electrode. Both functional layers are grown by the Langmuir-Blodgett method. An ac electric field is applied to the electrodes, and the local field having appeared in the dielectric is measured by the electroabsorption method. With allowance for the Lorentz factor, the local field is easily converted into the macroscopic field in the dielectric layer and, then, in the ferroelectric layer. The classical Sawyer-Tower scheme is used as an additional tool to determine the surface charge to be switched at the dielectric-ferroelectric interface.     

Corona-discharge-based neutralization of charged granular insulating materials in contact with an electrode of opposite polarity

Charge neutralization is a key operation in many electrostatic processes. A wide-range of charge neutralizers have already been developed for various applications: eliminate shock and ignition hazards, avoid electrostatic discharges that might affect the operation of electronic equipment, reduce electrostatic adhesion forces that might stick granular materials in pneumatic conveyors, and so on. The aim of the present paper is to evaluate several methods of charge neutralization for charged granular insulating materials spread on an electrode energized from a voltage source of opposite polarity, a situation encountered – for instance – in two-metallic-belt tribo-aero-electrostatic separators, and which is not covered by commercially-available solutions. Three corona-discharge-based charge neutralization systems are studied: (i) DC-biased AC voltage applied to a corona dual-type electrode; (ii) DC-biased AC voltage applied to a triode-type electrode system; (iii) DC voltage applied to a corona dual-type electrode. The charged samples of polycarbonate granules are obtained at the outlet of a tribo-aero-electrostatic separator. The electric charge per mass ratio of each sample is measured before and after neutralization. The third of the above-mentioned charge neutralization solutions seems to be the most effective solution, but it requires an appropriate adjustment of the DC voltage applied to the corona dual-type electrode.     

Detection of the Electric Potential Surface Distribution with a Local Probe Based on a Field Effect Transistor with a Nanowire Channel

Technical Physics - A non-destructive method of scanning probe microscopy for simultaneous measurements of the surface topography and electric field (charge, potential) distribution is...     

Space charge behavior and its modified electric field in the cross-linked polyethylene under applied voltage DC and different temperatures

In this paper, space charge behavior in dielectric material and the capacitive charge at an electrode-dielectric interface, at room temperature under an applied electric field, has been investigated. This was done for a single sample and for a combination of the sample and a non-stressed sample using the pulsed electro-acoustic (PEA) method. A negative charge injected at the dielectric interface under an electric field (polarization) and high temperatures was focused on. It was found that negative charge injection takes place under all the test conditions, and this charge can be affected by the electric field and the temperature.     

Relationship between surface potential and d33 constant in cellular piezoelectric polymers

The development of cellular piezoelectric polymers has shown very promising results thanks to their high d₃₃ piezoelectric constants which make them candidates for many applications. Cellular piezoelectric polymers, known as ferroelectrets, are obtained by means of an activation process which consists in generating an internal dipole with electrostatic charges produced by internal electric discharges. The most common system for this activation process is the application of a corona discharge on the surface of the sample in order to produce a high internal electric field. The theoretical electrostatic model of the process which is widely used is the Sessler model which relates the internal surface charge density, the air and polymer layers thickness, the dielectric permittivity of the polymer and the Young's Modulus of the cellular material to the d₃₃ piezoelectric constant. In our work, we relate the internal charges of the material with the d₃₃ piezoelectric constant by means of a surface potential scanning of cellular polypropylene biaxially stretched samples. Samples were charged by a corona discharge controlled with a triode electrode. Surface potentials were high enough to generate internal discharges and obtain measurable d₃₃ piezoelectric constants but low enough to be measured with spatial resolution by means of a 3 kV electrostatic probe. Surface potential profiles showed some deviations from the expected bell-shape profile due to the internal electric field generated by the internal static charge. These deviations can be numerically related to the measured d₃₃ piezoelectric constant with the electrostatic Sessler model.     

Nonambipolar magnetic-fluctuation-induced particle transport and plasma flow in the MST reversed-field pinch

First direct measurements of nonambipolar magnetic fluctuation-induced charge transport in the interior of a high-temperature plasma are reported. Global resistive tearing modes drive the charge transport which is measured in the vicinity of the resonant surface for the dominant core resonant mode. Finite charge transport has two important consequences. First, it generates a potential well along with locally strong electric field and electric field shear at the resonant surface. Second, this electric field induces a spontaneous E x B driven zonal flow.     

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.     

Triboelectrification of granular insulating materials as affected by dielectric barrier discharge (DBD) treatment

The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect.     

Hollow cathode effects in charge development processes in transienthollow cathode discharges

A detailed experimental study of space charge formation and ionization growth in transient hollow cathode discharges (THCD) is presented. The experiment was performed with an applied step voltage up to 30 kV, with rise time less than 50 ns. The discharge was operated in different gases, at pressures in the range 50-750 mTorr, with cathode apertures ranging from 1 to 5 mm diameter and 5 to 20 mm long, with 10 cm electrode separation. Spatial charge formation, both in the hollow cathode region (HCR) and inter electrode space, has been studied with a capacitive probe array. Properties of high energy electron beams have been measured with a beam-target scintillator-photomultiplier arrangement. Detailed correlations of the electron beam evolution with the charge probe signals inside and outside the HCR clearly demonstrate the role of the electron beam in the initial formation and late evolution of a virtual anode and, in turn, the field enhanced ionization when the anode potential is brought close to the HCR. These results clearly identify the different regimes in which the Hollow Cathode plays a significant role in ionization growth in the inter electrode space and in the processes which eventually lead to electric breakdown     

微环装置中等离子体电位测量

等离子体电位是托卡马克装置的一个重要参数。它的测量在放电机制、等离子体的平衡与稳定、等离子体-表面相互作用以及杂质控制等研究课题中有着极其重要的作用。 本文描述用朗谬尔探针,以及由它组成的对称双探钎系统(以下简称SDP系统)测量微环托卡马克边界区等离子体电位V_0的两种方法和结果。     

Measurements of air discharges from insulating,electrostatic dissipative and conductive materials with different ESD probes

In this work, we have compared the performance of three different kinds of passive resistor-transmission line ESD probes: an unshielded ball probe, a shielded ball probe with the ESD current collected on a coaxial wire tip, and a needle-like probe. We have measured discharges from ESD sources having different surface resistivities including charged insulator surfaces, electrostatic dissipative materials and metal plates. In compliance with the results, there is no single probe type that is ideal for all kinds of situations—there are significant differences between the probe responses comprising sensitivity, charge transferred and peak ESD current. As expected, the initiation of air discharges was suppressed in accordance with increasing surface resistivity of the ESD source.     

Generation and detection of electromagnetic field with charged material oscillation

We generated an electromagnetic field using the spatial oscillation of a charged material such as a polyimide film. The film was vibrated with acoustic waves at 1 Hz–1 kHz. For charged films, changes in electric field intensity with acoustic wave irradiation were detected using an antenna. The electric field intensity and phase were found to be related to the surface voltage and electrical polarity. The surface potential distribution matches the electric field distribution that was measured by scanning the local excitation. These results indicate that this phenomenon can be used to measure the electrical properties of charged materials.