Electric Space Charge Research Articles

Electric space charge threshold observation in polyurethane under high electric fields

Polyurethanes have been extensively studied for their strong electromechanical response. Previous studies have mainly investigated the impact of electrical charges on these polymers' DC conductivity, which was measured on the order of 10−10 S/m. The movement of electric charges is responsible for the macroscopic deformation of polymer films under an electric field. However, this study focused primarily on electric fields below 107 V/m, where the electric current complies with Ohm's law. In this paper, we examine the electric current above this field value and observe a deviation in the current from linearity with the applied field, especially for a high electric field of 106–107 V/m. This change is known in polymers under high electric fields but has never been observed in polyurethane. This suggests the injection of electrode charges into the polymer material. This article provides the threshold at which the transition occurs from linear (Ohm's law) to nonlinear conduction as a result of injected electric charges.

Detection of defect-induced luminescence in epoxy-based insulation materials via phase-resolved photon counting method

Electroluminescence (EL) has shown promise in detecting micro-defects in epoxy-based insulation materials. Understanding the various luminescence mechanisms caused by defects is crucial for improving the characterization and analysis of insulation defects. In light of this, this study proposes a photon counting-based approach to investigate the impact of defects on the entire evolutionary process of the luminescence mechanism. A phase-resolved photon counting (PRPC) method is proposed to examine the polarity and periodicity of photon counting results influenced by defects. Additionally, a simulation model based on the finite element method is established to analyze how defects modify the distribution of electric field and space charges. Observations suggest that the PRPC-based approach holds promise for advancing the defect analysis of epoxy insulation used in gas-insulated equipment.

Electronic properties of polyethylene naphthalate as derived from photo-stimulated discharge, luminescence experiments and quantum chemical calculation

The electronic properties of thin films of poly(ethylene 2,6-naphthalate)—PEN, are investigated based on their photo-physical (optical absorption, photoluminescence) and electrical (space charge distribution, photo-stimulated discharge) behavior. Photo-stimulated currents are associated with optical absorption of the material leading to space charge dissipation as demonstrated by space charge distribution measurement. Based on this set of experimental results and quantum chemical calculation performed on PEN macromolecular system, we propose a new scheme for the electronic levels of PEN. This scheme allows understanding the mechanisms at play in photo-stimulated discharge. One of the main conclusions of our work is that photo-stimulated current measurements do not probe the energy level of traps. Detrapping of charges results from a two-step process where the photon energy is absorbed by chromophores that restitute a part of this energy to trapped charges through various mechanisms. Moreover, the new scheme allows discussing the components of the luminescence excited under different stresses, being electric field, electronic and UV irradiation, charge recombination and thermal activation.

A NUMERICAL ANALYSIS ON THE SUBMICRON- AND MICRON-SIZED PARTICLE SEDIMENTATION IN A WIRE-TO-PLATE ELECTROSTATIC PRECIPITATOR

Electrostatic precipitators (ESPs) are frequently utilized in collecting fine organic and inorganic materials from continuous liquid with few moving parts and high efficiency using electrically charging the particles. In this study, cross-sectional 2D geometry of a wire-to-plate electrostatic precipitator the parametric data of which originally published elsewhere was numerically modeled and validated to investigate submicron-micron particle charging in terms of diffusion and field charging mechanisms and precipitation behavior of particles with detailed electric field properties. Electric field, gas flow, and particle trajectory equations are coupled and solved in a multiphysics solver. Particle tracking is realized with the Lagrangian approach. Results indicate variations in electric field strength and space charge density between corona electrodes, with space charge present in the entire precipitation channel. Between two different charging mechanisms, diffusion charging prevails for charge accumulated on submicron particles, whereas field charging becomes dominant for particles larger than 1μm diameter. However, for the ESP configuration considered in this study, particles reach a charge saturation in less than 0.7 seconds, regardless of their size. Although calculated precipitation efficiencies for micron-sized particles can reach to 100%, efficiencies for submicron particle range drop with increasing particle size, as diffusion charging rapidly loses its effectiveness, in 50-250nm range.

Enhancement and Broadening of the Internal Electric Field of Hole-Transport-Layer-Free Perovskite Solar Cells by Quantum Dot Interface Modification.

Hole-transport-layer-free perovskite solar cells have attracted strong interest due to their simple structure and low cost, but charge recombination is serious. Built-in electric field engineering is an intrinsic driver to facilitate charge separation transport and improve the efficiency of photovoltaic devices. However, the enhancement of the built-in electric field strength is often accompanied by the narrowing of the space charge region, which becomes a key constraint to the performance improvement of the device. Here, we propose an effective regulation method, the component engineering of quantum dots, to enhance the strength of the built-in electric field and broaden the range of space charge. By using all inorganic CsPbBrxI3-x (x = 0, 1, 2, 3) quantum dot interface modification to passivate the defects of MAPbI3 perovskite films, the regulation law of quantum dot components on the work function of perovskite films was revealed, and the mechanism of their influence on the internal electric field intensity and space charge region distribution was further clarified, thereby fundamentally solving the serious problem of charge recombination. As directly observed by electron-beam-induced current (EBIC), the introduction of CsPbBr2I quantum dots can effectively enhance the interfacial electric field intensity, widening the space charge region from 160 to 430 nm. Moreover, the efficiency of the hole-free transport layer perovskite solar cells modified by CsPbBr2I quantum dots was also significantly enhanced by 1.5 times. This is an important guideline for electric field modulation and efficiency improvement within photovoltaic devices with other simplified structures.

Electrical Conduction and Space Charge in Gamma-Irradiated XLPE

It is well known that ionizing radiation impact dielectric and mechanical properties of polymers, as a result of chain scission, crosslinking, and oxidation steps. The electrical conductivity is generally substantially increased after irradiation. We analyze such effects in XLPE after gamma-irradiation. Current measurements reveal a substantial increase in conductivity after irradiation at doses up to 200 kGy. Current-field characteristics change after irradiation and appear indicative of an ionic-type conduction. Space charge measurements confirm the mechanism with obvious heterocharge build-up after irradiation.

Study on space charge accumulation characteristics of 320 kV cross-linked polyethylene cable joints

High-Voltage Direct Current (HVDC) cable accessories are the key equipment to connect HVDC cables, and also the weak link in the cable system. In order to investigate the transport characteristics of space charge in cable joints, a two-dimensional axisymmetric cable joint model was established using the bipolar charge transport model, and its space charge and electric field distribution were analyzed through numerical simulation. Furthermore, the effects of the trap depth based on molecular chain displacement and temperature field on interface charge distribution of cable joint were compared with the basic model, respectively. The results show that the stress cone root and the top of the high-voltage shield are easy to accumulate space charges, which will lead to electric field distortion. The trap depth based on molecular chain displacement is larger than that of basic model at the insulation interface, which hinders the charge transport. The model without considering the effect of temperature field accumulates less charge, and the electric field and space charge at the stress cone root and the top of the high-voltage shield change gently with time. The above research results can provide a reference for the design and optimization of cable joints.

Enhanced high-temperature particle capture through an electrostatic precipitator with assistant electrodes

High-temperature electrostatic precipitators (ESPs) are a potentially effective technology for purifying high-temperature gases. In this study, a comprehensive numerical model was developed to investigate the electric field and particle migration characteristics of an ESP at temperatures ranging from 400 to 600 °C. Moreover, an optimized ESP with assistant electrodes for improved high-temperature particle capture was proposed. The electric field, flow field and particle capture characteristics of the two types of ESPs were compared to demonstrate the superiority of the optimized ESP. Results indicated that high temperatures had a negative impact on ESP performance. As the temperature increased, the operating voltage of the ESP decreased, leading to decreases in both the electric field strength and space charge density. The effective migration velocity of the particles also decreased with increasing temperature, and the inhibitory effect of high temperature on particle capture increased with increasing particle size. The optimized ESP with assistant electrodes exhibited more favorable electric field and flow field characteristics for particle capture compared to those of the conventional ESP. The optimized ESP exhibited higher electric field strength, which increased the electric field force on the particles and promoted particle capture. Meanwhile, the space charge density of the optimized ESP was lower, effectively inhibiting the occurrence of back corona. Moreover, the optimized ESP enhanced the ionic wind downstream of the discharge electrode, thereby promoting particle migration towards the collection electrode. Consequently, the ESP with assistant electrodes effectively improved the collection efficiency.

Non-thermal plasma actuator mechanism in interaction with fluid flow structure for aeronautical flow control

Plasma actuators generated by surface dielectric barrier discharge are developed for controlling flow in aeronautics applications. This research studies the simulation of cold plasma discharge at atmospheric pressure coupled with compressible fluid dynamics using COMSOL Multiphysics 5.4. Modeling of dielectric barrier discharge in air at high voltages is carried out in two dimensions. The development of electric field and space charge density are discussed in several cases to determine the discharge regime. Non-thermal plasma generates tangential ionic winds at the surface during corona discharge. The results are validated by the experimental results of the literature. The maximum electric wind velocity above the actuator grows linearly with the applied voltage, and simultaneously, the horizontal extension of the discharge grows with the applied voltage. The induced electrohydrodynamic force augments with the applied voltage amplitude, reaching saturation at higher voltages. Moreover, as the voltage rises, the discharge becomes filamentary, inducing a higher number of streamer pulses. Hence, the power consumption discharge increases abruptly as the voltage rises. In addition, the efficiency increases at higher voltage amplitudes and with the dielectric thickness. Our findings give a clear description of physical atmospheric plasma parameters in the surface discharge mechanism and the efficiency of the actuator plasma.

Numerical modeling of positive streamer propagation in alternative natural ester and traditional naphthenic oil under sub-microsecond pulsed voltages

In this paper, a two-dimensional axisymmetric numerical model of streamer discharge in alternative natural ester liquid and conventional naphthenic oil under a positive sub-microsecond impulse voltage is proposed. The model is based on the charge drift-diffusion approximation in a divergent electric field. Simulation shows that streamer propagation in naphthenic oil is divided into two stages: stage I with a small streamer velocity of 0–0.91 km s−1 and stage II with a rapidly rising streamer velocity up to 213 km s−1. In natural ester, the streamer velocity gradually slows down from 4.84 km s−1 to 2.11 km s−1. The electric field at the head of the streamer in natural ester ranges from 2.4 × 108 V m−1 to 2.5 × 108 V m−1 during propagation, which is visibly lower but more consistent than that in naphthenic oil (3.5 × 108 V m−1 to 8.4 × 108 V m−1). It is revealed that the different streamer features within the two types of oil are caused by the different competition between the Laplacian electric field and space charge effect at the streamer head. For streamer propagation in naphthenic oil, stage I is dominated by the Laplacian electric field whereas stage II is dominated by the space charge effect. In natural ester, the whole streamer propagation is dominated by the Laplacian electric field. Further, it is indicated that the streamer head consists of two specific discharging regions, i.e. the front region of the streamer head which guides new space charge accumulation and the back region of streamer head which guides density reduction of accumulated space charge. The expansion of the streamer tunnel is caused by the alternating space charges in these two regions. The work in this paper provides a theoretical reference for the practical application of alternative transformer liquids.

Recent advances in the application of scanning probe microscopy in interfacial electroanalytical chemistry

The electrochemical reaction mainly occurs at the electrode/electrolyte interface in the electrochemical system. For a fundamental insight into the interfacial reaction mechanism, in situ/operando analysis of the interfacial evolution at the microscale is essential. Scanning probe microscopy (SPM), noted for its high spatial resolution, real-time imaging, and multifunctional detection, is considered as one of the most important in situ analytical tools for the electrochemical interfaces from the atomic/molecular scale to the nanoscale. This review first introduces the brief principles of typical SPM, such as scanning tunneling microscopy, atomic force microscopy, and scanning electrochemical microscopy. The applications of in situ SPM in surface and interface analysis for electrochemical energy systems, including electrocatalysts and energy storage batteries, are then presented. In addition, in situ detection of the electric double layer and space charge layer is further discussed. Challenges and future developments in the field are proposed in the outlook.

Intensity limit in compact H- and H+ 2 cyclotrons

Compact H- cyclotrons are used all across the globe to produce medical isotopes. Machines with external ion sources have demonstrated average extracted currents on the order of a few mA, although reported operational numbers are typically around 1 mA or below. To explore the possibility of extracting even more current from such cyclotrons, it is important to understand the mechanisms that drive intensity limits and how they scale. In this paper we review some of the key aspects of the beam dynamics in the central region of compact cyclotrons, including rf electric focusing and space charge effects. We derive the scaling of the phase acceptance with the rf gap voltage, harmonic number, etc. We also explore the scaling with different types of ions such as H-, H+ 2 and H+ 3. We discuss the impact of mechanical erosion of the central region electrodes. Thoughout the paper, we use examples and experimental data from two compact H- cyclotrons for reference: the TR-30 series and the TRIUMF 500 MeV machine.

Ferroelectric nematic liquids with conics

Spontaneous electric polarization of solid ferroelectrics follows aligning directions of crystallographic axes. Domains of differently oriented polarization are separated by domain walls (DWs), which are predominantly flat and run along directions dictated by the bulk translational order and the sample surfaces. Here we explore DWs in a ferroelectric nematic (NF) liquid crystal, which is a fluid with polar long-range orientational order but no crystallographic axes nor facets. We demonstrate that DWs in the absence of bulk and surface aligning axes are shaped as conic sections. The conics bisect the angle between two neighboring polarization fields to avoid electric charges. The remarkable bisecting properties of conic sections, known for millennia, play a central role as intrinsic features of liquid ferroelectrics. The findings could be helpful in designing patterns of electric polarization and space charge.

Study and Numerical Simulation of Negative and Positive Corona Discharge: A Review

Two models to describe the phenomenon of corona discharge are presented: the first is known as the plasma model which with plasma chemistry defines the volumetric and surface reactions among charge carriers such as electrons, positive, and negative ions. This model uses Poisson's equation and a formulation of the space-charge density to calculate the electric field necessary to solve the species transport equations. Besides, only the plasma model determines the density of the charge carriers. The second is a simplified model which describes the corona discharge in terms of current conservation coupled with Poisson's equation. This model does not have any connection with the attributes of plasma chemistry. Both models propose solutions for the electric potential and space charge density distribution from the corona electrode to the ground electrode.

Tracking electronic band alignment across 2D bridge-channel MoS2 during charge transport

Commanding charge carrier diffusion in semiconducting channels requires the precise and realistic experimental realization of electronic energy band alignments at the interfaces and within the channels. We have demonstrated a non-contact and direct way to accurately probe the energy band bending at nanoscale spatial precision on MoS2 flakes laid on gold electrodes by mapping the surface potential landscape at non-equilibrium conditions during carrier injection. By systematically varying the charge carrier injection, the contrast gradient in surface potential profiles is studied along the MoS2 channel. Corresponding interfacial parameters, such as surface electric field (ξ), built-in potential (Ψbi), and space charge density (σ), are experimentally determined.

Experiment and numerical simulation on the fine particle migration behaviors for the collection efficiency enhancement of a wire-plate electrostatic precipitator in pig house

In this paper, an integrated numerical model is presented and validated to investigate the particle charging and migration behaviors in a wire-plate electrostatic precipitator (ESP) for the collection efficiency (η) enhancement of the ESP in the piggery. Calculations of the RNG k-ε model, corona model, and particle tracking model are coupled in our model by utilizing MATLAB and COMSOL Multiphysics. This model is used to investigate the influence of various factors, such as the particle diameter (dp), flow velocity (u), and applied voltage (V), on the performance of ESP. Simultaneously, a visual experimental platform for PM2.5 migration is established for verification. The calculated results show that the predicted values of potential distribution, u distribution, and η are in good agreement with the previously reported experimental data. Moreover, the calculated results indicate that two elliptical shapes are produced by a relatively high electric potential and space charge density in the surrounding of the discharge corona wires. Furthermore, η first decreases with the increase of dp, remains unchanged in the range of 0.1–1.0 μm, and then increases until became constant in the range of 1.0–10 μm, revealing the interaction between diffusion charging, electric field charge, and fluid drag. In addition, the experimental and calculation results indicate that the η of PM2.5 increases with the decrease of u and increase of V. Notably, η of 2.0 μm is 100% at u = 1 m/s, V = 50 kV. Therefore, both the migration behavior solution method and the rules of η dependence on PM2.5 provide a scientific parameter control method for improving the air quality in pig house.

Simulation of electric field and space charge of typical particle defects of HVDC cable

Simulation of electric field and space charge of typical particle defects of HVDC cable

High frequency doubling efficiency THz GaAs Schottky barrier diode based on inverted trapezoidal epitaxial cross-section structure

A high-performance terahertz Schottky barrier diode (SBD) with an inverted trapezoidal epitaxial cross-sectional structure featuring high varactor characteristics and reverse breakdown characteristics is reported in this paper. Inductively coupled plasma dry etching and dissolution wet etching are used to define the profile of the epitaxial layer, by which the voltage-dependent variation trend of the thickness of the metal-semiconductor contact depletion layer is modified. The simulation of the inverted trapezoidal epitaxial cross-section SBD is also conducted to explain the physical mechanism of the electric field and space charge region area. Compared with the normal structure, the grading coefficient M increases from 0.47 to 0.52, and the capacitance modulation ratio (C max/C min) increases from 6.70 to 7.61. The inverted trapezoidal epitaxial cross-section structure is a promising approach to improve the variable-capacity ratio by eliminating the accumulation of charge at the Schottky electrode edge. A 190 GHz frequency doubler based on the inverted trapezoidal epitaxial cross-section SBD also shows a doubling efficiency of 35% compared to that 30% of a normal SBD.

The Effect of Corona Wire Position and Radius in a Duct-Type ESP with Wavy Collecting Plates

Electrostatic precipitators (ESPs) have become one of the most effective methods for removing harmful particles from various industries. Many investigations in this subject are constantly developing due to the inherent benefits of using an ESP, and there are many robust initiatives taking place today all over the world. Different configurations of collection and discharging electrodes must be investigated to improve the ESP performance of ESPs. Many studies are working to enhance existing models in different ways. The geometry of the electrodes and the collecting plates is one area that could be improved. This paper investigates the wavy designs of collecting electrodes with varied corona electrode radius (range of variable corona radius (0.07-0.6 mm)) and position in a single-stage ESP. Wavy plates (WPs) and Inverted wavy plates (InvWPs) are compared to flat plates (FPs) using a numerical simulation tool. The results of this work show the impact of changing the corona radius when wavy and inverted wavy collecting electrodes are used on the electric potential, electric field strength, current density, and space charge density distribution, and particle collection efficiency. When compared to InvWPs and FPs, WPs show the highest performance in this range of particles. Although InvWPs can be utilized to reduce current density or space charge density, they do not increase particle collection efficiency.

Charge transport and space charge dynamics in EPDM/2D-nanoclay composite dielectrics

Composite dielectrics with two types of 2D-nanoclays (i.e., Kaolinite and Talc) incorporated in ethylene propylene diene monomer (EPDM) as the polymer matrix exhibit distinctly different electrical performances for high-voltage direct current (HVDC) cable insulations. This study investigated electrical conductivity and space charge as the key electrical characteristics of DC cable insulation in conjunction with dielectric spectroscopies. The findings of this study revealed that the composite dielectric with Talc 2D-nanoclays significantly suppressed space charge and thus minimized electric field distortion to less than 9% under 20 kV/mm at both measured temperatures of 25 °C and 50 °C with thermal gradient. In addition, the activation energy of electrical conductivity for the composite dielectric with Talc 2D-nanoclays is 0.45 eV which is notably lower than that of the composite dielectric with Kaolinite 2D-nanoclays, 0.95 eV. Based on the experimental results, the microstructural characteristics of composite dielectrics were discussed to provide insights into charge transport and space charge dynamics in the composite dielectrics. The charge transport mechanism attributed to the electronic and ionic conduction was explained, and the reasons for space charge accumulation were discussed. The larger interfacial area of 2D-nanoclay particles, the uniform and oriented distribution of 2D platelet-like nanoclay, and the smaller difference between the bandgap of polymer and 2D-nanoclay particles contribute to controlling the charge transport and suppressing the space charge accumulation in the composite dielectrics. Charge dynamics from the dielectric spectroscopy based on the Dissado-Hill model analysis confirms the explained mechanism.