Electric Field Density Research Articles

Achievement of high electric performances for bismuth titanate-based piezoceramics via hot press sintering

Bi4Ti3O12 (BIT) ceramic has great potential in high-temperature environment due to its high Curie temperature TC ~ 675 °C. In this work, hot press sintering (HPS) is applied on the 0.01 mol Ce and Nb/Cr co-doped BIT (BCTNC) ceramics to enhancing the low piezoelectric coefficient (d33 < 7 pC/N) and resistivity. Extremely high d33 (~39 pC/N) together with high TC (~672 °C) and high dc resistivity ρ (~1.49 ×107Ω∙cm at 500 °C) are obtained in HPS samples. The enhancement of piezoelectricity benefits from high density of domain and high poling electric field. Moreover, outstanding thermal stability of piezoelectric constant (d33 ~ 35 pC/N after annealing at 650 °C) and low dielectric loss (tanδ ~ 3.8% at 500 °C) are observed as well. These findings are instrumental in understanding HPS and provide a possible manipulation of crystallized mechanism and domains growing kinetics to enhance piezoelectric performances of BIT based ceramics.

Study and Numerical Simulation of the Electrical Properties of a Duct-Type Electrostatic Precipitator Using Seven Circular Corona Wires: A Review

The study of electrostatic precipitators (ESP) is of great importance in powder technology. Different physical and chemical processes occur during its operation. The objective of this investigation is to analyze and observe electrical phenomena using mathematical models such as Poisson's equation and the charge conservation equation. To carry out the simulation two flat plates and seven corona wires are geometrically arranged based on an ESP prototype. The general form of partial differential equations mentioned along with the boundary conditions was written in software and associated with the different parts of the geometry. For example, the electric field onset is calculated by Peak's law and set as one of the boundary conditions for the corona wires. Defining the space charge density distribution is an essential part because the next processes inside of ESP depend on this parameter. A specific method that splits the space charge density is used to solve these PDEs. Besides, a review of the concepts of the particle charging process, particle kinetics, and particle collection is introduced. The results obtained from the simulation such as the electric potential, electric field, and space charge density, agree with those proposed in some investigations.

Dependence of gain coefficient and response time on the applied electric field in LiNbO3:Fe crystal

In this paper, the characteristics of two-wave mixing in photorefractive crystal LiNbO3:Fe are theoretically and experimentally analyzed. The relationship between the gain coefficient and the external dc electric field is investigated. The effects of the external dc electric field, incident intensity and density of electron donor on the response time are analyzed It has been found that the gain coefficient can be increased by applying the external electric field when the incident intensity and beam crossing angle are 12 mW/cm2 and 15°, respectively. The response time of two-wave mixing can be reduced by enhancing the external electric field incident intensity or density of electron donor. Experimental results show that when the external electric field is increased from 0 to 8 kV/cm, the response time of LiNbO3:Fe crystal drops from 87 s to 72 s. Furthermore, the response time decreases rapidly and then slowly with the enhancement of the incident intensity. The response time reduces from 180 s to 42 s with the increase of the incident intensity when the external electric field is constant at 10 kV/cm. The response time with an external electric field is slightly shorter than that without an external electric field. The experimental results are consistent with the theoretical simulation. The present work can provide application guidance for the research of photorefractive crystals.

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.

Carrier Density Dependence of the Mobility in Disordered Organic Semiconductors with Gaussian Disorder

In this paper, the charge transport properties and energetic disorder are studied for pristine Si-PCPDTBT, mono-PCBM, bis-PCBM, and their blends of Si-PCPDTBT:mono-PCBM, Si-PCPDTBT:bis-PCBM. We show that the current density versus voltage curves of electron-only devices for mono-PCBM, bis-PCBM, Si-PCPDTBT:mono-PCBM, Si-PCPDTBT:bis-PCBM, and hole-only devices for Si-PCPDTBT, Si-PCPDTBT:mono-PCBM, Si-PCPDTBT:bis-PCBM cannot be accurately described using a conventional mobility model within which the mobility depends only on the electric field, but that a fully consistent description of all curves can be obtained using the improved extended Gaussian disorder model (IEGDM). Within the IEGDM, the presence of energetic disorder is described by a Gaussian density of states, and the mobility depends on the electric field and carrier density. Furthermore, we found that the mobility increases as the width of the Gaussian density of states decreases for both electron-only and hole-only devices, and the mobility is closely related to the energetic disorder. We view this as an indication that the energetic disorder appears to govern the charge transport in disordered organic semiconductors.

Multiphysics Simulation Study of the Electrorefining Process of Spent Nuclear Fuel from LiCl-KCl Eutectic Molten Salt

Electrorefining is an important unit operation for the pyroprocessing of spent nuclear fuel; however, the uncontrolled growth of uranium dendrites traps molten salt into the deposited uranium, increases the short-circuit risk, decreases the current efficiency, and thus hinders the engineering application of the electrorefining technology. In this study, the finite element method is applied to the study of the electrorefining dynamics subjected to convection, diffusion, electromigration, and electrode reaction. The velocity field, concentration field, electric field, and flux density field are evaluated. The local current density on the cathode is evaluated under different overall current densities, overpotentials, cathodic shapes and positions for the evaluation of dendritic growth. Finally, it is concluded that the uranium will be deposited priorly onto the cathode tip and the frontside of the cathode facing the anode, the position of the electrode and the shape of the cathode tip will not have significant influence to the priority of deposition, and a glass insulated tip can effectively improve the uneven growth of uranium dendrites on the cathode surface as proposed by Srihari et al. (Sep. Sci. Technol. 51, 1397).

An active microfluidic sensor based on slow-wave substrate integrated waveguide for measuring complex permittivity of liquids

In this paper, a microfluidic sensor based on slow-wave substrate integrated waveguide (SW-SIW) is proposed to measure the complex permittivity of liquids and it achieves an ultrahigh quality factor of 51156, which is much higher than previous reported designs. The proposed sensor consists of three-layer dielectric substrates and an active circuit. The traditional SIW has the fundamental mode of TE101, whose electric field is concentrated inside the SIW structure. The SW-SIW, which is evolved from traditional SIW structure, has the characteristic of relatively small electrical size due to large equivalent capacitance and the capability to confine the electrical field density further. The internal rows of blind via holes are connecting the top layer of second substrate to the bottom layer of third substrate. In order to further reduce the electrical size, an air cavity is formed in second substrate around blind via holes as it can increase the equivalent capacitance of SW-SIW resonator. The air cavity has an important impact on the resonant frequency of the sensor, and the electrical size could be reduced by enlarging the air cavity. In this paper, an appropriate air cavity is adopted with comprehensive consideration of detection sensitivity and electrical size. The polydimethylsiloxane (PDMS) microfluidic substrate is embedded in first substrate. When the resonator is excited, the electric field is confined above the surface of blind vias. The electric field varies with the volume fraction of aqueous solution injected into the microfluidic channel, and the resonant frequency and quality factor alter correspondingly. The variations in the resonant frequency and quality factor are applied to retrieve the complex permittivity of liquid samples. The proposed sensor is fabricated and tested, it has a dimension of 0.678λ0 × 0.432λ0 (λ0 is the wavelength in free space at 3.7 GHz), and the peak sensitivity and unloaded quality factor are about 2.5 % and 51156, which are improved by 67 % and 5015 % than traditional SIW sensor, respectively. In particular, the sensitivity of measuring loss tangent of liquid sample is improved by several times to hundreds of times with the loss tangent range from 0.1 to 0.9 than other reported sensors. The measured data has a good agreement with the reference complex permittivity.

Encoding Manipulation of DNA-Nanoparticle Assembled Nanorobot Using Independently Charged Array Nanopores.

During the past decades, scientists have developed different kinds of nanorobots based on various driving principles to realize controlled manipulation of them for potential applications like medical diagnosis and directed cargo delivery. In order to design a nanorobot with advantages of simple operation and precise control that can enrich the familyof intelligent nanorobots, an encoding manipulation method is proposed to control the movement of a DNA-nanoparticle assembled nanorobot by combing electrophoresis and electroosmosis effect in independently charged array nanopores. The nanorobot is composed of one nanoparticle and one or two ssDNAs. ssDNAs act as the legs of the nanorobot. The selective ion transport through charged nanopores can induce cooperation and competition between the electroosmosis and electrophoresis, which is the main power to activate the nanorobot. Thus by simply switching the applied electric field and surface charge density of each nanopore which is defined as the encoded nanopore according to a predetermined strategy, the well-controlled encoding manipulation including capturing, releasing, jumping, and crawling of the nanorobot is realized in this work. The study is expected to realize its value in many interesting applications like drug delivery, nanosurgery, and so on in the near future.

Simulation of Space Charge Dynamics in Low-Density Polyethylene Using the Gaussian Disorder Model

Space charge dynamics in a low-density polyethylene (LDPE) film is calculated using mobility based on the Gaussian disorder model (GDM), which is commonly used to describe hopping conduction in disordered materials. The GDM exhibits a negative differential mobility under a strong positional disorder. In simulations, injected charges do not form packet-like space charges when using a constant mobility model, whereas packet-like space charges appear when using the mobility based on the GDM. The simulation using the GDM mobility can reproduce the time and voltage dependences of space charge behavior in LDPE. The calculated space charge, electric field, and current density profiles show good agreement with experimental results.

Active Energy‐Efficient Terahertz Metasurfaces Based on Enhanced In‐Plane Electric Field Density

AbstractSubwavelength confinement of electromagnetic modes in periodic structures is essential to tailor light−matter interaction in space and time. Metamaterials with strong electromagnetic field confinement can be extremely sensitive to surface conditions, thereby enhancing the metadevice response for low‐energy electrical, thermal, and optical stimuli. It is important to note that the total field confinement matters, but the contribution of in‐plane electric field density is critical to efficiently harness and manipulate light via active metasurfaces. The authors experimentally demonstrate a new planar metal–semiconductor hybrid terahertz (THz) metasurface design that shows highly sensitive active THz amplitude modulation towards optical illumination. In the proposed design, in‐plane electric field density has been enhanced by 350% to lower the optical pump fluence requirement for energy‐efficient, active modulation of resonances compared to the conventional inductive‐capacitive resonant metamaterials. Such metasurfaces with large in‐plane electric field density can find many applications in developing ultrasensitive sensors and active THz electrical and optical modulators operational at extremely low energies.

High-Power Electromagnetic Pulse Effect Prediction for Vehicles Based on Convolutional Neural Network

This study presents a prediction model for high-power electromagnetic pulse (HPEMP) effects on aboveground vehicles based on convolutional neural networks (CNNs). Since a vehicle is often located aboveground and is close to the air-ground–half-space interface, the electromagnetic energy coupled into the vehicle by the ground reflected waves cannot be ignored. Consequently, the analysis of the vehicle’s HPEMP effect is a composite electromagnetic scattering problem of the half-space and the vehicles above it, which is often analyzed using different half-space numerical methods. However, traditional numerical methods are often limited by the complexity of the actual half-space models and the high computational demands of complex targets. In this study, a prediction method is proposed based on a CNN, which can analyze the electric field and energy density under different incident conditions and half-space environments. Compared with the half-space finite-difference time-domain (FDTD) method, the accuracy of the prediction results was above 98% after completing the training of the CNN network, which proves the correctness and effectiveness of the method. In summary, the CNN prediction model in this study can provide a reference for evaluating the HPEMP effect on the target over a complex half-space medium.

Reaction-Free Concentration Gradient Generation in Spatially Nonuniform AC Electric Fields.

The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating microscale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially nonuniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO2)-coated Ti/Au electrode pairs. Results from spatial and temporal analyses along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 μm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.

Full fluid moment modeling of rotating spokes in Penning-type configuration

Rotating spokes are observed in a partially magnetized plasma using a two-dimensional full fluid moment (FFM) model. In the present setup, where the radial electric field and plasma density gradient exist in opposite directions, it is observed that the spokes propagate in the direction of the diamagnetic drift and not the E × B drift. This is contrary to the modified Simon–Hoh instability, and the results suggest that the spokes can be driven by a strong diamagnetic drift. Different parameters, including magnetic field amplitude and physical domain size, influence the growth of the rotational instability as well as the dominant wave modes that arise. The propagation speed of the rotating spokes obtained from the FFM simulation are in good agreement with the observations in experimental and other computational work.

Direct observation of elemental fluctuation and oxygen octahedral distortion-dependent charge distribution in high entropy oxides

The enhanced compositional flexibility to incorporate multiple-principal cations in high entropy oxides (HEOs) offers the opportunity to expand boundaries for accessible compositions and unconventional properties in oxides. Attractive functionalities have been reported in some bulk HEOs, which are attributed to the long-range compositional homogeneity, lattice distortion, and local chemical bonding characteristics in materials. However, the intricate details of local composition fluctuation, metal-oxygen bond distortion and covalency are difficult to visualize experimentally, especially on the atomic scale. Here, we study the atomic structure-chemical bonding-property correlations in a series of perovskite-HEOs utilizing the recently developed four-dimensional scanning transmission electron microscopy techniques which enables to determine the structure, chemical bonding, electric field, and charge density on the atomic scale. The existence of compositional fluctuations along with significant composition-dependent distortion of metal-oxygen bonds is observed. Consequently, distinct variations of metal-oxygen bonding covalency are shown by the real-space charge-density distribution maps with sub-ångström resolution. The observed atomic features not only provide a realistic picture of the local physico-chemistry of chemically complex HEOs but can also be directly correlated to their distinctive magneto-electronic properties.

Performance Analysis and Optimization of Built-In Permanent Magnet and Salient-Pole Electromagnetic Hybrid Excitation Generators for Vehicles

To solve the problems of the low power density of pure electric excitation generator and nonadjustable magnetic field of pure permanent magnet (PM) generator, a salient-pole hybrid excitation generator (HEG) was proposed in this paper. The designed generator realized coexcitation of two magnetic fields by changing the shape of the pole shoes and embedding the combined-pole PM steels. Compared with other HEGs, it had the advantages of high power density, less excitation loss, and small volume. The paper deduced the analytical expressions of the main magnetic field and armature reaction magnetic field of the HEG and analyzed the armature reaction magnetic circuit, the main influencing parameters, and the influence law of each parameter on the generator output performance to complete the parameter matching of the whole machine. The prototype was trial manufactured and tested with the optimized parameters. The results show that the designed HEG has a low voltage regulation rate, good no-load characteristics, and regulation characteristics. It can ensure the regulated output voltage under rated load conditions and meet the application requirement.

Excellent energy storage and hardness performance of Sr0.7Bi0.2TiO3 ceramics fabricated by solution combustion-synthesized nanopowders

Relaxor ferroelectric Sr0.7Bi0.2TiO3 ceramics were prepared by two types of powders synthesized by solid-state reaction (SSR) and solution combustion synthesis (SCS). The effects of the synthesis techniques of precursor powders on the microstructure, dielectric and energy storage performance of the ceramics were investigated. Compared with the SSR-derived samples, the SCS-derived ceramics show purer phase, more refined grain size, more uniform and denser morphology. Consequently, higher insulating resistivity and activation energy are obtained, thus inhibiting the carrier migration and improving the breakdown field. For the 0.1 mm-thickness ceramics via using SCS nanopowders in place of SSR powders, the critical electric field and recoverable energy density are enhanced from 320 kV/cm and 2.60 J/cm3 to 380 kV/cm and 3.60 J/cm3, respectively. Particularly, a high recoverable energy density of 5.21 J/cm3 with a high efficiency of 91.55% at 543 kV/cm is realized in the 0.04 mm-thickness SCS-derived ceramics. Meanwhile, the Vickers hardness of ceramics is promoted from ∼ 7.15 GPa to ∼ 7.80 GPa by using SSR instead of SCS method. This work suggests that SCS is an effective method to obtain precursor powders for sintering the dielectric ceramics with excellent energy storage and hardness performance.

Analysis of multiscale structures at the quasi-perpendicular Venus bow shock

Context.Solar Orbiter is a European Space Agency mission with a suite of in situ and remote sensing instruments to investigate the physical processes across the inner heliosphere. During the mission, the spacecraft is expected to perform multiple Venus gravity assist maneuvers while providing measurements of the Venusian plasma environment. The first of these occurred on 27 December 2020, in which the spacecraft measured the regions such as the distant and near Venus magnetotail, magnetosheath, and bow shock.Aims.This study aims to investigate the outbound Venus bow shock crossing measured by Solar Orbiter during the first flyby. We study the complex features of the bow shock traversal in which multiple large amplitude magnetic field and density structures were observed as well as higher frequency waves. Our aim is to understand the physical mechanisms responsible for these high amplitude structures, characterize the higher frequency waves, determine the source of the waves, and put these results into context with terrestrial bow shock observations.Methods.High cadence magnetic field, electric field, and electron density measurements were employed to characterize the properties of the large amplitude structures and identify the relevant physical process. Minimum variance analysis, theoretical shock descriptions, coherency analysis, and singular value decomposition were used to study the properties of the higher frequency waves to compare and identify the wave mode.Results.The non-planar features of the bow shock are consistent with shock rippling and/or large amplitude whistler waves. Higher frequency waves are identified as whistler-mode waves, but their properties across the shock imply they may be generated by electron beams and temperature anisotropies.Conclusions.The Venus bow shock at a moderately high Mach number (∼5) in the quasi-perpendicular regime exhibits complex features similar to the Earth’s bow shock at comparable Mach numbers. The study highlights the need to be able to distinguish between large amplitude waves and spatial structures such as shock rippling. The simultaneous high frequency observations also demonstrate the complex nature of energy dissipation at the shock and the important question of understanding cross-scale coupling in these complex regions. These observations will be important to interpreting future planetary missions and additional gravity assist maneuvers.

Effects of humidity on the dynamics and electron recombination of a pin-to-pin discharge in He + H2O at atmospheric pressure

Control of the plasma chemistry is essential for the effectiveness of atmospheric pressure plasmas in many applications. For this, the effects of the humidity of the feed gas on the discharge chemistry need to be considered. Detailed studies are scarce and many of them are dominated by surface interactions, obscuring any volume effects. Here, a negative nanosecond pulsed discharge is generated in a pin–pin 3 mm gap geometry in He + H2O that enables the study of volume kinetics due to minimal surface area. The effect of humidity on the discharge development, electric field and electron density is investigated through experiments and modelling. It is found that the presence of water vapour affects both the electron density at the start of the pulse (remaining from the previous pulse) and the ionisation rates during the ignition phase, leading to a complex dependence of the discharge development speed depending on the water concentration. The electron decay is studied using the 0D global kinetics model GlobalKin. The dominant reactions responsible for the electron decay depending on the concentration of water vapour are determined by comparing experimental and simulated results and these reactions are grouped in simplified kinetic models. It is found that with water concentrations increasing from 0 to 2500 ppm, the complexity of the dominant reactions increases with in particular O2 +, H2O3 + and water clusters becoming important for high water concentrations. This work also provides experimental data for validation of kinetic models of plasmas in controlled environments.

An inventive multi-scale, multiphysics modelling approach and comparative analysis of distinctive features of planar ionization waves in air: II. Positive streamers

A robust numerical framework for positive streamer modelling based on electro-hydrodynamic equations coupled with Poisson and Helmholtz differential equations for the photoionization process is presented. The proposed multi-layer meshing scheme in a 2D non-axisymmetric finite-element model along with a hybrid meshing technique presented in part I of this series paper for negative streamers provide high accuracy, spatial resolution, and capability to present the major features of both positive and negative streamers. In addition, the presented model is utilized to simulate multi positive and negative streamers propagation in a non-uniform electric field in the air. The main characteristics of the positive and negative streamers including the morphology, distribution pattern of space charges, local electric field, diameter, length, and velocity are presented, discussed, and compared with the experiment. Moreover, the impacts of initial seed density and voltage on the propagation of streamers are presented and explained. The branching mechanism arising from Laplacian instability and its impact on the streamer parameters such as tip electric field and dominant charge density is explained.

Investigation of High Voltage Polymeric Insulators Performance under Wet Pollution.

In this paper, a unique approach based on electrical characteristics observed from measurements of contaminated polymeric insulators was established to calculate the electric field distribution over their surfaces. A case study using two different 33 kV polymeric insulator geometric profiles was performed to highlight the benefits of the proposed modeling approach. The conductance of the pollution layer was tested to establish a nonlinear field-dependent conductivity for pollution modeling. The leakage current (LC) of the polluted insulator was measured in a laboratory under clean and wet conditions. Then, using the finite element method (FEM), the electric field and current density distributions along the insulator were computed. The results showed that the insulators experienced an increase in the electric field (EF) magnitude ranging from 0.3 kV/cm to 3.6 kV/cm for the insulator with similar sheds (type I) and 2.2–4.5 kV/cm for the insulator with alternating sheds (big and small, type II) under the high rain condition with a flow rate of 9 L/h. Meanwhile, the highest electric field under fog was 1.74 kV/cm for the insulator with similar sheds and 2.32 kV/cm for an insulator with alternating sheds. Due to the larger diameter on the big shed and the longer leakage distance on the insulator with alternating sheds, the EF on the insulator with alternating sheds is higher than the EF on the insulator with similar sheds. The proposed modeling and simulation provided a detailed field condition estimation around the insulators. This is critical for forecasting the emergence of dry bands and the commencement of flashover on the surfaces of the insulators.