Average Electric Field Research Articles

Co‐Ni/MOF‐74 catalyst packed‐bed DBD plasma for ammonia synthesis

AbstractNonthermal plasma (NTP) provides a potential and sustainable route for the synthesis of ammonia. In this work, a Co–Ni/MOF‐74 catalyst was developed to synthesize ammonia from N2 and H2 in a dielectric barrier discharge (DBD) plasma at low temperature and atmospheric pressure. Co–Ni/MOF‐74 showed the highest ammonia synthesis rate up to 2608.70 μmol g−1 h−1 at 200°C, with V(N2):V(H2) ratio of 1:1 and specific energy input of 33.27 kJ L−1. The catalytic activity was increased by 19.57% for Co–Ni/MCM‐41 and 375% for Co‐Ni/Al2O3, respectively. It was observed that the average electric field (E) and power efficiency were enhanced while adding Co–Ni/MOF‐74 to the reaction system.

Instability of liquid film with odd viscosity and slip effect under the action of external electric field

The influence of odd viscosity on the instability of a liquid film flowing along a porous inclined plane under a normal electric field is investigated. It is assumed that the flow at the porous inclined plane satisfies the Beavers–Joseph slip boundary condition. By utilizing the long-wave approximation and employing the method of systematic asymptotic expansion, a nonlinear evolution equation for the film thickness under the influence of the electric field is derived. The stability analysis of this evolution equation reveals that the odd viscosity of the film has a stabilizing effect, while the electric field has a destabilizing effect. Additionally, the permeability of the porous inclined plane enhances the instability of the liquid film flow. Numerical simulations are conducted using a fast Fourier transform algorithm to solve the nonlinear evolution equations. The numerical results demonstrate that, within the stable region and with all parameters fixed, the wave amplitude decreases as the evolution time increases, indicating a gradual stabilization of the liquid film flow. Conversely, in the unstable region, the opposite behavior is observed. As the evolution time increases, the fluctuation amplitude grows larger, resulting in a gradual destabilization of the liquid film flow. Furthermore, when the evolution time is kept constant and the odd viscosity coefficient is nonzero, the film exhibits greater stability. The amplitude of the wave increases with the electrical parameter E. In the unstable region, an increase in the permeability β of the porous medium leads to a tendency for the film flow to stabilize.

Assessment of the electromagnetic field exposure due to wireless communication technologies in two university campuses of medellin, Colombia

Exposure to radiofrequency electromagnetic fields (RF-EMFs) is considered an area of significant importance in the medical and scientific community. However, the availability of exposure data for indoor and outdoor locations in universities is limited and currently inconsiderate in Latin America. The aim of this work was to evaluate the electric field levels due to mobile telecommunication technologies and Wi-Fi to which students and faculty staff from two campuses of a higher education institution are exposed. Using a portable spectrum analyzer, we carried out 516 short-term measurements in the 800–3000 MHz frequency range at both indoor and outdoor locations. These locations were chosen to cover all areas of the assessed buildings. The electric field differences between floors and buildings are discussed. Finally, we compared the electric field levels with exposure limits. The highest electric field level measured was 13.97 V/m at the 850 MHz band. However, the average electric field values were below 2 V/m. The greatest contribution to the total electric field was due to sources using the 850 MHz and 1900 MHz bands (98%), while the contribution of the Wi-Fi network was low (1.0%). The results show that all the electric field levels measured were lower than the ICNIRP reference levels for radio-frequency exposure.

Indirect Observations of Electric Fields at Comet 67P

AbstractNo spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At this time comet 67P was at a low outgassing rate and the plasma environment was relatively stable. The ion velocity distributions show the cometary ions on the first half of their gyration. We estimate the bulk drift velocity and the gyration speed from the distributions. By using the local measured magnetic field and assuming an E × B drift of the gyrocentre, we get an estimate for the average electric field driving this ion motion. We analyze a period of 13 hr, during which the plasma environment does not change drastically. We find that the average strength of the perpendicular electric field component is 0.21 mV/m. The direction of the electric field is mostly anti‐sunward. This is in agreement with previous results based on different methods.

Electrical conductivity anomalies study

Anomalous currents in a well-conducting body arise due to local electromagnetic induction inside the anomalous body, as well as due to conductive redistribution (and concentration) of currents induced in the host medium on a large territory equal to the external source size. The local induction generates the so-called anomaly of geomagnetic variations of the magnetic or inductive type. Its characteristic property is that the secondary anomalous field cannot be greater than the primary normal field of geomagnetic variations. However, in some places on the earth’s surface, the normalized anomalous fields are greater than 1. Analytical solution of the EM induction problem for circular cylinder yields the physical explanation of two types of anomalous geomagnetic fields. The first term (proportional to the normal electric field E0) describes the conductive anomaly type, the second term (proportional to the normal magnetic field B0) describes the inductive anomaly type. The conductive type usually is much greater than the inductive one. The normalized anomalous field of the conductive type is not limited to 1 or any other value. It is proportional to two functions: V(T) — the non-decreasing function of the period T (0≤V≤1, V=1 corresponds to DC) which describes the degree of filling of the conductor by anomalous currents (result of the skin effect inside the anomaly) and the normal impe­dance of inclosing cross-section — the decreasing function of the period. Product of these functions has a maximum at some period T0. The position T0 is closely related to the total lengthwise conductance G[S×m] of the anomalous body, that is, the scale of the anomaly. On the period T0, the anomalous fields and the induction vector become real C=Cu and the imaginary induction vector Cv passes through zero changing sign. Thus, the spectral properties of the geomagnetic response functions were studied for two-dimensional anomalies with a generalization to three-dimensional conductors with varying cross-section. 18 crustal electrical conductivity anomalies were considered and their integral lengthwise conductance G was obtained. At all anomalies, the G values turn out to be in a relatively narrow range G=(1—8)·108 S∙m; this has geophysical significance.

Electronic, nonlinear optical, UV–vis and NBO analysis of methyl methacrylate for optoelectronic and optical applications: DFT study and impact of conformation

Using Density Functional Theory (DFT) and time-dependent DFT (TD-DFT), we studied a compound widely used in daily life, namely: Methyl Methacrylate (MMA) monomer in its two stable isomers, cis-MMA and trans-MMA. The impact of conformation on the optical and electronic properties of MMA was highlighted. Structural parameters and thermodynamic properties were also assessed, and allowed to discuss the stability and reactivity of this compound. In addition, analysis of optoelectronic and electronic properties, global reactivity descriptors, natural bond orbital (NBO), and hole and electron reorganization energies was performed. The absorption and fluorescence properties, as well as the linear and nonlinear optical (NLO) properties of MMA were also investigated. The findings show that MMA is an insulator due to its wide band gap of 6.20 eV. It also exhibits good optoelectronic properties with high average electric field values of about 5.90 × 109 Vm−1 for cis-MMA and 5.42 × 109 Vm−1 for trans-MMA and high electric displacement values of at least 14.65 × 10-2 cm−2 for cis-MMA and 14.33 × 10-2 cm−2 for trans-MMA, suggesting a potential use for the design of piezoelectric and pyroelectric materials. In addition, trans-MMA has a dielectric constant close to that of good insulators; while cis-MMA exhibits a dielectric behaviour close to that of polymeric substances. Further, these materials are thermodynamically stable in its two conformations, with a good reactivity which can lead to good ability of polymerization. The analysis of the UV–vis spectra revealed that both forms of MMA absorb and emit mainly in the UV and that the Stokes shift of MMA is low, reducing its potential use in devices such as solar cells. At NLO level, MMA isomers exhibit weak optical properties such as second- and third-order optical susceptibility and cannot suitable for second and third harmonic generation; however, the conformation enhances second-order NLO response by at least 2 times when moving from cis- to trans-MMA, whereas the third-order response is almost unaffected. In addition, the conformation also affects the electronic and optoelectronic properties of MMA.

Shape optimisation of basin insulator for DC gas insulated switchgear/gas insulated transmission lines based on artificial bee colony algorithm

AbstractThe surface charge accumulation on the basin insulator is a particular problem in high‐voltage direct current (HVDC) gas insulated switchgears (GIS) and gas insulated transmission lines (GIL), which restricts the development and application of extra/ultra high‐voltage (EHV/UHV) technology. The surface charge distribution and anti‐flashover performance are closely related to the insulator shape. To obtain the optimal basin insulator, a shape optimisation model based on artificial bee colony algorithm was established, and the minimisation objective functions based on capacitive (initial) electric field distribution and resistive (steady‐state) electric field distribution were respectively constructed. The optimisation results of the two objective functions were calculated, and the electric field and charge distribution on the surface of the insulator before and after optimisation were evaluated and compared using the simulation model. The results indicated that the optimisation based on the capacitive electric field can significantly inhibit the surface charge accumulation, and the optimised insulator can significantly reduce the surface normal electric field and make the distribution of the tangential electric field more uniform, and the maximum tangential electric field can be reduced by 10%; the optimisation based on resistive electric field can achieve similar results, but requires more computational resources. Based on the results, the ‘anti‐charge’ basin insulator structure suitable for the DC field was given.

High optical spin-filtering in antiferromagnetic stanene nanoribbons induced by band bending and uniaxial strain

Non-equilibrium spin-polarized transport properties of antiferromagnetic stanene nanoribbons are theoretically studied under the combining effect of a normal electric field and linearly polarized irradiation based on the tight-binding model at room temperature. Due to the existence of spin-orbit coupling in stanene lattice, applying normal electric field leads to splitting of band degeneracy of spin-resolved energy levels in conduction and valence bands. Furthermore, unequivalent absorption of the polarized photons at two valleys which is attributed to an antiferromagnetic exchange field results in unequal spin-polarized photocurrent for spin-up and spin-down components. Interestingly, in the presence of band bending which has been induced by edge potentials, an allowable quantum efficiency occurs over a wider wavelength region of the incident light. It is especially important that the variation of an exchange magnetic field generates spin semi-conducting behavior in the bended band structure. Moreover, it is shown that optical spin-filtering effect is obtained under the simultaneous effect of uniaxial strain and narrow edge potential.

High-Energy Proton and Atmospheric-Neutron Irradiations of SiC Power MOSFETs: SEB Study and Impact on Channel and Drift Resistances

Accelerated single event burnout (SEB) tests with 200 MeV protons and atmospheric-neutrons were performed for commercial SiC power MOSFETs with different architectures ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e</i> ., planar gate, asymmetric trench and symmetric trench). The average electric fields over the depletion layer width and the electric field distributions are reported for the tested conditions and compared for the three architectures, confirming the necessity of a lower de-rating for the trench design to protect from SEB, compared to planar ones. In addition to the epitaxial layer design, the influence of other design parameters on the SEB threshold is discussed. Finally, to investigate the presence of precursor damage in the pre-SEB region, a methodology is presented and used to study the radiation-induced degradation of the channel and drift resistances of devices which survived the SEB tests.

Temperature-Dependent Surface Charge Accumulation for Vertical and Horizontal HVDC GIL

In this paper, the heat transfer process of DC gas-insulated transmission line (GIL) is comprehensively considered, including thermal conduction, thermal convection and thermal radiation. An electric-thermal field coupling model is established to characterize the surface charge accumulation characteristics of insulators. The temperature and insulator surface charge density distribution of a 3-D GIL model under different GIL installation ways (i.e. vertical and horizontal GIL) are obtained by finite element software. The results show that: under the identical load current, a large temperature difference (up to 5.7 °C) is shown between both surfaces of vertical GIL insulator, and the temperature on the insulator surface is distributed symmetrically along the center of the insulator. However, the temperature on both surfaces of the horizontal GIL is basically the same, but the temperature distribution varies greatly along the different radial directions of the insulator (up to 5.3 °C). By comparing the surface charge density distribution of insulators under both GIL installation ways, it is found that the surface charge density of horizontal GIL is more than 20% higher than that of vertical GIL. In addition, the volume conductivity distribution of insulator varies greatly under different GIL installation ways. The volume conductivity is positively correlated with the temperature distribution, while the normal electric field on the insulator surface is negatively correlated with volume conductivity distribution. It is hoped that this study can serve as a reference for the design and safe operation of DC GIL.

Vibration Triggered Leakage of Surface Charge on Epoxy Insulator Under DC Voltage

Surface charge accumulation is considered a critical threat to the safe operation of epoxy insulators installed in gas-insulated switchgear (GIS). This paper reports on the charge leakage phenomenon of the insulator with the occurrence of impact vibration under DC voltage. A full-sized disc insulator with a multi-arc surface profile was employed as the test sample. A vibration system was established to output vibration to the insulator in two Modes. In Mode I, the maximum acceleration was 338.9 m/s2 and the impact frequency was 1.1 Hz. In Mode II, the maximum acceleration decreased to 4.6 m/s2 but the impact frequency increased to 107.5 Hz. The charge densities on the insulator surface were measured before and after the vibrations. The results indicated that the vibration led to the obvious leakage of homo-charges during the DC stressing process, especially in the non-planar region. The leakage of homo-charges under positive stressing was more remarkable than that under negative stressing. The reduction of homo-charge quantity was more serious in Mode I than in Mode II. It is suggested that the vibration-triggered charge leakage is mainly due to charge de-trapping caused by micro-displacement of molecular chain occurring in the insulator with the vibration and subsequent charge release to the gas phase under the normal electric field, by which the surface charge accumulation quantity is remarkably reduced.

Estimation time delay from field emission to secondary electron emission avalanche in vacuum surface flashover

Vacuum surface flashover is the main factor limiting the development of pulsed power system. In this work, a quantitative dynamical model is built to investigate the vacuum surface flashover from field emission to secondary electron emission avalanche (SEEA). The results show that positive charges accumulating on the dielectric surface caused by field emission electrons play a dominant role when the normal electric field on the dielectric surface Edc is small. The growth of the number of positive surface charges exponentially decreases with the distance from the cathode triple junction (CTJ). With the increase in the density of positive surface charges, the growth of positive surface charges mainly depends on the secondary electrons cascade. As a result, the saturation state of Edc will first occur on the dielectric surface at a distance hundreds of micrometers from the CTJ. In addition, the effect of dielectric permittivity on positive surface charges is considered. The density of positive surface charges equals (1+εr) ε0Edc rather than 2ε0Edc. Particle-in-cell simulations are employed to verify the correctness of the theory model, and the agreement of comparisons is favorable. Furthermore, the space charge effect is discussed. When SEEA reaches saturation, electrons can significantly change the spatial distribution of the electric field.

Design Optimization and Flashover Probability Evaluation of a 3 MV, 3.4-m-Diameter Four-Level Axial Vacuum Insulator Stacks for a 15 MA Z-Pinch Accelerator

A four-level axial insulator stack is designed for a 15 MA Z-pinch accelerator. The height and diameter are 1.5 m and 3.4 m. The two upper levels operate at 2.5 MV, while the two bottom levels operate at 3.0 MV. The insulator ring stages in series, the vacuum flares, and water flares are optimized in details. By reiterative optimizations, the two upper levels consist of five 5-cm-thick insulator rings and four 0.8-cm-thick grading rings. While the two bottom levels consist of six insulator rings and five grading rings with the same individual insulator and grading ring. The inductance of each level is 14.02 nH, 15.48 nH, 18.71 nH, and 20.88 nH, respectively. The equivalent inductance is 4.21nH with the four levels in parallel. The voltage variations from average for the four levels are within ±4.9%, ±4.9%, ±2.1%, and ±2.2%, respectively. At the average operating electric field of 100 kV/cm, the predicted flashover probability for the two upper level and the two bottom level insulator stacks are about 0.29% and 0.53%, respectively.

Electrohydrodynamic Couette–Poiseuille Flow Instability of Two Viscous Conducting and Dielectric Fluid Layers Streaming through Brinkman Porous Medium

The electrohydrodynamic plane Couette–Poiseuille flow instability of two superposed conducting and dielectric viscous incompressible fluids confined between two rigid horizontal planes under the action of a normal electric field and pressure gradient through Brinkman porous medium has been analytically investigated. The lower plane is stationary, while the upper one is moving with constant velocity. The details of the base state mathematical model and the linearized model equations for the perturbed state are introduced. Following the usual procedure of linear stability analysis for viscous fluids, we derived two non-dimensional modified Orr–Sommerfeld equations and obtained the associated boundary and interfacial conditions suitable for the problem. The eigenvalue problem has been solved using asymptotic analysis for wave numbers in the long-wavelength limit to obtain a very complicated novel dispersion relation for the wave velocity through lengthy calculations. The obtained dispersion equation has been solved using Mathematica software v12.1 to study graphically the effects of various parameters on the stability of the system. It is obvious from the figures that the system in the absence of a porous medium and/or electric field is more unstable than in their presence. It is found also that the velocity of the upper rigid boundary, medium permeability, and Reynolds number have dual roles on the stability on the system, stabilizing as well as destabilizing depending on the viscosity ratio value. The electric potential, dielectric constant and pressure gradient are found to have destabilizing influences on the system, while the porosity of the porous medium, density ratio and Froude number have stabilizing influences. A depth ratio of less than one has a dual role on the stability of the system, while it has a stabilizing influence for values greater than one. It is observed that the viscosity stratification brings about a stabilizing as well as a destabilizing effect on the flow system.

Mechanism of superior charge suppression behavior of Si3N4 ceramics at solid-gas interface

Recent study has found excellent bulk and surface insulation property of Si3N4 ceramic which make it potential to serve as key insulation component in various energy transmission apparatus. Charge accumulation at gas-solid interface is a critical insulation property but few relevant study on Si3N4 can be found. This contribution has investigated the surface charge property of Si3N4 ceramic compared to traditional insulation polymer under different electrical-thermal stress. Through its comparison with the electric field distribution, the main source of the surface charge accumulation is analyzed, indicating that the superior surface charge suppression performance of Si3N4 lies on its low carrier density and conduction barrier, which considerably prevent charge injection and suppress the normal electric field which drives the charge to the gas-solid interface. The proposed mechanism is also validated by the characterization on conducting and space charge property for Si3N4 as well as dynamic simulation on surface charge accumulation.

Destructive breakdown studies of irradiated LGADs at beam tests for the ATLAS HGTD

In the past years, it has been observed at several beam test campaigns thatirradiated LGAD sensors break with a typical star shaped burn mark whenoperated at voltages much lower than those at which they were safely operatedduring laboratory tests. The study presented in this paper was designed todetermine the safe operating voltage that these sensors can withstand. Manyirradiated sensors from various producers were tested in two test beamfacilities, DESY (Hamburg) and CERN-SPS (Geneva), as part of ATLAS HighGranularity Timing Detector (HGTD) beam tests. The samples were placed in thebeam and kept under bias over a long period of time in order to reach a highnumber of particles crossing each sensor. Both beam tests lead to a similarconclusion, that these destructive events begin to occur when the averageelectric field in the sensor becomes larger than12 V/μm.

Optimization of insulators in ±550 kV HVDC GIS for offshore wind platform considering charge accumulation

High voltage direct current (HVDC) gas-insulated switchgear (GIS) plays a crucial role in developing far offshore wind power and attaining renewable energy and interconnection objectives. However, surface charge accumulation reduces the surface flashover voltage and restricts the development of DC GIS at the higher voltage. In this paper, the design criteria for a ± 550 kV DC insulator were proposed based on DC insulation testing. The influence of geometry on electric field and charge distribution of obtuse conical insulators, disk insulators, and conical insulators was systematically investigated. The results show that the threshold of the tangential electric field under the DC superimposed lighting impulse test for the ±550 kV DC insulator is 11.1 kV/mm. The simulation results indicate that the increasing inclination of the insulator enhances the normal electric field and surface charge density, while the increase in insulator size diminishes the tangential electric field dramatically. The obtuse conical insulator with an upper surface inclination angle of 30°, a lower surface included angle of 140°, and a diameter of 812.5 mm is ideal for ±550 kV DC GIS. The obtained results may provide guidance for the compact design of insulators and the development of DC GIS.

Effects of external magnetic and electric field on multipactor and plasma breakdown of high-power microwave window

In this work, we investigated the effects of an external magnetic field, a DC electrostatic field, and a normal rf electric field on the multipactor and plasma ionization breakdown process near a microwave window by performing kinetic particle-in-cell/Monte Carlo collision simulations, and the underlying mechanism is also given. The magnetic field, parallel to the surface and perpendicular to the tangential rf field, can effectively suppress the electron multipactor process by delaying the electron incidence on the dielectric window and push the plasma breakdown bulk away from the dielectric window. However, when the magnetic field is too strong, the mitigation effect is not significant, and may even enhance the multipactor process at the beginning of the plasma breakdown. The external DC electrostatic field, perpendicular to the surface, can inhibit electron multipactor when it points toward the surface. On the other hand, when the DC electric field direction is reversed, then the electron multipactor process is found to be promoted, and the gas ionization bulk is closer to the dielectric window. The external normal rf electric fields perpendicular to the surface with small amplitudes are found to be capable of promoting the multipactor process. With increasing the amplitude of normal rf electric field, the multipactor process can be suppressed to some degree at the initial stage of the plasma breakdown and the gas ionization bulk region is kept away from the dielectric window surface.

Self-sustaining conducting state and bipolar ionizing Gunn domains in pulse avalanche GaAs diodes

Domain instability in nonequilibrium electron-hole plasma leads to the formation of narrow moving regions of the ionizing electric field—collapsing Gunn domains. In pulse power electronics devices based on gallium arsenide, impact ionization in collapsing domains acts as an efficient mechanism for the generation of nonequilibrium carriers at low voltages and weak average electric fields.

Circuital Modeling of Polarization and Depolarization Currents in Polymeric Materials Under Low Electric Fields

This paper proposes a circuital model that describes polarization and depolarization currents observed in thin samples of polymeric materials under the application of an average electric field up to 30 kV/mm. The model employs the least possible number of parameters to fit the experimental measurements. A single carrier with negative charge is considered. The polarization curves are modelled by a power law to account for transport assisted by shallow traps. A model for the deep traps with a Gaussian distribution of the density of states is describes the depolarization curves. Experimental measurements made on various materials with different charging and discharging times suggest that a portion of the deep traps is filled within few seconds, while the time needed to release the trapped charges is in the order of several hours. The agreement between experimental and simulated currents confirms the validity of the proposed model, that can be seen as a generalization of the extended Debye model.