Initial Electric Field Research Articles

Study on the mechanism of sessile droplets evaporation enhanced by the electric field

The evaporation characteristics of a sessile droplet under a direct current electric field were numerically investigated, and a numerical model was developed based on the arbitrary Lagrange-Euler method, combining the flow, heat transfer, vapour transport, and electrostatic equations. The simulations were validated to be in good agreement with previously reported experiments. The results demonstrate that the electric field can enhance the evaporation of the sessile droplet with different evaporative cooling numbers (initial electric field intensity E0 = 280 kV·m−1; 32.9% decrease in the evaporation time for water) by the following three methods: increasing the surface area of the droplet evaporation (2.6%) through the electric-field-induced deformation, improving the heat transfer efficiency between the droplet and substrate (droplet average temperature increases by 2.3 K) through the internal vortex, and by enhancing the shearing effect on the vapour layer (450.3% increase in vapour diffusion distance dc) through the external vortex. Additionally, the evaporation of a sessile water droplet undergoing thermocapillary convection is further enhanced under the electric field (E0 = 280 kV·m−1; 20.0% decrease in the evaporation time). As the inhomogeneous temperature distribution inside the droplet was eliminated by thermocapillary convection, the evaporation efficiency was dominated by the increased surface area of the droplet evaporation and the enhanced shearing effect on the vapour layer. These results will provide a better understanding of the electro-hydrodynamic enhanced droplet evaporation.

Computational study of a microwave plasma reactor based on the TM112 mode for diamond deposition

One of the main features of microwave plasma reactors is the electric field structure in the resonant cavity, which must be both intense and uniform in front of the substrate. For this reason, transverse magnetic modes are often used, especially axisymmetric modes because they produce an axisymmetric plasma. Microwave plasma reactors can be differentiated according to the chosen mode, because this has a direct influence on the diamond film growth process, among other features such as the coupling technique and the used quartz window. Another attractive characteristic of said reactors is obtaining large activation areas of the plasma. In this paper, we propose a microwave plasma reactor based on the TM112 cylindrical mode, which is subject to a computational study. Unlike axisymmetric modes, which activate the plasma on the cavity axis, the TM112 cylindrical mode presents two activation plasma areas. The reactor was designed following the methodology described by Silva et al., and using the Plasma, Radiofrequency (RF), and Heat transfer modules of the software COMSOL Multiphysics. The obtained results are presented in two stages. The first one is related to the initial electric field distribution of the TM112 mode. Next, the generation of the hydrogen plasma was simulated from the interaction of H2 gas with the TM112 microwave field. The plasma activation process is described in detail from graphics of the time evolution of the electron density, hydrogen density, and their respective temperatures until a steady state is reached. Additionally, the influence of the pressure on the concentration and the temperature of both electrons and gas in a steady state is analyzed. The presented results can be useful for the design of plasma reactors for diamond deposition.

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.

Low-temperature preparation of La0.9Ca0.1CrO3 semiconductor ceramics by flash sintering

Flash sintering of La0.9Ca0.1CrO3 based ceramics can be triggered at very low furnace temperature compare with pure LaCrO3. Due to Ca2+ doped LaCrO3 could lead to the formation of oxygen vacancy, which increases the conductivity of the sample, and reduces the one set temperature of FS. La0.9Ca0.1CrO3 as a p-type semiconductor may be sintered to a dense state at a furnace temperature of 311 °C–140 °C under 15–35 V/cm. EDS results show that the volatilization of Cr elements is well controlled. The current density increases non-linearly to the set limit value in the voltage control stage under an initial electric field. ln(E2/Ton4) and 1/Ton have a good linear relationship, according to this relationship, the onset temperature (Ton) under electric field conditions of 25 and 22.5 V/cm is estimated to be completely consistent with the experimental value. Furthermore, flash sintering resulted in a higher density and smaller particle size within the sample compared to conventional sintering.

Quality attributes of pork tenderloin frozen under different high voltage electric fields with ultrahigh permittivity ceramic-enhanced electrodes

A novel high voltage electric field assisted freezing (HVEFF) system improved by ultrahigh permittivity ceramic electrodes was developed, and its effects on the quality attributes of frozen pork tenderloin were investigated. The relationship between the initial internal electric field strength of pork and the quality of frozen pork was studied. Results showed that the frozen samples obtained under the internal electric field strength of 6.25 × 104 V/m (corresponding to 6 kV) had less drip loss, less total colour change value, and better texture, other than the frozen samples under 12 kV and 18 kV. These results were confirmed by a further investigation into water distribution, protein thermal stability, and ice crystal size. Thereby, this study showed a great potential of ultrahigh permittivity material in improving the small sample-treating capacity of HVEFF.

Synergistic Effect of Temperature and Operating Voltage on Deep Charging of PEEK in the Space Solar Power Station

When the Space Solar Power Station operates in its geostationary orbit, deep dielectric charging may occur due to the implantation of the space electrons into the dielectrics and destroy the electronic devices. In this work, during the high-energy electron storms event, the deep dielectric charging characteristics of the poly-ether-ether-ketone flat plate have been studied by the Geant4 simulation as a function of temperature. It is found that the maximum electric field strength decreases when the temperature of the space environment increases, which is due to the increasing dark conductivity. When the front plate of the poly-ether-ether-ketone is biased at 10,000 V, and the back plate is grounded, the electrostatic discharge is the most likely to occur, while the case of 10,000 V on the front plate with the back plate suspended (ungrounded) is the safest. It is well analyzed through the influence of the initial electric field generated by the bias voltage on the electric field induced by the electron deposition.

Impact of the Cell Wall on Cyanide Biodegradation in the Model of the Respiratory Mechanism

Based on the general model of the respiratory mechanism of cyanide degradation by microorganisms, we introduce the impact of the cell wall on the degradation process under the conditions with and without the initial short-term pulsed electric field treatment. The research is conducted using non-linear phenomenological equations, and the solution approximation is obtained. Theoretical and experimental data are compared, and they are in good agreement. We demonstrate that the initial short-term pulsed electric field treatment increases the permeability of cyanide through the cell wall, as well as the rate of activation of the respiratory chains. The steady-state solutions and the maximum rate of cyanide addition are derived under the conditions that cyanide is continuously added to the solution with bacteria, and there is no initial pulsed electric field treatment.

New Insight Into Total-Ionizing-Dose Effect-Induced Breakdown Voltage Degradation for SOI LDMOS: Irradiation Charge Field Modulation

In this article, the concept of irradiation charge field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> ) is proposed to provide a new insight into total-ionizing-dose (TID) effect-induced breakdown voltage (BV) degradation for high-voltage silicon-on-insulator (SOI) lateral double-diffused metal–oxide-silicon (LDMOS). A unified explanation on TID-induced BV degradation is given that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> exerts modulation on net electric field, changing the relationship between lateral BV (BVL) and vertical BV (BVV). <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> would weaken electric field at silicon side of silicon/buried oxide interface and enhance that at oxide side, resulting in BVV increasing monotonously. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {rc}}$ </tex-math></inline-formula> would also weaken surface electric field at drain side and enhance that at source side, resulting in BVL changing with two potential trends: monotonic descent and nonmonotonic descent, corresponding to different initial surface breakdown points. Eventual BV degradation is determined by the combined result of BVV and BVL changing. Based on the new insight, a radiation hardening design strategy is proposed. Nonuniform initial surface electric field distribution with single drain peak is pursued, breaking the conventional optimization principle. Nonmonotonic descent of BV is achieved to enhance TID tolerance and verified by the developed 80-V SOI LDMOS with the proposed radiation hardening strategy.

Metastable argon dynamics in a pulsed microplasma at 43 GHz

Short pulses of millimeter wave (MMW) radiation at 43 GHz create microplasma within a photonic crystal for pressures from 40 to 600 Torr (1.3 × 103–8.0 × 104 Pa). Gas breakdown occurs within a photonic crystal, which acts as an electromagnetic resonator to create a strong initial electric field. The time response of the argon metastable density is experimentally determined during the pulse and in the afterglow using laser absorption. The metastable density overshoots the steady-state condition at the beginning of the pulse and during the afterglow. Modeling is presented to understand these observations. The overproduction of argon 1s5 at the beginning of each pulse is due to a concurrent overshoot in the MMW electric field within the photonic crystal. This field overheats the plasma electrons and enhances the production of excited states. The burst of argon metastables observed in the afterglow is due to the pooled energy of the plasma stored in electrons, ions, and excited states of argon. Understanding metastable production is an important intermediate step to ionization and is also critical in the study of diode-pumped rare gas lasers.

Radiation reaction effects in relativistic plasmas: The electrostatic limit.

We study the evolution of electrostatic plasma waves, using the relativistic Vlasov equationextended by the Landau-Lifshitz radiation reaction, accounting for the back-reaction due to the emission of single particle Larmor radiation. In particular, the Langmuir wave damping is calculated as a function of wave number, initial temperature, and initial electric field amplitude. Moreover, the background distribution function loses energy in the process, and we calculate the cooling rate as a function of initial temperature and initial wave amplitude. Finally, we investigate how the relative magnitude of wave damping and background cooling varies with the initial parameters. In particular, it is found that the relative contribution to the energy loss associated with background cooling decreases slowly with the initial wave amplitude.

Generalized Poincaré Beams in Tight Focus

We study the tight focus of generalized (hybrid) Poincaré beams. A conventional Poincaré beam is a coaxial superposition of two optical vortices, one with left circular polarization and a topological charge (TC) of m, while the other has a right circular polarization and a TC of −m. The generalized Poincaré beams are also composed of two optical vortices, but their TCs are different, for instance, p and q. Here, we theoretically investigate the generalized Poincaré beams with the TCs p = m + 1 and q = −m in tight focus. In this case, both transverse components of the strength vector of the initial electric field have a topological charge of 1/2, and the beam itself is a cylindrical vector beam of fractional order m + 1/2. Analytical expressions are derived for the components of the strength vectors of the electric and magnetic field at the focus as well as for the intensity distribution, the longitudinal component of the spin angular momentum (SAM), and for the components of the Poynting vector (energy flow density). We show that the intensity at the focus has 2m − 1 local maxima residing evenly in a certain circle radius with the center on the optical axis. We also demonstrate that the radial spin and orbital Hall effects occur at the focus, i.e., the longitudinal SAM component has different signs in the circles of different radii, and the azimuthal component of the transverse Poynting vector also has different signs.

Comparison of far electric field waveforms produced by rocket-triggered lightning strokes and subsequent strokes in natural lightning

• We measured the electric field waveforms produced by both RTL and NL at comparable far distances using same instrumentation, where the radiation field is dominant. Compared to previous work done by Mallick & Rakov (2014), we increase the sample size of RTL data and compare with NL data. • The majority of the parameters show comparable values. The distributions for 10%-to-90% risetime and HPW show less scatter for RTL than NL. The plateau type slow front occurs in RTL strokes more often than in NL strokes. The initial electric field peak and the various time parameters of field waveforms are very low. • For subsequent strokes in NL and field propagation over land, HPW values are typically of the order of 10 μs. • For 184 subsequent strokes in NL and 139 strokes in RTL, we found that the field zero-crossing time for RTL is slightly smaller than for NL. • The smaller electric field pulse widths that we measured for RTL compared to NL could be due to: 1. A faster current decay with height in RTL return strokes. 2. The bottom part of the channel for RTL is straighter than for NL. Using wideband electric field records obtained at the Lightning Observatory in Gainesville (LOG), Florida, we examined in detail the characteristics of far electric field waveforms produced by two categories of lightning return strokes. The first category includes return strokes of any order in lightning flashes triggered by a rocket extending a grounded wire toward the overhead thundercloud, which we label RTL (rocket-triggered lightning) strokes. The second category includes return strokes of order 2 and higher (that is, only subsequent strokes) in natural cloud-to-ground lightning flashes, which we label NL (natural lightning) strokes. Properties of RTL and NL strokes are expected to be similar. A total of 139 RTL strokes from years 2013 to 2016 and 184 NL strokes from years 2013 to 2015 were examined in this study. All strokes transported negative charge to ground and occurred at similar distances from LOG. Similarities and dissimilarities of waveform parameters for the two categories of strokes and their possible explanations are discussed in this paper. This is the first detailed comparison of electric field waveforms of RTL and NL strokes recorded at approximately the same distance (some tens of kilometers) and with the same instrumentation.

Differences of Electric Field Parameters for Lightning Strikes on Tall Towers and Nonelevated Objects

In this article, we analyzed the far electric field parameters of cloud-to-ground (CG) lightning striking tall towers in Guangzhou at the distance of 20–70 km, and compared with lightning striking nonelevated objects from the same thunderstorm near the tall towers. By comparing the waveform characteristics, we found that the far-field waveform of tall tower exhibits the characteristics of early narrow undershoot, zero crossing, oscillation damping attenuation and there is a secondary peak after the opposite polarity peak, which is absent in the CG lightning. The GM values of 10%–90% rise time, fall time and zero-crossing time of lightning strikes on tall towers are 1.6, 2.0, and 8.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s which are far less than 2.5 (1.8 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s), 7.9 (6.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s), and 28.1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s (28.7 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s) of the first return stroke (subsequent return stroke) of CG lightning. In addition, the initial electric field peak, the ratio of the opposite polarity overshoot amplitude to the initial peak, and the time interval between initial electric field peak and second peak of the lightning striking on tall tower are larger than those of the CG lightning.

Mechanism of nanostructure processing on Au and Ag nano-film by a nanosecond laser illuminating cantilevered scanning near-field optical microscopy tip.

Nanostructure processing by a laser illuminating cantilevered scanning near-field optical microscopy (SNOM) tip is a novel technology that has received extensive attention from researchers. In this paper, theoretical investigations of the mechanism for nanostructure fabrication on Au and Ag nano-film by this technology are realized by the finite element method. The light field intensity and temperature distribution on Au and Ag surfaces at the near-field of the SNOM tip apex after illumination is simulated. The results reveal that the laser is restricted and enhanced within the SNOM tip aperture during illumination. Locally excited surface plasmon polaritons, which induce near-field enhancement on the Au and Ag nano-film at the vicinity of the aperture, are significant for nanostructure fabrication. The impacts of several parameters such as aperture width w, gap between the apex and substrate g, and the initial electric field intensity |E0| of the laser on the temperature of the Au and Ag substrate surfaces during fabrication are deeply studied. It reveals that the surface temperature depends on both the enhancement of the light field intensity and the transmitted laser. The enhancement is dominant in affecting temperature when the gap is small, while the transmittance becomes the main factor influencing the surface temperature with the increase of the gap.

Numerical investigation of negative polarity electrical explosion of aluminum wire in vacuum

Numerical investigation was carried out on the evolution of inhomogeneous energy deposition of polarity effects in negative polarity electrical explosion of aluminum wire in vacuum. First, radial electric field distribution of the aluminum wire was simulated. The results showed that the initial electric field near electrodes was much smaller than that in the middle of the wire. A model of electrical wire explosion based on ZEUS-EW with artificial limitation on breakdown time of the aluminum wire was used to simulate the behavior of inhomogeneous energy deposition of the polarity effect. The complete evolution process of electrical explosion of the aluminum wire with inhomogeneous energy deposition was further explored and qualitatively divided into three stages according to the simulation results. Finally, the influence of some factors on the inhomogeneous energy deposition simulation was investigated. This study provides some help for a better understanding of the polarity effect in the process of wire explosion.

Microwave Radiation Associated with Lightning Initiation Events of Negative Cloud-to-Ground Flashes

In this paper, we examined the initiation events of ten negative cloud-to-ground (CG) flashes detected close to measurement stations on 12 November (CG-1 to CG-5) and 24 November (CG-6 to CG-10), 2019. All CG flashes were accompanied by microwave and very-high frequency (VHF) radiation pulses. We recorded all the CG flashes from two measurement stations (ST1 and ST2), which are separated by 13.3 km and consist of fast and slow antenna (FA and SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (~1 GHz). The key finding is that all of the microwave radiation pulses detected before the onset of initial electric field changes (IECs) preceded all VHF radiation pulses with an average lead time of 1.53 µs, ranging between 0.3 and 3.0 µs (for all CG flashes within reversal distance). A total of 50%, 17%, and 33% CG flashes were initiated by a single radiation pulse, two radiation pulses, and three radiation pulses, respectively, and were followed by IECs. Some VHF pulses are classified as short VHF radiation pulses (pulse duration less than 0.5 µs). The average duration from the first microwave and VHF pulses to the onset of IECs were 53.4 µs and 32.78 µs, respectively. The VHF radiation pulses detected before the IECs are suggested to be emitted by short-length positive streamers. Because the microwave radiation pulses were detected earlier (average lead time of 1.53 µs) than VHF radiation pulses, it is most likely that the microwave pulses were emitted by an electron avalanche process.

Electric field-assisted in situ fabrication of carbon/zirconia nanocomposites with tunable conductivity for electromagnetic interference shielding applications

Carbon/ceramic nanocomposites have been considered as ideal candidates for electromagnetic interference shielding (EMI) applications in harsh environments. However, the conventional fabrication methods of carbon/ceramic composites are often complicated, costly and time-consuming. Herein, by applying a DC electric field during hot pressing sintering, we realized the direct growth of graphene-like carbon nanosheets (GCNs) in zirconia ceramics during sintering, achieving in situ fabrication of GCNs/zirconia nanocomposites with both high EMI shielding effectiveness (>40 dB) and mechanical strength (>1000 MPa) in one step. In particular, we found that applying a DC electric field could significantly enhance the carburization during sintering, and GCNs are in situ formed at zirconia grain boundaries. When the initial electric field is constant, the amount of in situ formed GCNs could be controlled by simply adjusting the current density, resulting in the tunable electrical conductivity. These findings will provide new opportunities for both experimental and theoretical studies on carbon/ceramic EMI shielding materials and the DC electric field-assisted sintering technique.

Director orientational instability in a planar flexoelectric nematic cell with easy axis gliding

The orientational instability of a director in a planar flexoelectric nematic liquid crystal cell in a constant electric field oriented perpendicular to the cell substrates is investigated. The easy axis on the surface of one of the polymer substrates can change its orientation, which is due to the impact of the initial surface orientation, liquid crystal, and electric field. The influence of the latter leads to the reorientation of the elastic parts of the polymer molecules of the substrate, which is a consequence of the interaction of intrinsic or induced dipole moments with the electric field. The corresponding contribution of such an interaction to the surface free energy of the nematic is considered to be linear or quadratic in terms of the electric field strength E. It is established that the orientational instability of the director has a threshold in the case of quadratic effect of the electric field and is thresholdless if the effect is linear. The temporal behavior of the director after the application of voltage with the subsequent transition of the system to a stationary state and its return to the initial homogeneous state after switching off the voltage is studied. The characteristic turn-on/off times of the system and the time of reaching the stationary state are calculated and their dependence on the system parameters is investigated. The transmittance of the nematic liquid crystal cell is calculated for a normally incident light.

A study of cloud-to-ground lightning flashes initiated by fast positive breakdown

In this paper, we examine the initiation event of two tropical negative cloud to ground (CG) lightning flashes within reversal distance (<8 km) detected on 12 (CG1) and 24 (CG2) November 2019, respectively. The CG flashes were recorded using a fast antenna (FA), slow antenna (SA), magnetic field (B-field), and very high frequency (VHF) sensors located at two observation stations (ST1 and ST2) 13.26 km apart. The key finding is that CG1 flash was initiated by a short VHF pulse followed by a VHF burst (fast positive breakdown) while CG2 flash was initiated by a VHF burst (fast positive breakdown) not preceded by a short VHF pulse. The VHF burst was a precursor for initiation of a narrow bipolar event (NBE)-like pulse and initial electric field changes (IECs). Based on the VHF interferometer map, the VHF sources of NBE-like pulses have been propagated upward predominantly vertical. The initiation altitude, total length of the VHF sources propagation, estimated velocity of NBE-like pulse for CG1 flash were 4.5 ± 0.5 km, 1.9–3.8 km, and 2.4 × 108 to 4.8 × 108 ms−1, respectively, and for CG2 flash were 5.1 ± 0.8 km, 0.2–3.0 km, and 2.7 × 107 to 4.1 × 108 ms−1, respectively. It is evident that IECs process has been initiated during fast positive streamers propagation. It can be suggested that the IECs process resulted from charge transfer during a fast positive breakdown. The durations and magnitudes of IECs for CG1 flash were 248.5 μs and 27.97 V/m, respectively, and for CG2 flash were 265.8 μs and 2.31 V/m, respectively.

Ab Initio Study of the Mechanism of Proton Migration in Perovskite LaScO3

The mechanism of proton motion in a LaScO3 perovskite crystal was studied by ab initio molecular dynamics. The calculations were performed at different temperatures, locations, and initial velocity of the proton. Different magnitudes and directions of the external electric field were also considered. It is shown that initial location and interaction between proton and its nearest environment are of great importance to the character of the proton movement, while the magnitude and direction of the initial velocity and electric field strength are secondary factors characterizing its movement through the LaScO3 crystal. Four types of proton-jumping between oxygen atoms are determined and the probability of each of them is established. Energy barriers and characteristic times of these jumps are determined. The probable distances from a proton to other types of atoms present in perovskite are calculated. It is shown that the temperature determines, to a greater extent, the nature of the motion of a proton in a perovskite crystal than the magnitude of the external electric field. The distortion of the crystal lattice and its polarization provoke the formation of a potential well, which determines the path for the proton to move and its mobility in the perovskite crystal.