scholarly journals Characterization of Chaotic Electroconvection near Flat Inert Electrodes under Oscillatory Voltages

Micromachines ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 161 ◽  
Author(s):  
Jeonglae Kim ◽  
Scott Davidson ◽  
Ali Mani
Keyword(s):  
Electric Field ◽  
Electric Current ◽  
Electric Fields ◽  
Oscillation Frequency ◽  
Stokes Equations ◽  
Convective Transport ◽  
Constant Frequency ◽  
Wide Range ◽  
Oscillation Frequencies ◽  
Electroconvective Instability

The onset of electroconvective instability in an aqueous binary electrolyte under external oscillatory electric fields at a single constant frequency is investigated in a 2D parallel flat electrode setup. Direct numerical simulations (DNS) of the Poisson–Nernst–Planck equations coupled with the Navier–Stokes equations at a low Reynolds number are carried out. Previous studies show that direct current (DC) electric field can create electroconvection near ion-selecting membranes in microfluidic devices. In this study, we show that electroconvection can be generated near flat inert electrodes when the applied electric field is oscillatory in time. A range of applied voltage, the oscillation frequency and the ratio of ionic diffusivities is examined to characterize the regime in which electroconvection takes place. Similar to electroconvection under DC voltages, AC electroconvection occurs at sufficiently high applied voltages in units of thermal volts and is characterized by transverse instabilities, physically manifested by an array of counter-rotating vortices near the electrode surfaces. The oscillating external electric field periodically generate and destroy such unsteady vortical structures. As the oscillation frequency is reduced to O ( 10 − 1 ) of the intrinsic resistor–capacitor (RC) frequency of electrolyte, electroconvective instability is considerably amplified. This is accompanied by severe depletion of ionic species outside the thin electric double layer and by vigorous convective transport involving a wide range of scales including those comparable to the distance L between the parallel electrodes. The underlying mechanisms are distinctly nonlinear and multi-dimensional. However, at higher frequencies of order of the RC frequency, the electrolyte response becomes linear, and the present DNS prediction closely resembles those explained by 1D asymptotic studies. Electroconvective instability supports increased electric current across the system. Increasing anion diffusivity results in stronger amplification of electroconvection over all oscillation frequencies examined in this study. Such asymmetry in ionic diffusivity, however, does not yield consistent changes in statistics and energy spectrum at all wall-normal locations and frequencies, implying more complex dynamics and different scaling for electrolytes with unequal diffusivities. Electric current is substantially amplified beyond the ohmic current at high oscillation frequencies. Also, it is found that anion diffusivity higher than cation has stronger impact on smaller-scale motions (≲ 0.1 L).

The Effect of Electrostatic Forces on the Distribution of Drops in a Channel

2002 ◽  
Author(s):  
Arturo Ferna´ndez ◽  
Jiacai Lu ◽  
Asghar Esmaeeli ◽  
Gre´tar Tryggvason
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Hydrodynamic Interaction ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Dielectric Fluids ◽  
Wide Range ◽  
Leaky Dielectric Model

Direct numerical simulations are used to examine the effect of electric fields on the behavior of suspension of drops in dielectric fluids. The effect of electric field is modeled using the “leaky dielectric” model, coupled with the full Navier-Stokes equations. The governing equations are solved using a front-tracking/finite volume technique. The interaction of the drops is strongly dependant on the conductivity and the permittivity ratio, but fibration, where drops line up into long columns, takes place over a wide range of these parameters. The hydrodynamic interaction due to fluid circulation induced by the electric field has a strong influence on the drop distribution and the rate of fibration.

The vibration of electrified water drops

1971 ◽  
Vol 322 (1551) ◽  
pp. 523-534 ◽  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Axial Ratio ◽  
Uniform Electric Field ◽  
Interferometric Technique ◽  
Photographic Analysis ◽  
Wide Range ◽  
Water Drops ◽  
Strength And Deformation ◽  
A Charge

Pressure has been used as the principal parameter in calculations of the fundamental vibrational frequencies of spherical drops of radius R , density ρ, and surface tension T carrying a charge Q or uncharged spheroidal drops of axial ratio a / b situated in a uniform electric field of strength E . Freely vibrating charged drops have a frequency f = f 0 ( 1 - Q 2 /16π R 3 T ) ½ , as shown previously by Rayleigh (1882) using energy considerations; f 0 is the vibrational frequency of non-electrified drops (Rayleigh 1879). The fundamental frequency of an uncharged drop in an electric field will decrease with increasing field strength and deformation a / b and will equal zero when E ( R )/ T ) ½ = 1.625 and a / b = 1.86; these critical values correspond to the disintegration conditions derived by Taylor (1964). An interferometric technique involving a laser confirmed the accuracy of the calculations concerned with charged drops. The vibration of water drops of radius around 2 mm was studied over a wide range of temperatures as they fell through electric fields either by suspending them in a vertical wind tunnel or allowing them to fall between a pair of vertical electrodes. Photographic analysis of the vibrations revealed good agreement between theory and experiment over the entire range of conditions studied even though the larger drops were not accurately spheroidal and the amplitude of the vibrations was large.

scholarly journals Improving of electrical channels for magnetotelluric sounding instrumentation

2015 ◽  
Vol 4 (2) ◽  
pp. 149-154 ◽  
Author(s):  
A. M. Prystai ◽  
V. O. Pronenko
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Deep Structure ◽  
Experimental Tests ◽  
Magnetotelluric Sounding ◽  
Earth’S Crust ◽  
Geomagnetic Variations ◽  
The Earth ◽  
Wide Range ◽  
Earth's Crust

Abstract. The study of the deep structure of the Earth's crust is of great interest for both applied (e.g. mineral exploration) and scientific research. For this the electromagnetic (EM) studies which enable one to construct the distribution of electrical conductivity in the Earth's crust are of great use. The most common method of EM exploration is magnetotelluric sounding (MT). This passive method of research uses a wide range of natural geomagnetic variations as a powerful source of electromagnetic induction in the Earth, producing telluric current variations there. It includes the measurements of variations of natural electric and magnetic fields in orthogonal directions at the surface of the Earth. By this, the measurements of electric fields are much more complicated metrological processes, and, namely, they limit the precision of MT prospecting. This is especially complicated at deep sounding when measurements of long periods are of interest. The increase in the accuracy of the electric field measurement can significantly improve the quality of MT data. Because of this, the development of a new version of an instrument for the measurements of electric fields at MT – both electric field sensors and the electrometer – with higher levels relative to the known instrument parameter level – was initiated. The paper deals with the peculiarities of this development and the results of experimental tests of the new sensors and electrometers included as a unit in the long-period magnetotelluric station LEMI-420 are given.

scholarly journals Solar Opacities Constrained by Solar Neutrinos and Solar Oscillations

1990 ◽  
Vol 121 ◽  
pp. 61-80
Author(s):  
Arthur N. Cox
Keyword(s):  
Electric Fields ◽  
Oscillation Frequency ◽  
Convection Zone ◽  
Solar Surface ◽  
Solar Neutrinos ◽  
Photon Absorption ◽  
Solar Oscillations ◽  
Percent Reduction ◽  
Neutrino Production ◽  
Oscillation Frequencies

AbstractThis review discusses the current situation for opacities at the solar center, the solar surface, and for the few million kelvin temperatures that occur below the convection zone. The solar center conditions are important because they are crucial for the neutrino production, which continues to be predicted about 4 times that observed. The main extinction effects there are free-free photon absorption in the electric fields of the hydrogen, helium and the CNO atoms, free electron scattering of photons, and the bound-free and bound-bound absorption of photons by iron atoms with two electrons in the 1s bound level. An assumption that the iron is condensed-out below the convection zone, and the opacity in the central regions is thereby reduced, results in about a 25 percent reduction in the central opacity but only a 5 percent reduction at the base of the convection zone. Furthermore, the p-mode solar oscillations are changed with this assumption, and do not fit the observed ones as well as for standard models. A discussion of the large effective opacity reduction by weakly interacting massive particles (WIMPs or Cosmions) also results in poor agreement with observed p-mode oscillation frequencies. The much larger opacities for the solar surface layers from the Los Alamos Astrophysical Opacity Library instead of the widely used Cox and Tabor values show small improvements in oscillation frequency predictions, but the largest effect is in the discussion of p-mode stability. Solar oscillation frequencies can serve as an opacity experiment for the temperatures and densities, respectively, of a few million kelvin and between 0.1 and 10 g/cm3. Current oscillation frequency calculations indicate that possibly the Opacity Library values need an increase of typically 15 percent just at the bottom of the convection zone at 3×106K. Opacities have uncertainties at the photosphere and deeper than the convection zone ranging from 10 to 25 percent. The equation of state that supplies data for the opacity calculations fortunately has pressure uncertainties of only about 1 percent, but opacity uncertainties will always be much larger. A discussion is given about opacity experiments that the stars provide. Opacities in the envelopes of the Hyades G stars, the Cepheids, δ Scuti variables, and the β Cephei variables indicate that significantly larger opacities, possibly caused by iron lines, seem to be required.

The dependence of the rate of electrochemical charge transfer on the electric field at the metal-electrolyte interface

1972 ◽  
Vol 25 (2) ◽  
pp. 231 ◽  
Author(s):  
DB Matthews
Keyword(s):  
Electron Transfer ◽  
Charge Transfer ◽  
Potential Energy ◽  
Electric Field ◽  
Electric Fields ◽  
Potential Energy Curves ◽  
Energy Curve ◽  
Electrolyte Interface ◽  
Activated State ◽  
Wide Range

Electric fields at the metal-electrolyte interface are very high (of the order of 107 V/cm) and one intuitively expects that these fields should have a profound influence on the movement of charged species such as ions and electrons at the interface. Qualitatively, such field effects manifest themselves as deviations from linearity of Tafel plots or as a dependence of the symmetry factor on electrode potential. It is shown that Gurney's potential energy curve representation of charge transfer reactions yields only small changes in β over a wide range of potential, with the anharmonic (Morse) curves showing smaller changes than the harmonic (parabolic) curves. Superposition of the double layer electric field on these potential energy curves increases the curvature of the Tafel plots, but the effect is still not very large, being within the limits of uncertainty in determining the correct form of the potential energy curves. The effect of electric field on electron transfer is considered both from the viewpoint of change in electron transfer distance arising from a dependence of coordinates of the activated state on potential and from the viewpoint of a direct effect on the electron transfer barrier (analogous to field electron emission). The field emission effects are found to be even less than the effects of the field on the proton transfer potential energy barrier.

Time-Dependent Dielectric Breakdown in Thin Intrinsic SiO2 Films

1995 ◽  
Vol 386 ◽  
Author(s):  
J. S. Suehle ◽  
P. Chaparala
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
High Temperatures ◽  
Dielectric Breakdown ◽  
Operating Conditions ◽  
Time Dependent ◽  
Stress Tests ◽  
Time Dependent Dielectric Breakdown ◽  
Wide Range ◽  
Very High

ABSTRACTTime-Dependent Dielectric Breakdown studies were performed on 6.5-, 9-, 15-, 20-, and 22.5- nm thick SiO2 films over a wide range of stress temperatures and electric fields. Very high temperatures (400 °C) were used to accelerate breakdown so that stress tests could be performed at low electric fields close to those used for device operating conditions. The results indicate that the dependence of TDDB on electric field and temperature is different from that reported in earlier studies. Specifically, the electric-field-acceleration parameter is independent of temperature and the thermal activation energy was determined to be between 0.7 and 0.9 eV for stress fields below 7.0 MV/cm.Failure distributions of high-quality current-generation oxide films are shown to be of single mode and have dispersions that are not sensitive to stress electric field or temperature, unlike distributions observed for oxides examined in earlier studies. These results have implications on the choice of the correct physical model to describe TDDB in thin films. The data also demonstrate for the first time the reliability of silicon dioxide films at very high temperatures.

OSCILLATORY SQUEEZE FLOW OF ELECTRORHEOLOGICAL FLUID WITH TRANSITIONAL ELECTRIC FIELD

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1249-1255 ◽  
Author(s):  
JIE PENG ◽  
KE-QIN ZHU
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Phase Difference ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Electrorheological Fluid ◽  
Squeeze Flow ◽  
Field Frequency ◽  
Er Fluid ◽  
Oscillatory Squeeze Flow

The oscillatory squeeze flow of electrorheological (ER) fluid between two parallel discal electrode with transitional electric field is studied numerically in this paper. The ER fluid is modeled as Bingham-like fluid with the continuous modification model proposed by Papanastasiou. The numerical solutions based on the Navier-Stokes equations are presented by using the finite volume methods on the deforming grid. The force transmitted across the fluid under dc and ac electric fields are calculated. The effects of the electric field frequency and the phase difference between the ac electric field and mechanical oscillation are studied. The magnitude and the shape of the transmitted forces is shown to be not only a function of the applied voltage and the mechanical frequency but also the phase difference.

scholarly journals THE EFFECT OF CRITICAL ELECTRIC FIELDS ON THE ELECTRONIC DISTRIBUTION OF BILAYER ARMCHAIR GRAPHENE NANORIBBONS

2021 ◽  
pp. 98-112
Author(s):  
Lam Thuy Duong Nguyen ◽  
Thi Kim Quyen Nguyen ◽  
Nguyen Huu Hanh Pham ◽  
Dang Khoa Le ◽  
Van Chinh Ngo ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Energy Band ◽  
Graphene Nanoribbons ◽  
Strong Impact ◽  
Parallel Electric Field ◽  
Electronic Distribution ◽  
Wide Range ◽  
Armchair Graphene Nanoribbons ◽  
Armchair Graphene

We employed tight-binding calculations and Green’s function formalism to investigate the effect of applied electric fields on the energy band and electronic properties of bilayer armchair graphene nanoribbons (BL-AGNRs). The results show that the perpendicular electric field has a strong impact on modifying and controlling the bandgap of BL-AGNRs. At the critical values of this electric field, distortions of energy dispersion in subbands and the formation of new electronic excitation channels occur strongly. These originate from low-lying energies near the Fermi level and move away from the zero-point with the increment of the electric field. Phase transitions and structural changes clearly happen in these materials. The influence of the parallel electric field is less important in changing the gap size, resulting in the absence of the critical voltage over a very wide range [–1.5 V; 1.5 V] for the semiconductor-insulator group. Nevertheless, it is interesting to note the powerful role of the parallel electric field in modifying the energy band and electronic distribution at each energy level. These results contribute to an overall picture of the physics model and electronic structure of BL-AGNRs under stimuli, which can be a pathway to real applications in the future, particularly for electronic devices.

Electric field-controlled semiconductor nanorod assembly in solution: mechanistic insights from non-equilibrium molecular dynamics

2015 ◽  
Vol 93 (8) ◽  
pp. 888-890 ◽  
Author(s):  
Niall J. English
Keyword(s):  
Molecular Dynamics ◽  
Electric Field ◽  
Electric Fields ◽  
Self Assembly ◽  
Zero Field ◽  
Wide Range ◽  
Non Equilibrium Molecular Dynamics ◽  
Applied Fields ◽  
Preferential Alignment ◽  
Non Equilibrium

Non-equilibrium molecular dynamics (MD) of small, charged cadmium selenide nanorods have been carried out in the absence and presence of static applied electric fields. In the absence of applied fields, it was found that opposite dipolar alignment (antiferromagnetic) was achieved, along with self-assembly of the nanorods. However, in the case of induced electrophoresis in applied fields, the rods approached each other less readily, while at and above a field intensity of 0.05 V/Å, preferential alignment with the field was achieved for all rods, in contrast to the zero-field case. These results have implications for electric field-mediated control of nanorod assembly in solution, of key importance in a wide range of areas from photovoltaics to energy storage.

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