Gap Electric Field Research Articles

Electrohydrodynamic inter-electrode flow and liquid jet characteristics in charge injection atomizers

The governing equations of electrohydrodynamics pertinent to forced and free electroconvection have been examined in the context of an array of charge injection atomization systems for dielectric electrically insulating liquids. The underlying physics defining their operation has been described further by linking the internal charge injection process inside the atomizer with resulting charged liquid jet characteristics outside it. A new nondimensional number termed the electric jet Reynolds number ReE,j is required to describe charge injection systems universally. The electric jet Reynolds number ReE,j varies linearly with the inter-electrode gap electric Reynolds number ReE, and the inter-electrode gap Reynolds number ReE varies linearly with the conventional liquid jet Reynolds number Rej. These variations yield two new seemingly universal constants relevant in the description of two-phase charge injection systems. The first constant being \(\left( {\frac{{Q_{{\text{V}}} d}}{\epsilon }} \right)\left( {\frac{1}{E}} \right)\left( {\frac{d}{L}} \right)\sim 0.06\) which physically represents the ratio of jet to inter-electrode gap electric field multipled by a nondimensional geometric factor while it may also be physically seen as a forced flow charge injection strength term, analogous to the ‘C’ term described in single-phase free electroconvection. The second constant being \(\left(\frac{\kappa E}{U_{\rm inj}}\right)\left(\frac{L}{d}\right)\sim0.6\) which physically represents the ratio of inter-electrode gap ionic drift velocity, to the liquid jet velocity, multipled by a nondimensional geometric factor. These scalings have been found to be valid for charge injection systems regardless of fuel, voltage pulsation, electrode shape, orifice diameter, and inter-electrode gap length.

MECHANISM OF THE X-RAY AND SOFT GAMMA-RAY EMISSIONS FROM HIGH MAGNETIC FIELD PULSAR: PSR B1509–58

We use the outer gap model to explain the spectrum and the energy-dependent light curves of the X-ray and soft γ-ray radiations of the spin-down powered pulsar PSR B1509-58. In the outer gap model, most pairs inside the gap are created around the null charge surface and the gap's electric field separates the two charges to move in opposite directions. Consequently, the region from the null charge surface to the light cylinder is dominated by the outflow current while that from the null charge surface to the star is dominated by the inflow current. We suggest that the viewing angle of PSR B1509−58 only receives the inflow radiation. The incoming curvature photons are converted to pairs by the strong magnetic field of the star. The X-rays and soft γ-rays of PSR B1509−58 result from the synchrotron radiation of these pairs. Magnetic pair creation requires a large pitch angle, which makes the pulse profile of the synchrotron radiation distinct from that of the curvature radiation. We carefully trace the pulse profiles of the synchrotron radiation with different pitch angles. We find that the differences between the light curves of different energy bands are due to the different pitch angles of the secondary pairs, and that the second peak appearing at E > 10 MeV comes from the region near the star, where the stronger magnetic field allows pair creation to happen with a smaller pitch angle.

Comparative investigations of surface plasmon polaritons on dielectric and metallic gratings

We investigate the properties of Surface Plasmon Polaritons (SPPs) on two kinds of structures: metallic and dielectric gratings loaded on a metallic layer (MM grating and DM grating). The rigorous coupled wave analysis (RCWA) is used for all the simulation in this article. The characteristics of band gap, dispersion relation, reflectivity curves and resonant electric field distributions are comparative simulated and analyzed in MM and DM gratings. Compared with the sticky short-wavelength band edge and complicated surface electric field distributions of MM grating, it is found that the band gap edges of DM grating could be controlled flexibly and the surface fields are more smoothly, which can be used to facilitate the spectral tunability and tailor the optical response of DM structure. This work would provide help for understanding the intrinsic reason of the difference of SPPs in two kinds of structures and basis for choosing suitable structure (MM or DM) of SPPs devices aiming at different functions, especially for designing the dielectric loaded surface plasmon polaritions (DLSPPs) devices.

Characteristics of Atmospheric-Pressure Helium Barrier Pulse Discharges

The mechanism and evolution of atmospheric-pressure dielectric barrier discharge (DBD) in pure helium excited by repetitive voltage pulses have been numerically studied using a 1-D fluid model. The temporal and spatial distributions of the characteristic quantities, i.e., electron density, ion density, electron temperature, and gap electric field, are calculated, and the following characteristics are observed. There are many electrons in the gap before each of the two pulse discharges in one circle of the applied voltage pulse, the significant difference between the electron densities before each pulse discharge makes the two discharge modes in asymmetry, the breakdown in the second discharge is weaker than that in the first discharge, and a wide area of quasi-neutral plasma bulk can be obtained. In addition, the effects of the key parameters of the applied voltage pulse, such as amplitude, pulsewidth, frequency, rising time, and falling time, on the DBD are analyzed systematically, and in particular, the multipeak behavior and the structure transition of distribution of the charged particle densities are observed.

Edge saturation effects on the magnetism and band gaps in multilayer graphene ribbons and flakes

Using a density functional theory based electronic structure method and semi-local density approximation, we study the interplay of geometric confinement, magnetism and external electric fields on the electronic structure and the resulting band gaps of multilayer graphene ribbons whose edges are saturated with molecular hydrogen (H$_2$) or hydroxyl (OH) groups. We discuss the similarities and differences of computed features in comparison with the atomic hydrogen (or H-) saturated ribbons and flakes. For H$_2$ edge-saturation, we find \emph{shifted} labeling of three armchair ribbon classes and magnetic to non-magnetic transition in narrow zigzag ribbons whose critical width changes with the number of layers. Other computed characteristics, such as the existence of a critical gap and external electric field behavior, layer dependent electronic structure, stacking-dependent band gap induction and the length confinement effects remain qualitatively same with those of H-saturated ribbons.

임펄스전압에 대한 N2가스의 절연파괴특성

This paper aims to examine the possibility of using an environmentally friendly N₂ as an alternative gas to SF?. For this purpose, we have investigated breakdown characteristics of N₂ under impulse voltages in a quasi-uniform electric field gap. The 1.2/50[㎲] lightning impulse voltage, switching impulse voltages and oscillatory impulse voltages were applied at the test gap. The electric field utilization factor ranges from 0.5 to 0.8. The experimental data of SF6 and N₂ acquired in the same experimental condition are presented in parallel for comparison. As a result, the breakdown voltages in SF? and N₂ are linearly increased with the gas pressure, also the breakdown voltages in N₂ are increased with increasing the gap distance and electric field utilization factor. The positive breakdown voltages are higher than the negative breakdown voltages. The nagative basic lightning impulse withstand level of 150[㎸] in N₂ of about 0.5[㎫] is nearly equal to that in SF? of 0.15[㎫]. It is seen from the results obtained in this work that N₂ can be used as an eco-friendly alternative gas to SF? in distribution power equipment.

One-dimensional combined field and thermionic emission model and comparison with experimental results

An integrated theoretical model has been developed to predict the entire range of emission from thermionic to field emission, including the mixed emission regime. The model assumes a Sommerfeld free electron model supply function, for which the Fermi-Dirac distribution applies with a nonzero temperature. The electron transmission coefficient is calculated in one dimension using a transfer matrix method (TMM) to solve the steady-state Schrödinger equation. Emission current densities have been measured for a periodic copper knife-edge cathode to compare with the TMM model result. It is shown that the computational result utilizing this model provides good agreement with the experimental data. Unambiguous and reliable estimates of the effective field enhancement factor βeff (βeff=Es∕Eg, where Es is the cathode surface electric field and Eg is the gap electric field between the cathode and anode) and the effective work function ϕeff are obtained from experimental measurements using this model by simultaneously fitting thermionic and field emission data for the cathode. Comparing the experimental and theoretical results reveals that finite temperature thermal contributions to the current emission can be significant in the operation of many field emission cathodes.

Dynamic channel blocker/equalizer with high blocking extinction ratio

The effect of an interpixel gap on light leakage in a free-space liquid-crystal-based dynamic channel blocker/equalizer is studied. The electric field components along the driving electric field within the liquid crystal interpixel gap are numerically calculated. The results show nonuniform distributions in both width and thickness. The numeric results on the relation between gap width and electric field distribution are also presented. A 20-channel, 200-GHz channel-spacing blocker/equalizer on the C band with flat tops and a 40-dB extinction ratio is fabricated and examined.

Modeling of cold emission cathode by inclusion of combined field and thermionic emission processes

Emission currents have been measured at elevated temperatures for a periodic copper knife-edge cathode. To model the emission process of the cathode, we have combined thermionic and field emission processes. Electron tunneling is calculated using a transfer matrix method. Using this model, we accurately reproduced the experimental deviation and minimum in the ln(J∕Eg2) vs 1∕Eg plot, where Eg is the gap electric field and J is the emitted current density. This phenomenon has been widely observed but no comprehensive explanation has been put forth. Unambiguous and realistic estimates of the cathode effective field enhancement factor beta averaged (βeff=Esurface∕Egap) and effective work function Φ are obtained from experimental measurements using this model.

A comparative assessment of two optical fibre techniques for measuring the speed of the electric wind in a negative polarity, atmospheric corona discharge**This paper was presented at the 13th International Conference on Sensors and their Applications, held in Chatham, Kent, on 6–7 September 2005.

Two optical fibre anemometers, one based on a Mach–Zehnder interferometer (OFIA) and another a novel laser-optical fibre Bragg grating sensor (FBGA) have been constructed to measure the speed of the convective air flow generated in the point-plane gap of a negative corona discharge in atmospheric air. In both configurations the sensing section of the optical fibre anemometers is subjected to controlled, repetitive bursts of infrared radiation from a CO2 laser and the combination of localized heating and convective cooling by the corona wind results in an optical signal that is directly calibrated to the speed of the wind. Both the OFIA and FBGA successfully measured the speed of the corona wind in the discharge gap, with wind speeds ranging from 0 to 0.7 m s−1 observed at different locations in the discharge gap. However, the FBGA, due primarily to the ability to average sensor response over many measurements, exhibited an order of magnitude higher sensitivity than the OFIA (Δv ≈ 4 × 10−3 m s−1 compared to 3 × 10−2 m s−1). Both sensors yielded measurements of wind speed that were an order of magnitude lower than similar measurements using laser Doppler anemometry (LDA), indicating that the seed particles introduced as part of the LDA system are providing false reading of wind speed due to acceleration by the gap electric field.

Carrier recombination and differential diode quality factors in the dark forward bias current-voltage characteristics of a-Si:H solar cells

A careful study has been carried out on dark forward bias current-voltage characteristics in high-quality well-controlled a-Si:H solar cell structures. Contributions of potential barriers in the intrinsic layers adjacent to the p and n contacts on carrier injection have been clearly identified and carrier recombination in the p∕i regions systematically controlled and clearly separated from that in the bulk of the intrinsic layers. It is found that the recombination in the p∕i regions results in voltage-independent diode quality factor, n, with values very close to 1 whereas recombination in the bulk results in bias-dependent differential diode quality factors, n(V). These n(V) characteristics are consistent with Shockley-Read-Hall recombination through a continuous distribution of gap states in the intrinsic layers which have spatially uniform distributions of gap states and electric field. Based on an analytical model the n(V) characteristics are interpreted in terms of Gaussian-like energy distributions of gap states in both undiluted and diluted protocrystalline a-Si:H intrinsic layers. Gaussian-like distributions are identified centered around as well as ∼0.3eV away from midgap with differences in their distributions for the two materials in the annealed states and their evolution upon introducing light-induced defects. These results demonstrate that forward bias dark currents and, in particular, n(V) characteristics offer a reliable probe for characterizing the gap states of the native- and light-induced defect states in a-Si:H solar cells as well as mechanisms limiting their performance.

Gnevyshev gap, Forbush decreases, ICMEs and solar wind electric field: relationships

Abstract We have studied annual frequency distribution of the Forbush decreases for three solar cycles (20, 21, 22); most are associated with the fast ICMEs and SSCs. The frequency varies in step with the solar cycle but the distribution has a notable gap embedded in it, near the maximum of the cycle leading to two peaks in Forbush decreases per cycle. We show that the gap coincides with the epoch of solar polar field reversal. There is an indication of an odd/even cycle effect in the frequency distribution of Forbush decreases and the associated SSCs. We find that two peaks in Forbush decrease and SSC distributions are separated by the Gnevyshev gap; second peaks occur well before the onset of the high-speed streams in the descending phase of a cycle which do not cause Forbush decreases but do contribute to a peak in the geomagnetic activity index Ap. We compare Forbush decrease and SSC distributions with the corresponding distribution of the solar wind electric field and find that a large amplitude of the electric field of itself does not cause a Forbush decrease to occur unless it is also associated with a fast ICME/SSC.

Polarization properties of ion-excitation mechanisms in high-voltage gaps

We investigate the excitation of atomic levels in a high-voltage discharge gap by studying the spectrum of the $2p\ensuremath{-}3d$ transitions of Li I atoms flowing in the gap. The Stark splitting of this transition, due to the gap electric field, enables resolving the lines originating from different magnetic sublevels of the $3d$ level. We show that the atomic level populations are dominated by excitations due to ions accelerated in the gap. The directionality of the ion beam induces magnetic sublevel populations that are remarkably different from the statistical distribution, where the major role is played by the relatively low-energy ions accelerated near the ion-emitting surface. By accounting for the polarization properties of the beam-induced level excitations we were able to obtain good agreement with observed populations of atomic levels with different ${m}_{l}$ values.

Satellite Formation in Transfer Gaps

Toned electrophotographic images often exhibit toner satellites around alphanumeric characters and halftone dots. Among the electrophotographic subsystems, transfer is believed to be a frequent and even dominant source of such image artifacts. This paper reports on toner adhesion, detachment, and disruption as determined using a laboratory ultracentrifuge and an electrostatic detachment cell (ESD). The simplicity of this apparatus helps isolate factors contributing to satellite formation such as toner particle size, surface treatment, transfer gap (pre-nip or post-nip) and transfer electric field. Measurements have confirmed that surface-treatment can decrease adhesion and/or cohesion and increase the number, but not the spatial extent, of laterally displaced toners after gap-jumping. Results from both the ultracentrifuge and the ESD show that, even for highly surface-treated toner, only a small fraction of toner is removed by the normally-directed electrostatic forces encountered during transfer from photoconductor to paper. In contrast, relatively weak tangential forces cause toner to move laterally; suggesting an additional mechanism for satellite formation that need not involve gap jumping.

Generalized representation of beam coupling coefficient in ungridded reentrant cavity

The Beam coupling coefficient and cavity voltage in an ungridded reentrant cavity, in which the gap electric field varies in hyperbolic cosine function and electrons move only along the axial direction, are derived from the analytical expressions of Kosmahl and Branch on electric fields in the cavity.

Mechanisms of electrical coupling between pyramidal cells.

Direct electrical coupling between neurons can be the result of both electrotonic current transfer through gap junctions and extracellular fields. Intracellular recordings from CA1 pyramidal neurons of rat hippocampal slices showed two different types of small-amplitude coupling potentials: short-duration (5 ms) biphasic spikelets, which resembled differentiated action potentials and long-duration (>20 ms) monophasic potentials. A three-dimensional morphological model of a pyramidal cell was employed to determine the extracellular field produced by a neuron and its effect on a nearby neuron resulting from both gap junctional and electric field coupling. Computations were performed with a novel formulation of the boundary element method that employs triangular elements to discretize the soma and cylindrical elements to discretize the dendrites. An analytic formula was derived to aid in computations involving cylindrical elements. Simulation results were compared with biological recordings of intracellular potentials and spikelets. Field effects produced waveforms resembling spikelets although of smaller magnitude than those recorded in vitro. Gap junctional electrotonic connections produced waveforms resembling small-amplitude excitatory postsynaptic potentials. Intracellular electrode measurements were found inadequate for ascertaining membrane events because of externally applied electric fields. The transmembrane voltage induced by the electric field was highly spatially dependent in polarity and wave shape, as well as being an order of magnitude larger than activity measured at the electrode. Membrane voltages because of electrotonic current injection across gap junctions were essentially constant over the cell and were accurately depicted by the electrode. The effects of several parameters were investigated: 1) decreasing the ratio of intra to extracellular conductivity reduced the field effects; 2) the tree structure had a major impact on the intracellular potential; 3) placing the gap junction in the dendrites introduced a time delay in the gap junctional mediated electrotonic potential, as well as deceasing the potential recorded by the somatic electrode; and 4) field effects decayed to one-half of their maximum strength at a cell separation of approximately 20 micron. Results indicate that the in vitro measured spikelets are unlikely to be mediated by gap junctions and that a spikelet produced by the electric field of a single source cell has the same waveshape as the measured spikelet but with a much smaller amplitude. It is hypothesized that spikelets are a manifestation of the simultaneous electric field effects from several local cells whose action potential firing is synchronized.

A-Si:H Photo Diode With Variable Spectral Sensitivity

AbstractA novel two terminal thin film photo diode for color detection has been developed. The device structure which is based on standard amorphous silicon nipin multilayers exhibits three or even more linearly independent spectral sensitivity peaks and provides linearity over a wide range of illumination levels. Band gap engineering and electric field tailoring allow a precise voltage controlled shift of the collection region of photo generated carriers. The steady-state as well as the transient device characteristics have been studied in detail. Emphasis was put on optimization of the spectral sensitivity of the color diodes. Furthermore, an electronic color correction algorithm is presented which results in an improved color separation.

The Input Admittance of Thin Prolate Spheroidal Dipole Antennas with Finite Gap Widths

The input admittance of a thin prolate spheroidal dipole antenna of major and minor axes a, b and fed by a gap of finite width 2d operating at the wavelength /spl lambda/ (k=2/spl pi///spl lambda/) is expressed as a very slowly convergent sum of symmetric prolate spheroidal angle and radial modal functions whose computation in this paper is facilitated by a novel method for evaluating radial functions of the second kind for small and large order with high accuracy. Then, by using Infeld's (1947) method of replacing a sum by an integral, the slowly convergent part of the admittance is evaluated. Three different types of distributions for the gap electric field are considered, and numerical results for the admittance are given as a function of the spheroidal dipole's length (0/spl les/2a/spl les//spl lambda/) with its thickness (2b/spl ges/2/spl times/10/sup -5//spl lambda/), as well as the gap ratio d/b, as parameters. >

The input admittance of thin prolate spheroidal dipole antennas with finite gap widths

The input admittance of a thin prolate spheroidal dipole antenna of major and minor axes a, b and fed by a gap of finite width 2d operating at the wavelength /spl lambda/ (k=2/spl pi///spl lambda/) is expressed as a very slowly convergent sum of symmetric prolate spheroidal angle and radial modal functions whose computation in this paper is facilitated by a novel method for evaluating radial functions of the second kind for small and large order with high accuracy. Then, by using Infeld's (1947) method of replacing a sum by an integral, the slowly convergent part of the admittance is evaluated. Three different types of distributions for the gap electric field are considered, and numerical results for the admittance are given as a function of the spheroidal dipole's length (0/spl les/2a/spl les//spl lambda/) with its thickness (2b/spl ges/2/spl times/10/sup -5//spl lambda/), as well as the gap ratio d/b, as parameters. >

Hybrid thin-slot algorithm for the analysis of narrow apertures in finite-difference time-domain calculations

A technique to incorporate a half-space aperture integral equation into a finite-difference time-domain (FDTD) code based on the offset Yee mesh (see K.S. Yee, ibid., vol. AP-14, p.302-7, 1966) is presented. To introduce the technique, linear apertures that are electrically narrow in both width and depth are discussed. The method incorporates an independent time-marching solution for the aperture problem into the FDTD code so that the aperture formally does not exist within the main FDTD mesh. A feedback scheme is introduced so that full exterior and interior coupling is included in the aperture solution. The technique is particularly useful for the analysis of apertures that are narrow both in width and depth with regard to the FDTD spatial cell. Previous thin-slot methods are shown to significantly underestimate the transverse gap electric field for this case, and an explanation for this is provided with the aid of the hybrid algorithm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>