Two-dimensional Electric Field Research Articles

A new method for the interaction between multiple DEP particles: iterative dipole moment method

Dielectrophoresis for bio-particle manipulation has been drawing much attention in recent years. The equivalent dipole moment has been widely used to calculate dielectrophoretic forces on a particle, but this method falls short to describe the interaction between neighboring particles. The Maxwell stress tensor method (MST) is theoretically rigorous for particle interaction, but it will cost huge computing resource. In this paper, an iterative dipole moment method (IDM) is presented to investigate the interaction between multiple dielectrophoretic particles in a two-dimensional electric field. Without any cumbersome numerical computation, the inter-particle forces and the particle trajectories calculated by the IDM method are found to be in good agreement with those by the MST method for some published results. Furthermore, it is found that the final stable particle chain patterns strongly depend on the initial configuration of the particle distribution. An arbitrary small disturbance to the particle locations may lead to dramatically different motion trajectories and final particle chains.

A novel micro electric field sensor with X–Y dual axis sensitive differential structure

This paper presents a novel X–Y dual axis sensitive sensor for static electric field measurement. Compared with the existent electric field micro sensors, which can only detect one axial direction electric field, this sensor is capable of two-dimensional electric field sensing. In the design of the micro sensor, the combination of angular comb-drives and serpentine springs can bring the advantage of achieving large in-plane rotation, which enlarges the vibration amplitudes and results in more induced charges. Moreover, the push–pull electrostatic actuation method and the adopted differential sensing electrodes both can reduce the impact of common mode interference. Two pairs of sensing elements are located differentially to form a cross-like shape, with each pair to get X and Y component of the electric field respectively. Experimental results agree well with the electric field calibration theory and show high measurement accuracy. In the range from 0 to 25kV/m, the errors of electric field value are better than 8%.

Prediction of ions migration behavior in mortar under 2-D ALMT application to inhibit ASR

This study investigated four electric field configurations of two-dimensional accelerate lithium migration technique (ALMT), including line-to-line, plane-to-line, contour-to-line and plane-to-plane, and analyzed the ion migration behavior and efficiency. It was found that the free ion distribution diagram and voltage distribution diagram were similar, and ions migrated in the power line direction. The electrode modules were used for the mortar specimen with w/c ratio of 0.5. The effectively processed areas accounted for 14.1%, 39.0%, 49.4% and 51.4% of total area respectively on Day 28. Larger electrode area was more advantageous to ion migration. In addition, it was proved that the two-dimensional electric field could be divided into different equifield line active regions, and regarded as affected by one-dimensional electric field, and the ion migration results in various equifield line active regions were predicted by using the duration analysis method based on the theoretical model of ion migration obtained from one-dimensional test.

Highly precise and accurate terahertz polarization measurements based on electro-optic sampling with polarization modulation of probe pulses.

We have developed an electro-optic (EO) sampling method with polarization modulation of probe pulses; this method allows us to measure the direction of a terahertz (THz) electric-field vector with a precision of 0.1 mrad in a data acquisition time of 660 ms using a 14.0-kHz repetition rate pulsed light source. Through combination with a THz time-domain spectroscopy technique, a time-dependent two-dimensional THz electric field was obtained. We used a photoelastic modulator for probe-polarization modulation and a (111)-oriented zincblende crystal as the EO crystal. Using the tilted pulse front excitation method with stable regeneratively amplified pulses, we prepared stable and intense THz pulses and performed pulse-by-pulse analog-to-digital conversion of the signals. These techniques significantly reduced statistical errors and enabled sub-mrad THz polarization measurements. We examined the performance of this method by measuring a wire-grid polarizer as a sample. The present method will open a new frontier of high-precision THz polarization sensitive measurements.

4H-SiC Diode Avalanche Breakdown Voltage Estimation by Simulation and Junction Termination Extension Analysis

This paper presents and compares different avalanche breakdown voltage estimation methods in 4H-SiC (silicon carbide) using finite element simulation results on Schottky diode. 4H-SiC avalanche breakdown voltage and depletion width estimated with Baligas equations have shown to be higher than other estimation techniques and simulation results, especially for voltages higher than 5kV. This paper discusses the impact of choosing different junction termination extension (JTE) structures on two-dimensional junction curvature effects and electric field crowding for Schottky diodes Space-Modulated JTE (SMJTE) structure with optimum JTE dose and dimension could achieve up to 90% of the parallel plane breakdown voltage. For ultra high voltage devices (>15 kV) the SMJTE has significant improvement in terms of breakdown voltage. It also has a wider optimum JTE dose window. For 1 kV device there is not a significant difference in breakdown voltage between JTE and SMJTE structures.

Galvanotactic behavior of Tetrahymena pyriformis under electric fields

Tetrahymena pyriformis, a eukaryotic ciliate, swims toward a cathode in straight or cross-shaped microchannels under an applied electric field, a behavioral response called cathodal galvanotaxis. In straight channel experiments, a one-dimensional electric field was applied, and the galvanotactic swimming behavior of Tetrahymena pyriformis was observed and described in detail while the polarity of this field is switched. In most individual cases, the cell would immediately switch its direction toward the cathode; however, exceptional cases have been observed where cells exhibit a turning delay or do not turn after a polarity switch. In cross-channel experiments, feedback control using vision-based tracking was used to steer a cell in the microchannel intersection using a two-dimensional electric field generated by four electrodes placed at four ends of the cross channel. The motivation for this work is to study the swimming behavior of Tetrahymena pyriformis as a microrobot under the control of electric fields.

Equifield line simulation and ion migration prediction for concrete under 2-D electric field

This study attempted to find a proper method applicable to simulating practical equifield lines of two-dimensional Accelerate Lithium Migration Technique (ALMT), and evaluate the feasibility of using the theoretical ion migration model of one-dimensional ALMT to predict the ion migration behavior of two-dimensional ALMT. The result showed that the electrolyte or carbon plate can be used as matrix to draw equifield line graph similar to that by using mortar as matrix. Using electrolyte electrode module for simulation has advantages of simple production, easy measurement, rapidness, and economy. The electrolyte module can be used to simulate the equifield line distribution diagram in practical two-dimensional electrode configuration firstly. Then, several equifield line zones were marked, and several subzones under one-dimensional ALMT were separated from various equifield line zones. The theoretical free content distribution of alkali in concrete under two-dimensional electric field effect could be obtained from duration analysis.

Approximation for modelling electro-osmotic mixing in the boundary layer of membrane systems

A Computational Fluid Dynamics (CFD) model is used to compare the reliability and accuracy of the Helmholtz–Smoluchowski (HS) approximation against a one-dimensional charge density distribution (CD) solution of an electro-osmotic perturbation in a 2D membrane channel for reverse osmosis (RO). Electro-osmotic flow within the boundary layer is induced via the placement of a pair of electrodes parallel to the membrane surface and perpendicular to the bulk flow. Although this electrode configuration results in a two-dimensional electric field, the HS approximation considers only the electric field in the direction tangential to the membrane and not the normal component. The effect of the normal component of the electric field (Ey) on the flow field in the CD solution is compared against the solution using the HS approximation and it is found that the effect of Ey is minimal. Greater agreement between the CD solution and the HS approximation is found at higher bulk solute mass fractions, such as typically found on the membrane surface in RO systems. The relationships between cross-flow velocity, perturbation velocity and mixing are explored.

Analytical model for high-voltage SOI device with composite-k dielectric buried layer

An analytical model for a novel high voltage silicon-on-insulator device with composite-k (relative permittivity) dielectric buried layer (CK SOI) is proposed. In this structure, the composite-k buried layer is composed by alternating Si3N4 and low-k (k = 2.65) dielectric in the lateral direction. Due to the composite-k buried layer, the breakdown voltage (BV) is improved both by the vertical and lateral direction. Taking the modulation effect of accumulated interface holes into account, an analytical model is developed. In the blocking state, the proposed model revealed the mechanism of hole accumulation above the Si3N4 buried layer and investigated the modulation effect of accumulated holes on the two-dimensional (2-D) potential and electric field distributions. This analytical model is verified by the simulation results. Compared with the low-k dielectric buried layer SOI (LK SOI), simulation results show that the BV for CK SOI is enhanced by 21% and the specific on-resistance is reduced by 32%, respectively.

Fabrication and characterization of V-gate AlGaN/GaN high-electron-mobility transistors

V-gate GaN high-electron-mobility transistors (HEMTs) are fabricated and investigated systematically. A V-shaped recess geometry is obtained using an improved Si3N4 recess etching technology. Compared with standard HEMTs, the fabricated V-gate HEMTs exhibit a 17% higher peak extrinsic transconductance due to a narrowed gate foot. Moreover, both the gate leakage and current dispersion are dramatically suppressed simultaneously, although a slight degradation of frequency response is observed. Based on a two-dimensional electric field simulation using Silvaco “ATLAS" for both standard HEMTs and V-gate HEMTs, the relaxation in peak electric field at the gate edge is identified as the predominant factor leading to the superior performance of V-gate HEMTs.

Light absorption enhancement in polymer solar cells with nano-Ag

The thickness of an active layer is limited by its low mobility of carriers in a polymer solar cell composed of the blend bulk-heterojunction formed by P3HT as donor material and PCBM as acceptor material, which can affect the light absorption of the polymer solar cell. Metal nanocrystals-doped polymer active layer can enhance its inner electrical field and absorb light due to the surface plasmon resonance (SPR) effect of the nanocrystals. Two-dimensional electrical field distributions in the polymer solar cells are simulated based on finite difference time domain (FDTD) approach, under the assumption that the diameter of doping nano-Ag is 50 nm, the distance between two nanocrystals is 50nm and the incident light wavelength is 400 nm or 500 nm. The electrical field distributions over the cross-section of nano-Ag are also simulated at the incident light angle of 15°, 45°, 60°, respectively. The light absorption of different devices are calculated, in which the sizes of nano-Ag take 10 nm, 20 nm and 50 nm, respectively, Particles of nano-Ag are dispersed in PEDOT:PSS layer. Moreover, the light absorption is calculated at the incident light angles of 15°, 45°, 60°, respectively. Results show that the electrical field is redistributed due to the SPR effect caused by nano-Ag in the polymer active layer. A larger size of nano-Ag leads to light scattering in a wider angle, thus results in more light absorption by the device. Here, the colloid of nano-Ag is prepared from an organic salt of Ag, and the polymer solar cell with nano-Ag is fabricated in the structure of glass /ITO (～100 nm) /PEDOT:PSS (40 nm) /P3HT:PCBM (～100 nm)/(nano-Ag) /LiF (1 nm) /Al (120 nm). Furthermore, experimental results show that the nano-Ag doped in P3HT:PCBM layer increases light absorption and improves the electrical performance of the device, which enhances the incident photon conversion efficiency (IPCE) in spectrum at 520nm by 17.9%.

PARTICLE ACCELERATION AT A FLARE TERMINATION SHOCK: EFFECT OF LARGE-SCALE MAGNETIC TURBULENCE

We investigate the acceleration of charged particles (both electrons and protons) at collisionless shocks predicted to exist in the vicinity of solar flares. The existence of standing termination shocks has been examined by flare models and numerical simulations e.g., Shibata,Forbes. We study electron energization by numerically integrating the equations of motion of a large number of test-particle electrons in the time-dependent two-dimensional electric and magnetic fields generated from hybrid simulations (kinetic ions and fluid electron) using parameters typical of the solar flare plasma environment. The shock is produced by injecting plasma flow toward a rigid piston. Large-scale magnetic fluctuations -- known to exist in plasmas and known to have important effects on the nonthermal electron acceleration at shocks -- are also included in our simulations. For the parameters characteristic of the flaring region, our calculations suggest that the termination shock formed in the reconnection outflow region (above post-flare loops) could accelerate electrons to a kinetic energy of a few MeV within 100 ion cyclotron periods, which is of the order of a millisecond. Given a sufficient turbulence amplitude level ($\delta B^2/B_0^2 \sim 0.3$), about 10% of thermal test-particle electrons are accelerated to more than 15 keV. We find that protons are also accelerated, but not to as high energy in the available time and the energy spectra are considerably steeper than that of the electrons for the parameters used in our simulations. Our results are qualitatively consistent with the observed hard X-ray emissions in solar flares.

Complex 2D Electric Field Solution in Undoped Double-gate MOSFETs

A new technique to calculate the channel electric field in Double-gate MOSFETs and Schottky barrier Double-gate MOSFETs (SB-DG-MOSFETs) in sub-threshold region is presented. 2D Poissons equation is solved in an analytical closed form with the conformal mapping technique. The estimated solution of the two-dimensional electric field with its complex components is analyzed with the bias conditions for accumulation and inversion regions, which have been applied and studied in detail. A comparison with data simulated by 2D TCAD Sentaurus simulator for channel lengths down to 22 nm was made and is in a good agreement to this simulation results.

An analytical expression of electric potential and field of organic thin film transistors

The two-dimensional electric potential and field of an organic thin-film transistor (OTFT) is derived by conformal mapping using the Schwarz-Christoffel-transformation of the Poisson equation. In this paper we compare this analytical closed-form solution to field simulation results from Silvaco TCAD. Inter alia the potential close to the surface is calculated and we found excellent accordance to the numerical simulations and thus proofed its usability for charge transport calculations. Thus, it is used for calculation of the drain-source-current in the channel.

Density distribution of large planar plasma sheet

A large plasma sheet with a size of 60 cm60 cm2 cm is generated in an apparatus with a hollow cathode. The electron density distribution of the large area plasma sheet is measured. Since the duration of high voltage pulse is short, we change measurement methods. Besides, modification is used for electron saturation current to get the real density. The two-dimensional electron density and electrical field distribution are calculated at discharge currents ranging from 1 to 6 A. Meanwhile we discuss other parameters related to density distribution. The electron density distribution is important for plasma sheet to steer microwave. It is encouraging that the large area plasma sheet generated by the hollow cathode is uniform and has sufficient electron density to reflect X-band (812 GHz) microwaves.

The light absorption enhancement in polymer solar cells with periodic nano-structures gratings

The thickness of the active layer is limited by its low carrier mobility in the polymer solar cell composed of the blend bulk-heterojunction formed by P3HT as donor material and PCBM as acceptor material, which can affect the light absorption in the polymer solar cell. Nano-structure gratings inserted into polymer layer can redistribute the electrical field inside the device and improve its light absorption. Two-dimensional electrical field distributions inside the polymer solar cell are simulated with the grating period of 1 μ, fill ratio of 0.5 and incident wavelengths of 500 nm and 700 nm based on finite difference time domain. The light absorptions by the devices with different grating depths and fill ratios are calculated based on rigorous coupled wave. The analysis illustrates that light spots occur in the device due to the light diffraction caused by the gratings and the light absorption is increased by 4.2% with a grating fill ratio of 0.5, depth of 10 nm and an incident light wavelength of 512 nm. In experiment, nano-structure gratings are introduced into the devices by the micro-printing technology with PDMS and polymer solar cell is structured with ITO/ PEDOT:PSS gratings/ P3HT:PCBM/ LiF/ Al. The experimental results from the planar and the grating devices prove that the nano-structure gratings embedded in PEDOT:PSS layer increase the power conversion efficiency by 31%.

Single-shot diagnostic for the three-dimensional field distribution of a terahertz pulse based on pulsed digital holography

In this Letter, a pulsed digital holographic approach for detecting the three-dimensional (3D) field distribution of a freely propagating single terahertz (THz) pulse based on an electro-optic (E-O) sampling technique is proposed, by which the 3D field distribution of a single THz pulse sampled at different time points can be recorded in real-time on a series of subholograms and will be finally reconstructed as a series of two-dimensional spatial electric field distributions in a time series with a time resolution of femtosecond order. Simulation is carried out to demonstrate the process of the implementation, which confirmed the feasibility of the proposal.

Two-dimensional kinetic model of a short high-current vacuum arc discharge

A two-dimensional kinetic model of a short high-current vacuum arc discharge has been developed in which magnetized electrons move in the hydrodynamic regime and fast cathode ions move in the free-flight regime in a two-dimensional electric field. The model includes the distribution of ions over the emission angles at the cathode boundary of the plasma. A method has been proposed for calculating the distribution of the plasma density in the gap. The two-dimensional distributions of the plasma density, electric field, discharge current density, and trajectories of ions in an external longitudinal magnetic field have been calculated. It has been shown that ion trajectories intersect each other and some ion trajectories return to the cathode. The number of ion trajectories reaching the anode decreases with a decrease in the external magnetic field. The ion “starvation” effect appears near the anode and can lead to the violation of steady-state current transfer and to the formation of an anode spot. It has been found that the kinetic description of the motion of ions does not indicate the appearance of a shock wave.

Directional Electric Field Sensitivity of a Liquid Crystal Infiltrated Photonic Crystal Fiber

The directional sensitivity of nematic liquid crystal infiltrated polarization-maintaining photonic crystal fiber to an externally applied electric field is evaluated for two-dimensional electric field sensing. Selectively infiltrated and infiltration length optimized polarization-maintaining photonic crystal fiber is used as a probe. Using a polarimetric scheme, the polarized transmission properties of the infiltrated fiber are evaluated in terms of the orientation of the fiber polarization axis in an electric field. It is shown that the sensor has varying sensitivity to electric fields oriented at different angles with respect to the fiber polarization axis. The proposed low-cost all-fiber sensor can be used for two-dimensional directional electric field sensing.

Particle modelling of the hybrid negative ion source

In this paper we present results of different particle-based models of expansion and extraction regions for the ITER negative ion source. Results show the important role of electron-induced processes (eV excitation and dissociation) and gas–surface and plasma–surface interactions (atom recombinative desorption and ion neutralization) for the production of negative ion precursors. The spatial distribution of neutral and ionized caesium as well as the drag due to the deuterium flow and its re-evaporation from the plasma grid is calculated. The self-consistent two-dimensional electric field distribution in the extraction region allows a better understanding of the transport of surface-produced negative ions towards the orifice. The model delivers an extraction probability of less than 25%.