Nonuniform Injection Research Articles

Atomization and Flow Characteristics of Liquid Sheet Produced by Jet Impingement

Aiming at elucidating the relationship between a liquid sheet atomization and the detailed flowfield inside the sheet produced by an impingement-type injector, numerical computation, experimental observation, and theoretical analysis were performed. A numerical methodwas developed to examine atomization phenomena. First, themethod was verified through quantitative comparisonwith a corresponding experiment of pinch off. Then, experimental and theoretical analyses were conducted on the atomization of an axisymmetric liquid sheet through Kelvin–Helmholtztype instability, which was produced by two opposing watexr jets. The numerical results showed qualitative resemblance to the corresponding experimental and theoretical analyses. Finally, it was clarified that a nonuniform injection velocity profile resulted in a velocity distribution with an inflection point inside the sheet. As a result, the sheet tended to be unstable and enhanced atomization.

Tradeoffs in the Realization of Electrically Pumped Vertical External Cavity Surface Emitting Lasers

The design and realization of substrate emitting 980-nm electrically pumped vertical-external-cavity surface-emitting lasers (EP-VECSELs) is reported. A method to characterize the detuning of the cavity and spontaneous emission of the epitaxial material is described, and an experimental study of the effect of substrate doping on the operating characteristics of devices is presented. A reduction in optical loss and enhanced current-gain characteristics with a reduction in substrate doping from 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> to 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> is demonstrated. Spatial carrier distributions, evidenced by near-field profiling of devices without external feedback indicate similar current spreading behavior for the two-substrate dopings. Devices with diameter greater than 70 μm and current spreading layer thickness of 100 μm are shown to suffer from nonuniform carrier injection into the active region. Power scaling properties of the devices are investigated in both pulsed and CW operation. We realize devices with CW powers of 133 mW at 981 nm from a 150 μm device with 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> substrate doping at 0 °C, which is limited by nonoptimal cavity-gain peak detuning.

Efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with nonuniform current spreading

We demonstrate that the efficiency droop phenomenon in multiple quantum well InGaN/GaN light-emitting diodes (LEDs) may be connected to the current crowding effect. A numerical model of internal quantum efficiency calculation is presented that takes into account nonuniform lateral carrier injection in the active region. Based on this model, we examine the effect of current crowding on the efficiency droop using comparison of simulated internal quantum efficiency of InGaN LEDs with low and high uniformity of current spreading. The results of simulations and measurements show that the devices with low uniformity of current spreading exhibit higher efficiency droop and lower roll-off current value.

Design Rules and Characterisation of Electrically Pumped Vertical External Cavity Surface Emitting Lasers

We present an experimental study of the effect of substrate doping on the operating characteristics of substrate emitting electrically pumped vertical external cavity surface emitting lasers. We demonstrate a reduction in substrate doping from 2×1018 to 4×1017 cm-3 leads to reduced optical loss and enhanced current–gain characteristics. Spatial carrier distributions, evidenced by near field profiling of devices without external feedback indicates essentially identical behavior for the two substrate dopings. Devices with diameter greater than 100 µm and current spreading layer thickness of 100 µm suffer from non-uniform carrier injection into the active region, below this diameter output power scales linearly with device diameter. We show CW powers of 130 mW from a 100 µm device with 4×1017 cm-3 substrate doping at 0 °C can be obtained.

Intensity dynamics in a waveguide array laser

We consider experimentally and theoretically the optical field dynamics of a five-emitter laser array subject to a ramped injection current. We have achieved experimentally an array that produces a robust oscillatory power output with a nearly constant π phase shift between the oscillations from each waveguide. The output power also decreases linearly as a function of waveguide number. Those behaviors persisted for pump currents varying between 380 and 500 mA with only a slight change in phase. Of note is the fact that the fundamental frequency of oscillation increases with injection current, and higher harmonics are produced above a threshold current of approximately 380 mA. Experimental observations and theoretical predictions are in agreement. A low dimensional model was also developed and the impact of the nonuniform injection current studied. A nonuniform injection current is capable of shifting the bifurcations of the waveguide array providing a valuable method of array tuning without additional gain or structural alterations to the array.

Injection of Water Above Gas for Improved Sweep in Gas EOR: Nonuniform Injection and Sweep in 3D

Summary In gas-injection enhanced oil recovery (EOR), simultaneous injection of water and gas from parallel horizontal wells with water injected from the upper well [sometimes called modified simultaneous water and gas (SWAG) injection], can give deeper penetration of gas before gravity segregation than SWAG from the same well. Most previous studies of this process were limited to 2D, in which the injection rate is uniform along each well. In 3D, we find that gas injection can be far from uniform, even in homogeneous reservoirs—which are the focus of this study. If gas injection is nonuniform in homogeneous reservoirs, it surely would be so in heterogeneous reservoirs. In some cases, there is an inherent instability in uniform injection along the gas well, even as the water well continues to inject nearly uniformly along its length. In our results, the uniformity of gas injection increases with increasing total injection rate and decreasing vertical distance between gas- and water-injection wells. The instability leading to nonuniform injection depends on the relation between gas saturation and gas relative permeability; we speculate that effects of gas flow on hydrostatic pressure, and therefore on gas-injection pressure, may also play a role. We find that in some cases, lateral movement of gas from the injection point partially mitigates the effects of nonuniform gas injection. Injecting gas from separate, independent segments along the horizontal well improves sweep somewhat by increasing the number of points at which gas exits the well.

Numerical study of homogeneous bubbly flow: Influence of the inlet conditions to the hydrodynamic behavior

This paper discusses the role of the gas injection pattern on the large scale structures in a homogeneous pseudo-2D bubble column operated at relatively high gas hold-ups up to 8%. Seven cases with different inlet configuration have been studied experimentally by Harteveld et al. Each of these cases has been simulated using a (parallel) Euler–Lagrange model developed by Darmana et al. The presence of coherent structures for both uniform and non-uniform gas injection is studied. Furthermore, the influence of the gas injection pattern on the dynamics is investigated, while the statistical (average and fluctuating) quantities are compared with the PIV/PTV and LDA measurement data of Harteveld et al. The results show that the model resembles the observed experimental flow structures to a large extent.

Physical Model of Field Enhancement and Edge Effects of FinFET Charge-Trapping NAND Flash Devices

The physical model for field enhancement (FE) and the edge effects of body-tied FinFET charge-trapping NAND Flash devices are extensively studied in this paper. First, analytical equations are derived to provide insight to the FE effect for FinFET devices, and these analytical results are validated by 3-D TCAD simulation and experimental verification. Next, complicated programming and erasing characteristics and transconductance and subthreshold slope (gm/SS) behaviors are completely explained by the nonuniform injection behavior along various corner edges in FinFET. FE allows high program and erase speed and larger memory window. On the other hand, the edge effect complicates the device DC I-V, as well as programming and erasing characteristics, and these must be taken into account in memory circuit design.

Influence of double slot suction (injection) into water boundary layer flows over sphere

The objective of this work is to study the effect of non-uniform double slot suction (injection) into steady laminar water boundary layers over a sphere with variable viscosity and Prandtl number. The implicit finite difference scheme with quasi-linearization technique has been applied to find the non-similar solutions and also to overcome the difficulties arising at the starting point of the stream-wise coordinate, at the edges of the slot and at the point of separation. Results indicate that the separation can be delayed by non-uniform double slot suction and also by moving the slots downstream direction but the effect of non-uniform double slot injection is just the opposite.

Role of non-uniform slot injection (suction) model on the separation of a laminar boundary layer flow

An analysis is performed to study the influence of non-uniform slot injection (suction) on a steady incompressible laminar boundary layer flow in a diverging channel with an exponentially decreasing free-stream velocity. The difficulties in obtaining the non-similar solutions at the starting point of the streamwise coordinate, at the edges of the slot and at the point of separation are overcome by applying an implicit finite difference scheme with the quasi-linearization technique and an appropriate selection of the finer step sizes along the streamwise direction. It is observed that the separation can be delayed by non-uniform slot suction and also by moving the slot downstream but the effect of non-uniform slot injection is just reverse.

Quantum-enhanced uniformity of carrier injection into successive quantum wells of multi-quantum-well structures

In multiple quantum well (MQW) structures carrier injection into distant quantum wells (QWs) described in a semi-classical way seems to be less effective than to closer ones. This may considerably affect performance of such MQW devices. Therefore, in the present paper a quantum-mechanical phenomenon, which may play a significant role in making the distribution of particles confined in a multi-well potential uniform, is presented. The time needed to distribute uniformly the particle is compared with the radiative lifetime in typical MQW lasers. Obtained results suggest that the described quantum-enhanced effect is in many cases effective enough to neglect originally non-uniform carrier injection into successive QWs of such a structure. It makes theoretical analysis of recombination phenomena in standard MQW diode lasers considerably easier.

Magnetic vortex driven by non-uniform injection of spin-polarized current in nano-scale spin valves

We demonstrate that a current pulse of a non-uniform spin-polarized current density in a nanomagnet can drive, apart from magnetization reversal a static magnetic vortex. This vortex configuration can be achieved in low shape anisotropy spin valves of elliptical cross-sectional area. These non-uniform configurations exist also in presence of either ion mill damages below the nano-aperture or thermal effects at low temperature. We performed a numerical experiment of spin-torque driven ferromagnetic resonance in a magnetic vortex configuration, our results predict a frequency response with a few maxima and minima related to small oscillation of the vortex state around its equilibrium configuration.

Non-uniform double slot suction (injection) into water boundary layer flows over a cylinder

An analysis is performed to study the effect of non-uniform double slot suction (injection) into a steady two-dimensional laminar boundary layer flow when fluid properties such as viscosity and Prandtl number are inverse linear functions of temperature. Non-similar solutions have been obtained from the starting point of the streamwise co-ordinate to the exact point of separation. By applying an implicit finite difference scheme in combination with the quasi-linearization technique and an appropriate selection of the finer step sizes along the streamwise direction, the difficulties arising at the starting point of the streamwise co-ordinate, at the edges of the slot and at the point of separation have been overcome. The results indicate that the separation can be delayed by non-uniform double slot suction and also by moving the slot downstream. However, the effect of non-uniform double slot injection is just the opposite.

Hot carrier effects in n-MOSFETs with SiO 2/HfO 2/HfSiO gate stack and TaN metal gate

Charge trapping and trap generation in field-effect transistors with SiO 2/HfO 2/HfSiO gate stack and TaN metal gate electrode are investigated under uniform and non-uniform charge injection along the channel. Compared to constant voltage stress (CVS), hot carrier stress (HCS) exhibits more severe degradation in transconductance and subthreshold swing. By applying a detrapping bias, it is demonstrated that charge trapping induced degradation is reversible during CVS, while the damage is permanent for hot carrier injection case.

Impact of Lateral Nonuniform Doping and Hot Carrier Injection on Capacitance Behavior of High Voltage MOSFETs

A detailed analysis of capacitance behavior of high-voltage MOSFET (HV-MOS), for example, LDMOS, using device simulation is made. The impact of lateral nonuniform doping and drift region are separately analyzed. It is shown that the peaks in CGD and CGS capacitances of HV-MOS originate from lateral nonuniform doping. The peak value of CDG capacitance can be higher than WLCox for nonzero drain biases. The drift region decreases the CGD capacitance and increases the peaks in CGS in strong inversion and also gives rise to peaks in CGG capacitances increasing with higher drain bias. It is also shown that trapped charge due to hot carrier injection modulates the peaks' amplitude and position in capacitances depending on hot hole or electron injection at drain or source side. This capacitance analysis will facilitate in optimization of the HV-MOS structure and also help in modeling of HV-MOS, including the hot carrier degradation.

Estimation of laboratory-scale dispersivities using an annulus-and-core device

This paper investigates the use of two-dimensional radial column experiments to estimate longitudinal, and transverse dispersivity at the laboratory scale. The experimental device is an device: it is based on a classical column system, of which the inlet reservoir is divided into three independent concentric zones, allowing non-uniform tracer injection. The outlet reservoir is similarly adapted, so that information on the radial distribution of concentration becomes available through mean effluent concentration measurements in each annular zone. In this study, we only investigated continuous tracer injections through the central inlet zone. An analytical solution to a similar problem was available in the literature, and was adapted to compute effluent concentrations. The influence of the simplified boundary conditions of the solution was assessed by means of a numerical model. A general methodology is suggested to obtain transport parameters from breakthrough curve analysis, involving (i) the determination of effective porosity and longitudinal dispersivity from the full averaged breakthrough curve using classical one-dimensional tools and (ii) the determination of transverse dispersivity from the breakthrough curves recorded in the annular zones. Preliminary experiments were performed on a glass bead porous medium, on a gravel sand and on a natural medium sand. It is found that the rapidity of the test, its low cost, and the ability to simultaneously estimate three transport parameters comes at the price of potentially larger experimental errors. Transverse dispersivities were found to be higher than values previously reported in the literature, probably as a result of plume meandering, which cannot be detected nor corrected when using annulus-and-core devices. (C) 2008 Elsevier B.V. All rights reserved.

Bandgap dependence of current crowding effect in 3–5 µm InAsSb/InAs planar light emitting devices

Electroluminescence power profiles and 2D micropatterns have been obtained from InAsSb/InAs planar LEDs tuned at several wavelengths within the 3–5 µm band. Light confined to a small region around the top opaque contact was observed (cw mode, I > 10 mA, T = 300 K). A computer simulation showed that the reason behind the decrease of the emitting area is the current crowding that ensures non-uniform injection into the active region. The effect becomes more apparent in longer wavelength devices (emitting areas of 3.4 and 4.2 µm emitting devices are related as >10:1), providing direct evidence that the current crowding is affected by the bandgap energy of an active layer.

Multiple slot suction/injection into an exponentially decreasing free stream flow

An analysis is performed to obtain the non-similar solution of a steady incompressible laminar boundary layer flow for an exponentially decreasing free stream velocity with non-uniform multiple slot injection (suction). The difficulties in obtaining the non-similar solutions at the starting point of the stream-wise coordinate, at the edges of the slot and at the point of separation are overcome by applying an implicit finite difference scheme in combination with the quasi-linearization technique and an appropriate selection of the finer step sizes along the stream-wise direction. Results are presented for ϵ=0.001 and for different values of mass transfer parameter, − 0.075≤A≤1.0. It is observed that the separation can be delayed by non-uniform multiple slot suction and also by moving the slots downstream but the effect of non-uniform multiple slot injection is just reverse.

Micromagnetic Modeling of Magnetization Reversal in Nano-Scale Point Contact Devices

This paper deals with micromagnetic model of magnetization reversal in nano scale-point contact devices driven by nonuniform injection of a spin-polarized current. A computational study of the magnetization reversal in the nanosecond regime will be presented considering the influence of the current density distribution below the aperture region on the reversal time. For high current values, a strong dependence of the reversal time on the current distribution has been observed. Finally, results of micromagnetic simulations show that the reversal time versus current behaviour (at T=0K) is monotonic, very different from the switching processes observed in standard spin valves and magnetic tunnel junctions with uniform current injection.

Non-uniform double slot injection (suction) on a forced flow over a slender cylinder

A general analysis has been developed to investigate the influence of non-uniform double slot injection (suction) on the steady non-similar incompressible laminar boundary layer flow over a slender cylinder, where the slender cylinder is inline with the flow. Non-similar solutions are obtained starting from the origin of the stream-wise coordinate along the stream-wise direction by using an implicit finite difference scheme in combination with the quasilinearization technique. Numerical results are reported to display the effects of non-uniform double slot injection/suction on skin friction coefficient and heat transfer rate at the wall. Further, the effects of viscous dissipation and Prandtl number on velocity and temperature profile, and skin friction and heat transfer co-efficients are also presented in this paper.