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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The formation and structure of plasma wakes behind large high-voltage space platforms in ionosphere

Theory and particle simulation results are presented for ionospheric plasma flow over space platforms in the large-dimension and high-voltage range. Both the transient formation of the space-charge wake and its steady state structure are studied. The wake-side ion impact and current collection are obtained. It is found that the wake behind a high-voltage plate is characterized by two ion-rich sheaths embedded in a quasi-neutral background wake. The embedded sheath is formed by the ions passing through the sheath around the plate edge and serves as their trajectory path. Depending on the surface potential, the plate dimension, and the angle of attack, the embedded sheath may either extend downstream or curve back to the plate causing a high, localized ion flux density at the location it strikes.

Wang, J.↗
NASA NTRS1992

Ionospheric plasma flow over large high-voltage space platforms. I - Ion-plasma-time scale interactions of a plate at zero angle of attack. II - The formation and structure of plasma wake

The paper presents the theory and particle simulation results for the ionospheric plasma flow over a large high-voltage space platform at a zero angle of attack and at a large angle of attack. Emphasis is placed on the structures in the large, high-voltage regime and the transient plasma response on the ion-plasma time scale. Special consideration is given to the transient formation of the space-charge wake and its steady-state structure.

Wang, J.↗
NASA NTRS1993

Voltage-To-Frequency Converter For Pressure Calibration

Measurements of pressures on walls of wind tunnels and on surfaces of models in wind tunnels made with help of electronically scanned pressure-measurement (ESP) system. Voltage-to-frequency converter circuit, designed to convert 0- to 5-Vdc analog output voltage from high-line-pressure, low-differential-pressure standard to required frequency range. Enables selection of wider variety of high-accuracy pressure standards to enhance accuracy of measurement of ESP instrumentation while requiring little modification of manufacturer's system and no modification of operating software of system. Useful primarily in wind-tunnel instrumentation and readily adaptable to commercial instruments currently in use.

Sealey, Bradley S.↗
NASA NTRS1992

Modelling a single phase voltage controlled rectifier using Laplace transforms

The development of a 20 kHz, AC power system by NASA for large space projects has spurred a need to develop models for the equipment which will be used on these single phase systems. To date, models for the AC source (i.e., inverters) have been developed. It is the intent of this paper to develop a method to model the single phase voltage controlled rectifiers which will be attached to the AC power grid as an interface for connected loads. A modified version of EPRI's HARMFLO program is used as the shell for these models. The results obtained from the model developed in this paper are quite adequate for the analysis of problems such as voltage resonance. The unique technique presented in this paper uses the Laplace transforms to determine the harmonic content of the load current of the rectifier rather than a curve fitting technique. Laplace transforms yield the coefficient of the differential equations which model the line current to the rectifier directly.

Kraft, L. Alan↗
NASA NTRS1992

Changes in impedance of Ni/Cd cells with voltage and cycle life

Impedances of aerospace design Super Ni/Cd cells are being measured as functions of voltage and number of cycles. The cells have been cycled over 4400 cycles to date. Analysis of the impedance data has been made using a number of equivalent circuits. The model giving the best fit over the whole range of voltage has a parallel circuit of a kinetic resistance and a constant phase element in series with the ohmic resistance. The values for the circuit elements have been treated as empirical parameters, and no attempt has been made as yet to correlate them with physical and chemical changes in the electrode. No significant changes have been seen as yet with the exception of a decrease in kinetic resistance at low states of charge in the first 500 cycles.

Reid, Margaret A.↗
NASA NTRS1993

High voltage spacecraft electrical systems design

Factors which must be considered when designing the best and the most cost-effective high-voltage electrical system for a spacecraft are discussed with particular attention given to the EMC considerations, high-voltage power bus, and harnesses. It is emphasized that the use of serial data buses and lines greatly simplify the harness design and weight. Careful attention to the grounding concept and the EMC requirements is necessary for insuring a 'quiet' spacecraft.

Stone, R. E.↗
NASA NTRS1992

Arcing rates for High Voltage Solar Arrays - Theory, experiment, and predictions

All solar arrays have biased surfaces that can be exposed to the space environment. It has been observed that when the array bias is less than a few hundred volts negative, then the exposed conductive surfaces may undergo arcing in the space plasma. A theory for arcing is developed on these high voltage solar arrays that ascribes the arcing to electric field runaway at the interface of the plasma, conductor, and solar cell dielectric. Experiments were conducted in the laboratory for the High Voltage Solar Array experiment that will fly on the Japanese Space Flyer Unit (SFU) in 1994. The theory was compared in detail with the experiment and shown to give a reasonable explanation for the data. The combined theory and ground experiments were then used to develop predictions for the SFU flight.

Hastings, Daniel E.↗
NASA NTRS1992

Noise and current-voltage characterization of complementary heterojunction field-effect transistor (CHFET) structures below 8 K

Noise and current-voltage characterization of complementary heterojunction field-effect transistor (CHFET) structures below 8 K are presented. It is shown that the CHFET exhibits normal transistor operation down to 6 K. Some of the details of the transistor operation, such as the gate-voltage dependence of the channel potential, are analyzed. The gate current is examined and is shown to be due to several mechanisms acting in parallel. These include field-emission and thermionic-field-emission, conduction through a temperature-activated resistance, and thermionic emission. The input referred noise for n-channel CHFETs is presented and discussed. The noise has the spectral dependence of 1/f noise, but does not exhibit the usual area dependence.

Cunningham, Thomas J.↗
NASA NTRS1994

Low-Voltage Bypass Device

Improved bypass device provides low-resistance current shunt around low-voltage power cell when cell fails in open-circuit condition during operation. In comparison with older bypass devices for same application, this one weighs less, generates less heat, and has lower voltage drop (less resistance). Bypass device connected in parallel with power cell. Draws very little current during normal operation of cell.

Wilson, J. P.↗
NASA NTRS1994

Reducing Ripple In A Switching Voltage Regulator

Ripple voltage in output of switching voltage regulator reduced substantially by simple additional circuitry adding little to overall weight and size of regulator. Heretofore, additional filtering circuitry needed to obtain comparable reductions in ripple typically as large and heavy as original regulator. Current opposing ripple current injected into filter capacitor.

Paulkovich, John↗
NASA NTRS1993

Automatic calibration of inductive voltage dividers for the NASA Zeno experiment

Two inductive voltage dividers (IVDs) used for temperature measurements in NASA's Zeno experiment were tested. In order to obtain the required resolution of 10 parts per billion, a 30-bit binary inductive voltage divider developed at the National Institute of Standards and Technology was used to measure the differential linearity of the Zeno IVDs. Automatic measurements were performed on the dividers in the Zeno engineering model at frequencies of 266 and 351 Hz over a ratio range of 0.55-0.56. The measured differential linearity limits the temperature resolution to 5/micro-K.

Avramov, Svetlana↗
NASA NTRS1997

Flight Demonstration of a Shock Location Sensor Using Constant Voltage Hot-Film Anemometry

Flight tests have demonstrated the effectiveness of an array of hot-film sensors using constant voltage anemometry to determine shock position on a wing or aircraft surface at transonic speeds. Flights were conducted at the NASA Dryden Flight Research Center using the F-15B aircraft and Flight Test Fixture (FTF). A modified NACA 0021 airfoil was attached to the side of the FTF, and its upper surface was instrumented to correlate shock position with pressure and hot-film sensors. In the vicinity of the shock-induced pressure rise, test results consistently showed the presence of a minimum voltage in the hot-film anemometer outputs. Comparing these results with previous investigations indicate that hot-film anemometry can identify the location of the shock-induced boundary layer separation. The flow separation occurred slightly forward of the shock- induced pressure rise for a laminar boundary layer and slightly aft of the start of the pressure rise when the boundary layer was tripped near the airfoil leading edge. Both minimum mean output and phase reversal analyses were used to identify the shock location.

Moes, Timothy R.↗
NASA NTRS1996

Computation of Static Shapes and Voltages for Micromachined Deformable Mirrors with Nonlinear Electrostatic Actuators

In modeling micromachined deformable mirrors with electrostatic actuators whose gap spacings are of the same order of magnitude as those of the surface deformations, it is necessary to use nonlinear models for the actuators. In this paper, we consider micromachined deformable mirrors modeled by a membrane or plate equation with nonlinear electrostatic actuator characteristics. Numerical methods for computing the mirror deformation due to given actuator voltages and the actuator voltages required for producing the desired deformations at the actuator locations are presented. The application of the proposed methods to circular deformable mirrors whose surfaces are modeled by elastic membranes is discussed in detail. Numerical results are obtained for a typical circular micromachined mirror with electrostatic actuators.

Wang, P. K. C.↗
NASA NTRS2000

Influence of the Polysilicon Gate on the Random Dopant Induced Threshold Voltage Fluctuations in Sub 100 nm MOSFETS with Thin Gate Oxides

In this paper for the first time we study the influence of the polysilicon gate on the random dopant induced threshold voltage fluctuations in sub 100 nm MOSFETs with tunnelling gate oxides. This is done by using an efficient 3D 'atomistic' simulation technique described elsewhere. Devices with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveale that the polysilicon gate is responsible for a substantial fraction of the threshold voltage fluctuations in both devices when the gate oxide is scaled to tunnelling thickness in the range of 1 - 2 nm.

Asenov, Asen↗
NASA NTRS1999

Random Dopant Induced Threshold Voltage Lowering and Fluctuations in Sub 50 nm MOSFETs: a Statistical 3D 'Atomistic' Simulation Study

A 3D 'atomistic' simulation study of random dopant induced threshold voltage fluctuations and lowering in sub 50 nm MOSFETs is presented. The attention is focused mainly on devices with 30 nm effective channel length which represent the expected level of scaling at the end of the Silicon Roadmap. An efficient algorithm, based on a single 3D ap solution of the Poisson equation and a simplified current continuity equation, is used in the simulations. Large samples of microscopically different devices (typically 200) arc used in order to obtain statistically reliable results. The influence of different aspects of the conventional MOSFET design on the threshold voltage fluctuations and lowering are investigated. Results for fluctuation resistant device architectures based on low-doped epitaxial channel MOSFETs are also presented.

Asenov, Asen↗
NASA NTRS2000

SNW 2000 Proceedings. Oxide Thickness Variation Induced Threshold Voltage Fluctuations in Decanano MOSFETs: a 3D Density Gradient Simulation Study

We use the density gradient (DG) simulation approach to study, in 3D, the effect of local oxide thickness fluctuations on the threshold voltage of decanano MOSFETs in a statistical manner. A description of the reconstruction procedure for the random 2D surfaces representing the 'atomistic' Si-SiO2 interface variations is presented. The procedure is based on power spectrum synthesis in the Fourier domain and can include either Gaussian or exponential spectra. The simulations show that threshold voltage variations induced by oxide thickness fluctuation become significant when the gate length of the devices become comparable to the correlation length of the fluctuations. The extent of quantum corrections in the simulations with respect to the classical case and the dependence of threshold variations on the oxide thickness are examined.

Asenov, Asen↗
NASA NTRS1999

Quantum Mechanical Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations and Lowering in Sub 0.1 Micron MOSFETs

A detailed study of the influence of quantum effects in the inversion layer on the random dopant induced threshold voltage fluctuations and lowering in sub 0.1 micron MOSFETs has been performed. This has been achieved using a full 3D implementation of the density gradient (DG) formalism incorporated in our previously published 3D 'atomistic' simulation approach. This results in a consistent, fully 3D, quantum mechanical picture which implies not only the vertical inversion layer quantisation but also the lateral confinement effects manifested by current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical fluctuations, is an increase in both threshold voltage fluctuations and lowering.

Asenov, Asen↗