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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 865 records · Page 48

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Hybrid power semiconductor

The voltage rating of a bipolar transistor may be greatly extended while at the same time reducing its switching time by operating it in conjunction with FETs in a hybrid circuit. One FET is used to drive the bipolar transistor while the other FET is connected in series with the transistor and an inductive load. Both FETs are turned on or off by a single drive signal of load power, the second FET upon ceasing conductions, rendering one power electrode of the bipolar transistor open. Means are provided to dissipate currents which flow after the bipolar transistor is rendered nonconducting.

Chen, D. Y.↗

NASA NTRS1988

Knowledge-based operation and management of communications systems

Expert systems techniques are being applied in operation and control of the Defense Communications System (DCS), which has the mission of providing reliable worldwide voice, data and message services for U.S. forces and commands. Thousands of personnel operate DCS facilities, and many of their functions match the classical expert system scenario: complex, skill-intensive environments with a full spectrum of problems in training and retention, cost containment, modernization, and so on. Two of these functions are: (1) fault isolation and restoral of dedicated circuits at Tech Control Centers, and (2) network management for the Defense Switched Network (the modernized dial-up voice system currently replacing AUTOVON). An expert system for the first of these is deployed for evaluation purposes at Andrews Air Force Base, and plans are being made for procurement of operational systems. In the second area, knowledge obtained with a sophisticated simulator is being embedded in an expert system. The background, design and status of both projects are described.

Heggestad, Harold M.↗

NASA NTRS1989

The 5-kW arcjet power electronics

The initial design and evaluation of a 5 kW arcjet power electronics breadboard which as been integrated with a modified 1 kW design laboratory arcjet is presented. A single stage, 5 kW full bridge, pulse width modulated (PWM), power converter was developed which was phase shift regulated. The converter used metal oxide semiconductor field effect transistor (MOSFET) power switches and incorporated current mode control and an integral arcjet pulse ignition circuit. The unoptimized power efficiency was 93.5 and 93.9 percent at 5 kW and 50A output at input voltages of 130 and 150V, respectively. Line and load current regulation at 50A output was within one percent. The converter provided up to 6.6 kW to the arcjet with simulated ammonia used as a propellant.

Gruber, R. P.↗

NASA NTRS1989

5-kW arcjet power electronics

Gruber, R. P.↗

NASA NTRS1990

Optical interconnections and networks; Proceedings of the Meeting, The Hague, Netherlands, Mar. 14, 15, 1990

The conference presents papers on interconnections, clock distribution, neural networks, and components and materials. Particular attention is given to a comparison of optical and electrical data interconnections at the board and backplane levels, a wafer-level optical interconnection network layout, an analysis and simulation of photonic switch networks, and the integration of picosecond GaAs photoconductive devices with silicon circuits for optical clocking and interconnects. Consideration is also given to the optical implementation of neural networks, invariance in an optoelectronic implementation of neural networks, and the recording of reversible patterns in polymer lightguides.

Bartelt, Hartmut↗

NASA NTRS1994

Standardized laser initiated ordnance

Launch vehicles and spacecraft use explosively initiated devices to effect numerous events from lift-off to orbit. These explosive devices are electrically initiated by way of electro-mechanical switching networks. Today's technology indicates that upgrading to solid state control circuits and laser initiated explosive devices can improve performance, streamline operations and reduce costs. This paper describes a plan to show that these technology advancements are viable for Air Force Space and Missile System Center (SMC) program use, as well as others.

Gageby, James V.↗

NASA NTRS2003

Evolutionary Technique for Automated Synthesis of Electronic Circuits

A method for evolving a circuit comprising configuring a plurality of transistors using a plurality of reconfigurable switches so that each of the plurality of transistors has a terminal coupled to a terminal of another of the plurality of transistors that is controllable by a single reconfigurable switch. The plurality of reconfigurable switches being controlled in response to a chromosome pattern. The plurality of reconfigurable switches may be controlled using an annealing function. As such, the plurality of reconfigurable switches may be controlled by selecting qualitative values for the plurality of reconfigurable switches in response to the chromosomal pattern, selecting initial quantitative values for the selected qualitative values, and morphing the initial quantitative values. Typically, subsequent quantitative values will be selected more divergent than the initial quantitative values. The morphing process may continue to partially or to completely polarize the quantitative values.

Stoica, Adrian↗

NASA NTRS2004

Broadband, Low-Loss Phase Shifters Based on Thin Ferroelectric Films

Several different types of microwave transmission line phase shifters based on thin ferroelectic films have been developed at the NASA Glenn Research Center. These include a series of coupled microstrip lines, slotline incorporating Marchand balms, odd-mode coplanar strips, and hybrid devices incorporating a switch to toggle the output termination between an open and virtual short circuit. A review of the theory of operation of each of these devices will be presented along with measured performance. Also, devices of the first variety have been subjected to total dose (proton) radiation exposure using a 200 MeV beam energy with a total dose up to nearly 1 kRad (Si). Results of these radiation tests will be discussed.

Romanofsky, Robert↗

NASA NTRS2007

Thin, nearly wireless adaptive optical device

A thin, nearly wireless adaptive optical device capable of dynamically modulating the shape of a mirror in real time to compensate for atmospheric distortions and/or variations along an optical material is provided. The device includes an optical layer, a substrate, at least one electronic circuit layer with nearly wireless architecture, an array of actuators, power electronic switches, a reactive force element, and a digital controller. Actuators are aligned so that each axis of expansion and contraction intersects both substrate and reactive force element. Electronics layer with nearly wireless architecture, power electronic switches, and digital controller are provided within a thin-film substrate. The size and weight of the adaptive optical device is solely dominated by the size of the actuator elements rather than by the power distribution system.

Knowles, Gareth↗

NASA NTRS2008

Thin, nearly wireless adaptive optical device

Knowles, Gareth↗

NASA NTRS2009

Thin nearly wireless adaptive optical device

A thin nearly wireless adaptive optical device capable of dynamically modulating the shape of a mirror in real time to compensate for atmospheric distortions and/or variations along an optical material is provided. The device includes an optical layer, a substrate, at least one electronic circuit layer with nearly wireless architecture, an array of actuators, power electronic switches, a reactive force element, and a digital controller. Actuators are aligned so that each axis of expansion and contraction intersects both substrate and reactive force element. Electronics layer with nearly wireless architecture, power electronic switches, and digital controller are provided within a thin-film substrate. The size and weight of the adaptive optical device is solely dominated by the size of the actuator elements rather than by the power distribution system.

Knowles, Gareth J.↗

DOE OSTI2014

Energy loss in spark gap switches

The paper reports on numerical study of the energy loss in spark gap switches. The operation of the switches is analyzed using the Braginsky model which allows calculation of the time dependence of the spark channel resistance. The Braginsky equation is solved simultaneously with generator circuit equations for different load types. Based on the numerical solutions, expressions which determine both the energy released in a spark gap switch and the switching time are derived.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Optimization of DARHT Axis 1 Injector Voltage

The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility provides flash radiography capabilities using two electron Linear Induction Accelerators (LIA’s). Axis-1 of DARHT produces a 20- MeV, 2-kA, 80-ns-FWHM electron beam. The strict requirements for flash radiography require a detailed understanding of the LIA’s performance, including precision measurements of the injector electron beam energy. The technique for time resolved measurement of the electron beam energy using electron Permanent Magnet Spectrometer (ePMSpec) has been developed. The electron energy then is used to infer the voltage produced by the injector pulsed power. The injector pulsed power of DARHT I consists of a 1.5-MV, glycol-insulated Blumlein that is pulsecharged by a step-up transformer and switched by four, laser-triggered spark gaps. A series of increasing impedance transmission lines are used to transform the output voltage of the Blumlein to a maximum of 3.8MV at the diode. Figure 1a shows a graphic of the Axis-1 prime power tank, Blumlein and downstream transmission lines. The injector pulse power is designed to produce voltage on a velvet cathode located in the vacuum vessel. The specifications of the voltage-pulse flat-top over 60ns is +/-1%. A key element in the high-voltage circuit is the ethylene glycol Blumlein. The outer volume, adjacent to the laser triggered switches of the Blumlein, is a peaking capacitor. This is an independent volume that contains a mixture of ethylene glycol and water to make it an adjustable capacitor of 380 to 750 pF.

43 PARTICLE ACCELERATORS↗

NASA NTRS1973

The application of standardized control and interface circuits to three dc to dc power converters.

Standardized control and interface circuits were applied to the three most commonly used dc to dc converters: the buck-boost converter, the series-switching buck regulator, and the pulse-modulated parallel inverter. The two-loop ASDTIC regulation control concept was implemented by using a common analog control signal processor and a novel digital control signal processor. This resulted in control circuit standardization and superior static and dynamic performance of the three dc-to-dc converters. Power components stress control, through active peak current limiting and recovery of switching losses, was applied to enhance reliability and converter efficiency.

Yu, Y.↗

DOE OSTI2017

Ultrafast Reverse Recovery Time Measurement for Wide-Bandgap Diodes

A system is presented that is capable of measuring sub-nanosecond reverse recovery times of diodes in wide-bandgap materials over a wide range of forward biases (0 – 1 A) and reverse voltages (0 – 10 kV). The system utilizes the step recovery technique and comprises a cable pulser based on a silicon (Si) Photoconductive Semiconductor Switch (PCSS) triggered with an Ultra Short Pulse Laser (USPL), a pulse charging circuit, a diode biasing circuit, and resistive and capacitive voltage monitors. The PCSS based cable pulser transmits a 130 ps rise time pulse down a transmission line to a capacitively coupled diode, which acts as the terminating element of the transmission line. The temporal nature of the pulse reflected by the diode provides the reverse recovery characteristics of the diode, measured with a high bandwidth capacitive probe integrated into the cable pulser. Furthermore, this system was used to measure the reverse recovery times (including the creation and charging of the depletion region) for two Avogy gallium nitride (GaN) diodes; the initial reverse recovery time was found to be 4 ns and varied minimally over reverse biases of 50 – 100 V and forward current of 1 – 100 mA.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2019

Realization of all-optical plasmonic MIM split square ring resonator switch

In this work, a configuration of nano plasmonic switch is proposed and investigated. The structure is comprised of the combination of split square ring and straight waveguides. Simulations are done based on Finite-Difference-Time Domain method. The structure is based on metal-insulator-metal configuration. Split square ring and straight waveguides are consisted of air, which are situated in a silver background. The proposed switch can confine light to sub-wavelength dimensions (on the order of nano meter); therefore it can be used in highly integrated optical circuits. The split square ring structure can operate both directly or reversely based on the split position. The transmitted powers in different cases of split square switch are acceptable and higher than 0.6. Therefore, the proposed switch is an appropriate candidate for highly integrated optical communication systems.

42 ENGINEERING↗

DOE OSTI2021

A High-Efficiency Isolated PFC AC-DC Topology with Reduced Number of Semiconductor Devices

A new three-level isolated ac-dc power factor correction (PFC) topology with a minimum number of semiconductor devices is the focus of this paper. This topology provides a high input power factor (PF), soft-switching, and higher efficiency than existing isolated ac-dc converters. Furthermore, the proposed circuit has lower voltage rating requirements for the secondary side devices, which leads to a lower total cost and minimizes total converter losses. This article presents a theoretical analysis describing the complete characterization of this new topology, and experimental results on a 1-kW prototype showing high PF and efficiency throughout the operating range.

42 ENGINEERING↗

NASA NTRS1996

Hybrid-Circuit Module For Dc-To-Dc Power Converter

Power hybrid module is general-purpose power-switching module providing flexibility in design and application. Complete dc-to-dc power converter constructed by adding input/output filters and feedback circuitry to module to suit specific application.

Vorperian, Vatche↗