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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Power and Efficiency Optimized in Traveling-Wave Tubes Over a Broad Frequency Bandwidth

A traveling-wave tube (TWT) is an electron beam device that is used to amplify electromagnetic communication waves at radio and microwave frequencies. TWT's are critical components in deep space probes, communication satellites, and high-power radar systems. Power conversion efficiency is of paramount importance for TWT's employed in deep space probes and communication satellites. A previous effort was very successful in increasing efficiency and power at a single frequency (ref. 1). Such an algorithm is sufficient for narrow bandwidth designs, but for optimal designs in applications that require high radiofrequency power over a wide bandwidth, such as high-density communications or high-resolution radar, the variation of the circuit response with respect to frequency must be considered. This work at the NASA Glenn Research Center is the first to develop techniques for optimizing TWT efficiency and output power over a broad frequency bandwidth (ref. 2). The techniques are based on simulated annealing, which has the advantage over conventional optimization techniques in that it enables the best possible solution to be obtained (ref. 3). Two new broadband simulated annealing algorithms were developed that optimize (1) minimum saturated power efficiency over a frequency bandwidth and (2) simultaneous bandwidth and minimum power efficiency over the frequency band with constant input power. The algorithms were incorporated into the NASA coupled-cavity TWT computer model (ref. 4) and used to design optimal phase velocity tapers using the 59- to 64-GHz Hughes 961HA coupled-cavity TWT as a baseline model. In comparison to the baseline design, the computational results of the first broad-band design algorithm show an improvement of 73.9 percent in minimum saturated efficiency (see the top graph). The second broadband design algorithm (see the bottom graph) improves minimum radiofrequency efficiency with constant input power drive by a factor of 2.7 at the high band edge (64 GHz) and increases simultaneous bandwidth by 500 MHz.

Wilson, Jeffrey D.↗
DOE OSTI2020

High-Bandwidth Low-Inductance Current Shunt for Wide-Bandgap Devices Dynamic Characterization

High bandwidth sensors are required to measure the wide-bandgap devices' transient behavior because of their fast switching speed. In addition to high bandwidth, the current sensor must introduce little extra parasitic inductance to the switching power loop. The analysis of conventional shunt resistors shows the key to high bandwidth is the coaxial structure and its parasitic inductance is proportional to its transient heat energy rating. Additionally, by combining the structure of coaxial shunt resistor and alumina substrate surface mount thin film resistors, a novel surface mount coaxial shunt resistor is introduced. Experimental measurement verifies its capability of achieving very high bandwidth while introducing very low parasitic inductance. The design can achieve up to 2.23-GHz measurement bandwidth while keeping its parasitic inductance as low as 0.12 nH. Application in gallium nitride heterojunction-field-effect-transistors double pulse test shows it can faithfully capture the transient current waveform while introducing little interference to the switching behavior.

42 ENGINEERING↗
NASA NTRS1982

Propagation of wide bandwidth signals through strongly turbulent ionized media

Analytic and numerical techniques are presented which directly address the problem of propagation of wide bandwidth signals through random ionized media. This work is applicable to the problems of satellite communication and space based radar observation through a disturbed ionospheric propagation channel that would result from a high altitude chemical release or nuclear detonation. An analytic solution is presented for the two-position, two-frequency mutual coherence function for spherical wave propagation in the strong scattering limit. This solution is used to derive simple expressions for the power impulse response function and to determine its relationship to the important parameters of decorrelation distance and coherence bandwidth which describe the disturbed propagation channel. Results for mean time delay and time delay jitter are presented and compared to direct simulation results and to other theoretical calculations. A numerical/analytical solution to the parabolic wave equation is presented in the form of a multiple phase-screen (MPS) propagation simulation. In this very general solution technique, the random medium is divided into a finite number of layers. The field fluctuation through each layer is obtained by replacing the layer by a centrally located thin phase-screen, whose statistical properties are determined from the statistics of the electron-density irregularities. The waveform then propagates from phase-screen to phase-screen via an exact solution to the Fresnel-Kirchnoff equation. For wide bandwidth waveforms, numerical solutions are obtained at a number of discrete frequencies centered about the carrier and then time-domain solutions are obtained by Fourier transform techniques. Detailed results are presented for a number of interesting cases including propagation of a 20 MHz bandwidth signal through a finite barium cloud at a carrier frequency of 100 MHz. One of the major uses of the MPS propagation simulation has been to provide realizations of the received signal after propagation through a disturbed channel. The MPS simulation obtains a general solution of the parabolic wave equation under both weak and strong scattering conditions. A second technique to directly obtain realizations of wide bandwidth waveforms is presented here. This technique is limited to the case of strong scattering but requires only a fraction of the computer resources needed for MPS signal generation. Detailed comparisons of the two signal generation techniques are presented.

Random Media↗
DOE OSTI2017

Bandwidth Study on Energy Use and Potential Energy Savings Opportunities in U.S. Seawater Desalination Systems

Energy bandwidth studies can serve as foundational references in framing the range (or bandwidth) of potential energy savings opportunities in U.S. industrial sectors. This bandwidth study examines energy consumption and potential energy savings opportunities in U.S. seawater desalination plants. The study relies on multiple sources to estimate the energy used for five seawater desalination unit operations. Energy savings opportunities for the unit operations are based on technologies currently in use or under development. This study also examines the energy consumption implications of wider adoption of seawater desalination to meet increased U.S. municipal water demand for two scenarios based on the bandwidth analysis. This report builds upon the foundational information and analysis approach described in Volume 1: Survey of Available Information in Support of the Energy-Water Bandwidth Study of Desalination Systems.

energy energy bandwidth study, desalination, desal↗
DOE OSTI2018

An evaluation of low-cost heuristics for matrix bandwidth and profile reductions

Hundreds of heuristics have been proposed to resolve the problems of bandwidth and profile reductions since the 1960s. We found 132 heuristics that have been applied to these problems in reviews of the literature. Among them, 14 were selected for which no other simulation or comparison revealed that the heuristic could be superseded by any other algorithm in the analyzed articles with respect to bandwidth or profile reduction. We also considered the computational costs of the heuristics during this process. Therefore, these 14 heuristics were selected as potentially being the best low-cost methods to solve the bandwidth and/or profile reduction problems. Results of the 14 selected heuristics are evaluated in this work. For evaluation on the set of test problems, a metric based on the relative percentage distance to the best possible bandwidth or profile is proposed. The most promising heuristics for several application areas are identified. Moreover, it was found that the FNCHC and GPS heuristics showed the best overall results in reducing the bandwidth of symmetric and asymmetric matrices among the evaluated heuristics, respectively. In addition, the NSloan and MPG heuristics showed the best overall results in reducing the profile of symmetric and asymmetric matrices among the heuristics among the evaluated heuristics, respectively.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Engineering the gain-bandwidth product of phototransistor diodes

In recent years, phototransistors have considerably expanded their field of application, including for instance heterodyne detection and optical interconnects. Unlike in low-light imaging, some of these applications require fast photodetectors that can operate in relatively high light levels. Since the gain and bandwidth of phototransistors are not constant across different optical powers, the devices that have been optimized for operation in low light level cannot effectively be employed in different technological applications. We present an extensive study of the gain and bandwidth of short-wavelength infrared phototransistors as a function of optical power level for three device architectures that we designed and fabricated. The gain of the photodetectors is found to increase with increasing carrier injection. Based on a Shockley-Read-Hall recombination model, we show that this is due to the saturation of recombination centers in the phototransistor base layer. Eventually, at a higher light level, the gain drops, due to the Kirk effect. As a result of these opposing mechanisms, the gain-bandwidth product is peaked at a given power level, which depends on the device design and material parameters, such as doping and defect density. Guided by this physical understanding, we design and demonstrate a phototransistor which is capable of reaching a high gain-bandwidth product for high-speed applications. The proposed design criteria can be employed in conjunction with the engineering of the device size to achieve a wide tunability of the gain and bandwidth, hence paving the way toward fast photodetectors for applications with different light levels.

Bianconi, Simone (ORCID:0000000238286513)↗
DOE OSTI2019

A high bandwidth microelectromechanical system-based nanopositioner for scanning tunneling microscopy

Limited Z-axis bandwidth of piezotube scanners used in conventional Scanning Tunneling Microscopes (STMs) has been a major limiting factor in achieving high scan speeds in STM applications. Slow Z-axis dynamics of typical piezotube scanners combined with the weight of the STM tip/tip holder assembly, that the scanner has to carry, substantially limit the achievable Z-axis bandwidth in both imaging and lithography modes. To tackle this issue, we introduce a high bandwidth microelectromechanical-system-based nanopositioner to be integrated into an existing STM scanner. The device is designed to replace the STM tip and fine Z-positioning mechanisms in the conventional STM setup, while providing an order of magnitude higher bandwidth in Z axis. The device is microfabricated using double silicon-on-isolator technology, and standard cleanroom processes. Experiments show that tunneling current between the device tip and a highly ordered pyrolytic graphite sample can be successfully established and maintained in air using the proposed device in a feedback loop. Results suggest that the proposed device uniquely combines a very high resolution and a large stroke with a substantially larger Z-axis bandwidth compared to that of conventional STM piezotube scanners, enabling higher scanning speeds in STM operations.

42 ENGINEERING↗
DOE OSTI2021

Ultranarrow bandwidth pulses from a regeneratively mode-locked fiber laser

We report on the generation of transform-limited nanosecond pulse with an ultranarrow bandwidth from a regeneratively mode-locked erbium-doped fiber laser. A narrow bandwidth fiber Bragg grating is combined with a bulk amplitude electro-optic modulator to shape pulse evolution inside a ring cavity, and regenerative mode locking is applied to produce a stationary shape of pulses in the nanosecond regime (2.05 ns in duration). Spectral characterization via high bandwidth optoelectronic devices shows that optical pulses have an ultranarrow bandwidth of 220 MHz. Numerical simulation reveals that the shape of the narrow spectral filter has a strong effect on the duration and bandwidth of output pulses.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Impact of increased smoothing by spectral dispersion bandwidth on stimulated Brillouin scattering in laser driven Hohlraums

Experiments were conducted at the National Ignition Facility (NIF) to investigate the impact of increased smoothing by spectral dispersion (SSD) bandwidth on the production of stimulated Brillouin scattering (SBS) within an indirect-drive inertial confinement fusion (ICF) Hohlraum. This was done in a subscale gold Hohlraum driven by 192 laser beams depositing 1.1 MJ of energy. The laser bandwidth was increased from 45 to 118 GHz (before frequency tripling) on the 30° and 50° cones, where backscatter could be measured using the Full Aperture Backscatter Station (FABS). It was expected that this 2.6-fold increase in bandwidth would suppress SBS generated within the Hohlraum plasma and lower the backscattered SBS energy on the 50° cones by over a factor of four. Experimental results, however, show that this SSD change only reduced the 50° cone SBS during the main capsule drive by -18±31% and -4.5±7.8% over the entire pulse. This is small compared to expected shot-to-shot SBS reproducibility (∼30%), such that the result can be considered within normal performance fluctuations. New 3D parallel paraxial code (pF3D) simulations, accounting for beam refractive intensification reproduce this result, suggesting that closer to 300 GHz of bandwidth would have been required to mitigate SBS to the expected level. Delivering such a high bandwidth is not feasible at NIF when operating at high peak power and would potentially prevent NIF’s ability to use cross-beam energy transfer (CBET) for implosion symmetry tuning.

Physics↗
DOE OSTI2019

Minimum Spectral Bandwidth in Echo Seeded Free Electron Lasers

This paper examines the impact of non-linear longitudinal phase distortions on the spectral bandwidth in echo seeded free electron lasers (FELs). It extends the existing theory developed in Hemsing for echo-enabled harmonic generation (EEHG) to include finite laser pulse durations. An analytic expression for the shape of the optimized longitudinal bunching envelope is derived, and is used to determine the laser and electron beam pulse durations that minimize the seeded bandwidth in the presence of arbitrary phase distortions. The time-bandwidth product (TBP) is also derived, and is shown that the TBP and the bandwidth increase by no more than 2–√ from their transform-limited values when the bandwidth is minimized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1991

The effect of bandwidth on telerobot system performance

The purpose of the experiment was to determine the effect that various slave-joint bandwidths have on telerobot system performance. The telerobot system consisted of a slave arm controlled by a master. The slave incorporated an impedance loop to provide local compliance in addition to the compliance provided by the operator via force feedback. Three joint bandwidths, 0.5, 1.0, and 2.0 Hz, were used. The performance measures were the task completion time and the sums of the squared forces and moments exerted on the environment. The task consisted of peg-in-hole insertion and removal. The results of the experiment indicate a significant performance decrease at 0.5-Hz bandwidth relative to the 1- and 2-Hz bandwidths. There was no significant change in performance between the 1- and 2-Hz bandwidths.

Uebel, Mark↗
NASA NTRS1990

Enhanced spectral efficiency using bandwidth switchable SAW filtering for mobile satellite communications systems

Currently proposed mobile satellite communications systems require a high degree of flexibility in assignment of spectral capacity to different geographic locations. Conventionally this results in poor spectral efficiency which may be overcome by the use of bandwidth switchable filtering. Surface acoustic wave (SAW) technology makes it possible to provide banks of filters whose responses may be contiguously combined to form variable bandwidth filters with constant amplitude and phase responses across the entire band. The high selectivity possible with SAW filters, combined with the variable bandwidth capability, makes it possible to achieve spectral efficiencies over the allocated bandwidths of greater than 90 percent, while retaining full system flexibility. Bandwidth switchable SAW filtering (BSSF) achieves these gains with a negligible increase in hardware complexity.

Peach, Robert↗
NASA NTRS1992

Adaptive low-bandwidth tracking of Galileo and Pioneer 10 carriers

In the Deep Space Network, tracking of residual carrier phase typically occurs with a fixed-bandwidth phase-locked loop using a bandwidth sufficiently wide to prevent loss of lock under worst-case conditions of signal dynamics, received signal phase noise, and receiver phase noise. Much of the time, however, such a high bandwidth is not required and may inflict unnecessarily heavy penalties on loop signal-to-noise ratios. This article describes a technique for improving tracking performance by permitting initial tracking at narrow bandwidths and gradually widening the loop as needed. The cost is a requirement for signal buffering, which is relatively inexpensive for low data rate applications. Results based on off-line processing of recorded carrier data from Galileo and Pioneer 10 are presented, and show potential 10-16 dB gains in loop SNR over worst-case fixed-bandwidth tracking.

Watola, D. A.↗
NASA NTRS1992

Investigation of the bandwidth of multimode optical fibers used with 1550-nm LED and laser sources

Multimode optical fibers are not intended to be used with 1550-nm sources; however, it is desirable to utilize 1300/1550-nm wavelength division multiplexing (WDM) on some multimode fibers at Kennedy Space Center (KSC). No information from fiber vendors nor from the literature is available to support this use. Preliminary studies at KSC have suggested that these fibers might be usable at 1550-nm if the fibers possessed enough bandwidth when sourced by LEDs. Detailed bandwidth studies were made on 12 multimode fibers using 1300- and 1550-nm lasers and LEDs. The results showed that the modal bandwidth at 1550-nm was about 50 percent of the 1300-nm value and that the chromatic dispersion could be predicted by extrapolating the vendor's specifications for wavelengths outside the 1550-nm region. Utilizing these data, predictions of the fiber's optical bandwidth were accurately made. Problems with launch conditions and possible differential attenuation at connectors was noted at 1300-nm but was less significant at 1550-nm. It appears that the multimode fibers studied will offer adequate performance in the 1550-nm region for a number of current KSC needs. Studies of additional fibers are encouraged to gain more confidence and better understanding of the 1550-nm bandwidth of KSC's multimode optical fibers before committing to 1300/1550-nm WDM.

White, Preston A., III↗
NASA NTRS2004

A Wide-Bandwidth, Low-Noise SIS Receiver Design for Millimeter and Submillimeter Wavelengths

In principle, millimeter and submillimeter heterodyne receivers using state-of-the-art SIS detectors are capable of extremely large instantaneous bandwidths with noise temperatures within a few Kelvin of the quantum limit. We are applying modem design tools, such as 3D electromagnetic simulators and Caltech's SuperMix SIS analysis package, to develop a new generation of waveguide SIS mixers with very broad RF and IF bandwidths. Our initial design consists of a double-sideband mixer targeted for the 180- 300 GHz band that uses a single SIS junction excited by a full bandwidth, fixed-tuned waveguide probe on a silicon substrate. The IF output band, limited by the MMIC low-noise IF preamplifier, is 6-18 GHz, providing an instantaneous RF bandwidth of 24 GHz (double-sideband). The SIS mixer conversion loss is predicted to be no more than 1-2 dB (single-sideband) with mixer noise temperatures across the band within 10 Kelvin of the quantum limit. The single-sideband receiver noise temperature goal is 70 Kelvin. The wide instantaneous bandwidth and low noise will result in an instrument capable of a variety of important astrophysical observations beyond the capabilities of current instruments. Lab testing of the receiver will begin in the summer of 2002, and a demonstration on the CSO should occur in the spring of 2003.

Sumner, Matthew↗
NASA NTRS2005

Out-of-Band 40 DB Bandwidth of EESS (Active) Spaceborne SARS

This document presents a study of out of band (OOB) 40 dB bandwidth requirements of spaceborne SARs in the Earth Exploration-Satellite Service (active) and Space Research Service (active). The purpose of the document is to study the OOB 40 dB bandwidth requirements and compare the 40 dB bandwidth B-40 as measured in simulations with that calculated using the ITU-R Rec SM.1541 equations. The spectra roll-off and resulting OOB 40 dB bandwidth of the linear FM signal is affected by the time-bandwidth product and the rise/fall times. Typical values of these waveform characteristics are given for existing EESS (active) sensors.

spaceborne sensor antenna↗
DOE OSTI2019

Minimum Spectral Bandwidth in Echo Seeded Free Electron Lasers

This paper examines the impact of non-linear longitudinal phase distortions on the spectral bandwidth in echo seeded free electron lasers (FELs). It extends the existing theory developed in Ref.~\cite{HemsingBunchingPhase} for echo-enabled harmonic generation (EEHG) to include finite laser pulse durations. An analytic expression for the shape of the optimized longitudinal bunching envelope is derived, and is used to determine the laser and electron beam pulse durations that minimize the seeded bandwidth in the presence of arbitrary phase distortions. The time-bandwidth product (TBP) is also derived, and is shown that the TBP and the bandwidth increase by no more than $\sqrt{2}$ from their transform-limited values when the bandwidth is minimized.

Hemsing, Erik↗
DOE OSTI2019

Variable bandwidth filter

A variable bandwidth filter is described herein, wherein a bandwidth of a passband of the variable bandwidth filter is dynamically tunable. The variable bandwidth tuner is implemented on a CMOS chip, and acts to filter analog signals. The variable bandwidth filter comprises a plurality of finite impulse response (FIR) filters, wherein each FIR filter comprises a plurality of tunable transconductors. The tunable transconductors are tunable in their gain.

Rodenbeck, Christopher T.↗