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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 NTRS1984

Integrated optical signal processing with magnetostatic waves

Magneto-optical devices based on Bragg diffraction of light by magnetostatic waves (MSW's) offer the potential of large time-bandwidth optical signal processing at microwave frequencies of 1 to 20 GHz and higher. A thin-film integrated-optical configuration, with the interacting MSW and guided-optical wave both propagating in a common ferrite layer, is necessary to avoid shape-factor demagnetization effects. The underlying theory of the MSW-optical interaction is outlined, including the development of expressions for optical diffraction efficiency as a function of MSW power and other relevant parameters. Bradd diffraction of guided-optical waves by transversely-propagating magnetostatic waves and collinear TE/TM mode conversion included by MSW's have been demonstrated in yttrium iron garnet (YIG) thin films. Diffraction levels as large as 4% (7 mm interaction length) and a modulation dynamic range of approx 30 dB have been observed. Advantages of these MSW-based devices over the analogous acousto-optical devices include: much greater operating frequencies, tunability of the MSW dispersion relation by varying either the RF frequency or the applied bias magnetic field, simple broad-band MSW transducer structures (e.g., a single stripline), and the potential for very high diffraction efficiencies.

Fisher, A. D.↗
NASA NTRS1980

A 163 micron laser heterodyne radiometer for OH

A 163 micron (1.836 THz) radiometer developed for airplane and/or balloon platforms is described. The laser local oscillator is a CO2 pumped methanol laser operating at a frequency which is approx. 1 GHz from the J = 3/2 - 1/2 transition of OH. The laser is used directly as a local oscillator or is translated in frequency to closer coincidence with the OH emission, depending on achieved detector IF bandwidth. Frequency translation techniques which are described are diode mixing and a method of single sideband generation using an external Stark modulated gas cell. The photoconductive mixer used is a strained Ge crystal, doped with Ga, originally used as an incoherent detector. The uniaxial strain on the Ga doped Ge crystal shifts the threshold for photoconduction from 100/cm to frequencies as low as 50/cm. These detectors are currently being characterized as mixers in the laboratory. Of particular interest are the effect of local oscillator power and strain on IF, bandwidth detector impedance, and conversion loss. Preliminary results of these tests are described and compared with theorectical expectations.

Pickett, H. M.↗
NASA NTRS1990

Time resolved spectra in the infrared absorption and emission from shock heated hydrocarbons

The wavelength range of a previously constructed multichannel fast recording spectrometer was extended to the mid-infrared. With the initial configuration, light intensities were recorded simultaneously with a silicon-diode array simultaneously at 20 adjacent wavelengths, each with a 20-micron time resolution. For studies in the infrared, the silicon diodes were replaced by a 20-element PbSe array of similar dimensions, cooled by a three-stage thermoelectric device. It is proposed that infrared emissions could be due to shock-heated low molecular-weight hydrocarbons. The full Swan band system appeared in time-integrated emission spectra from shock-heated C2H2; no soot was generated. At low resolution, the profiles on the high-frequency side of the black body maximum show no distinctive features. These could be fitted to Planck curves, with temperatures that declined with time from an initial high that was intermediate between T5 (no conversion) and T5(eq).

Bauer, S. H.↗
NASA NTRS2015

Spatiotemporal Coherence of Mean and Extreme Aerosol Particle Events over Eastern North America as Observed from Satellite

Quantifying spatiotemporal scales of coherence and variability of aerosol particle properties provides (i) metrics for evaluating observational data sets and model simulations, (ii) inferences regarding dominant causes of variability, and (iii) information that is necessary to determine their climate forcing and air quality impacts. Accordingly, analyses of columnar aerosol optical depth (AOD) and Ångstrom exponent (AE) from the MODerate resolution Imaging Spectroradiometer (MODIS) on the Aqua and Terra satellites, and AErosol RObotic NETwork (AERONET) stations are used to evaluate the spatially averaged (Level-3) MODIS products, and to characterize the spatiotemporal scales of variability (and coherence) of aerosol particles over eastern North America (2000-2013). Results show a high degree of consistency in AOD retrievals from the different data sets but larger discrepancies in AE estimates, highest mean AOD and lowest day-to-day variability during the summer, and largest scales of spatial coherence in summer and fall. Consistent with the scales of spatial coherence from MODIS data, in both data sets power spectra indicate AOD variability is manifest primarily on synoptic and annual time scales. Conversely, AE variability in MODIS data is primarily focused on seasonal, semiannual, and annual time scales, and there is an additional mode of AE variability at approx. 30 days in the AERONET measurements. The frequency of cooccurrence of extreme AOD values (>local 90th percentile) decreases to below 50% at approx. 150 km from a central grid cell, but is above that expected by random chance over almost all of eastern North America, indicating supra-regional scale extreme events.

MODIS↗
NASA NTRS1972

Efficient second harmonic generation of picosecond laser pulses.

Efficient conversion to the second harmonic (SH) using KD2PO4 and CsH2AsO4 crystals inside a folded cavity of a high-power-dye mode-locked neodymium-glass laser is reported. For the first time, frequency-doubled picosecond light pulses have been obtained in CsH2AsO4 with peak powers of the order of 1 GW/sq cm at 0.531 micron for an effective pump power density of 4 GW/sq cm.

Rabson, T. A.↗
NASA NTRS1991

Lower hybrid waves excited through linear mode coupling and the heating of ions in the auroral and subauroral magnetosphere

Two related aspects of the linear mode conversion mechanism are considered: (1) the controlled heating of suprathermal ions in the ionosphere and magnetosphere over a powerful VLF/ELF transmitter using lower hybrid (LH) waves excited by the electromagnetic (EM) transmitter signals through linear mode conversion; (2) the excitation of intense LH waves in the auroral regions through the linear conversion of VLF/ELF EM auroral hiss, and the subsequent heating of ions by the excited LH waves. Experimental results are used to demonstrate that strong LH waves can be excited by EM waves down to frequencies as low as 2 kHz in the subauroral low-altitude magnetosphere. It is also shown that an approximately 250 kW VLF/ELF transmitter operating in the subauroral region at 2 kHz could excite sufficiently intense LH waves to heat suprathermal 1 eV H(+) ions and 16 eV O(+) ions to roughly 50 eV in a region extending in altitude from 1000 to 5000 km above the transmitter with a horizontal scale of about 500 km. If coherent wave stochastic heating occurs, the O(+) energy gain could be as large as 200 eV.

Bell, T. F.↗
NASA NTRS1999

RF Bonding Investigation: The Effects of a Space Environment on Coatings

Coatings are commonly used in the aerospace industry for corrosion control of metals. The impedance of these coatings can reduce the effectiveness of EMI filters. This paper documents the effects of a space environment on a variety of coatings applied to electrical bonding surfaces. Nickel plating, anodizing, and chemical conversion coatings of alodine and iridite are investigated. The test fixture is designed to simulate a feed-through filter in a metal chassis. The filter insertion loss will be shown as a function of frequency and coating.

Krome, Mark E.↗
NASA NTRS2004

Silicon Carbide Diodes Characterization at High Temperature and Comparison With Silicon Devices

Commercially available silicon carbide (SiC) Schottky diodes from different manufacturers rated at 200, 300, 600, and 1200 V, were electrically tested and characterized as a function of temperature up to 300 C. Electrical tests included both steady state and dynamic tests. Steady state tests produced forward and reverse I-V characteristic curves. Transient tests evaluated the switching performance of the diodes in either a hard-switched DC to DC buck converter or a half-bridge boost converter. For evaluation and comparison purposes, the same tests were performed with current state-of-the-art ultra fast silicon (Si) pn-junction diodes of similar ratings and also a Si Schottky diode. The comparisons made were forward voltage drop at rated current, reverse current at rated voltage, and turn-off peak reverse recovery current and reverse recovery time. In addition, efficiency measurements were taken for the buck DC to DC converter using both the SiC Schottky diodes and the Si pn-junction diodes at different temperatures and frequencies. The test results showed that at high temperature, the forward voltage drop for SiC Schottky diodes is higher than the forward drop of the ultra fast Si pn-junction diodes. As the temperature increased, the forward voltage drop of the SiC Schottky increased while for the ultra fast Si pn-junction diodes, the forward voltage drop decreased as temperature increased. For the elevated temperature steady state reverse voltage tests, the SiC Schottky diodes showed low leakage current at their rated voltage. Likewise, for the transient tests, the SiC Schottky diodes displayed low reverse recovery currents over the range of temperatures tested. Conversely, the Si pn-junction diodes showed increasing peak reverse current values and reverse recovery times with increasing temperature. Efficiency measurements in the DC to DC buck converter showed the advantage of the SiC Schottky diodes over the ultra fast Si pn-junction diodes, especially at the higher temperatures and higher frequencies.

Lebron-Velilla, Ramon C.↗
NASA NTRS1983

Image-optimized, frequency-scalable mixers for millimeter-wave applications

A unique IF measurement procedure for evaluating mixer performance and identifying optimum circuit boundary conditions is presented. The technique is applied to a scalable mm-wave single-sideband (image-sum enhanced) mixer design which provides 3.5 to 5 dB typical conversion loss from conventional, packaged devices.

Peterson, D. F.↗
NASA NTRS1972

Study of aircraft electrical power systems

The formulation of a philosophy for devising a reliable, efficient, lightweight, and cost effective electrical power system for advanced, large transport aircraft in the 1980 to 1985 time period is discussed. The determination and recommendation for improvements in subsystems and components are also considered. All aspects of the aircraft electrical power system including generation, conversion, distribution, and utilization equipment were considered. Significant research and technology problem areas associated with the development of future power systems are identified. The design categories involved are: (1) safety-reliability, (2) power type, voltage, frequency, quality, and efficiency, (3) power control, and (4) selection of utilization equipment.

Source record↗
NASA NTRS1984

Severe storm electricity

Severe storms and lightning were measured with a NASA U2 and ground based facilities, both fixed base and mobile. Aspects of this program are reported. The following results are presented: (1) ground truth measurements of lightning for comparison with those obtained by the U2. These measurements include flash type identification, electric field changes, optical waveforms, and ground strike location; (2) simultaneous extremely low frequency (ELF) waveforms for cloud to ground (CG) flashes; (3) the CG strike location system (LLP) using a combination of mobile laboratory and television video data are assessed; (4) continued development of analog-to-digital conversion techniques for processing lightning data from the U2, mobile laboratory, and NSSL sensors; (5) completion of an all azimuth TV system for CG ground truth; (6) a preliminary analysis of both IC and CG lightning in a mesocyclone; and (7) the finding of a bimodal peak in altitude lightning activity in some storms in the Great Plains and on the east coast. In the forms on the Great Plains, there was a distinct class of flash what forms the upper mode of the distribution. These flashes are smaller horizontal extent, but occur more frequently than flashes in the lower mode of the distribution.

Rust, W. D.↗
NASA NTRS2016

Experimental Comparison of Piezoelectric and Magnetostrictive Shunt Dampers

A novel mechanism called the vibration ring is being developed to enable energy conversion elements to be incorporated into the driveline of a helicopter or other rotating machines. Unwanted vibration is transduced into electrical energy, which provides a damping effect on the driveline. The generated electrical energy may also be used to power other devices (e.g., health monitoring sensors). PZT (piezoceramic) and PMN-30PT (single crystal) stacks, as well as a Tb_0.3 Dy_0.7 Fe_1.92 (Terfenol-D) rod with a bias magnet array and a pickup coil, were tested as alternative energy conversion elements to use within the vibration ring. They were tuned for broadband damping using shunt resistors, and dynamic compression testing was conducted in a high-speed load frame. Energy conversion was experimentally optimized at 750Hz by tuning the applied bias stress and resistance values. Dynamic testing was conducted up to 1000Hz to determine the effective compressive modulus, shunt loss factor, internal loss factor, and total loss factor. Some of the trends of modulus and internal loss factor versus frequency were unexplained. The single crystal device exhibited the greatest shunt loss factor whereas the Terfenol-D device had the highest internal and total loss factors. Simulations revealed that internal losses in the Terfenol-D device were elevated by eddy current effects, and an improved magnetic circuit could enhance its shunt damping capabilities. Alternatively, the Terfenol-D device may be simplified to utilize only the eddy current dissipation mechanism (no pickup coil or shunt) to create broadband damping.

energy conversion↗
NASA NTRS2016

Experimental Comparison of Piezoelectric and Magnetostrictive Shunt Dampers

A novel mechanism called the vibration ring is being developed to enable energy conversion elements to be incorporated into the driveline of a helicopter or other rotating machines. Unwanted vibration is transduced into electrical energy, which provides a damping effect on the driveline. The generated electrical energy may also be used to power other devices (e.g., health monitoring sensors). PZT (piezoceramic) and PMN-30%PT (single crystal) stacks, as well as a Tb_0.3 Dy_0.7 Fe_1.92 (Terfenol-D) rod with a bias magnet array and a pickup coil, were tested as alternative energy conversion elements to use within the vibration ring. They were tuned for broadband damping using shunt resistors, and dynamic compression testing was conducted in a high-speed load frame. Energy conversion was experimentally optimized at 750Hz by tuning the applied bias stress and resistance values. Dynamic testing was conducted up to 1000Hz to determine the effective compressive modulus, shunt loss factor, internal loss factor, and total loss factor. Some of the trends of modulus and internal loss factor versus frequency were unexplained. The single crystal device exhibited the greatest shunt loss factor whereas the Terfenol-D device had the highest internal and total loss factors. Simulations revealed that internal losses in the Terfenol-D device were elevated by eddy current effects, and an improved magnetic circuit could enhance its shunt damping capabilities. Alternatively, the Terfenol-D device may be simplified to utilize only the eddy current dissipation mechanism (no pickup coil or shunt) to create broadband damping.

piezoelectric↗
NASA NTRS1972

Parallel operation of two Brayton-cycle alternators with parasitic speed controllers

The experimental paralleling characteristics of two 1200 Hz Brayton-cycle alternators are presented. Since the Brayton power conversion system uses electric speed controllers, the paralleling requirements are somewhat different from those for conventional ground-based systems. Results include the transient effects of synchronizing the two alternators with various phase-angle, voltage, and frequency differences. Based on these results, the effects of synchronizing differences can be defined, and adjustment requirements of the parasitic speed controllers during synchronizing can be established. Data indicate that parasitically loaded alternators are able to parallel over a wide range of synchronizing differences. However, equilibrium could not be reached in extreme cases where alternator load differences were great and, at the same time, the phase-angle error was large (150 deg or more).

Perz, D. A.↗
NASA NTRS1979

Economical synthesis of potassium superoxide

High-frequency discharge in oxygen can be used to prepare superoxides of alkali and alkaline-earth metals. Since no direct-current discharge at the electrodes is present, no sputtering can contaminate the product, hence a high conversion efficiency.

Bell, A. T.↗
NASA NTRS1984

Conversion of microwave signals by superconducting films in the resistive state

The main characteristics of a superconducting thin film microwave mixer, i.e., conversion efficiency and bandwidth are analyzed. The optimum operating regime of the nonlinear element is determined. Results of calculations are compared with the experimental ones. Experimental data on the noise in the superconducting films in a wide frequency range are presented.

Yeru, I. I.↗
NASA NTRS1991

Observations of Enhanced Radar Backscatter (ERB) from Millstone Hill

Intense enhancements of the incoherent radar backscatter spectrum from the topside ionosphere were observed with the Millstone Hill UHF radar. Enhancements occurring at the local ion acoustic frequency causing large asymmetries in the measured ion line may be produced by current driven instabilities. These enhancements pose a practical problem for space surveillance systems because their cross section and spectral width are characteristic of satellites. Conversely, their hard target signature complicates the study of naturally occurring ERB events; it is nearly impossible to distinguish them from satellites based on a single measurement. Statistical comparisons of observed coherent echo distributions with predictions from a satellite catalog were used to broadly identify periods of ERB activity. A series of experiments using multiple diagnostics, including satellite instruments, for simultaneous observations have established the association of ERB with large fluxes of soft suprathermal electrons carrying field aligned currents. Zenith data are also presented which show the asymmetric growth of ion acoustic waves directly above Millstone Hill. Details of these results are presented.

Lee, M. C.↗
NASA NTRS1994

Spatial frequency multiplier with active linearly tapered slot antenna array

A frequency multiplier with active linearly tapered slot antennas (LTSA's) has been demonstrated at the second harmonic frequency. In each antenna element, a GaAs monolithic microwave integrated circuit (MMIC) distributed amplifier is integrated with two LTSA's. The multiplier has a very wide bandwidth and large dynamic range. The fundamental-to-second harmonic conversion efficiency is 8.1 percent. The spatially combined second harmonic signal is 50 dB above the noise level. The design is suitable for constructing a large array using monolithic integration techniques.

Simons, Rainee N.↗