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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Meteorological radar facility (MRF) slot conductance investigations

A preliminary meteorological radar facility (MRF) array design was completed in support of the slot conductance measurement program. Three different slot measurement techniques were evaluated. The selection of the probe comparison measurement technique was selected as the principal experimental method with the impedance measurement technique chosen to measure a few higher conductance slots to be used as reference slots. The impedance of 43 slots in 0.9 x 0.4 inch standard waveguide and of 40 slots in 0.835 x 0.4 inch waveguide was measured. Also, impedance measurements were made of a few slots using image planes to simulate mutual coupling effects. The measured and theoretical conductance, susceptance, and radiation phase data are presented in graphic form as a function of slot displacement for constant slot length, and of slot length for constant slot displacement. It is concluded that the proposed MRF array design approach is a feasible one.

Ratkevich, A. E.↗
NASA NTRS2007

Aperture-Coupled Thin-Membrane L-Band Antenna

The upper part of the figure depicts an aperture-coupled L-band antenna comprising patterned metal conductor films supported on two thin polyimide membranes separated by an air gap. In this antenna, power is coupled from a microstrip line on the lower surface of the lower membrane, through a slot in a metal ground plane on the upper surface of the lower membrane, to a radiating metal patch on the upper surface of the upper membrane. The two-membrane configuration of this antenna stands in contrast to a three-membrane configuration heretofore considered as the basis for developing arrays of dual-polarization, wideband microwave antennas that could be thin and could be, variously, incorporated into, or supported on, thin structures, including inflatable structures. By reducing the number of membranes from three to two, the present design simplifies the problems of designing and fabricating such antennas or arrays of such antennas, including the problems of integrating such antennas or arrays with thin-membrane-mounted transmit/ receive modules. In addition, the use of aperture (slot) coupling eliminates the need for rigid coaxial feed pins and associated solder connections on thin membranes, making this antenna more mechanically reliable, relative to antennas that include coaxial feed pins. This antenna is designed for a nominal frequency of 1.26 GHz. The polyimide membranes are 0.05 mm thick and have a relative permittivity of 3.4. The radiating patch is square, 8.89 cm on each side. This radiating patch lies 1.27 cm above the ground plane. The feeding microstrip line is 0.12 mm wide and has a characteristic impedance of 50 . The aperture-coupling slot, etched in the ground plane, is 0.48 mm wide and 79.5 mm long. In order to maximize coupling, the microstrip line is extended beyond the middle of the slot by a length of 36 mm, which corresponds to a transmission- line electrical length of about a quarter wavelength. The other end of the microstrip line is transformed to a 50-Ohm coplanar waveguide line, which is used for connection to a transmit/receive module. Some plated-through vias are added to the outer conductors of the coplanar waveguide to suppress parallel-plate modes. The measured and calculated 10-dB-return-loss bandwidth of the antenna is 100 MHz. By eliminating the radiating patch and the upper membrane that supports it, and performing two other simple modifications, one can convert the two-membrane antenna described above to a paper-thin single-membrane antenna, shown in the lower part of the figure. One modification is to increase the slot length to 104.95 mm; the other is to extend the microstrip to 36.68 mm past the middle of the slot. With these modifications, the slot now becomes a half-wavelength radiator with a nearly omnidirectional radiation pattern. In one potential use, such a paper-thin antenna could be pasted on an automobile window to enable omnidirectional communication.

Huang, John↗
NASA NTRS2019

Development of Large-Scale Magnetic Calorimeter Arrays

We describe performance of large-scale arrays of metallic magnetic calorimeters (MMCs) we are developing to meet requirements of the Lynx X-ray Microcalorimeter (LXM) instrument in the astrophysics mission concept Lynx. We have fabricated prototypes with 55,800 x-ray pixels thermally connected to 5,688 MMC sensors. Subarrays demonstrate three types of pixels, which have different energy and spatial resolution goals in LXM. Pixel pitch is 50 or 25 µm. For two subarrays, use of position sensitive detectors, in a "hydra" configuration with 25 x-ray absorbers per sensor, helps achieve a large focal plane by increasing pixel count relative to readout channels. Since each absorber has a different thermal link to its sensor, it generates a different pulse shape and enables discrimination of pixel position. Superconducting wiring from all sensors was brought out to the perimeter of the overall array using multiple buried metal layers planarized by Chemical Mechanical Planarization to achieve high critical current, low inductance, and high fabrication yield. An automated, algorithmic approach was used to layout the complex wiring pattern. For readout with existing small arrays of Superconducting Quantum Interference (SQUID) amplifiers, 112 selected pixels were connected to wire bond pads. In hydras, we successfully identified 25 pulse shapes using rise-time and pulse height. Pulse shapes were similar to simulations. We measured noise and responsivity to substrate temperature and applied x-ray pulses. While we designed sensors to have high inductance to relative to stray inductance of wiring, we had only mismatched (lower input inductance) SQUIDs available in our current apparatus, giving non-optimized resolution. We compared measured and calculated energy resolutions. We have the required sensitivity to reach < 3 eV FWHM resolution for 6 keV x-rays, required for the LXM Main Array, and the ability to discriminate the 25 different absorber pixels down to energies < 300 eV.

microcalorimeters↗
DOE OSTI2023

Strain effects on stability of topological ferroelectric polar configurations in (PbTiO3) n /(SrTiO3) n superlattices

The (PbTiO3)n/(SrTiO3)n (PTO/STO) superlattice system has been shown to exhibit interesting topological phases (e.g., vortices and skyrmions) in addition to normal ferroelectric domain states. Existing studies are mostly focused on the dependence of topological polar distributions and properties of PTO/STO superlattice on its periodicity. Here, we study the strain effect on the topological phase transitions and ferroelectric domain structures employing phase-field simulations. We summarized in an isotropic strain (in-plane misfit strain along the x direction is equal to that along the y direction) periodicity phase diagram displaying the stability regions of different polar topological states, including normal ferroelectric twins, vortices, skyrmions, and mixtures of vortices and twins. We also analyzed the polarization configurations under anisotropic in-plane strains (in-plane misfit strain along the x direction is not equal to that along the y direction) and demonstrated that the strain anisotropy can be used to tune the directions of vortex arrays along either the [100] pc or [010] pc directions or labyrinth vortex arrays. This work offers guidance to manipulating polar structures in the PTO/STO superlattices via strain engineering.

Physics↗
NASA NTRS1981

Multispectral mapper - Imaging spectroscopy as applied to the mapping of earth resources

An instrument concept that uses solid-state array imaging has been developed for a future land observing system. The design concept is responsive to a variety of use needs and provides improved capabilities over the planned Landsat Thematic Mapper. A comparison of the differing approaches to the instrument design was made, resulting in the selection of a concept which uses a spectrograph coupled to a line-array imager to provide simultaneous spatial and spectral resolution. The design provides an inherent solution to the problem of achieving precise registration among the spectral bands. Data processing on the focal plane is used to select the spectral bands and their band widths. Onboard capabilities include radiometric correction, selection of instantaneous field-of-view and swath width, and data compression.

Wellman, J. B.↗
NASA NTRS1984

Asymmetric spline surfaces - Characteristics and applications

Asymmetric spline surfaces appear useful for the design of high-quality general optical systems (systems without symmetries). A spline influence function defined as the actual surface resulting from a simple perturbation in the spline definition array shows that a subarea is independent of others four or more points away. Optimization methods presented in this paper are used to vary a reflective spline surface near the focal plane of a decentered Schmidt-Cassegrain to reduce rms spot radii by a factor of 3 across the field.

Stacy, J. E.↗
NASA NTRS1992

Advanced photovoltaic power systems using tandem GaAs/GaSb concentrator modules

In 1989, Boeing announced the fabrication of a tandem gallium concentrator solar cell with an energy conversion efficiency of 30 percent. This research breakthrough has now led to panels which are significantly smaller, lighter, more radiation resistant, and potentially less expensive than the traditional silicon flat plate electric power supply. The new Boeing tandem concentrator (BTC) module uses an array of lightweight silicone Fresnel lenses mounted on the front side of a light weight aluminum honeycomb structure to focus sunlight onto small area solar cells mounted on a thin back plane. This module design is shown schematically. The tandem solar cell in this new module consists of a gallium arsenide light sensitive cell with a 24 percent energy conversion efficiency stacked on top of a gallium antimonide infrared sensitive cell with a conversion efficiency of 6 percent. This gives a total efficiency 30 percent for the cell-stack. The lens optical efficiency is typically 85 percent. Discounting for efficiency losses associated with lens packing, cell wiring, and cell operating temperature still allows for a module efficiency of 22 percent which leads to a module power density of 300 Watts/sq. m. This performance provides more than twice the power density available from a single crystal silicon flat plate module and at least four times the power density available from amorphous silicon modules. The fact that the lenses are only 0.010 ft. thick and the aluminum foil back plane is only 0.003 ft. thick leads to a very lightweight module. Although the cells are an easy to handle thickness of 0.020 ft., the fact that they are small, occupying one-twenty-fifth of the module area, means that they add little to the module weight. After summing all the module weights and given the high module power, we find that we are able to fabricate BTC modules with specific power of 100 watts/kg.

Fraas, L. M.↗
NASA NTRS2011

High-Efficiency Ka-Band Waveguide Two-Way Asymmetric Power Combiner

NASA is planning a number of Space Exploration, Earth Observation and Space Science missions where Ka-band solid-state power amplifiers (SSPAs) could have a role. Monolithic microwave integrated circuit (MMIC) based SSPAs with output powers on the order of 10 W at Ka-band frequencies would be adequate to satisfy the data transmission rate requirements at the distances involved. MMICs are a type of integrated circuit fabricated on a GaAs wafer, which operates at micro wave frequencies and performs the function of signal amplification. The highest power Ka-band (31.8 to 32.3 GHz) SSPA to have flown in space had an output power of 2.6 W with an overall efficiency of 14.3 percent. This SSPA was built around discrete GaAs pHEMT (high electron mobility transistor) devices and flew aboard the Deep Space One spacecraft. State-of-the-art GaAs pHEMT-based MMIC power amplifiers (PAs) can deliver RF power at Ka-band frequencies anywhere from 3 W with a power added efficiency (PAE) of 32 percent to 6 W with a PAE of 26 percent. However, to achieve power levels higher than 6 W, the output of several MMIC PAs would need to be combined using a high-efficiency power combiner. Conventional binary waveguide power combiners, based on short-slot and magic-T circuits, require MMIC PAs with identical amplitude and phase characteristics for high combining efficiency. However, due to manufacturing process variations, the output powers of the MMIC PAs tend to be unequal, and hence the need to develop unequal power combiners. A two-way asymmetric magic-T based power combiner for MMIC power amplifiers, which can take in unequal inputs, has been successfully designed, fabricated, and characterized over NASA s Deep Space Network (DSN) frequency range of 31.8 to 32.3 GHz. The figure is a transparent view of the a sym - metric combiner that shows the 4-port configuration and the internal structure. The rod, post, and iris are positioned by design to achieve the desired asymmetric power ratio, phase equality, and port isolation. Although the combiner was designed for an input power ratio of 2:1, it can be custom-designed for any arbitrary power ratio and frequency range. The manufactured prototype combiner was precision machined from aluminum and is less than 2 in.3 (32.8 cm3). Previously investigated rectangular waveguide unequal power combiners were based on shunt/series coupling slots, E-plane septums, or H-plane T-junctions. All the prior art unequal power combiners operated at or below X-band (10 GHz) frequencies and were primarily used in the feed network of antenna arrays. The only reported asymmetric magic-T was developed as a 2:1 power divider for operation at a much lower frequency, around 500 MHz. The measured power ratio when tested as a power divider was very close to 2 and the phase balance was within 2.6, resulting in near ideal performance. When tested as a combiner using two MMIC SSPAs with a 2:1 power output ratio, an efficiency greater than 90 percent was demonstrated over the 500 MHz DSN frequency range. The return loss at the combiner output port (1) was greater than 18 dB and the input port (2 and 3) isolation was greater than 22 dB. The results show the asymmetric combiner to be a good candidate for high-efficiency power combining of two or more SSPAs needed to achieve the 6 to 10 W required by space communications systems of future NASA missions.

Wintucky, E. G.↗
NASA NTRS2018

Far-Field Pattern Measurement and Simulation of VHF Antenna at 60 MHz for Europa Clipper Mission

This paper presents measurements and simulations of a linearly polarized VHF folded dipole operating at 60 MHz for NASA’s upcoming Europa Clipper mission. The spacecraft contains a ground penetrating radar, consisting of an array of four VHF antennas, that will characterize the surface of Jupiter’s icy moon Europa. Measured far-field radiation patterns and reflection coefficients above a 50×80m perfect ground plane are compared to predicted results using commercial software. Normalized Far-Field radiation pattern cuts are measured utilizing a biconical antenna and receiver mounted on a flying drone. Simulations of the radiation pattern show that the number of lobes increases with the distance of the antenna from the ground due to the ground-bounce phenomenon. In addition, the measured and simulated reflection coefficients stay unchanged for height above 2 meters, which matches the predicted calculation of the reactive-near field region of this antenna. However, the antenna electrical parameters are optimized for use on the spacecraft and become detuned in the presence of a ground plane. Simulated and measured return loss discrepancy less than 0.5 dB is presented. Radiation pattern comparisons show similar agreement when taking into account the effect of far-field measurement uncertainties.

Decrossas, Emmanuel↗
NASA NTRS1993

Photodetector Array For Neural Network

Integrated circuit performs 1,024 threshold operations in parallel. Designed for use in postprocessing output of optical correlator in optoelectronic neural network. Overall function of device to put out digital signals indicative of location(s) of bright spot(s) on detector plane. Response time less than commercial charge-coupled-device (CCD) imaging detector operating at standard television frame rate.

Langenbacher, Harry↗
DOE OSTI2021

Defect-Enabled Phase Programming of Transition Metal Dichalcogenide Monolayers

The ability to tune the local electronic transport properties of group VI transition metal dichalcogenide (TMD) monolayers by strain-induced structural phase transformations (“phase programming”) has stimulated much interest in the potential applications of such layers as ultrathin programmable and dynamically switchable nanoelectronics components. In this manuscript, we propose a new approach toward controlling TMD monolayer phases by employing macroscopic in-plane strains to amplify heterogeneous strains arising from tailored, spatially extended defects within the monolayer. Furthermore, the efficacy of our proposed approach is demonstrated via numerical simulations of emerging domains localized around arrays of holes, grain boundaries, and compositional heterointerfaces. Quantitative relations between the macroscopic strains required, spatial resolution of domain patterns, and defect configurations are developed. In particular, the introduction of arrays of holes is identified as the most feasible phase programming route.

2D materials↗
DOE OSTI2023

Line emission mapper microcalorimeter spectrometer

The line emission mapper (LEM) is a probe-class mission concept that is designed to detect x-ray emission lines from hot ionized gas (T > 10 6 K) that will enable us to test galaxy evolution theories. It will permit us to study the effects of stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. The key to being able to study the hot gases that are otherwise invisible to current imaging x-ray spectrometers is that the energy resolution is sufficient to use cosmological redshift to separate extragalactic source lines from foreground Milky Way emission. LEM incorporates a large-format microcalorimeter array instrument called the LEM microcalorimeter spectrometer (LMS) with a light-weight x-ray optic with 10” half power diameter angular resolution. The LMS microcalorimeter array has pixels with 15" pixel pitch over a 33' field of view (FOV) optimized for the 0.3 to 2 keV energy band. The central 7' region of the array has an energy resolution of 1.3 eV at 1 keV and the rest of the FOV has 2.5 eV energy resolution at 1 keV. The array will be read out with state-of-the-art time-division multiplexing. We present an overview of the LMS instrument, including details of the entire detection chain, the focal plane assembly, as well as the cooling system and overall mechanical and thermal design. For each of the key technologies, we discuss the current technology readiness level and the plan to advance them to be ready for flight. We also describe the current system design and our estimate for the mass, power, and data rate of the instrument. The design details presented concentrate primarily on the unique aspects of the LMS design compared with prior missions and confirm that the type of microcalorimeter instrument needed for LEM is not only feasible but also technically mature.

47 OTHER INSTRUMENTATION↗
NASA NTRS1992

Development and test of an IR camera for astronomical observation at the Palomar 200-in. observatory using the NICMOS II array

A NICMOS II array, a NIR (0.80 - 2.6 micron) imaging system, was integrated into the California Institute of Technology Palomar Observatory camera. The Palomar camera system which consists of six discrete subsystems including a focal plane, an electrical interface, data acquisition electronics, a dewar, dewar optics, and the software is described. The performance and calibration data for each subsystem are presented. Emphasis is placed on test data on the focal plane performance.

Bruce, Carl↗
NASA NTRS1993

Probe impedance measurements for millimeter-wave integrated horn antennas

In order to achieve an impedance-matched millimeter-wave integrated horn antenna mixer array, the characteristics of the antenna probes inside the horn must be known. This paper describes impedance measurements for various probes in low-frequency model horns of two different types: (1) a 3 x 3 array made of aluminum by electric discharge machining and (2) a half horn made of copper sheet placed on a big copper-clad circuit board that was used as an image plane. The results of measurements indicate that the presence of the horn increases the effective length of the probe element, in agreement with reports of Guo et al. (1991) and theoretical analysis of Eleftheriades et al. (1991). It was also found that the resonant frequencies can be controlled by changing the length of the probes or by loading the probes.

Guo, Yong↗
NASA NTRS1995

Quantitative rainbow schlieren deflectometry

In the rainbow schlieren apparatus, a continuously graded rainbow filter is placed in the back focal plane of the decollimating lens. Refractive-index gradients in the test section thus appear as gradations in hue rather than irradiance. A simple system is described wherein a conventional color CCD array and video digitizer are used to quantify accurately the color attributes of the resulting image, and hence the associated ray deflections. The present system provides a sensitivity comparable with that of conventional interferometry, while being simpler to implement and less sensitive to mechanical misalignment.

Greenberg, Paul S.↗
NASA NTRS1993

Hover Acoustic Characteristics of the XV-15 with Advanced Technology Blades

An experiment has been performed to investigate the far-field hover acoustic characteristics of the XV-15 aircraft with advanced technology blades (ATB). An extensive, high-quality, far-field acoustics data base was obtained for a rotor tip speed range of 645-771 ft/s. A 12-microphone, 500-ft radius semicircular array combined with two aircraft headings provided acoustic data over the full 360-deg azimuth about the aircraft with a resolution of 15 deg. Altitude variations provided data from near in-plane to 45 deg below the rotor tip path plane. Acoustic directivity characteristics in the lower hemisphere are explored through pressure time histories, narrow-band spectra, and contour plots. Directivity patterns were found to vary greatly with azimuth angle, especially in the forward quadrants. Sharp positive pressure pulses typical of blade-vortex interactions were found to propagate aft of the aircraft and were most intense at 45 deg below the rotor plane. Modest overall sound pressure levels were measured near in-plane indicating that thickness noise is not a major problem for this aircraft when operating in the hover mode with ATB. Rotor tip speed reductions reduced the average overall sound pressure level (dB (0.0002 dyne/cm(exp 2)) by nearly 8 dB in-plane, and 12.6 deg below the rotor plane.

Conner, David A.↗
NASA NTRS2009

Improved Scanners for Microscopic Hyperspectral Imaging

Improved scanners to be incorporated into hyperspectral microscope-based imaging systems have been invented. Heretofore, in microscopic imaging, including spectral imaging, it has been customary to either move the specimen relative to the optical assembly that includes the microscope or else move the entire assembly relative to the specimen. It becomes extremely difficult to control such scanning when submicron translation increments are required, because the high magnification of the microscope enlarges all movements in the specimen image on the focal plane. To overcome this difficulty, in a system based on this invention, no attempt would be made to move either the specimen or the optical assembly. Instead, an objective lens would be moved within the assembly so as to cause translation of the image at the focal plane: the effect would be equivalent to scanning in the focal plane. The upper part of the figure depicts a generic proposed microscope-based hyperspectral imaging system incorporating the invention. The optical assembly of this system would include an objective lens (normally, a microscope objective lens) and a charge-coupled-device (CCD) camera. The objective lens would be mounted on a servomotor-driven translation stage, which would be capable of moving the lens in precisely controlled increments, relative to the camera, parallel to the focal-plane scan axis. The output of the CCD camera would be digitized and fed to a frame grabber in a computer. The computer would store the frame-grabber output for subsequent viewing and/or processing of images. The computer would contain a position-control interface board, through which it would control the servomotor. There are several versions of the invention. An essential feature common to all versions is that the stationary optical subassembly containing the camera would also contain a spatial window, at the focal plane of the objective lens, that would pass only a selected portion of the image. In one version, the window would be a slit, the CCD would contain a one-dimensional array of pixels, and the objective lens would be moved along an axis perpendicular to the slit to spatially scan the image of the specimen in pushbroom fashion. The image built up by scanning in this case would be an ordinary (non-spectral) image. In another version, the optics of which are depicted in the lower part of the figure, the spatial window would be a slit, the CCD would contain a two-dimensional array of pixels, the slit image would be refocused onto the CCD by a relay-lens pair consisting of a collimating and a focusing lens, and a prism-gratingprism optical spectrometer would be placed between the collimating and focusing lenses. Consequently, the image on the CCD would be spatially resolved along the slit axis and spectrally resolved along the axis perpendicular to the slit. As in the first-mentioned version, the objective lens would be moved along an axis perpendicular to the slit to spatially scan the image of the specimen in pushbroom fashion.

Mao, Chengye↗
NASA NTRSDate not supplied

Wind Tunnel PSD and MVD Characterization Using New 1D2D Optical Array Probes

This work explores characterization of the liquid clouds using a combination of a forward scattering probe and two Optical Array Probes. Current OAP probes provide particle shape, size, and number concentration from two-dimensional shadow images. However, past studies have shown that such images are subject to distortion when outside of the focal plane. This affects the retrieval of particle size distributions, particularly in the Supercooled Large Droplet size range. In this article, the use of a Droplet Measurement Technologies Cloud Droplet Probe and two new OAPs produced by Science Engineering Associates, is examined using wind tunnel data, to assess suitability for use in a wind tunnel calibration in SLD conditions. The new OAP probes exploit a flexible and simple grey scale imaging method to eliminate some present shortcomings of commonly used OAPs, and to reduce correction factors. Spinning disk measurements were used to specify probe depth of field, and average size errors. Composite spectra covering the nominal 2-3200 µm size range were formed by crossing over from the CDP to 1D2D-X at 48 µm, and then to the 1D2D-Y at about 400 µm. A good overlap was found at the crossover points without any artificial scaling. Composite spectra adequately closed the liquid water content distribution, and provided integrated LWCs within about 35% of the hot-wire LWCs used for tunnel calibration. This discrepancy was at least partially attributed to LWC underestimation by the hot-wire at high MVD. A model of probe performance was used to show an example of expected accuracy of ideal probes subject to the same OAP distortions and using the same mitigating procedures and corrections, predicting PSD Median Volume Diameter and integrated LWC errors of less than 10%.

Aircraft Icing↗