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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Phase and contrast moiré signatures in two-dimensional cone beam interferometry

Neutron interferometry has played a distinctive role in fundamental science and characterization of materials. Moiré neutron interferometers are candidate next-generation instruments: they offer microscopy-like magnification of the signal, enabling direct camera recording of interference patterns across the full neutron wavelength spectrum. Here we demonstrate the extension of phase-grating moiré interferometry to two-dimensional geometries. Our fork-dislocation phase gratings reveal phase singularities in the moiré pattern, and we explore orthogonal moiré patterns with two-dimensional phase gratings. Our measurements of phase topologies and gravitationally induced phase shifts are in good agreement with theory. These techniques can be implemented in existing neutron instruments to advance interferometric analyses of emerging materials and precision measurements of fundamental constants. Published by the American Physical Society 2024

Sarenac, D. (ORCID:0000000185753367)↗
NASA NTRS1976

Interactions of satellite-speed helium atoms with satellite surfaces. 2: Energy distributions of reflected helium atoms

Energy transfer in collisions of satellite-speed (7,000 m/sec) helium atoms with a cleaned 6061-T6 satellite-type aluminum surface was investigated using the molecular-beam technique. The amount of energy transferred was determined from the measured energy of the molecular-beam and the measured spatial and energy distributions of the reflected atoms. Spatial distributions of helium atoms scattered from a 6061-T6 aluminum surface were measured. The scattering pattern exhibits a prominent backscattering, probably due to the gross surface roughness and/or the relative lattice softness of the aluminum surface. Energy distributions of reflected helium atoms from the same surface were measured for six different incidence angles. For each incidence angle, distributions were measured at approximately sixty scattering positions. At a given scattering position, the energy spectra of the reflected helium atoms and the background gas were obtained using the retarding-field energy analyzer.

Liu, S. M.↗
NASA NTRS1975

Single laser beam of spatial coherence from an array of GaAs lasers - Free-running mode

Spatially coherent radiation from a monolithic array of three GaAs lasers in a free-running mode is reported. The lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent-beam formation makes use of the Fourier-transformation property of the internal lenses. Transverse mode control is accomplished by a spatial filter. The optical cavity is similar to that used for the phase-controlled mode of spatially coherent-beam formation; only the spatial filters are different. In the far field (when restored by an external lens), the intensities of the lasers in the array are concentrated in a single laser beam of spatial coherence, without any grating lobes. The far-field distribution of the laser array in the free-running mode differs significantly from the interference pattern of the phase-controlled mode. The modulation characteristics of the optical waveforms of the two modes are also quite different because modulation is related to the interaction of the spatial filter with the longitudinal modes of the laser array within the optical cavity. The modulation of the optical waveform of the free-running mode is nonperiodic, confirming that the fluctuations of the optical fields of the lasers are random.

Philipp-Rutz, E. M.↗
NASA NTRS1985

Simulation of the enhanced traffic alert and collision avoidance system (TCAS 2)

The OSU aircraft code is used to analyze and simulate the TCAS 2 circular array which is mounted on the fuselage of a Boeing 737 aircraft. It is shown that the sum and difference patterns radiated by the circular array are distorted by the various structures of the aircraft, i.e., wings, tail, etc. Furthermore, monopulse curves are calculated and plotted for several beam positions and THETA angles. As expected, the worst cases of distortion occur when the beams are pointed toward the tail of the aircraft.

Rojas, R. G.↗
NASA NTRS1988

Low-noise interferometer for microwave radiometry

An interferometer for precision measurements in microwave radiometry is proposed which uses two low-noise heterodyne receivers based on SIS tunnel junction mixers in the 40-50-GHz band. The antenna interference pattern has lobes which lead to positive output signals and lobes which give negative output, and the radiometer measures the difference in the power from these lobes without beam switching or instrument motion. The present system cancels instrumental signals, has a very low 1/f noise in the output, and has a zero outpus signal when viewing a uniform source. It is noted that application of the interferometer may be limited to radiometry with relatively large beams.

Timbie, P. T.↗
NASA NTRS1988

Vehicle antenna for the mobile satellite experiment

A low profile, low cost, printed circuit, electronically steered, right hand circularly polarized phase array antenna system has been developed for the Mobile Satellite Experiment (MSAT-X) Program. The success of this antenna is based upon the development of a crossed-slot element array and detailed trade-off analyses for both the phased array and pointing system design. The optimized system provides higher gain at low elevation angles (20 degrees above the horizon) and broader frequency coverage (approximately 8 1/2 percent bandwidth) than is possible with a patch array. Detailed analysis showed that optimum performance could be achieved with a 19 element array of a triangular lattice geometry of 3.9 inch element spacing. This configuration has the effect of minimizing grating lobes at large scan angles plus it improves the intersatellite isolation. The array has an aperture 20 inches in diameter and is 0.75 inch thick overall, exclusive of the RF and power connector. The pointing system employs a hybrid approach that operates with both an external rate sensor and an internal error signal as a means of fine tuning the beam acquisition and track. Steering the beam is done electronically via 18, 3-bit diode phase shifters. A nineteenth phase shifter is not required as the center element serves as a reference only. Measured patterns and gain show that the array meets the stipulated performance specifications everywhere except at some low elevation angles.

Peng, Sheng Y.↗
NASA NTRS1989

Noncontact temperature pattern measuring device

Laser pyrometer techniques are utilized to accurately image a true temperature distribution on a given target without touching the target and without knowing the localized emissivity of the target. The pyrometer utilizes a very high definition laser beam and photodetector, both having a very narrow focus. The pyrometer is mounted in a mechanism designed to permit the pyrometer to be aimed and focused at precise localized points on the target surface. The pyrometer is swept over the surface area to be imaged, temperature measurements being taken at each point of focus.

Elleman, Daniel D.↗
NASA NTRS1993

Pinhole Calibrator For Particle-Sizing Instrument

Rotating-pinhole calibrator designed for use in calibrating and testing optical instrument measuring sizes of cloud droplets, dust particles, and other small particles suspended in flowing air. Easily attachable to particle-size-measuring instrument and suitable for both quick verification of calibration in field and detailed calibration studies in laboratory. Calibrator used to determine such operating parameters of instrument as optical collection angles, depth of field, profile of laser beam used to measure particles, and response to trajectory of particle. Also used to align instrument. Pinhole reused any number of times without risk of variation in diffraction pattern. Furthermore, size of pinhole chosen precisely and at will.

Hovenac, Edward↗
NASA NTRS1994

Experimental evaluation of shape memory alloy actuation technique in adaptive antenna design concepts

Creation of an antenna system that could autonomously adapt contours of reflecting surfaces to compensate for structural loads induced by a variable environment would maximize performance of space-based communication systems. Design of such a system requires the comprehensive development and integration of advanced actuator, sensor, and control technologies. As an initial step in this process, a test has been performed to assess the use of a shape memory alloy as a potential actuation technique. For this test, an existing, offset, cassegrain antenna system was retrofit with a subreflector equipped with shape memory alloy actuators for surface contour control. The impacts that the actuators had on both the subreflector contour and the antenna system patterns were measured. The results of this study indicate the potential for using shape memory alloy actuation techniques to adaptively control antenna performance; both variations in gain and beam steering capabilities were demonstrated. Future development effort is required to evolve this potential into a useful technology for satellite applications.

Kefauver, W. Neill↗
NASA NTRS1995

ACTS on-orbit multibeam antenna pattern measurements

The Advanced Communication Technology (ACTS) is a key to NASA's goal of developing high-risk, advanced communications technology using multiple frequency bands to support the nation's future communication needs. Using the multiple, dynamic hopping spot beams and advanced on board switching and processing systems, ACTS will open a new era in communications satellite technology. One of the key technologies to be validated as part of the ACTS program is the multibeam antenna (MBA) with rapidly reconfigurable hopping and fixed spot beams to serve users equipped with small-aperture terminals within the coverage areas. The MBA test program is designed to evaluate the on-orbit ACTS antenna performance. The main parameters measured are beam shape, beam center location and gain.

Acosta, R.↗
NASA NTRSDate not supplied

The PCM is Dead! Long Live O-PCM!

The ability to reconfigure the optical behavior of a device enables free-space applications ranging from imaging to sensing and signal control. Such optical devices can be compacted via meta-surfaces, patterned structures with feature sizes below the incident wavelength. Leveraging geometry in addition to material properties and CMOS fabrication techniques has allowed meta-surfaces for lenses, holograms, beam steerers and more. To incorporate multiple optical functions into one device, various methods of device control have been implemented, such as stretching of flexible substrates, tuning the refractive index of the comprising meta-atoms via the electro-optic or the thermo-optic effects, phase transition materials such as VO2 and more. Chalcogenide glasses used as optical phase change materials, such as Ge¬2Sb2Te5 (GST), have gained increased traction in the optics community for potential use in the near infrared (NIR) and mid infrared (MIR) bands, including the telecom bands. Various chalcogenides such as Sb2Se3, Sb2S3, Ge2Sb¬2Se5 and Ge2Sb2Se4Te (GSST) have been investigated due to their broad NIR or MIR transparency window and large changes in refractive index. In their amorphous phase, these materials usually display a lower refractive index and low absorption when compared to their crystalline state which display a higher refractive index and typically larger extinction coefficients. The amorphous-crystalline reversible switching can be done via fast melt-quenching thermal processes triggered by laser or electrical impulses, relying on a substrate as a heat sink. The potential of PCMs in photonic devices can be limited by intrinsic material limitations as well as by device fabrication issues. To explore the cyclability of GSST, a PCM with large refractive index contrast and on-chip electrothermal switching on a silicon-on-insulator platform has been done to analyze potential failure mechanisms from both a material and device perspective. A brief outline of the instrumentation and phase change contrast analysis is provided. Dewetting of the PCM, delamination of and damage in the PECVD SiNx protective layer, elemental migration in the PCM and optical contrast decay have been observed in cycled GSST devices. Guidelines for device performance improvement are proposed, and an improved design with larger endurance is shown in progress.

reconfigurable photonics↗
DOE OSTI2020

Multi-beam resin curing system and method for whole-volume additive manufacturing

A multi-beam volumetric resin curing system and method for whole-volume additive manufacturing of an object includes a bath containing a photosensitive resin, a light source for producing a light beam, and a spatial light modulator which produces a phase- or intensity-modulated light beam by impressing a phase profile or intensity profile of an image onto a light beam received from the light source. The system and method also include projection optics which then produces multiple sub-image beams from the modulated light beam which are projected to intersect each other in the photosensitive resin to cure select volumetric regions of the resin in a whole-volume three-dimensional pattern representing the object.

Shusteff, Maxim↗
DOE OSTI2023

Multi-beam resin curing system and method for whole-volume additive manufacturing

A multi-beam volumetric resin curing system and method for whole-volume additive manufacturing of an object includes a bath containing a photosensitive resin, a light source for producing a light beam, and a spatial light modulator which produces a phase- or intensity-modulated light beam by impressing a phase profile or intensity profile of an image onto a light beam received from the light source. The system and method also include projection optics which then produces multiple sub-image beams from the modulated light beam which are projected to intersect each other in the photosensitive resin to cure select volumetric regions of the resin in a whole-volume three-dimensional pattern representing the object.

Shusteff, Maxim↗
DOE OSTI2024

Field-Emission Properties of Vertically Aligned Carbon Nanotube Cathodes of Varying Geometries

This work characterizes the bulk emission properties of carbon nanotube (CNT) forest cathodes fabricated with various geometries. Geometries explored include dense nanotube forests of varying height grown on 5×5 mm silicon (Si) substrates and discrete, patterned CNT pillars fabricated using UV photolithography. Dense forests heights ranged from 526 μ m to 1.41 mm, with packing fraction for dense forest calculated to be 4e10 nanotubes/cm2 based on an average nanotube separation distance of 100 nm for fixed growth dense forests. Patterned sample micro pillar heights ranged from 47 to 393 μ m with pillar widths on tested samples ranging from 250 to 270 μ m . Properties explored include emission current, turn-on field, and emission current performance over time. A parallel plate electron beam diode with a 100- μ m A-K gap and an automated test apparatus were developed to provide a configurable experiment that provides accurate and repeatable measurements for dc, dc sweep, and timed performance testing. Operating voltages for the voltage sweeps spanned from 0 to −350 V. Furthermore, testing has shown evidence of a hysteresis effect on the emission current tied to the applied field history as well as shifting of the turn-on field magnitude throughout the testing period, suggesting a conditioning effect during use. Three separate emission regions in the I–V curves during sweep testing have also been observed. In the geometric study, dense forests and patterned samples were sweep tested up to a peak applied voltage of −250 V, with the taller samples generally performing better. Currents produced in the geometric study from the dense forest emitters ranged from 36.8 to 572.34 μ A , with current densities ranging from 15 to 2.29 mA/cm2. Currents produced from the patterned micropillar emitters ranged from 39.4 to 317.51 μ A , with current densities ranging from 67 to 3 mA/cm2. DC time testing s...

36 MATERIALS SCIENCE↗
DOE OSTI2020

Geometrically Tunable Beamed Light Emission from a Quantum‐Dot Ensemble Near a Gradient Metasurface

Abstract Optical metasurfaces have been widely investigated in recent years as a means to tailor the wavefronts of externally incident light for passive device applications. At the same time, their use in active optoelectronic devices such as light emitters is far less established. This work explores their ability to control the radiation properties of a nearby continuous ensemble of randomly oriented incoherent dipole sources via near‐field interactions. Specifically, a film of colloidal quantum dots is deposited on a plasmonic metasurface consisting of a 1D array of metallic nanoantennas on a metal film. The array is designed to introduce a linear phase profile upon reflection, and a bi‐periodic nanoparticle arrangement is introduced to ensure adequate sampling of the desired phase gradient. Highly directional radiation patterns are correspondingly obtained from the quantum dots at an enhanced emission rate. The underlying radiation mechanism involves the near‐field excitation of surface plasmon polaritons at the metal film, and their selective diffractive scattering by the metasurface into well‐collimated beams along predetermined geometrically tunable directions. These results underscore the distinctive ability of metasurfaces to control radiation properties directly at the source level, which is technologically significant for the continued miniaturization and large‐scale integration of optoelectronic devices.

Wang, Xiaowei↗
NASA NTRS1983

Directivity of planar array feeds for satellite reflector applications

Array-fed reflector antennas are used extensively in today's contour and multiple beam satellite antennas. To determine the directivity of these antennas theoretically, the total radiated power of the array feed must be accurately computed. In this paper, a closed-form expression for the radiated power is obtained for arrays with the well-known (cos theta q-type element patterns. The formulation is general, and takes into account polarization, nonsymmetric E- and H-plane element patterns, nonuniform element spacings and arbitrary complex excitation coefficients. Selective numerical data are presented to demonstrate the usefulness of this result. Comparisons are made with the available results obtained using direct numerical integration techniques, and with other available data based on less general formulations. Excellent agreement is observed for all cases. In particular, data are presented on the directivity of seven-element cluster feeds used in multiple beam designs, and an array feed for producing a contour beam covering the United States Eastern Time Zone (ETZ).

Rahmat-Samii, Y.↗
DOE OSTI2023

Arrays of glass wedges for multi-dimensional optical diagnostics

There is a common need in the advancement of optical diagnostic techniques to increase the dimensionality of measurements. For example, point measurements could be improved to multi-point, line, planar, volumetric, or time-resolved volumetric measurements. In this work, a unique optical element is presented to enable multi-dimensional measurements, namely, an array of glass wedges. A light source is passed through the wedges, and different portions of the illumination are refracted by different amounts depending on the glass wedge angle. Subsequent optics can be used to focus the light to multiple points, lines, or planes. Basic characterization of a glass wedge array is presented. Additional wedge-array configurations are discussed, including the use of a periodic intensity mask for multi-planar measurements via structured illumination. The utility of this optical element is briefly demonstrated in (a) multi-planar flame particulate measurements, (b) multi-point femtosecond-laser electronic excitation tagging for flow velocimetry, and (c) multi-line nitric oxide molecular tagging velocimetry in a hypersonic shock-tunnel. One significant advantage of this optical component is its compatibility with high-energy laser sources, which may be a limiting factor with other beam-splitting or beam-forming elements such as some diffractive optics. Additionally, an array of glass wedges is simple and easily customizable compared to other methods for forming multiple closely spaced illumination patterns. In conclusion, suggestions for further development and applications are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗