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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Embedded Coplanar Strips Traveling-Wave Photomixers

The electric field distribution in photomixers with electrodes deposited on the surface has already been calculated. It was shown that the strength of the electric field diminishes rapidly with depth. It was argued that the resulting reduction of the effective interaction volume of the device lowers the optical-to-heterodyne conversion. In this paper, we will present the results of our investigation on the influence of the electrode placement on the performance of photomixers. We have fabricated and measured traveling-wave photomixer devices which have both embedded and surface electrodes - the nominal spacing between the electrodes was 2 micrometers. Devices were made using either low-temperature-grown (LTG)-GaAs or ErAs:GaAs as the photoconductive material. The dark current, photocurrent, and radio frequency (RF) emission were measured at nominally 1 THz. The experimental data show a surprising difference in the behavior of ErAs:GaAs devices when the electrodes are embedded. A factor of two increase in RF radiation is observed for electric fields < 20 kV/cm. No such improvement was observed for the LTG-GaAs devices. We argue that the distinctive behavior of the two photoconductive materials is due to differences in the crystal structure - LTG-GaAs is isotropic, while ErAs:GaAs is uniaxial. We find that the carrier mobility in-plane (parallel) to the ErAs layers in the ErAs:GaAs superlattice is larger than orthogonal to these layers. The data indicate that carrier velocity overshoot is responsible for the excess radiation produced for the embedded electrode ErAs:GaAs devices.

Wyss, R. A.↗
NASA NTRS2015

On Possible Arc Inception on Low Voltage Solar Array

Recent analysis of spacecraft failures during the period of 1990-2013 demonstrated clearly that electrostatic discharges caused more than 8 percent of all registered failures and anomalies, and comprised the most costly losses (25 percent) for operating companies and agencies. The electrostatic discharges on spacecraft surfaces are the results of differential charging above some critical (threshold) voltages. The mechanisms of differential charging are well known, and various methods have been developed to prevent a generation of significant electric fields in areas of triple junctions. For example, low bus voltages in Low Earth Orbit plasma environment and slightly conducting layer over cover-glass (ITO) in Geosynchronous Orbit surroundings are believed to be quite reliable measures to prevent discharges on respective surfaces. In most cases, the vulnerable elements of spacecraft (solar arrays, diode boards, etc.) go through comprehensive ground tests in vacuum chambers. However, tests articles contain the miniscule fragments of spacecraft components such as 10-30 solar cells of many thousands deployed on spacecraft in orbit. This is one reason why manufacturing defects may not be revealed in ground tests but expose themselves in arcing on array surface in space. The other reason for ineffectiveness of discharge preventive measures is aging of all materials in harsh orbital environments. The expected life time of modern spacecraft varies within the range of five-fifteen years, and thermal cycling, radiation damages, and mechanical stresses can result in surface erosion on conductive layers and microscopic cracks in cover-glass sheets and adhesive films. These possible damages may cause significant increases in local electric field strengths and subsequent discharges. The primary discharges may or may not be detrimental to spacecraft operation, but they can produce the necessary conditions for sustained arcs initiation. Multiple measures were developed to prevent sustained discharges between adjacent strings, and many ground tests were performed to determine threshold parameters (voltage and current) for sustained arcs. And again, manufacturing defects and aging in space environments may result in considerable decrease of critical threshold parameters. This paper is devoted to the analysis of possible reasons behind arcing on spacecraft with low bus voltages.

low voltage solar array↗
NASA NTRS1974

Lunar electrical conductivity, permeability,and temperature from Apollo magnetometer experiments

Magnetometers were deployed at four Apollo sites on the moon to measure remanent and induced lunar magnetic fields. Measurements from this network of instruments were used to calculate the electrical conductivity, temperature, magnetic permeability, and iron abundance of the lunar interior. Global lunar fields due to eddy currents, induced in the lunar interior by magnetic transients, were analyzed to calculate and electrical conductivity profile for the moon, and those profiles were used to calculate the lunar temperature for an assumed lunar material of olivine. Simultaneous measurements by magnetometers on the lunar surface and in orbit around the moon were use to construct a whole-moon hysteresis curve, from which the global lunar magnetic permeability is determined. Total iron abundance (sum of iron in the ferromagnetic and paramagnetic states) was calculated for two assumed compositional models of the lunar interior. Other lunar models with an iron core and with a shallow iron-rich layer also discussed in light of the measured global lunar permeability. Simultaneous magnetic field and solar plasma pressure measurements show that the remanent fields at the Apollo 12 and 16 sites interact with, and are compressed by, the solar wind. Velocities and thicknesses of the earth's magnetopause and bow shock were also estimated from simultaneous magnetometer measurements.

Dyal, P.↗
NASA NTRS1974

Lunar interactions: Abstracts of papers presented at the Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon

Reviewed are the active mechanisms relating the moon to its environment and the linkage between these mechanisms and their records in the lunar sample and geophysical data. Topics: (1) large scale plasma interactions with the moon and non-magnetic planets; (2) ancient and present day lunar surface magnetic and electric fields; (3) dynamics and evolution of the lunar atmosphere; (4) evolution of the solar plasma; (5) lunar record of solar radiations; (6) non-meteoritic and meteoritic disturbance and transport of lunar surface materials; and (7) future lunar exploration.

Criswell, D. R.↗
NASA NTRS1980

Conduction through punctures in metal-backed dielectrics

A theoretical mechanism to explain the main features of experiments with punctured spacecraft-thermal-blanket materials is presented. The model is based on consideration of the electric fields developed about punctures; the focusing of primary electrons toward the punctures; the generation, migration, and cascade of secondary electrons along the surface; and the radiation induced conductivity characteristics of thin dielectric films. Qualitative predictions of the model agree with experiment results

Meulenberg, A.↗
NASA NTRS2007

Calligraphic Poling of Ferroelectric Material

Calligraphic poling is a technique for generating an arbitrary, possibly complex pattern of localized reversal in the direction of permanent polarization in a wafer of LiNbO3 or other ferroelectric material. The technique is so named because it involves a writing process in which a sharp electrode tip is moved across a surface of the wafer to expose the wafer to a polarizing electric field in the desired pattern. The technique is implemented by use of an apparatus, denoted a calligraphic poling machine (CPM), that includes the electrode and other components as described in more detail below.

Mohageg, Makan↗
NASA NTRS2011

Method for Predicting and Optimizing System Parameters for Electrospinning System

An electrospinning system using a spinneret and a counter electrode is first operated for a fixed amount of time at known system and operational parameters to generate a fiber mat having a measured fiber mat width associated therewith. Next, acceleration of the fiberizable material at the spinneret is modeled to determine values of mass, drag, and surface tension associated with the fiberizable material at the spinneret output. The model is then applied in an inversion process to generate predicted values of an electric charge at the spinneret output and an electric field between the spinneret and electrode required to fabricate a selected fiber mat design. The electric charge and electric field are indicative of design values for system and operational parameters needed to fabricate the selected fiber mat design.

Wincheski, Russell A.↗
DOE OSTI2023

Microstructure characterization of electric field assisted sintering (EFAS) sintered metallic and ceramic materials using local thermal diffusivity measurement

Electric Field Assisted Sintering (EFAS, also referred to as spark plasma sintering) is a powerful technology for the consolidation of powder materials. The high heating rate during the sintering process is critical for minimizing energy consumption, but it can also cause microstructure heterogeneities in sintered parts, such as spatially varied porosity. The examination of localized porosity usually requires the use of a scanning electron microscope with a carefully prepared surface. In this paper, photothermal radiometry is used to measure local thermal diffusivity and extract localized porosity of EFAS-sintered parts by using a percolation-threshold model. Applying this approach, we identified the radial position-dependent porosity variation in EFAS parts, which is likely formed due to the large temperature gradient during the sintering process. This approach has a unique advantage because it can measure samples with minimal or no surface preparation, enabling the possibility of in situ characterization in EFAS with proper system modification. Necessary modifications on the measurement approach for EFAS deployment and in situ characterization are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High efficiency hexagonal boron nitride neutron detectors with 1 cm 2 detection areas

We report the realization of 1 cm 2 hexagonal boron nitride (h-BN) thermal neutron detectors with an unprecedented detection efficiency of 59%. This was achieved through improvements in material quality, as reflected in a sixfold enhancement in the electron mobility and lifetime product and a threefold reduction in the surface recombination field, which resulted in a higher detection efficiency at a lower applied electric field over that of a previous state-of-the-art lateral detector with a detection area of 30 mm 2 . The attainment of 1 cm 2 h-BN neutron detectors capable of retaining a high detection efficiency represents a significant milestone toward the practical applications of h-BN detectors.

42 ENGINEERING↗
NASA NTRS2015

Coarsening Dynamics and Marangoni Effects in Thin Liquid Crystal Bubbles in Microgravity

The Observation and Analysis of Smectic Islands in Space (OASIS) flight hardware was successfully launched on SpaceX-6 on April 15, 2015 and was operated in the Microgravity Science Glovebox (MSG) on board the International Space Station (ISS). The OASIS project comprises a series of experiments that probe the interfacial and hydrodynamic behavior of spherical-bubble freely suspended liquid crystal (FSLC) membranes in space. These are the thinnest known stable condensed phase structures, making them ideal for studies of two-dimensional (2D) coarsening dynamics and thermocapillary phenomena in microgravity. The OASIS experimental investigation was carried out using four different smectic A and C liquid crystal materials in four separate sample chambers housed inside the MSG. In this report, we present the behavior of collective dynamics on 2D bubble surface, including the equilibrium spatial organization and interaction of islands in electric fields and temperature gradients, and the diffusion and coalescence-driven coarsening dynamics of island emulsions in microgravity. We have observed spontaneous bubble thickening behavior caused by gradients between the bubble-blowing needle and ambient air temperatures. A uniform, thicker band forms during coarsening as a result of non-uniform heating by the LED illumination panels. These are proposed to be a result of Marangoni convection on the bubble surface.

microgravity↗
DOE OSTI2022

Theory of optical axion electrodynamics and application to the Kerr effect in topological antiferromagnets

Abstract Emergent axion electrodynamics in magneto-electric media is expected to provide novel ways to detect and control material properties with electromagnetic fields. However, despite being studied intensively for over a decade, its theoretical understanding remains mostly confined to the static limit. Here, we introduce a theory of axion electrodynamics at general frequencies. We define a proper optical axion magneto-electric coupling through its relation to optical surface Hall conductivity and provide ways to calculate it in lattice systems. By employing our formulas, we show that axion electrodynamics can lead to a significant Kerr effect in thin-film antiferromagnets at wavelengths that are seemingly too long to resolve the spatial modulation of magnetism. We identify the wavelength scale above which the Kerr effect is suppressed. Our theory is particularly relevant to materials like MnBi 2 Te 4 , a topological antiferromagnet whose magneto-electric response is shown here to be dominated by the axion contribution even at optical frequencies.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Electronic materials high-T(sub c) superconductivity polymers and composites structural materials surface science and catalysts industry participation

The fifth year of the Center for Advanced Materials was marked primarily by the significant scientific accomplishments of the research programs. The Electronics Materials program continued its work on the growth and characterization of gallium arsenide crystals, and the development of theories to understand the nature and distribution of defects in the crystals. The High Tc Superconductivity Program continued to make significant contributions to the field in theoretical and experimental work on both bulk materials and thin films and devices. The Ceramic Processing group developed a new technique for cladding YBCO superconductors for high current applications in work with the Electric Power Research Institute. The Polymers and Composites program published a number of important studies involving atomistic simulations of polymer surfaces with excellent correlations to experimental results. The new Enzymatic Synthesis of Materials project produced its first fluorinated polymers and successfully began engineering enzymes designed for materials synthesis. The structural Materials Program continued work on novel alloys, development of processing methods for advanced ceramics, and characterization of mechanical properties of these materials, including the newly documented characterization of cyclic fatigue crack propagation behavior in toughened ceramics. Finally, the Surface Science and Catalysis program made significant contributions to the understanding of microporous catalysts and the nature of surface structures and interface compounds.

Source record↗
NASA NTRS1989

Electromagnetic properties of material coated surfaces

The electromagnetic properties of material coated conducting surfaces were investigated. The coating geometries consist of uniform layers over a planar surface, irregularly shaped formations near edges and randomly positioned, electrically small, irregularly shaped formations over a surface. Techniques to measure the scattered field and constitutive parameters from these geometries were studied. The significance of the scattered field from these geometries warrants further study.

Beard, L.↗
DOE OSTI2021

Exceeding 200 ns Lifetimes in Polycrystalline CdTe Solar Cells

CdTe photovoltaics has achieved one of the lowest levelized costs of electricity among all energy sources. However, for decades, carrier lifetimes have been inferior to those of other prevalent solar cell materials. This quality has inhibited common methods to improve solar cell efficiency such as back-surface fields, electron reflectors, or bifacial solar cells. In this work, a significant increase in carrier lifetime to values exceeding 200 ns in fully functional CdTe solar cells is demonstrated. The increased lifetime is achieved by large CdSeTe grains at the absorber/emitter interface, intragrain passivation in the absorber layer, and chemical passivation by forming nanoscale oxidized tellurium species at the transparent conducting oxide interface. The carrier lifetime is correlated to the open-circuit voltage and enables paths for back-surface manipulation and novel cell architectures to further improve CdTe photovoltaic performance.

14 SOLAR ENERGY↗
DOE OSTI2022

Effect of Semiconducting Layer on Cable Insulation Damage Detection Using Surface Wave Reflectometry

This paper presents a study of the effect of the semiconducting layer present in medium and high voltage cables on surface wave propagation and its feasibility in detecting insulation damage on cables. Simulation studies were conducted using Ansys High Frequency Structure Simulator (HFSS). It was observed that attenuation increased with thicker semiconducting layer and higher conductivity of the layer. For instance, on a 24.4 mm diameter power cable, the electric field strength associated with a 1 GHz surface wave declines with distance and fades away after 30 m when a 2 mm thick semiconducting layer is present. More results as a function of semiconducting layer thickness, material conductivity and permittivity, distance of a damaged section, etc. will be presented.

reflectometry, unshielded power cable, semiconduct↗
NASA NTRS1995

Advanced Modeling of Micromirror Devices

The flexure-beam micromirror device (FBMD) is a phase only piston style spatial light modulator demonstrating properties which can be used for phase adaptive corrective optics. This paper presents a complete study of a square FBMD, from advanced model development through final device testing and model verification. The model relates the electrical and mechanical properties of the device by equating the electrostatic force of a parallel-plate capacitor with the counter-acting spring force of the device's support flexures. The capacitor solution is derived via the Schwartz-Christoffel transformation such that the final solution accounts for non-ideal electric fields. The complete model describes the behavior of any piston-style device, given its design geometry and material properties. It includes operational parameters such as drive frequency and temperature, as well as fringing effects, mirror surface deformations, and cross-talk from neighboring devices. The steps taken to develop this model can be applied to other micromirrors, such as the cantilever and torsion-beam designs, to produce an advanced model for any given device. The micromirror devices studied in this paper were commercially fabricated in a surface micromachining process. A microscope-based laser interferometer is used to test the device in which a beam reflected from the device modulates a fixed reference beam. The mirror displacement is determined from the relative phase which generates a continuous set of data for each selected position on the mirror surface. Plots of this data describe the localized deflection as a function of drive voltage.

Michalicek, M. Adrian↗
NASA NTRS1998

Directional Electrostatic Accretion Process Employing Acoustic Droplet Formation

The present invention is directed to an apparatus for manufacturing a free standing solid metal part. In the present invention, metal droplets are ejected in a nozzleless fashion from a free surface pool of molten metal by applying focused acoustic radiation pressure. The acoustic radiation pressure is produced by high intensity acoustic tone bursts emitted from an acoustic source positioned at the bottom of the pool which directs the acoustic energy at the pool surface. The metal droplets are electrostatically charged so their trajectory can be controlled by electric fields that guide the droplets to predetermined points on a target. The droplets impinge upon the target and solidify with the target material. The accretion of the electrostatically directed solidified droplets forms the free standing metal part.

Oeftering, Richard↗
NASA NTRS2012

Radiation Shielding System Using a Composite of Carbon Nanotubes Loaded with Electropolymers

Single-wall carbon nanotubes (SWCNTs) coated with a hydrogen-rich, electrically conducting polymer such as polyethylene, receive and dissipate a portion of incoming radiation pulse energy to electrical signals that are transmitted along the CNT axes, and are received at energy-dissipating terminals. In this innovation, an array of highly aligned nanowires is grown using a strong electric field or another suitable orientation procedure. Polyethylene (PE), polymethymlethacrylate (PMMA), or other electrically conducting polymer is spin-coated onto the SWCNTs with an average thickness of a few hundred nanometers to a few tenths of micrometers to form a PE/SWCNT composite. Alternatively, the polymer is spin-coated onto the nanowire array or an anodized alumina membrane (AAM) to form a PE/metal core shell structure, or PE can be electropolymerized using the SWCNTs or the metal nanowires as an electrode to form a PE/SWCNT core shell structure. The core shell structures can be extruded as anisotropic fibers. A monomer can be polymerized in the presence of SWCNTs to form highly cross-linked PE/SWCNT films. Alternatively, Pb colloid solution can be impregnated into a three-dimensional PE/SWCNT nanostructure to form a PW/SWCNT/Pb composite structure. A face-centered cubic (FCC) arrangement provides up to 12 interconnection channels connected to each core, with transverse channel dimensions up to 20 nm, with adequate mechanical compressive strength, and with an associated electrical conductivity of around 3 Seimens/cm for currents ranging from 0.01 to 10 mA. This threedimensional nanostructure is used as a host material to house appropriate radiation shielding material such as hydrogen- rich polymer/CNT structures, metal nanoparticles, and nanowires. Thicknesses of this material required to attenuate 10 percent, 50 percent, and 90 percent of an incident beam (gamma, X-ray, ultraviolet, neutron, proton, and electron) at energies in the range of 0 440 MeV are being determined, for example, by measuring fluence rate reduction. For example, a radiation field arrives first at an exposed surface of the innovation and produces an associated first electric field within the metal-like fingers of the three-dimensional nanostructure. This field is intensified near the exposed tips of the fingers, and this intensified field generates an intensified second electric field near the adjacent exposed tips of the coated CNSs. This generates an associated electrical current in the CNSs, and the associated electropolymer coating. The current is received by the second substrate transport component and is transported to the dissipation mechanism located contiguously to the second substrate.

McKay, Chris↗