Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Dielectric materials”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Damage Detection and Electrical Performance Impact of Flat-Flexible Circuits

Flat-flexible circuits or ‘flex circuits’ have varied applications in electronics and in explosive detonation systems. They pose advantages over conventional coaxial cables in their ability to fit into small mechanical envelopes and routings. A typical flex circuit is composed of a laminated assembly of multiple layers of conductor and dielectric materials. Copper, because of its high electrical conductivity, is one of the primary materials used in flex circuit conductors. The conductor must maintain structural integrity and electrical continuity when the flexible circuit is bent during processing or to fit an application envelope. Under some strain conditions a cable may have degraded electrical performance even though visible damage may not be evident. Dislocation density can increase by mechanisms such as dislocation forest hardening, where gliding dislocations in primary slip planes get pinned at obstacles and form Frank-Read sources. Dislocation density increases within the conductor layers may impact electrical resistivity but would not necessarily result in visible mechanical failure. In some detonation applications, such as for building implosion for demolition, the time for signal transmission and voltage used for firing detonators can be critical. If the resistance in a single flex cable within a building demolition array is too high, the resultant demolition shape may be asymmetric, leading to unplanned damage to nearby structures and potential hazards to public safety. This study will apply non-destructive evaluation techniques to evaluate the detectability of damage accumulation in flat, flexible copper-conductor cables and discuss potential implications to their practical use.

42 ENGINEERING↗
DOE OSTI2022

Topology Optimization of Manufacturable Photonic Crystals With Complete Bandgaps [Dissertation]

Periodic structures consisting of dielectric material, i.e. photonic crystals, are capable of prohibiting electromagnetic waves within frequency ranges referred to as bandgaps. This principle was first demonstrated with alternating slabs of material and later demonstrated with three-dimensional (3D) structures capable of reflecting waves from any incident angle. A number of potential applications for photonic bandgap structures exist, including loss-less sharp corner waveguides, fiber optics, and radome design. Further, many optical devices could benefit from the perfect-mirror behavior of photonic crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Control of light-matter interactions in hybrid structured environments with novel nanomaterials of different dimensionalities

The project calls for exploration of individual nanomaterials and the ability to fabricate functional structures without degrading the properties of components. The rich photophysics of novel semiconductors like transition metal dichalcogenides (TMDs), lead halide perovskites (LHPs) and nanocrystal quantum dots (NQDs) can be gainfully exploited in integrated photonic structures alongside conventional semiconducting and dielectric materials. Realization of the prospects of such hybrid structures crucially depends on the ability to fabricate these “designer” assemblies while preserving and enhancing the optoelectronic properties of individual components. We study emission properties of these materials at both bulk and single particles levels to elucidate their intrinsic photophysical properties in order to minimize energy losses and facilitate their judicious integration via control of energy/charge flows and photon-exciton interconversions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Evaluation of Oxygen Consumption as a Sensitive Measure of Electrical Cable Polymer Insulation Degradation

Polymers used as dielectric materials in nuclear grade electrical cables, such as cross-linked polyethylene (XLPE) and ethylene-propylene rubber (EPR), are long-lived and durable. Estimating the decades-long useful service life of polymers experimentally in a feasible timeframe of weeks or months requires greatly accelerated aging in the laboratory at elevated temperatures and/or gamma dose rates. Many limitations of accelerated aging, such as due to artefacts of the process including diffusion limited oxidation and dose rate effects, have been identified that can make accurate lifetime prediction at service conditions challenging. This can be due to differences in degradation mechanisms between rapid and extended aging or to the presence of induction periods during which early aging is undetectable using common metrics of polymer insulation characterization such as tensile elongation at break. Conceptually, an ideal measure of aging would track clearly and predictably with material changes throughout the lifecycle of the evolving material state from early aging through end of useful life. With such a metric accelerated aging could be performed at much milder conditions, conditions closer to those found in long term service, and end of life calculated from the early data. Oxygen consumption has previously been proposed as a sensitive measure of insulation polymer oxidation that might meet such desirable characteristics. In this work, nuclear cable insulation samples of the two most common types, XLPE and EPR, from two of the most sourced manufacturers, RSCC and The Okonite Company, were subjected to gamma irradiation at dose rates of 100, 200, and 300 Gy/hr for up to 42 days at 26°C. The aged samples were used to evaluate oxygen consumption as a sensitive measure of aging for these materials and these conditions. For comparison and validation, the aged samples were also characterized using the more conventional tests of mass change, density, carbonyl index, and yellowness index. For both materials, oxygen consumption during irradiation was found to track consistently with applied dose—oxygen consumption rate was linear with time. Mass change and carbonyl index were also clearly proportional to exposure dose. Yellowness index, a surface sensitive measure, was observed to increase linearly with dose at low exposure levels before plateauing. Sample density was not observed to change under the conditions explored. Oxygen consumption was found to be a particularly sensitive metric to measure the degradation of polymeric cable insulation exposed to radiation. Oxygen consumption was compared to Arrhenius and time-temperature-superposition methods for activation energy calculation using literature date and found to be a useful and viable alternative for lifetime prediction. The techniques developed in this work are anticipated to be valuable in the estimation of insulation aging rates under mild conditions approaching service conditions. Direction comparison of useful life prediction by oxygen consumption with prediction via Arrhenius methodology for thermal aging and existing methods for radiation and combined thermal/radiation aging would serve to further validate this promising approach and refine our understanding of material-specific aging rates.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Vibration Analysis of a Unimorph Nanobeam with a Dielectric Layer of Both Flexoelectricity and Piezoelectricity

In this study, for the first time, free and forced vibrational responses of a unimorph nanobeam consisting of a functionally graded base, along with a dielectric layer of both piezoelectricity and flexoelectricity, is investigated based on paradox-free local/nonlocal elasticity. The formulation and boundary conditions are attained by utilizing the energy method Hamilton’s principle. In order to set a comparison, the formulation of a model in the framework of differential nonlocal is first presented. An effective implementation of the generalized differential quadrature method (GDQM) is then utilized to solve higher-order partial differential equations. This method can be utilized to solve the complex equations whose analytic results are quite difficult to obtain. Lastly, the impact of various parameters is studied to characterize the vibrational behavior of the system. Additionally, the major impact of flexoelectricity compared to piezoelectricity on a small scale is exhibited. The results show that small-scale flexoelectricity, rather than piezoelectricity, is dominant in electromechanical coupling. One of the results that can be mentioned is that the beams with higher nonlocality have the higher voltage and displacement under the same excitation amplitude. The findings can be helpful for further theoretical as well as experimental studies in which dielectric material is used in smart structures.

36 MATERIALS SCIENCE↗
NASA NTRS1963

A THEORETICAL AND EXPERIMENTAL INVESTIGATION OF FLUSH MOUNTING CONFIGURATIONS FOR LOG PERIODIC STRUCTURES

Many types of log periodic structures have been described in the literature; but, as far as is known, flush-mounted log periodic antennas have not been studied heretofore. The purpose of this study is to investigate, primarily by experimental methods, the input impedance and radiation characteristics of a particular type of log periodic antenna when flush-mounted over a suitable cavity or recess in a conducting surface. The particular type of log periodic antenna chosen for use in the investigation is referred to as a monopole-tooth antenna and is described in detail in Part II of the report. A suitable cavity over which the monopole-tooth antenna may be mounted is described in Part III, and experimentally determined characteristics of the antenna-cavity assembly are presented in Part IV. The first objective of the study was to obtain an optimum or nearoptimum design of the antenna-cavity assembly. This objective has been reached within the limits of the experimental approach, and the results obtained are summarized in Part V of the report. A second objective, which will be reported upon at a future date, is to establish optimum design criteria and performance characteristics of the antenna-cavity assembly when the cavity is filled with low-loss dielectric material.

RADIATION FUNCTION↗
NASA NTRS1971

Development of integral covers on solar cells

The electron-beam technique for evaporating a dielectric material onto solar cells is investigated. A process has been developed which will provide a highly transparent, low stress, 2 mil thick cover capable of withstanding conventional space type qualification tests including humidity, thermal shock, and thermal cycling. The covers have demonstrated the ability to withstand 10 to the 15th power 1 MeV electrons and UV irradiation with minor darkening. Investigation of the cell AR coating has produced a space qualifiable titanium oxide coating which will give an additional 6% current output over similar silicon oxide coated cells when covered by glass.

Stella, P.↗
NASA NTRS1971

A thermal conductivity cell for small powdered samples.

A thermal conductivity cell is described for making measurements of the thermal conductivity and thermal diffusivity of small samples of powdered dielectric materials. The principle used is that of the line heat source. A novel way is described for applying this method so that much smaller samples than normal may be tested. This size requirement is necessary for investigations involving limited samples as does the Lunar Science Program. The method is checked by measuring the conductivity of standard samples and comparing the results with those found in the literature.

Cremers, C. J.↗
NASA NTRS1973

Single grid accelerator for an ion thrustor

A single grid accelerator system for an ion thrustor is discussed. A layer of dielectric material is interposed between this metal grid and the chamber containing an ionized propellant for protecting the grid against sputtering erosion.

Margosian, P. M.↗
NASA NTRS1972

The particle track record of the lunar surface.

Information about lunar surface history revealed by fossil particle tracks is summarized. Such tracks are the result of damage left in dielectric materials by highly ionizing charged particles including heavy solar and galactic cosmic ray nuclei, heavy nuclei recoiling from cosmic ray induced spallation reactions, and induced- and spontaneous-fission fragments. From the distribution of cosmic ray and spallation tracks in the lunar rock, surface residence times of 1 to 30 million years and rock erosion rates of 1 to 10 A/yr have been determined. Particle tracks also record surface orientation and depth history of the rocks and contain information about ancient solar activity.

Comstock, G. M.↗
NASA NTRS1972

Integrally covered silicon solar cells.

The electron-beam technique for evaporating dielectric materials onto solar cells has been examined and developed. Titanium oxide cell antireflection coatings have been obtained which compare to silicon monoxide in environmental capabilities and which provide 3 to 4% improvement over SiO for glass covered cells. Evaporation processes have been obtained which provide a 50 to 100 micromil thick transparent (0.5 to 1.0% absorption per mil), low stressed integral cover capable of surviving space type qualification testing. Irradiation with 10 to the 15th power 1-MeV electrons shows 2% darkening, and long term UV irradiation incurs approximately 1.3% cover darkening for 50 micromil thick covers.

Stella, P. M.↗
NASA NTRS1973

Thermal shielding by subliming volume reflectors in convective and intense radiative environments.

The behavior of dielectric materials having densely packed internal scattering centers subject to extreme convective and radiative environments is analyzed. Experiments have shown that these materials act as volume reflectors of incident radiation even when the exposed surface is being eroded by thermochemical ablation. The analysis was applied to interpret experiments of subliming Teflon models exposed to combined radiative and convective fluxes up to 1.7 kW/sq cm for several seconds. Results show that, although the exposed surface receded at an apparently steady rate, the internal temperature climbed continually, due to internal absorption of radiation and would have caused failure internally if the test duration were extended a few seconds. Thus, performance is time-limited by the internal absorption coefficient. Results were obtained for larger configurations and other materials. Typically, Teflon shells may withstand radiant fluxes up to 20 kW/sq cm for about 5 sec and fritted quartz up to 50 kW/sq cm for about 8 sec (corresponding to the Jupiter entry).

Howe, J. T.↗