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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Increased Accuracy in the Measurement of the Dielectric Constant of Seawater at 1.413 GHz

This paper describes the latest results for the measurements of the dielectric constant at 1.413 GHz by using a resonant cavity technique. The purpose of these measurements is to develop an accurate relationship for the dependence of the dielectric constant of sea water on temperature and salinity which is needed by the Aquarius inversion algorithm to retrieve salinity. Aquarius is the major instrument on the Aquarius/SAC-D observatory, a NASA/CONAE satellite mission launched in June of20ll with the primary mission of measuring global sea surface salinity to an accuracy of 0.2 psu. Aquarius measures salinity with a 1.413 GHz radiometer and uses a scatterometer to compensate for the effects of surface roughness. The core part of the seawater dielectric constant measurement system is a brass microwave cavity that is resonant at 1.413 GHz. The seawater is introduced into the cavity through a capillary glass tube having an inner diameter of 0.1 mm. The change of resonance frequency and the cavity Q value are used to determine the real and imaginary parts of the dielectric constant of seawater introduced into the thin tube. Measurements are automated with the help of software developed at the George Washington University. In this talk, new results from measurements made since September 2010 will be presented for salinities 30, 35 and 38 psu with a temperature range of O C to 350 C in intervals of 5 C. These measurements are more accurate than earlier measurements made in 2008 because of a new method for measuring the calibration constant using methanol. In addition, the variance of repeated seawater measurements has been reduced by letting the system stabilize overnight between temperature changes. The new results are compared to the Kline Swift and Meissner Wentz model functions. The importance of an accurate model function will be illustrated by using these model functions to invert the Aquarius brightness temperature to get the salinity values. The salinity values will be compared to co-located in situ data collected by Argo buoys.

Zhou, Y.↗
NASA NTRS2012

New Dielectric Measurement Data to Determine the Permittivity of Seawater at 1.4313 Hz

This paper describes the new measurements - made in 2010-2011 - of the dielectric constant of seawater at 1.413 GHz using a resonant cavity technique. The purpose of these measurements is to develop an accurate relationship concerning the dependence of the dielectric constant of seawater on temperature and salinity for use by the Aquarius inversion algorithm. Aquarius is a NASA/CONAE satellite mission launched in June of 2011 with the primary mission of measuring global sea surface salinity with a 1.413 GHz radiometer to an accuracy of 0.2 psu. A brass microwave cavity resonant at 1.413 GHz has been used to measure the dielectric constant of seawater. The seawater is introduced into the cavity through a capillary glass tube having an inner diameter of 0.1 mm. The change of resonant frequency and the cavity Q value are used to determine the real and imaginary parts of the dielectric constant of seawater. Measurements are automated with Visual Basic software developed at the George Washington University. In this paper, new results from measurements made since September 2010 will be presented for salinities of 30, 35 and 38 psu with a temperature range of 0 C to 35 C in intervals of 5 C. These measurements are more accurate than earlier measurements made in 2008. The new results will be compared to the Klein-Swift (KS) and Meissner-Wentz (MW) model functions. The importance of an accurate model function will be illustrated by using these model functions to invert the Aquarius brightness temperature to retrieve the salinity values. The salinity values will be compared to co-located in situ data collected by Argo buoys.

Lang, R.↗
NASA NTRS2014

Negative Dielectric Constant Material Based on Ion Conducting Materials

Metamaterials or artificial negative index materials (NIMs) have generated great attention due to their unique and exotic electromagnetic properties. One exemplary negative dielectric constant material, which is an essential key for creating the NIMs, was developed by doping ions into a polymer, a protonated poly(benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at megahertz (MHz) frequencies due to its reduced plasma frequency and an induction effect. The magnitude of the negative dielectric constant and the resonance frequency were tunable by doping concentration. The highly doped PBI showed larger absolute magnitude of negative dielectric constant at just above its resonance frequency than the less doped PBI.

Gordon, Keith L.↗
NASA NTRS2016

Accurate Measurements of the Dielectric Constant of Seawater at L Band

This paper describes measurements of the dielectric constant of seawater at a frequency of 1.413 GHz, the center of the protected band (i.e., passive use only) used in the measurement of sea surface salinity from space. The objective of the measurements is to accurately determine the complex dielectric constant of seawater as a function of salinity and temperature. A resonant cylindrical microwave cavity in transmission mode has been employed to make the measurements. The measurements are made using standard seawater at salinities of 30, 33, 35, and 38 practical salinity units over a range of temperatures from 0 degree C to 35 degree C in 5 degree C intervals. Repeated measurements have been made at each temperature and salinity. Mean values and standard deviations are then computed. The total error budget indicates that the real and imaginary parts of the dielectric constant have a combined standard uncertainty of about 0.3 over the range of salinities and temperatures considered. The measurements are compared with the dielectric constants obtained from the model functions of Klein and Swift and those of Meissner and Wentz. The biggest differences occur at low and high temperatures.

Measurements↗
NASA NTRS2016

Submillimeter and Far-Infrared Dielectric Properties of Thin Films

The complex dielectric function enables the study of a material's refractive and absorptive properties and provides information on a material's potential for practical application. Commonly employed line shape profile functions from the literature are briefly surveyed and their suitability for representation of dielectric material properties are discussed. An analysis approach to derive a material's complex dielectric function from observed transmittance spectra in the far-infrared and submillimeter regimes is presented. The underlying model employed satisfies the requirements set by the Kramers-Kronig relations. The dielectric function parameters derived from this approach typically reproduce the observed transmittance spectra with an accuracy of less than 4%.

Cataldo, Giuseppe↗
NASA NTRS2017

Negative Dielectric Constant Material Based on Ion Conducting Materials

Metamaterials or artificial negative index materials (NIMs) have generated great attention due to their unique and exotic electromagnetic properties. One exemplary negative dielectric constant material, which is an essential key for creating the NIMs, was developed by doping ions into a polymer, a protonated poly (benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at megahertz (MHz) frequencies due to its reduced plasma frequency and an induction effect. The magnitude of the negative dielectric constant and the resonance frequency were tunable by doping concentration. The highly doped PBI showed larger absolute magnitude of negative dielectric constant at just above its resonance frequency than the less doped PBI.

Gordon, Keith L.↗
NASA NTRS2017

Packaging Technology for Dielectric-Coating-Less Heavy Ion Radiation Testing of High-Voltage (HV) Electronic Parts

Testing high voltage (HV) electronic parts (greater than 300 V) for sudden event effects (SEE) caused by cosmic rays in the space environment, consisting of energetic heavy-ions, and neutron radiation in the upper atmosphere is a crucial step towards using these parts in spacecraft and aircraft. Due to the nature of cosmic radiation and neutrons, electronic parts are tested for SEE without any packaging and/or shielding over the top of the device. In the case of commercial HV parts, the top of the packaging is etched off and then a thin dielectric coating is placed over the part in order to avoid electrical arcing between the device surface and wire bonds and other components. Even though the effects of the thin dielectric layer on SEE testing can be accounted for, the dielectric layer significantly hinders post testing failure analysis. Replicating the test capability of state-of-the-art packaging while eliminating the need for post radiation test processing of the die surface (that obscures failure analysis) is the goal. To that end, a new packaging concept for HV parts has been developed that requires no dielectric coating over the part. Testing of prototype packages used with Schottky diodes (rated at 1200V) has shown no electrical arcing during testing and leakage currents during reverse bias testing are within the manufactures specifications.

High Voltage↗
NASA NTRS2016

A FDTD Solution of Scattering of Laser Beam with Orbital Angular Momentum by Dielectric Particles: Far-Field Characteristics

Electromagnetic (EM) beams with orbital angular momentum (OAM) may have great potential applications in communication technology and in remote sensing of the Earth-atmosphere system and outer planets. Study of their interaction with optical lenses and dielectric or metallic objects, or scattering of them by particles in the Earth-atmosphere system, is a necessary step to explore the advantage of the OAM EM beams. In this study, the 3-dimensional (3D) scattered-field (SF) finite-difference time domain (FDTD) technique with the convolutional perfectly matched layer (CPML) absorbing boundary conditions (ABC) is applied to calculate the scattering of the purely azimuthal (the radial mode number is assumed to be zero) Laguerre–Gaussian (LG) beams with the OAM by dielectric particles. We found that for OAM beam׳s interaction with dielectric particles, the forward-scattering peak in the conventional phase function (P11) disappears, and light scattering peak occurs at a scattering angle of ~15° to 45°. The disappearance of forward-scattering peak means that, in laser communications most of the particle-scattered noise cannot enter the receiver, thus the received light is optimally the original OAM-encoded signal. This feature of the OAM beam also implies that in lidar remote sensing of the atmospheric particulates, most of the multiple-scattering energy will be off lidar sensors, and this may result in an accurate profiling of particle layers in the atmosphere or in the oceans by lidar, or even in the ground when a ground penetration radar (GPR) with the OAM is applied. This far-field characteristics of the scattered OAM light also imply that the optical theorem, which is derived from plane-parallel wave scattering case and relates the forward scattering amplitude to the total cross section of the scatterer, is invalid for the scattering of OAM beams by dielectric particles.

Electromagnetic beams↗
NASA NTRS2019

Experimental Study on Mitigation of Lifetime-Limiting Dielectric Cracking in Extreme Temperature 4H-SiC JFET Integrated Circuits

While NASA Glenn Research Center's "Generation 10" 4H-SiC Junction Field Effect Transistor (JFET) integrated circuits (ICs) have uniquely demonstrated 500 °C electrical operation for durations of over a year, this experimental work has also revealed that physical cracking of chip dielectric passivation layers ultimately limits extreme-environment operating lifetime [1-3]. The prevention of such dielectric passivation cracks should therefore improve IC high temperature durability and yield, leading to more beneficial technology adoption into aerospace, automotive, and energy systems. This report describes Generation 10.2, 11.1, and 11.2 die tested under unbiased and unpackaged accelerated age testing at 500 °C, 600 °C, 720 °C, and 800 °C in air-atmosphere ovens for 100- and 200-hour duration. Additional samples were separately subjected to 10 thermal cycles between the same high temperatures (with 10-hour high-temperature soak each cycle) and 50 °C. It is shown that having two stoichiometric Si3N4 layers in the interconnect dielectric stack substantially decreases the amount of dielectric cracking observed following these oven tests.

Spry, D. J.↗
NASA NTRS2020

SCoBi Multilayer: A Signals of Opportunity Reflectometry Model for Multilayer Dielectric Reflections

A multilayer module is incorporated into the Signals of Opportunity (SoOp) Coherent Bistatic Scattering model (SCoBi) for determining the reflections and propagation of electric fields within a series of multilayer dielectric slabs. This module can be used in conjunction with other SCoBi components to simulate complex, bistatic simulation schemes that include features such as surface roughness, vegetation, antenna effects, and multilayer soil moisture interactions on reflected signals. This paper introduces the physics underlying the multilayer module and utilizes it to perform a simulation study of the response of SoOp-R measurements with respect to subsurface soil moisture parameters. For a frequency range of 100–2400 MHz, it is seen that the SoOp-R response to a single dielectric slab is mostly frequency insensitive; however, the SoOp-R response to multilayer dielectric slabs will vary between frequencies. The relationship between SoOp-R reflectivity and the contributing depth is visualized, and the results show that SoOp-R measurements can display sensitivity to soil moisture below the penetration depth. By simulation of simple soil moisture profiles with different wetting and drying gradients, the dielectric contrast between layers is shown to be the greatest contributing factor to subsurface soil moisture sensitivity. Overall, it is observed that different frequencies can sense different areas of a soil moisture profile, and this behavior can enable subsurface soil moisture data products from SoOp-R observations.

Dylan Boyd↗
NASA NTRS2024

Dielectric Permittivity Measurements of Geologic Samples at Venus Surface Temperatures

Synthetic-aperture radar (SAR) and radar sounding are two powerful remote sensing techniques used to examine the surface and subsurface of planets. Their value is critical in the case of Venus due to this planet’s global and visually opaque cloud layer. The recently selected VERITAS and EnVision orbital missions, slated to study the planet in the early 2030’s, employ radar instruments to image the surface (VERITAS and EnVision) and probe the subsurface (EnVision). For both techniques, the complex dielectric permittivity of the surface and subsurface materials control radar backscatter intensity and penetration depth. Since the 1970’s, many studies have characterized the dielectric permittivity of geologic materials collected both on Earth and on the Moon to constrain the radar reflectivity and transparency at a variety of radar frequencies [e.g., 1]. Two consistent findings from those studies are that complex permittivity depends on both the density (or porosity) and the composition of the material. Denser materials and more metal-rich compositions tend to have higher permittivity values and to incur greater propagation path loss. Water content also elevates permittivity of otherwise dry rocks/soils/regolith [e.g., 2]. However, permittivity is independent of frequency for the 0.5-18 GHz range, within which SAR imaging commonly lies. The one aspect poorly explored thus far is the effect of elevated temperatures on dielectric permittivity. Previous work suggests that increased lattice vibrations and flow of free electrons associated with an increase in temperature elevate both the real (reflectivity) and imaginary (path loss) parts of the complex permittivity. We are currently conducting a 3-year campaign to measure the complex dielectric permittivity of Venusrelevant geologic materials at Venus surface temperatures (380°C - 460°C) and with frequencies relevant to VERITAS, EnVision, and Magellan imaging synthetic aperture radars.

M Barmatz↗
NASA NTRS2018

Seawater Dielectric Measurements at L-Band with Latest Improvements

Recently, the dielectric constant of seawater at L-band was determined by employing a resonant cavity technique. A dielectric model function has been developed based on the measurement data and the model function has been used for retrieving the ocean salinity. The results indicate that additional accuracy is still needed to resolve the bias correlated with sea surface temperature. This paper reports the improvements that have been made recently for the development of a more accurate seawater dielectric model function. The additional measurements for the open ocean will be addressed in the paper.

L-band↗
NASA NTRS2021

Debye Dielectric Model Function for Seawater Based on Expanded L-Band Measurement Data Set

New seawater dielectric measurements have recently been made over a broad range of salinities and temperatures at the George Washington University (GW). These measurements have been used to refine the existing dielectric model function of seawater for salinity retrieval. The mathematical structure of the new model function has been investigated to: (a) look for a physical basis for the mathematical form; and (b) to optimize the accuracy of data fitting. The Debye model has been chosen to represent the dielectric constant of seawater as a function of salinity (S), temperature (T) and frequency (f). The retrieved salinity using the Debye model has good agreement with the in-situ data collected by Argo floats. The global differences in retrieved salinity and in-situ data will be presented at the meeting.

ocean salinity↗
NASA NTRS2022

Model for Dielectric Constant of Seawater based on L-band Measurements with Conductivity by Definition

This article reports an improvement in the model for the dielectric constant of seawater used to fit laboratory measurements of the dielectric constant at the L-band. The new model (dielectric constant as a function of salinity, temperature, and frequency) is based on the response of a polar molecule proposed by Debye and fits the same measurement as reported in earlier work but uses a functional form for conductivity, σ(S,T) , that is given by the definition of salinity. The new version of this model fits the data well and has the advantages that the relaxation time constant is allowed to be a function of temperature and salinity and is well behaved when extrapolated to high salinities.

L-band↗
NASA NTRS1972

Dielectric constants of soils at microwave frequencies

A knowledge of the complex dielectric constant of soils is essential in the interpretation of microwave airborne radiometer data of the earth's surface. Measurements were made at 37 GHz on various soils from the Phoenix, Ariz., area. Extensive data have been obtained for dry soil and soil with water content in the range from 0.6 to 35 percent by dry weight. Measurements were made in a two arm microwave bridge and results were corrected for reflections at the sample interfaces by solution of the parallel dielectric plate problem. The maximum dielectric constants are about a factor of 3 lower than those reported for similar soils at X-band frequencies.

Geiger, F. E.↗
NASA NTRS1971

Dielectric siphons.

The normally weak polarization force density, exerted on insulating dielectric liquids by a nonuniform electric field, is enhanced if high pressures are used. The nonuniform electric field acts as an elastic ?wall' to contain and guide the dielectric fluid. A general theory for these electrohydrodynamic (EHD) conduits has been developed. An illustrative example of the EHD conduits is the dielectric siphon consisting of two U-shaped electrodes held adjacent to each other by insulating nylon screws.

Jones, T. B.↗
NASA NTRS1972

Waveguide excited dielectric spheres as feeds.

The results of experiments with dielectric obstacles of various geometries placed directly upon the apertures of circular and rectangular waveguides are presented. It is found that dielectric spheres, and in some instances dielectric cubes, two to four wavelengths in dimension produce directive patterns with low sidelobe levels. For some cross sections, the measured gain of these antennas is greater (6 dB in some cases) than that produced by optimum horns having apertures of identical cross section. The linearity of the polarization of these antennas is essentially the same as that of an open-end waveguide antenna.

Chatterjee, J. S.↗
NASA NTRS1972

Dielectric breakdown in a dilute plasma.

Description of tests performed to determine the effects of high voltages on dielectrics that are to insulate solar cell arrays operating at voltages up to 16 kV from the electrically active plasma of the space environment at 500 km altitude. The tests were performed on dielectrics considered for this application at positive bias voltages as high as 20 kV dc relative to ground in an argon plasma with electron number densities of approximately one million per cu cm. Teflon specimens displayed higher breakdown voltages than all other dielectrics tested.

Mckinzie, D. J., Jr.↗