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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The SIR-B observations of microwave backscatter dependence on soil moisture, surface roughness, and vegetation covers

An experiment was conducted from an L-band SAR aboard Space Shuttle Challenger in October 1984 to study the microwave backscatter dependence on soil moisture, surface roughness, and vegetation cover. The results based on the analyses of an image obtained at 21-deg incidence angle show a positive correlatlion between scattering coefficient and soil moisture content, with a sensitivity comparable to that derived from the ground radar measurements reported by Ulaby et al. (1978). The surface roughness strongly affects the microwave backscatter. A factor of two change in the standard deviation of surface roughness height gives a corresponding change of about 8 dB in the scattering coefficient. The microwave backscatter also depends on the vegetation types. Under the dry soil conditions, the scattering coefficient is observed to change from about -24 dB for an alfalfa or lettuce field to about -17 dB for a mature corn field. These results suggest that observations with a SAR system of multiple frequencies and polarizations are required to unravel the effects of soil moisture, surface roughness, and vegetation cover.

Wang, J. R.↗
NASA NTRS1993

Microwave techniques for physical property measurements

Industrial processing of metals and ceramics is now being streamlined by the development of theoretical models. High temperature thermophysical properties of these materials are required to successfully apply these theories. Unfortunately, there is insufficient experimental data available for many of these properties, particularly in the molten state. Microwave fields can be used to measure specific heat, thermal diffusivity, thermal conductivity and dielectric constants at high temperatures. We propose to (1) develop a microwave flash method (analogous to the laser flash technique) that can simultaneously measure the thermal diffusivity and specific heat of insulators and semiconductors at high temperatures, (2) an appropriate theory and experimental apparatus to demonstrate the measurement of the specific heat of a metal using a new microwave ac specific heat technique, and (3) experimental methods for noncontact measurement of the real and imaginary dielectric constants.

Barmatz, M.↗
DOE OSTI2022

Methane Catalytic Pyrolysis by Microwave and Thermal Heating over Carbon Nanotube-Supported Catalysts: Productivity, Kinetics, and Energy Efficiency

Methane catalytic pyrolysis, which is the reaction to produce hydrogen and carbon without emitting CO 2 , represents an approach for decarbonization using natural gas as an energy resource. In this work, the endothermic pyrolysis reaction was carried out under two heating scenarios: convective thermal heating and microwave-driven irradiative heating. The pyrolysis reaction was conducted at 550-600 °C over carbon nanotube-supported Ni-Pd and Ni-Cu catalysts. On both catalysts, an enhanced methane conversion rate was observed under microwave irradiation. The enhanced catalytic activity was hypothetically caused by the presence of free electrons in the carbon atoms within CNT that enabled the CNT support to absorb microwave energy effectively and to be heated efficiently by microwave. The microwave catalytic pyrolysis has shown improvement in kinetics, where the apparent activation energy dropped from 45.5 kJ/mol under conventional convective heating to 24.8 kJ/mol under microwave irradiation. When the methane conversion rate is increased by 37 %, the microwave power consumption only changed by 10.8 %. The research demonstrated the potential of transforming natural gas to clean hydrogen and value-added carbon in a more energy-efficient way. Process simulation and techno-economic analysis showed that potentially hydrogen minimum selling price of about $1 /kg H 2 could be achieved.

03 NATURAL GAS↗
NASA NTRS1974

Study, selection, and preparation of solid cationic conductors

Crystal chemical principles and transport theory have been used to predict structures and specific compounds which might find application as solid electrolytes in rechargeable high energy and high power density batteries operating at temperatures less than 200 C. Structures with 1-, 2-, and 3-dimensional channels were synthesized and screened by nuclear magnetic resonance, dielectric loss, and conductivity. There is significant conductivity at room temperature in some of the materials but none attain a level that is comparable to beta-alumina. Microwave and fast pulse methods were developed to measure conductivity in powders and in small crystals.

Roth, W. L.↗
NASA NTRS2010

Application of Reflected Global Navigation Satellite System (GNSS-R) Signals in the Estimation of Sea Roughness Effects in Microwave Radiometry

In February-March 2009 NASA JPL conducted an airborne field campaign using the Passive Active L-band System (PALS) and the Ku-band Polarimetric Scatterometer (PolSCAT) collecting measurements of brightness temperature and near surface wind speeds. Flights were conducted over a region of expected high-speed winds in the Atlantic Ocean, for the purposes of algorithm development for salinity retrievals. Wind speeds encountered were in the range of 5 to 25 m/s during the two weeks deployment. The NASA-Langley GPS delay-mapping receiver (DMR) was also flown to collect GPS signals reflected from the ocean surface and generate post-correlation power vs. delay measurements. This data was used to estimate ocean surface roughness and a strong correlation with brightness temperature was found. Initial results suggest that reflected GPS signals, using small low-power instruments, will provide an additional source of data for correcting brightness temperature measurements for the purpose of sea surface salinity retrievals.

Voo, Justin K.↗
NASA NTRS2010

Technique for Performing Dielectric Property Measurements at Microwave Frequencies

A paper discusses the need to perform accurate dielectric property measurements on larger sized samples, particularly liquids at microwave frequencies. These types of measurements cannot be obtained using conventional cavity perturbation methods, particularly for liquids or powdered or granulated solids that require a surrounding container. To solve this problem, a model has been developed for the resonant frequency and quality factor of a cylindrical microwave cavity containing concentric cylindrical samples. This model can then be inverted to obtain the real and imaginary dielectric constants of the material of interest. This approach is based on using exact solutions to Maxwell s equations for the resonant properties of a cylindrical microwave cavity and also using the effective electrical conductivity of the cavity walls that is estimated from the measured empty cavity quality factor. This new approach calculates the complex resonant frequency and associated electromagnetic fields for a cylindrical microwave cavity with lossy walls that is loaded with concentric, axially aligned, lossy dielectric cylindrical samples. In this approach, the calculated complex resonant frequency, consisting of real and imaginary parts, is related to the experimentally measured quantities. Because this approach uses Maxwell's equations to determine the perturbed electromagnetic fields in the cavity with the material(s) inserted, one can calculate the expected wall losses using the fields for the loaded cavity rather than just depending on the value of the fields obtained from the empty cavity quality factor. These additional calculations provide a more accurate determination of the complex dielectric constant of the material being studied. The improved approach will be particularly important when working with larger samples or samples with larger dielectric constants that will further perturb the cavity electromagnetic fields. Also, this approach enables the ability to have a larger sample of interest, such as a liquid or powdered or granulated solid, inside a cylindrical container.

Barmatz, Martin B.↗
DOE OSTI2020

Studies of Autoionizing States relevant to Dielectronic Recombinaton

Doubly excited autoionizing states of alkaline earth atoms are explored by multistep laser spectroscopy, which is precisely the inverse process to dielectronic recombination, the recombination of hot electron with ions via an autoionizing state. Dielectronic recombination is an important mechanism leading to power loss in high temperature plasmas. Measurements included the autoionization rates of atoms in zero field and in the presence of electric and magnetic fields, as might be encountered in a plasma. To mimic the effects of the rapidly varying fields of electron collisions measurements were made in the presence of microwave electric fields. These experiments are analogous to experiments conducted with combined high intensity infrared and vuv laser fields, In laser/microwave experiments the effects of laser pulse envelope timing relative to the microwave phase were explored extensively.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Emerging applications of high temperature superconductors for space communications

Proposed space missions require longevity of communications system components, high input power levels, and high speed digital logic devices. The complexity of these missions calls for a high data bandwidth capacity. Incorporation of high temperature superconducting (HTS) thin films into some of these communications system components may provide a means of meeting these requirements. Space applications of superconducting technology has previously been limited by the requirement of cooling to near liquid helium temperatures. Development of HTS materials with transition temperatures above 77 K along with the natural cooling ability of space suggest that space applications may lead the way in the applications of high temperature superconductivity. In order for HTS materials to be incorporated into microwave and millimeter wave devices, the material properties such as electrical conductivity, current density, surface resistivity and others as a function of temperature and frequency must be well characterized and understood. The millimeter wave conductivity and surface resistivity were well characterized, and at 77 K are better than copper. Basic microwave circuits such as ring resonators were used to determine transmission line losses. Higher Q values than those of gold resonator circuits were observed below the transition temperature. Several key HTS circuits including filters, oscillators, phase shifters and phased array antenna feeds are feasible in the near future. For technology to improve further, good quality, large area films must be reproducibly grown on low dielectric constant, low loss microwave substrates.

Heinen, Vernon O.↗
NASA NTRS1974

Investigation of microwave hologram techniques for application to earth resources

An investigation of microwave hologram techniques for application to earth resources was conducted during the period from June 1971 to November 1972. The objective of this investigation has been to verify the feasibility of an orbital microwave holographic radar experiment. The primary advantage of microwave hologram radar (MHR) over the side-looking airborne radar (SLAR) is that of aspect or viewing angle; the MHR has a viewing angle identical with that of photography and IR systems. The combination of these systems can thus extend the multispectral analysis concept to span optical through microwave wavelengths. Another advantage is the capacity of the MHR system to generate range contours by operating in a two-frequency mode. It should be clear that along-track resolution of an MHR can be comparable with SLAR systems, but cross-track resolution will be approximately an order of magnitude coarser than the range resolution achievable with an arbitrary SLAR system. An advantage of the MHR over the SLAR is that less average transmitter power is required. This reduction in power results from the much larger receiving apertures associated with MHR systems.

Larson, R. W.↗
NASA NTRS1989

Investigations of microwave plasmas - Applications in electrothermal thruster systems

Experimental studies which have been conducted to develop understanding of plasma processes used for spacecraft propulsion are reviewed. The techniques discussed are calorimetry and volume measurements using the TM 011 and TM 012 modes in the microwave cavity system. The use of plasmas in electrical propulsion and microwave induction is reviewed. Plasma containment, microwave power production, energy distribution, and the pressure and flow dependence of the energy distribution are addressed. The plasma dimensions and their dependence on pressure, flow, and power are considered.

Haraburda, Scott S.↗
NASA NTRSDate not supplied

Literature Review of Microwave Regeneration of CO2 Capture Sorbent Materials

Utilizing liquid amines for air revitalization applications has been of continued interest for many decades. They have the advantage of being regenerable sorbents with long lifetimes and a high acuteness for carbon dioxide. While their usage on Earth for flue gas and submarines has been explored for some time now, they are still being researched for use in microgravity environments. To succeed in a microgravity environment, such as usage on the International Space Station, an air revitalization system that is reliant on liquid amines as its sorbent must have a low Equivalent System Mass (ESM), among many other performance parameters. One way of optimizing this ESM number is through bringing down the systems power consumption with the use of microwave heating of the liquid sorbent. Microwave heating allows the liquid sorbent to be heated in a much more efficient way when compared to conventional types of heating techniques, such as convection or conduction. This paper will explore the physical mechanisms behind microwave heating, and how it could potentially be applied to a liquid amine carbon capture system, laying out any concerns and future constraints that a system designer may encounter.

Tiago Faria Costa↗
NASA NTRS2004

An Analytical Calibration Approach for the Polarimetric Airborne C Band Radiometer

Passive microwave remote sensing is sensitive to the quantity and distribution of water in soil and vegetation. During summer 2000, the Microwave Geophysics Group at the University of Michigan conducted the 7th Radiobrightness Energy Balance Experiment (REBEX-7) over a corn canopy in Michigan. Long time series of brightness temperatures, soil moisture and micrometeorology on the plot scale were taken. This paper addresses the calibration of the NASA GSFC polarimetric airborne C band microwave radiometer (ACMR) that participated in REBEX-7. Passive polarimeters are typically calibrated using an end-to-end approach based upon a standard artificial target or a well-known geophysical target. Analyzing the major internal functional subsystems offers a different perspective. The primary goal of this approach is to provide a transfer function that not only describes the system in its entirety but also accounts for the contributions of each subsystem toward the final modified Stokes parameters. This approach also serves as a realistic instrument simulator, a useful tool for future designs. The ACMR architecture can be partitioned into several functional subsystems. Each subsystem was extensively measured and the estimated parameters were imported into the overall system model. We will present the results of polarimetric antenna measurements, the instrument model as well as four Stokes observations from REBEX-7 using a first order inversion.

Pham, Hanh↗
NASA NTRS1969

Microwave radiometric studies and ground truth measurements of the NASA/USGS Southern California test site

The field measurement program conducted at the NASA/USGS Southern California Test Site is discussed. Ground truth data and multifrequency microwave brightness data were acquired by a mobile field laboratory operating in conjunction with airborne instruments. The ground based investigations were performed at a number of locales representing a variety of terrains including open desert, cultivated fields, barren fields, portions of the San Andreas Fault Zone, and the Salton Sea. The measurements acquired ground truth data and microwave brightness data at wavelengths of 0.8 cm, 2.2 cm, and 21 cm.

Edgerton, A. T.↗
NASA NTRS1982

Development of visible/infrared/microwave agriculture classification and biomass estimation algorithms, volume 2

Agricultural crop classification models using two or more spectral regions (visible through microwave) were developed and tested and biomass was estimated by including microwave with visible and infrared data. The study was conducted at Guymon, Oklahoma and Dalhart, Texas utilizing aircraft multispectral data and ground truth soil moisture and biomass information. Results indicate that inclusion of C, L, and P band active microwave data from look angles greater than 35 deg from nadir with visible and infrared data improved crop discrimination and biomass estimates compared to results using only visible and infrared data. The active microwave frequencies were sensitive to different biomass levels. In addition, two indices, one using only active microwave data and the other using data from the middle and near infrared bands, were well correlated to total biomass.

Rosenthal, W. D.↗
NASA NTRS1986

High spatial resolution passive microwave sounding systems

Two extensive series of flights aboard the ER-2 aircraft were conducted with the MIT 118 GHz imaging spectrometer together with a 53.6 GHz nadir channel and a TV camera record of the mission. Other microwave sensors, including a 183 GHz imaging spectrometer were flown simultaneously by other research groups. Work also continued on evaluating the impact of high-resolution passive microwave soundings upon numerical weather prediction models.

Staelin, D. H.↗
NASA NTRS1988

Microwave remote sensing of soil moisture

Knowledge of soil moisture is important to many disciplines, such as agriculture, hydrology, and meteorology. Soil moisture distribution of vast regions can be measured efficiently only with remote sensing techniques from airborne or satellite platforms. At low microwave frequencies, water has a much larger dielectric constant than dry soil. This difference manifests itself in surface emissivity (or reflectivity) change between dry and wet soils, and can be measured by a microwave radiometer or radar. The Microwave Sensors and Data Communications Branch is developing microwave remote sensing techniques using both radar and radiometry, but primarily with microwave radiometry. The efforts in these areas range from developing algorithms for data interpretation to conducting feasibility studies for space systems, with a primary goal of developing a microwave radiometer for soil moisture measurement from satellites, such as EOS or the Space Station. These efforts are listed.

Shiue, J. C.↗
NASA NTRS1995

Improved Dichroics For Microwave Reflector Antenna Systems

Panel contains array of grid and square conductive loops as array elements designed to reflect most of incident electromagnetic radiation in K(subu) band (13.5 to 15.5 GHz) and to pass that in X band (7 to 9 GHz). Designed to exhibit this dichroic property at angles of incidence up to 40 degrees in transverse electric, transverse magnetic, or circular polarization. Concept of gridded-square-loop dichroic array related to double-loop dichroic arrays described in "Frequency-Selective Microwave Reflectors" (NPO-18701). Improved version exhibits smaller shift of resonant frequency with angle of incidence.

Wu, Te-Kao↗
NASA NTRS1967

The microwave phase effect of Mercury.

Mercury brightness temperatures from contact conduction and radiative transfer equation solutions, noting dependence on heliocentric longitude and phase angle

Morrison, D.↗