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At least 199 records · Page 11

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NASA NTRS1978

Ionosphere/microwave beam interaction study

The microwave beam of the Solar Power Satellite (SPS) is predicted to interact with the ionosphere producing thermal runaway up to an altitude of about 100 kilometers at a power density threshold of 12 mW/cm sq (within a factor of two). The operation of the SPS at two frequencies, 2450 and 5800 MHz, is compared. The ionosphere interaction is less at the higher frequency, but the tropospheric problem scattering from heavy rain and hail is worse at the higher frequency. Microwave signals from communication satellites were observed to scintillate, but there is some concern that the uplink pilot signal may be distorted by the SPS heated ionosphere. The microwave scintillations are only observed in the tropics in the early evenings near the equinoxes. Results indicate that large phase errors in the uplink pilot signal can be reduced.

Gordon, W. E.↗

NASA NTRS1995

Plasma Enhanced Microwave Joining

A new method for plasma enhanced microwave joining of high purity (99.8%) alumina has been developed. The controlled application of a plasma between the adjoining surfaces of two rods permits the initial heating of low microwave absorbing alumina to sufficiently high temperatures where they can effectively absorb microwave energy. With this technology, the adjacent surfaces of alumina rods can be melted and welded together in less than three minutes using approximately 400 watts of microwave energy. Four point bending tests measured fracture strengths of up to 132 MPa at the joined interface.

microwave↗

NASA NTRS1993

Preliminary investigation of high power microwave plasmas for electrothermal thruster use

Results are reported from preliminary tests to evaluate the high power microwave electrothermal thruster concept, which employs a free-floating plasma discharge maintained by applied CW microwave power to heat a propellant gas flow. Stable plasmas have been created and maintained in He, N2, and H2 as propellants in both the TM(sub 011) and TM(sub 012) modes at discharge pressures from 10 Pa to 69 kPa. Vortical inflow of the propellant gas was observed to cause the formation of on-axis 'spike' plasmas. Operation in the spike plasma condition yields maximum power absorption with minimum wall heating and maximum propellant-heating efficiency; plasmas of the three propellant gases were investigated in the spike condition in an open channel to a maximum applied power level of 11.2 kW (in N2). Microwave power coupling efficiencies of over 90 percent were routinely obtained at absorbed power levels up to 2 kW. Magnetic nozzle effects were investigated with a superconducting solenoid Al magnet applying a high magnetic field to the plasmas in, and exiting from, the discharge tube.

Power, John L.↗

NASA NTRS1993

Preliminary investigation of high power microwave plasmas for electrothermal thruster use

Results are reported from preliminary tests to evaluate the high power microwave electrothermal thruster (MET) concept, which employs a free-floating plasma discharge maintained by applied CW microwave power to heat a propellant gas flow. Stable plasmas have been created and maintained in helium (He), nitrogen (N2), and hydrogen (H2) as propellants in both the TM(sub 011) and TM(sub 012) modes at discharge pressures from 10 Pa to 69 kPa. Reproducible starting conditions of pressure and power have been documented for all the plasmas. Vortical inflow of the propellant gas was observed to cause the formation of on-axis 'spike' plasmas. The formation and unformation conditions of these plasmas were studied. Operation in the spike plasma condition enables maximum power absorption with minimum wall heating and offers maximum efficiency in heating the propellant gas. In the spike condition, plasmas of the three propellant gases were investigated in an open channel configuration to a maximum applied power level of 11.2 kW (in N2). Microwave power coupling efficiencies of over 90 percent were routinely obtained at absorbed power levels up to 2 kW. Magnetic nozzle effects were investigated with a superconducting solenoid Al magnet applying a high magnetic field to the plasmas in and exiting from the discharge tube.

Power, John L.↗

NASA NTRS2004

Exploring New Pathways in Precipitation Assimilation

Precipitation assimilation poses a special challenge in that the forward model for rain in a global forecast system is based on parameterized physics, which can have large systematic errors that must be rectified to use precipitation data effectively within a standard statistical analysis framework. We examine some key issues in precipitation assimilation and describe several exploratory studies in assimilating rainfall and latent heating information in NASA's global data assimilation systems using the forecast model as a weak constraint. We present results from two research activities. The first is the assimilation of surface rainfall data using a time-continuous variational assimilation based on a column model of the full moist physics. The second is the assimilation of convective and stratiform latent heating retrievals from microwave sensors using a variational technique with physical parameters in the moist physics schemes as a control variable. We will show the impact of assimilating these data on analyses and forecasts. Among the lessons learned are (1) that the time-continuous application of moisture/temperature tendency corrections to mitigate model deficiencies offers an effective strategy for assimilating precipitation information, and (2) that the model prognostic variables must be allowed to directly respond to an improved rain and latent heating field within an analysis cycle to reap the full benefit of assimilating precipitation information. of microwave radiances versus retrieval information in raining areas, and initial efforts in developing ensemble techniques such as Kalman filter/smoother for precipitation assimilation. Looking to the future, we discuss new research directions including the assimilation

Hou, Arthur↗

DOE OSTI2020

Electron cyclotron resonance (ECR) magnetometry with a plasma reservoir

The local magnetic field in a Penning–Malmberg trap is found by measuring the temperatures that result when electron plasmas are illuminated by microwave pulses. Multiple heating resonances are observed as the pulse frequencies are swept. The many resonances are due to electron bounce and plasma rotation sidebands. The heating peak corresponding to the cyclotron frequency resonance is identified to determine the magnetic field. A new method for quickly preparing low density electron plasmas for destructive temperature measurements enables a rapid and automated scan of microwave frequencies. This technique can determine the magnetic field to high precision, obtaining an absolute accuracy better than 1 ppm and a relative precision of 26 ppb. One important application is in situ magnetometry for antihydrogen-based tests of charge-parity-time symmetry and of the weak equivalence principle.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1999

Microwave Induced Direct Bonding of Single Crystal Silicon Wafers

We have heated polished doped single-crystal silicon wafers in a single mode microwave cavity to temperatures where surface to surface bonding occurred. The absorption of microwaves and heating of the wafers is attributed to the inclusion of n-type or p-type impurities into these substrates. A cylindrical cavity TM (sub 010) standing wave mode was used to irradiate samples of various geometry's at positions of high magnetic field. This process was conducted in vacuum to exclude plasma effects. This initial study suggests that the inclusion of impurities in single crystal silicon significantly improved its microwave absorption (loss factor) to a point where heating silicon wafers directly can be accomplished in minimal time. Bonding of these substrates, however, occurs only at points of intimate surface to surface contact. The inclusion of a thin metallic layer on the surfaces enhances the bonding process.

Budraa, N. K.↗

NASA NTRSDate not supplied

Scaleup of Microwave Powder Bed Fusion for Lunar Infrastructure Construction

NASA and its partners are seeking to establish a sustainable and permanent presence on the Moon. Like explorers on Earth, making use of natural resources upon arrival at the destination will be paramount. In-situ resource utilization of the lunar regolith will enable efficient construction of lunar infrastructure. Transforming the granular regolith into a solid can be achieved in many ways. One method is to use microwave energy to sinter the regolith into various structures. The lunar regolith has a low thermal conductivity, but microwaves can volumetrically heat it to bind the granular particles together in an energy efficient manner. One concept that is being developed and evaluated to sinter the regolith into infrastructure uses the Moon’s surface as a powder bed. Regolith would be added to the sintered lunar structure to build up layers to create structures such as landing pads, blast shields, roads, etc. Microwave systems, concept of operations, and sintering protocols are being developed to create a sub-element structure targeted for a lunar demonstration mission.

microwave↗

DOE OSTI2023

Microwave resonance enhanced CO 2 reduction using biochar

The conventional process for CO 2 conversion requires high energy and expensive catalysts, and shows poor product selectivity. Here, in this study, we address these challenges by investigating an environmentally friendly method for CO production through the variable frequency microwave-driven CO 2 Boudouard reaction over biochar. We hypothesized that tuning the microwave frequency to align with the dielectric properties of biochar, and thereby induce a resonance effect, could significantly enhance reaction efficiency. Experiments were conducted to explore the effect of microwave frequency on CO 2 conversion efficiency in the variable frequency microwave reactor operating within a frequency range of 2430–6000 MHz. Results reveal a significant resonance effect at 4225 MHz resulting in an outstanding CO 2 conversion of 96.3%, in sharp contrast to the complete absence of conversion observed at the conventional 2450 MHz. The resonance frequency not only facilitated exceptional conversion but also remarkably improved energy efficiency, yielding a productivity of 1427.5 µmol/kJ of CO. This represents a remarkable 474-fold increase compared to electrical heating. Furthermore, continuous microwave irradiation at this optimized frequency demonstrated remarkable stability and induced substantial enhancements in the pore structure and surface area of biochar. This innovative approach provides promising insights into sustainable and efficient CO production processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Microwave-Assisted Activation of Mo/HZSM5 in Methane Dehydroaromatization

Natural gas flaring is a significant challenge for oil and gas producers. One viable option to mitigate flaring is the conversion of natural gas into valuable chemicals. Applying microwave energy to heterogenous catalyst materials offers advantages in terms of higher rates and product selectivities in comparison to traditional thermal systems which can be designed for on-demand chemical production in modular reactor systems. Methane dehydroaromatization (MDHA) produces transportable, liquid aromatic products directly from natural gas, which is ideal for remote production but is hindered by low thermodynamic yields and rapid deactivation. The stability and performance of the Mo/ZSM5 catalyst is often determined by the state and nature of Mo in the catalyst, which in turn is dictated by the temperature and gaseous environment during catalyst activation. In this study, the Mo/HZSM5 catalyst was activated under three different heating modes (thermal, microwave E-field, and microwave H-field) and four different gas environments (CO, He, CH4+H2, and H2). All the activated catalysts were characterized using different tools and performance evaluated in MDHA.

methane dehydroaromatization↗

NASA NTRS2007

Two-Band, Low-Loss Microwave Window

A window for a high-sensitivity microwave receiving system allows microwave radiation to pass through to a cryogenically cooled microwave feed system in a vacuum chamber, while keeping ambient air out of the chamber and helping to keep the interior of the chamber cold. The microwave feed system comprises a feed horn and a low-noise amplifier, both of which are required to be cooled to a temperature of 15 K during operation. The window is designed to exhibit very little microwave attenuation in two frequency bands: 8 to 9 GHz and 30 to 40 GHz. The window is 15 cm in diameter. It includes three layers (see figure): 1) The outer layer is made of a poly(tetrafluoroethylene) film 0.025 mm thick. This layer serves primarily to reflect and absorb solar ultraviolet radiation to prolong the life of the underlying main window layer, which is made of a polyimide that becomes weakened when exposed to ultraviolet. The poly(tetrafluoroethylene) layer also protects the main window layer against abrasion. Moreover, the inherent hydrophobicity of poly(tetrafluoroethylene) helps to prevent the highly undesirable accumulation of water on the outer surface. 2) The polyimide main window layer is 0.08 mm thick. This layer provides the vacuum seal for the window. 3) A 20-mm-thick layer of ethylene/ propylene copolymer foam underlies the main polyimide window layer. This foam layer acts partly as a thermal insulator: it limits radiational heating of the microwave feed horn and, concomitantly, limits radiational cooling of the window. This layer has high compressive strength and provides some mechanical support for the main window layer, reducing the strength required of the main window layer. The ethylene/propylene copolymer foam layer is attached to an aluminum window ring by means of epoxy. The outer poly(tetrafluoroethylene) film and the main polyimide window layer are sandwiched together and pressed against the window ring by use of a bolted clamp ring. The window has been found to introduce a microwave loss of only about 0.4 percent. The contribution of the window to the noise temperature of the microwave feed system has been found to be less than 1 K at 32 GHz and 0.2 K at 8.4 GHz.

Britcliffe, Michael↗

DOE OSTI2024

Insights into Designing an Efficient and Reliable Microwave-Assisted Methane Dehydroaromatization Process: Effect of Microwave Absorber on Catalyst Performance

Microwave-assisted methane dehydroaromatization has the potential to address challenges of traditional dehydroaromatization reactions. However, catalysts for microwave-enhanced reaction systems require effective coupling of fields with the catalyst to produce heat and reach reaction temperatures. Here, this work presents an in-depth understanding of the effect of the addition of silicon carbide as a microwave absorber on catalyst performance among other variables, the viability of the microwave reactor configuration, and insights into designing an effective and reliable microwave-based methane dehydroaromatization process. The effect of other parameters including temperature, weight hourly space velocity, role of microwave absorber, and methane concentration during microwave-assisted methane dehydroaromatization reaction are studied. Mo/ZSM-5 was found to suffer from low permittivity and nonuniform heating under microwave conditions. Mixing silicon carbide powder as a microwave absorber with the catalyst was found to provide more uniform heating. When assessing the catalytic performance of the mixture, it was found that higher methane partial pressures at 2000 cc/g cat .h and a temperature range of 500-600°C produced the highest amount of benzene. The formation of graphitic carbon on the spent catalyst increased with temperature, gas-solid contact period, and methane concentration, which resulted in higher methane conversion and benzene selectivity. The study indicates that under microwave heating the presence of localized carbon enhanced catalyst life by coupling with microwave energy, leading to localized heating, and improving benzene selectivity.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1991

Global water cycle

The primary objective is to determine the scope and interactions of the global water cycle with all components of the Earth system and to understand how it stimulates and regulates changes on both global and regional scales. The following subject areas are covered: (1) water vapor variability; (2) multi-phase water analysis; (3) diabatic heating; (4) MSU (Microwave Sounding Unit) temperature analysis; (5) Optimal precipitation and streamflow analysis; (6) CCM (Community Climate Model) hydrological cycle; (7) CCM1 climate sensitivity to lower boundary forcing; and (8) mesoscale modeling of atmosphere/surface interaction.

Robertson, Franklin R.↗

NASA NTRS2003

Endothelium Preserving Microwave Treatment for Atherosclerosis

This slide presentation reviews the use of microwave technology for treating Atherosclerosis while preserving the endothelium. The system uses catheter antennas as part of the system that is intended to treat atherosclerosis. The concept is to use a microwave catheter for heating the atherosclerotic lesions, and reduce constriction in the artery.

Fink, Patrick↗

NASA NTRS1978

Microwave diagnostic for the determination of the electron temperature of a low density shock-heated argon plasma

The diffraction, defocusing and beam bending effects of microwaves transmitted through a bounded shock-heated argon plasma with low electron density are investigated with the purpose of developing an accurate method for electron temperature (Te) determination. This report describes the evaluation technique and presents results for an argon plasma with pressure between 3 and 10 torr, and T2 between 5500 and 9500 K. The electron temperature values obtained have a range of uncertainty between -20% and +10% only. The electron temperature is equal or lower by approximately 1000 K in comparison to the heavy particle temperature (T2).

Schneider, C. P.↗

NASA NTRS2003

Method for Selective Thermal Ablation

A method, simulation, and apparatus are provided that are highly suitable for treatment of benign prostatic hyperplasia (BPH). A catheter is disclosed that includes a small diameter disk loaded monopole antenna surrounded by fusion material having a high heat of fusion and a melting point preferably at or near body temperature. Microwaves from the antenna heat prostatic tissue to promote necrosing of the prostatic tissue that relieves the pressure of the prostatic tissue against the urethra as the body reabsorbs the necrosed or dead tissue. The fusion material keeps the urethra cool by means of the heat of fusion of the fusion material. This prevents damage to the urethra while the prostatic tissue is necrosed. A computer simulation is provided that can be used to predict the resulting temperature profile produced in the prostatic tissue. By changing the various control features of the catheter and method of applying microwave energy a temperature profile can be predicted and produced that is similar to the temperature profile desired for the particular patient.

Arndt, G. Dickey↗

NASA NTRS2003

Method for selective thermal ablation

Arndt, G. Dickey↗

NASA NTRS1974

In-situ measurements of lunar heat flow

During the Apollo program two successful heat flow measurements were made in situ on the lunar surface. At the Apollo 15 site a value of 0.0000031 watts/sqcm was measured and at the Apollo 17 site a value of 0.0000022 watts/sqcm was determined. Both measurements have uncertainty limits of + or - 20% and have been corrected for perturbing topographic effects. The apparent difference between the observations may correlate with observed variations in the surface abundance of thorium. Comparison with earlier determinations of heat flow, using the microwave emission spectrum from the moon, gives support to the high gradients and heat flows observed in situ.

Langseth, M. G.↗