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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Diagnostics of seeded RF plasmas: An experimental study related to the gaseous core reactor

Measurements of the temperature profiles in an RF argon plasma were made over magnetic field intensities ranging from 20 amp turns/cm to 80 amp turns/cm. The results were compared with a one-dimensional numerical treatment of the governing equations and with an approximate closed form analytical solution that neglected radiation losses. The average measured temperatures in the plasma compared well with the numerical treatment, though the experimental profile showed less of an off center temperature peak than predicted by theory. This may be a result of the complex turbulent flow pattern present in the experimental torch and not modeled in the numerical treatment. The radiation term cannot be neglected for argon at the power levels investigated. The closed form analytical approximation that neglected radiation led to temperature predictions on the order of 1000 K to 2000 K higher than measured or predicted by the numerical treatment which considered radiation losses.

Thompson, S. D.↗
NASA NTRS1973

Increase in transmittance of unbacked aluminum filters exposed to RF or dc discharges in oxygen

Results of an experimental study of the effect of discharges in oxygen on the oxide thickness and transmittance of aluminum filters. The studies were performed by exposing the filters to RF discharges and dc glow discharges in oxygen. In all experiments except one in which an aluminum ring was used as the cathode an increase in the transmittance of the filters is noted. It is thus demonstrated that the transmittance of aluminum filters increases on exposure to electrical discharges in oxygen, although it is not certain whether this phenomenon is caused by atomic oxygen.

Hunter, W. R.↗
NASA NTRS1975

An investigation of errors and data processing techniques for an RF multilateration system

The development of an RF Multilateration system to provide accurate position and velocity measurements during the approach and landing phase of Vertical Takeoff Aircraft operation is discussed. The system uses an angle-modulated ranging signal to provide both range and range rate measurements between an aircraft transponder and multiple ground stations. Range and range rate measurements are converted to coordinate measurements and the coordinate and coordinate rate information is transmitted by an integral data link to the aircraft. Data processing techniques are analyzed to show advantages and disadvantages. Error analyses are provided to permit a comparison of the various techniques.

Britt, C. L., Jr.↗
NASA NTRS1974

RF voltage breakdown and the Paschen curve

A representation based on the similarity relations for voltage breakdown is shown to be useful in combining RF and dc voltage breakdown data. The representation for the uniform field geometry is given.

Woo, R.↗
NASA NTRS1975

Effects of dc bias on the fabrication of amorphous GdCo RF sputtered films

An investigation has been conducted on the effects of a dc bias field applied to Gd(1-x)Co(x) thin films during RF sputter deposition. Such films may possess uniaxial magnetic anisotropy with easy axis perpendicular to the plane of the film and may be used in magnetic bubble devices. Uniformity in composition, thickness and magnetic properties has been achieved and film composition has been controlled to within one percent. However, significant variations of magnetic properties were observed from film to film.

Bourne, H. C., Jr.↗
NASA NTRS1975

An RF link analysis of MSBLS during ALT

An analysis of the microwave scanning beam landing system (MSBLS) ground station to orbiter radio frequency (RF) link was made to determine if the expected signal levels will be compatible with orbiter receiver capabilities. Of primary interest was whether or not loss of data will occur due to interference caused by the orbiter 101 nose boom which provides additional air data during the approach and landing test. The results of the analysis indicate that a small amount of data loss may occur due to the proximity of the MSBLS antennas and the nose boom. Tabulated data of antenna radiation patterns are given.

Speir, R. E.↗
NASA NTRS1978

Low loss, flexible, lightweight corporate RF feed system for SAR antenna application

Mechanical and electrical efficiency constraints imposed by the SEASAT-A synthetic aperture radar antenna posed difficult design problems. After consideration of available standard cable and waveguide systems, it was determined that an optimum design could be obtained from a suspended substrate RF feed system. Size and mechanical flexibility constraints forced the design of a flexible, suspended substrate section capable of 180-degree flexure. Original design goal for insertion loss over power division was 1 db; measured results indicated 0.6 db maximum across the band. Multipactor testing of system components indicated system breakdown capability in excess of 4 kW compared to a specification input maximum of 1500 W.

Schiavone, F.↗
NASA NTRS1980

RF-sputtered and ion-plated solid lubricants

Report reviews advances in tribological uses of RF-sputtered and ion-plated films of solid film lubricants (laminar solids, soft metals, organic polymers) and wear-resistant refractory compounds.

Spalvins, T.↗
NASA NTRS1980

A reliable solid-state RF transfer switch

Highly-reliable lightweight solid-state RF (radio frequency) transfer switch replaces less reliable mechanical switch in handling medium power for S-band power amplifier.

Dodd, R. W.↗
NASA NTRS1980

Ultrasonic spectrum analysis using frequency-tracked gated RF pulses

A new method of ultrasonic frequency analysis is introduced which employs frequency-tracked gated RF drive pulses rather than shock-excited broadband spikes to generate the ultrasonic waveform. The new technique, a variation of the sampled-continuous wave technique, eliminates problems associated with finite pulse widths of conventional methods. It is shown to yield correct ultrasonic wave velocity measurements of the sample irrespective of receiver gate width or position provided any portions of two successive echoes are gated simultaneously into the spectrum analyzer. The experimental observations are substantiated by a theoretical model based on the time-frequency domain formulation of ultrasonic frequency analysis.

Cantrell, J. H., Jr.↗
NASA NTRS1981

The 34-meter antenna-subreflector translations to maximize RF gain

The extension of the 26 meter antenna to 34 meter diameter decreased the F/D ratio. This F/D change resulted in unacceptable gain losses due to the hyperboloid's lateral deflections. A three direction translating mounting device was added to the hyperboloid. This device was controlled by a microprocessor to minimize the offsets of the phase centers in the cassegrain RF system and also compensated for boresight directions. The use of the radiation program to predict the gain losses from displacements computed by a structural computing program using an analytical model of the 34 meter reflector structure is discussed. Field test results showed accurate predictions for the Y and Z hyperboloid translations. In the X direction, the prediction value was low. However, the computed gain losses vs primary foci offsets by the radiation program were verified by field tests.

Katow, M. S.↗
NASA NTRS1981

DSS 14 64-meter antenna. Computed RF pathlength changes under gravity loadings

Using a computer model of the reflector structure and its supporting assembly of the 64-m antenna rotating about the elevation axis, the radio frequency (RF) pathlengths changes resulting from gravity loadings were computed. A check on the computed values was made by comparing the computed foci offsets with actual field readings of the Z or axial focussing required for elevation angle changes.

Katow, M. S.↗
NASA NTRS1980

The RF spectra of first and subsequent lightning return strokes in the 1- to 200-km range

An experimental characterization of the frequency spectra of first and subsequent stroke electric fields are presented over a distance range from about 1 km, where the fields are primarily electrostatic, to 200 km, where they are primarily radiation. Spectra are presented to about 700 kHz for lightning within 12 km and to about 300 kHz for lightning at 50 and 200 km. It is shown that the return stroke ground wave spectrum beyond 50 km has a peak near 4 kHz but that within 10 km the spectrum shows a steady increase with decreasing frequency to 1 kHz. Frequency spectra at all ranges fall off roughly as 1/f for frequencies between 5 and 100 kHz, while the falloff above 100 kHz is faster as the distance to the stroke increases. From this high-frequency attenuation an RF conductivity for central Florida of between 0.002 and 0.005/ohm/m was determined.

Serhan, G. I.↗
NASA NTRS1980

Structural and compositional characterization of RF sputter-deposited Ni-Cr + Cr2O3 films

An RF-sputtered chrome oxide coating with metallic binders was developed. The chrome oxide coating has high-temperature capabilities and is wear resistant, and has some self-lubricating properties. A nichrome metallic binder was added in the coating to improve its ductility without significant loss in the hardness. The sputtering parameters were optimized to obtain a smooth coating with the maximum adherence. The coatings were applied using bias-sputter and sputter-deposit modes on the heat treated and annealed foil substrates. The coating applied on annealed foils using the sputter-deposit mode was smooth and had the best adherence. Metallurgical examinations showed that the coating was Ni-Cr + Cr2O3. The coating as applied was amorphous and it crystallized during substrate heat treatment.

Bhushan, B.↗
NASA NTRS1983

RF Sputtering of Gold Contacts On Niobium

Reliable gold contacts are deposited on niobium by combination of RF sputtering and photolithography. Process results in structures having gold only where desired for electrical contact. Contacts are stable under repeated cycling from room temperature to 4.2 K and show room-temperature contact resistance as much as 40 percent below indium contacts made by thermalcompression bonding.

Barr, D. W.↗
NASA NTRS1981

A broadband RF continuously variable time delay device

A method for implementation of continuously variable time delay of broadband RF signals is described. The method uses Bragg Cell and optical heterodyne technology. The signal to be delayed is applied to the Bragg Cell acoustic transducer, and the delay time is the acoustic transit time from this transducer to the incident light beam. By translating the light beam, the delay is varied. Expressions describing the Bragg Cell diffraction, lens Fourier transformation, and the optical heterodyne processes are developed. Specifications for the variable delay including bandwidth, range of delay, and insertion loss are provided. Applications include radar signal processing, spread spectrum intercept, radar ECM, and adaptive array antenna processing.

Freyre, F. W.↗
NASA NTRS1982

Quad aperture RF definition

A single STS package 118 m diameter hoop/column antenna is capable of providing service for appr. 250,000 mobile users. The selected quad aperture configuration is able to provide at least 25 db C/I without cable blockage, column scatter, coupling between quad apertures, and tolerance effects. A feed can be designed which uses single polarized radiating elements while the overall system employs dual polarization. The quad aperture concept can eliminate the use of diplexers and their associated losses. The critical technology issues in the RF area include the design of the radiating elements, BFN, monolithic power amplifiers and receiver front end, tolerance control and packaging of the feed.

Foldes, P.↗
NASA NTRS1982

Some properties of RF sputtered hafnium nitride coatings

Hafnium nitride coatings were deposited by reactive RF sputtering from a hafnium target in nitrogen and argon gas mixtures. The rate of deposition, composition, electrical resistivity and complex index of refraction were investigated as a function of target substrate distance and the fraction nitrogen, (fN2) in the sputtering atmosphere. The relative composition of the coatings is independent on fN2 for values above 0.1. The electric resistivity of the hafnium nitride films changes over 8 orders of magnitude when fN2 changes from 0.10 to 0.85. The index of refraction is almost constant at 2.8(1-0.3i) up to fN2 = 0.40 then decreases to 2.1(1 - 0.01i) for higher values of fN2.

Aron, P. R.↗