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At least 1,585 records · Page 88

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Multiple band circularly polarized microstrip antenna

A multiple antenna assembly for communicating electromagnetic radiation is disclosed. An antenna element stack is constructed of a plurality of elliptical lamina antenna elements mutally separated by layers of dielectric material, and separated from a ground plane by dielectric material. The antenna assembly is coupled through a feed line in contact with the top antenna element. A conductor joins the remaining antenna elements to the ground plane. Each individual antenna element is operable for communication reception and transmission within a frequency band determined by the size of the particular antenna element. The sizes of the antenna elements may be selected to provide electromagnetic radiation communication over several distinct frequency bands, or to connect the individual bands into a broad band.

Yu, I. P.↗

NASA NTRS1979

Microwave dielectric measurements of lunar soil with a coaxial line resonator method

A method is given for sensitive dielectric measurements at a series of microwave frequencies using a section of coaxial line. The line is used as a 1-port cavity resonator; it resonates when the electrical length of the center conductor equals 1, 2 . . . , N half-wave lengths. The dielectric properties of an Apollo 17 dried soil sample were measured in vacuum over a temperature range of 173 to 373 K. The relative permittivity and the loss tangent were determined and the frequency dependence was very small. The derivative with respect to temperature, per degree, was 0.00045 for the permittivity and 0.00002 for the loss tangent.

Bussey, H. E.↗

NASA NTRS1980

Space environmental interactions with biased spacecraft surfaces

Large, high-voltage space power systems are being proposed for future space missions. These systems must operate in the charged-particle environment of space, and interactions between this environment and the high-voltage surfaces are possible. Ground simulation testing has indicated that dielectric surfaces that usually surround biased conductors can influence these interactions. For positive voltages greater than 100 V, it has been found that the dielectrics contribute to discharges. Using these experimental results a large, high-voltage power system operating in geosynchronous orbit was analyzed with the NASCAP code. Results of this analysis indicated that very strong electric fields exist in these power systems. A technology investigation is required to understand the interactions and develop techniques to alleviate any impact on power system performance.

Stevens, N. J.↗

NASA NTRS1982

Improved Model for MOS Breakdown

With an improved model, accelerated high-field tests can be used to predict gate-oxide breakdown in metal-oxide-semi-conductor (MOS) structures. Principal mechanism in MOS breakdown is mobile-ion emission from metal/oxide interface, which occurs during application of positive gate-bias field. Breakdown is related to clustering of emitted ions at localized defect sites in oxide/silicon interface. Using new model to interpret data, tests that normally take several weeks at low fields to accumulate sufficient statistics can be completed in only a few hours at high fields.

Li, S. P.↗

NASA NTRS1982

Selective Etching of Semiconductor Glassivation

Selective etching technique removes portions of glassivation on a semi-conductor die for failure analysis or repairs. A periodontal needle attached to a plastic syringe is moved by a microprobe. Syringe is filled with a glass etch. A drop of hexane and vacuum pump oil is placed on microcircuit die and hexane is allowed to evaporate leaving a thin film of oil. Microprobe brings needle into contact with area of die to be etched.

Casper, N.↗

NASA NTRS1980

The automated array assembly task of the low-cost silicon solar array project, phase 2

Several specific processing steps as part of a total process sequence for manufacturing silicon solar cells were studied. Ion implantation was identified as the preferred process step for impurity doping. Unanalyzed beam ion implantation was shown to have major cost advantages over analyzed beam implantation. Further, high quality cells were fabricated using a high current unanalyzed beam. Mechanically masked plasma patterning of silicon nitride was shown to be capable of forming fine lines on silicon surfaces with spacings between mask and substrate as great as 250 micrometers. Extensive work was performed on advances in plated metallization. The need for the thick electroless palladium layer was eliminated. Further, copper was successfully utilized as a conductor layer utilizing nickel as a barrier to copper diffusion into the silicon. Plasma etching of silicon for texturing and saw damage removal was shown technically feasible but not cost effective compared to wet chemical etching techniques.

Coleman, M. G.↗

NASA NTRS1980

Risk to the public from carbon fibers released in civil aircraft accidents

Because carbon fibers are strong, stiff, and lightweight, they are attractive for use in composite structures. Because they also have high electrical conductivity, free carbon fibers settling on electrical conductors can cause malfunctions. If released from the composite by burning, the fibers may become a hazard to exposed electrical and electronic equipment. As part of a Federal study of the potential hazard associated with the use of carbon fibers, NASA assessed the public risk associated with crash fire accidents of civil aircraft. The NASA study projected a dramatic increase in the use of carbon composites in civil aircraft and developed technical data to support the risk assessment. Personal injury was found to be extremely unlikely. In 1993, the year chosen as a focus for the study, the expected annual cost of damage caused by released carbon fibers is only $1000. Even the worst-case carbon fiber incident simulated (costing $178,000 once in 34,000 years) was relatively low-cost compared with the usual air transport accident cost. On the basis of these observations, the NASA study concluded that exploitation of composites should continue, that additional protection of avionics is unnecessary, and that development of alternate materials specifically to overcome this problem is not justified.

Source record↗

NASA NTRS1980

Fast ion transport in silver halide solid solutions and multiphase systems

The incorporation of homovalent ions, e.g., I(-) in AgBr, leads to a substantial increase in ionic conductivity sigma. The charge compensation concept does not explain the enhancement. AgBr + 30 mol. % AgI exhibits sigma approximately 7/omega/cm at 380 C, which is approximately 170% larger than that of alpha-AgI, the best known superionic conductor, at its melting point. The purely elastic displacement caused by the foreign ion is suggested to be the origin of such a unique behavior. Furthermore, AgI-AgBr two-phase systems display sigma approximately 10 to the 3rd times higher than predicted by the classical theories.

Shahi, K.↗

NASA NTRS1980

The reverse laser drilling of transparent materials

Within a limited range of incident laser-beam intensities, laser drilling of a sapphire wafer initiates on the surface of the wafer where the laser beam exits and proceeds upstream in the laser beam to the surface where the laser beam enters the wafer. This reverse laser drilling is the result of the constructive interference between the laser beam and its reflected component on the exit face of the wafer. Constructive interference occurs only at the exit face of the sapphire wafer because the internally reflected laser beam suffers no phase change there. A model describing reverse laser drilling predicts the ranges of incident laser-beam intensity where no drilling, reverse laser drilling, and forward laser drilling can be expected in various materials. The application of reverse laser drilling in fabricating feed-through conductors in silicon-on-sapphire wafers for a massively parallel processer is described.

Anthony, T. R.↗

NASA NTRS1980

Nordheim-Gorter like behavior and one carrier conduction in a quasi-one-dimensional system

A linear correlation has been observed between the thermopower and the conductivity in the high-temperature state (T greater than 220 K) of the TTF halide and pseudohalide salts. It is suggested that this correlation indicates conduction by a single type of carrier under two types of scattering and represents the first reported extension of the Nordheim-Gorter behavior to any quasi-one-dimensional conductor.

Datta, T.↗

NASA NTRS1981

Experimental simulation of space plasma interactions with high voltage solar arrays

Operating high voltage solar arrays in the space environment can result in anomalously large currents being collected through small insulation defects. Tests of simulated defects have been conducted in a 45-cm vacuum chamber with plasma densities of 100,000 to 1,000,000/cu cm. Plasmas were generated using an argon hollow cathode. The solar array elements were simulated by placing a thin sheet of polyimide (Kapton) insulation with a small hole in it over a conductor. Parameters tested were: hole size, adhesive, surface roughening, sample temperature, insulator thickness, insulator area. These results are discussed along with some preliminary empirical correlations.

Stillwell, R. P.↗

NASA NTRS1981

Heat flow from Io /JI/

The existing ground-based measurements of Io's thermal emission at infrared wavelengths of 8.4, 10.6, and 21 microns have been reexamined. Present in these data is the signature of hot spots, presumably similar to the hot spots seen by the IRIS experiment on Voyager. It is possible to extract from these data the total amount of power radiated. Since the hot spots are believed to be a result of deep-seated activity in Io and since the remainder of Io's surface is an extraordinarily poor thermal conductor, the power radiated by the hot spots is essentially the total heat flow. The analysis yields a heat flow of 2 + or - 1 W/sq m. This value is tremendously large in comparison to the average heat flow of the earth (0.06 W/sq m) and the moon (0.02 W/sq m), but is characteristic of active geothermal areas on the earth. A heat flow this large requires that the interior of Io be at least partially molten on a global scale.

Matson, D. L.↗

NASA NTRS1981

Ignitor plug erosion and arc initiation processes in a one-millipound pulsed plasma thruster

The results are presented of a one-millipound pulsed plasma ignition system study. The preliminary data indicate that inductively coupling the ignition plug cathode to the thruster cathode is more beneficial to ignitor plug longevity than resistive coupling. These benefits arise from the ability of the coupling conductor to control the build-up of a carbonaceous deposit on the plug face. The deposit build-up is a strong function of the peak coupling current experienced during thruster operation. The relationship between the ignitor plug discharge and thruster discharge is shown to be very complex with equivalent circuit elements which are dynamic in nature. A preliminary representation of this equivalent circuit is developed.

Aston, G.↗

NASA NTRS1982

Electrical Connector for Graphite Heating Elements

Connection method applies force to two interfaces: that between heating element proper and heating-element support members and between heating-element support members and metal conductor. Inner rod of new connector system is maintained in tension by a spring (for example, Belleville washers). Connection is sufficiently complaint so tension remains within desired range, regardless of thermal expansion and contraction of various elements.

Mackintosh, B. H.↗

NASA NTRS1982

Extracting Silicon From Sodium-Process Products

New acid leaching process purifies silicon produced in reaction between silicon fluoride and sodium. Concentration of sodium fluoride and other impurities and byproducts remaining in silicon are within acceptable ranges for semi-conductor devices. Leaching process makes sodium reduction process more attractive for making large quantities of silicon for solar cells.

Kapur, V.↗

NASA NTRS1982

Glass for Solid State Devices

Glass film has low intrinsic compressive stress for isolating active layers of magnetic-bubble and other solid-state devices. Solid-state device structure incorporates low-stress glasses as barrier and spacer layers. Glass layers mechanically isolate substrate, conductor, and nickel/iron layers.

Bailey, R. F.↗

NASA NTRS1983

Tangleproof Rotary Electrical Coupling

New rotary coupling connects large number of electrical cables to turntable without stressing cables or tangling them. Device accommodates 246 cables containing total of 758 conductors and allows turntable to rotate through arc of 320 degrees. At extremes of rotation, cables are loose enough that they are not pulled taut and overstressed. At halfway point, cables are not so loose that they become entangled.

Keller, F.↗

NASA NTRS1983

Preventing Freezeup in Silicon Ribbon Growth

Carefully-shaped heat conductor helps control thermal gradients crucial to growth of single-crystal silicon sheets for solar cells. Ends of die through which silicon sheet is drawn as ribbon from molten silicon. Profiled heat extractor prevents ribbon ends from solidifying prematurely and breaking.

Mackintosh, B.↗