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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 NTRS1984

The study of microstrip antenna arrays and related problems

The physical layout of the array elements and the proximity of the microstrip feed network makes the input impedance and radiation pattern values dependent upon the effects of mutual coupling, feedline discontinuities and feed point location. The extent of these dependences was assessed and a number of single patch and module structures were constructed and measured at an operating frequency of approximately 4.0 GHz. The empirical results were compared with the ones which were theoretically predicted by the cavity model of thin microstrip antennas. Each element was modelled as an independent radiating patch and each microstrip feedline as an independent, quasi-TEM transmission line. The effects of the feedline discontinuities are approximated by lumped L-C circuit models.

Lo, Y. T.↗
NASA NTRS1987

AC impedance study of degradation of porous nickel battery electrodes

AC impedance spectra of porous nickel battery electrodes were recorded periodically during charge/discharge cycling in concentrated KOH solution at various temperatures. A transmission line model (TLM) was adopted to represent the impedance of the porous electrodes, and various model parameters were adjusted in a curve fitting routine to reproduce the experimental impedances. Degradation processes were deduced from changes in model parameters with electrode cycling time. In developing the TLM, impedance spectra of planar (nonporous) electrodes were used to represent the pore wall and backing plate interfacial impedances. These data were measured over a range of potentials and temperatures, and an equivalent circuit model was adopted to represent the planar electrode data. Cyclic voltammetry was used to study the characteristics of the oxygen evolution reaction on planar nickel electrodes during charging, since oxygen evolution can affect battery electrode charging efficiency and ultimately electrode cycle life if the overpotential for oxygen evolution is sufficiently low.

Lenhart, Stephen J.↗
NASA NTRS1989

The application of electrochemical impedance spectroscopy for characterizing the degradation of Ni(OH)2/NiOOH electrodes

Electrochemical impedance spectra of rolled and bonded and sintered porous nickel battery electrodes were recorded periodically during charge/discharge cycling in concentrated KOH solution at various temperatures. A transmission line model (TLM) was adopted to represent the impedance of the porous electrodes, and various model parameters were adjusted in a curve fitting routine to reproduce the experimental impedances. Degradation processes for rolled and bonded electrodes were deduced from changes in model parameters with electrode cycling time. In developing the TLM, impedance spectra of planar (non-porous) electrodes were used to represent the pore wall and backing plate interfacial impedances. These data were measured over a range of potentials and temperatures, and an equivalent circuit model was adopted to represent the planar electrode data. Cyclic voltammetry was used to study the characteristics of the oxygen evolution reaction on planar nickel electrodes during charging, since oxygen evolution can affect battery electrode charging efficiency and ultimately electrode cycle life if the overpotential for oxygen evolution is sufficiently low. Transmission line modeling results suggest that porous rolled and bonded nickel electrodes undergo restructuring during charge/discharge cycling prior to failure.

Macdonald, D. D.↗
NASA NTRS2006

Modeling of the Near Field Coupling Between an External Loop and an Implantable Spiral Chip Antennas in Biosensor Systems

In this paper, the near field coupling between an external hand-held loop antenna and an implantable miniature (1x1 mm) printed square spiral chip antenna used in bio-MEMS sensors for contact-less powering and RF telemetry is investigated. The loop and the spiral are inductively coupled and effectively form a transformer. The numerical results include the quasi-stationary magnetic field pattern of the implanted antenna, near zone wave impedance as a function of the radial distance and the values of the lumped elements in the equivalent circuit model for the transformer.

Simons, Rainee N.↗
NASA NTRS1971

Response of a radial-bladed centrifugal pump to sinusoidal disturbances for noncavitating flow

A radial-bladed centrifugal pump was run in water with sinusoidal fluctuations of pressure and flow rate imposed at the pump inlet. Since the flow was noncavitating, zero gain was assumed in computing pump impedance. The inertive reactance became greater than the resistance at relatively low frequencies. An electric circuit model was developed in order to explain the trends of inertance and resistance with frequency.

Anderson, D. A.↗
NASA NTRS1973

Linearized stability analysis and design of a flyback dc-dc boost regulator.

Analytic expressions for the small-signal power-stage describing functions of a switched dc-dc boost regulator are derived from an approximate continuous circuit model which is developed by a time-averaging technique. Closed-loop stability is attained through the design of frequency compensation of the loop gain. Open- and closed-loop regulator output impedances are derived from the linearized models for the given configuration. The analysis and design are compared with and confirmed by breadboard measurements.

Wester, G. W.↗
NASA NTRS1974

NASA Lewis 10 by 10 foot supersonic wind tunnel

Performance data are presented for this tunnel, which has a Mach number range from 2.0 to 3.5. The tunnel circuit, model support systems, auxiliary systems, instrumentation, control room equipment, and automatic recording and computing equipment are described. Information is presented on criteria for designing models, and on shop facilities available to users.

Aiello, R. A.↗
NASA NTRS1975

Application of acoustic surface wave technology to shuttle radar

The application of surface acoustic wave (SAW) signal processing devices in the space shuttle was explored. In order to demonstrate the functions which a SAW device might perform, a breadboard pulse compression filter (PCF) module was assembled. The PCF permits a pulse radar to operate with a large duty cycle and low peak power, a regime favorable to the use of solid state RF sources. The transducer design, strong coupling compensation, circuit model analysis, fabrication limitations, and performance evaluation of a PCF are described. The nominal value of the compression ratio is 100:1 with 10-MHz bandwidth centered at 60 MHz and 10-microsecond dispersive delay. The PCF incorporates dispersive interdigital transducers and a piezoelectric lithium niobate substrate.

Source record↗
NASA NTRS1979

Study of the Effects of Impurities on the Properties of Silicon Materials and Performance of Silicon Solar Cell

Numerical solutions were obtained from the exact one dimensional transmission line circuit model to study the following effects on the terrestrial performance of silicon solar cells: interband Auger recombination; surface recombination at the contact interfaces; enhanced metallic impurity solubility; diffusion profiles; and defect-impurity recombination centers. Thermal recombination parameters of titanium impurity in silicon were estimated from recent experimental data. Based on those parameters, computer model calculations showed that titanium concentration must be kept below 6x10 to the 12th power Ti/cu cm in order to achieve 16% AM1 efficiency in a silicon solar cell of 250 micrometers thick and 1.5 ohm-cm resistivity.

Sah, C. T.↗
NASA NTRS1978

Compression of Jupiter's magnetosphere by the solar wind

Simultaneous sets of interplanetary and planetary data obtained by Pioneer 10 and Pioneer 11 are compared with a view toward identifying major changes in the solar wind and their possible influence on the Jovian magnetosphere. The results are discussed relative to variations in magnetopause location, pressure balance at the magnetopause, acceleration of energetic trapped radiation, plasma density from the response time of the Jovian magnetosphere, and time constants of magnetospheric circuit models. A major finding is that three out of four cases in which the Pioneers reentered the magnetosheath are the result of time variations associated with changing interplanetary conditions. The compressibility of the Jovian magnetosphere is enhanced because the field inside the magnetopause is not the planetary field but is primarily caused by currents inside the magnetosphere, presumably the equatorial current sheet.

Smith, E. J.↗
NASA NTRS1981

CADAT network translator

Program converts cell-net data into logic-gate models for use in test and simulation programs. Input consists of either Place, Route, and Fold (PRF) or Place-and-Route-in-Two-Dimensions (PR2D) layout data deck. Output consists of either Test Pattern Generator (TPG) or Logic-Simulation (LOGSIM) logic circuitry data deck. Designer needs to build only logic-gate-model circuit description since program acts as translator. Language is FORTRAN IV.

Pitts, E. R.↗
NASA NTRS1980

Study of the effects of impurities on the properties of silicon materials and performance of silicon solar cell

Zinc is a major residue impurity in the preparation of solar grade silicon material by the zinc vapor reduction of silicon tetrachloride. It was found that in order to get a 17 percent AMl cell efficiency, the concentration of the zinc recombination centers in the base region of silicon solar cells must be less than 4 x 10 to the 11th power Zn/cu cm in the p-base n+/p/p+ cell and 7 x 10 to the 11th power Zn/cu cm in the n-base p+/n/n+ cell for a base dopant impurity concentration of 5 x 10 to the 14th power atoms/cu cm. If the base dopant impurity concentration is increased by a factor of 10 to 5 x 10 to the 15th power atoms/cu cm, then the maximum allowable zinc concentration is increased by a factor of about two for a 17 percent AMl efficiency. The thermal equilibrium electron and hole recombination and generation rates at the double acceptor zinc cancers were obtained from previous high field measurements as well as new measurements at zero field. The rates were used in the exact d.c. circuit model to compute the projections.

Sah, C. T.↗
NASA NTRS1979

Power combining in an array of microwave power rectifiers

This work analyzes the resultant efficiency degradation when identical rectifiers operate at different RF power levels as caused by the power beam taper. Both a closed-form analytical circuit model and a detailed computer-simulation model are used to obtain the output dc load line of the rectifier. The efficiency degradation is nearly identical with series and parallel combining, and the closed-form analytical model provides results which are similar to the detailed computer-simulation model.

Gutmann, R. J.↗
NASA NTRS1981

Study of the effects of impurities on the properties of silicon materials and performance of silicon solar cell

The effect of silicon film thickness on the energy conversion efficiency of a back surface field solar cell is investigated. A computer-aided design study on the dependence of efficiency peaks on the concentrations of the recombination and dopant impurities is presented. The illuminated current voltage characteristics of over 100 cell designs were obtained using the transmission line circuit model to numerically solve the Shockley Equations. Using an AM1 efficiency of 17% as a target value, it is shown that the efficiency versus thickness dependence has a broad maximum which varies less than 1% over more than three-to-one range of cell thickness from 30 to 100 microns. Optical reflecting back surface will give only a slight improvement of AM1 efficiency, about 0.7%, in this thickness range. The sensitive dependence of efficiency on patchiness across the back surface field, low high junction in thin cells is noted.

Sah, C. T.↗
NASA NTRS1981

Effect of zinc impurity on silicon solar-cell efficiency

Zinc is a major residue impurity in the preparation of solar-grade silicon material by the zinc vapor reduction of silicon tetrachloride. This paper projects that in order to get a 17-percent AM1 cell efficiency for the Block IV module of the Low-Cost Solar Array Project, the concentration of the zinc recombination centers in the base region of silicon solar cells must be less than 4 x 10 to the 11th Zn/cu cm in the p-base n+/p/p+ cell and 7 x 10 to the 11th Zn/cu cm in the n-base p+/n/n+ cell for a base dopant impurity concentration of 5 x 10 to the 14 atoms/cu cm. If the base dopant impurity concentration is increased by a factor of 10 to 5 x 10 to the 15th atoms/cu cm, then the maximum allowable zinc concentration is increased by a factor of about two for a 17-percent AM1 efficiency. The thermal equilibrium electron and hole recombination and generation rates at the double-acceptor zinc centers are obtained from previous high-field measurements as well as new measurements at zero field described in this paper. These rates are used in the exact dc-circuit model to compute the projections.

Sah, C.-T.↗
NASA NTRS1982

Effect of thickness on silicon solar cell efficiency

A computer-aided-design study on the dependence of the efficiency peak of a back-surface field solar cell on the concentrations of the recombination and dopant impurities is presented. The illuminated current-voltage characteristics of more than 100 cell designs are obtained using the transmission line circuit model to numerically solve the Shockley equations. Using an AM 1 efficiency of 17% as a target value, it is shown that the efficiency versus thickness dependence has a broad maximum which varies by less than 1% over more than a three-to-one range of cell thicknesses from 30 to 100 microns. An optically reflecting back surface will give only a slight improvement of AM 1 efficiency, about 0.7%, in this thickness range. Attention is given to the dependence of the efficiency on patchiness across the back-surface field low-high junction in thin cells.

Sah, C.-T.↗
NASA NTRS1981

Fabrication of multijunction high voltage concentrator solar cells by integrated circuit technology

Standard integrated circuit technology has been developed for the design and fabrication of planar multijunction (PMJ) solar cell chips. Each 1 cm x 1 cm solar chip consisted of six n(+)/p, back contacted, internally series interconnected unit cells. These high open circuit voltage solar cells were fabricated on 2 ohm-cm, p-type 75 microns thick, silicon substrates. A five photomask level process employing contact photolithography was used to pattern for boron diffusions, phorphorus diffusions, and contact metallization. Fabricated devices demonstrated an open circuit voltage of 3.6 volts and a short circuit current of 90 mA at 80 AMl suns. An equivalent circuit model of the planar multi-junction solar cell was developed.

Valco, G. J.↗
NASA NTRS1984

GaAs dual-gate FET for operation up to K-band

A high-frequency equivalent-circuit model of a GaAs dual-gate FET and analytical expressions for the input/output impedances, transconductance, unilateral gain, and stability factor are presented. It is found that the gain of a dual-gate FET is higher than of a single-gate FET at low frequency but decreases faster as frequency increases because of the capacitive shunting effect of the second gate. A dual-gate power FET suitable for variable-gain-amplifier applications up to K-band has been developed. At 10 GHz, a 1.2-mm-gatewidth device has achieved an output power of 1.1 W with 10.5-dB gain and 31-percent power-added efficiency. At 20 GHz, the same device delivered an output power of 340 mW with 5.3-dB gain. At K-band, a dynamic-gain control range of up to 45 dB was obtained with an insertion phase change of no more than + or 2 degrees for the first 10 dB of gain control.

Kim, B.↗