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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Modeled performance of monolithic, 3-terminal InP/Ga(0.47)In(0.53)As concentrator solar cells as a function of temperature and concentration ratio

Using measured device parameters from a monolithic three-terminal In/GaInAs (0.75 eV) tandem concentrator solar cell, a numerical model is constructed that calculates efficiency as a function of temperature and concentration ratio. The device measurements indicate that the series resistance in the InP top cell severely limits the maximum efficiency at high concentration ratios. Results from the model in which a single-junction InP concentrator solar cell that has a lower resistance by a factor of six was substituted for the top cell show that peak 20 C air-mass-zero (AM0) efficiencies should approach 30 percent at concentration ratios greater than 100. At 80 C, this tandem cell should exceed 24 percent AM0 efficiency.

Osterwald, C. R.↗
NASA NTRS1993

Monolithic Continuous-Flow Bioreactors

Monolithic ceramic matrices containing many small flow passages useful as continuous-flow bioreactors. Ceramic matrix containing passages made by extruding and firing suitable ceramic. Pores in matrix provide attachment medium for film of cells and allow free movement of solution. Material one not toxic to micro-organisms grown in reactor. In reactor, liquid nutrients flow over, and liquid reaction products flow from, cell culture immobilized in one set of channels while oxygen flows to, and gaseous reaction products flow from, culture in adjacent set of passages. Cells live on inner surfaces containing flowing nutrient and in pores of walls of passages. Ready access to nutrients and oxygen in channels. They generate continuous high yield characteristic of immobilized cells, without large expenditure of energy otherwise incurred if necessary to pump nutrient solution through dense biomass as in bioreactors of other types.

Stephanopoulos, Gregory↗
NASA NTRS1992

A study of subterahertz HEMT monolithic oscillators

A detailed study of monolithic InP-based HEMT oscillators for subterahertz operation is presented. InAlAs/InGaAs HEMT's have been optimized for high frequency operation and showed very high maximum oscillation frequencies (f(sub max)) of 310 GHz using offset self-aligned gamma-gate technology. Power characteristics of HEMT oscillators are reported. An oscillation power of more than 10 mW was evaluated by large-signal analysis at 320 GHz using HEMT's with f(sub max) = 450 GHz, V(sub br) = 10 V and a gate width (W(sub g)) of 8 x 22.5 microns. Oscillator topology studies showed that complex feedback schemes such as dual and active feedback enhance the negative resistance. Push-push oscillator designs based on harmonic signal generation can finally be used to overcome the frequency barrier imposed by f(sub max).

Kwon, Youngwoo↗
NASA NTRS1992

Monolithic millimeter-wave diode grid frequency multiplier arrays

Monolithic diode frequency multiplier arrays, including barrier-N-N(+) (BNN) doubler, multi-quantum-barrier-varactor (MQBV) tripler, Schottky-quantum-barrier-varactor (SQBV) tripler, and resonant-tunneling-diode (RTD) tripler arrays, have been successfully fabricated with yields between 85 and 99 percent. Frequency doubling and/or tripling have been observed for all the arrays. Output powers of 2.4-2.6 W (eta = 10-18 percent) at 66 GHz with the BNN doubler and 3.8-10 W (eta = 1.7-4 percent) at 99 GHz with the SQBV tripler have been achieved.

Liu, Hong-Xia L.↗
NASA NTRS1993

Every Good Virtue You Ever Wanted in a Q-switched Solid-state Laser and More: Monolithic, Diode-pumped, Self-q-switched, Highly Reproducible, Diffraction-limited Nd:yag Laser

The applications of Q-switched lasers are well known, for example, laser radar, laser remote sensing, satellite orbit determination, Moon orbit and 'moon quake' determination, satellite laser communication, and many nonlinear optics applications. Most of the applications require additional properties of the Q-switched lasers, such as single-axial and/or single-transverse mode, high repetition rate, stable pulse shape and pulse width, or ultra compact and rugged oscillators. Furthermore, space based and airborne lasers for lidar and laser communication applications require efficient, compact, lightweight, long-lived, and stable-pulsed laser sources. Diode-pumped solid-state lasers (DPSSL) have recently shown the potential for satisfying all of these requirements. We will report on the operating characteristics of a diode-pumped, monolithic, self-Q-switched Cr,Nd:YAG laser where the chromium ions act as a saturable absorber for the laser emission at 1064 nm. The pulse duration is 3.5 ns and the output is highly polarized with an extinction ratio of 700:1. It is further shown that the output is single-longitudinal-mode with transform-limited spectral line width without pulse-to-pulse mode competition. Consequently, the pulse-to-pulse intensity fluctuation is less than the instrument resolution of 0.25 percent. This self-stabilization mechanism is because the lasing mode bleaches the distributed absorber and establishes a gain-loss grating similar to that used in the distributed feedback semiconductor lasers. A repetition rate above 5 KHz has also been demonstrated. For higher power, this laser can be used for injection seeding an amplifier (or amplifier chain) or injection locking of a power oscillator pumped by diode lasers. We will discuss some research directions on the master oscillator for higher output energy per pulse as well as how to scale the output power of the diode-pumped amplifier(s) to multi-kilowatt average power.

Chen, Y. C.↗
NASA NTRS1991

A high efficiency Ka-band monolithic pseudomorphic HEMT amplifier

A monolithic three-stage Ka-band amplifier has been designed and fabricated on a doped channel heterostructure. Devices with gate length of 0.2 micron and gate width of 50, 100, and 250 micron were cascaded. The gate and drain bias networks were also integrated. The small signal gain is 31 dB and the amplifier is capable of an output power of 190 mW with 23 dB gain and 30.2 percent power added efficiency at 31 GHz. This is a record efficiency for a multistage MMIC at this frequency.

Saunier, Paul↗
NASA NTRS1993

High-efficiency high-gain monolithic heterostructure FET amplifier at 31 GHz

A three-stage heterostructure FET monolithic amplifier has achieved a power-added efficiency of 36 percent with 200 mW output and 18 dB gain at 31 GHz. At a higher drain voltage, the output power increases to 280 mW (with 17.5 dB gain and 31 percent PAE) at a power density of 0.7 W/mm. The MMIC chip measures 2.63 x 1.35 sq mm and requires only a single drain bias and a single gate bias.

Tserng, H. Q.↗
NASA NTRS1993

High magnetic field trapping in monolithic single-grain YBa2Cu3O(7-delta) bulk materials

Results of our study on high magnetic field trapping in unirradiated, high quality monolithic single-grain YBa2Cu3O(7-delta) disks are reported. A record high 4 T trapped field at the surface of the unirradiated disks is observed. However, below 11 K, large flux avalanches caused by thermal instability severely limit the remnant trapped field. Therefore, flux avalanche, rather than Jc x d, dictates the maximum trapped field at low temperatures. To overcome this problem, a strong high temperature superconductor trapped field magnet is proposed. A novel application of the avalanche effect is also mentioned.

Gao, L.↗
NASA NTRS1992

Catalytic ignition model in monolithic reactor with in-depth reaction

A transient model has been developed to study ignition in a monolithic catalytic reactor. Special features are the inclusion of thermal and species structures in the porous catalytic layer and the resolution of small-time-scale events. Catalyst loading is used as a parameter to study these structure variations before and after ignition. Regions where the catalytic reaction is kinetically controlled and regions where the reaction is diffusionally controlled are identified in both steady and transient states.

Tien, Ta-Ching↗
NASA NTRS1993

Single-frequency lasing of monolithic Ho,Tm:YLF

Single-frequency lasing in monolithic crystals of holmium-thulium-doped YLF (Ho,Tm:YLF) is reported. A maximum single-frequency output power of 6 mW at a wavelength of 2.05 microns is demonstrated. Frequency tuning is also described.

Koch, Grady J.↗
NASA NTRS1994

Monolithic Three-Stage 32-GHz Power Amplifier

Monolithic three-stage 32-GHz power amplifier compact and offers state-of-the-art performance. Operates at frequencies around 32 GHz. Designed for use aboard communication satellite and is also suitable for terrestrial applications in which moderate power and high efficiency needed.

Saunier, Paul↗
NASA NTRS1993

Low temperature synthesis of monolithic transparent Ta2O5 gels from hydrolysis of metal alkoxide

Tantalum oxide gels in the form of transparent monoliths and powder were prepared from hydrolysis of tantalum pentaethoxide under controlled conditions using different mole ratios of Ta(OC2H5)5:C2H50H:H20:HCl. Alcohol acts as the mutual solvent and HCl as the deflocculating agent. For a fixed alkoxide:water:HCl ratio, time of gel formation increased with the alcohol to alkoxide mole ratio. Thermal evolution of the physical and structural changes in the gel was monitored by differential thermal analysis, thermogravimetric analysis, x-ray diffraction, and infrared spectroscopy. On heating to approximately 400 C, the amorphous gel crystallized into the low temperature orthorhombic phase Beta-Ta2O5, which transformed into the high temperature tetragonal phase Alpha-Ta2O5 when further heated to approximately 1450 C. The volume fraction of the crystalline phase increased with the firing temperature. The Alpha-Ta205 converted back into the low temperature phase, Beta-Ta2O5, on slow cooling through the transformation temperature of 1360 C indicating a slow but reversible transformation.

Bansal, Narottam P.↗
NASA NTRS1994

A monolithic Si bolometer array for the Caltech Submillimeter Observatory

We are developing a submillimeter continuum camera for the Caltech Submillimeter Observatory (CSO) located on Mauna Kea. The camera will employ a monolithic Si bolometer array which was developed by Moseley et al. at the NASA Goddard Space Flight Center (GSFC). The camera will be cooled to a temperature of about 300 mK in a He-3 cryostat, and will operate primarily at wavelengths of 350 and 450 micrometers. We plan to use a bolometer array with 1x24 directly illuminated pixels, each pixel of dimension 1x2 sq mm, which is about half of the F/4 beam size at these wavelengths. Each pixel is 10 to 12 micrometers thick and is supported only by four thin Si legs formed by wet chemical etch. The pixels are doped n-type by phosphorus implantation, compensated by boron implantation. Signals from the bolometer pixels are first amplified by cryogenically cooled FET's. The signals are further amplified by room-temperature amplifiers and then separately digitized by 16 bit A/D converters with differential inputs. The outputs of the A/D converters are fed into a digital signal processing board via fiber-optic cables. The electronics and data acquisition system were designed by the Goddard group. We will report the status of this effort.

Wang, Ning↗
NASA NTRS1994

Electron-irradiated two-terminal, monolithic InP/Ga0.47In0.53As tandem solar cells and annealing of radiation damage

Radiation damage results from two-terminal monolithic InP/Ga(0.47)In(0.53)As tandem solar cells subject to 1 MeV electron irradiation are presented. Efficiencies greater than 22 percent have been measured by the National Renewable Energy Laboratory from 2x2 sq cm cells at 1 sun, AMO (25 C). The short circuit current density, open circuit voltage and fill factor are found to tolerate the same amount of radiation at low fluences. At high fluence levels, slight differences are observed. Decreasing the base amount of radiation at the Ga(0.47)In(0.53)As bottomcell improved the radiation resistance of J(sub sc) dramatically. This is turn, extended the series current flow through the subcell substantially up to a fluence of 3x10(exp 15) cm(exp -2) compared to 3x10(exp 14) cm(exp -2), as observed previously. The degradation of the maximum power output form tandem device is comparable to that from shallow homojunction (SHJ) InP solar cells, and the mechanism responsible for such degradation is explained in terms of the radiation response of the component cells. Annealing studies revealed that the recovery of the tandem cell response is dictated by the annealing characteristics exhibited by SHJ InP solar cells.

Cotal, H. L.↗
NASA NTRS1995

Stability mechanical considerations, and AC loss in HTSC monoliths, coils, and wires

For monolithic high-T(sub c) superconductors (HTSC's) calculations are presented of: (1) the initial flux jump field, H(sub fj), in melt-processed YBCO based on a field and temperature dependent J(sub c), and (2) the radial and circumferential stresses in solid and hollow cylinders containing trapped magnetic flux. For model multi filamentary (MF) HTSC/Ag strands calculations are presented of: (1) the limiting filament diameters for adiabatic and dynamic stability, and (2) the hysteretic and eddy current components of AC loss. Again for MF HTSC/Ag composite strands the need for filamentary subdivision and twisting is discussed.

Sumption, M. D.↗
NASA NTRS1996

Package Holds Five Monolithic Microwave Integrated Circuits

Packages protect and hold monolithic microwave integrated circuit (MMIC) chips while providing dc and radio-frequency (RF) electrical connections for chips undergoing development. Required to be compact, lightweight, and rugged. Designed to minimize undesired resonances, reflections, losses, and impedance mismatches.

Mysoor, Narayan R.↗
NASA NTRS1995

Demonstration of a Monolithic Micro-Spectrometer System

The starting design of a spectrometer based on a modified Czerny-Turner configuration containing five precision surfaces encapsulated in a monolithic structure is described. Since the purpose at the early stages of the development was to demonstrate the feasibility of the technology and not an attempt to address a specific sensing problem, the first substrate material chosen was optical quality polymethyl methacrylate (PMMA). The final system design decision was narrowed down to two possible configurations containing five and six precision surfaces. The five surface design was chosen since it contained one less precision optical surface, yet included multiple off-axis spheres. In this particular design and material system, the mass was kept below 7 g. The wavelength range (bandpass) design goal was 1 micrometer (0.6 - 1.6 micrometers). The PMMA is particularly transparent in this wavelength region and there are interesting effects to monitor within this band. The optical system was designed and optimized using the ZEMAX optical design software program to be entirely alignment free (self aligning).

Rajic, S.↗