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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Optically-switched submillimeter-wave oscillator and radiator having a switch-to-switch propagation delay

A submillimeter wave-generating integrated circuit includes an array of N photoconductive switches biased across a common voltage source and an optical path difference from a common optical pulse of repetition rate f sub 0 providing a different optical delay to each of the switches. In one embodiment, each incoming pulse is applied to successive ones of the N switches with successive delays. The N switches are spaced apart with a suitable switch-to-switch spacing so as to generate at the output load or antenna radiation of a submillimeter wave frequency f on the order of N f sub 0. Preferably, the optical pulse has a repetition rate of at least 10 GHz and N is of the order of 100, so that the circuit generates radiation of frequency of the order of or greater than 1 Terahertz.

Spencer, Michael G.↗
NASA NTRS1982

Dynamic switch matrix for the TDMA satellite switching system

Future high capacity satellite communication systems require signal processing on board satellites. The on-board signal processing includes switching of RF signals between multiple antennas to provide interconnection between the uplink and downlink beams. This paper describes the development of a dynamic switch matrix for a TDMA satellite switching system to be used in the next generation communications satellites. In this paper, a dynamic switch matrix, which includes the microwave switch matrix, the distribution control unit and the timing source, will be described. Several different microwave switch matrix architectures and switching devices were evaluated and compared. A unique coupler crossbar switch matrix architecture with dual-gate field effect transistor as switching element was developed. Experimental results of both microwave switch matrix (MSM) and distribution control unit (DCU) are presented. These test results verify the MSM with coupler crossbar architecture and dual-gate FET as switching element will meet the future SS-TDMA system requirements. Finally, the reliability of the dynamic switch matrix is addressed. The analysis shows reliability of 0.9981 for 7 year space operation can be achieved for the designed dynamic switch matrix.

Ho, P. T.↗
NASA NTRS2005

Different Pathogenesis of CCR5-Using Primary HIV-1 Isolates from Non-Switch and Switch Virus Patients in Human Lymphoid Tissue Ex Vivo

CCR5-utilizing HIV-1 variants (R5) typically transmit infection and dominate its early stages, whereas emergence of CXCR4-using (X4 or R5X4) HIV-1 is often associated with disease progression. However, such a switch in co-receptor usage can only be detected in approximately onehalf of HIV-infected patients (switch virus patients), and progression to immunodeficiency may also occur in patients without detectable switch in co-receptor usage (non-switch virus patients). Here, we used a system of ex vivo-infected tonsillar tissue to compare the pathogenesis of sequential primary R5 HIV-1 isolates from the switch and non-switch patients. Inoculation of ex vivo tissue with these R5 isolates resulted in viral replication and CCR5(+)CD4(+) T cell depletion. The levels of such depletion by HIV-1 isolated from non-switch virus patients were significantly higher than those by R5 HIV-1 isolates from switch virus patients. T cell depletion seemed to be controlled by viral factors and did not significantly vary between tissues from different donors. In contrast, viral replication did not correlate with the switch status of the patients; in tissues fiom different donors it varied 30-fold and seemed to be controlled by a combination of viral and tissue factors. Nevertheless, replication-level hierarchy among sequential isolates remained constant in tissues from various donors. Viral load in vivo was higher in switch virus patients compared to non-switch virus patients. The high cytopathogenicity of CCR5(+)CD4(+) T cells by R5 HIV-1 isolates from non-switch virus patients may explain the steady decline of CD4(+) T cells in the absence of CXCR4 using virus; elimination of target cells by these isolates may limit their own replication in vivo.

Iarlsson, Ingrid↗
NASA NTRS2006

Air-bridge and Vertical CNT Switches for High Performance Switching Applications

Carbon nanotubes are attractive for switching applications since electrostatically-actuated CNT switches have low actuation voltages and power requirements, while allowing GHz switching speeds that stem from the inherently high elastic modulus and low mass of the CNT.Our first NEM structure, the air-bridge switch, consists of suspended single-walled nanotubes (SWNTs) that lie above a sputtered Nb base electrode, where contact to the CNTs is made using evaporated Au/Ti. Electrical measurements of these air-bridge devices show well-defined ON and OFF states as a dc bias of a few volts is applied between the CNT and the Nb-base electrode. The CNT air-bridge switches were measured to have switching times down to a few nanoseconds. Our second NEM structure, the vertical CNT switch, consists of nanotubes grown perpendicular to the substrate. Vertical multi-walled nanotubes (MWNTs) are grown directly on a heavily doped Si substrate, from 200 - 300 nm wide, approximately 1 micrometer deep nano-pockets, with Nb metal electrodes to result in the formation of a vertical single-pole-double-throw switch architecture.

nanoelectromechanical systems (NEMS) devices↗
NASA NTRS1987

Study of optoelectronic switch for satellite-switched time-division multiple access

The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix.

Su, Shing-Fong↗
NASA NTRS2011

Heat Switches Providing Low-Activation Power and Quick-Switching Time for Use in Adiabatic Demagnetization Refrigerators

An adiabatic demagnetization refrigerator (ADR) is a solid-state cooler capable of achieving sub-Kelvin temperatures. It neither requires moving parts nor a density gradient in a working fluid making it ideal for use in space-based instruments. The flow of energy through the cooler is controlled by heat switches that allow heat transfer when on and isolate portions of the cooler when off. One type of switch uses helium gas as the switching medium. In the off state the gas is adsorbed in a getter thus breaking the thermal path through the switch. To activate the switch, the getter is heated to release helium into the switch body allowing it to complete the thermal path. A getter that has a small heat capacity and low thermal conductance to the body of the switch requires low-activation power. The cooler benefits from this in two ways: shorter recycle times and higher efficiency. We describe such a design here.

Kimball, Mark O.↗
NASA NTRS2011

Heat Switches Providing Low-Activation Power and Quick-Switching Time for Use in Cryogenic Multi-Stage Refrigerators

An adiabatic demagnetization refrigerator (ADR) is a solid-state cooler capable of achieving sub-Kelvin temperatures. It neither requires moving parts nor a density gradient in a working fluid making it ideal for use in space-based instruments. The flow of energy through the cooler is controlled by heat switches that allow heat transfer when on and isolate portions of the cooler when off. One type of switch uses helium gas as the switching medium. In the off state the gas is adsorbed in a getter thus breaking the thermal path through the switch. To activate the switch, the getter is heated to release helium into the switch body allowing it to complete the thermal path. A getter that has a small heat capacity and low thermal conductance to the body of the switch requires low-activation power. The cooler benefits from this in two ways: shorter recycle times and higher efficiency. We describe such a design here.

Kimball, Mark O.↗
NASA NTRS1986

Organization of the channel-switching process in parallel computer systems based on a matrix optical switch

After a classification and analysis of electronic and optoelectronic switching devices, the design principles and structure of a matrix optical switch is described. The switching and pair-exclusion operations in this type of switch are examined, and a method for the optical switching of communication channels is elaborated. Finally, attention is given to the structural organization of a parallel computer system with a matrix optical switch.

Golomidov, Y. V.↗
NASA NTRS2000

Finite Ground Coplanar Waveguide Shunt MEMS Switches for Switched Line Phase Shifters

Switches with low insertion loss and high isolation are required for switched line phase shifters and the transmit/receive switch at the front end of communication systems. A Finite Ground Coplanar (FGC) waveguide capacitive, shunt MEMS switch has been implemented on high resistivity Si. The switch has demonstrated an insertion loss of less than 0.3 dB and a return loss greater than 15 dB from 10 to 20, GHz. The switch design, fabrication, and characteristics are presented.

Ponchak, George E.↗
NASA NTRS2019

Gate Drive Technology Evaluation and Development to Maximize Switching Speed of SiC Discrete Devices and Power Modules in Hard Switching Applications

To understand the limitation of maximizing the switching speed of SiC low current discrete devices and high current power modules in hard switching applications, double pulse tests are conducted and the testing results are analyzed. For power modules, the switching speed is generally limited by the parasitics rather than the gate drive capability. For the discrete SiC device, the conventional voltage source gate drive (VSG) is not sufficient to maximize the switching speed even if the external gate resistance is minimized. The limitation of existing current source gate drives (CSG) are analyzed, and a CSG dedicated for SiC discrete devices is proposed, which can provide constant current during the switching transient regardless of the high Miller voltage and large internal gate resistance. Compared with the conventional VSG, the proposed CSG achieves 67% faster turnon time and 50% turn-off time, and 68% reduction in switching loss at full load condition.

Handong Gui↗
NASA NTRS1981

A high capacity satellite switched TDMA microwave switch matrix

A description is given of the conceptual design of a high-capacity satellite switched-time division multiple access (SS-TDMA) microwave switch matrix fabricated with GaAs monolithic microwave integrated circuits (MMICs), including integration of both microwave and control logic circuits into the monolithic design. The technology required for a 30/20 GHz communications system includes an on-board SS-TDMA switch matrix. A conceptual design study that has been completed for a wideband, high-capacity (typically 100 x 100) channel switch matrix using technology anticipated for 1987 is described, noting that the study resulted in a switch matrix design concept using a coupled crossbar architecture implemented with MMIC. The design involves basic building block MMIC, permitting flexible growth and efficient wraparound redundancy to increase reliability.

Cory, B. J.↗
NASA NTRS1966

Solid-state switch increases switching speed

Solid state switch for commutating capacitors in an RC commutated network increases switching speed and extends the filtering or commutating frequency spectrum well into the kilocycle region. The switch is equivalent to the standard double- pole double-throw /DPDT/ relay and is driven from digital micrologic circuits.

Mc~gowan, G. F.↗
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 NTRS1967

Hybrid solid state switch replaces motor- driven power switch

Hybrid solid state switch replaces existing motor-driven power switches used on spacecraft. It uses a transistor circuit to limit the open circuit voltage and allow small relay contacts to handle high transient currents at reasonable cycle life.

Booth, R. A.↗
NASA NTRS1993

Characteristics of switching plasma in an inverse-pinch switch

Characteristics of the plasma that switches on tens of giga volt-ampere in an inverse-pinch plasma switch (INPIStron) have been made. Through optical and spectroscopic diagnostics of the current carrying plasma, the current density, the motion of current paths, dominant ionic species have been determined in order to access their effects on circuit parameters and material erosion. Also the optimum operational condition of the plasma-puff triggering method required for azimuthally uniform conduction in the INPIStron has been determined.

Lee, Ja H.↗
NASA NTRS2002

MEMS, Ka-Band Single-Pole Double-Throw (SPDT) Switch for Switched Line Phase Shifters

Ka-band MEMS doubly anchored cantilever beam capacitive shunt devices are used to demonstrate a MEMS SPDT switch fabricated on high resistivity silicon (HRS) utilizing finite ground coplanar waveguide (FGC) transmission lines. The SPDT switch has an insertion loss (IL), return loss (RL), and isolation of 0.3dB, 40dB, and 30 dB, respectively at Ka-band.

Scardelletti, Maximilian C.↗
NASA NTRS1974

Evaluation report for toggle switches: Micro Switch and Cutler-Hammer models per MIL-S-3950

Several models of hermetically sealed toggle switches meeting the requirements of MIL-S-3950, were evaluated to determine the probability that they would withstand the environmental requirements of, and therefore be suitable for use on, the space shuttle vehicle. The evaluation was started with a comparison of the environmental requirements for space shuttle hardware. This was followed with in-house testing for those environments where a reasonably firm conclusion could not be drawn in the comparison. Space simulation, acceleration, and vibration testing were performed in-house.

Labberton, D.↗