Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Amplifiers”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

The QBO as Potential Amplifier and Conduit to Lower Altitudes of Solar Cycle Influence

The solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO), which is generated primarily by small-scale gravity waves. Salby and Callaghan analyzed the QBO observations covering more than 40 years and found that it contains a relatively large SC signature at 20 km. Following up on a 2D study with our Numerical Spectral Model (NSM), we discuss here a 3D study in which we simulated the QBO under the influence of the SC. For a SC period of 10 years, the amplitude of the relative variations of radiative forcing is taken to vary from 0.2% at the surface to 2% at 50 km to 20% at 100 km and above. This model produces in the lower stratosphere a relatively large modulation of the QBO, which appears to be related to the SC and is in qualitative agreement with the observations. Further studies are needed, (1) to determine whether the effect is real and the results are robust and (2) to explore the mechanism(s) that may amplify the SC effect. Quasi-decadal oscillations, generated internally by the QBO interacting with the seasonal cycles, may interfere with or aid the SC effect.

Mayr, Hans G.↗
NASA NTRS2005

The QBO as Potential Amplifier and Conduit to Lower Altitudes of Solar Cycle Influence?

The solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO), which is generated primarily by small-scale gravity waves (GW). Following up on a 2D study with our Numerical Spectral Model (NSM), we discuss here a 3D study in which we simulated the QBO under the influence of the SC. For a SC period of 10 years, the relative amplitude of radiative forcing is taken to vary exponentially with height, i.e., 0.2% at the surface, 2% at 50 km, 20% at 100 km and above. Applying spectral analysis to filter out and identify the SC signature, this model produces a relatively large modulation in the QBO of the lower stratospheric circulation, which is in qualitative agreement with the results obtained by Salby and Callaghan (2000) who analyzed zonal wind observations covering more than 40 years. The modeled SC modulation of the QBO extends to high latitudes where it produces temperature variations of about 1 K in the troposphere below 10 km. We report that the SC also generates in the model a hemispherically symmetric Equatorial Annual Oscillation (EAO, with 12-month period) that is largely confined to low latitudes. Under the influence of the GWs, the SC modulated EA0 propagates down into the lower stratosphere like the QBO. As is the case for the QBO, the energy of this EA0 is partially redistributed by the meridional circulation and planetary waves, presumably, to generate measurable SC signatures in the tropospheric temperature of the polar regions, which may be related to the so called Arctic Oscillation (Thompson and Wallace, 1998). The larger SC influence at higher altitudes is apparently transferred to the lower and denser regions of the atmosphere by tapping the momentum from the upward propagating GWs that drive the oscillations. The SC modulation of the QBO period could prove to be very effective in this process, as our earlier 2D study indicated. Further studies are needed, (1) to make sure that the SC effects are real and the numerical results are robust, and (2) to explore more fully the mechanism(s) that may conspire to amplify the SC effect. Quasi-decadal oscillations, generated internally by the QBO interacting with the seasonal cycles, may interfere with, or aid, the SC influence.

Mayr, Hans G.↗
NASA NTRS2002

Power-Efficient, High-Current-Density, Long-Life Thermionic Cathode Developed for Microwave Amplifier Applications

A power-efficient, miniature, easily manufactured, reservoir-type barium-dispenser thermionic cathode has been developed that offers the significant advantages of simultaneous high electron-emission current density (>2 A/sq cm) and very long life (>100,000 hr of continuous operation) when compared with the commonly used impregnated-type barium-dispenser cathodes. Important applications of this cathode are a wide variety of microwave and millimeter-wave vacuum electronic devices, where high output power and reliability (long life) are essential. We also expect it to enable the practical development of higher purveyance electron guns for lower voltage and more reliable device operation. The low cathode heater power and reduced size and mass are expected to be particularly beneficial in traveling-wave-tube amplifiers (TWTA's) for space communications, where future NASA mission requirements include smaller onboard spacecraft systems, higher data transmission rates (high frequency and output power) and greater electrical efficiency.

Wintucky, Edwin G.↗
NASA NTRS2006

Ka-Band Wide-Bandgap Solid-State Power Amplifier: Prototype Combiner Spurious Mode Suppression and Power Constraints

Results of prototype hardware activities related to a 120-W, 32-GHz (Ka-band) solid-state power amplifier (SSPA) architecture study are presented. Spurious mode suppression and the power-handling capability of a prototype 24-way radial combiner and a prototype 2-way septum binary combiner were investigated. Experimental data indicate that a commercial absorptive filter, designed to pass the circular TE01 mode, effectively suppressed the higher-order modes generated by a narrowband, flower-petal-type mode transducer. However, the same filter was not effective in suppressing higher-order modes generated by the broadband Marie mode transducer that is used in the prototype waveguide radial combiner. Should greater filtering be required by a particular SSPA application, a broadband mode filter that can suppress specifically those higher-order modes that are generated by the Marie transducer will need to be developed. A back-to-back configuration of the prototype radial combiner was tested with drive power up to approximately 50 W. No anomalous behavior was observed. Power measurements of the septum combiner indicate that up to 10-W radio frequency (RF) can be dissipated in the integrated resistive element before a permanent performance shift is observed. Thus, a given adder (a single-stage, 2-way combiner) can safely combine two 20-W sources, and the adder will not be damaged in the event of a source failure. This result is used to calculate the maximum source power that can be safely combined as a function of the number of sources combined and the number of source failures allowed in a multi-stage combiner. The analysis shows that SSPA power >140 W can be generated by power combining 16 sources producing 10 W each. In this configuration, up to three sources could fail with the guarantee that the combiner would not be damaged. Finally, a modified prototype septum combiner design was verified. The improved design reduced the assembly time from over 2 hours to about 15 minutes per adder.

Khan, P.↗
NASA NTRS2005

Temperature Tolerant Evolvable Systems Utilizing FPGA Boards and Bias-Controlled Amplifiers

Space missions often require radiation and extreme-temperature hardened electronics to survive the harsh environments beyond Earth's atmosphere. Traditional approaches to preserve electronics incorporate shielding, insulation and redundancy at the expense of power and weight. However, a novel way of bypassing these problems is the concept of evolutionary hardware. A reconfigurable device, consisting of several switches interconnected with analog/digital parts, is controlled by an evolutionary processor (EP). When the EP detects degradation in the circuit it sends signals to reconfigure the switches, thus forming a new circuit with the desired output. This concept has been developed since the mid-l990s, but one problem remains-the EP cannot degrade substantially. For this reason, extensive testing at extreme temperatures (-180 to 120 C) has been done on devices found on FPGA boards (taking the role of the EP), such as the Analog to Digital and the Digital to Analog Converter. The EP is used in conjunction with a bias-controlled amplifier and a new prototype relay board, which is interconnected with 6 G4-FETs, a tri-input transistor-like element developed at JPL. The greatest improvements to be made lie in the reconfigurable device, so future design and testing of the G4-FET chip is required.

Kumar, Nikhil R.↗
NASA NTRS2004

High-Resolution Displacement Sensor Using a SQUID Array Amplifier

Improvement in the measurement of displacement has profound implications for both exploration technologies and fundamental physics. For planetary exploration, the new SQUID-based capacitive displacement sensor will enable a more sensitive gravity gradiometer for mapping the interior of planets and moons. A new concept of a superfluid clock to be reported by Penanen and Chui at this workshop is also based on a high-resolution displacement sensor. Examples of high-impact physics projects that can benefit from a better displacement sensor are: detection of gravitational waves, test of the equivalence principle, search for the postulated "axion" particle, and test of the inverse square law of gravity. We describe the concept of a new displacement sensor that makes use of a recent development in the Superconducting Quantum Interference Device (SQUID) technology. The SQUID array amplifier, invented by Welty and Martinis (IEEE Trans. Appl. Superconductivity 3, 2605, 1993), has about the same noise as a conventional SQUID; however, it can work at a much higher frequency of up to 5 MHz. We explain how the higher bandwidth can be translated into higher resolution using a bridge-balancing scheme that can simultaneously balance out both the carrier signal at the bridge output and the electrostatic force acting on the test mass.

Chui, Talso↗
NASA NTRS1999

Can El Nino Amplify the Solar Forcing of Climate?

ENSO (El Nino and the Southern Oscillation) is considered as a stochastic driver that excites the atmospheric anomaly states, such as Pacific North American pattern. This can make the 11 year solar activity forcing feasible to climate through stochastic resonance -- a phenomenon that amplifies a weak input to a nonlinear bistable system by the assistance of noise.

ENSO El Nino Oscillation climate stochastic resona↗
NASA NTRS2003

Amplifier arrays for CMB polarization

Cryogenic low noise amplifier technology has been successfully used in the study of the cosmic microwave background (CMB). MMIC (Monolithic Millimeter wave Integrated Circuit) technology makes the mass production of coherent detection receivers feasible.

CMB↗
NASA NTRS2006

Towards Terahertz MMIC Amplifiers: Present Status and Trends

This viewgraph presentation surveys the fastest Monolithic Millimeter-wave Integrated Circuit (MMIC) amplifiers to date; summarize previous solid state power amp results to date; reviews examples of MMICs, reviews Power vs. Gate periphery and frequency; Summarizes previous LNA results to date; reviews Noise figure results and trends toward higher frequency

FET ampllifiers↗
NASA NTRS2007

Fabrication of a Thermally Isolated and Pre-amplified Transistor Module with Polyimide Micro-wires for Cryogenic Detectors

For use in cryogenic applications such as bolometer and x-ray microcalorimeter arrays, pre-amplifying Junction Field Effect Transistors (JFETs) are often required for the readout electronics. The optimum operating temperature of the JFETs is 130 Kelvin while the cryogenic detectors operate in the milli-Kelvin range. Thus, the JFETs must be heated up but thermally isolated from the surrounding cryogenic instruments. In the past, the thermal isolation was accomplished by suspending the JFETs with low conductance wires such as manganium or stainless steel on a Kevlar support platform [I]. This also achieved electrical connections. However, this assembly required manual soldering work, which could raise a reliability issue for the cryogenic applications. In order to eliminate the manual work, polyimide micro-wires were developed [2]. The wires must be of sufficient length to decrease the heat load and in tension to prevent microphonic noise from vibration of the wires: the polyimide wires were patterned into llS"shaped curves over a thin metal wires such as aluminum, titanium, or niobium. The bilayer of the films were then suspended by etching silicon substrate thus to make freestanding air bridges (enough explanation?). In this paper, we present a method to fabricate micromachined JFET mechanical modules suspended by polyimide Pyraline micro-wires and heated up with built-in aluminum micro-heaters.

Oh, L. H.↗
NASA NTRS1994

Self-amplified optical pattern recognition system

A self amplifying optical pattern recognizer includes a geometric system configuration similar to that of a Vander Lugt holographic matched filter configuration with a photorefractive crystal specifically oriented with respect to the input beams. An extraordinarily polarized, spherically converging object image beam is formed by laser illumination of an input object image and applied through a photorefractive crystal, such as a barium titanite (BaTiO.sub.3) crystal. A volume or thin-film dif ORIGIN OF THE INVENTION The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 USC 202) in which the Contractor has elected to retain title.

Liu, Hua-Kuang↗
NASA NTRS1980

Push-pull switching power amplifier

A true push-pull switching power amplifier is disclosed utilizing two dc-to-dc converters. Each converter is comprised of two inductances, one inductance in series with a DC source and the other inductor in series with the output load, and an electrical energy transferring device with storage capability, namely storage capacitance, with suitable switching means between the inductances to obtain DC level conversion, where the switching means allows bidirectional current (and power) flow, and the switching means of one dc-to-dc converter is driven by the complement of a square-wave switching signal for the other dc-to-dc converter for true push-pull operation. For reduction of current ripple, the inductances in each of the two converters may be coupled, and with proper design of the coupling, the ripple can be reduced to zero at either the input or the output, but preferably the output.

Cuk, Slobodan M.↗
NASA NTRS1999

Charge integration successive approximation analog-to-digital converter for focal plane applications using a single amplifier

An analog-to-digital converter for on-chip focal-plane image sensor applications. The analog-to-digital converter utilizes a single charge integrating amplifier in a charge balancing architecture to implement successive approximation analog-to-digital conversion. This design requires minimal chip area and has high speed and low power dissipation for operation in the 2-10 bit range. The invention is particularly well suited to CMOS on-chip applications requiring many analog-to-digital converters, such as column-parallel focal-plane architectures.

Zhou, Zhimin↗
NASA NTRS1997

Multi-pass light amplifier

A multiple-pass laser amplifier that uses optical focusing between subsequent passes through a single gain medium so that a reproducibly stable beam size is achieved within the gain region. A confocal resonator or White Cell resonator is provided, including two or three curvilinearly shaped mirrors facing each other along a resonator axis and an optical gain medium positioned on the resonator axis between the mirrors (confocal resonator) or adjacent to one of the mirrors (White Cell). In a first embodiment, two mirrors, which may include adjacent lenses, are configured so that a light beam passing through the gain medium and incident on the first mirror is reflected by that mirror toward the second mirror in a direction approximately parallel to the resonator axis. A light beam translator, such as an optical flat of transparent material, is positioned to translate this light beam by a controllable amount toward or away from the resonator axis for each pass of the light beam through the translator. The optical gain medium may be solid-state, liquid or gaseous medium and may be pumped longitudinally or transversely. In a second embodiment, first and second mirrors face a third mirror in a White Cell configuration, and the optical gain medium is positioned at or adjacent to one of the mirrors. Defocusing means and optical gain medium cooling means are optionally provided with either embodiment, to controllably defocus the light beam, to cool the optical gain medium and to suppress thermal lensing in the gain medium.

Plaessmann, Henry↗
NASA NTRS1996

Multi-pass light amplifier

A multiple-pass laser amplifier that uses optical focusing between subsequent passes through a single gain medium so that a reproducibly stable beam size is achieved within the gain region. A resonator or a White Cell cavity is provided, including two or more mirrors (planar or curvilinearly shaped) facing each other along a resonator axis and an optical gain medium positioned on a resonator axis between the mirrors or adjacent to one of the mirrors. In a first embodiment, two curvilinear mirrors, which may include adjacent lenses, are configured so that a light beam passing through the gain medium and incident on the first mirror is reflected by that mirror toward the second mirror in a direction approximately parallel to the resonator axis. A light beam translator, such as an optical flat of transparent material, is positioned to translate this light beam by a controllable amount toward or away from the resonator axis for each pass of the light beam through the translator. A second embodiment uses two curvilinear mirrors and one planar mirror, with a gain medium positioned in the optical path between each curvilinear mirror and the planar mirror. A third embodiment uses two curvilinear mirrors and two planar mirrors, with a gain medium positioned adjacent to a planar mirror. A fourth embodiment uses a curvilinear mirror and three planar mirrors, with a gain medium positioned adjacent to a planar mirror. A fourth embodiment uses four planar mirrors and a focusing lens system, with a gain medium positioned between the four mirrors. A fifth embodiment uses first and second planar mirrors, a focusing lens system and a third mirror that may be planar or curvilinear, with a gain medium positioned adjacent to the third mirror. A sixth embodiment uses two planar mirrors and a curvilinear mirror and a fourth mirror that may be planar or curvilinear, with a gain medium positioned adjacent to the fourth mirror. In a seventh embodiment, first and second mirrors face a third mirror, all curvilinear, in a White Cell configuration, and a gain medium is positioned adjacent to one of the mirrors.

Plaessmann, Henry↗