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Dual Common Planes for Time Multiplexing of Dual-Color QWIPs

With external control, commercial single-color readout integrated circuits could be used. A proposed improved method of externally controlled time multiplexing of the readouts of focal plane arrays of pairs of stacked quantum well infrared photodetectors (QWIPs) that operate in different wavelength bands is based on a dual detector common plane circuit configuration. The method would be implemented in a QWIP integrated-circuit chip hybridized with a readout integrated circuit (ROIC) chip.

Posted in: Semiconductors & ICs, Briefs

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MMIC Power Amplifier Puts Out >40 mW From 75 to 110 GHz

This amplifier operates over the full frequency band of the WR-10 waveguide. A three-stage monolithic microwave integrated circuit (MMIC) W-band amplifier has been constructed and tested in a continuing effort to develop amplifiers as well as oscillators, frequency multipliers, and mixers capable of operating over wide frequency bands that extend above 100 GHz. There are numerous potential uses for MMICs like these in scientific instruments, radar systems, communication systems, and test equipment operating in this frequency range. This amplifier can be characterized, in part, as a lower-frequency, narrower band, higher-gain version of the one described in “Power Amplifier With 9 to 13 dB of Gain from 65 to 146 GHz” (), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 44. This amplifier includes four InP high-electron-mobility transistors (HEMTs), each having a gate periphery of 148 µm. In the third amplifier stage, two of the HEMTs are combined in parallel to maximize the output power. The amplifier draws a current of 250 mA at a supply potential of 2.5 V.

Posted in: Semiconductors & ICs, Briefs

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Design and Selection Considerations for High-Temperature Aerospace Accelerometers

Considerations include material selection, construction, and radiation tolerance. Accelerometers used for shock and vibration measurement in extreme environments require special consideration in the design and manufacturing process. Certain unique applications can require the same accelerometer to function from -54 to 649 °C (-65 to 1,200 ° F). This might include such applications as vibration measurement on gas turbine engines, in flight, or in test cells; rocket motor vibration measurements; and thruster vibration. These accelerometers also may need to function in nuclear radiation environments, and possibly in a combination of temperature extremes and radiation. This might include nuclear power generation or space vehicle applications. Materials and construction must then be selected not only to enhance high temperature performance, but also to allow operation in the presence of gamma and neutron radiation

Posted in: Physical Sciences, Briefs

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Microscale Regenerative Heat Exchanger

Materials and dimensions are chosen to optimize performance at microscale. The device illustrated in Figure 1 is designed primarily for use as a regenerative heat exchanger in a miniature Stirling engine or Stirling-cycle heat pump. A regenerative heat exchanger (sometimes called, simply, a “regenerator” in the Stirling-engine art) is basically a thermal capacitor: Its role in the Stirling cycle is to alternately accept heat from, then deliver heat to, an oscillating flow of a working fluid between compression and expansion volumes, without introducing an excessive pressure drop. These volumes are at different temperatures, and conduction of heat between these volumes is undesirable because it reduces the energy-conversion efficiency of the Stirling cycle. Hence, among the desired characteristics of a regenerative heat exchanger are low pressure drop and low thermal conductivity along the flow axis.

Posted in: Physical Sciences, Briefs

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Multimode-Guided-Wave Ultrasonic Scanning of Materials

Two documents discuss a method of characterizing advanced composite materials by use of multimode-guided ultrasonic waves. The method at an earlier stage of development was described in “High-Performance Scanning Acousto-Ultrasonic System” (), NASA Tech Briefs, Vol. 30, No. 3 (March 2006), page 62. To recapitulate: A transmitting transducer excites modulated (e.g., pulsed) ultrasonic waves at one location on a surface of a plate specimen. The waves interact with microstructure and flaws as they propagate through the specimen to a receiving transducer at a different location. The received signal is analyzed to determine the total (multimode) ultrasonic response of the specimen and utilize this response to evaluate microstructure and flaws. The analysis is performed by software that extracts parameters of signals in the time and frequency domains. Scanning is effected by using computer controlled motorized translation stages to position the transducers at specified pairs of locations and repeating the measurement, data-acquisition, and data-analysis processes at the successive locations. The instant documents reiterate the prior description and summarize capabilities of the hardware and software of the method at the present state of development. One document presents results of a scan of a specimen containing a delamination.

Posted in: Physical Sciences, Briefs

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Satellite Multiangle Spectropolarimetric Imaging of Aerosols

One instrument would implement a synergistic combination of multispectral, multiangle, and polarimetric techniques. A proposed remote-sensing instrument, to be carried aboard a spacecraft in orbit around the Earth, would gather data on the spatial distribution and radiative characteristics of tropospheric aerosols. These data are needed for better understanding of the natural and anthropogenic origins of aerosols, and of the effects of aerosols on climate and atmospheric chemistry.

Posted in: Physical Sciences, Briefs

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Measuring Attitude of a Large, Flexible, Orbiting Structure

A document summarizes a proposed metrology subsystem for precisely measuring the attitude of a large and flexible structure in space.

Posted in: Physical Sciences, Briefs

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