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  • Other Sources  (2,346)
  • COMPOSITE MATERIALS  (1,199)
  • ELECTRONICS AND ELECTRICAL ENGINEERING  (1,147)
  • 1990-1994  (2,346)
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  • Other Sources  (2,346)
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  • 1
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    Transverse shear stresses and their sensitivity coefficients in multilayered composite panels (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A computational procedure is presented for the accurate determination of transverse shear stresses and their sensitivity coefficients in flat multilayered composite panels subjected to mechanical and thermal loads. The sensitivity coefficients measure the sensitivity of the transverse shear stresses to variations in the different lamination and material parameters of the panel. The panel is discretized by using either a three-field mixed finite element model based on a two-dimensional first- order shear deformation plate theory or a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the laminate. The evaluation of transverse shear stresses can be conveniently divided into two phases. The first phase consists of using a superconvergent recovery technique for evaluating the in-plane stresses in the different layers. In the second phase, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of the transverse shear stresses. The effectiveness of the computational procedure is demonstrated by means of numerical examples of multilayered cross-ply panels subjected to transverse loading, uniform temperature change, and uniform temperature gradient through the thickness of the panel. In each case the standard of the comparison is taken to be the exact solution of the three dimensional thermoelasticity equations of the panel.
    Keywords: COMPOSITE MATERIALS
    Type: AIAA Journal (ISSN 0001-1452); 32; 6; p. 1259-1269
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  • 2
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    Consideration of velocity saturation in the design of GaAs varactor diodes (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The design of GaAs Schottky barrier varactor diodes is reconsidered in light of the recent discovery of velocity saturation effects in these devices. Experimental data is presented which confirms that improved multiplier performance can be achieved.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Microwave and Guided Wave Letters (ISSN 1051-8207); 3; 6; p. 161-163.
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  • 3
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    Silicon micromachined waveguides for millimeter-wave and submillimeter-wave frequencies (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Rectangular waveguide is commonly used up to high millimeter-wave frequencies. However, conventional machining techniques for waveguides operating above a few hundred GHz are complicated and costly. The development of silicon micro-machining techniques to create silicon-based waveguide circuits, which can operate up to high submillimeter-wave frequencies, is reported. As a first step, WR-10 waveguide has been fabricated from (110) silicon wafers. Insertion loss measurements of gold plated silicon waveguide show performance comparable to standard metal waveguides. It is suggested that active devices and planar circuits can be integrated with the waveguides, solving the traditional mounting problems.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Microwave and Guided Wave Letters (ISSN 1051-8207); 3; 3; p. 61-63.
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  • 4
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    A new rectenna circuit using a bow-tie antenna for the conversion of microwave power to dc power (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The novel rectenna circuit presented, which integrated a bowtie antenna with a diode, is capable of broadband, high-efficiency operation, and is insensitive to incident field angle. The device is noted, moreover, to behave as a lowpass filter for dc output. For 2.45 GHz operation, a 79-percent conversion efficiency has been demonstrated.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Microwave and Optical Technology Letters (ISSN 0895-2477); 6; 11; p. 655, 656.
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  • 5
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    Repair of oxidation protection coatings on carbon-carbon using preceramic polymers (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The paper describes a field-applicable technique for the repair of damage to SiC protective coatings on carbon/carbon composites, using commercial preceramic polymers, such as perhydropolysilazane developed by the Southwest Research Institute and several commercial polymers (NICALON, PS110, PS116, PS117, NCP-200, and PHPS were tested). After being applied on the damaged panel and oxidized at 1400 C, these polymers form either SiC or Si3N4 (or a mixture of both). It was found that impact damaged carbon/carbon specimens repaired with perhydropolysilazane exhibit substantial oxidation resistance. Many of the other tested preceramic polymer were found to be unsuitable for the purpose of repair due to either low ceramic yield, foaming, or intumescence.
    Keywords: COMPOSITE MATERIALS
    Type: In: Damage and oxidation protection in high temperature composites. Vol. 1; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-53937 23-24); p. 131-138.
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  • 6
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    Approaches to polymer-derived CMC matrices (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The use of polymeric precursors to ceramics permits the fabrication of large, complex-shaped ceramic matrix composites (CMC's) at temperatures which do not degrade the fiber. Processing equipment and techniques readily available in the resin matrix composite industry can be adapted for CMC fabrication using this approach. Criteria which influence the choice of candidate precursor polymers, the use of fillers, and the role of fiber architecture and ply layup are discussed. Three polymer systems, polycarbosilanes, polysilazanes, and polysilsesquioxanes, are compared as candidate ceramic matrix precursors.
    Keywords: COMPOSITE MATERIALS
    Type: In: International SAMPE Technical Conference, 24th and International SAMPE Metals and Metals Processing Conference, 3rd, Toronto, Canada, Oct. 20-22, 1992, Proceedings. Vol. 24 (A93-53376 23-23); p. T950-T961.
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  • 7
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    Unfulfilled needs in IR astronomy focal-plane readout electronics (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The NOAO's 8-m IR optimized telescope for Mauna Kea and NASA's SIRTF show that from 1 to 200 microns there are a number of unfulfilled needs in readout electronics. These include: extremely low readnoise, less than 10 electrons, stable operation at temperatures as low as 2 K, high well capacity, greater than 1 e 7 electrons, and integration times from 30 msec to over 100 sec. Sensors for adaptive optics systems are required with readnoise less than 10 electrons and response times of 30 msec. They should be highly efficient from 1 to 2.5 microns, but may have small formats. Ground-based imagers at these wavelengths need comparable readnoise but longer integration times, and the largest possible formats are essential. To achieve these goals improved cryogenic MOSFETS are essential and complete cryogenic CMOS circuits are highly desirable. Experimental cryoptimized MFETS promise to exceed the above noise requirements at 77 K and approach the needs at 2 K.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Infrared readout electronics; Proceedings of the Meeting, Orlando, FL, Apr. 21, 22, 1992 (A93-53076 23-33); p. 168-174.
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  • 8
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    AE 152 cascode readout for far-IR focal plane arrays (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The Amber Engineering AE 152 readout is a 32-channel multiplexer built as part of the FIR focal plane array development effort for the Space Infrared Telescope Facility (SIRTF). The design of the device addresses a number of constraints peculiar to the operation of germanium photoconductors. In particular, the need for a very high level of bias stability is solved by a nonswitched operation of the first stage. Additionally, the readout was optimized for the detector capacitance expected of large bulk photoconductors (about 0.7 pF) and for the slow operating speeds anticipated for this astronomical application. Fabricated in a 1.25-micron C-MOS process, the circuit utilizes a cascode input stage to provide gain at the front end while avoiding the Miller effect. The AE 152 also includes an internal offset correction and a shift register multiplexer for the output. We present test data for this device at a variety of temperatures, and show read noises as low as 8 electrons at a temperature of 77 K.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Infrared readout electronics; Proceedings of the Meeting, Orlando, FL, Apr. 21, 22, 1992 (A93-53076 23-33); p. 55-62.
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  • 9
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    256x256 switched-FET multiplexer for spaceborne astronomical applications (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A novel cryogenic design of a source follower per detector (SFD) direct readout multiplexer is demonstrated. This design has proven to be a good prototype for the development of new low-noise large-area cryogenic multiplexers. In the absence of clocking noise, the readout demonstrates as low as about 30 electrons of rms read noise. There is still an excess noise component feeding through when the array is clocked, which manifests itself only at the lower temperatures. The shape of this component is dependent on a number of the bias voltages, and especially on the temperature of the chip. Analysis of the noise spectral density of the unit cell under various bias conditions shows that there is an excess spectral noise component at the lower temperatures.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Infrared readout electronics; Proceedings of the Meeting, Orlando, FL, Apr. 21, 22, 1992 (A93-53076 23-33); p. 40-48.
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  • 10
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    A 26 to 220 GHz harmonic mixer-receiver (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A wideband mm-wave harmonic mixer-receiver has been developed using a wideband integrated-circuit antenna, a back-to-back Schottky-barrier diode chip and microwave circuit design. The design is planar, simple to build and yields excellent performance from 26 to 180 GHz. Application areas include wideband early warning systems, wideband search and rescue systems and the extension of spectrum analyzer and power meter range to the mm-wave region.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Microwave Journal (ISSN 0192-6225); 36; 7; p. 103-108.
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