Tech Briefs

Wavefront Sensing With Switched Lenses for Defocus

It is no longer necessary to translate a camera to precisely controlled defocus positions.

In an alternative hardware design for an apparatus used in image-based wavefront sensing, defocus diversity is introduced by means of fixed lenses that are mounted in a filter wheel (see figure) so that they can be alternately switched into a position in front of the focal plane of an electronic camera recording the image formed by the optical system under test. [The terms “image-based”, “wavefront sensing”, and “defocus diversity” are defined in the first of the three immediately preceding articles, “Broadband Phase Retrieval for Image-Based Wavefront Sensing” (GSC-14899-1).] Each lens in the filter wheel is designed so that the optical effect of placing it at the assigned position is equivalent to the optical effect of translating the camera a specified defocus distance along the optical axis.

Posted in: Briefs, TSP, Physical Sciences, Calibration, Imaging and visualization, Remote sensing, Switches, Test procedures
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Smooth Phase Interpolated Keying

Excellent performance can be obtained without excessive complexity.

Smooth phase interpolated keying (SPIK) is an improved method of computing smooth phase-modulation waveforms for radio communication systems that convey digital information. SPIK is applicable to a variety of phase-shift-keying (PSK) modulation schemes, including quaternary PSK (QPSK), octonary PSK (8PSK), and 16PSK. In comparison with a related prior method, SPIK offers advantages of better performance and less complexity of implementation.

Posted in: Briefs, Electronics & Computers, Communication protocols, Data exchange, Wireless communication systems
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Maintaining Stability During a Conducted-Ripple EMC Test

Ripple is now injected via amplifier-controlled FETs instead of a transformer.

An improved technique, and electronic circuitry to implement the technique, have been developed for a military-standard electromagnetic- compatibility (EMC) test in which one analyzes susceptibility to low-frequncy ripple conducted into the equipment under test via a DC power line. In the traditional technique for performing the particular test, the ripple is coupled onto the DC power line via a transformer. Depending upon some design details of the equipment under test, the inductance of the transformer can contribute a degree of instability that results in an oscillation of amplitude large enough to destroy the equipment.

Posted in: Briefs, TSP, Electronics & Computers, Electric cables, Electromagnetic compatibility, Electronic equipment, Test procedures, Military vehicles and equipment
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Photodiode Preamplifier for Preamplifier for Weak Signals

This circuit suppresses noise without sacrificing timing accuracy.

An improved preamplifier circuit has been designed for processing the output of an avalanche photodiode (APD) that is used in a high-resolution laser ranging system to detect laser pulses returning from a target. The improved circuit stands in contrast to prior such circuits in which the APD output current pulses are made to pass, variously, through wide-band or narrow-band load networks before preamplification. A major disadvantage of the prior wide-band load networks is that they are highly susceptible to noise, which degrades timing resolution. A major disadvantage of the prior narrow-band load networks is that they make it difficult to sample the amplitudes of the narrow laser pulses ordinarily used in ranging.

Posted in: Briefs, Electronics & Computers, Amplifiers, Lasers, Performance upgrades
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Advanced High-Definition Video Cameras

A product line of high-definition color video cameras, now under development, offers a superior combination of desirable characteristics, including high frame rates, high resolutions, low power consumption, and compactness. Several of the cameras feature a 3,840 × 2,160-pixel format with progressive scanning at 30 frames per second. The power consumption of one of these cameras is about 25 W. The size of the camera, excluding the lens assembly, is 2 by 5 by 7 in. (about 5.1 by 12.7 by 17.8 cm).

Posted in: Briefs, Electronics & Computers, Imaging and visualization, Product development, Performance tests
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Circuit for Full Charging of Series Lithium-Ion Cells

Differences among cells would no longer prevent full charging.

An advanced charger has been proposed for a battery that comprises several lithium-ion cells in series. The proposal is directed toward charging the cells in as nearly an optimum manner as possible despite unit-to-unit differences among the nominally identical cells.

Posted in: Briefs, Semiconductors & ICs, Optimization, Lithium-ion batteries, Off-board vehicle charging systems
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Analog Nonvolatile Computer Memory Circuits

Digital data would be stored in analog form in FFETs.

In nonvolatile random-access memory (RAM) circuits of a proposed type, digital data would be stored in analog form in ferroelectric field-effect transistors (FFETs). This type of memory circuit would offer advantages over prior volatile and nonvolatile types:

In a conventional complementary metal oxide/semiconductor static RAM, six transistors must be used to store one bit, and storage is volatile in that data are lost when power is turned off. In a conventional dynamic RAM, three transistors must be used to store one bit, and the stored bit must be refreshed every few milliseconds. In contrast, in a RAM according to the proposal, data would be retained when power was turned off, each memory cell would contain only two FFETs, and the cell could store multiple bits (the exact number of bits depending on the specific design).
Posted in: Briefs, TSP, Semiconductors & ICs, Computer software and hardware, Integrated circuits, Data management
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World Wind 3D Earth Viewing

World Wind allows users to zoom from satellite altitude down to any place on Earth, leveraging high-resolution LandSat imagery and SRTM (Shuttle Radar Topography Mission) elevation data to experience Earth in visually rich 3D. In addition to Earth, World Wind can also visualize other planets, and there are already comprehensive data sets for Mars and the Earth’s moon, which are as easily accessible as those of Earth.

Posted in: Briefs, Software, Imaging and visualization, Satellite communications, Human machine interface (HMI)
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JavaGenes Molecular Evolution

JavaGenes is a general-purpose, evolutionary software system written in Java. It implements several versions of a genetic algorithm, simulated annealing, stochastic hill climbing, and other search techniques. This software has been used to evolve molecules, atomic force field parameters, digital circuits, Earth Observing Satellite schedules, and antennas. This version differs from version 0.7.28 in that it includes the molecule evolution code and other improvements. Except for the antenna code, JaveGenes is available for NASA Open Source distribution.

Posted in: Briefs, Software, Mathematical models, Antennas, Computer software and hardware, Electronic control systems
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Accounting for Uncertainties in Strengths of SiC MEMS Parts

Fracture strength of a part can be predicted as one statistical distribution.

A methodology has been devised for accounting for uncertainties in the strengths of silicon carbide structural components of microelectromechanical systems (MEMS). The methodology enables prediction of the probabilistic strengths of complexly shaped MEMS parts using data from tests of simple specimens. This methodology is intended to serve as a part of a rational basis for designing SiC MEMS, supplementing methodologies that have been borrowed from the art of designing macroscopic brittle material structures.

Posted in: Briefs, TSP, Materials, Finite element analysis, Microelectromechanical devices, Prognostics, Materials properties, Silicon alloys
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