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At least 433 records · Page 24

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NASA NTRS1974

Coherent optical noise suppression device

The present work describes a scheme for a noise suppression system to be used with an afocal coherent optical data processor. The noise averaging scheme is based on the simple principle of moving input and output film planes together during exposure; the noise pattern remains stationary while the desired (filtered) image moves through it. The noise suppression system consists of a drive motor, right-angle gear box, reversing gear assemblage, right-angle gear drive, and micrometer adjusting translation tables. The device was tested by using a Sayce target containing fundamental spatial frequencies from 5 lines/mm to 100 lines/mm as the input signal. The output was photographed on Pan-X 35-mm film with and without the noise suppression system in operation. Microdensitometer scans of the exposed output film show that without noise averaging, resolution is good to about 80 lines/mm, while with noise averaging, it is good to about 35 lines/mm. A brief analysis of errors in the mechanical parts of the system reponsible for the upper limit of resolution is presented.

Horner, J. L.↗

NASA NTRS1982

Dynamics and mechanism of cavitation erosion on perspex and epoxy resins tested in a rotating disk device

The cavitation erosion behavior including the initiation, dynamics and mechanism of damage process on perspex and epoxy resin specimens tested in a rotating disk device were discussed with respect to exposure time. The inception of erosion always took place at the location nearest to the center of rotation of the disk. Subsequently, as exposure time increased, erosion initiated at other locations as well. Light optical photographs and scanning electron micrographs clearly indicate that most of the material loss appears to occur form the networks of cracks due to their interaction and pits indicate particle debris. The optical degradation (loss of transmittance) on perspex was observed to be more on the rear side than on the front side.

Rao, P. V.↗

NASA NTRS1983

Cavitation erosion characteristics of poly(methyl methacrylate) in a rotating disk device

Veerabhadra Rao, P.↗

NASA NTRS1985

The prototype MOSAIC detector

The prototype of the MOSAIC (Mosaicked Optical Self-scanned Array Imaging Camera) system, a photon-counting detector designed for use in the far ultraviolet, is described. MOSAIC has a two-dimensional format of 2400 x 2400 pixels, and is easily expandable. Readout is accomplished electronically via charge-coupled devices, making possible remote observations. Preliminary results of computer simulations of the system are presented.

Weistrop, D.↗

NASA NTRS2004

A MEMS Micro-Translation Stage with Long Linear Translation

A MEMS Micro-Translation Stage (MTS) actuator concept has been developed that is capable of traveling long distances, while maintaining low power, low voltage, and accuracy as required by many applications, including optical coupling. The Micro-Translation Stage (MTS) uses capacitive electrostatic forces in a linear motor application, with stationary stators arranged linearly on both sides of a channel, and matching rotors on a moveable shuttle. This creates a force that allows the shuttle to be pulled along the channel. It is designed to carry 100 micron-sized elements on the top surface, and can travel back and forth in the channel, either in a stepping fashion allowing many interim stops, or it can maintain constant adjustable speeds for a controlled scanning motion. The MTS travel range is limited only by the size of the fabrication wafer. Analytical modeling and simulations were performed based on the fabrication process, to assure the stresses, friction and electrostatic forces were acceptable to allow successful operation of this device. The translation forces were analyzed to be near 0.5 micron N, with a 300 micron N stop-to-stop time of 11.8 ms.

Ferguson, Cynthia K.↗

NASA NTRS2000

Evaluation of Data Retention and Imprint Characteristics of FRAMs Under Environmental Stresses for NASA Applications

A major reliability issue for all advanced nonvolatile memory (NVM) technology devices including FRAMs (Ferroelectric random access memories) is the data retention characteristics over extended period of time, under environmental stresses and exposure to total ionizing dose (TID) radiation effects. For this testing, 256 Kb FRAMs in 28-pin plastic DIPS, rated for industrial grade temperature range of -40 C to +85 C, were procured. These are two-transistor, two-capacitor (2T-2C) design FRAMs. In addition to data retention characteristics, the parts were also evaluated for imprint failures, which are defined as the failure of cells to change from a "preferred" state, where it has been for a significant period of time to an opposite state (e.g., from 1 to 0, or 0 to 1). These 256 K FRAMs were subjected to scanning acoustic microscopy (C-SAM); 1,000 temperature cycles from -65 C to +150 C; high temperature aging at 150 C, 175 C, and 200 C for 1,000 hours; highly accelerated stress test (HAST) for 500 hours; 1,000 hours of operational life test at 125 C; and total ionizing dose radiation testing. As a preconditioning, 10 K read/write cycles were performed on all devices. Interim electrical measurements were performed throughout this characterization, including special imprint testing and final electrical testing. Some failures were observed during high temperature aging test at 200 C, during HAST testing, and during 1,000 hours of operational life at 125 C. The parts passed 10 Krad exposure, but began showing power supply current increases during the dose increment from 10 Krad to 30 Krad, and at 40 Krad severe data retention and parametric failures were observed. Failures from various environmental group testing are currently being analyzed.

Sharma, Ashok K.↗

NASA NTRS1986

Test of IR arrays on the Kuiper Airborne Observatory

NASA's Kuiper Airborne Observatory, which is a C-141 transport aircraft equipped with a 90-cm, all-reflective altazimuth telescope, has been engaged in the Kuiper Infrared Technology Experiment. Attention is presently given to the Experiment's flight series for state-of-the-art two-dimensional, 500-element arrays that use either blocked impurity band or bulk silicon devices. The switched FET readout scheme used on the three arrays flown thus far yields exceptionally low crosstalk. System sensitivities are found to be sufficient for the detection of both pointlike and extended sources; several of each type have been used in staring and scanning experiments.

Russell, R. W.↗

NASA NTRS1994

Velocity surface measurements for ZnO films over /001/-cut GaAs

A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

Kim, Yoonkee↗

NASA NTRS1977

Dynamics and control simulation of the Spacelab Experiment Pointing Mount

Computer simulations were developed to evaluate the performance of four Experiment Pointing Mounts (EPM) being considered for Spacelab experiments in the 1980-1990 time frame. The system modeled compromises a multibody system consisting of the shuttle, a mechanical isolation device, the EPM, celestial and inertial sensors, bearings, gimbal torque motors and associated nonlinearities, the experiment payload, and control and estimator algorithms. Each mount was subjected to a common disturbance (shuttle vernier thruster firing and man push off) and command (stellar pointing or solar raster scan) input. The fundamental limitation common to all mounts was found to be sensor noise. System dynamics and hardware nonlinearities have secondary effects on pointing performance for sufficiently high bandwidth.

Marsh, E. L.↗

NASA NTRS1981

Tuned feedback damping with application to the Galileo spacecraft

An adaptive controller has been developed which uses phase-locked-loops as the adaptive devices. The controller provides active damping to systems which have their underdamped frequencies known only to within a particular range (e.g. plus or minus 20% uncertainty). The design and analysis of the controller is presented along with an application of such a controller to the scan platform pointing system of the Galileo spacecraft, a system with sensors and actuators separated by flexible structure.

Macala, G. A.↗

NASA NTRS1995

Ka-band MMIC subarray technology program (Ka-Mist)

The broad objective of this program was to demonstrate a proof of concept insertion of Monolithic Microwave Integrated Circuit (MMIC) device technology into an innovative (tile architecture) active phased array antenna application supporting advanced EHF communication systems. Ka-band MMIC arrays have long been considered as having high potential for increasing the capability of space, aircraft, and land mobile communication systems in terms of scan performance, data rate, link margin, and flexibility while offering a significant reduction in size, weight, and power consumption. Insertion of MMIC technology into antenna systems, particularly at millimeter wave frequencies using low power and low noise amplifiers in close proximity to the radiating elements, offers a significant improvement in the array transmit efficiency, receive system noise figure, and overall array reliability. Application of active array technology also leads to the use of advanced beamforming techniques that can improve beam agility, diversity, and adaptivity to complex signal environments.

Pottenger, Warren↗

NASA NTRS1972

A system for simulating aerial or orbital TV observations of geographic patterns

A system which simulates observation of the earth surface by aerial or orbiting television devices has been developed. By projecting color slides of photographs taken by aircraft and orbiting sensors upon a rear screen system, and altering scale of projected image, screen position, or TV camera position, it is possible to simulate alternatives of altitude, or optical systems. By altering scan line patterns in COHU 3200 series camera from 525 to 945 scan lines, it is possible to study implications of scan line resolution upon the detection and analysis of geographic patterns observed by orbiting TV systems.

Latham, J. P.↗

NASA NTRS1993

Scanning For Hotspots In Lamp Filaments

Scanning photometer designed for use in investigation of failures of incandescent lamp filaments. Maps brightness as function of position along each filament to identify bright (hot) spots, occurring at notches and signifying incipient breaks or rewelds. Also used to measure nonuniformity in outputs of such linear devices as light-emitting diodes, and to measure diffraction patterns of lenses.

Powers, Charles E.↗

NASA NTRS1981

Video image processor on the Spacelab 2 Solar Optical Universal Polarimeter /SL2 SOUP/

The SOUP instrument is designed to obtain diffraction-limited digital images of the sun with high photometric accuracy. The Video Processor originated from the requirement to provide onboard real-time image processing, both to reduce the telemetry rate and to provide meaningful video displays of scientific data to the payload crew. This original concept has evolved into a versatile digital processing system with a multitude of other uses in the SOUP program. The central element in the Video Processor design is a 16-bit central processing unit based on 2900 family bipolar bit-slice devices. All arithmetic, logical and I/O operations are under control of microprograms, stored in programmable read-only memory and initiated by commands from the LSI-11. Several functions of the Video Processor are described, including interface to the High Rate Multiplexer downlink, cosmetic and scientific data processing, scan conversion for crew displays, focus and exposure testing, and use as ground support equipment.

Lindgren, R. W.↗

NASA NTRS1986

A sphere-scanning radiometer for rapid directional measurements of sky and ground radiance

The development of the Portable Apparatus for Rapid Acquisition of Bidirectional Observations of the Land and Atmosphere (PARABOLA) and a transportable platform system is examined. The PARABOLA is a three channel rotating head radiometer which samples in 15 deg instantaneous field-of-view sectors using a sensor head, data recording unit, and an internal power pack. The composition and operation of the sensor scan, data, and power systems are described. The calibration and laboratory testing of the instrument is discussed. The field testing of a tripod-and-boom mount apparatus, a boom-equipped instrument van, and a hot-air balloon mount, in order to select the proper support device for the PARABOLA sensor head is analyzed. The design and functions of the Transportable Pickup Mount System, which is a lightweight, collapsible boom apparatus, are described.

Deering, D. W.↗

NASA NTRS1994

(abstract) A Miniature, High-Sensitivity, Electron-Tunneling Accelerometer

A prototype low-noise accelerometer has been fabricated with an electron-tunneling transducer. By measuring the tunneling current between an electrode on the proof mass and a feedback-controlled monitor electrode, very small accelerations can be detected with high responsivity. This particular prototype (10x10x1.5 mm) was designed for underwater acoustic measurement from a few hertz to 1 kHz. The measured responsivity below the fundamental device resonance at 100 Hz is roughly 1500 volts per m/s(sup 2) with a measured noise spectral density of 10(sup -6) m/s(sup 2) per root hertz or less between 30 and 300 Hz. The noise floor is controlled primarily by 1/f noise in the tunneling current although the noise floor reaches the theoretical molecular-agitation limit at 100 hertz. The responsivity and directivity of the device were measured in a standard gradient-hydrophone calibrator; the noise floor was determined in a vacuum-ionization chamber assembled from commercial off-the-shelf components; and the detailed dynamics of the proof-mass motion were examined using a heterodyne laser interferometer that was scanned across the surface and synchronously detected with respect to the excitation.

accelerometer electron tunneling acoustic measurem↗

NASA NTRS2014

Thrust Measurement of Dielectric Barrier Discharge (DBD) Plasma Actuators: New Anti-Thrust Hypothesis, Frequency Sweeps Methodology, Humidity and Enclosure Effects

We discuss thrust measurements of Dielectric Barrier Discharge (DBD) plasma actuators devices used for aerodynamic active flow control. After a review of our experience with conventional thrust measurement and significant non-repeatability of the results, we devised a suspended actuator test setup, and now present a methodology of thrust measurements with decreased uncertainty. The methodology consists of frequency scans at constant voltages. The procedure consists of increasing the frequency in a step-wise fashion from several Hz to the maximum frequency of several kHz, followed by frequency decrease back down to the start frequency of several Hz. This sequence is performed first at the highest voltage of interest, then repeated at lower voltages. The data in the descending frequency direction is more consistent and selected for reporting. Sample results show strong dependence of thrust on humidity which also affects the consistency and fluctuations of the measurements. We also observed negative values of thrust, or "anti-thrust", at low frequencies between 4 Hz and up to 64 Hz. The anti-thrust is proportional to the mean-squared voltage and is frequency independent. Departures from the parabolic anti-thrust curve are correlated with appearance of visible plasma discharges. We propose the anti-thrust hypothesis. It states that the measured thrust is a sum of plasma thrust and anti-thrust, and assumes that the anti-thrust exists at all frequencies and voltages. The anti-thrust depends on actuator geometry and materials and on the test installation. It enables the separation of the plasma thrust from the measured total thrust. This approach enables more meaningful comparisons between actuators at different installations and laboratories. The dependence on test installation was validated by surrounding the actuator with a grounded large-diameter metal sleeve. Strong dependence on humidity is also shown; the thrust significantly increased with decreasing humidity, e.g., 44 percent increase as relative humidity changed from 18 percent and dew point 33 degF to 50 percent and dew point of 57 degF.

Ashpis, David E.↗

NASA NTRS2014

Dielectric Barrier Discharge (DBD) Plasma Actuators Thrust-Measurement Methodology Incorporating New Anti-Thrust Hypothesis

We discuss thrust measurements of Dielectric Barrier Discharge (DBD) plasma actuators devices used for aerodynamic active flow control. After a review of our experience with conventional thrust measurement and significant non-repeatability of the results, we devised a suspended actuator test setup, and now present a methodology of thrust measurements with decreased uncertainty. The methodology consists of frequency scans at constant voltages. The procedure consists of increasing the frequency in a step-wise fashion from several Hz to the maximum frequency of several kHz, followed by frequency decrease back down to the start frequency of several Hz. This sequence is performed first at the highest voltage of interest, then repeated at lower voltages. The data in the descending frequency direction is more consistent and selected for reporting. Sample results show strong dependence of thrust on humidity which also affects the consistency and fluctuations of the measurements. We also observed negative values of thrust or "anti-thrust", at low frequencies between 4 Hz and up to 64 Hz. The anti-thrust is proportional to the mean-squared voltage and is frequency independent. Departures from the parabolic anti-thrust curve are correlated with appearance of visible plasma discharges. We propose the anti-thrust hypothesis. It states that the measured thrust is a sum of plasma thrust and anti-thrust, and assumes that the anti-thrust exists at all frequencies and voltages. The anti-thrust depends on actuator geometry and materials and on the test installation. It enables the separation of the plasma thrust from the measured total thrust. This approach enables more meaningful comparisons between actuators at different installations and laboratories. The dependence on test installation was validated by surrounding the actuator with a large diameter, grounded, metal sleeve.

Ashpis, David E.↗