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At least 1,207 records · Page 67

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Method and apparatus for determining time, direction, and composition of impacting space particles

A space particle collector for recording the time specific particles are captured, and its direction at the time of capture, utilizes an array of targets, each comprised of an MOS capacitor on a chip charged from an external source and discharged upon impact by a particle through a tab on the chip that serves as a fuse. Any impacting particle creates a crater, but only the first will cause a discharge of the capacitor. A substantial part of the metal film around the first crater is burned off by the discharge current. The time of the impulse which burns the tab, and the identification of the target, is recorded together with data from flight instruments. The metal film is partitioned into pie sections to provide a plurality of targets on each of an array of silicon wafers, thus increasing the total number of identified particles that can be collected. It is thus certain which particles were captured at what specific times.

Kinard, William H.↗

NASA NTRS1991

Silicon dioxide with a silicon interfacial layer as an insulating gate for highly stable indium phosphide metal-insulator-semiconductor field effect transistors

A novel gate insulator consisting of silicon dioxide (SiO2) with a thin silicon (Si) interfacial layer has been investigated for high-power microwave indium phosphide (InP) metal-insulator-semiconductor field effect transistors (MISFETs). The role of the silicon interfacial layer on the chemical nature of the SiO2/Si/InP interface was studied by high-resolution X-ray photoelectron spectroscopy. The results indicated that the silicon interfacial layer reacted with the native oxide at the InP surface, thus producing silicon dioxide, while reducing the native oxide which has been shown to be responsible for the instabilities in InP MISFETs. While a 1.2-V hysteresis was present in the capacitance-voltage (C-V) curve of the MIS capacitors with silicon dioxide, less than 0.1 V hysteresis was observed in the C-V curve of the capacitors with the silicon interfacial layer incorporated in the insulator. InP MISFETs fabricated with the silicon dioxide in combination with the silicon interfacial layer exhibited excellent stability with drain current drift of less than 3 percent in 10,000 sec, as compared to 15-18 percent drift in 10,000 sec for devices without the silicon interfacial layer. High-power microwave InP MISFETs with Si/SiO2 gate insulators resulted in an output power density of 1.75 W/mm gate width at 9.7 GHz, with an associated power gain of 2.5 dB and 24 percent power added efficiency.

Kapoor, V. J.↗

NASA NTRS1992

Characterization of polybenzimidazole (PBI) film at high temperatures

Polybenzimidazole, a linear thermoplastic polymer with excellent thermal stability and strength retention over a wide range of temperatures, was evaluated for its potential use as the main dielectric in high temperature capacitors. The film was characterized in terms of its dielectric properties in a frequency range of 50 Hz to 100 kilo-Hz. These properties, which include the dielectric constant and dielectric loss, were also obtained in a temperature range from 20 C to 300 C with an electrical stress of 60 Hz, 50 V/mil present. The alternating and direct current breakdown voltages of silicone oil impregnated films as a function of temperature were also determined. The results obtained indicate that while the film remained relatively stable up to 200 C, it exhibited an increase in its dielectric properties as the temperature was raised to 300 C. It was also found that conditioning of the film by heat treatment at 60 C for six hours tended to improve its dielectric and breakdown properties. The results are discussed and conclusions made concerning the suitability of the film as a high temperature capacitor dielectric.

Hammoud, Ahmad N.↗

NASA NTRS1992

High speed, nondestructive readout from thin-film ferroelectric memory

High-speed polarization-direction-dependent photoresponse from ferroelectric lead zirconate titanate (PbZr(0.53)Ti(0.47)O3) thin films sandwiched between conducting electrodes to form a memory capacitor is reported. Laser pulses with a full width at half maximum of around 10 ns at 532-nm wavelength are utilized to readout the photoresponse signal from individual polarized elements. Such readout is repeated over a million times, with no detectable degradation in the photoresponse or the remanent polarization suggesting its potential as a nondestructive readout (NDRO) of nonvolatile polarization state in thin-film ferroelectric memories. In principle both electronic as well as thermal mechanisms could be triggered by such photon exposure of ferroelectric thin films. A comparison of the photoresponse from capacitors with semitransparent and opaque top electrodes suggests that the observed NDRO signal is primarily due to thermally triggered mechanisms.

Thakoor, Sarita↗

NASA NTRS1993

Rapid, Nondestructive Readout From Ferroelectric Memory

Proposed devices with nondestructive readout offer attractive alternatives for rugged, solid-state memories suitable for contactless optical addressing and parallel processing and for nonvolatile analog memories. Pulses of light from lasers induce photoresponses in ferroelectric capacitors. Magnitude and polarity of response of each capacitor indicates magnitude and polarity of remanent polarization which, in turn, represents datum stored in that memory cell.

Thakoor, Sarita↗

NASA NTRS1992

An evaluation of corrosion protection by two epoxy primers on 2219-T87 and 7075-T73 aluminum

A comparison of the corrosion protection provided by two amine epoxy primers was made using salt fog, alternate immersion, and total immersion as exposure media. The study is the result of a request to use an unqualified low volatile organic carbon (VOC) primer (AKZO 463-6-78) in place of the current primer (AKZO 463-6-3) because environmental regulations have eliminated use of the current primer in many states. Primed, scribed samples of 2219-T87 and 7075-T73 aluminum were exposed to 5-percent NaCl salt fog and 3.5-percent NaCl alternate immersion for a period of 90 days. In addition, electrode samples immersed in 3.5-percent NaCl were tested using electrochemical impedance spectroscopy (EIS). The EG&G model 368 ac impedance measurement system was used to monitor changing properties of AKZO 463-6-78 and AKZO 463-6-3 primed 2219-T87 aluminum for a period of 30 days. The response of the corroding system of a frequency scan can be modeled in terms of an equivalent circuit consisting of resistors and capacitors in a specific arrangement. Each resistor/capacitor combination represents physical processes taking place within the electrolyte, at the electrolyte/primer surface, within the coating, and at the coating/substrate surface. Values for the resistors and capacitors are assigned following a nonlinear least squares fit of the data to the equivalent circuit. Changes in the values of equivalent circuit parameters during the 30-day exposure allow assessment of the time to and mechanism of coating breakdown.

Mendrek, M. J.↗

NASA NTRS1991

High accuracy switched-current circuits using an improved dynamic mirror

The switched-current technique, a recently developed circuit approach to analog signal processing, has emerged as an alternative/compliment to the well established switched-capacitor circuit technique. High speed switched-current circuits offer potential cost and power savings over slower switched-capacitor circuits. Accuracy improvements are a primary concern at this stage in the development of the switched-current technique. Use of the dynamic current mirror has produced circuits that are insensitive to transistor matching errors. The dynamic current mirror has been limited by other sources of error including clock-feedthrough and voltage transient errors. In this paper we present an improved switched-current building block using the dynamic current mirror. Utilizing current feedback the errors due to current imbalance in the dynamic current mirror are reduced. Simulations indicate that this feedback can reduce total harmonic distortion by as much as 9 dB. Additionally, we have developed a clock-feedthrough reduction scheme for which simulations reveal a potential 10 dB total harmonic distortion improvement. The clock-feedthrough reduction scheme also significantly reduces offset errors and allows for cancellation with a constant current source. Experimental results confirm the simulated improvements.

Zweigle, G.↗

NASA NTRS1993

Flexible heating head for induction heating

An induction heating head includes a length of wire having first and second opposite ends and being wound in a flat spiral shape to form an induction coil, a capacitor connected to the first and second ends of the wire, the induction coil and capacitor defining a tank circuit, and a flexible, elastomeric body molded to encase the induction coil. When a susceptor is placed in juxtaposition to the body, and the tank circuit is powered, the susceptor is inductively heated.

Fox, Robert L.↗

NASA NTRS1994

Plasma treatment of polymer dielectric films to improve capacitive energy storage

Demand for compact instrumentation, portable field equipment, and new electromagnetic weapons is creating a need for new dielectric materials with higher energy storage capabilities. Recognizing the need for higher energy storage capacitors, the Army Research Lab at Fort Monmouth, NJ, initiated a program a year ago to investigate potential methods for increasing the dielectric strength of polyvinylidene difluoride (PVDF) film, which is the highest energy density material commercially available today. Treatment of small area PVDF films in a CF4/O2 plasma showed that the dielectric strength of PVDF films can be increased by as much as 20 percent when treated in a 96 percent CF4/4 percent O2 plasma. This 44 percent increase in energy storage of a PVDF capacitor is significant considering that the treatment can be implemented in a conventional metallizing chamber, with minimum capital investment. The data shows that improved breakdown strength may be unique to PVDF film and the particular CF4/O2 gas mixture, because PVDF film treated with 100 percent CF4, 100 percent O2, Ar gas plasma, and electron irradiation shows no improvement in breakdown strength. Other data presented includes dissipation factor, dielectric constant, and surface tension measurements.

Yializis, A.↗

NASA NTRS1994

Steering capaciflector sensor

A capacitive type proximity sensor having substantial range and sensitivity between a machine and an intruding object in the immediate vicinity of the machine and having a steerable sensing field has an outer electrical conductor on the machine forming one electrode of a sensor capacitor, the other electrode is the object. The outer conductor is a thin sheet of conductive material with a pair (or more) of intermediate electrical conductors located between the outer conductor and the machine. The pair of intermediate electrical conductors are in close proximity to each other and together form a surface having a size substantially larger than the outer conductor to act as a shield for reducing the parasitic capacitance between the outer conductor and the machine and to steer the sensor field. The pair of intermediate conductors are thin sheets of conductive material substantially wider than the first conductor. The outer and pair of intermediate conductors are attached to a surface on the machine in electrical isolation and with no gaps between the conductors and no gap between the surface and the pair of intermediate conductors. The outer and pair of intermediate conductors are also in conformance with each other and the surface of the machine, and the surface of the machine acts as a ground plane. Variable gain voltage follower circuits are used for coupling, in phase, the instantaneous voltage at the outer electrical conductor to the pair of intermediate electrical conductors and a signal generator is coupled to the outer conductor and is responsive to the capacitance of the sensor capacitor for generating a control signal to the machine.

Jenstrom, Del T.↗

NASA NTRS1995

Operational characteristics of a 200 C LC parallel resonant circuit

Research efforts are currently underway at the NASA Lewis Research Center to design and demonstrate an inverter capable of operating with a baseplate temperature of 200 C. In support of this project, various electrical components including capacitors, inductors, transformers, cables, and semiconductor switches are being developed or evaluated for integration into the inverter. In this work, a parallel LC resonant circuit was constructed and evaluated under simultaneous electrical and thermal stressing. The tests were performed in the temperature range of 25 to 200 C with an applied voltage of up to 90 V, 20 kHz. The individual components were comprised of high temperature film capacitors and powder core inductors developed in-house. The circuit was characterized in terms of the component currents and case temperatures as well as frequency of resonance as a function of applied bias and temperature. The results obtained, which have indicated good functional stability up to 200 C, are presented and discussed.

Baumann, Eric D.↗

NASA NTRS1995

Improved L-C resonant decay technique for Q measurement of quasilinear power inductors: New results for MPP and ferrite powdered cores

The L-C resonant decay technique for measuring circuit Q or losses is improved by eliminating the switch from the inductor-capacitor loop. A MOSFET switch is used instead to momentarily connect the resonant circuit to an existing voltage source, which itself is gated off during the decay transient. Very reproducible, low duty cycle data could be taken this way over a dynamic voltage range of at least 10:1. Circuit Q is computed from a polynomial fit to the sequence of the decaying voltage maxima. This method was applied to measure the losses at 60 kHz in inductors having loose powder cores of moly permalloy and an Mn-Zn power ferrite. After the copper and capacitor losses are separated out, the resulting specific core loss is shown to be roughly as expected for the MPP powder, but anomalously high for the ferrite powder. Possible causes are mentioned.

Niedra, Janis M.↗

NASA NTRS1995

Multilayer Thin-Film Microcapacitors

Miniature capacitors containing multiple alternating thin-film dielectric and metal layers proposed, especially for use in integrated and hybrid electronic circuits. Because capacitance inversely proportional to thickness of dielectric layers, use of thin, high-quality dielectric layers affords capacitance and energy-storage densities much greater than now available. These devices much smaller and more reliable than state-of-art capacitors.

Thakoor, Sarita↗

NASA NTRS1995

Advanced Modeling of Micromirror Devices

The flexure-beam micromirror device (FBMD) is a phase only piston style spatial light modulator demonstrating properties which can be used for phase adaptive corrective optics. This paper presents a complete study of a square FBMD, from advanced model development through final device testing and model verification. The model relates the electrical and mechanical properties of the device by equating the electrostatic force of a parallel-plate capacitor with the counter-acting spring force of the device's support flexures. The capacitor solution is derived via the Schwartz-Christoffel transformation such that the final solution accounts for non-ideal electric fields. The complete model describes the behavior of any piston-style device, given its design geometry and material properties. It includes operational parameters such as drive frequency and temperature, as well as fringing effects, mirror surface deformations, and cross-talk from neighboring devices. The steps taken to develop this model can be applied to other micromirrors, such as the cantilever and torsion-beam designs, to produce an advanced model for any given device. The micromirror devices studied in this paper were commercially fabricated in a surface micromachining process. A microscope-based laser interferometer is used to test the device in which a beam reflected from the device modulates a fixed reference beam. The mirror displacement is determined from the relative phase which generates a continuous set of data for each selected position on the mirror surface. Plots of this data describe the localized deflection as a function of drive voltage.

Michalicek, M. Adrian↗

NASA NTRS1996

A Geophysical Flow Experiment in a Compressible Critical Fluid

The first objective of this experiment is to build an experimental system in which, in analogy to a geophysical system, a compressible fluid in a spherical annulus becomes radially stratified in density through an A.C. electric field. When this density gradient is demonstrated, the system will be augmented so that the fluid can be driven by heating and rotation and tested in preparation for a microgravity experiment. This apparatus consists of a spherical capacitor filled with critical fluid in a temperature controlled environment. To make the fluid critical, the apparatus will be operated near the critical pressure, critical density, and critical temperature of the fluid. This will result in a highly compressible fluid because of the properties of the fluid near its critical point. A high voltage A.C. source applied across the capacitor will create a spherically symmetric central force because of the dielectric properties of the fluid in an electric field gradient. This central force will induce a spherically symmetric density gradient that is analogous to a geophysical fluid system. To generate such a density gradient the system must be small (approx. 1 inch diameter). This small cell will also be capable of driving the critical fluid by heating and rotation. Since a spherically symmetric density gradient can only be made in microgravity, another small cell, of the same geometry, will be built that uses incompressible fluid. The driving of the fluid by rotation and heating in these small cells will be developed. The resulting instabilities from the driving in these two systems will then be studied. The second objective is to study the pattern forming instabilities (bifurcations) resulting from the well controlled experimental conditions in the critical fluid cell. This experiment will come close to producing conditions that are geophysically similar and will be studied as the driving parameters are changed.

Hegseth, John↗

NASA NTRS1996

Design and Laboratory Validation of a Capacitive Sensor for Measuring the Recession of Thin-Layered Ablator

Flight vehicles are typically instrumented with subsurface thermocouples to estimate heat transfer at the surface using inverse analysis procedures. If the vehicle has an ablating heat shield, however, temperature time histories from subsurface thermocouples no longer provide enough information to estimate heat flux at the surface. In this situation, the geometry changes and thermal energy leaves the surface in the form of ablation products. The ablation rate is required to estimate heat transfer to the surface. A new concept for a capacitive sensor has been developed to measure ablator depth using the ablator's dielectric effect on a capacitor's fringe region. Relying on the capacitor's fringe region enables the gage to be flush mounted in the vehicle's permanent structure and not intrude into the ablative heat shield applied over the gage. This sensor's design allows nonintrusive measurement of the thickness of dielectric materials, in particular, the recession rates of low-temperature ablators applied in thin (0.020 to 0.060 in. (0.05 to 0.15 mm)) layers. Twenty capacitive gages with 13 different sensing element geometries were designed, fabricated, and tested. A two-dimensional finite-element analysis was performed on several candidate geometries. Calibration procedures using ablator-simulating shims are described. A one-to-one correspondence between system output and dielectric material thickness was observed out to a thickness of 0.055 in. (1.4 mm) for a material with a permittivity about three times that of air or vacuum. A novel method of monitoring the change in sensor capacitance was developed. This technical memorandum suggests further improvements in gage design and fabrication techniques.

Gregory K Noffz↗

NASA NTRS1996

Space Electrochemical Research and Technology

Individual papers presented at the conference address the following topics: development of a micro-fiber nickel electrode for nickel-hydrogen cell, high performance nickel electrodes for space power application, bending properties of nickel electrodes for nickel-hydrogen batteries, effect of KOH concentration and anions on the performance of a Ni-H2 battery positive plate, advanced dependent pressure vessel nickel hydrogen spacecraft cell and battery design, electrolyte management considerations in modern nickel hydrogen and nickel cadmium cell and battery design, a novel unitized regenerative proton exchange membrane fuel cell, fuel cell systems for first lunar outpost - reactant storage options, the TMI regenerable solid oxide fuel cell, engineering development program of a closed aluminum-oxygen semi-cell system for an unmanned underwater vehicle, SPE OBOGS on-board oxygen generating system, hermetically sealed aluminum electrolytic capacitor, sol-gel technology and advanced electrochemical energy storage materials, development of electrochemical supercapacitors for EMA applications, and high energy density electrolytic capacitor.

Richard M Wilson↗

NASA NTRS1996

Sol-gel Technology and Advanced Electrochemical Energy Storage Materials

Advanced materials play an important role in the development of electrochemical energy devices such as batteries, fuel cells, and electrochemical capacitors. The sol-gel process is a versatile solution for use in the fabrication of ceramic materials with tailored stoichiometry, microstructure, and properties. This processing technique is particularly useful in producing porous materials with high surface area and low density, two of the most desirable characteristics for electrode materials. In addition,the porous surface of gels can be modified chemically to create tailored surface properties, and inorganic/organic micro-composites can be prepared for improved material performance device fabrication. Applications of several sol-gel derived electrode materials in different energy storage devices are illustrated in this paper. V2O5 gels are shown to be a promising cathode material for solid state lithium batteries. Carbon aerogels, amorphous RuO2 gels and sol-gel derived hafnium compounds have been studied as electrode materials for high energy density and high power density electrochemical capacitors.

Chung-tse Chu↗