Electrical indication of airflow rate
Adaption of gas-flow measurement technique originally developed by C. C. Thomas in 1911 is used for temperature measurements which are easily converted to electrical signals.
Murrish, C.↗
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High power ac/dc variable R dynamic electrical load simulator
A study program was undertaken to investigate various concepts and techniques for identifying and simulating both the steady-state and dynamic characteristics of electrical loads for use during integrated system test and evaluation. The development of hardware capable of providing the simulation capability is discussed. A general purpose simulator was developed with the capability of realizing a variety of models where element values were discretely variable. The different models, each corresponding to real spacecraft equipment, are set up manually for each case by suitable switching and patching. The models are capable of duplicating the dynamic and steady-state response of real loads at full power.
Joncas, K. P.↗
Neuroprotection trek--the next generation: neuromodulation I. Techniques--deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation
Neuromodulation denotes controlled electrical stimulation of the central or peripheral nervous system. The three forms of neuromodulation described in this paper-deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation-were chosen primarily for their demonstrated or potential clinical usefulness. Deep brain stimulation is a completely implanted technique for improving movement disorders, such as Parkinson's disease, by very focal electrical stimulation of the brain-a technique that employs well-established hardware (electrode and pulse generator/battery). Vagus nerve stimulation is similar to deep brain stimulation in being well-established (for the treatment of refractory epilepsy), completely implanted, and having hardware that can be considered standard at the present time. Vagus nerve stimulation differs from deep brain stimulation, however, in that afferent stimulation of the vagus nerve results in diffuse effects on many regions throughout the brain. Although use of deep brain stimulation for applications beyond movement disorders will no doubt involve placing the stimulating electrode(s) in regions other than the thalamus, subthalamus, or globus pallidus, the use of vagus nerve stimulation for applications beyond epilepsy-for example, depression and eating disorders-is unlikely to require altering the hardware significantly (although stimulation protocols may differ). Transcranial magnetic stimulation is an example of an external or non-implanted, intermittent (at least given the current state of the hardware) stimulation technique, the clinical value of which for neuromodulation and neuroprotection remains to be determined.
Review, Tutorial↗
Enhancement of dielectronic recombination by plasma electric microfields
A description is presented of an application of techniques from Stark-broadening theory considered by Griem (1974) to the computation of dielectronic recombination rated for multiply charged Fe ions under the influence of plasma electric microfields. Attention is given to a dielectronic recombination process for which the effects of surrounding charged particles have been found to be important at surprisingly low densities.
Jacobs, V. L.↗
Power conditioning techniques
The technological developments required to reduce the electrical power system component weights from the state-of-the-art 2.0 kg/kW to the range of 0.1 to 0.2 kg/kW are discussed. Power level requirements and their trends in aerospace applications are identified and presented. The projected weight and launch costs for a 1MW power converter built using state-of-the-art technology are established to illustrate the need for reliable, ultralightweight advanced power components. The key factors affecting converter weight are given and some of the tradeoffs between component ratings and circuit topology are identified. The weight and launch costs for a 1MW converter using 0.1 kg/kW technology are presented. Finally, the objectives and goals of the Multi-Megawatt Program at the NASA Lewis Research Center, which is funded by the SDIO through the Air Force, are given.
Baumann, E. D.↗
Optical and electrical properties of thin superconducting films
Infrared spectroscopic techniques can provide a vital probe of the superconducting energy gap which is one of the most fundamental physical properties of superconductors. Currently, the central questions regarding the optical properties of superconductors are how the energy gap can be measured by infrared techniques and at which frequency the gap exists. An effective infrared spectroscopic method to investigate the superconducting energy gap, Eg, was developed by using the Bomem DA 3.01 Fourier Transformation Spectrophotometer. The reflectivity of a superconducting thin film of YBaCuO deposited on SrTiO3 was measured. A shoulder was observed in the superconducting state reflectance R(sub S) at 480/cm. This gives a value of Eg/kT(sub c) = 7.83, where k is the Boltzmann constant and T(sub c) is the superconducting transition temperature, from which, it is suggested that YBaCuO is a very strong coupling superconductor.
Covington, Billy C.↗
Techniques For Focusing In Zone Electrophoresis
In two techniques for focusing in zone electrophoresis, force of applied electrical field in each charged particle balanced by restoring force of electro-osmosis. Two techniques: velocity-gradient focusing (VGF), suitable for rectangular electrophoresis chambers; and field-gradient focusing (FGF), suitable for step-shaped electrophoresis chambers.
Sharnez, Rizwan↗
Electro optical system to measure strains at high temperature
The measurement of strains at temperatures of the order of 1000 C has become a very important field of research. Technological advances in areas such as the analysis of high speed aircraft structures and high efficiency thermal engines require operational temperatures of this order of magnitude. Current techniques for the measurement of strains, such as electrical strain gages, are at the limit of their useful range and new methods need to be developed. Optical techniques are very attractive in this type of application because of their noncontacting nature. Holography is of particular interest because a minimal preparation of the surfaces is required. Optoelectronics holography is specially suited for this type of application, from the point of view of industrial use. There are a number of technical problems that need to be overcome to measure strains using holographic interferometry at high temperatures. Some of these problems are discussed, and solutions are given. A specimen instrumented with high temperature strains gages is used to compare the results of both technologies.
Sciammarella, Cesar A.↗
Estimating the Performance of a Concentrating Solar Array
Comprehensive mathematical-analysis technique developed for array of solar-photovoltaic panels equipped with truncated-pyramid concentrators. Hollow pyramidal concentrator reflects Sunlight onto panel of photovoltaic cells. Comprehensive optical, thermal, and electrical analysis performed on array of units. Technique applicable, with modifications, to analysis and design of other multiple-cell reflecting photovoltaic systems.
French, E. P.↗
Venus Surface Composition from Radio/radar Measurements
Three different radio techniques were used to study the electrical properties of the surface of Venus. The reflectivity of the surface at near normal incidence was studied using radar from the Pioneer Venus Orbiter (PVO) spacecraft. These measurements have inferred the corresponding dielectric constants. Surface emissivities were calculated using measurements of thermal emission brightness temperature obtained both from spacecraft and from the ground. These measurements also have inferred dielectric constant. The degree of linear polarization associated with thermal energy emitted from the surface at various angles was examined. The dielectric constant was calculated. The radar data have provided the highest surface resolution of the three techniques, and were the first to show the unusually high values of Fresnel reflection coefficient (approaching 0.40 in extreme cases) that are associated with many of the elevated regions of Venus. The distribution of small scale surface roughness was estimated.
Pettengill, G. H.↗
Calligraphic Poling of Ferroelectric Material
Calligraphic poling is a technique for generating an arbitrary, possibly complex pattern of localized reversal in the direction of permanent polarization in a wafer of LiNbO3 or other ferroelectric material. The technique is so named because it involves a writing process in which a sharp electrode tip is moved across a surface of the wafer to expose the wafer to a polarizing electric field in the desired pattern. The technique is implemented by use of an apparatus, denoted a calligraphic poling machine (CPM), that includes the electrode and other components as described in more detail below.
Mohageg, Makan↗
Oxidation Characterization of Hafnium-Based Ceramics Fabricated by Hot Pressing and Electric Field-Assisted Sintering
Ceramic borides, such as hafnium diboride (HfB2) and zirconium diboride (ZrB2), are members of a family of materials with extremely high melting temperatures referred to as Ultra High Temperature Ceramics (UHTCs). UHTCs constitute a class of promising materials for use in high temperature applications, such as sharp leading edges on future-generation hypersonic flight vehicles, because of their high melting points. The controlled development of microstructure has become important to the processing of UHTCs, with the prospect of improving their mechanical and thermal properties. The improved oxidation resistance of HfB2 has also become important if this material is to be successfully used at temperatures above 2000 C. Furthermore, the use of UHTCs on the leading edges of vehicles traveling at hypersonic speeds will mean exposure to a mixed oxidation environment comprised of both molecular and atomic oxygen. The current study has investigated the high-temperature oxidation behavior of HfB2-based materials in a pure O2 environment, as well as in environments containing different levels of dissociated oxygen (O/O2). Materials were processed by two techniques: conventional hot pressing (HP) and electric field-assisted sintering (FAS). Their oxidation behavior was evaluated in both a tube furnace at 1250 C for 3 hours and in a simulated re-entry environment in the Advanced Heating Facility (AHF) arcjet at NASA Ames Research Center, during a 10-minute exposure to a cold wall heat flux of 250W/sq cm and stagnation pressure of 0.1-0.2 atm. The microstructure of the different materials was characterized before and after oxidation using scanning electron microscopy (SEM).
Gasch, Matt↗
Satellite measurements of high latitude convection electric fields.
This paper reviews the first results of satellite experiments to measure magnetospheric convection electric fields using the double-probe technique. The earliest successful measurements were made with the low-altitude (680-2530 km) polar orbiting Injun-5 spacecraft. The Injun-5 results are compared with the initial findings of the electric field experiment on the polar orbiting OGO-6 satellite. Electric field measurements from the OGO-6 satellite have substantiated many of the initial Injun-5 observations with improved accuracy and sensitivity. The OGO-6 detector revealed the persistent occurrence of anti-sunward convection across the polar cap region at velocities not generally detectable with the Injun-5 experiment. The OGO-6 observations also provided information indicating that the location of the electric field reversal shifts equatorward during periods of increased magnetic activity. The implications of the electric field measurements for magnetospheric and auroral structure are summarized, and a list of specific recommendations for improving future experiments is presented.
Cauffman, D. P.↗
Photovoltaic power system reliability considerations
An example of how modern engineering and safety techniques can be used to assure the reliable and safe operation of photovoltaic power systems is presented. This particular application is for a solar cell power system demonstration project designed to provide electric power requirements for remote villages. The techniques utilized involve a definition of the power system natural and operating environment, use of design criteria and analysis techniques, an awareness of potential problems via the inherent reliability and FMEA methods, and use of fail-safe and planned spare parts engineering philosophy.
Lalli, V. R.↗
Electrical resistivity and conductivity of tungsten-fiber-reinforced copper composites
Electric resistivity and conductivity of tungsten- fiber-reinforced copper composites made by liquid phase infiltration techniques
TUNGSTEN↗
Brayton Power Conversion Unit Tested: Provides a Path to Future High-Power Electric Propulsion Missions
Closed-Brayton-cycle conversion technology has been identified as an excellent candidate for nuclear electric propulsion (NEP) power conversion systems. Advantages include high efficiency, long life, and high power density for power levels from about 10 kWe to 1 MWe, and beyond. An additional benefit for Brayton is the potential for the alternator to deliver very high voltage as required by the electric thrusters, minimizing the mass and power losses associated with the power management and distribution (PMAD). To accelerate Brayton technology development for NEP, the NASA Glenn Research Center is developing a low-power NEP power systems testbed that utilizes an existing 2- kWe Brayton power conversion unit (PCU) from previous solar dynamic technology efforts. The PCU includes a turboalternator, a recuperator, and a gas cooler connected by gas ducts. The rotating assembly is supported by gas foil bearings and consists of a turbine, a compressor, a thrust rotor, and an alternator on a single shaft. The alternator produces alternating-current power that is rectified to 120-V direct-current power by the PMAD unit. The NEP power systems testbed will be utilized to conduct future investigations of operational control methods, high-voltage PMAD, electric thruster interactions, and advanced heat rejection techniques. The PCU was tested in Glenn s Vacuum Facility 6. The Brayton PCU was modified from its original solar dynamic configuration by the removal of the heat receiver and retrofitting of the electrical resistance gas heater to simulate the thermal input of a steady-state nuclear source. Then, the Brayton PCU was installed in the 3-m test port of Vacuum Facility 6, as shown. A series of tests were performed between June and August of 2002 that resulted in a total PCU operational time of about 24 hr. An initial test sequence on June 17 determined that the reconfigured unit was fully operational. Ensuing tests provided the operational data needed to characterize PCU performance over its full operating range. The primary test variables used in operating the Brayton PCU were heater input power and rotor speed. Testing demonstrated a maximum steady-state alternating-current power output of 1835 W at a gas heater power of 9000 W and a rotor speed of 52000 rpm. The corresponding measured turbine inlet gas temperature was 1076 K, and the compressor inlet gas temperature was 282 K. When insulation losses from the gas heater were neglected, the Brayton cycle efficiency for the maximum power point was calculated to be 24 percent. The net direct-current power output was 1750 W, indicating a PMAD efficiency of about 95 percent.
Mason, Lee S.↗
Shape Measurement of Large Aerospace Structures Using Sensitivity Electrical TDR Distributed Strain Sensor
Electrical time domain reflectometry (ETDR) sensing technique can be best described as "closed-loop radar," where the information is derived from the reflections of a voltage pulse sent through a transmission medium. The ETDR sensing technique is a well-developed method and has been widely used to locate and evaluate discontinuities in long coaxial power transmission cables. The ETDR technique provides a true distributed sensing capability which can not only sense the distributed loading condition of the structure but also can pin-point the location of disturbance, such as the locations of stress concentration and structural damages. Proof-of-concept experiments have been conducted using photoelastic specimens with embedded commercial coaxial cables, i.e., RG85/U and RG174, to demonstrate the stress/strain sensing capability of ETDR sensors for structural health monitoring application. Although the test results showed that the ETDR sensor signals capture specimen deformation pattern both in bending and tension and indicate the location and type of crack damages of the photoelastic specimen; yet, the low signal-to-noise ratio of the sensor signal smears the details of the strain measurement that the ETDR signals can convey. A high-sensitivity ETDR coaxial strain sensor prototype newly developed at Clark Atlanta University will be presented. The construction of the prototype sensing cable as well as its electrical properties relevant to distributed strain sensing application will be shown in details. Test results of the sensitivity and tension responses of the ETDR signal of the prototype sensor will be presented and compared with those of commercial coaxial cables. Promising potentials of the ETDR distributed strain sensing method for shape measurement application of large aerospace structures will also be demonstrated using long slender beam with surface-bonded ETDR distributed strain sensor.
Lin, Mark W.↗
Recent Advancements in Electrical Capacitance Mass Gauging for Cryogenic PropellantTanks
The current lack of unsettled mass gauging is a key roadblock for many space activities, such as orbital refueling, missions to the Moon and Mars, and nuclear thermal and nuclear electric propulsion technologies. Liquid can form any one of an infinite number of configurations in microgravity, such as floating in globs or accumulating on tank surfaces in discontiguous volumes, or both. Capacitive sensing requires no moving parts and dissipates close to zero heat, making it an ideal candidate for cryogenic fluid mass gauging in settled and unsettled configurations. Capacitive sensing has a history of proven use in space propellant tanks, including tanks on the space shuttle, Saturn V, and the Apollo Lunar Excursion Module. Modern capacitive sensor technology allows using the entire tank as the capacitor volume by placing electrodes on the tank walls and propellant management surfaces. Capacitance is directly related to density, and therefore to mass for fixed volumes. In this presentation, we discuss the concepts behind whole-tank capacitance mass gauging and associated engineering challenges. We describe recent efforts to develop a micro-g unsettled cryogenic mass gauge using whole-tank capacitance sensing, including the development of test beds, electronics, and algorithms. We describe several mathematical processing techniques, including empirical-based averaging, electrical capacitance volume tomography, and spatial regularization. A modeling study, performed using settled configurations in gravity and no gravity, and with a set of 100 random fluid configurations, has indicated that spatial regularization, in which capacitance measurements are weighted to account for non-uniform electric fields, yields a mass fraction accuracy of 8% for any fluid configuration. Such a sensor is expected to operate in real time with a sampling frequency of at least 1 kHz.
cryogenic↗