Search NASA⌕ Search

SEARCH · Search NASA

Results for “Tech”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Improved CLARAty Functional-Layer/Decision-Layer Interface

Improved interface software for communication between the CLARAty Decision and Functional layers has been developed. [The Coupled Layer Architecture for Robotics Autonomy (CLARAty) was described in Coupled-Layer Robotics Architecture for Autonomy (NPO-21218), NASA Tech Briefs, Vol. 26, No. 12 (December 2002), page 48. To recapitulate: the CLARAty architecture was developed to improve the modularity of robotic software while tightening coupling between planning/execution and basic control subsystems. Whereas prior robotic software architectures typically contained three layers, the CLARAty contains two layers: a decision layer (DL) and a functional layer (FL).] Types of communication supported by the present software include sending commands from DL modules to FL modules and sending data updates from FL modules to DL modules. The present software supplants prior interface software that had little error-checking capability, supported data parameters in string form only, supported commanding at only one level of the FL, and supported only limited updates of the state of the robot. The present software offers strong error checking, and supports complex data structures and commanding at multiple levels of the FL, and relative to the prior software, offers a much wider spectrum of state-update capabilities.

Estlin, Tara↗
NASA NTRS2008

Thin-Film Magnetic-Field-Response Fluid-Level Sensor for Non-Viscous Fluids

An innovative method has been developed for acquiring fluid-level measurements. This method eliminates the need for the fluid-level sensor to have a physical connection to a power source or to data acquisition equipment. The complete system consists of a lightweight, thin-film magnetic-field-response fluid-level sensor (see Figure 1) and a magnetic field response recorder that was described in Magnetic-Field-Response Measurement-Acquisition System (LAR-16908-1), NASA Tech Briefs, Vol. 30, No. 6 (June 2006), page 28. The sensor circuit is a capacitor connected to an inductor. The response recorder powers the sensor using a series of oscillating magnetic fields. Once electrically active, the sensor responds with its own harmonic magnetic field. The sensor will oscillate at its resonant electrical frequency, which is dependent upon the capacitance and inductance values of the circuit.

Woodard, Stanley E.↗
NASA NTRS2008

Fabrication of Gate-Electrode Integrated Carbon-Nanotube Bundle Field Emitters

A continuing effort to develop carbon-nanotube-based field emitters (cold cathodes) as high-current-density electron sources has yielded an optimized device design and a fabrication scheme to implement the design. One major element of the device design is to use a planar array of bundles of carbon nanotubes as the field-emission tips and to optimize the critical dimensions of the array (principally, heights of bundles and distances between them) to obtain high area-averaged current density and high reliability over a long operational lifetime a concept that was discussed in more detail in Arrays of Bundles of Carbon Nanotubes as Field Emitters (NPO-40817), NASA Tech Briefs, Vol. 31, No. 2 (February 2007), page 58. Another major element of the design is to configure the gate electrodes (anodes used to extract, accelerate, and/or focus electrons) as a ring that overhangs a recess wherein the bundles of nanotubes are located, such that by virtue of the proximity between the ring and the bundles, a relatively low applied potential suffices to generate the large electric field needed for emission of electrons.

Toda, Risaku↗
NASA NTRS2008

Compact Dielectric-Rod White-Light Delay Lines

Optical delay lines of a proposed type would be made from rods of such dielectric materials as calcium fluoride, fused silica, or sapphire. These would offer advantages over prior optical delay lines, as summarized below. Optical delay lines are key components of opto-electronic microwave oscillators, narrow-band opto-electronic microwave filters, evanescent-field optical biochemical detectors, and some Fourier-Transform spectrum analyzers. Heretofore, optical delay lines used in such applications have been of two types: resonators and coiled long optical fibers, both of which have disadvantages: Resonators are compact, but excitation must be provided by narrow-band lasers. Wide-band (including noisy) laser light cannot be coupled efficiently to narrow-band resonators. When light is coupled into a narrowband resonator from a source of reasonably high power, a significant amount of optical energy circulates within the resonator, causing nonlinear loss and significant noise. Typically, a coil-type optical delay line is made of fused-silica fiber, which exhibits fundamental loss. To overcome the limit imposed by the optical loss in fused silica, it would be necessary to use fibers having crystalline cores. Although space is saved by winding fibers into coils, fiber-coil delay lines are still inconveniently bulky. The proposed compact dielectric-rod delay lines would exploit the special class of non-diffracting light beams that are denoted Bessel beams because their amplitudes are proportional to Bessel functions of the radii from their central axes. High-order Bessel beams can have large values of angular momentum. They can be generated with the help of whispering-gallery-mode optical resonators, as described, for example, in "Simplified Generation of High-Angular-Momentum Light Beams" (NPO-42965) NASA Tech Briefs, Vol. 31, No. 3 (March 2007), page 8a. In a delay line according to the proposal, the dielectric rod would be dimensioned to function as a multimode waveguide. Suitably chosen high-angular-momentum modes in such a waveguide exhibit low group velocity (hence, long delay) and no resonance. Such a delay line could perform well at any wavelength or range of wavelengths within the transparency wavelength band of the dielectric material, and the maximum possible group delay achievable through suitable design would be limited only by the optical loss in the rod material.

Maleki, Lute↗
NASA NTRS2008

Hand-Held Units for Short-Range Wireless Biotelemetry

Special-purpose hand-held radiotransceiver units have been proposed as means of short-range radio powering and interrogation of surgically implanted microelectromechanical sensors and actuators. These units are based partly on the same principles as those of the units described in "Printed Multi- Turn Loop Antennas for RF Biotelemetry" (LEW-17879-1), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 48. Like the previously reported units, these units would make it unnecessary to have wire connections between the implanted devices and the external equipment used to activate and interrogate them. Like a unit of the previously reported type, a unit of the type now proposed would include a printed-circuit antenna on a dielectric substrate. The antenna circuitry would include integrated surface-mount inductors for impedance tuning. Circuits for processing the signals transmitted and received by the antenna would be included on the substrate. During operation, the unit would be positioned near (but not in electrical contact with) a human subject, in proximity to a microelectromechanical sensor or actuator that has been surgically implanted in the subject. It has been demonstrated that significant electromagnetic coupling with an implanted device could be established at a distance of as much as 4 in. (.10 cm). During operation in the interrogation mode, the antenna of the unit would receive a radio telemetry signal transmitted by the surgically implanted device. The antenna substrate would have dimensions of approximately 3.25 by 3.75 inches (approximately 8.3 by 9.5 cm). The substrate would have a thickness of the order of 30 mils (of the order of a somewhat less than a millimeter). The substrate would be made of low-radiofrequency- loss dielectric material that could be, for example, fused quartz, alumina, or any of a number of commercially available radio-frequency dielectric composite materials. The antenna conductors would typically be made of copper or a combination of chromium and gold. The choice of metal and the thickness of the metal layer(s) would depend on the choice of substrate material. For example, on a quartz or alumina substrate, one would typically use a layer of chromium 150 A thick and a layer of gold 2 m thick. The proposed units and the implanted devices that they would interrogate or activate would be inherently safe to use. They would operate at low radiated-power levels for short interrogation times (typically, milliseconds). Hence, there would be little local heating of tissues surrounding the implanted devices and little absorption of radio energy by such sensitive body parts as the eyes and the brain. Because the implanted devices would not depend on battery power and would be activated only during short interrogation intervals and would otherwise be in the goff h state most of the time, the useful lifetimes of the implanted devices would be greater than those of comparable battery-powered implanted devices. The compactness of the hand-held transceiver units would facilitate transport and storage and would facilitate self-diagnosis by patients able to handle the units while away from medical facilities.

Miranda, Felix A.↗
NASA NTRS2008

Wearable Wireless Telemetry System for Implantable BioMEMS Sensors

Telemetry systems of a type that have been proposed for the monitoring of physiological functions in humans would include the following subsystems: Surgically implanted or ingested units that would comprise combinations of microelectromechanical systems (MEMS)- based sensors [bioMEMS sensors] and passive radio-frequency (RF) readout circuits that would include miniature loop antennas. Compact radio transceiver units integrated into external garments for wirelessly powering and interrogating the implanted or ingested units. The basic principles of operation of these systems are the same as those of the bioMEMS-sensor-unit/external-RFpowering- and-interrogating-unit systems described in "Printed Multi-Turn Loop Antennas for Biotelemetry" (LEW-17879-1) NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 48, and in the immediately preceding article, "Hand-Held Units for Short-Range Wireless Biotelemetry" (LEW-17483-1). The differences between what is reported here and what was reported in the cited prior articles lie in proposed design features and a proposed mode of operation. In a specific system of the type now proposed, the sensor unit would comprise mainly a capacitive MEMS pressure sensor located in the annular region of a loop antenna (more specifically, a square spiral inductor/ antenna), all fabricated as an integral unit on a high-resistivity silicon chip. The capacitor electrodes, the spiral inductor/antenna, and the conductor lines interconnecting them would all be made of gold. The dimensions of the sensor unit have been estimated to be about 110.4 mm. The external garment-mounted powering/ interrogating unit would include a multi-turn loop antenna and signal-processing circuits. During operation, this external unit would be positioned in proximity to the implanted or ingested unit to provide for near-field, inductive coupling between the loop antennas, which we have as the primary and secondary windings of an electrical transformer.

Simons, Rainee N.↗
NASA NTRS2008

Fast Offset Laser Phase-Locking System

Figure 1 shows a simplified block diagram of an improved optoelectronic system for locking the phase of one laser to that of another laser with an adjustable offset frequency specified by the user. In comparison with prior systems, this system exhibits higher performance (including higher stability) and is much easier to use. The system is based on a field-programmable gate array (FPGA) and operates almost entirely digitally; hence, it is easily adaptable to many different systems. The system achieves phase stability of less than a microcycle. It was developed to satisfy the phase-stability requirement for a planned spaceborne gravitational-wave-detecting heterodyne laser interferometer (LISA). The system has potential terrestrial utility in communications, lidar, and other applications. The present system includes a fast phasemeter that is a companion to the microcycle-accurate one described in High-Accuracy, High-Dynamic-Range Phase-Measurement System (NPO-41927), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 22. In the present system (as in the previously reported one), beams from the two lasers (here denoted the master and slave lasers) interfere on a photodiode. The heterodyne photodiode output is digitized and fed to the fast phasemeter, which produces suitably conditioned, low-latency analog control signals which lock the phase of the slave laser to that of the master laser. These control signals are used to drive a thermal and a piezoelectric transducer that adjust the frequency and phase of the slave-laser output. The output of the photodiode is a heterodyne signal at the difference between the frequencies of the two lasers. (The difference is currently required to be less than 20 MHz due to the Nyquist limit of the current sampling rate. We foresee few problems in doubling this limit using current equipment.) Within the phasemeter, the photodiode-output signal is digitized to 15 bits at a sampling frequency of 40 MHz by use of the same analog-to-digital converter (ADC) as that of the previously reported phasemeter. The ADC output is passed to the FPGA, wherein the signal is demodulated using a digitally generated oscillator signal at the offset locking frequency specified by the user. The demodulated signal is low-pass filtered, decimated to a sample rate of 1 MHz, then filtered again. The decimated and filtered signal is converted to an analog output by a 1 MHz, 16-bit digital-to-analog converters. After a simple low-pass filter, these analog signals drive the thermal and piezoelectric transducers of the laser.

Shaddock, Daniel↗
NASA NTRS2008

LiGa(OTf)(sub 4) as an Electrolyte Salt for Li-Ion Cells

Lithium tetrakis(trifluoromethane sulfo - nato)gallate [abbreviated "LiGa(OTf)4" (wherein "OTf" signifies trifluoro - methanesulfonate)] has been found to be promising as an electrolyte salt for incorporation into both liquid and polymer electrolytes in both rechargeable and non-rechargeable lithium-ion electrochemical cells. This and other ingredients have been investigated in continuing research oriented toward im proving the performances of rechargeable lithium-ion electrochemical cells, especially at low temperatures. This research at earlier stages, and the underlying physical and chemical principles, were reported in numerous previous NASA Tech Briefs articles. As described in more detail in those articles, lithiumion cells most commonly contain nonaqueous electrolyte solutions consisting of lithium hexafluorophosphate (LiPF6) dissolved in mixtures of cyclic and linear alkyl carbonates, including ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Although such LiPF6-based electrolyte solutions are generally highly ionically conductive and electrochemically stable, as needed for good cell performance, there is interest in identifying alternate lithium electrolyte salts that, relative to LiPF6, are more resilient at high temperature and are less expensive. Experiments have been performed on LiGa(OTf)4 as well as on several other candidate lithium salts in pursuit of this interest. As part of these experiments, LiGa(OTf)4 was synthesized by the reaction of Ga(OTf)3 with an equimolar portion of LiOTf in a solvent consisting of anhydrous acetonitrile. Evaporation of the solvent yielded LiGa(OTf)4 as a colorless crystalline solid. The LiGa(OTf)4 and the other salts were incorporated into solutions with PC and DMC. The resulting electrolyte solutions exhibited reasonably high ionic conductivities over a relatively wide temperature range down to 40 C (see figure). In cyclic voltammetry measurements, LiGa(OTf)4 and the other salts exhibited acceptably high electrochemical stability over the relatively wide potential window of 0 to 5 V versus Li+/Li. 13C nuclear-magneticresonance measurements yielded results that suggested that in comparison with the other candidate salts, LiGa(OTf)4 exhibits less ion pairing. Planned further development will include optimization of the salt and solvent contents of such electrolyte solutions and incorporation of LiGa(OTf)4 into gel and solid-state polymer electrolytes. Of the salts, LiGa(OTf)4 is expected to be especially desirable for incorporation into lithium polymer electrolytes, wherein decreased ion pairing is advantageous and the large delocalized anions can exert a plasticizing effect.

Reddy, V. Prakash↗
NASA NTRS2008

Image Compression Algorithm Altered to Improve Stereo Ranging

A report discusses a modification of the ICER image-data-compression algorithm to increase the accuracy of ranging computations performed on compressed stereoscopic image pairs captured by cameras aboard the Mars Exploration Rovers. (ICER and variants thereof were discussed in several prior NASA Tech Briefs articles.) Like many image compressors, ICER was designed to minimize a mean-square-error measure of distortion in reconstructed images as a function of the compressed data volume. The present modification of ICER was preceded by formulation of an alternative error measure, an image-quality metric that focuses on stereoscopic-ranging quality and takes account of image-processing steps in the stereoscopic-ranging process. This metric was used in empirical evaluation of bit planes of wavelet-transform subbands that are generated in ICER. The present modification, which is a change in a bit-plane prioritization rule in ICER, was adopted on the basis of this evaluation. This modification changes the order in which image data are encoded, such that when ICER is used for lossy compression, better stereoscopic-ranging results are obtained as a function of the compressed data volume.

Kiely, Aaron↗
NASA NTRS2008

Magnetic Compensation for Second-Order Doppler Shift in LITS

The uncertainty in the frequency of a linear-ion-trap frequency standard (LITS) can be reduced substantially by use of a very small magnetic inhomogeneity tailored to compensate for the residual second-order Doppler shift. An effect associated with the relativistic time dilatation, one cause of the second-order Doppler shift, is ion motion that is attributable to the trapping radio-frequency (RF)electromagnetic field used to trap ions. The second-order Doppler shift is reduced by using a multi-pole trap; however it is still the largest source of systematic frequency shift in the latest generation of LITSs, which are among the most stable clocks in the world. The present compensation scheme reduces the frequency instability of the affected LITS to about a tenth of its previous value. The basic principles of prior generation LITSs were discussed in several prior NASA Tech Briefs articles. Below are recapitulated only those items of basic information necessary to place the present development in context. A LITS includes a microwave local oscillator, the frequency of which is stabilized by comparison with the frequency of the ground state hyperfine transition of 199Hg+ ions. The comparison involves a combination of optical and microwave excitation and interrogation of the ions in a linear ion trap in the presence of a nominally uniform magnetic field. In the current version of the LITS, there are two connected traps (see figure): (1) a quadrupole trap wherein the optical excitation and measurement take place and (2) a 12-pole trap (denoted the resonance trap), wherein the microwave interrogation takes place. The ions are initially loaded into the quadrupole trap and are thereafter shuttled between the two traps. Shuttling ions into the resonance trap allows sensitive microwave interrogation to take place well away from loading interference. The axial magnetic field for the resonance trap is generated by an electric current in a finely wound wire coil surrounded by magnetic shields. In the quadrupole and 12-pole traps, the potentials are produced by RF voltages applied to even numbers (4 and 12, respectively) of parallel rods equally spaced around a circle. The polarity of the voltage on each rod is opposite that of the voltage on the adjacent rod. As a result, the amplitude of the RF trapping field is zero along the centerline and increases, with radius, to a maximum value near the rods.

Burt, Eric↗
NASA NTRS2008

Piezoelectric Bolt Breakers and Bolt Fatigue Testers

A proposed family of devices for inducing fatigue in bolts in order to break the bolts would incorporate piezoelectric actuators into resonant fixtures as in ultrasonic/ sonic drills/corers and similar devices described in numerous prior NASA Tech Briefs articles. These devices were originally intended primarily for use as safer, more-reliable, more-versatile alternatives to explosive bolts heretofore used to fasten spacecraft structures that must subsequently be separated from each other quickly on command during flight. On Earth, these devices could be used for accelerated fatigue testing of bolts. Fatigue theory suggests that a bolt subjected to both a constant-amplitude dynamic (that is, oscillatory) stress and a static tensile stress below the ultimate strength of the bolt material will fail faster than will a bolt subjected to only the dynamic stress. This suggestion would be applied in a device of the proposed type. The device would be designed so that the device and the bolt to be fatigue-tested or broken would be integral parts of an assembly (see figure). The static tension in the tightened bolt would apply not only the clamping force to hold the joined structures (if any) together but also the compression necessary for proper operation of the piezoelectric actuators as parts of a resonant structural assembly. The constant-amplitude dynamic stress would be applied to the bolt by driving the piezoelectric actuators with a sinusoidal voltage at the resonance frequency of longitudinal vibration of the assembly. The amplitude of the excitation would be made large enough so that the vibration would induce fatigue in the bolt within an acceptably short time. In the spacecraft applications or in similar terrestrial structural-separation applications, devices of the proposed type would offer several advantages over explosive bolts: Unlike explosive bolts, the proposed devices would be reusable, could be tested before final use, and would not be subject to catastrophic misfire. In fatigue-testing applications, devices of the proposed type would offer advantages of compactness and low cost, relative to conventional fatigue- testing apparatuses. In both structural- separation and fatigue-testing applications, bolts to be broken or tested could be instrumented with additional ultrasonic transducers for monitoring of pertinent physical properties and of fatigue failure processes.

Sherrit, Stewart↗
NASA NTRS2008

Parallel-Processing Software for Creating Mosaic Images

A computer program implements parallel processing for nearly real-time creation of panoramic mosaics of images of terrain acquired by video cameras on an exploratory robotic vehicle (e.g., a Mars rover). Because the original images are typically acquired at various camera positions and orientations, it is necessary to warp the images into the reference frame of the mosaic before stitching them together to create the mosaic. [Also see "Parallel-Processing Software for Correlating Stereo Images," Software Supplement to NASA Tech Briefs, Vol. 31, No. 9 (September 2007) page 26.] The warping algorithm in this computer program reflects the considerations that (1) for every pixel in the desired final mosaic, a good corresponding point must be found in one or more of the original images and (2) for this purpose, one needs a good mathematical model of the cameras and a good correlation of individual pixels with respect to their positions in three dimensions. The desired mosaic is divided into slices, each of which is assigned to one of a number of central processing units (CPUs) operating simultaneously. The results from the CPUs are gathered and placed into the final mosaic. The time taken to create the mosaic depends upon the number of CPUs, the speed of each CPU, and whether a local or a remote data-staging mechanism is used.

Klimeck, Gerhard↗
NASA NTRS2008

Four-Point-Latching Microactuator

An experimental inchworm-type linear microactuator is depicted. This microactuator is a successor to one described in "MEMS-Based Piezoelectric/Electrostatic Inchworm Actuator" (NPO-30672), NASA Tech Briefs, Vol. 27, No. 6 (June 2003), page 68. Both actuators are based on the principle of using a piezoelectric transducer operated in alternation with electrostatically actuated clutches to cause a slider to move in small increments. However, the design of the present actuator incorporates several improvements over that of the previous one. The most readily apparent improvement is in geometry and, consequently, in fabrication: In the previous actuator, the inchworm motion was perpendicular to the broad faces of a flat silicon wafer on which the actuator was fabricated, and fabrication involved complex processes to form complex three-dimensional shapes in and on the wafer. In the present actuator, the inchworm motion is parallel to the broad faces of a wafer on which it is fabricated. The components needed to produce the in-plane motion are nearly planar in character and, consequently, easier to fabricate. Other advantages of the present design are described, including that the previous actuator contained two clutches (denoted 'holders' in the cited prior article), the present actuator contains four clutches. The operational sequence of the previous two-clutch actuator is similar. However, the two-clutch configuration is susceptible to tilt of the slider and a consequent large increase in drag. Hence, the primary operational advantages of the present four-point-latching design over the prior two-point-latching design are less drag and greater control robustness arising from greater stability of the orientation of the slider.

Toda, Risaku↗
NASA NTRS2008

Gimballed Shoulders for Friction Stir Welding

In a proposed improvement of tooling for friction stir welding, gimballed shoulders would supplant shoulders that, heretofore, have been fixedly aligned with pins. The proposal is especially relevant to self-reacting friction stir welding. Some definitions of terms, recapitulated from related prior NASA Tech Briefs articles, are prerequisite to a meaningful description of the proposed improvement. In friction stir welding, one uses a tool that includes (1) a rotating shoulder on top (or front) of the workpiece and (2) a pin that rotates with the shoulder and protrudes from the shoulder into the depth of the workpiece. In conventional friction stir welding, the main axial force exerted by the tool on the workpiece is reacted through a ridged backing anvil under (behind) the workpiece. When conventional friction stir welding is augmented with an auto-adjustable pin-tool (APT) capability, the depth of penetration of the pin into the workpiece is varied in real time by a position- or forcecontrol system that extends or retracts the pin as needed to obtain the desired effect. In self-reacting (also known as self-reacted) friction stir welding as practiced heretofore, there are two shoulders: one on top (or front) and one on the bottom (or back) of the workpiece. In this case, a threaded shaft protrudes from the tip of the pin to beyond the back surface of the workpiece. The back shoulder is held axially in place against tension by a nut on the threaded shaft. Both shoulders rotate with the pin and remain aligned coaxially with the pin. The main axial force exerted on the workpiece by the tool and front shoulder is reacted through the back shoulder and the threaded shaft into the friction-stir-welding machine head, so that a backing anvil is no longer needed. A key transmits torque between the bottom shoulder and the threaded shaft, so that the bottom shoulder rotates with the shaft. This concludes the prerequisite definitions of terms.

Carter, Robert↗
NASA NTRS2009

Improved Starting Materials for Back-Illuminated Imagers

An improved type of starting materials for the fabrication of silicon-based imaging integrated circuits that include back-illuminated photodetectors has been conceived, and a process for making these starting materials is undergoing development. These materials are intended to enable reductions in dark currents and increases in quantum efficiencies, relative to those of comparable imagers made from prior silicon-on-insulator (SOI) starting materials. Some background information is prerequisite to a meaningful description of the improved starting materials and process. A prior SOI starting material, depicted in the upper part the figure, includes: a) A device layer on the front side, typically between 2 and 20 m thick, made of p-doped silicon (that is, silicon lightly doped with an electron acceptor, which is typically boron); b) A buried oxide (BOX) layer (that is, a buried layer of oxidized silicon) between 0.2 and 0.5 m thick; and c) A silicon handle layer (also known as a handle wafer) on the back side, between about 600 and 650 m thick. After fabrication of the imager circuitry in and on the device layer, the handle wafer is etched away, the BOX layer acting as an etch stop. In subsequent operation of the imager, light enters from the back, through the BOX layer. The advantages of back illumination over front illumination have been discussed in prior NASA Tech Briefs articles.

Pain, Bedabrata↗
NASA NTRS2009

Synthetic Foveal Imaging Technology

Synthetic Foveal imaging Technology (SyFT) is an emerging discipline of image capture and image-data processing that offers the prospect of greatly increased capabilities for real-time processing of large, high-resolution images (including mosaic images) for such purposes as automated recognition and tracking of moving objects of interest. SyFT offers a solution to the image-data processing problem arising from the proposed development of gigapixel mosaic focal-plane image-detector assemblies for very wide field-of-view imaging with high resolution for detecting and tracking sparse objects or events within narrow subfields of view. In order to identify and track the objects or events without the means of dynamic adaptation to be afforded by SyFT, it would be necessary to post-process data from an image-data space consisting of terabytes of data. Such post-processing would be time-consuming and, as a consequence, could result in missing significant events that could not be observed at all due to the time evolution of such events or could not be observed at required levels of fidelity without such real-time adaptations as adjusting focal-plane operating conditions or aiming of the focal plane in different directions to track such events. The basic concept of foveal imaging is straightforward: In imitation of a natural eye, a foveal-vision image sensor is designed to offer higher resolution in a small region of interest (ROI) within its field of view. Foveal vision reduces the amount of unwanted information that must be transferred from the image sensor to external image-data-processing circuitry. The aforementioned basic concept is not new in itself: indeed, image sensors based on these concepts have been described in several previous NASA Tech Briefs articles. Active-pixel integrated-circuit image sensors that can be programmed in real time to effect foveal artificial vision on demand are one such example. What is new in SyFT is a synergistic combination of recent advances in foveal imaging, computing, and related fields, along with a generalization of the basic foveal-vision concept to admit a synthetic fovea that is not restricted to one contiguous region of an image.

Hoenk, Michael↗
NASA NTRS2009

Radial Halbach Magnetic Bearings

Radial Halbach magnetic bearings have been investigated as part of an effort to develop increasingly reliable noncontact bearings for future high-speed rotary machines that may be used in such applications as aircraft, industrial, and land-vehicle power systems and in some medical and scientific instrumentation systems. Radial Halbach magnetic bearings are based on the same principle as that of axial Halbach magnetic bearings, differing in geometry as the names of these two types of bearings suggest. Both radial and axial Halbach magnetic bearings are passive in the sense that unlike most other magnetic bearings that have been developed in recent years, they effect stable magnetic levitation without need for complex active control. Axial Halbach magnetic bearings were described in Axial Halbach Magnetic Bearings (LEW-18066-1), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), page 85. In the remainder of this article, the description of the principle of operation from the cited prior article is recapitulated and updated to incorporate the present radial geometry. In simplest terms, the basic principle of levitation in an axial or radial Halbach magnetic bearing is that of the repulsive electromagnetic force between (1) a moving permanent magnet and (2) an electric current induced in a stationary electrical conductor by the motion of the magnetic field. An axial or radial Halbach bearing includes multiple permanent magnets arranged in a Halbach array ("Halbach array" is defined below) in a rotor and multiple conductors in the form of wire coils in a stator, all arranged so the rotary motion produces an axial or radial repulsion that is sufficient to levitate the rotor. A basic Halbach array (see Figure 1) consists of a row of permanent magnets, each oriented so that its magnetic field is at a right angle to that of the adjacent magnet, and the right-angle turns are sequenced so as to maximize the magnitude of the magnetic flux density on one side of the row while minimizing it on the opposite side. The advantage of this configuration is that it makes it possible to approach the theoretical maximum force per unit area that could be exerted by a given amount of permanent-magnet material. The configuration is named after physicist Klaus Halbach, who conceived it for use in particle accelerators. Halbach arrays have also been studied for use in magnetic-levitation ("maglev") railroad trains. In a radial Halbach magnetic bearing, the basic Halbach arrangement is modified into a symmetrical arrangement of sector-shaped permanent magnets mounted on the outer cylindrical surface of a drum rotor (see Figure 2). The magnets are oriented to concentrate the magnetic field on their radially outermost surface. The stator coils are mounted in a stator shell surrounding the rotor.

Eichenberg, Dennis J.↗
NASA NTRS2009

Evolutionary Computing Methods for Spectral Retrieval

A methodology for processing spectral images to retrieve information on underlying physical, chemical, and/or biological phenomena is based on evolutionary and related computational methods implemented in software. In a typical case, the solution (the information that one seeks to retrieve) consists of parameters of a mathematical model that represents one or more of the phenomena of interest. The methodology was developed for the initial purpose of retrieving the desired information from spectral image data acquired by remote-sensing instruments aimed at planets (including the Earth). Examples of information desired in such applications include trace gas concentrations, temperature profiles, surface types, day/night fractions, cloud/aerosol fractions, seasons, and viewing angles. The methodology is also potentially useful for retrieving information on chemical and/or biological hazards in terrestrial settings. In this methodology, one utilizes an iterative process that minimizes a fitness function indicative of the degree of dissimilarity between observed and synthetic spectral and angular data. The evolutionary computing methods that lie at the heart of this process yield a population of solutions (sets of the desired parameters) within an accuracy represented by a fitness-function value specified by the user. The evolutionary computing methods (ECM) used in this methodology are Genetic Algorithms and Simulated Annealing, both of which are well-established optimization techniques and have also been described in previous NASA Tech Briefs articles. These are embedded in a conceptual framework, represented in the architecture of the implementing software, that enables automatic retrieval of spectral and angular data and analysis of the retrieved solutions for uniqueness.

Terrile, Richard↗