Technology Focus Electronics/Computers€¦ · cation for calculation of whirl flutter mode subcritical damping, a loads and safety monitor, ... board are four field-programmable

Technology Focus

Electronics/Computers

Software

Materials

Mechanics/Machinery

Manufacturing

Bio-Medical

Physical Sciences

Information Sciences

Books and Reports

03-08 March 2008

https://ntrs.nasa.gov/search.jsp?R=20090020467 2020-07-21T19:04:44+00:00Z

NASA Tech Briefs, March 2008 1

INTRODUCTIONTech Briefs are short announcements of innovations originating from research and develop-

ment activities of the National Aeronautics and Space Administration. They emphasizeinformation considered likely to be transferable across industrial, regional, or disciplinary linesand are issued to encourage commercial application.

Availability of NASA Tech Briefs and TSPsRequests for individual Tech Briefs or for Technical Support Packages (TSPs) announced herein shouldbe addressed to

National Technology Transfer CenterTelephone No. (800) 678-6882 or via World Wide Web at www2.nttc.edu/leads/

Please reference the control numbers appearing at the end of each Tech Brief. Information on NASA’s Innovative Partnerships Program (IPP), its documents, and services is also available at the same facility oron the World Wide Web at http://ipp.nasa.gov.

Innovative Partnerships Offices are located at NASA field centers to provide technology-transfer access toindustrial users. Inquiries can be made by contacting NASA field centers listed below.

Ames Research CenterLisa L. Lockyer(650) [email protected]

Dryden Flight Research CenterGregory Poteat(661) [email protected]

Glenn Research CenterKathy Needham(216) [email protected]

Goddard Space Flight CenterNona Cheeks(301) [email protected]

Jet Propulsion LaboratoryKen Wolfenbarger(818) [email protected] Space Center

Michele Brekke(281) [email protected]

Kennedy Space CenterDavid R. Makufka(321) [email protected]

Langley Research CenterMartin Waszak(757) [email protected]

Marshall Space Flight CenterJim Dowdy(256) [email protected]

Stennis Space CenterJohn Bailey(228) 688-1660 [email protected]

Carl Ray, Program ExecutiveSmall Business Innovation Research (SBIR) & Small Business Technology Transfer (STTR) Programs(202) [email protected]

Doug Comstock, DirectorInnovative Partnerships Program Office(202) [email protected]

NASA Field Centers and Program Offices

5 Technology Focus: DataAcquisition

5 WRATS Integrated Data Acquisition System

6 Breadboard Signal Processor for Arraying DSNAntennas

7 Digital Receiver Phase Meter

8 Split-Block Waveguide Polarization Twist for 220to 325 GHz

9 Electronics/Computers9 Nano-Multiplication-Region Avalanche

Photodiodes and Arrays

10 Tailored Asymmetry for Enhanced Coupling toWGM Resonators

11 Disabling CNT Electronic Devices by Use ofElectron Beams

13 Mechanics/Machinery13 Conical Bearingless Motor/Generators

14 Integrated Force Method for IndeterminateStructures

17 Bio-Medical17 Carbon-Nanotube-Based Electrodes for

Biomedical Applications

18 Compact Directional Microwave Antenna forLocalized Heating

19 Using Hyperspectral Imagery To Identify Turfgrass Stresses

21 Physical Sciences21 Shaping Diffraction-Grating Grooves To Optimize

Efficiency

22 Low-Light-Shift Cesium Fountain WithoutMechanical Shutters

23 Magnetic Compensation for Second-OrderDoppler Shift in LITS

24 Nanostructures Exploit Hybrid-PolaritonResonances

25 Microfluidics, Chromatography, and Atomic-ForceMicroscopy

26 Model of Image Artifacts From Dust Particles

29 Information Sciences29 Pattern-Recognition System for Approaching

a Known Target

30 Orchestrator Telemetry Processing Pipeline

30 Scheme for Quantum Computing Immune toDecoherence

31 Books & Reports31 Spin-Stabilized Microsatellites With Solar

Concentrators

31 Phase Calibration of Antenna Arrays Aimed atSpacecraft

31 Ring Bus Architecture for a Solid-State Recorder

31 Image Compression Algorithm Altered ToImprove Stereo Ranging

03-08 March 2008


This document was prepared under the sponsorship of the National Aeronautics and Space Administration. Neither the United States Govern-ment nor any person acting on behalf of the United States Government assumes any liability resulting from the use of the information containedin this document, or warrants that such use will be free from privately owned rights.


Technology Focus: Data Acquisition

WRATS Integrated Data Acquisition SystemThis new system substantially improves tiltrotor aeroelastic test methods.NASA Langley Research Center, Hampton, Virginia

The Wing and Rotor Aeroelastic TestSystem (WRATS) data acquisition sys-tem (DAS) is a 64-channel data acquisi-tion display and analysis system specifi-cally designed for use with the WRATS1/5-scale V-22 tiltrotor model of theBell Osprey. It is the primary data ac-quisition system for experimental aero-elastic testing of the WRATS model forthe purpose of characterizing the aero-mechanical and aeroelastic stability ofprototype tiltrotor configurations. TheWRATS DAS was also used during aero-elastic testing of Bell Helicopter Tex-tron’s Quad-Tiltrotor (QTR) designconcept, a test which received interna-tional attention. The LabVIEW-baseddesign is portable and capable of pow-ering and conditioning over 64 chan-nels of dynamic data at sampling ratesup to 1,000 Hz. The system includes a60-second circular data archive, an in-tegrated model swashplate excitationsystem, a moving block damping appli-cation for calculation of whirl fluttermode subcritical damping, a loads andsafety monitor, a pilot-control consoledisplay, data analysis capabilities, andinstrumentation calibration functions.Three networked computers runningcustom-designed LabVIEW software ac-quire data through National Instru-ments data acquisition hardware.

The aeroelastic model (see figure)was tested with the DAS at two facilitiesat NASA Langley, the Transonic Dynam-ics Tunnel (TDT) and the RotorcraftHover Test Facility (RHTF). Because ofthe need for seamless transition betweentesting at these facilities, DAS isportable. The software is capable of har-monic analysis of periodic time historydata, Fast Fourier Transform calcula-tions, power spectral density calcula-tions, and on-line calibration of test in-strumentation. DAS has a circular bufferarchive to ensure critical data is not lostin event of model failure/incident, aswell as a sample-and-hold capability forphase-correct time history data. The sys-tem has an interface to drive TDT textoverlay display video monitors and an in-terface to trigger digital video recording

Wing and Rotor Aeroelastic Test System 9 (WRATS).

WRARTS DAS front panel graphical user interface.

The WRATS model was tested with the DAS at the Transonic Dynamics Tunnel at NASA Langley. Shownbelow is the LabVIEW-based WRATS DAS front-panel graphical user interface.

6 NASA Tech Briefs, March 2008

(DVR) systems.DAS uses NI SCXI signal-condition-

ing hardware to power, amplify, andanti-alias-filter the 64 channels of sam-ple-and-hold time-correlated data atsample rates up to 1,000 Hz. TheWRATS data system as a whole maxi-mizes efficient tiltrotor aeroelastic testpractices at the TDT by allowing seam-less integration of model swashplatestik-stir excitation commands with data

acquisition capabilities and post-pointdamping analysis. Following analysis,the system reports key results to a MAT-LAB-based data logging system forarchiving, organization, and reportingof test results.

In addition to test efficiency, the sys-tem improves the safety-of-flight envi-ronment of the test process by calculat-ing and monitoring critical modelloads, stress, and parameters in real

time during testing. In the event of un-safe conditions or loads, audible, syn-thesized voice alerts are provided to thetest crew in addition to visual displaycues on the WRATS Loads Monitor dis-plays, which are networked with theWRATS data system.

This work was done by David J. Piatak ofLangley Research Center. Further informationis contained in a TSP (see page 1). LAR-17486

Breadboard Signal Processor for Arraying DSN Antennas The processors can be used to combine signals in interferometry and telecommunications.NASA’s Jet Propulsion Laboratory, Pasadena, California

A recently developed breadboard ver-sion of an advanced signal processor forarraying many antennas in NASA’sDeep Space Network (DSN) can acceptinputs in a 500-MHz-wide frequencyband from six antennas. The nextbreadboard version is expected to ac-cept inputs from 16 antennas, and a fol-lowing developed version is expected tobe designed according to an architec-ture that will be scalable to accept in-puts from as many as 400 antennas.These and similar signal processorscould also be used for combining mul-tiple wide-band signals in non-DSN ap-plications, including very-long-baselineinterferometry and telecommunica-tions.

This signal processor performs func-tions of a wide-band FX correlator and abeam-forming signal combiner. [Theterm “FX” signifies that the digital sam-ples of two given signals are fast Fouriertransformed (F), then the fast Fouriertransforms of the two signals are multi-plied (X) prior to accumulation.] Inthis processor, the signals from the vari-ous antennas are broken up into chan-nels in the frequency domain (see fig-ure). In each frequency channel, the

data from each antenna are correlatedagainst the data from each other an-tenna; this is done for all antenna base-lines (that is, for all antenna pairs). Theresults of the correlations are used toobtain calibration data to align the an-tenna signals in both phase and delay.Data from the various antenna fre-quency channels are also combined andcalibration corrections are applied. Thefrequency-domain data thus combinedare then synthesized back to the timedomain for passing on to a telemetry re-ceiver.

The inputs from the antennas arepreprocessed signals in an intermediate-frequency (IF) band from 700 to 1,200MHz. High-speed commercial off-the-shelf analog-to-digital-converter (ADC)integrated circuits sample the inputs to8 bits at a rate of 1,280 MHz. The sam-ple data are transmitted via fiber-opticlinks to signal-processing boards in acommercial high-performance, modu-lar, digital chassis that conforms to anindustry standard known as the Ad-vanced Telecommunications Architec-ture (ATCA). The physical and electri-cal characteristics of an ATCA chassisare governed by a specification known

as PICMG 3.0 (wherein “PICMG” signi-fies the PCI Industrial Computer Manu-facturers Group and “PCI” signifies pe-ripheral component interface).

Mounted on each signal-processingboard are four field-programmable gatearray (FPGA) integrated-circuit chipsthat are interconnected both on theboard and through the ATCA back planeby serial links capable of operating atspeeds up to 2.5 Gb/s. Each FPGA chipcan be programmed, independently ofthe other FPGA chips, to perform suchspecific functions as implementing filterbanks to convert time-domain data to fre-quency-domain data in frequency chan-nels, wide- and narrow-band cross-corre-lation, combining of the individualfrequency channels, and implementingsynthesizing filter banks for convertingfrequency-domain data back to the timedomain.

This work was done by Andre Jongeling,Elliott Sigman, Kumar Chandra, JosephTrinh, Melissa Soriano, Robert Navarro,Stephen Rogstad, Charles Goodhart, RobertProctor, Michael Jourdan, and BennoRayhrer of Caltech for NASA’s Jet PropulsionLaboratory. Further information is containedin a TSP (see page 1). NPO-43646

ADCIF Signal FromAntenna 1

IF Signal FromAntenna 2 ADC

Delay Line Filter Bank

Delay Line Filter Bank

Correlator

Combiner

Cross-Correlation Data

Synthesizer Receiver

PhaseRotator

PhaseRotator

This Block Diagram is a simplified representation the signal flow downstream of the inputs from two antennas. Each filter bank converts time-domain datato frequency-domain data in 400 overlapping 1.25-MHz-wide frequency channels that span the IF range from 700 to 1,200 MHz. The combiner, synthesizer,and receiver were undergoing development at the time of reporting the information for this article.


Digital Receiver Phase MeterA commercial digital receiver is modified into a two-channel phase meter.NASA’s Jet Propulsion Laboratory, Pasadena, California

The software of a commerciallyavailable digital radio receiver hasbeen modified to make the re-ceiver function as a two-channellow-noise phase meter. This phasemeter is a prototype in the contin-uing development of a phasemeter for a system in which radio-frequency (RF) signals in the twochannels would be outputs of aspaceborne heterodyne laser in-terferometer for detecting gravi-tational waves. The frequencies ofthe signals could include a com-mon Doppler-shift component ofas much as 15 MHz. The phasemeter is required to measure therelative phases of the signals inthe two channels at a samplingrate of 10 Hz at a root power spec-tral density <5 microcycle/(Hz)1/2

and to be capable of determiningthe power spectral density of thephase difference over the fre-quency range from 1 mHz to 1Hz. Such a phase meter could alsobe used on Earth to perform sim-ilar measurements in laser metrol-ogy of moving bodies.

To illustrate part of the principleof operation of the phase meter,the figure includes a simplifiedblock diagram of a basic single-channel digital receiver. The inputRF signal is first fed to the inputterminal of an analog-to-digitalconverter (ADC). To prevent aliasing er-rors in the ADC, the sampling rate mustbe at least twice the input signal fre-quency. The sampling rate of the ADC isgoverned by a sampling clock, whichalso drives a digital local oscillator(DLO), which is a direct digital fre-quency synthesizer. The DLO producessamples of sine and cosine signals at aprogrammed tuning frequency. Thesine and cosine samples are mixed with(that is, multiplied by) the samples fromthe ADC, then low-pass filtered to obtainin-phase (I) and quadrature (Q) signalcomponents. A digital signal processor(DSP) computes the ratio between theQ and I components, computes thephase of the RF signal (relative to that ofthe DLO signal) as the arctangent of thisratio, and then averages successive suchphase values over a time interval speci-fied by the user.

The specific commercially availabletwo-channel digital receiver includes adual-channel, 65-MHz, 14-bit peripheralcomponent interface (PCI) bus data-ac-quisition card with a daughter boardthat contains a pair of narrow-bandtuner integrated-circuit chips. The inputstage of the card consists of two ADCs. Inthe tuner chips, input signals having fre-quencies up to 35 MHz can be translatedto zero frequency, then digitally low-passfiltered to a bandwidth between 1 kHzand 1 MHz. The output samples of thetuner chips are fed to a two-part swapbuffer. When each half of the swapbuffer becomes filled up to a limit (e.g.,1M sample) specified by the user, thecontents of the buffer are transferred,via PCI interface, to an external com-puter for further analysis.

The factory-supplied receiver soft-ware includes basic driver components

and provides many options to controltuning frequencies, sampling rates, andother operational parameters. Thephase-meter version of the software in-corporates many of the basic drivercomponents, but a significant effort wasmade in modifying other parts of thesoftware to make the receiver functionas a dedicated two-channel phasemeter. In essence, the net effect of themodification is to cause the externalcomputer to calculate differences be-tween the phases in each successive pairof buffered samples from tuner chipsand calculate the average phase differ-ence over the time interval representedby the buffer contents.

This work was done by Martin Marcinand Alexander Abramovici of Caltech forNASA’s Jet Propulsion Laboratory. For moreinformation, contact [email protected]

BASIC SINGLE-CHANNEL DIGITAL RECEIVER

TWO-CHANNEL DIGITAL RECEIVER PHASE METER

ADCRF Signal

sin cos

Complex Mixer

DSPDigital Low-Pass Filter

Clock DLO

Tuner

1MSampleBuffer

1MSampleBuffer

ADCControl

PCIInterface

Computer

ExternalClock

ExternalTrigger

InternalClock

InternalTrigger

Mu

ltip

lexe

rTuner

ADC

ADC

RF Signal inChannel 1

RF Signal inChannel 2

These Block Diagrams depict the principles of operation of (1) a basic single-channel digital receiver and (2)the present two-channel digital phase meter, which utilizes the original hardware and modified software ofa commercial two-channel digital receiver.


Split-Block Waveguide Polarization Twist for 220 to 325 GHzThis device is superior to conventional twisted rectangular waveguides for submillimeterwavelengths.NASA’s Jet Propulsion Laboratory, Pasadena, California

A split-block waveguide circuit that ro-tates polarization by 90° has been de-signed with WR-3 input and output wave-guides, which are rectangular waveguidesused for a nominal frequency range of220 to 325 GHz. Heretofore, twisted rec-tangular waveguides equipped withflanges at the input and output have beenthe standard means of rotating the polar-izations of guided microwave signals.However, the fabrication and assembly of

such components become difficult athigh frequency due to decreasing wave-length, such that twisted rectangularwaveguides become impractical at fre-quencies above a few hundred gigahertz.Conventional twisted rectangular wave-guides are also not amenable to integra-tion into highly miniaturized subassem-blies of advanced millimeter- andsubmillimeter-wave detector arrays nowundergoing development. In contrast,

the present polar-ization-rotatingwaveguide canreadily be incorpo-rated into complexintegrated wave-guide circuits suchas miniaturized de-tector arrays fabri-cated by either con-ventional endmilling of metalblocks or by deepreactive ion etchingof silicon blocks.Moreover, the pres-ent split-block de-sign can be scaledup in frequency toat least 5 THz.

The main step infabricating a split-

block polarization-rotating waveguide ofthe present design is to cut channelshaving special asymmetrically shapedsteps into mating upper and lowerblocks (see Figure 1). The dimensions ofthe steps are chosen to be consistentwith the WR-3 waveguide cross section,which is 0.864 by 0.432 mm. The chan-nels are characterized by varying widthswith constant depths of 0.432, 0.324, and0.216 mm and by relatively large cornerradii to facilitate fabrication. The stepseffect both a geometric transition andthe corresponding impedance-matchedelectromagnetic-polarization transitionbetween (1) a WR-3 rectangular wave-guide oriented with the electric fieldvector normal to the block mating sur-faces and (2) a corresponding WR-3waveguide oriented with its electric fieldvector parallel to the mating surfaces ofthe blocks.

A prototype has been built andtested. Figure 2 presents test results in-dicative of good performance overnearly the entire WR-3 waveguide fre-quency band.

This work was done by John Ward andGoutam Chattopadhyay of Caltech forNASA’s Jet Propulsion Laboratory. Furtherinformation is contained in a TSP (see page 1).NPO-42985

Figure 1. A Channel Having Asymmetric Steps is cut into the lower block.An identical channel is cut into the upper block. Then with the help ofalignment pins, the blocks are assembled so that the two channels mergeinto one channel that makes a transition between two orthogonal orien-tations of a WR-3 waveguide.

Figure 2. The Return Loss and Transmission of a prototype of a polarization-rotating waveguide like that of Figure 1 was measured over the nominal fre-quency band of WR-3 waveguide.

LOWER BLOCK

Front Face

Lower Half of Polarization-Rotating

Waveguide

UPPER AND LOWER BLOCKS ASSEMBLED — FRONT VIEW

Waveguide Opening 0.432 mm Wide 0.864 mm High

UPPER AND LOWER BLOCKS ASSEMBLED — REAR VIEW

Waveguide Opening 0.864 mm Wide 0.432 mm High

ENLARGED TOP VIEW OF LOWER HALF OF POLARIZATION-ROTATING WAVEGUIDE

0.864 mm

This Step 0.216 mm Deep



0.432 mm

220 235 250 265 280 295 310 325–40

–30

–20

–10

0

Frequency, GHz

Ret

urn

Lo

ss a

nd

Tra

nsm

issi

on

, dB

Transmission

Return Loss


Electronics/Computers

Nano-Multiplication-Region Avalanche Photodiodes and ArraysOxide embedding structures and nanoscale multiplication regions would afford improvementsin performance.NASA’s Jet Propulsion Laboratory, Pasadena, California

Nano-multiplication-region avalanchephotodiodes (NAPDs), and imaging ar-rays of NAPDs integrated with comple-mentary metal oxide/semiconductor(CMOS) active-pixel-sensor integratedcircuitry, are being developed for appli-cations in which there are requirementsfor high-sensitivity (including photon-counting) detection and imaging atwavelengths from about 250 to 950 nm.With respect to sensitivity and to suchother characteristics as speed, geometricarray format, radiation hardness, powerdemand of associated circuitry, size,weight, and robustness, NAPDs and ar-

rays thereof are expected to be superiorto prior photodetectors and arrays in-cluding CMOS active-pixel sensors(APSs), charge-coupled devices (CCDs),traditional APDs, and microchannel-plate/CCD combinations.

Figure 1 depicts a conceptual NAPDarray, integrated with APS circuitry, fab-ricated on a thick silicon-on-insulatorwafer (SOI). Figure 2 presents selectedaspects of the structure of a typical singlepixel, which would include a metaloxide/semiconductor field-effect tran-sistor (MOSFET) integrated with theNAPD. The NAPDs would reside in sili-

con islands formed on the buried oxide(BOX) layer of the SOI wafer. The sili-con islands would be surrounded byoxide-filled insulation trenches, which,together with the BOX layer, would con-stitute an oxide embedding structure.There would be two kinds of silicon is-lands: NAPD islands for the NAPDs andMOSFET islands for in-pixel and globalCMOS circuits. Typically, the silicon is-lands would be made between 5 and 10μm thick, but, if necessary, the thicknesscould be chosen outside this range. Theside walls of the silicon islands would beheavily doped with electron-acceptor im-purities (p+-doped) to form anodes forthe photodiodes and guard layers forthe MOSFETs.

A nanoscale reach-through structureat the front (top in the figures) centralposition of each NAPD island wouldcontain the APD multiplication region.Typically, the reach-through structurewould be about 0.1 μm in diameter andbetween 0.3 and 0.4 nm high. The toplayer in the reach-through structurewould be heavily doped with electron-donor impurities (n+-doped) to make itact as a cathode. A layer beneath thecathode, between 0.1 and 0.2 nm thick,would be p-doped to a concentration≈1017 cm–3. A thin n+-doped polysiliconpad would be formed on the top of thecathode to protect the cathode againsterosion during a metal-silicon alloyingstep that would be part of the process offabricating the array. This NAPD struc-ture would be amenable to either frontor back illumination. To enable back il-lumination, it would be necessary toetch away, from underneath the NAPDsilicon islands, the corresponding por-tions of a handle wafer supporting theSOI substrate.

The advantages of the NAPD conceptover prior photodetector and array con-cepts are attributable to the oxide em-bedding SOI structure and thenanoscale multiplication region. Theelectrically insulating property of theoxide embedding structure would pre-vent cross-talk among pixels. The

Figure 1. A Typical NAPD Array, characterized by a high fill factor, would be integrated with activepixel circuits and an on-chip readout circuit.

Ultraviolet

Visible NearInfrared

ReadoutCircuit

Handle Substrate

OxideInsulation

NAPD Active PixelCircuit

PhotonIncidence

Oxide Cathode (n+)Guard

Layer (p+)Front

Illumination

Back Illumination

MOSFET

NAPD

Anode (p+)

5 to10 μm

0.3 to0.3 to0.4 0.4 μm0.3 to0.4 μm

0.1 to0.2 μmAbout

0.1 μm

HandleHandleWaferWaferHandleWafer

n+

p

Reach-ThroughStructure

IntrinsicSilicon

Buried OxideBuried OxideBuried Oxide

Figure 2. Each Pixel of an array like that of Figure 1 would contain an NAPD structure integrated withan active pixel circuit structure that, in this example, would be a MOSFET structure.


nanoscale design of the multiplicationregion could be tailored to obtainunique avalanche properties. In con-trast, (1) the pixels of a traditional APDarray are all built on one common sub-strate, leading to severe cross-talk and(2) a traditional APD contains a rela-tively large multiplication region, withinwhich electron avalanches are localizedto a few small volumes. Efforts have beenmade to obtain uniformity in the multi-plication regions of traditional APDs,

but inasmuch as electron avalanches arevery sensitive to the local electric-fieldfluctuations, it is difficult to obtain uni-formity in large arrays of conventionalAPDs.

This work was done by Xinyu Zheng, Be-dabrata Pain, and Thomas Cunningham ofCaltech for NASA’s Jet Propulsion Laboratory.Further information is contained in a TSP(see page 1).

In accordance with Public Law 96-517,the contractor has elected to retain title to this

invention. Inquiries concerning rights for itscommercial use should be addressed to:

Innovative Technology Assets ManagementJPLMail Stop 202-2334800 Oak Grove DrivePasadena, CA 91109-8099(818) 354-2240E-mail: [email protected] to NPO-42276, volume and number

of this NASA Tech Briefs issue, and thepage number.

Tailored Asymmetry for Enhanced Coupling to WGM ResonatorsSurfaces are made to have optimum combinations of curvatures in orthogonal planes.NASA’s Jet Propulsion Laboratory, Pasadena, California

Coupling of light into and out of whis-pering-gallery-mode (WGM) optical res-onators can be enhanced by designingand fabricating the resonators to havecertain non-axisymmetric shapes (seefigure). Such WGM resonators also ex-hibit the same ultrahigh values of theresonance quality factor (Q) as do priorWGM resonators. These WGM res-onators are potentially useful as tunablenarrow-band optical filters havingthroughput levels near unity, high-speedoptical switches, and low-threshold laserresonators. These WGM resonatorscould also be used in experiments to in-vestigate coupling between high-Q andchaotic modes within the resonators.

For a WGM resonator made of an op-tically nonlinear material (e.g., lithiumniobate) or another material having ahigh index of refraction, a prism madeof a material having a higher index of re-fraction (e.g., diamond) must be used aspart of the coupling optics. For couplingof a beam of light into (or out of) thehigh-Q resonator modes, the beam mustbe made to approach (or recede from)the resonator at a critical angle deter-mined by the indices of refraction of theresonator and prism materials. In thecase of a lithium niobate/diamond in-terface, this angle is approximately 22°.

For a beam of laser light travelingthrough the prism and having a typicalaxisymmetric cross-sectional power den-sity that varies as a Gaussian function ofradius from its cylindrical axis, the crosssection of the phase front changes fromcircular to elliptical at the interface. Inthe case of the lithium niobate/dia-mond interface, the ratio between thelengths of the semimajor and semiminoraxes of the ellipse is about 2.7. In order

to optimize the coupling of the beaminto the high-Q modes of the resonator,the ratio between the horizontal and ver-tical curvatures of the resonator must bemade to equal the aforesaid material-de-pendent ratio between the lengths ofthe axes of the ellipse. (Here, “vertical”and “horizontal” refer to planes ontowhich are projected the narrowest andwidest views, respectively, of the res-onator, as in the figure.) It is difficult tofabricate a WGM resonator surface tosuch an exacting specification at a spe-cific point on its surface, but the task canbe simplified as described next if onedoes not insist on a specific location.

If the WGM resonator is shaped to havea constant radius of curvature at its periph-ery as seen in a vertical plane but is asym-metrical (or at least non-axisymmetric) ina horizontal plane (for example, if itsshape in a horizontal plane is elliptical),then its horizontal radius of curvature andthe ratio between the two curvatures variescontinuously with position along the pe-riphery. Consequently, by suitable choiceof the shape, it is possible to make theratio between these curvatures equal thedesired material-dependent ratio at somelocation along the periphery.

Several working prototype WGM res-onators have been designed and fabri-cated according to this concept. In tests,these resonators exhibited Q values ofabout 108 and coupling efficiencies >0.7.

This work was done by Makan Mohagegand Lute Maleki of Caltech for NASA’s JetPropulsion Laboratory. Further information iscontained in a TSP (see page 1).

In accordance with Public Law 96-517, thecontractor has elected to retain title to this in-vention. Inquiries concerning rights for itscommercial use should be addressed to:


of this NASA Tech Briefs issue, and the pagenumber.

Top View

Circular Outline, Constant Radius ofCurvature in Horizontal Plane

Non-Axisymmetric (e.g., Elliptical) Outline,Varying Radius of Curvature in

Horizontal Plane

Radius of Curvature in Vertical PlaneEqual Everywhere Along the Periphery

AXISYMMETRIC RESONATOR(PRIOR DESIGN)

NON-AXISYMMETRIC RESONATOR(PRESENT DESIGN)

Radius of Curvature in Vertical PlaneEqual Everywhere Along the Periphery

Top View

Side View

Side View

In the Non-Axisymmetric Resonator, the varia-tion of curvature along the periphery in the hor-izontal plane is chosen such that the ratio be-tween the horizontal and vertical curvatures hasthe optimum value at some location.


Bombardment with tightly focusedelectron beams has been suggested as ameans of electrically disabling selectedindividual carbon-nanotubes (CNTs) inelectronic devices. Evidence in supportof the suggestion was obtained in an ex-periment in which a CNT field-effecttransistor was disabled (see figure) by fo-cusing a 1-keV electron beam on a CNTthat served as the active channel of afield-effect transistor (FET).

Such bombardment could be usefulin the manufacture of nonvolatile-mem-

ory circuits containing CNT FETs. Ulti-mately, in order to obtain the best elec-tronic performances in CNT FETs andother electronic devices, it will be neces-sary to fabricate the devices such thateach one contains only a single CNT asan active element. At present, this is dif-ficult because there is no way to grow asingle CNT at a specific location andwith a specific orientation. Instead, thecommon practice is to build CNTs intoelectronic devices by relying on spatialdistribution to bridge contacts. This

practice results in some devices contain-ing no CNTs and some devices contain-ing more than one CNT. Thus, CNTFETs have statistically distributed elec-tronic characteristics (including switch-ing voltages, gains, and mixtures ofmetallic and semiconducting CNTs).

According to the suggestion, by usinga 1-keV electron beam (e.g., a beamfrom a scanning electron microscope),a particular nanotube could be ren-dered electrically dysfunctional. Thisprocedure could be repeated as manytimes as necessary on different CNTs ina device until all of the excess CNTs inthe device had been disabled, leavingonly one CNT as an active element(e.g., as FET channel).

The physical mechanism throughwhich a CNT becomes electrically dis-abled is not yet understood. On onehand, data in the literature show thatelectron kinetic energy >86 keV isneeded to cause displacement damagein a CNT. On the other hand, inasmuchas a 1-keV beam focused on a small spot(typically a few tens of nanometers wide)deposits a significant amount of energyin a small volume, the energy densitymay suffice to thermally induce struc-tural and/or electronic changes that dis-able the CNT. Research may be war-ranted to investigate this effect in detail.

This work was done by Mihail Petkov ofCaltech for NASA’s Jet Propulsion Laboratory.Further information is contained in a TSP(see page 1).NPO-41343

Disabling CNT Electronic Devices by Use of Electron BeamsSelected CNTs would be burned out.NASA’s Jet Propulsion Laboratory, Pasadena, California

After Exposure

Before Exposure

–20.01

0.1

1

10

100

–1 0

Gate Potential, V

1 2

Cu

rren

t, n

A

The Functionality of a CNT FET was destroyed by exposure to a focused 1-keV electron beam.


Mechanics/Machinery

Motor/generators based on conicalmagnetic bearings have been inventedas an improved alternative to prior suchmachines based, variously, on radialand/or axial magnetic bearings. Boththe present and prior machines aremembers of the class of so-called “bear-ingless” or “self bearing” (in the sense ofnot containing mechanical bearings) ro-tary machines. Each motor/generatorprovides both a torque and force allow-ing it to either function as a motor andmagnetic bearing or a generator andmagnetic bearing concurrently. Becausethey are not subject to mechanical bear-ing wear, these machines have poten-tially long operational lives and canfunction without lubrication and overwide ranges of speed and temperaturethat include conditions under which lu-bricants would become depleted, de-graded, or ineffective and mechanicalbearings would fail.

The figure shows three typical con-figurations of conical bearinglessmotor/generators. The main ele-ments of each motor/generator areconcentric rotor and stator portionshaving conically tapered surfaces fac-ing each other across a gap. Because aconical motor/generator imposesboth radial and axial magnetic forces,it acts, in effect, as a combination ofan axial and a radial magnetic bear-ing. Therefore, only two conicalmotor/generators — one at each endof a rotor — are needed to effect com-plete magnetic leviation of the rotor,whereas previously, it was necessary touse a combination of an axial and a ra-dial magnetic bearing at each end ofthe rotor to achieve complete mag-netic levitation and a separate motorto provide torque.

The stator portion of eachmotor/generator consists of a magneticcore and back iron with a number ofteeth and slots at the gap and wires(electromagnet coils) wound in theslots. The rotor consists largely of a mag-netic core and, depending on the spe-cific design, could also include perma-nent magnets. Except for the conical

configuration, the rotor and stator re-semble those of prior radial magneticbearings and bearingless motors.

As in prior magnetic bearings andbearingless motors, electric currents aredriven through the coils, producingmagnetic fluxes in the core and rotorthat result in torques and forces on therotor; a feedback control system adjuststhe current waveforms, in response tothe positions of the ends of the rotor asmeasured by sensors, to produce the ra-dial and axial forces needed to maintainrotor levitation at the desired radial andaxial position. For motor or generatoroperation, times for electronic switchingof coil connections for input or outputcurrents are determined in response tothe rotation angle as measured by an-other sensor.

Unlike in prior bearingless motors,it is not necessary to use one set ofcoils for levitation interspersed withanother sets of coils for motor/genera-tor operation. Instead, an improvedcontrol scheme provides for the use ofa single set of coils for both levitationand motor/generator operation. Thescheme requires at least six coils (forthree or more pole pairs) in each bear-ing. In its motor aspect, the schemeprovides for simultaneous operation ofthe equivalent of three overlappingthree-phase motors. In addition, thismotor configuration provides a certainamount of fault tolerance; if any of thepole-pair coils or the drive circuitry ofa pole pair fails, the remaining twothree-phase subsystems can continueto provide magnetic levitation andmotor/generator operation.

This work was done by P. Kascak and R.Jansen of the University of Toledo and T.Dever of QSS Group, Inc. for Glenn ResearchCenter. Further information is contained in aTSP (see page 1).

Inquiries concerning rights for the commer-cial use of this invention should be addressedto NASA Glenn Research Center, InnovativePartnerships Office, Attn: Steve Fedor, MailStop 4–8, 21000 Brookpark Road, Cleveland,Ohio 44135. Refer to LEW-17638-1/39-1/40-1.

Conical Bearingless Motor/Generators Advantages include high-speed, long-life operation in a compact form factor. John H. Glenn Research Center, Cleveland, Ohio

Rotor

Rotor

Rotor

Stator

Stator

Stator

Stator

Stator

Stator

Axis of Rotation

Axis of Rotation

Axis of Rotation

Conical Bearingless Motor/Generators both levi-tate and rotate the rotor with respect to the sta-tors. These are simplified cross-sectional views ofrepresentative configurations of machines de-scribed in the text. Although stators traditionallyenclose rotors, conical bearingless motor/gener-ators lend themselves equally well to designs inwhich rotors enclose stators.


Two methods of solving indetermi-nate structural-mechanics problemshave been developed as products of re-search on the theory of strain compati-bility. In these methods, stresses are con-sidered to be the primary unknowns (incontrast to strains and displacementsbeing considered as the primary un-knowns in some prior methods). One ofthese methods, denoted the integratedforce method (IFM), makes it possibleto compute stresses, strains, and dis-placements with high fidelity by use ofmodest finite-element models that entailrelatively small amounts of computation.The other method, denoted the com-pleted Beltrami Mitchell formulation(CBMF), enables direct determinationof stresses in an elastic continuum withgeneral boundary conditions, withoutthe need to first calculate displacementsas in traditional methods.

The equilibrium equation, the com-patibility condition, and the materiallaw are the three fundamental conceptsof the theory of structures. For almost150 years, it has been commonly sup-posed that the theory is complete. How-ever, until now, the understanding ofthe compatibility condition remained

incomplete, and the compatibility con-dition was confused with the continuitycondition. Furthermore, the compati-bility condition as applied to structuresin its previous incomplete form was in-consistent with the strain formulationin elasticity.

Strength-of-materials problems havebeen classified into determinate and in-determinate problems. A determinateproblem is analyzed primarily on thebasis of the equilibrium concept and canbe well understood. The solution of anindeterminate problem requires an ad-ditional compatibility condition, ofwhich, until now, there has not been ex-clusive comprehension. In traditionalstress-analysis methods, the compatibil-ity condition has been improvised bymanipulating the equilibrium concept,variously, by rewriting it in displacementvariables or through a method known inthe art as the redundant force method.Such improvisation has made traditionalindeterminate analysis cumbersome.

The research that led to the develop-ment of the IMF and the CBMF in-cluded the derivation of a variationalfunctional. The stationary condition ofthis functional yielded not only the tra-

ditional equations of the mechanics ofsolids but also new equations that wereidentified as constituting the boundarycompatibility condition that was missingfrom the strain equations as originallyformulated by St. Venant circa 1860. Itshould be noted that the IFM and theCBMF can be further specialized intofour indirect methods known as the re-dundant force method, stiffnessmethod, the hybrid method, and thetotal formulation (see table)

The use of the compatibility equationshas systematized indeterminate analysis —especially for problems that involve varia-tions in temperature and initial deforma-tions. Solving indeterminate problems hasbecome straightforward through use ofthe IFM because the IFM bestows simulta-neous emphasis on force equilibrium andthe deformation compatibility condition.

A report, “Integrated Force Method So-lution to Indeterminate Structural Me-chanics Problems” (NASA/TP-2004-207430) introduces the IFM to academia,especially to engineering students in civil,mechanical, aeronautical, and other engi-neering disciplines. Although the reportis written for use in college education, itshould be valuable to researchers who

Integrated Force Method for Indeterminate Structures Indeterminate structural-mechanics problems can now be solved systematically. John H. Glenn Research Center, Cleveland, Ohio

Integrated ForceMethod (IFM)

Redundant Force Method

Stiffness Method (DM)

Hybrid Method (HF)

Washizu Method (WM)

Method Primary VariablesVariationalFunctional

Elasticity Structures Elasticity Structures

Stresses

Stress Function

Displacements

Stresses andDisplacements

Stresses, Strains, andDisplacements

Forces

Redundants

Displacements orDeflections

Forces and Deflections

Forces, Deformations,and Deflections

IFM VariationalFunctional

ComplementaryEnergy

Potential Energy

ReissnerFunctional

WashizuFunctional

Completed Beltrami-Michell Formulation (CBMF)

Airy Formulation

Navier Formulation (NF)

Reissner Method (RM)

Total Formulation (TF)

Selected Characteristics of the IFM and CBMF are listed along with those of other methods of structural mechanics.


wish to work on the IFM or to comple-ment their understanding of the compat-ibility condition of structural mechanics.

This work was done by Dale A. Hopkinsand Gary R. Halford of Glenn Research Cen-

ter and Surya N. Patnaik of Ohio AerospaceInstitute. Further information is contained ina TSP (see page 1).

Inquiries concerning rights for the com-mercial use of this invention should be ad-

dressed to NASA Glenn Research Center, In-novative Partnerships Office, Attn: SteveFedor, Mail Stop 4–8, 21000 BrookparkRoad, Cleveland, Ohio 44135. Refer toLEW-17883-1.


Bio-Medical

A nanotube array based on verticallyaligned nanotubes or carbon nanofibershas been invented for use in localizedelectrical stimulation and recording ofelectrical responses in selected regionsof an animal body, especially includingthe brain. There are numerous estab-

lished, emerging, and potential applica-tions for localized electrical stimulationand/or recording, including treatmentof Parkinson’s disease, Tourette’s syn-drome, and chronic pain, and researchon electrochemical effects involved inneurotransmission.

Carbon-nanotube-based electrodesoffer potential advantages over metalmacroelectrodes (having diameters ofthe order of a millimeter) and micro-electrodes (having various diametersranging down to tens of microns)heretofore used in such applications.These advantages include the following:• Stimuli and responses could be local-

ized at finer scales of spatial and tempo-ral resolution, which is at subcellularlevel, with fewer disturbances to, andless interference from, adjacent regions.

• There would be less risk of hemor-rhage on implantation because nano-electrode-based probe tips could beconfigured to be less traumatic.

• Being more biocompatible than aremetal electrodes, carbon-nanotube-based electrodes and arrays would bemore suitable for long-term or perma-nent implantation.

• Unlike macro- and microelectrodes, ananoelectrode could penetrate a cellmembrane with minimal disruption.Thus, for example, a nanoelectrodecould be used to generate an actionpotential inside a neuron or in prox-imity of an active neuron zone. Suchstimulation may be much more effec-tive than is extra- or intracellular stim-ulation via a macro- or microelectrode.

• The large surface area of an array at amicron-scale footprint of non-insulatednanoelectrodes coated with a suitableelectrochemically active material con-taining redox ingredients would make itpossible to obtain a pseudocapacitancelarge enough to dissipate a relativelylarge amount of electric charge, so thata large stimulation current could be ap-plied at a micron-scale region withoutexhausting the redox ingredients.

• Carbon nanotube array is more compat-ible with the three-dimensional networkof tissues. Particularly, a better electrical-neural interface can be formed.

• A carbon nanotube array inlaid in insu-lating materials with only the ends ex-posed is an extremely sensitive electro-analysis tool that can measure the localneurotransmitter signal at extremelyhigh sensitivity and temporal resolution.

Carbon-Nanotube-Based Electrodes for Biomedical ApplicationsStimuli and responses could be localized to within nanometers.Ames Research Center, Moffett Field, California

Carbon Nanotubes connected to metal contact layers would protrude from surfaces of microelectrodepads. In use, the array would be positioned so that at least some nanotubes would be in electrical con-tact with cell components or intercellular structures of interest.

Microelectrode Pads

Conformal Electro-ActiveCoating Layer Carbon

Nanotubes

Substrate

InsulatingLayer

Metal Contact Layer

CarbonNanotubes

Substrate

InsulatingLayer

Metal Contact Layer

TOP VIEW OF AN ARRAY

ENLARGED SIDE-VIEW CROSS SECTIONOF A STIMULATING ELECTRODE

ENLARGED SIDE-VIEW CROSS SECTIONOF A RECORDING ELECTRODE


A nanoelectrode array according tothe invention (see figure) would includetwo or more microelectrode pads on anelectrically insulating substrate. Thesizes of the microelectrode pads and thedistances between them could rangefrom as little as about a micron to aslarge as hundreds of microns, the exactvalues depending on the intended use.Each microelectrode pad could be elec-trically addressed, either individually orin combination with one or more otherpads for localized stimulation and/orrecording. Each microelectrode padwould support either a stimulating or arecording electrode. In either case, theelectrode would comprise a subarray ofmultiple nanoelectrodes in the form ofcarbon nanotubes electrically connectedto, and protruding perpendicularlyfrom, a metal contact layer on an electri-cally insulating substrate.

In the case of a stimulating electrode,the protruding portions of the carbonnanotubes would be treated to deposita thin electro-active coating layer that

would impart the desired amount ofpseudocapacitance. Depending on theapplication, the exposed surface of themetal contact layer between the nano-electrodes would be coated with anelectrically insulating material (e.g., sil-ica or a nonconductive polymer), orwith an electrically conductive or elec-tro-active polymer.

In the case of a recording electrode, itis desirable to minimize the size of theelectrically exposed portion of each car-bon nanotube so as to maximize the de-gree of localization and to minimizenoise (thereby maximizing sensitivity).Therefore, an insulating layer would bedeposited to sufficient thickness thatonly the tip(s) of the longest carbonnanotube(s) would protrude.

The term carbon nanotube here cov-ers a general class of carbon materials,including multi-walled carbon nan-otubes (MWCNTs) and nanofibers(CNFs). These nanostructured carbonmaterials have physical and chemicalproperties that make them especially

suitable for use as nanoelectrodes ac-cording to this invention. Well-alignedarrays of MWCNTs/CNFs have beengrown by plasma-enhanced chemicalvapor deposition on metal lines thathave been pre-patterned by use of litho-graphic techniques. A previously pub-lished “bottom-up” scheme for fabricat-ing an array of MWCNTs/CNFs thatprotrude from metal lines embedded inan SiO2 matrix has been adopted as thebasis of a scheme for fabricating nano-electrode arrays according to the inven-tion. The fabrication processes involvedin these schemes are compatible withthose used in manufacturing semicon-ductor devices. Hence, it should be pos-sible to fabricate the nanoelectrode ar-rays at relatively low cost.

This work was done by Jun Li and M.Meyyappan of Ames Research Center andRussell Andrews, an Ames associate.

Inquiries concerning rights for the commer-cial use of this invention should be addressedto the Ames Innovative Partnerships Office at(650) 604-2954. Refer to ARC-15062-1.

A directional, catheter-sized cylindri-cal antenna has been developed for lo-calized delivery of microwave radiationfor heating (and thus killing) diseasedtissue without excessively heating nearbyhealthy tissue. By “localized” is meantthat the antenna radiates much more ina selected azimuthal direction than inthe opposite radial direction, so that itheats tissue much more on one sidethan it does on the opposite side. Thisantenna can be inserted using either acatheter or a syringe. A 2.4-mm proto-type was tested, although smaller anten-nas are possible.

Prior compact, cylindrical antennasdesigned for therapeutic localized hyper-thermia do not exhibit such directional-ity; that is, they radiate in approximatelyaxisymmetric patterns. Prior directionalantennas designed for the same purposehave been, variously, (1) too large to fitwithin catheters or (2) too large, afterdeployment from catheters, to fit withinthe confines of most human organs. Incontrast, the present antenna offers ahigh degree of directionality and is com-pact enough to be useable as a catheterin some applications.

The antenna de-sign is a hybrid ofmonopole-antennaand transmission-linedesign elements. Theantenna (see Figure1) is formed from anopen-ended coplanarwaveguide in whichthe gap between themiddle conductorstrip and the twoouter (ground) con-ductor strips tapersfrom (1) a smallervalue more charac-teristic of a transmis-sion line to (2) alarger value morecharacteristic of aleaky transmissionline or an antenna.The coplanar wave-guide is wrappedaround a polytetraflu-oroethylene (PTFE)tube, and its abuttingedges are solderedtogether to form the

Compact Directional Microwave Antenna for Localized HeatingHeating is concentrated on one side.Lyndon B. Johnson Space Center, Houston, Texas

Transmission Line Antenna

0.020 in. 0.010 in.

0.070 in.

Middle Conductor

Strip

Outer (Ground) Conductor Strips

COPLANAR WAVEGUIDE BEFORE IT IS ROLLED INTO A CYLINDER

Male CoaxialConnector

ExtrudedPTFE

SemirigidCoaxial Cable

ExposedCentral Conductor

Adapter CCPW

Solder Joint BetweenCentral Conductor of Adapter andMiddle Conductor Strip of CCPW

Solder Joint BetweenOuter Conductor of Adapter andGround Conductor Strip of CCPW

GroundConductor

MiddleConductor

Strip

COMPLETE CCPW ANTENNA ASSEMBLY

ADAPTER

Figure 1. A Coplanar Waveguide With a Taper is rolled into a cylinderand joined with a coaxial-cable adapter to form a narrow antenna thatradiates predominantly to one side.


Using Hyperspectral Imagery To Identify Turfgrass StressesStress maps could enable more-efficient management of large turfgrass fields.Stennis Space Center, Mississippi

The use of a form of remote sensingto aid in the management of large turf-grass fields (e.g. golf courses) has beenproposed. A turfgrass field of interestwould be surveyed in sunlight by use ofan airborne hyperspectral imaging sys-tem, then the raw observational datawould be preprocessed into hyperspec-tral reflectance image data. These datawould be further processed to identifyturfgrass stresses, to determine the spa-tial distributions of those stresses, andto generate maps showing the spatialdistributions.

Until now, chemicals and water haveoften been applied, variously, (1) indis-criminately to an entire turfgrass fieldwithout regard to localization of spe-cific stresses or (2) to visible and possi-bly localized signs of stress — for exam-ple, browning, damage from traffic, orconspicuous growth of weeds. Indi-scriminate application is uneconomicaland environmentally unsound; theamounts of water and chemicals con-sumed could be insufficient in some

areas and excessive in most areas, andexcess chemicals can leak into the envi-ronment. In cases in which developingstresses do not show visible signs at first,it could be more economical and effec-tive to take corrective action before vis-ible signs appear. By enabling earlyidentification of specific stresses andtheir locations, the proposed methodwould provide guidance for planningmore effective, more economical, andmore environmentally sound turfgrass-management practices, including appli-cation of chemicals and water, aeration,and mowing.

The underlying concept of using hy-perspectral imagery to generate stressmaps as guides to efficient manage-ment of vegetation in large fields is notnew; it has been applied in the growthof crops to be harvested. What is newhere is the effort to develop an algo-rithm that processes hyperspectral re-flectance data into spectral indices spe-cific to stresses in turfgrass. Thedevelopment effort has included a

study in which small turfgrass plots thatwere, variously, healthy or subjected toa variety of controlled stresses were ob-served by use of a hand-held spectrora-diometer. The spectroradiometer read-ings in the wavelength range from 350to 1,000 nm were processed to extracthyperspectral reflectance data, which,in turn, were analyzed to find correla-tions with the controlled stresses. Sev-eral indices were found to be corre-lated with drought stress and to bepotentially useful for identifyingdrought stress before visible symptomsappear.

This work was done by Kendall Hutto andDavid Shaw of Mississippi State Universityfor Stennis Space Center.

Inquiries concerning rights for its commer-cial use should be addressed to:

Mississippi State, MS 39762 Phone No.: (662) 325-9575 E-mail: [email protected] Refer to SSC-00270-1, volume and num-

ber of this NASA Tech Briefs issue, and thepage number.

cylindrical antenna structure, now de-noted a cylindrical coplanar waveguide(CCPW), in which there is only oneground conductor. In operation, thewide-gap region between the middleconductor strip and the ground conduc-tor permits radiation into the top side,

while the larger ground side limits radia-tion on the back side.

For a test of directionality, the antennawas inserted in a piece of biomedical sim-ulation material, called “phantom” in theart, formulated to have thermal and elec-tromagnetic properties similar to those of

human tissue. The phantom was instru-mented with two fiber-optic temperatureprobes: one at 3 mm radially outwardfrom the middle conductor of the CCPWand one 3 mm radially outward from theground conductor on the opposite side.The catheter was excited with a power of5 W at a frequency of 2.45 GHz. The tem-perature measurements, plotted in Fig-ure 2, showed that, as desired, there wasconsiderably more heating on the mid-dle-conductor side. As indicated in Fig-ure 2, the temperature difference be-tween the targeted direction and theback side is about 13°C. This difference issufficient to provide localized ablation(killing of targeted diseased cells) whilepreserving the healthy tissue.

This work was done by Patrick W. Fink,Gregory Y. Lin, Andrew W. Chu, Justin A.Dobbins, G. Dickey Arndt, and Phong Ngo ofJohnson Space Center.

This invention is owned by NASA, and apatent application has been filed. Inquiriesconcerning nonexclusive or exclusive licensefor its commercial development should be ad-dressed to the Patent Counsel, Johnson SpaceCenter, (281) 483-0837. Refer to MSC-23781.

15 0 50 100 150 200 250 300 350

20

25

30

35

40

Time, Seconds

Tem

per

atu

re, °

C

Middle-Conductor-Strip Side

Power Removed

Power Applied

Ground-Conductor Side

Figure 2. The Temperature Rises on Opposite Sides of the antenna were unequal, as desired, in a massof simulated tissue heated with microwave power by use of the antenna.


A method of shaping diffraction-grat-ing grooves to optimize the spectral effi-ciency, spectral range, and image qualityof a spectral imaging instrument isunder development. The method isbased on the use of an advanced designalgorithm to determine the possiblycomplex shape of grooves needed to ob-tain a desired efficiency-versus-wave-length response (see figure). Then elec-tron-beam fabrication techniques areused to realize the required grooveshape. The method could be used, forexample, to make the spectral efficiencyof the grating in a given wavelengthrange proportional to the inverse of thespectral efficiency of a photodetector

array so that the overall spectral effi-ciency of the combination of the gratingand the photodetector array would beflat. The method has thus far been ap-plied to one-dimensional gratings only,but in principle, it is also applicable totwo-dimensional gratings.

The algorithm involves calculationsin the spatial-frequency domain. Thespatial-frequency spectrum of a gratingis represented as a diffraction-orderspectral-peak-width function multipliedby an efficiency function for a singlegrating groove. This representation af-fords computational efficiency and ac-curacy by making it possible to consideronly the response from one grating

groove (one period of the grating), in-stead of from the whole grating area, indetermining the response from the en-tire grating. This combination of effi-ciency and accuracy is crucial for futureextensions of the algorithm to two-di-mensional designs and to designs inwhich polarization must also be takeninto account.

The algorithm begins with the defini-tion of target values of relative efficiencythat represent the desired spectral re-sponse of the grating in certain spectralfrequencies calculated from the diffrac-tion order and wavelength. The gratingperiod is divided into a number of cells— typically, 100. The phase contributionfrom each cell is determined from thephase of the incident electromagneticwave and the height of the grating sur-face in the cell. The total contributionfrom all cells to each target value is thencalculated. Then a method known tospecialists as the optimum-rotation-angle method is used to adjust theheight of each cell so that the total re-sponse from all cells is optimized. Thecomputation is iterative and continuesuntil the desired response is obtained.In the event that the desired response isunphysical, the algorithm neverthelessstrives to generate a grating-grove pro-file for which the response approximatesthe desired one as closely as possible.

This work was done by John Backlund,Daniel Wilson, Pantazis Mouroulis, PaulMaker, and Richard Muller of NASA’s JetPropulsion Laboratory. Further informationis contained in a TSP (see page 1).

In accordance with Public Law 96-517,the contractor has elected to retain title to thisinvention. Inquiries concerning rights for itscommercial use should be addressed to:



Physical Sciences

PRIOR ART: SINGLE-BLAZE GRATING

PRIOR ART: TWO-ZONE (DUAL-BLAZE) GRATING

PRESENT ART: POSSIBLY COMPLEX GROOVE SHAPECHOSEN TO OBTAIN DESIRED SPECTRAL RESPONSE

Boundary Between Zones ofDifferent Angles

Shaping Diffraction-Grating Grooves To Optimize EfficiencySpectral response of a grating could be tailored to complement responses of other components. NASA’s Jet Propulsion Laboratory, Pasadena, California

All of the Grooves of a Grating are designed to have the same possibly complex shape, which is cho-sen in an iterative process to obtain a desired spectral response. This approach offers greater designflexibility than does a prior method of tailoring the spectral response of a grating by dividing the grat-ing into two or more zones that contain conventional sawtooth grooves having different blaze an-gles.


A new technique for reducing errors ina laser-cooled cesium fountain frequencystandard provides for strong suppressionof the light shift without need for me-chanical shutters. Because mechanicalshutters are typically susceptible to failureafter operating times of the order ofmonths, the elimination of mechanicalshutters could contribute significantly tothe reliability of frequency standards thatare required to function continuously forlonger time intervals.

With respect to the operation of anatomic-fountain frequency standard, theterm “light shift” denotes an undesiredrelative shift in the two energy levels ofthe atoms (in this case, cesium atoms) inthe atomic fountain during interroga-tion by microwaves. The shift in energylevels translates to a frequency shift thatreduces the precision and possibly accu-racy of the frequency standard. For rea-sons too complex to describe within thespace available for this article, the lightshift is caused by any laser light thatreaches the atoms during the micro-wave-interrogation period, but isstrongest for near-resonance light. Inthe absence of any mitigating design fea-ture, the light shift, expressed as a frac-tion of the standard’s frequency, could

be as large as ≈2 × 10–11, the largest errorin the standard.

In a typical prior design, to suppresslight shift, the intensity of laser light isreduced during the interrogation pe-riod by using a single-pass acousto-optic modulator to deflect the major-ity of light away from the main opticalpath. Mechanical shutters are used toblock the remaining undeflected lightto ensure complete attenuation. With-out shutters, this remaining unde-flected light could cause a light shiftof as much as ≈10–15, which is unac-ceptably large in some applications.

The new technique implementedhere involves additionally shifting thelaser wavelength off resonance by a rel-atively large amount (typically of theorder of nanometers) during micro-wave interrogation. In this design,when microwave interrogation is notunderway, the atoms are illuminatedby a slave laser locked to the lasing fre-quency of a lower power master laser.The locking is achieved by injecting asmall amount of master laser light intothe slave laser. This light is injected viaa polarizing beam splitter after passingthrough a double-pass acousto-opticmodulator (see figure). The output of

the slave laser is then sent through thesingle-pass acousto-optic modulatormentioned above to optical fibers that,in turn, feed the light to the collectionregion of the atomic fountain.

During microwave interrogation,the radio-frequency power applied tothe double-pass acousto-optic modula-tor is turned off in order to cut off theinjection light and detune the slavelaser to its free-running wavelength,which is typically nanometers awayfrom the resonant master laser. Evenin the absence of other measures, thistuning away from resonance reducesthe light shift by about four orders ofmagnitude. Further cutting the radio-frequency power to the single-passacousto-optic modulator causes atten-uation of the slave-laser output beam.It has been verified experimentallythat this combination of frequencyshift and attenuation reduces the lightshift to <10–15, and it has been esti-mated that the resultant shift could beas low as 2 × 10–19.

This work was done by William Klipsteinand Daphna Enzer of Caltech for NASA’s JetPropulsion Laboratory. For more informa-tion, contact [email protected]

Low-Light-Shift Cesium Fountain Without Mechanical ShuttersLight shift is reduced by a combination of detuning and attenuation.NASA’s Jet Propulsion Laboratory, Pasadena, California

Double-PassAcousto-Optical

Modulator

Single-PassAcousto-Optical

Modulator OpticalFibers

Output toAtom-Collection Region

PolarizingBeam Splitter

MasterLaser

SlaveLaser

Laser Illumination of Atoms in the collection region of an atomic fountain is shifted away from the resonance frequency (by use of the double-pass acousto-optical modulator) and attenuated (by use of the single-pass acousto-optical modulator) during microwave interrogation.


Magnetic Compensation for Second-Order Doppler Shift in LITSFractional frequency stability could be the lowest ever achieved.NASA’s Jet Propulsion Laboratory, Pasadena, California

The uncertainty in the frequency of alinear-ion-trap frequency standard(LITS) can be reduced substantially byuse of a very small magnetic inhomo-geneity tailored to compensate for theresidual second-order Doppler shift. Aneffect associated with the relativistic timedilatation, one cause of the second-orderDoppler shift, is ion motion that is attrib-utable to the trapping radio-frequency(RF)electromagnetic field used to trapions. The second-order Doppler shift isreduced by using a muli-pole trap; how-ever it is still the largest source of system-atic frequency shift in the latest genera-tion of LITSs, which are among the moststable clocks in the world. The presentcompensation scheme reduces the fre-quency instability of the affected LITS toabout a tenth of its previous value.

The basic principles of prior genera-tion LITSs were discussed in severalprior NASA Tech Briefs articles. Below arerecapitulated only those items of basicinformation necessary to place the pres-ent development in context. A LITS in-cludes a microwave local oscillator, thefrequency of which is stabilized by com-parison with the frequency of theground state hyperfine transition of199Hg+ ions. The comparison involves acombination of optical and microwaveexcitation and interrogation of the ionsin a linear ion trap in the presence of anominally uniform magnetic field.

In the current version of the LITS,there are two connected traps (see fig-ure): (1) a quadrupole trap wherein theoptical excitation and measurementtake place and (2) a 12-pole trap (de-noted the resonance trap), wherein themicrowave interrogation takes place.The ions are initially loaded into thequadrupole trap and are thereafter shut-tled between the two traps. Shuttlingions into the resonance trap allows sensi-tive microwave interrogation to takeplace well away from loading interfer-ence. The axial magnetic field for theresonance trap is generated by an elec-tric current in a finely wound wire coilsurrounded by magnetic shields.

In the quadrupole and 12-pole traps,the potentials are produced by RF volt-ages applied to even numbers (4 and 12,respectively) of parallel rods equallyspaced around a circle. The polarity ofthe voltage on each rod is opposite that

of the voltage on the adjacent rod. As aresult, the amplitude of the RF trappingfield is zero along the centerline and in-creases, with radius, to a maximum valuenear the rods.

As the number of ions temporallyvaries in a small range about a targetvalue, space-charge repulsion causes theensemble of ions to occupy a varying vol-ume within the trap. The change in ra-dial occupation results in a change inthe time-averaged magnitude of thetrapping RF field sampled by the ionsand a change in ion micromotion ampli-tude, which will cause a correspondingchange in the second-order Dopplershift. (The first-order Doppler shift iseliminated by the geometry of the trapand the polarization of interrogating mi-crowave field.)

In a 12-pole trap, the ions are free par-ticles for most of their trajectories, inter-acting with significant RF amplitude onlyat the edges of the trap. As a result, thetime-averaged RF amplitude sampled bythe ions is significantly smaller, for thesame number of ions trapped, than it is ina typical quadrupole trap used in an ear-lier-generation LITS. The sensitivity tothe second-order Doppler shift is morethan 10 times smaller than in the case ofa quadrupole-trap LITS, making thelong-term stability of a 12-pole-trap LITScomparable to or even better than that ofthe best hydrogen masers. Nevertheless,the second-order Doppler shift remainsthe largest shift in the LITS, and the

problem is to reduce it even further.As a solution to this problem, the pres-

ent compensation scheme exploits thefollowing facts:• The ion-number-dependent second-

order Doppler shift is negative and in-creases in magnitude as the number ofions increases.

• Heretofore, in designing a LITS, greatcare has been taken to provide a uni-form magnetic field within the trap sothat as the volume occupied by theions changes, the average magneticfield sampled by the ions does notchange.

• Notwithstanding the nominal unifor-mity of the magnetic field as de-scribed above, it is possible to intro-duce a well-controlled magnetic-fieldinhomogeneity, such that ions in achanging occupation volume samplea slightly different magnetic field.The resulting inhomogeneity in thesecond-order Zeeman shift can beused to counteract the second-orderDoppler shift.Accordingly, in the present compensa-

tion scheme, one or more coaxial com-pensation coil(s) is or are used to gener-ate one or more small magnetic-fieldinhomogeneities. The placement of,and currents in, the coils can be chosento obtain either a positive or negativechange in the second-order Zeemanshift with a change in the number ofions. By careful adjustment of the cur-rent(s) in the compensation coil(s), the

A Typical Latest-Generation Multipole LITS contains a quadrupole trap and another multipole (e.g., 12-pole) trap surrounded by a coil that generates a nominally uniform axial magnetic field. In the presentcompensation scheme, a controlled magnetic inhomogeneity is introduced by use of a compensation coil.

Compensation Coil

Quadrupole TrapMultipole (12-Pole) Trap

Note: Not to scale. Magnetic Shields

Magnetic-Field Coil


Nanostructures Exploit Hybrid-Polariton ResonancesInfrared absorption or scattering by molecules of interest can be greatly enhanced.NASA’s Jet Propulsion Laboratory, Pasadena, California

Nanostructured devices that exploitthe hybrid-polariton resonances arisingfrom coupling among photons,phonons, and plasmons are subjects ofresearch directed toward the develop-ment of infrared-spectroscopic sensorsfor measuring extremely small quanti-ties of molecules of interest. The spec-troscopic techniques in question are sur-face enhanced Raman scattering (SERS)and surface enhanced infrared absorp-tion (SEIRA). An important intermedi-ate goal of this research is to increasethe sensitivity achievable by these tech-niques. The basic idea of the approachbeing followed in this research is to en-gineer nanostructured devices andthereby engineer their hybrid-polaritonresonances to concentrate infrared radi-ation incident upon their surfaces insuch a manner as to increase the absorp-tion of the radiation for SEIRA andmeasure the frequency shifts of surfacevibrational modes.

The underlying hybrid-polariton-reso-nance concept is best described by refer-ence to experimental devices that havebeen built and tested to demonstrate theconcept. The nanostructure of each suchdevice includes a matrix of silicon car-bide particles of approximately 1 micronin diameter that are supported on apotassium bromide (KBr) or poly(tetra-fluoroethylene) [PTFE] window. Thesegrains are sputter-coated with gold grainsof 40-nm size (see figure).

From the perspective of classical elec-trodynamics, in this nanostructure, thatincludes a particulate or otherwiserough surface, the electric-field portionof an incident electromagnetic field be-comes concentrated on the particleswhen optical resonance conditions aremet. Going beyond the perspective ofclassical electrodynamics, it can be seenthat when the resonance frequencies ofsurface phonons and surface plasmonsoverlap, the coupling of the resonances

gives rise to an enhanced radiation-ab-sorption or -scattering mechanism.

The sizes, shapes, and aggregation ofthe particles determine the frequenciesof the resonances. Hence, the task of de-signing a nanostructure to exhibit thedesired radiation-absorption propertiestranslates, in large part, to selecting par-ticle sizes and shapes to obtain the de-sired enhanced coupling of energy fromphotons to plasmons and phonons. Tobroaden the spectral region(s) of en-hanced absorption, one would select adistribution of particle sizes and shapes.

In a test, the infrared spectra of one ofthe experimental nanostructures de-scribed above were measured beforeand after the nanostructure was coatedwith an approximately-monomolecular-thickness layer of poly(methyl methacry-late) [PMMA]. Among other things, themeasurements showed that in the af-

fected wavelength range, in the pres-ence of the nanostructure, the magni-tude of absorption by the thin PMMAfilm was comparable to the absorptionby a considerably thicker PMMA filmwithout the nanostructure.

This work was done by Mark Anderson ofCaltech for NASA’s Jet Propulsion Laboratory.




Circumferential Belts were formed by diamond turning on the initially cylindrical surface of a CaF2 rod.The radial depths and axial widths of the belts were chosen to make some of the belts act as single-mode and some as multi-mode WGM resonators.

Infrared Radiation

Analyte

KBr or PTFEKBr or PTFESubstrateSubstrate

KBr or PTFESubstrate

second order Zeeman shift can be madeto almost exactly cancel the residual sec-ond-order Doppler shift.

In an experimental implementationof this scheme, a 5-turn compensationcoil was placed between the quadru-pole and 12-pole traps and was excited

with a current of 3 mA. With this com-pensation scheme, the measured frac-tional frequency stability of the second-order Doppler shift is 3 × 10–17. As aresult, all systematics in the clock, andthe clock itself, should have a long-term stability of better than 5 × 10–17,

which would be the best ever measuredin any clock.

This work was done by Eric Burt andRobert Tjoelker of Caltech for NASA’s JetPropulsion Laboratory. For more informa-tion, contact [email protected]


A Raman-and-atomic-force microscope(RAFM) has been shown to be capable ofperforming several liquid-transfer andsensory functions essential for the opera-tion of a microfluidic “laboratory on achip” that would be used to performrapid, sensitive chromatographic andspectro-chemical analyses of unprece-dentedly small quantities of liquids. Themost novel aspect of this developmentlies in the exploitation of capillary andshear effects at the atomic-force-micro-scope (AFM) tip to produce shear-drivenflow of liquids along open microchannelsof a microfluidic device. The RAFM canalso be used to perform such functions asimaging liquids in microchannels; remov-ing liquid samples from channels for verysensitive, tip-localized spectrochemicalanalyses; measuring a quantity of liquidadhering to the tip; and dip-pen deposi-tion from a chromatographic device.

A commercial Raman-spectroscopysystem and a commercial AFM were inte-grated to make the RAFM so as to beable to perform simultaneous topo-graphical AFM imaging and surface-en-hanced Raman spectroscopy (SERS) atthe AFM tip. The Raman-spectroscopysystem includes a Raman microprobe at-tached to an optical microscope, thetranslation stage of which is modified toaccommodate the AFM head. TheRaman laser excitation beam, which isaimed at the AFM tip, has a wavelengthof 785 nm and a diameter of about 5 μm,and its power is adjustable up to 10 mW.The AFM is coated with gold to enabletip-localized SERS.

Heretofore, the use of microfluidic de-vices for “laboratory on a chip” applica-tions has been inhibited by the need forvery high pressures to pump fluidsthrough capillary channels at sufficientrates. Shear-driven flow offers an alterna-tive by eliminating the need for pressure.In the basic form of shear-driven pump-ing, illustrated at the top of Figure 1, twoparallel plates with a liquid between themare driven laterally with respect to eachother, causing the liquid to be pumpedbetween the plates. Shear-driven pump-ing makes it possible to produce veryrapid flows along very narrow channelsaligned along the sliding direction. Thebasic form of shear-driven pumping isused in shear-driven chromatography(SDC), in which the stationary plate is

functionalized to effect chromatographicseparation. In the present approach toshear-driven pumping, illustrated at themiddle and bottom of Figure 1, liquid ad-hering to the RAFM tip and cantilever(or to the tip only) is simply draggedalong a microchannel by moving the tipas in normal AFM operation.

In addition to moving a sample of liq-uid along a microchannel, the RAFMcould be used to perform several otheroperations:• A sample of liquid could be removed

from a microchannel and placed in an-other microchannel.

• A sample of liquid clinging to theRAFM tip after removal from a mi-crochannel could be subjected toSERS to determine its chemical com-position.

• The RAFM could be operated as a con-

ventional AFM in a tapping mode totopographically map the surface of aliquid in a microchannel.

• The change in frequency of vibrationof the cantilever-and-tip structurecould be measured to determine themass of liquid clinging to the tip.

• In a generalization from the conceptof dip-pen nanolithography, one couldperform dip-pen microchromatogra-phy, in which a chromatographic liq-uid would be discharged from a mi-crochromatographic column at thebase of the cantilever as the AFM tipwas moved along a microchannel (seeFigure 2). The liquid would flow alongthe cantilever onto the tip and wouldbe deposited in the microchannel.After evaporation of the eluent (sol-vent), the resulting deposits of analytesalong the channel could be analyzed

Microfluidics, Chromatography, and Atomic-Force MicroscopyCapillary and shear effects are exploited to transport small quantities of liquids.NASA’s Jet Propulsion Laboratory, Pasadena, California

Figure 1. Shear-Driven Pumping is a viable technique for moving small quantities of liquid rapidlyalong a microchannel.

LiquidMoving Top Plate

Stationary Bottom Plate

AFM Cantilever

AFM Tip AFM Cantilever

AFM Tip

Microchannel

Microchannel

Liquid

Liquid

BASIC SHEAR-DRIVEN PUMPING

TWO FORMS OF SHEAR-DRIVEN PUMPING USING ATOMIC-FORCE MICROSCOPE


A mathematical model of image arti-facts produced by dust particles onlenses has been derived. Machine-visionsystems often have to work with cameralenses that become dusty during use.Dust particles on the front surface of alens produce image artifacts that can po-tentially affect the performance of a ma-chine-vision algorithm. The present

model satisfies a need for a means of syn-thesizing dust image artifacts for testingmachine-vision algorithms for robust-ness (or the lack thereof) in the pres-ence of dust on lenses.

A dust particle can absorb light orscatter light out of some pixels, therebygiving rise to a dark dust artifact. It canalso scatter light into other pixels,

thereby giving rise to a bright dust arti-fact. For the sake of simplicity, thismodel deals only with dark dust artifacts.The model effectively represents darkdust artifacts as an attenuation imageconsisting of an array of diffuse dark-ened spots centered at image locationscorresponding to the locations of dustparticles. The dust artifacts are computa-

Model of Image Artifacts From Dust ParticlesThis first-order geometric-optics-based model yields realistic predictions.NASA’s Jet Propulsion Laboratory, Pasadena, California

Figure 1. A Geometric-Optics Model of shadowing is used to compute the effects of dust particles on an image.

by conventional AFM profiling.This work was done by Mark Anderson

of Caltech for NASA’s Jet Propulsion Labora-tory.




Figure 2. The Moving AFM Tip would deposit the outflow of a microchromatography column along amicrochannel. After subsequent evaporation of the solvent, the AFM could be used to profile the de-posited analytes.

AFM Tip

MotionDeposited Analytes

Microchannel

AFM CantileverLiquid Flowing Along Cantilever

Outlet ofMicrochromatographic Column

Front Surface of Lens

Pixel’s Image in Object Space

Dust Particle

ShadowEntrance

Pupil

CollectionCones

ImageDetector


tionally incorporated into a given testimage by simply multiplying the bright-ness value of each pixel by a transmis-sion factor that incorporates the factorof attenuation, by dust particles, of thelight incident on that pixel.

With respect to computation of the at-tenuation and transmission factors, themodel is based on a first-order geomet-ric (ray)-optics treatment of the shadowscast by dust particles on the image detec-tor. In this model, the light collected bya pixel is deemed to be confined to apair of cones defined by the location ofthe pixel’s image in object space, the en-trance pupil of the lens, and the locationof the pixel in the image plane (see Fig-ure 1). For simplicity, it is assumed thatthe size of a dust particle is somewhatless than the diameter, at the front sur-face of the lens, of any collection conecontaining all or part of that dust parti-cle. Under this assumption, the shape ofany individual dust particle artifact is theshape (typically, circular) of the aper-ture, and the contribution of the parti-cle to the attenuation factor for a givenpixel is the fraction of the cross-sectionalarea of the collection cone occupied bythe particle. Assuming that dust particlesdo not overlap, the net transmission fac-tor for a given pixel is calculated as oneminus the sum of attenuation factorscontributed by all dust particles affect-ing that pixel.

In a test, the model was used to synthe-size attenuation images for random distri-butions of dust particles on the front sur-face of a lens at various relative aperture(F-number) settings. As shown in Figure2, the attenuation images resembled dustartifacts in real test images recorded whilethe lens was aimed at a white target.

This work was done by Reg Willson of Cal-tech for NASA’s Jet Propulsion Laboratory.

The software used in this innovation isavailable for commercial licensing. Pleasecontact Karina Edmonds of the CaliforniaInstitute of Technology at (818) 393-2827.Refer to NPO-42437.

Test Image Taken at f/22 Attenuation Image for f/22



Figure 2. Test Images Containing Dust Artifacts recorded at various relative apertures are shownalongside the corresponding synthetic attenuation images.


Information Sciences

Pattern-Recognition System for Approaching a Known TargetMultiple image features are utilized in a multiphase data-fusion process.NASA’s Jet Propulsion Laboratory, Pasadena, California

A closed-loop pattern-recognition sys-tem is designed to provide guidance formaneuvering a small exploratory roboticvehicle (rover) on Mars to return to alanded spacecraft to deliver soil androck samples that the spacecraft wouldsubsequently bring back to Earth. Thesystem could be adapted to terrestrialuse in guiding mobile robots to ap-proach known structures that humanscould not approach safely, for such pur-poses as reconnaissance in military orlaw-enforcement applications, terrestrialscientific exploration, and removal ofexplosive or other hazardous items.

The system has been demonstrated inexperiments in which the Field IntegratedDesign and Operations (FIDO) rover (aprototype Mars rover equipped with avideo camera for guidance) is made to re-turn to a mockup of Mars-lander space-craft. The FIDO rover camera au-tonomously acquires an image of thelander from a distance of 125 m in an out-door environment. Then under guidanceby an algorithm that performs fusion ofmultiple line and texture features in digi-tized images acquired by the camera, therover traverses the intervening terrain,using features derived from images of thelander truss structure. Then by use of pre-cise pattern matching for determining theposition and orientation of the rover rela-tive to the lander, the rover aligns itself withthe bottom of ramps extending from thelander, in preparation for climbing theramps to deliver samples to the lander.

The most innovative aspect of the sys-tem is a set of pattern-recognition algo-rithms that govern a three-phase visual-guidance sequence for approaching thelander. During the first phase, a multifea-ture fusion algorithm integrates the out-puts of a horizontal-line-detection algo-rithm and a wavelet-transform-basedvisual-area-of-interest algorithm for de-tecting the lander from a significant dis-tance. The horizontal-line-detection al-gorithm is used to determine candidatelander locations based on detection of ahorizontal deck that is part of the lander.The wavelet transform is then performedon an acquired image, and a texture sig-

nature is extracted in a local window ofthe wavelet coefficient space for each ofthe candidate lander locations. The mul-tifeature fusion algorithm eliminatesfalse positives arising from terrain fea-tures. The multifeature fusion algorithmis coupled with a three-dimensional vi-sual-terminal-guidance algorithm thatcan extract and utilize cooperative fea-tures of the lander to accurately, itera-tively estimate the pose of the rover rela-tive to the lander and then steer therover to the bottom of the ramps.

The second phase begins when therover has arrived at ≈25 m from the lan-der and ends at a distance of ≈5 m. Inas-much as the distance is more importantthan the position of the rover duringthis phase, the system utilizes parallelline features extracted from a truss struc-ture that is part of the lander. In order tocorrectly distinguish the truss structure,the deck, which appears as a set of nearlylevel lines, is detected first. Any parallellines below the deck are considered tobe parts of the truss structure. Averagedistances between parallel lines are thenused to estimate the distance from therover to the lander, and the centroid ofthe parallel lines is used to compute theheading from the rover to the lander.

During the third phase, distinctive pat-tern of six stripes on the ramps is utilizedin a close-range algorithm for positioningthe rover within 10 cm of the bottom ofthe ramps. At the beginning of this phase,when the rover is ≈5 m from the lander,

the rover circles around the lander. Theclose-range algorithm includes threemajor steps: feature extraction, featurematch, and pose estimation. The featuresare the six stripes, which are arranged sothat any two of them is a topologically andspatially unique combination, so as togreatly reduce uncertainty and computa-tional complexity.

An edge-detection subalgorithm is ap-plied first. Then all straight-line seg-ments are extracted. In order to find thestripes, the close-range algorithm looksfor the ramps, which are defined by a setof long straight and nearly parallel lines(see figure). When a single stripe is de-tected in the image, a linear affine trans-formation based on its four corners canbe constructed. If transformation pro-vides a correct match with a knownstripe, it can help to find other matches.A search on all stripes is performed tofind the best matches. Once the matchesare found, the position and orientationof the rover relative to the lander are es-timated by use of the outside corners ofthe stripes. A minimum of four stripes isused to ensure safe navigation.

This work was done by Terrance Hunts-berger and Yang Cheng of Caltech for NASA’sJet Propulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).


ORIGINAL IMAGE DETECTED RAMP FEATURES

Features of the Ramps are used in close-range navigation.


Orchestrator is a software applicationinfrastructure for telemetry monitor-ing, logging, processing, and distribu-tion. The architecture has been appliedto support operations of a variety ofplanetary rovers. Built in Java with theEclipse Rich Client Platform, Orches-trator can run on most commonly usedoperating systems. The pipeline sup-ports configurable parallel processingthat can significantly reduce the timeneeded to process a large volume ofdata products.

Processors in the pipeline implementa simple Java interface and declare theirrequired input from upstream proces-sors. Orchestrator is programmaticallyconstructed by specifying a list of Javaprocessor classes that are initiated at

runtime to form the pipeline. Input de-pendencies are checked at runtime.Fault tolerance can be configured to at-tempt continuation of processing in theevent of an error or failed input depend-ency if possible, or to abort further pro-cessing when an error is detected.

This innovation also provides supportfor Java Message Service broadcasts oftelemetry objects to clients and providesa file system and relational database log-ging of telemetry. Orchestrator supportsremote monitoring and control of thepipeline using browser-based JMX con-trols and provides several integrationpaths for pre-compiled legacy dataprocessors.

At the time of this reporting, the Or-chestrator architecture has been used by

four NASA customers to build telemetrypipelines to support field operations.Example applications include high-vol-ume stereo image capture and process-ing, simultaneous data monitoring andlogging from multiple vehicles. Exampletelemetry processors used in field testoperations support include vehicle posi-tion, attitude, articulation, GPS location,power, and stereo images.

This work was done by Mark Powell,David Mittman, Joseph Joswig, ThomasCrockett, and Jeffrey Norris of Caltech forNASA’s Jet Propulsion Laboratory.


Orchestrator Telemetry Processing Pipeline A multi-platform architecture is used to build and manage a telemetry-processing pipeline. NASA’s Jet Propulsion Laboratory, Pasadena, California

A constructive scheme has been de-vised to enable mapping of any quan-tum computation into a spintronic cir-cuit in which the computation isencoded in a basis that is, in principle,immune to quantum decoherence. Thescheme is implemented by an algo-rithm that utilizes multiple physicalspins to encode each logical bit in sucha way that collective errors affecting allthe physical spins do not disturb thelogical bit. The scheme is expected tobe of use to experimenters working onspintronic implementations of quan-tum logic.

Spintronic computing devices usequantum-mechanical spins (typically,electron spins) to encode logical bits. Bitsthus encoded (denoted qubits) are po-tentially susceptible to errors caused bynoise and decoherence. The traditionalmodel of quantum computation is basedpartly on the assumption that each qubitis implemented by use of a single two-state quantum system, such as an electronor other spin-1⁄2 particle. It can be surpris-ingly difficult to achieve certain gate op-erations — most notably, those of arbi-

trary one-qubit gates — in spintronichardware according to this model. How-ever, ironically, certain two-qubit interac-tions (in particular, spin-spin exchangeinteractions) can be achieved relativelyeasily in spintronic hardware.

Therefore, it would be fortunate if itwere possible to implement any one-qubit gate by use of a spin-spin exchangeinteraction. While such a direct repre-sentation is not possible, it is possible toachieve an arbitrary 1-qubit gate indi-rectly by means of a sequence of fourspin-spin exchange interactions, whichcould be implemented by use of four ex-change gates. Accordingly, the presentscheme provides for mapping any one-qubit gate in the logical basis into anequivalent sequence of at most fourspin-spin exchange interactions in thephysical (encoded) basis. The complex-ity of the mathematical derivation of thescheme from basic quantum principlesprecludes a description within this arti-cle; it must suffice to report that the der-ivation provides explicit constructionsfor finding the exchange couplings inthe physical basis needed to implement

any arbitrary one-qubit gate. These con-structions lead to spintronic encodingsof quantum logic that are more efficientthan those of a previously publishedscheme that utilizes a universal but fixedset of gates.

Given this mapping, universal quan-tum computation could be achieved inthe encoded basis if, in addition, it werealso possible to implement a controlled-NOT (CNOT) gate in the encodedbasis. It had been demonstrated in priorresearch that such encoded construc-tion of a CNOT gate is possible. Hence,in the present scheme, the mapping ofarbitrary one-qubit gates is augmentedwith the encoded construction of CNOTgates, making it theoretically possible toperform universal quantum computa-tion in the encoded basis.

This work was done by Colin Williamsand Farrokh Vatan of Caltech for NASA’s JetPropulsion Laboratory.


Scheme for Quantum Computing Immune to DecoherenceThe spintronic encodings of this scheme are more efficient than those of a prior scheme.NASA’s Jet Propulsion Laboratory, Pasadena, California


Books & Reports

Spin-Stabilized Microsatel-lites With Solar Concentra-tors

A document proposes the develop-ment of spin-stabilized microsatellitespowered by solar photovoltaic cells aidedby solar concentrators. Each such satellitewould have a cylindrical or other axisym-metric main body with solar cellsmounted in a circumferential beltlikearray on its exterior surface. The solarconcentrator would be a halo-like outrig-ger cylindrical Fresnel lens array thatwould be deployed from and would sur-round the main body, connected to themain body via spokes or similar structuralmembers.

The spacecraft would be oriented withits axis of symmetry perpendicular to theline of sight to the Sun and would be setinto rotation about this axis. In effect, thesolar cells and concentrator would be ori-ented and rotated in a “rotisserie” mode,making it possible to take advantage of theconcentration of solar light while prevent-ing localized overheating of the solar cells.In addition, the mechanical stabilizationinherently afforded by the rotation couldbe exploited as a means of passive attitudecontrol or, at least, of reducing the re-quirement for active attitude control.

This work was done by Paul Timmermanand Virgil Shields of Caltech for NASA’s JetPropulsion Laboratory. Further informationis contained in a TSP (see page 1). NPO-43055

Phase Calibration of An-tenna Arrays Aimed atSpacecraft

A document describes a method of cali-brating phase differences among groundantennas in an array so that the maximum-intensity direction of the far-field interfer-ence pattern of the array coincides with thedirection for aiming the antennas to enableradio communication with a distant space-craft. The method pertains to an array typi-cally comprising between two and four 34-m (or similar size) antennas. The antennasare first calibrated pair-wise to maximizethe uplink power received at a differentspacecraft that is close enough for commu-

nication via a single ground antenna. In the calibration procedure, the

phase of the signal transmitted by one ofthe antennas is ramped through a com-plete cycle, thereby causing the interfer-ence pattern to sweep over this closerspacecraft and guaranteeing that, atsome point during the sweep, this space-craft is illuminated at maximum intensity.The varying received uplink power ismeasured by a receiver in the closerspacecraft and the measurement data aretransmitted to a ground station to enabledetermination of the optimum phase ad-justment for the direction to the closerspacecraft. This adjustment is then trans-lated to the look direction of the distantspacecraft, which could not be reachedeffectively using only one antenna.

This work was done by Victor Vilnrotter,Dennis Lee, Leslie Paal, Ryan Mukai, andTimothy Cornish of Caltech for NASA’s JetPropulsion Laboratory. Further informationis contained in a TSP (see page 1). NPO-43647

Ring Bus Architecture for aSolid-State Recorder

A document concisely describes a ringbus architecture for a proposed solid-staterecorder (SSR) that would serve as bufferof data to be transmitted from a spacecraftto Earth. This architecture would affordfault tolerance needed for reliable opera-tion in an anticipated high-radiation envi-ronment in which traditional SSRs cannotoperate reliably. Features of the architec-ture include one or more controllerboards and multiple memory boards inter-connected in a ringlike topology. The in-terconnections would be high-speed seriallinks complying with the Institute of Elec-trical and Electronics Engineers (IEEE)standard 1393 (which pertains to a space-borne fiber-optic data bus).

Accordingly, each controller and mem-ory board would be equipped with anIEEE-1393-compliant ring-bus-interfaceunit. The ringlike topology and the multi-plicity of memory boards (and, optionally,of controller boards) would afford the re-dundancy needed for fault tolerance.Each board would be a fault-containmentregion. The IEEE 1393 links could be

routed so that the SSR would continue tofunction even in the event of multiple fail-ures. This architecture would also supportscalability over a wide range. In a fully re-dundant configuration, it could accom-modate between 1 and 125 memoryboards.

This work was done by W. John Walker,Edward Kopf, and Brian Cox of Caltech forNASA’s Jet Propulsion Laboratory. Furtherinformation is contained in a TSP (see page1). NPO-45132

Image Compression Algo-rithm Altered To ImproveStereo Ranging

A report discusses a modification of theICER image-data-compression algorithmto increase the accuracy of ranging compu-tations performed on compressed stereo-scopic image pairs captured by camerasaboard the Mars Exploration Rovers.(ICER and variants thereof were discussedin several prior NASA Tech Briefs articles.)Like many image compressors, ICER wasdesigned to minimize a mean-square-errormeasure of distortion in reconstructed im-ages as a function of the compressed datavolume. The present modification of ICERwas preceded by formulation of an alterna-tive error measure, an image-quality metricthat focuses on stereoscopic-ranging qual-ity and takes account of image-processingsteps in the stereoscopic-ranging process.This metric was used in empirical evalua-tion of bit planes of wavelet-transform sub-bands that are generated in ICER.

The present modification, which is achange in a bit-plane prioritization rule inICER, was adopted on the basis of this eval-uation. This modification changes theorder in which image data are encoded,such that when ICER is used for lossy com-pression, better stereoscopic-ranging re-sults are obtained as a function of the com-pressed data volume.

This work was done by Aaron Kiely of Cal-tech for NASA’s Jet Propulsion Laboratory.Further information is contained in a TSP(see page 1).

This software is available for commerciallicensing. Please contact Karina Edmonds ofthe California Institute of Technology at(626) 395-2322. Refer to NPO-44647.

National Aeronautics andSpace Administration

Documents

Technology Focus Electronics/Computers€¦ · cation for calculation of whirl flutter mode subcritical damping, a loads and safety monitor, ... board are four field-programmable