Technology Focus Electronics/Computers - NASA · 2013-04-10 · Surgical Implants 19 Mechanics 19 Stochastic Representation of Chaos Using Terminal Attractors 20 Two High-Temperature

Technology Focus

Electronics/Computers

Software

Materials

Mechanics

Machinery/Automation

Manufacturing & Prototyping

Bio-Medical

Physical Sciences

Information Sciences

Books and Reports

05-06 May 2006

https://ntrs.nasa.gov/search.jsp?R=20100025712 2020-05-25T02:02:19+00:00Z

NASA Tech Briefs, May 2006 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 and Mission Directorates listed below.

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

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

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

Jet Propulsion LaboratoryKen Wolfenbarger(818) [email protected]

Johnson Space CenterHelen Lane(713) [email protected]

Kennedy Space CenterJim Aliberti(321) [email protected]

Langley Research CenterRay P. Turcotte(757) [email protected]

John H. Glenn Research Center atLewis FieldRobert Lawrence(216) [email protected]

Marshall Space Flight CenterVernotto McMillan(256) [email protected]

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

Carl RaySmall Business Innovation Research Program (SBIR) &Small Business TechnologyTransfer Program (STTR)(202) [email protected]

Frank SchowengerdtInnovative Partnerships Program(Code TD)(202) [email protected]

John MankinsExploration Systems Researchand Technology Division(202) [email protected]

Terry HertzAeronautics and Space MissionDirectorate(202) [email protected]

Glen MucklowMission and Systems Management Division (SMD)(202) [email protected]

Granville PaulesMission and Systems Management Division (SMD)(202) [email protected]

Gene TrinhHuman Systems Research andTechnology Division (ESMD)(202) [email protected]

John RushSpace Communications Office(SOMD)(202) [email protected]

NASA Field Centers and Program Offices

NNAASSAA MMiissssiioonn DDiirreeccttoorraatteess

At NASA Headquarters there are four Mission Directorates underwhich there are seven major program offices that develop andoversee technology projects of potential interest to industry:

5 Technology Focus: Electronics5 T-Shaped Emitter Metal Structures for HBTs

6 Rigorous Estimation of SNR of a PSKCommunication Link

7 Advanced Ka-Band Transceiver With MonopulseTracking

8 EMI Filters for Low-Temperature Applications

9 Lightweight Electronic Camera for Research onClouds

9 Pilot Weather Advisor System

11 Electronics/Computers11 Waveguide Power-Amplifier Module for 80 to

150 GHz

11 Better Back Contacts for Solar Cells on FlexibleSubstrates

12 Tunable, Highly Stable Lasers for Coherent Lidar

13 Optical Profilometers Using Adaptive SignalProcessing

14 Improved Photon-Emission-Microscope System

15 Software15 Program Synthesizes UML Sequence Diagrams

15 Aspect-Oriented Subprogram Synthesizes UMLSequence Diagrams

15 Updated Computational Model of Cosmic RaysNear Earth

15 Software for Alignment of Segments of aTelescope Mirror

16 Simulation of Dropping of Cargo With Parachutes

16 DAVE-ML Utility Programs

16 Robust Control for the Mercury Laser Altimeter

17 Materials17 Thermally Stable Piezoelectric and Pyroelectric

Polymers

17 Combustion Synthesis of Ca3(PO4)2 Net-ShapeSurgical Implants

19 Mechanics19 Stochastic Representation of Chaos Using

Terminal Attractors

20 Two High-Temperature Foil Journal Bearings

21 Using Plates To Represent Fillets in Finite-ElementModeling

23 Manufacturing & Prototyping23 Repairing Chipped Silicide Coatings on Refractory

Metal Substrates

23 Simplified Fabrication of Helical Copper Antennas

25 Physical Sciences25 Graded-Index “Whispering-Gallery” Optical

Microresonators

25 Manufacture of Sparse-Spectrum OpticalMicroresonators

26 Exact Tuning of High-Q Optical Microresonatorsby Use of UV

29 Information Sciences29 Automation for “Direct-to” Clearances in Air-

Traffic Control

31 Books & Reports31 Improved Traps for Removing Gases From

Coolant Liquids

31 Lunar Constellation of Frozen Elliptical InclinedOrbits

05-06 May 2006


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: Electronics

T-Shaped Emitter Metal Structures for HBTsFabrication yields are increased.NASA’s Jet Propulsion Laboratory, Pasadena, California

Cross Sections of Base/Emitter Junctions containing self-aligned base metal structures, in the prior standard shape and the innovative T shape, are shownhere at three stages of fabrication.

[100]

[011]

[011]

[100]

[011]

[011]

[100]

[011]

[011]

[100]

[011]

[011]

EmitterEmitterMetalMetal

EmitterMetal

Emitter EpitaxEmitter EpitaxEmitter Epitaxial Material

Base Epitaxial Material


EmitterMetal

Emitter Epitaxial MaterialEmitter Epitaxial MaterialEmitter Epitaxial Material


PRIOR STANDARD SHAPE T SHAPE

After two wet etches of the emitter epitaxial material to reach the base epitaxial material and, in the prior standard shape, to undercut the emitter metal.

After lithography, deposition, and liftoff of base metal. In the prior standard shape, the base metal is kept thinner than the emitter epitaxial material to prevent shorting with the emitter metal.

Looking in the [011] Direction

After emitter lithography, deposition, and liftoff of emitter metal.

After two wet etches of the emitter epitaxy to reach the base epitaxy and, in the prior standard shape, to undercut the emitter metal.

After lithography, deposition, and liftoff of base metal.

Looking in the [011] Direction

After lithography, deposition, and liftoff of emitter metal.

Emitter epitaxial material must be

carefully etched to form a gap between this material and the

base metal.


EmitterMetal

Emitter Epitaxial MaterialEmitter Epitaxial MaterialEmitter Epitaxial Material


Base metal can bethicker than the emitter

epitaxial material.

BaseMetal

DepositedVertically

BaseMetal

BaseMetal

DepositedVertically

Undercutting ofemitter metal not

necessary here.

Overhang provides a gapbetween base

metal andemitter

epitaxialmaterial.

NPO-41034ABPI

8-4-04 es

Undercutting ofemitter metal not

necessary here.

Metal emitter structures in a class ofdevelopmental InP-based high-speedheterojunction bipolar transistors(HBTs) have been redesigned to have T-shaped cross sections. More precisely,

the modified cross sections can be char-acterized as having highly stylized Tshapes that are modified versions ofprior trapezoidal shapes (see figure). T-cross-section metal features have been

widely used in Schottky diodes and high-electron-mobility transistors, but not inHBTs. As explained below, the purposeserved by the present T cross-sectionalshapes is to increase fabrication yields be-

6 NASA Tech Briefs, May 2006

yond those achievable with the priorcross-sectional shapes.

At the beginning of the program to de-velop these HBTs, some of the HBTs werefabricated to contain self-aligned basemetal structures and some to containnon-self-aligned base metal structures.For the ones containing self-aligned basemetal structures, fabrication lots exhib-ited low yields and high degrees ofnonuniformity, which were attributableto inadequate definition of base/emitterjunctions. Yields were reduced by theneed to reject transistors that had leakyjunctions. One of the primary causes ofleakage at the junctions was short-circuit-ing of the base metal to emitter semicon-ductor epitaxial material that had notbeen sufficiently removed from the vicin-ity of the base metal during the wet-etchundercut procedure. The existence ofthis cause was observed in some casesfrom scanning electron microscopy andindirectly deduced from the observationthat the yields of HBTs containing non-

self-aligned base metal structures weremore than double the yields of HBTs con-taining self-aligned base metal structures.

The incidence of leakage is smaller inthe non-self-aligned case because thebase metal is spaced farther from theemitter at the outset. In contrast, in theself-aligned case, the base metal is sepa-rated from the emitter epitaxial materialby only the amount of the emitter un-dercut effected in the aforementionedetching. Self-aligned base metal struc-tures are preferred over non-self-alignedones because the resulting base resist-ances are smaller, leading to better tran-sistor performances.

The T-shaped cross section reducesthe likelihood of short-circuiting of basemetal to epitaxial emitter material,thereby helping to increase fabricationyield, in the following way: The over-hang portion of the T acts as an awning-like deposition mask. The base metal isdeposited predominantly unidirection-ally (vertically downward in the figure)

by evaporation, and deposition is pre-vented or reduced in the shadow areathat lies under the overhang and adja-cent to the emitter epitaxial material.

The T shape also offers other benefits:• Requirements for controlling undercut

etching are relaxed; as a consequence,emitter/base definition processes aresimplified.

• The relaxation of requirements makesit possible to use thicker base metal de-posits, thereby reducing the induc-tances and the electrical and thermalresistances of base metal structures.This work was done by King Man Fung,

Lorene Samoska, James Velebir, RichardMuller, Pierre Echternach, and Peter Siegel ofCaltech; Peter Smith of Cree, Inc.; SuzanneMartin of Wavestream Corp.; Roger Malik ofRJM Semiconductor; and Mark Rodwell,Miguel Urteaga, Vamsi Paidi, and ZackGriffith of UC Santa Barbara for NASA’s JetPropulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).NPO-41034

Rigorous Estimation of SNR of a PSK Communication LinkIt is not necessary to use a separate link to assess propagation conditions.John H. Glenn Research Center, Cleveland, Ohio

An improved method of estimatingthe signal-to-noise ratio (SNR) of aphase-shift keying (PSK) communicationlink is founded on a rigorous statisticalanalysis of the input to, and the outputfrom, the PSK demodulator in the re-ceiver. Many methods to estimate SNRratios of PSK communication links havebeen developed previously, and all ofthem are defective (that is, not rigorous)in that all of them are based on tacit andunwarranted assumptions made for thesake of analytical simplification. In addi-tion, some of the prior methods involve(1) the use of a separate receiver, de-noted the propagation receiver, to meas-ure a beacon signal distinct from the PSKcommunication signal and (2) extrapola-tion of the result of the measurement toan estimate the SNR of the PSK commu-nication channel. In contrast, the im-proved method is free of unwarrantedsimplifying assumptions and does not re-quire the use of a propagation receiver.

One basic concept shared by boththe improved method and the priormethods is that the effect of noise inthe communication link is not onlypresent in the input to the demodula-tor but is also convolved within the

output of the demodulator. The math-ematical analysis in this method isbased on (1) established theories ofstatistical analysis of flows of the signaland noise through a generic M-ary PSKdemodulator, and (2) techniques ofmaximum-likelihood estimation the-ory. In this analysis, one employs,rather than neglects, all the subtleties

of the statistics that characterize thestochastic nature of the phase-modu-lated signal to derive an estimationprocedure that utilizes the inherentphase characteristics of the input toand the output from the demodulator.

The complexity of the analysis pre-cludes a detailed description in this arti-cle. It must suffice to summarize as fol-

In-Phase Carrier Frequency�Reference Signal

Input�Signal + Noise

Phase Shift�+90

In-Phase Output Ec(t)

Es(t)

E(t)( )EsEc

tan-1

A BPSK Demodulator Is Modified to obtain the phase error, θE(t), in a composite signal.


Advanced Ka-Band Transceiver With Monopulse TrackingThis system would offer advantages over a conventional TWTA-based system.NASA’s Jet Propulsion Laboratory, Pasadena, California

A proposed Ka-band transmitting/receiving system would embody aunique combination of establishedand semi-proven design features. Al-though this system is intended prima-rily for telecommunication use aboarda spacecraft, its design could beadapted to terrestrial military andcommercial radar systems. Systems likethis one could be especially suitable asreplacements for prior systems inwhich traveling-wave-tube amplifiers(TWTAs) are used in the final trans-mitter stages.

The proposed system (see figure)would include a monopulse receivingfeedback loop and a mirror that couldbe moved by piezoelectric actuators inthe feedback loop to adjust the aim ofthe transmitted and received radiobeams. Unlike in a phased-array track-ing system, phase shifters (which can becomplex and expensive) would not beneeded in this monopulse tracking sys-tem. Moreover, the monopulse-trackingloop could be combined with other sub-systems used in established subreflectorand antenna designs.

Instead of a TWTA, the final trans-mitter power amplifier in the pro-posed system would be a quasi-opticalpower amplifier (QOPA) — a combi-nation of a planar array of 25 ampli-fiers and corresponding planar arraysof antenna elements, such that free-space power combining would takeplace at the output. The goal of thisQOPA would be to operate at a powerof 20 W and produce a minimum gain

This Ka-Band Transmitting/Receiving System would include a monopulse tracking loop in the receiverand a quasi-optical power amplifier in the transmitter.

QuartzWindow

To or From Main Reflectoror Subreflector

PiezoelectricActuators

Amplifier Array Active CoolingDevice

Drive Array

HardHorn

Input

MonopulseReceiving Array Movable

Convex Mirror

FSS

CROSS SECTION OF SYSTEM

ENLARGED BOTTOM VIEW OF QUASI-OPTICAL POWER AMPLIFIER

Drive ArrayAmplifier Array

Transmitting Array

NPO30559

5-6-02 bs

lows: The analysis begins with a descrip-tion of the signal and noise in the caseof binary PSK. This description serves asa foundation for a statistical connectionbetween Gaussian noise and the SNR.This connection leads to a probabilisticdescription that establishes a rigorousconnection between the SNR and themeasured phase error of the BPSK sig-nal entering the receiver demodulator.Then techniques of maximum-likeli-hood estimation theory are used to ob-tain analytical expressions for biasedand unbiased estimates of the SNR fromeasily measured phase errors.

The method requires the use of a

modified BPSK demodulator to obtainthe time-dependent phase error, θE(t)in a composite output signal. TheSNR-estimation procedure begins withthe acquisition of a sequence of sam-ples θE(ti) at k successive samplingtimes ti (i = 1 to k). Next, one calcu-lates a biased estimate, γ*, of the SNR(γ) by use of the equation

Finally, an unbiased estimate, γˆ, is ob-tained from a lookup table that contains

solution values for a nonlinear equationthat describes the relationship betweenγ* and γˆ. Although the method was de-rived for BPSK, it can be applied (withmodifications) to quaternary andhigher-order PSK.

This work was done by Robert M. Man-ning of Glenn Research Center. Furtherinformation is contained in a TSP (see page1).

Inquiries concerning rights for the commer-cial use of this invention should be addressedto NASA Glenn Research Center, CommercialTechnology Office, Attn: Steve Fedor, MailStop 4-8, 21000 Brookpark Road, Cleveland,Ohio 44135. Refer to LEW-17597-1.

γ κ θκ

∗

=

−

= ( )

∑ sin2

1

1

Ε tii


of 13 dB in the frequency range from31.8 to 32.3 GHz.

The amplifiers would be identical tocommercially available GaAs monolithicmicrowave integrated circuits (MMICs).Accompanying the QOPA, on the samecircuit board, there would be two ar-rays of antenna elements: a drive array(a planar array of identical input an-tenna elements) and a transmittingarray (a planar array of identical out-put antenna elements). The drive arraywould be fed via a hard horn, provid-ing uniform illumination to each arrayelement. By use of microstrip transmis-sion lines, all of equal length, the inputand output terminals of the MMIC am-plifiers would be connected to the cor-responding drive and transmitting an-tenna elements, respectively. This

QOPA design would offer the followingadvantages (among others):• The separation of the input and out-

put drive arrays helps eliminate theproblem, encountered in prior QOPAsystems, of oscillation and allows theuse of high-gain amplifiers.

• Unlike a TWTA, the MMIC amplifierswould not necessitate a high-voltagepower supply.

• The array of MMIC amplifiers could beactively cooled from its back side; un-like in prior QOPA arrays, it would notbe necessary to rely on edge cooling,which is less effective and thus limitsthe achievable power to a lower level.This is important for future inclusionof wide band-gap devices such as GaN.

• The failure of a single amplifier wouldnot be catastrophic: as long as the

other amplifiers continued to operate,the loss in performance would be rela-tively small. For maximum efficiency,the independent bias lines allow indi-vidual modules to be turned off as out-put power demands change.The system would include a fre-

quency-selective surface (essentially, aradio-frequency dichroic reflector) in-tended to reflect the transmitted beamwhile passing the received monopulsebeam. The FSS would provide between40 and 60 dB of isolation between thetransmitted and received beams.

This work was done by Abdur Khan, DanHoppe, Larry Epp, and Raul Perez of Caltechfor NASA’s Jet Propulsion Laboratory.Further information is contained in a TSP (seepage 1).NPO-30559

EMI Filters for Low-Temperature ApplicationsUnlike ferrite-core filters, these should work well under cryogenic conditions.NASA’s Jet Propulsion Laboratory, Pasadena, California

Filters that suppress electromagneticinterference (EMI) on signal cables con-nected to cryogenic electronic equip-ment can be made from cores consistingof high-permeability materials. Thebasic principle of operation of these fil-ters is the same as that of the ferrite-corecommon-mode EMI filters now com-monly used on cables that connect com-puters with peripheral equipment.

The ferrite-core filters are effective atroom temperature but not at low tem-peratures, because their relative perme-abilities decrease from ≈15,000 at roomtemperature to ≈20 at a temperature of4 K. In cases of cables that connect cryo-genic electronic equipment with room-temperature electronic equipment, ithas been common practice to place theferrite filters at the room-temperatureends of the cables. This makes it neces-sary for the filtered signals to traversethe cables; during such traversal, cross-talk with other cables can cause the fil-tered signals to become recontami-nated with EMI before they reach thecryogenic equipment. Hence, it wouldbe preferable to place the EMI filters atthe cryogenic ends of the cables. Thepresent development makes this a vi-able option.

An inductive EMI filters blocks EMIdue to its impedance to high frequencyEMI signals. Since the impedance is pro-portional to the permeability, a material

with high permeability forms the core ofsuch a filter. Several metallic alloys likeCryoperm 10 and VITROVAC are knownto have relative permeability exceeding14,000 at low temperature. However,their relative permeabilities decrease rap-idly at frequencies higher than a few hun-dred hertz due to eddy current, whichprevents the magnetic field from pene-trating the material. Because ferrite is an

insulator, eddy current is not present.Therefore it works at high frequencies.However, all known materials with highpermeabilities at low temperatures aremetallic. Therefore, for the purpose ofconstructing cores for low-temperatureEMI filters, it is desirable to prepare thehigh-permeability materials in the formof thin foils or fine powders to reduce theeffects of eddy currents. Preliminary

Relative Permeability was measured with a superconducting quantum interference device (SQUID)magnetometer at 4 K.

100 101 102 103 104 105

Frequency, Hz

Rel

ativ

e Pe

rmea

bili

ty

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7 x 104

NPO-30901 ABPI

01-06-04 LE


measurements and calculations haveshown that when foil thicknesses or parti-cle sizes are reduced to <25 µm, eddy cur-rents become unimportant.

We have performed low-temperaturetest (see figure) of a cobalt-based mag-netic material made by Honeywellcalled Meglas 2714A, which has very

high permeability at room temperatureand is available in form of tape-woundcores of various sizes. These cores arewound from 18-µm thick ribbons to re-duce eddy current for high-frequencyoperations. The relative permeability ishigher than 10,000 at frequencies up to100 kHz, the limit of capability of our

measurement. EMI filters made fromthis material should work at low tem-perature.

This work was done by Talso Chui andHung Quach of Caltech for NASA’s JetPropulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).NPO-30901

“Micro-CPI” (wherein “CPI” signifies“cloud-particle imager”) is the name of asmall, lightweight electronic camera thathas been proposed for use in researchon clouds. The Micro-CPI would be in-corporated into a small autonomous orremotely piloted airplane of a type thatis now used in meteorological researchand that is capable of remaining aloft fortimes long enough (typically about 30hours) to collect statistically significantsets of data.

According to a preliminary design, theMicro-CPI would have a mass <1.5 kg andwould consume less than 7 W of electricpower. It would acquire and digitizehigh-resolution (3-µm-pixel) images of

ice particles and water drops at a rate upto 1,000 particles (and/or drops) persecond. The Micro-CPI incorporates aparticle detection laser that triggers thecamera imaging laser, and also countsand sizes very small (<1-µm) aerosol par-ticles and cloud drops up to about 100µm in diameter. The Micro-CPI couldrecord data for an observation time ofmore than 30 hours and could operateautonomously.

Although a quantitative estimate ofthe cost of the Micro-CPI is not yetavailable, it has been projected that thecost would be low, relative to the costsof cameras of conventional design thatcould offer the same imaging capabili-

ties. This is fortunate because therecould be a potential need in the com-ing years to launch hundreds or eventhousands of small uninhabited aircraftcarrying cameras of Micro-CPI designas part of an effort to measure proper-ties of clouds on a global scale. Thereare also potential applications in themeasurement of drop-size distributionsin sprays, especially in the agriculturaland painting industries.

This work was done by Paul Lawson ofSPEC Inc. for Goddard Space Flight Cen-ter. Further information is contained in aTSP (see page 1).GSC-14950-1

Lightweight Electronic Camera for Research on CloudsThis camera would rapidly acquire image data on aerosol particles.Goddard Space Flight Center, Greenbelt, Maryland

Pilot Weather Advisor System Cockpit displays of weather affecting flight are updated every five minutes. John H. Glenn Research Center, Cleveland, Ohio

The Pilot Weather Advisor (PWA) sys-tem is an automated satellite radio-broadcasting system that providesnearly real-time weather data to pilots ofaircraft in flight anywhere in the conti-nental United States. The system was de-signed to enhance safety in two distinctways: First, the automated receipt of in-formation would relieve the pilot of thetime-consuming and distracting task ofobtaining weather information via voicecommunication with ground stations.Second, the presentation of the infor-mation would be centered around amap format, thereby making the spatialand temporal relationships in the sur-rounding weather situation much easierto understand. Starting in the early1990s, the PWA system was developed byViGYAN, Inc., under the NASA SBIRprogram. The system recently became

commercially viable and was sold toWSI, a leading provider of weather serv-ices in aviation. The system is now mar-keted under the brand name “WSI In-Flight.”

The PWA system includes a groundprocessor (see figure), wherein a com-puter running special-purpose softwareconverts, compresses, and schedules theweather data. The compressed data arethen transmitted through a ground sta-tion to a geosynchronous satellite, fromwhence they are broadcast to cover thecontinental United States. The signal isacquired by a light, low-drag antennamounted on a subscriber’s aircraft, andis then interpreted by an equally light-weight receiver. In the cockpit of eachInFlight equipped aircraft, the data areprocessed, by use of other special-pur-pose software and hardware, into an

easy-to-interpret graphical display. Thedisplay is presented on a portable orpanel-mounted unit. The data, whichinclude graphical meteorological avia-tion reports (METARs), terminal aero-drome forecasts (TAFs), and Next Gen-eration Weather Radar (NEXRAD)images, as well as other weather prod-ucts, are updated every five minutes.

Accessibility of the system to light gen-eral aviation was a design goal becausesuch airplanes are more susceptible tochanges in weather than are larger,higher-flying airplanes. The lightweight,low-drag nature of the PWA airbornecomponents and the relatively low cost ofacquiring and using the equipment makethe PWA system affordable for incorpora-tion into lower-cost single-engine air-planes, which constitute the largest seg-ment of the aviation market. Hence,


success of this design goal was achieved.In addition, the PWA system is also attrac-tive for use in higher-priced general-avia-tion airplanes because the weather infor-mation that it provides covers longerranges than do onboard weather radarand lightning detectors with which suchairplanes are often equipped.

This work was done by Glenn Lindamoodand Konstantinos (Gus) Martzaklis ofGlenn Research Center; Keith Hoffler,Damon Hill, Sudhir C. Mehrotra, and E.Richard White of ViGYAN, Inc.; Bruce D.Fisher of NASA Langley Research Center;Norman L. Crabill of Aero Space Consul-tants; and Allen D. Tucholski of Akima Corp.

Further information is contained in a TSP(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, Cleve-land, Ohio 44135. Refer to LEW-17702-1.

The Pilot Weather Advisor System is designed to enhance the weather-related safety of general aviation aircraft by providing frequent weather updates.

GroundStation

MonitoringNetwork

GroundProcessor

Source of WeatherData

LEW-17702-1ABPI

9-21-04 es

Satellite


Electronics/Computers

Waveguide Power-Amplifier Module for 80 to 150 GHzThe amplifier can now be connected to other equipment more easily.NASA’s Jet Propulsion Laboratory, Pasadena, California

A waveguide power-amplifier modulecapable of operating over the frequencyrange from 80 to 150 GHz has been con-structed. The module comprises a previ-ously reported power amplifier pack-aged in a waveguide housing that is

compatible with WR-8 waveguides. (WR-8 is a standard waveguide size for thenominal frequency range from 90 to 140GHz.) Because the amplifier in its un-packaged form was a single, fragile InPchip, it was necessary to use specialprobes to make electrical connectionsbetween the amplifier and test equip-ment in order to measure the powergain and other aspects of amplifier per-formance. In contrast, the waveguidepower-amplifier module is robust andcan be bolted to test equipment and toother electronic circuits with which the

amplifier must be connected for normaloperation.

The amplifier in its unpackaged formwas reported in “Power Amplifier With9 to 13 dB of Gain from 65 to 146 GHz”(NPO-20880), NASA Tech Briefs, Vol. 25,

No. 1 (January 2001), page 44. To reca-pitulate: the amplifier provides threestages of amplification, implemented bymeans of four InP high-electron-mobil-ity transistors in a grounded coplanarwaveguide circuit with lumped-elementinterstage and shunt capacitors. The cir-cuit also features a unique coplanarwaveguide power-combining structurein the output stage. The output radio-frequency power was measured to be 25to 40 mW from 106 to 140 GHz.

The figure shows selected aspects ofthe amplifier in its present packaged

form. In addition to packaging in a wave-guide housing, the amplifier was modi-fied to suppress low-frequency oscilla-tions, to which the amplifier waspreviously susceptible because it hadhigh gain at DC. The modifications con-

sisted mostly of special placement of by-pass capacitors and radio-frequencychokes within the package. The packagedamplifier was found to operate stably, andto produce a gain of at least 7 dB whileproducing output power of at least 10 mWat frequencies from 80 to 150 GHz.

This work was done by Lorene Samoska,Sander Weinreb, and Alejandro Peralta ofCaltech for NASA’s Jet Propulsion Labo-ratory. Further information is contained ina TSP (see page 1).NPO-30576

The Amplifier Module features a housing that is compatible with WR-8 waveguides. (Note: The largest dimension of the waveguide block is smaller thanthe size of a quarter.)

NPO-30576ABPI

4-28-04 CC

Power Amplifier

Power Amplifier Closeup of WR8 Module with PA chip

PowerAmpChip

Caps

Alumina Probe Transition

Input Waveguide Output Waveguide

Better Back Contacts for Solar Cells on Flexible SubstratesAdvantages are greater efficiency and tighter adhesion.John H. Glenn Research Center, Cleveland, Ohio

Improved low-resistance, semitranspar-ent back contacts, and a method of fabri-cating them, have been developed forsolar photovoltaic cells that are made

from thin films of I-III-VI2 semiconductormaterials on flexible, high-temperature-resistant polyimide substrates or super-strates. [The term “I-III-VI2” is an abbrevi-

ated indication that the semiconductormaterials are compounds of elements inperiods IB, IIIA, and VIA of the periodictable in the stoichiometric ratio of 1:1:2.


More specifically, these are compoundsof general empirical formula Cu(In, Ga,or Al)(Se or S)2.] The innovative aspectof the present development lies in the ex-tension, to polyimide substrates or super-strates, of a similar prior development ofimproved low-resistance, semitransparentback contacts for I-III-VI2 solar cells onglass substrates or superstrates. A cell in-corporating this innovation can be usedeither as a stand-alone photovoltaic de-vice or as part of a monolithic stack con-taining another photovoltaic device thatutilizes light of longer wavelengths.

The figure depicts a generic deviceincorporating these innovations in the

substrate configuration. The semi-transparent back contact that is themain focus of this article consists oftwo layers: The first layer deposited onthe substrate is a transparent, electri-cally conductive oxide (for example,ZnO, InSnO2, or SnO2). This layer actsmainly as a current collector. The sec-ond layer performs as contact inter-face layer capable of making goodelectrical contact with the solar-ab-sorber material; this layer is depositedover the conducive oxide to a thick-ness of <40 Å.

A solar-absorber layer — a p-doped I-III-VI2 semiconductor layer, possibly hav-

ing an n-doped surface sublayer — isgrown over the thin metal layer by co-evaporation or another suitable thin-film deposition technique. Next, a layerof CdS that serves as a window and/or aheterojunction partner with the I-III-VI2

semiconductor is deposited on the semi-conductor surface by a chemical-bath orother suitable technique that does notdamage the semiconductor surface. Fi-nally, another transparent, electricallyconductive oxide layer (typically ofInSnO2) that is mostly transparent to thesolar spectrum is deposited over theCdS.

The semitransparency of the back con-tact enables the cell to function whetherilluminated from the front or the backsurface. Also relative to the opaque backcontacts of prior such cells, the semi-transparent back contact enables this cellto operate at a lower temperature, and,consequently, with greater energy-con-version efficiency. During the course ofdevelopment, it was discovered that theinnovative semitransparent back contactincreases the adhesion between the poly-imide and the solar-absorber (I-III-VI2

semiconductor) layer — an importantadvantage, inasmuch as adhesion be-tween polyimide substrates and tradi-tional opaque molybdenum back con-tacts had been found to be problematic.

This work was done by Lawrence M.Woods and Rosine M. Ribelin of ITN En-ergy Systems, Inc., for Glenn ResearchCenter. Further information is containedin a TSP (see page 1).

Inquiries concerning rights for the commer-cial use of this invention should be addressedto NASA Glenn Research Center, CommercialTechnology Office, Attn: Steve Fedor, Mail Stop4–8, 21000 Brookpark Road, Cleveland, Ohio44135. Refer to LEW-17376.

The Semitransparent Back Contact in this device consists of the two layers between the polyimide andsolar-absorber layers.

TTrransparent Conductiansparent Conductivve Oxide OxideeTransparent Conductive Oxide

TTrransparent Conductiansparent Conductivve Oxide OxideeTransparent Conductive Oxide

SemiconductorCu (In, Ga, or Al) (Se or S)

2

CdSCdSCdS

PPolyimidolyimideePolyimide

LEW-17376

2-5-03 es

ThinMetalLayer

MetalContact Strips

Tunable, Highly Stable Lasers for Coherent LidarDesigns have been refined to satisfy competing requirements for stability and tenability.Marshall Space Flight Center, Alabama

Practical space-based coherent laserradar systems envisioned for globalwinds measurement must be very effi-cient and must contend with uniqueproblems associated with the largeplatform velocities that the instru-ments experience in orbit. To com-pensate for these large platform-in-duced Doppler shifts in space-basedapplications, agile-frequency offset-locking of two single-frequency

Doppler reference lasers was thor-oughly investigated. Such techniquesinvolve actively locking a frequency-agile master oscillator (MO) source toa comparatively static local oscillator(LO) laser, and effectively producingan offset between MO (the lidar slaveoscillator seed source, typically) andheterodyne signal receiver LO thatlowers the bandwidth of the receiverdata-collection system and permits use

of very high-quantum-efficiency, rea-sonably-low-bandwidth heterodynephotoreceiver detectors and circuits.Similar techniques are being appliedin atmospheric CO2 differential-ab-sorption lidar work, where MO sourcesneed to be actively offset-locked toCO2 reference cells for continuous ab-solute-calibration purposes. ActiveMO/LO offset-locking is also highlyapplicable to lidar problems involving


very high target velocities with respectto a static or moving lidar platform.

Efforts to date have focused on devel-opment of Tm,Ho:YLF lasers operatingnear 2.05 µm, which have much poten-

tial for both efficient space-based windlidar systems and CO2 DIAL measure-ments. The locking techniques are read-ily applicable to any number of otherwavelengths and laser formats.

Recent work on MO/LO offset lock-ing has focused on increasing the off-set locking range, improving thegraded-InGaAs photoreceiver per-formance, and advancing the maturityof the offset locking electronics. Fig-ure 1 provides a schematic diagram ofthe offset-locking system. Improve-ments to the design of the tunable MOlaser resonator resulted in continuous,fast, SLM piezo-tuning range of 25GHz—more than double the range ofthe initial prototype. Major progresswas also made in the performance ofvery wideband, 2-µm-sensitive hetero-dyne photoreceivers. The fiber-cou-pled, hybridized-preamplifier photo-receivers developed most recentlyexhibited heterodyne detection band-width of 4 GHz to the 3 dB point, andadequate bandwidth to demonstraterobust offset-locking to 10 GHz. Thisadvanced component is now offered asa standard product. Remarkably, thesevery small (30-µm active area diame-ter), thin, fast PIN (positive/intrin-sic/negative) devices exhibit ≈70 per-cent quantum efficiency to 4 GHz,adequate for direct use as a hetero-dyne receiver in many applications.With some degradation in locking ro-bustness, MO/LO offsets of as much as13.2 GHz were obtained. Settlingtimes were typically 15 ms for 1 GHzsteps, and locking stability was meas-ured at 30 kHz over 20-s intervals. Thesystem incorporated a LabVIEW-basedGUI and robust auto-locking servo,greatly enhancing its usefulness in off-set locking experiments and use as awideband photoreceiver calibration in-strument. Figure 2 shows a typicallocking stability result.

This work was done by Sammy W. Hender-son, Charley P. Hale, and David M. E’Epag-nier of Coherent Technologies, Inc. for Mar-shall Space Flight Center. For furtherinformation, contact Kent Blanchard atctilidar.com or (303) 379-3264.MFS-31434

Figure 1. Tm,Ho:YLF MO/LO Offset Locking System incorporates the described improvements.

Figure 2. Heterodyne Beat Note Stability is depicted when Tm,Ho:YLF MO and LO lasers are activelyoffset-locked 7.5 GHz apart. Locking stability is ≈30 kHz over many seconds. [SA = signal analyzer;RBW = resolution bandwidth; VBW = video bandwidth; SWP = duration of frequency sweep; Att = at-tenuation; A\g = antenna gain.]

Wideband 2-µmDetector

LocalOscillator

WidebandMaster

Oscillator

DetectorAmplifier

PhaseLock-Loop

ProgrammableReferenceOscillator

MO PZT DriveVoltage

ComputerControl

MFS 31434 Fig. 1ABPI

2-12-04 bs

Optical Profilometers Using Adaptive Signal ProcessingSizes would be reduced, leading to development of hand-held profilometers.John F. Kennedy Space Center, Florida

A method of adaptive signal processinghas been proposed as the basis of a newgeneration of interferometric optical pro-filometers for measuring surfaces. Manycurrent optical surface-measuring pro-

filometers utilize white-light-interferome-try and, because of optical and mechanicalcomponents essential to their operation,are comparable in size to desktop comput-ers. In contrast, the proposed profilome-

ters would be portable, hand-held units.Sizes could be thus reduced because theadaptive-signal-processing method wouldmake it possible to substitute lower-powercoherent light sources (e.g., laser diodes)


for white light sources and would elimi-nate the need for most of the optical com-ponents of current white-light profilome-ters. Furthermore, whereas the heightscanning ranges of current surface-meas-uring profilometers are of the order ofmillimeters, the adaptive-signal-processingmethod would make it possible to attainscanning ranges of the order of decime-ters in the proposed profilometers.

The figure depicts the optical layout ofa simple Michelson interferometer con-figured for use as a profilometer, accord-ing to the proposal, for measuring the de-viation from flatness of a nominally flatsurface that contains a pit. The pit can be

characterized as comprising multiplefacets at different depth, each producinga coherence function having signal inten-sity proportional to its size. As a result,the output of the photodetector in thisinterferometer would include a multi-tude of overlapping coherence functionsthat cannot be easily discriminated.

A complete overlapping-coherence-function profile of the surface areawithin the interrogating light beamwould be collected by recording and pro-cessing the photodetector output as afunction of height while scanning the ad-justable mirror through the interrogationdepth. The adjustable mirror could be

mounted on a piezoelectric actuator forrapid scanning in height. Optionally, adigitally controlled micromirror devicecould also be used to scan the light beamlaterally (horizontally in the figure)across the surface. Modern digital signal-processing hardware would be used torapidly acquire and process the photode-tector output and the overlapping coher-ence signals contained therein accordingto the adaptive method described below.

In this method, a Fourier transform of asynthetic intensity-versus-depth signal gen-erated from a mathematical model of thesurface to be measured would be sub-tracted from the Fourier transform of theintensity-versus-depth signal obtained bythe interferometer scan of the surface to bemeasured. The result of the subtractionwould be an error signal. The coefficientsof the model, representing the sizes anddepths of facets in the pit, would be ad-justed to minimize the error signal. To ob-tain the coherence function needed for themodel, it would be necessary to perform acalibration measurement, prior to opera-tion, in which a reference mirror known tobe optically smooth and flat would be sub-stituted for the surface to be measured.

This work was done by Gregory A. Hall,Robert Youngquist, and Wasfy Mikhael ofKennedy Space Center. Further informa-tion is contained in a TSP (see page 1).KSC-12647

A Simple Michelson Interferometer could constitute the optical subsystem of a profilometer, providedthat the adjustable mirror were scanned and the output of the photodetector processed as describedin the text.

Laser Diode

Photodetector

Beam Splitter

AdjustableMirror

PiezoelectricActuatorSurface To Be Measured

(Flat Except for a Pit)

KSC-12647ABPI

12-20-04 es

Improved Photon-Emission-Microscope System An advanced photon-emission microscope is combined with the latest image-processing software.NASA’s Jet Propulsion Laboratory, Pasadena, California

An improved photon-emission-micro-scope (PEM) instrumentation systemhas been developed for use in diagnos-ing failure conditions in semiconductordevices, including complex integratedcircuits. This system is designed prima-rily to image areas that emit photons, atwavelengths from 400 to 1,100 nm, as-sociated with device failures caused byleakage of electric current throughSiO2 and other dielectric materials usedin multilayer semiconductor structures.In addition, the system is sensitiveenough to image areas that emit pho-tons during normal operation. This sys-tem supplants a prior PEM systembased on a photon-intensified, gated,charge-coupled-device (CCD) camera.

This system includes an optical mi-croscope fitted with a low-light-level im-aging subsystem based on a state-of-the-

art high-resolution (1,024 × 1,024 pixel),cooled, back-illumination CCD camerain a light-proof enclosure. Anothermajor subsystem is a computer runningthe latest in Windows-based image-pro-cessing software, which can facilitategeneration of test reports and researchpapers by putting out image files inpopular formats, including taggedimage file (TIF), bit map (BMP), andJoint Photographic Experts Group(JPG) formats.

A device under test (DUT) is placedon a translation stage under the mi-croscope. This stage enables move-ment of the DUT along both axes per-pendicular to the optical axis, as wellas along the optical axis for focusing.Any of several microscope objectivelenses affording different magnifica-tions (5×, 20×, 50×, and 100× with

extra long working distance) can beselected. The exposure time is pro-grammable between 5 millisecondsand 2 hours. Provisions for setups ofexternal equipment, including thepower supply for the DUT and digitalmultimeters, can be incorporated intocustom software.

In operation, the system integrates thephotons emitted from the DUT, and theresulting bright spots (showing the loca-tions of substantial emission of photons)are displayed superimposed on an imageof the DUT that was acquired previouslyunder visible light. Failure-analysis engi-neers can use the information in this dis-play to locate failure sites on the DUT.

This work was done by Duc Vu of Caltechfor NASA’s Jet Propulsion Laboratory.Further information is contained in a TSP(see page 1). NPO-42121


Software

Program Synthesizes UMLSequence Diagrams

A computer program called “Ration-al Sequence” generates UniversalModeling Language (UML) sequencediagrams of a target Java program run-ning on a Java virtual machine (JVM).Rational Sequence thereby performs areverse engineering function that aidsin the design documentation of thetarget Java program. Whereas previ-ously, the construction of sequence di-agrams was a tedious manual process,Rational Sequence generates UML se-quence diagrams automatically fromthe running Java code. Moreover,there is no need to insert instrumenta-tion code into the target Java program.Rational Sequence employs the JavaNative Interface application program-ming interface to create a softwareprofiler that plugs into the JVM. Oncethe user starts the target Java program,Rational Sequence acts as a nonintru-sive observer, generating UML dia-grams representing the observed activ-ity. Every method call, objectinstantiation, or thread event of thetarget Java program is tracked by theprofiler. Once the Java program hasended, the profiler generates a UMLmodel that contains packages, classes,and all method calls observed duringthe execution of the target program.The user can control the way the UMLmodel is generated by specifying pack-ages and/or classes to be included inthe diagrams.

This program was written by Matthew R.Barry and Richard N. Osborne of UnitedSpace Alliance for Johnson Space Center.For further information, contact the JohnsonTechnology Transfer Office at (281) 483-3809.MSC-23656

Aspect-Oriented Subprogram SynthesizesUML Sequence Diagrams

The Rational Sequence computerprogram described in the immediatelypreceding article includes a subpro-gram that utilizes the capability for as-pect-oriented programming when thatcapability is present. This subprogramis denoted the Rational Sequence (As-

pectJ) component because it uses As-pectJ, which is an extension of the Javaprogramming language that intro-duces aspect-oriented programmingtechniques into the language. The Ra-tional Sequence (AspectJ) componentis compiled with a target Java applica-tion program on an AspectJ compiler.The user then starts the Java applica-tion program. Thereafter, the RationalSequence (AspectJ) component pub-lishes every visible method call to aUniversal Modeling Language (UML)sequence diagram. When the Java ap-plication program ends, a sequencerproceeds to generate a UML modelthat contains packages, classes, and allmethod calls that occurred during theexecution of the program. The usercan control the way the UML model isgenerated by specifying, via the aspectsource code, packages and/or classesto be included in the diagrams. Likethe rest of Rational Sequence, the As-pectJ component complies with theUML specification.

This program was written by Matthew R.Barry and Richard N. Osborne of UnitedSpace Alliance for Johnson Space Center.For further information, contact the JohnsonTechnology Transfer Office at (281) 483-3809.MSC-23655

Updated ComputationalModel of Cosmic Rays Near Earth

An updated computational model ofthe galactic-cosmic-ray (GCR) environ-ment in the vicinity of the Earth,Earth’s Moon, and Mars has been de-veloped, and updated software hasbeen developed to implement the up-dated model. The GCR model andsoftware in their original forms, devel-oped during the early 1990s, werebased on balloon and satellite datafrom 1954 to 1992. This model ac-counts for solar modulation of the cos-mic-ray contribution for each elementfrom hydrogen through iron by com-putationally propagating the local in-terplanetary spectrum of each elementthrough the heliosphere. The propa-gation is effected by solving theFokker-Planck diffusion, convection,energy-loss boundary-value problem.

Since August 1997, the AdvancedComposition Explorer NASA satellitehas provided new data on GCR energyspectra. These new data were used toupdate the original model and greatlyimprove the accuracy of prediction ofinterplanetary GCR. The updated soft-ware was also simplified significantly,relative to the original software. Theupdated model and software are ex-pected to provide highly accurateGCR-environment data for use by in-terplanetary-mission planners in plan-ning for protecting astronauts againstradiation and ensuring radiation hard-ness of electronic equipment.

This program was written by Patrick M.O’Neill of Johnson Space Center. For fur-ther information, contact the Johnson Tech-nology Transfer Office at (281) 483-3809.MSC-23891

Software for Alignment ofSegments of a TelescopeMirror

The Segment Alignment Mainten-ance System (SAMS) software is de-signed to maintain the overall focusand figure of the large segmented pri-mary mirror of the Hobby-Eberly Tele-scope. This software reads measure-ments made by sensors attached to thesegments of the primary mirror andfrom these measurements computesoptimal control values to send to actu-ators that move the mirror segments.The software also acts as a logger forthe collected data, a server fromwhich the hardware of the controlcomputer can acquire control infor-mation and other computers can col-lect data, and a monitoring and diag-nostic system. The software provides agraphical user interface throughwhich human operators can exert con-trol. The software supports fourmodes of operation:• Operate — The server acquires the sen-

sory data and processes them intocommands for the actuators.

• Calibrate — Calibration tests are per-formed on the edge sensors and the re-lationships between actuator com-mands and sensor responses arequantified.

• Standby — The server is initialized instandby mode, from which it can


make the transition to any of theother three modes.

• Diagnostic — This mode provides ac-cess to all sensory data in real time andis intended for use in diagnosis of sen-sor anomalies.This program was written by Drew P. Hall,

Richard T. Howard, William C. Ly, John M.Rakoczy, and John M. Weir of MarshallSpace Flight Center. For further informa-tion, contact Jim Dowdy, CommercializationProject Lead, at [email protected]

Simulation of Dropping of Cargo With Parachutes

Decelerator System Simulation(DSS) is a computer program for pre-dicting and analyzing the dynamics of aload of cargo dropped with parachutesfrom an aircraft. A DSS simulation runsfrom the first motion in the aircraftuntil the payload reaches the ground.Intended for use in support of airdroptests for the X-38 program, DSS was de-veloped by modifying and augmentingan older program, denoted UD233A,used for simulating the dynamics of aspace-shuttle solid rocket boosterfalling with a parachute. The main ef-fort in converting UD233A into DSS in-volved development of computationalmodels for simulating the inflation ofone or more parachute(s), the dynam-ics of the payload and the slings con-necting the parachute(s) with the pay-load, and the extraction of the payloadand parachutes from the aircraft.

This program was written by Peter Cuth-bert of Johnson Space Center. For further

information, contact the Johnson TechnologyTransfer Office at (281) 483-3809.MSC-2363

DAVE-ML Utility ProgramsDAVEtools is a set of Java archives

(*.jar files) that embodies tools for ma-nipulating flight-dynamics models thathave been encoded in dynamic aero-space vehicle exchange markup lan-guage (DAVE-ML). [DAVE-ML is an ap-plication program, written inExtensible Markup Language (XML),for encoding complete computationalmodels of the dynamics of aircraft andspacecraft. The goal in the continuingdevelopment of DAVE-ML is to expe-dite the exchange and validation of dy-namical models, via the Internet, in amanner that is consistent and is inde-pendent of computational-simulationfacilities, computing languages, andsimulation software.] At present, DAVE-tools includes two tools:• dave (a basic DAVE-ML parser), which

generates a Java-based version of amodel encoded in DAVE-ML and

• dave2sl, which builds on dave to createSimulink® representations of modelsencoded in DAVE-ML.The manipulations that can be per-

formed at the present early stage of de-velopment are rather limited. More im-portantly, DAVEtools serves as an exampleof how to write an import software toolfor a DAVE-ML file.

This program was written by Bruce Jacksonof Langley Research Center. For further in-formation, access http://daveml.nasa.gov.LAR-16879-1

Robust Control for the Mercury Laser Altimeter

Mercury Laser Altimeter Science Al-gorithms is a software system for con-trolling the laser altimeter aboard theMessenger spacecraft, which is toenter into orbit about Mercury in2011. The software will control the al-timeter by dynamically modifyinghardware inputs for gain, threshold,channel-disable flags, range-windowstart location, and range-windowwidth, by using ranging informationprovided by the spacecraft and noisecounts from instrument hardware. Inaddition, because of severe bandwidthrestrictions, the software also selectsreturns for downlink. To reduce mis-sion risk, the software incorporatesthree different modes of operation.The three modes are denoted as fixed,range-driven, and closed-loop (oradaptive). The fixed mode providesfixed hardware inputs for all but thethreshold. The range-driven mode re-ceives and utilizes ranging informa-tion from the spacecraft regarding itsslant range to the planet or asteroid.The adaptive mode is capable of im-proving upon the ranging informationprovided by the spacecraft by use of aclosed-loop range-estimation algo-rithm. The software is sufficiently ro-bust that it could be used on othermissions, and in fact, this has alreadybeen proposed.

This program was written by Jacob S.Rosenberg of Goddard Space Flight Cen-ter. Further information is contained in aTSP (see page 1).GSC-14876-1


Materials

Thermally Stable Piezoelectric and Pyroelectric PolymersNeither mechanical nor solvent treatment is necessary for orientation of polymer molecules.Langley Research Center, Hampton, Virginia

A class of thermally stable piezoelectricand pyroelectric polymers, and an im-proved method of making them, havebeen invented. These polymers can beused as substrates for a wide variety ofelectromechanical transducers, sensors,and actuators.

In order to enable a material to pro-duce an electrostatic potential in responseto mechanical excitation (piezoelectricity)or in response to thermal excitation (pyro-electricity), the material must be electri-cally polarized; that is, its molecules mustbe at least partially aligned in a preferredelectric-dipole orientation. The preferredorientation or polarization occurs natu-rally in quartz and some crystalline materi-als, and can be induced in some ceramicsand polymers by application of strongelectric or mechanical fields.

Prior to this invention, poly(vinylidenefluoride) [PVF2] was the only commer-cially available piezoelectric polymer. Inorder to be able to exploit the piezoelec-tricity of PVF2, it was necessary to orientits molecules by mechanical drawing ofsheets or by dissolving the PVF2 in a sol-vent and then subjecting it to an electricfield while causing the solvent to evapo-rate. In contrast, the polymers of the pres-ent invention are rendered piezoelectricand/or pyroelectric by means of an ori-entation process that does not involve ei-ther a solvent or a mechanical treatment.

The polymers suitable for this inven-tion include polyarylates, polyquinoxa-lines, polyphenylene ethers, polycarbon-ates, polyphenylene sulfides, polysulfones,polyaryletherketones, polyimides, pol-yarylene ethers, polybenzimidazoles,

polyazomethines and possibly other ther-mally stable polymers. These polymershave softening temperatures greater thanabout 100 °C, and, once polarized, theyretain their polarizations (and, hence,their piezoelectric and pyroelectric prop-erties) at temperatures up to their soften-ing temperatures.

A polymeric substrate to be renderedpiezoelectric and/or pyroelectric ac-cording to the invention is prepared bydepositing metal electrodes on oppositefaces. The electrode metal can be gold,silver, or any other suitable low-electri-cal-resistivity metal that is not readily ox-idized at the temperature to be used inthe treatment described next. The metalelectrodes are connected to a source ofhigh voltage, and the electrode/sub-strate/electrode sandwich is immersedin a heating bath containing silicone oilor other suitable low-permittivity dielec-tric liquid (see figure). In the bath, theelectrode/substrate/electrode sandwichis heated to the softening temperatureof the polymer to increase the mobilityof the polymer molecules. A voltage is

applied to the electrodes to generate anelectric field (typically between 50 and200 MV/m) large enough to orient thepolymer molecules but not so large as tocause dielectric breakdown of the poly-mer substrate. The voltage can be low-frequency AC or DC. The voltage ismaintained for an interval of time suffi-cient to obtain the desired degree of po-larization. The electrode/substrate/electrode sandwich is then cooled whilemaintaining the voltage. Once the tem-perature is well below the softening tem-perature, the voltage is turned off, andthe induced orientation remains frozeninto the polymer.

This work was done by Joycelyn O. Simp-son and Terry L. St. Clair of Langley Re-search Center. Further information is con-tained in a TSP (see page 1).

This invention has been patented by NASA(U.S. Patent Nos. 5,891,581, 5,909,905,and 6,379,809). Inquiries concerningnonexclusive or exclusive license for its com-mercial development should be addressed tothe Patent Counsel, Langley Research Center,at (757) 864-3521. Refer to LAR-15279.

A Polymer Substrate Is Heated to its softening temperature in a low-permittivity dielectric liquid whilea high voltage is applied to metal electrodes on opposite faces to induce electric polarization. When theelectrode/substrate/electrode sandwich is cooled, the polarization remains frozen into the substrate.

Source ofHigh Voltage

Low-Permittivity Liquid

Heating Bath

Dielectric Substrate

Metal Electrodes

LAR15279

10-2-02 bs

Combustion Synthesis of Ca3(PO4)2 Net-Shape Surgical ImplantsMore-biocompatible materials are produced in fewer processing steps.John H. Glenn Research Center, Cleveland, Ohio

Self-propagating high-temperaturecombustion synthesis (SHS) is the basis ofa method of making components ofporous tricalcium phosphate [Ca3(PO4)2]and related compounds in net sizes and

shapes for use as surgical implants thatare compatible with bone. Ca3(PO4)2-based materials are among those pre-ferred for use in orthopedic, restorative,and reconstructive surgery. As explained

below, the SHS method offers advantagesover prior methods of manufacturingCa3(PO4)2-based surgical implants.

Ca3(PO4)2 occurs in at least two crys-talline forms: a monoclinic form de-


noted the α phase and an orthorhombicform denoted the β phase. The β phaseis the preferred form for bone replace-ments because it can be resorbed by thebody, facilitating bone remodeling. Atan appropriate porosity, β Ca3(PO4)2 re-sembles natural bone and serves as ascaffold into which osteogenic cells canmigrate. Thus, bone becomes directly at-tached to and grows into a β Ca3(PO4)2

implant. The body generally resorbs βCa3(PO4)2 within about two years, re-placing it with natural bone.

Prior methods of making surgical im-plants of Ca3(PO4)2 and related materialshave not yet been perfected. The priormethods involve, variously, synthesis ofCa3(PO4)2-containing bioceramics fromaqueous solutions, sintering, sol-gel pro-cessing, and/or casting of polymericfoams mixed with slurries of Ca3(PO4)2-containing bioceramic particles. All ofthese prior methods are energy- andlabor-intensive, and each requires severaltime-consuming steps. Of particular in-terest is the sintering method, which in-cludes molding by compacting a powderinto a die having the size and shape ofthe desired part, then heating to temper-ature just high enough that the powderparticles undergo solid-state bonding toeach other but do not melt. The greatdisadvantage of this method is that at thehigh sintering temperature, β Ca3(PO4)2

becomes converted to α Ca3(PO4)2,which is not preferable as a bone replace-ment material.

Relative to any of the prior methods,the present SHS-based method requires

fewer steps, takes less time, enables bet-ter tailoring of porosity, and yields agreater ratio between the desired βphase and the undesired α phase. Pro-cessing according to this method beginswith preparation of a mixture of CaOand P2O5 powders and possibly other in-gredients described below. Processingmust be done in a protective dry, nonre-active atmosphere (e.g., argon) becauseP2O5 is hygroscopic and strongly reac-tive. The mixture is compacted into acombustible or noncombustible die hav-ing the size and shape of the desiredpart. If the die is noncombustible, thepreform of compacted powder is thenremoved from the die carefully so as notto deform or break it.

Next, the compacted powder preformis heated to initiate the main combus-tion synthesis reaction,

3CaO + P2O5 → Ca3(PO4)2,which is accompanied by some other re-actions that yield a variety of calcium-,oxygen-, and phosphorus-containingbyproducts. The main combustion syn-thesis reaction is exothermic and self-sustaining: once it has been initiated, awavefront comprising a reaction zonemoves through the mixture. In the reac-tion zone and its vicinity, the reactanthaving the lowest melting temperaturemomentarily spreads by means of capil-lary action, leading to a large dispersionof the reaction products.

In general, Ca3(PO4)2 is formed if themixture contains between about 60 and90 mole percent of CaO and betweenabout 10 and 40 mole percent of P2O5.

The proportions of these ingredients canbe adjusted to tailor the proportions ofthe α and β phases of Ca3(PO4)2 in thecombustion-synthesis product. Option-ally, the reaction mixture can includeone or more dopants and/or a gasifyingagent. Also optionally, the combustion-synthesis product can be subjected to afurther process of controlled heatingand cooling to increase the ratio be-tween the β and α phases of Ca3(PO4)2.

Process parameters can also be variedto tailor the degree of porosity, the pro-portion of interconnected pores, andthe shapes of the pores in the finishedproduct, and to impart functionallygraded porosity as might be required fora particular application. Examples ofsuch parameters include, but are notlimited to, the pressure used to compactthe reactant mixture, the amount of thegasifying agent, the proportions of CaOand P2O5 in the reactant mixture, thesizes of the reactant powder particles,and the pressure of the atmosphere inwhich the reaction takes place.

This work was done by Reed A. Ayers,Martin Castillo, Guglielmo Gottoli, John J.Moore, and Steven J. Simske of the ColoradoSchool of Mines for Glenn Research Cen-ter. Further information is contained in aTSP (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-17951-1.


Mechanics

Stochastic Representation of Chaos Using Terminal AttractorsFictitious control forces stabilize what would otherwise be unstable computed trajectories.NASA’s Jet Propulsion Laboratory, Pasadena, California

A nonlinear version of the Liouvilleequation based on terminal attractors ispart of a mathematical formalism for de-scribing postinstability motions of dy-namical systems characterized by expo-nential divergences of trajectoriesleading to chaos (including turbulenceas a form of chaos). The formalism canbe applied to both conservative systems(e.g., multibody systems in celestial me-chanics) and dissipative systems (e.g.,viscous fluids).

This formalism at an earlier stage ofdevelopment was reported in “Extensionof Liouville Formalism to PostinstabilityDynamics” (NPO-30393), NASA TechBriefs, Vol. 27, No. 9 (September 2003),page 56. To recapitulate: The problem isto predict the postinstability motions ofa dynamic system governed by a systemof nonlinear equations and subject toinitial conditions. The formalism of non-linear dynamics does not afford meansto discriminate between stable and un-stable motions: an additional stabilityanalysis is necessary for such discrimina-tion. However, an additional stabilityanalysis does not suggest any modifica-tions of a mathematical model thatwould enable the model to describepostinstability motions efficiently. Themost important type of instability thatnecessitates a postinstability descriptionis associated with positive Lyapunov ex-ponents. Such an instability leads to ex-ponential growth of small errors in ini-tial conditions or, equivalently,exponential divergence of neighboringtrajectories.

The development of the present for-malism was undertaken in an effort toremove positive Lyapunov exponents.The means chosen to accomplish this iscoupling of the governing dynamicalequations with the corresponding Liou-ville equation that describes the evolu-tion of the flow of error probability. Theunderlying idea is to suppress the diver-gences of different trajectories that cor-respond to different initial conditions,without affecting a target trajectory,which is one that starts with prescribedinitial conditions.

This formalism applies to a system ofn first-order ordinary differential equa-tions in n unknown dynamical (state)variables:

where i is an integer between 1 and n, xi

is one of the unknown dynamical vari-ables, the overdot signifies differentia-tion with respect to time, x is the vectorof all the dynamical variables (x1,x2,...xn),and t is time. The prescribed initial con-ditions are given by

The corresponding Liouville equationfor the evolution of the probability dis-tribution, P(x1,x2,...xn,t ), of errors in theinitial conditions is

where f is the vector of all the forcingfunctions ( f1,f2,...fn). It is assumed thatthis probability distribution peaks atzero error (representing the prescribedinitial conditions).

Fictitious control (stabilizing) forces[F = (F1,F2,...Fn)] are added to the systemof differential equations. The form ofthese forces differs from that of the ficti-tious stabilizing force described in thecited previous article: Whereas previ-ously, the fictitious stabilizing force wasproportional to the gradient of the prob-ability density in the space of the dynam-

ical variables, the present fictitious con-trol forces are functions of the differ-ences between expected and actual val-ues of the dynamical variables xi:

where γ i is a positive constant and xi isthe expected value of xi , as given by

The control forces have two impor-tant properties:• Because they vanish as x → <x>, they

do not affect the target trajectory; and• Because the magnitudes of their deriv-

atives approach as x → <x>, theymake the target trajectory infinitelystable. In other words, the target tra-jectory becomes a terminal attractor.The resulting modified system of dy-

namical equations is

The corresponding modified Liouvilleequation is

wherein the terminal attractors act asnonlinear sinks of probability.

At the limit as xi → <xi >, one can neglectthe real force fi as being much smallerthan the control force Fi, making it possi-ble to decompose the Liouville equation

∂∂

= −∂

∂+ −( )

=∑P

t xP f x x

ii

n

i i i i1

13γ

,

&x f x xi i i i i= + −( )γ13

x X PdX dXi i n=−∞

∞

∫ 1...

F x xi i i i≡ −( )γ13

∂∂

+ ∇ =Pt

Pi( )f 0

x xi i= 0,

&x f t ti i= [ ( ), ],x

The Probability Distribution of Error about a target trajectory becomes flattened in uncontrolled evo-lution as close neighboring trajectories diverge. However, when evolution is controlled by fictitiousstabilizing forces that create a terminal attractor in probability space, the distribution of error be-comes more sharply peaked about the target trajectory.

P

x

t

P

x

t

Uncontrolled Evolution Controlled Evolution

NPO-41519ABPI

4-5-05 es


into n independent equations and to ex-press P as a product of n probabilities Pi:

By use of these equations, it can beshown that the control forces create apowerful terminal attractor in probabil-ity space that corresponds to occur-

rence of the target trajectory with prob-ability one (see figure). In configura-tion space (space in the sense in which“space” is understood in casual conver-sation), the effect of the control forcesis to suppress exponential divergenceof close neighboring trajectories with-out affecting the target trajectory. As aresult, the post-instability motion is rep-resented by a set of functions that de-scribe the evolution of such statisticalinvariants such as expectations, vari-

ances, and higher moments of the sta-tistics of the state variables xi as func-tions of time.

This work was done by Michail Zak of Cal-tech for NASA’s Jet Propulsion Labora-tory. Further information is contained in aTSP (see page 1).

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-41519.

∂ ′

∂= −

∂ ′

∂−( )

=

Pt

Px

x x

P x x x

ii

i

ii i

n

γ13

1 2

and

( , ... ) ′′=∏Pii

n

i1

( )x

Two High-Temperature Foil Journal Bearings These are prototypes of foil bearings for aircraft gas turbine engines. John H. Glenn Research Center, Cleveland, Ohio

An enlarged, high-temperature-com-pliant foil bearing has been built andtested to demonstrate the feasibility ofsuch bearings for use in aircraft gas tur-bine engines. At 150 mm in diameter,this is the largest foil bearing known todate. This bearing is a scaled-up versionof a patented 100-mm-diameter foilbearing, augmented by coating the foilwith a proprietary high-temperature ma-terial. In a companion development, afoil bearing as described above has beencombined with a 150-mm-diameter ac-tive magnetic bearing to make a hybridfoil magnetic bearing.

Foil bearings are attractive for use insome machines in which (1) speeds ofrotation, temperatures, or both exceedmaximum allowable values for rolling-element bearings; (2) conventional lu-bricants decompose at high operatingtemperatures; and/or (3) it is neces-sary or desirable not to rely on conven-tional lubrication systems. In a foilbearing, the lubricant is the workingfluid (e.g., air or a mixture of combus-tion gases) in the space between thejournal and the shaft in the machinein which the bearing is installed. At noor low speed, the shaft is supported atby a spring-loaded foil journal lining.Once the shaft is rotating rapidlyenough, the hydrodynamic and viscousforces exerted by the flow of workingfluid between the foil and the shaftforce the foil away from the shaft, sothat the shaft becomes supported by afilm of the working fluid.

The present enlarged, high-tempera-ture foil bearing has been tested atspeeds up to 27,000 rpm (at 150 mm di-ameter, corresponding to a surfacespeed of 212 m/s) and at temperatures

in excess of 1,200 °F (>649 °C). Thesespeed and temperature limits exceedthose of rolling-element bearings by sev-eral fold.

The hybrid foil magnetic bearing wasconceived to take advantage of thestrengths of the foil and the active mag-netic bearing while utilizing each bear-ing to compensate for the weakness ofthe other, for the overall purpose of ob-taining high load capacity at all speedsand temperatures (see figure). The ac-tive magnetic bearing exhibits excellentperformance at low speed, where thesurface coating on the foil bearing haslimited load capacity. The foil bearing

exhibits excellent performance at highspeed, where the active magnetic bear-ing can fail in response to shocks andother transient disturbances.

Unlike a conventional active mag-netic bearing, the hybrid foil magneticbearing can operate without need for aseparate protective auxiliary/backupbearing. In case of failure of the activemagnetic bearing in the hybrid foilmagnetic bearing, the foil bearingplays the role of the backup bearing, sothat a rotor can continue to run on thefoil bearing alone and then come downto a safe stop. The hybrid foil magneticbearing exhibits both the high load ca-

The Hybrid Foil Magnetic Bearing was photographed in operation at a speed of 15,000 rpm at a tem-perature of 1,200 °F (>649 °C)


pacity of the foil bearing and the highstatic stiffness and control versatility ofthe active magnetic bearing. Hence,the hybrid foil magnetic bearing systemimplements a significant advance inrange of operation and reliability.

This work was done by Hooshang Heshmatof Mohawk Innovative Technology, Inc. forGlenn Research Center. Further informa-tion is contained in a TSP (see page 1).

Inquiries concerning rights for the commer-cial use of this invention should be addressed

to NASA Glenn Research Center, InnovativePartnerships Office, Attn: Steve Fedor, MailStop 4–8, 21000 Brookpark Road, Cleve-land, Ohio 44135. Refer to LEW-17643-1.

Using Plates To Represent Fillets in Finite-Element ModelingStructural deflections are approximated by use of simplified computational submodels of fillets.Marshall Space Flight Center, Alabama

A method that involves the use of fic-titious plate elements denoted bridgeplates has been developed for repre-senting the stiffnesses of fillets in finite-element calculations of deflections,stresses, and strains in structures. In theabsence of this method, it would be nec-essary to either neglect the effects of fil-lets to minimize the computational bur-den or else incur a large computationalburden by using complex computa-tional models to represent the fillets ac-curately. In effect, the bridge plates ofthe present method are reduced-ordermodels of fillets that do not yield accu-rate stresses within fillets but do make itpossible to accurately calculate the dy-namic characteristics of the structureand to approximate the effects of filletson stresses and strains elsewhere in astructure that contains the fillets. Suchapproximations are accurate enoughfor final modal analysis and preliminarystress analyses.

In a finite-element model accordingto this method, the model of a fillet in-cludes bridge plates that connect thetangent lines of the fillets. For a givenfillet, the bridge plates are character-ized by a thickness (t b) and a pseudoYoung’s modulus (E b) to represent themass and stiffness of the fillet as accu-rately as possible. It is necessary to calcu-late t b and E b in advance, by means ofthe procedure described in the nextparagraph.

One generates two simultaneousnonlinear wide-beam-deflection equa-tions for the rotation at the tangentlines: an equation applicable to thebridge-plate representation and anequation derived from an analytic rep-resentation of the fillet. These equa-tions are formulated in terms of theindependent variables r/t and t wall/t,where r is the fillet radius, t wall is thethickness of the non-filleted section ofa wall adjacent to the filleted section,

and t is a thickness variable, the valueof which one seeks. The equations aresolved numerically to obtain t b and E b.In addition, surface fits of the solu-tions are obtained for use as the equiv-alent of closed-form equations for t b

and E b.The method has been verified in cal-

culations pertaining to a representativefilleted structure. The bridge-platemodel yielded a level of accuracy for thecalculation of natural frequencies andmode shapes better than or equal to thatobtained by use of a high-fidelity solidmodel of the fillet, even though thebridge-plate model contained 90 per-cent fewer degrees of freedom.

This work was done by Andrew Brown ofMarshall Space Flight Center. For fur-ther information, access the Technical Sup-port Package (TSP) free on-line atwww.techbriefs.com/tsp under the Me-chanics category.MFS-31992


Manufacturing & Prototyping

Repairing Chipped Silicide Coatings on Refractory MetalSubstratesTwo methods have been demonstrated to be feasible. John F. Kennedy Space Center, Florida

The space shuttle orbiter’s reaction con-trol system (RCS) is a series of smallthrusters that use hypergolic fuels to orientthe orbiter in space. The RCS thrusters areconstructed from a special niobium-basedalloy — the C-103. This alloy retains excel-lent mechanical properties from cryogenictemperature all the way up to 2,500 °F(1,370 °C). Despite its excellent, high-tem-perature properties, C-103 is susceptible torapid oxidation at elevated temperatures.Were the naked C-103 alloy exposed to theoperational thruster environment, it wouldrapidly oxidize, at least losing all of its struc-tural integrity, or, at worst, rapidly “burn-ing.” Either failure would be catastrophic.To prevent this rapid oxidation duringthruster firing, the RCS thrusters arecoated with a silicide-based protective coat-ing — the R512a. Over time, this protectivecoating becomes weathered and begins todevelop chips. Launch Commit Criterialimit the diameter and depth of an accept-able pit; otherwise, the thruster must be re-moved from the orbiter — a very costly,time-consuming procedure. The authorshave developed two methods to repairdamaged R512a coatings on C-103.

For the first repair technique, metalfoundries, semiconductor manufacturers,and many other industries have developedand routinely use coatings that can easily bepainted on metal to protect it from corro-sion, including oxidation, to temperaturesin excess of 2,500 °F (1,370 °C). These coat-ings are typically a well-chosen oxide in aspecial organic binder that adheres tometallic surfaces. The organic binder is se-

lected, so that upon exposure to elevatedtemperature, the ceramic is held in proxim-ity to the substrate and forms somewhat ofa chemical bond to the surface. If thebinder is freed from the surface, the ce-ramic deposit remains and maintains an ef-fective oxygen barrier. Commercially avail-able, off-the-shelf ceramic paints may beused to repair chipped R512a and protectthe underlying C-103 from subsequent oxi-dation. The authors have identified severalcandidates that aid in the protection of C-103. This first repair technique is consid-ered somewhat temporary. The ideal usefor the ceramic paints would be to repair anRCS nozzle when a chip is discovered, say,at the launch pad. It would serve as a pro-tective coating for at least one mission, pre-vent the rollback of the shuttle, and post-pone the replacement of the nozzle until amore opportune time in the ground-pro-cessing flow.

The second repair technique is based onusing the native coating material of theRCS nozzles. In this case, the chipped areais ground out and a “green” R512a coatingis applied to the repair area. After thegreen coating has dried, it must be heatedat extreme elevated temperatures while invacuum or inert atmosphere to initiate thesolid-state reaction between the R512a andthe C-103. In the early 80’s, a repair processwas developed using a variant of the nativecoating and a focused quartz lamp to heatthe local area. Due to the bulky size of thelamp and focusing assembly, only the areasalong the outer periphery of the nozzlescould be repaired. The authors have devel-

oped a technique using a fiber-coupled,high-powered laser as heat source to suc-cessfully fuse the green R512a to C-103.The resulting repaired areas on testcoupons are chemically and structurallyequivalent to the native coated areas. Sincethe fiber-coupled laser assembly is quitesmall and easy to handle, all areas of thenozzle are accessible for repair, includingthe throat area. Since this repair techniqueresults in a protective barrier that is equiv-alent to the original coating, it is consid-ered to be a permanent repair. Thermalmodeling and calculations have shownthat during the fusing process, all otherareas of the nozzle remain within specifica-tions, so that the processes are viable in situon actual thrusters, although not whilethey are installed on the orbiter.

The two techniques are complementaryin the sense that the ceramic paints are eas-ily applied and do not require excessivetemperatures. While not as desirable as thepermanent repair, they could be appliedfor moderate protection until the perma-nent laser-repair technique is available tothe repair area. Both repair techniqueswere originally intended for RCS nozzles,but the process could easily be applied toother geometries of R512a/C-103. Addi-tionally, the two repair techniques may beadapted to other high-temperature coat-ing/substrate systems.

This work was done by Robert Youngquist ofKennedy Space Center and Christopher D.Immer and Francisco Lorenzo-Luaces of ASRCAerospace. Further information is contained ina TSP (see page 1). KSC-12690/29

Simplified Fabrication of Helical Copper AntennasFrom concept to working prototype takes just a few hours.Lyndon B. Johnson Space Center, Houston, Texas

A simplified technique has been de-vised for fabricating helical antennas foruse in experiments on radio-frequencygeneration and acceleration of plasmas.

These antennas are typically made ofcopper (for electrical conductivity) andmust have a specific helical shape andprecise diameter.

Such an antenna could be made bybending a single long piece of coppertubing or bending smaller pieces of cop-per tubing, then welding the pieces to-


gether. It could also be made by machin-ing from a single large piece of copper. Itis extremely difficult to bend copper tub-ing into a helix with a precise pitch anddiameter. It is also difficult to create thehelical shape from multiple pieces oftubing; moreover, welding separatepieces distorts the shape. Machining ahollow cylindrical helix from a block orcylinder of copper entails the use of acomplex, expensive, three-dimensional-milling machine in a process that entailslong setup and machining times.

In the present simplified technique,one begins by creating a two-dimensionalpaper template of a desired helical an-tenna shape. The template is pasted onthe outer surface of a copper pipe thathas the desired inner and outer diame-

ters. Holes are drilled at the locationswhere corners are required to exist in thefinal helical antenna. Manually, using ahacksaw, diagonal cuts are made in theouter cylindrical surface of the pipe, fol-lowing the lines on the template. Usually,after hacksawing, only a little filing isneeded to smooth the edges of the result-ing antenna. If the antenna must bewater-cooled, then copper tubing can bebrazed onto the outer surface of the an-tenna. This tubing is not required to fol-low the precisely defined shape of the an-tenna.

This fabrication technique would notbe suitable for mass production, but it isideal for a laboratory environment. Theadvantages of the this technique are thefollowing:

• Precise antennas can be made from in-expensive, stock-size copper pipes.

• No welding of separate pieces isneeded, and so there is no welding-in-duced distortion of antenna shapes.

• Prototype antennas can be fabricatedfairly rapidly, without the need for com-plex three-dimensional-milling ma-chines or computer-aided drafting tools.

• Notwithstanding the reliance on hand-work, the total fabrication time (as lit-tle as a few hours) is competitive with,and probably less than, that of any au-tomated process that could be used forthis purpose.This work was done by Andrew Petro of John-

son Space Center. Further information is con-tained in a TSP (see page 1).MSC-24076


Physical Sciences

Graded-Index “Whispering-Gallery” Optical MicroresonatorsImprovements would include equidistant resonances and reduced evanescent field.NASA’s Jet Propulsion Laboratory, Pasadena, California

Graded-index-of-refraction dielectricoptical microresonators have been pro-posed as a superior alternative to priordielectric optical microresonators,which include microspheres (describedin several prior NASA Tech Briefs articles)and microtori wherein electromagneticwaves propagate along circumferentialpaths in “whispering-gallery” modes.The design and method of fabricationof the proposed microresonators wouldafford improved performance by ex-ploiting a combination of the propaga-tion characteristics of the whispering-gallery modes and the effect of a gradedindex of refraction on the modes.

The prior microresonators have beenshown to be capable of functioning ascompact, high-performance optical filterscharacterized by rarefied spectra of nar-row resonance lines. For many applica-tions, the frequency intervals between res-onances are required to be equal.Unfortunately, the techniques used tofabricate the prior microresonators can-not be used to obtain equidistant reso-nances. The variation of frequency spac-ing of resonances is a consequence of thefrequency dependence of the radial distri-bution of the whispering-gallery resonantmodes: In a given microresonator thatdoes not have a graded index of refrac-tion, higher-frequency modes propagateon paths slightly closer to the surface, rel-ative to lower-frequency modes. In otherwords, the higher-frequency modes prop-agate circumferentially at slightly largerradii and, consequently, slightly longer

optical path lengths. The variation of op-tical path lengths results in nonuniformspacing of resonance frequencies.

Optical path length is a function ofboth distance (in the common geomet-rical sense) and the index of refraction.A microresonator according to the pro-posal would be fabricated from agraded-index-of-refraction cylinder.The parameters of the fabricationprocess would be chosen such that theindex of refraction of the cylinderwould decrease with radius by anamount calculated on the basis of thepropagation characteristics of the de-sired resonances. Although higher-fre-quency modes would still travel geomet-rically longer distances, the indices ofrefraction at the larger radii would belower (the waves would travel faster).With proper choice of the rate of de-crease of the index of refraction with ra-dius, the circumferential paths at allradii would have identical optical pathlengths and consequently, to first order,the resonances would be equidistant infrequency.

Additional potential advantages of theproposal include the following:• Fabrication should be straightforward:

Graded-index-of-refraction optical com-ponents are widely available in the formof lenses and optical fibers. Such com-ponents can be formed into microres-onators by use of standard mechanical-and flame-polishing techniques.

• The proposed grading of indices of re-fraction would push the whispering-

gallery modes slightly deeper into theresonator material, so that the evanes-cent fields would be smaller. As a re-sult, losses attributable to imperfec-tions of surfaces would be less than inthe prior microresonators.

• The designs of the prior microres-onators exploit evanescent-field cou-pling via airgaps. Vibrations give rise tosmall changes in the airgaps, therebycausing fluctuations in couplingstrength. In the proposed microres-onators, the greater depth of propaga-tion of the resonant modes wouldmake it possible to use zero-gap cou-pling, so that vibration would nolonger cause fluctuations in thestrengths of coupled optical signals.This work was done by Anatoliy

Savchenkov, Lute Maleki, VladimirIltchenko, and Andrey Matsko of Caltech forNASA’s Jet Propulsion Laboratory. Fur-ther information is contained in a TSP (seepage 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:

Innovative Technology Assets ManagementJPLMail Stop 202-2334800 Oak Grove DrivePasadena, CA 91109-8099(818) 354-2240E-mail: [email protected] to NPO-30590, volume and number

of this NASA Tech Briefs issue, and thepage number.

Manufacture of Sparse-Spectrum Optical MicroresonatorsMultiple units having the same spectral parameters could be produced.NASA’s Jet Propulsion Laboratory, Pasadena, California

An alternative design for dielectricoptical microresonators and a relativelysimple process to fabricate them havebeen proposed. The proposed microres-onators would exploit the same basic

physical phenomena as those of micro-torus optical resonators and of the mi-crosphere optical resonators describedin several prior NASA Tech Briefs articles.The resonances in such devices are asso-

ciated with the propagation of electro-magnetic waves along circumferentialpaths in “whispering-gallery” modes.The main advantage afforded by theproposal is that the design and the fab-


rication process are expected to beamenable to production of multiple mi-croresonators having reproducible spec-tral parameters — including, most no-tably, high values of the resonancequality factor (Q) and reproducible res-onance frequencies.

High-Q optical microresonators arekey components in many contem-plated advanced optoelectronic appli-cations, including high-stability, nar-row-line-width microlasers;spectrometers; remote-sensing sys-tems; memory devices; and opticaldelay lines. In all such applications,there are requirements for stable andrepeatable spectra that contain the res-onance spectral lines of interest anddo not contain unwanted lines: inother words, there are requirementsfor microresonators that exhibit highQ with reproducible sparse spectra. Al-though prior microsphere and micro-torus optical resonators have beenshown to have the potential to satisfythese requirements, the techniquesused heretofore to fabricate them, in-volving melting individual resonatorsunder manual control, do not yield re-producible spectral parameters and,therefore, are not suitable for produc-tion of multiple, functionally identicalunits.

The figure depicts a microresonatorand the fabrication thereof accordingto the proposal. In preparation for fab-rication of a batch of microresonators,one would choose a silica tube of pre-cisely calibrated diameter (typicallyabout 6 mm), so that all the resonatorsin the batch could be relied upon tohave the same diameter. One wouldcut the tube into shorter segments —one for each resonator. By use of a di-amond cutter, a circumferential V

groove would be made on the outersurface of each segment. By polishingwith a diamond disk, all the materialwould be removed from one end of thesegment (the lower end in the figure),up to the edge of the groove. Thus,what would remain at the polished endof the tube would be a quasi-toroidalresonator structure having a conicalouter surface.

The edge region would be fire-pol-ished by use of a hydrogen/oxygentorch to eliminate the roughness ofthe cut edge and conical surface andthe residual roughness of the me-chanically polished end face of thetube segment. This smoothing of thesurface would reduce the loss oflight propagating in whispering-gallery modes, thereby helping toensure high Q (anticipated to be109). The fire polishing would alsoround the edge slightly, but the ra-dius of curvature of the edge wouldbe small enough that the spectrumwould remain sparse.

This work was done by Anatoliy Savchenkov,Vladimir Iltchenko, Lute Maleki, and DimitriKossakovski of Caltech for NASA’s JetPropulsion Laboratory. Further informationis contained in a TSP (see page 1).




A Microresonator Would Be Fabricated from alength of silica tube by a process of diamond cut-ting, mechanical polishing, and fire polishing.

DiamondCutter

Segment ofQuartz Tube

Polishing Disk

Conical Surfaceof Resonator

Region of"Whispering-

Gallery" Modes

FINISHED MICRORESONATOR

ENLARGED VIEW OF END SHOWINGSLIGHTLY ROUNDED EDGE

NPO30588

7-11-02 bs

Exact Tuning of High-Q Optical Microresonators by Use of UVResonance frequencies can be shifted permanently by controlled amounts.NASA’s Jet Propulsion Laboratory, Pasadena, California

In one of several alternative ap-proaches to the design and fabricationof a “whispering-gallery” optical mi-croresonator of high resonance quality(high Q), the index of refraction of theresonator material and, hence, the reso-nance frequencies (which depend onthe index of refraction) are tailored byuse of ultraviolet (UV) light. The princi-ples of operation of optical microres-

onators, and other approaches to thedesign and fabrication of optical mi-croresonators, have been described inprior NASA Tech Briefs articles, includingthe two immediately preceding this one.

In this approach, a microresonatorstructure is prepared by forming it froman ultraviolet-sensitive material. Thenthe structure is subjected to controlledexposure to UV light while its reso-

nance frequencies are monitored. Thisapproach is applicable, for example, tothe fabrication of optical microres-onators from silica doped with germa-nium. This material exhibits low opticalloss at a wavelength of 1,550 nm — awavelength often used in optical com-munication systems. It is also highlysensitive to UV light: its peak sensitivityoccurs at a wavelength of 334 nm, and


its index of refraction can be shifted byas much as 10–2 by irradiating it at anargon-ion-laser wavelength of 351 nm.

Fabrication begins with softening aGe-doped SiO2 rod by use of a hydro-gen/oxygen microburner and stretch-ing the rod into a filament ≈30 µm wide.The tip of the filament is heated in thehydrogen/oxygen flame to form asphere having a diameter between about100 µm and about 1 mm (see Figure 1).Then the resonance frequencies of thesphere used as a microresonator aremeasured while the sphere is irradiatedwith UV light at a power of 1.5 W froman argon-ion laser that can be operatedat either of two wavelengths: 379 or 351nm. Irradiation at the longer wavelengthheats the sphere and thereby temporar-ily shifts the resonance frequencies butdoes not cause a permanent change inthe index of refraction. Irradiation at

the shorter wavelength changes theindex of refraction permanently.

At first, for the purpose of adjust-ing the optics that focus the laserlight on the sphere, the laser is operatedat the longer wavelength and theadjustments performed to maximizethe shift of resonance frequencies.Then the laser is operated at theshorter wavelength while the reso-nance frequencies are monitored.The UV radiation is terminated whenthe resonance frequencies haveshifted by the desired amount. For ex-ample, a typical shift of ≈10 GHz canbe achieved in a microsphere of 240-µm diameter (see Figure 2).

This work was done by AnatoliySavchenkov, Lute Maleki, Vladimir

Iltchenko, and Timothy Handley of Caltechfor NASA’s Jet Propulsion Laboratory.Further information is contained in a TSP(see page 1).




Figure 1. A Spherical Optical Microresonator(microsphere) is formed by melting one end ofa Ge-doped SiO2 filament.

Microsphere

Light Path

Filament

NPO30589 Fig 1

6-26-02 bsFigure 2. The Shift in Resonance Frequencies of a Ge-doped SiO2 microsphere of 240-µm diameter wasmeasured as a function of time of exposure to laser light at a wavelength of 351 nm.

7

10

20

30

40

50

13 20

Time, Minutes

Freq

uenc

y, G

Hz

27 33

NPO30589 Fig 2

6-26-02 bs


Information Sciences

Automation for “Direct-to” Clearances in Air-Traffic ControlAir-traffic controllers can be more productive and flight times can be reduced.Ames Research Center, Moffett Field, California

A method of automation, and a sys-tem of computer hardware and softwareto implement the method, have been in-vented to assist en-route air-traffic con-trollers in the issuance of clearances tofly directly to specified waypoints or nav-igation fixes along straight paths that de-viate from previously filed flight plans.Such clearances, called “direct-to” clear-ances, have been in use since before theinvention of this method and system.Usually, they are issued when requestedby pilots; less frequently, controllersissue them on their own initiatives.

A typical flight-plan trajectory consistsof multiple straight segments. As such, itcannot minimize flight time because it de-viates from both a great circle and fromthe shortest-flight-time non-great-circletrajectory that could theoretically be gen-erated if the wind field at every point inspace and time could be predicted andtaken into account in assessing alternativetrajectories. Given these complications, itis sometimes possible to save time by fly-ing along an alternative straight-line seg-ment that bypasses a flight-plan waypoint:this is the main reason for seeking and is-suing a direct-to clearance.

The primary requirement guiding thedesign of the present system was to in-crease the productivity of controllersand the efficiency of aircraft trajectorieswithin the constraints of the current air-traffic-control environment. This re-quirement ruled out dependence onsuch new infrastructure as automatedtwo-way air/ground data links. It alsoeliminated from consideration the spec-ification of curved or multi-segment tra-jectories that provide the minimum timeto fly to destinations in spatially varyingwind fields: neither the infrastructure oftoday’s air-traffic control system nor thenavigation equipment on most aircraftsupport the specification of such typesof trajectories to aircraft while in flight.

The system utilizes four-dimensional(time plus three spatial coordinates) tra-jectory information generated by theCenter-TRACON (terminal radar ap-proach control) Automation System(CTAS), which is in current use by air-traf-

fic controllers. The CTAS trajectory com-putations utilize all known informationabout an aircraft, including its capabili-ties, its current three-dimensional coordi-nates and velocity, and meteorologicalconditions (including winds) specified ona grid that spans the entire airspace of thecontinental United States.

The system first finds all aircraft flyingon inefficient routes, then determineswhether it is possible to save time by by-

passing some route segments, whetherpotential direct-to fixes lie within a rec-tangular geographical area that containsthe air-traffic-control center using thesystem, then finally determines whetherthe improved route is free of conflictswith other aircraft (see Figure 1). Air-craft that survive these tests are consid-ered to be eligible for direct-to clear-ances. The system displays a list of alleligible aircraft in order of decreasing

Figure 1. The Flowchart illustrates the steps of computation and decision in the automated genera-tion of a list of aircraft eligible for direct-to clearances.

List of all tracked aircraftand their flight plans.

Choose next aircraftfrom the list.

Isdestination airport

inside or outside limit rectanglefor this aircraft

?

Doestime saved along

direct-to route exceed oneminute?

Call CTAS trajectory synthesizer andcompute two trajectories to direct-to fix:

1. Along flight-plan route and2. Along direct-to route.

Call CTAS Conflict Probe/Trail Plannerand check for conflicts along direct-to

route.

Get direct-to fixfor this airport

from database.

Find fix or waypoint closest to boundary

of limit rectangle.

Database of direct-tofixes for adapted airports.

Add aircraft and conflict status todirect-to list.

Yes

No

InsideOutside

ARC14359 Fig 1

3-11-02 bs


potential time savings. This list enablesan air-traffic controller (see Figure 2) toeasily identify and work with the highest-pay-off aircraft, thereby contributing toa significant increase in the productivityof both the air-traffic controller and theaircraft. Another display generated bythe system is a graphical user interface,through which the air-traffic controllercan issue the direct-to clearance to theaircraft by a simple point-and-click ac-tion on a computer mouse.

This work was done by Heinz Erzbergerand David McNally of Ames ResearchCenter. Further information is contained ina TSP (see page 1).

This invention has been patented by NASA(U.S. Patent No. 6,314,362). Inquiries con-cerning rights for the commercial use of thisinvention should be addressed to the AmesTechnology Partnerships Division at (650)604-2954. Refer to ARC-14359-1.Figure 2. This Display helps the controller identify and work with the highest-pay-off aircraft.

ARC-14359 FIG 2ABPI

3-27-06 ca


Books & Reports

Improved Traps for Removing Gases FromCoolant Liquids

Two documents discuss improvementsin traps for removing noncondensablegases (e.g., air) from heat-transfer liq-uids (e.g., water) in spacecraft coolingsystems. Noncondensable gases must beremoved because they can interfere withoperation. A typical trap includes a cylin-drical hydrophobic membrane inside acylindrical hydrophilic membrane, allsurrounded by an outer cylindrical im-permeable shell. The input mixture ofgas bubbles and liquid flows into the an-nular volume between the membranes.Bubbles pass into the central hollow ofthe hydrophobic membrane and arevented. The liquid flows outwardthrough the hydrophilic membrane andis recirculated. The proposed improve-ments include the following: 1. The outer membrane would be made of

a more hydrophilic, commercially avail-able material so that membrane porescould be made smaller without increas-ing the pressure drop. Decreasing thepore size would increase the bubble pres-

sure, thereby increasing the degree of re-tention of bubbles in the trap.

2. Multiple hydrophobic membraneswould be used to increase ventingarea at the downstream end, wherebubbles tend to collect.

3. Upstream of the venting area, the hy-drophobic membranes would becoated with a dense polymer to reduceevaporation of the coolant liquid.This work was done by John Holladay of

Marshall Space Flight Center and StephenRitchie of the University of Alabama. For fur-ther information, contact Sammy Nabors,MSFC Commercialization Assistance Lead,at [email protected]. MFS-32037-1

Lunar Constellation ofFrozen Elliptical InclinedOrbits

A document discusses the design oforbits of spacecraft for relaying commu-nications between Earth stations and ro-botic and human explorers in craters inone of the polar regions on the Moon.In simplest terms, the basic problem isto design a constellation of orbits toprovide continuous and preferably re-

dundant communication coverage ofone of the poles with a minimal numberof spacecraft and little or no controlledmaneuvering of the spacecraft to main-tain the orbits. The design method in-volves the use of analytical techniquesfor initial selection of orbits, followed bya numerical procedure for tuning thecoverage of the constellation to obtain adesign. In an example application, themethod leads to a constellation of threespacecraft having elliptical, inclined or-bits, the apoapsides of which would re-main in the hemisphere (North orSouth) containing the pole of interest.The orbits would be stable and wouldmaintain the required spacecraft forma-tion for at least 10 years, without needfor controlled maneuvering if gravita-tion is the only force considered to af-fect the orbits. A small amount of con-trolled maneuvering would be neededto counteract effects of solar-radiationpressure and other perturbations.

This work was done by Todd Ely andGary Noreen of Caltech for NASA’s JetPropulsion Laboratory. Further infor-mation is contained in a TSP (see page 1).NPO-40992

National Aeronautics andSpace Administration

Technology Focus Electronics/Computers - NASA · 2013-04-10 · Surgical Implants 19 Mechanics 19 Stochastic Representation of Chaos Using Terminal Attractors 20 Two High-Temperature

Documents