Technology Focus Computers/Electronics · Non-Square QAM 10 Measuring Radiation Patterns of...

Technology Focus

Computers/Electronics

Software

Materials

Mechanics

Machinery/Automation

Manufacturing

Bio-Medical

Physical Sciences

Information Sciences

Books and Reports

09-04 September 2004

https://ntrs.nasa.gov/search.jsp?R=20110020517 2020-03-01T12:10:36+00:00Z

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 Commercial Technology Team, its documents, and services is also available at the same facility or on the World Wide Web at www.nctn.hq.nasa.gov.

Commercial Technology Offices and Patent Counsels are located at NASA field centers to providetechnology-transfer access to industrial users. Inquiries can be made by contacting NASA field centersand program offices 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 CenterCharlene E. Gilbert(281) [email protected]

Kennedy Space CenterJim Aliberti(321) [email protected]

Langley Research CenterJesse Midgett(757) [email protected]

John H. Glenn Research Center atLewis FieldLarry Viterna(216) [email protected]

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

Stennis Space CenterRobert Bruce(228) [email protected]

Carl RaySmall Business InnovationResearch Program (SBIR) &Small Business TechnologyTransfer Program (STTR)(202) 358-4652 [email protected]

Benjamin NeumannInnovativeTechnology TransferPartnerships (Code TD)(202) [email protected]

John MankinsOffice of Space Flight (Code TD)(202) 358-4659 [email protected]

Terry HertzOffice of Aero-SpaceTechnology (Code RS)(202) 358-4636 [email protected]

Glen MucklowOffice of Space Sciences(Code SM)(202) 358-2235 [email protected]

Roger CrouchOffice of Microgravity ScienceApplications (Code U)(202) 358-0689 [email protected]

Granville PaulesOffice of Mission to Planet Earth(Code Y) (202) 358-0706 [email protected]

NASA Field Centers and Program Offices

NASA Program Offices

At NASA Headquarters there are seven major program offices that develop and oversee technology projects of potential interest to industry:

NASA Tech Briefs, September 2004 1

5 Technology Focus:Composites/Plastics

5 Brazing SiC/SiC Composites to Metals

5 Composite-Material Tanks With ChemicallyResistant Liners

6 Thermally Conductive Metal-Tube/Carbon-Composite Joints

7 Improved BN Coatings on SiC Fibers in SiC Matrices

9 Electronics/Computers

9 Iterative Demodulation and Decoding of Non-Square QAM

10 Measuring Radiation Patterns of ReconfigurablePatch Antennas on Wafers

11 Low-Cutoff, High-Pass Digital Filtering of Neural Signals

13 Software

13 Further Improvement in 3DGRAPE

13 Ground Support Software for SpaceborneInstrumentation

13 MER SPICE Interface

13 Simulating Operation of a Planetary Rover

14 Analyzing Contents of a Computer Cache

14 Discrepancy Reporting Management System

15 Mechanics

15 Silicone-Rubber Microvalves Actuated by Paraffin

17 Machinery/Automation

17 Hydraulic Apparatus for Mechanical Testing of Nuts

19 Manufacturing

19 Heat Control via Torque Control in Friction Stir Welding

19 Manufacturing High-Quality Carbon Nanotubesat Lower Cost

20 Setup for Visual Observation of Carbon-Nanotube Arc Process

21 Bio-Medical

21 Solution Preserves Nucleic Acids in Body-FluidSpecimens

21 Oligodeoxynucleotide Probes for Detecting intact Cells

23 Physical Sciences

23 Microwave-Spectral Signatures Would RevealConcealed Objects

24 Digital Averaging Phasemeter for HeterodyneInterferometry

26 Optoelectronic Instrument Monitors pH in aCulture Medium

26 Imaging of γ-Irradiated Regions of a Crystal

27 Photodiode-Based, Passive UltravioletDosimeters

28 Discrete Wavelength-Locked External Cavity Laser

31 Books & Reports

31 Flexible Shields for Protecting Spacecraft Against Debris

31 Part 2 of a Computational Study of a Drop-LadenMixing Layer

31 Controllable Curved Mirrors Made From Single-Layer EAP Films

31 Demonstration of a Pyrotechnic Bolt-RetractorSystem

09-04 September 2004

This document was prepared under the sponsorship of the National Aeronautics and Space Administration. Neither the United States Governmentnor any person acting on behalf of the United States Government assumes any liability resulting from the use of the information contained in thisdocument, or warrants that such use will be free from privately owned rights.



Technology Focus: Composites/Plastics

Brazing SiC/SiC Composites to MetalsSuccess depends on suitable process conditions and adequate titanium contents in brazing alloys.Marshall Space Flight Center, Alabama

Experiments have shown that activebrazing alloys (ABAs) can be used tojoin SiC/SiC composite materials tometals, with bond strengths sufficientfor some structural applications. TheSiC/SiC composite coupons used in theexperiments were made from polymer-based SiC fiber preforms that werechemical-vapor-infiltrated with SiC toform SiC matrices. Some of the metalcoupons used in the experiments weremade from 304 stainless steel; otherswere made from oxygen-free, high-con-ductivity copper.

Three ABAs were chosen for the ex-periments: two were chosen randomlyfrom among a number of ABAs thatwere on hand at the time; the thirdABA was chosen because its titaniumcontent (1.25 percent) is less thanthose of the other two ABAs (1.75 and4.5 percent, respectively) and it was de-sired to evaluate the effect of reducingthe titanium content, as describedbelow. The characteristics of ABAs thatare considered to be beneficial for thepurpose of joining SiC/SiC to metal in-clude wettability, reactivity, and adhe-sion to SiC-based ceramics. Prior to fur-ther development, it was verified that

the three chosen ABAs have these char-acteristics.

For each ABA, suitable vacuum braz-ing process conditions were establishedempirically by producing a series of(SiC/SiC)/ABA wetting samples. Thesesamples were then sectioned and sub-jected to scanning electron microscopy(SEM) and energy-dispersive x-ray spec-trometry (EDS) for analysis of their mi-crostructures and compositions. Speci-mens for destructive mechanical testswere fabricated by brazing of lap jointsbetween SiC/SiC coupons 1/8-in. (≈3.2-mm) thick and, variously, stainless steelor copper tabs. The results of destructivemechanical tests and the SEM/EDSanalysis were used to guide the develop-ment of a viable method of brazing theaffected materials.

The 1.75-percent-Ti ABA was found tobe well suited for joining the SiC/SiCcomposite with 304 stainless steel. The(SiC/SiC)/Cu joints made by use of the1.75- and 4.5-percent-Ti ABAs werefound to be stronger than were the(SiC/SiC)/Cu joints made by use of the1.25-percent-Ti. At the time of reportingthe information for this article, it was be-lieved that the 1.25-percent titanium

content was insufficient for reacting withthe SiC/SiC composite; however, it wasuncertain whether an observed difficultyin producing joints of acceptably highquality was caused at least in part by sur-face contaminants that could consumewhat little titanium was available for re-acting with SiC.

The strengths of the (SiC/SiC)/stain-less-steel joints tested ranged up to amaximum of 24.5 MPa for joints madewith the 1.75-percent Ti ABA. Thestrengths of the (SiC/SiC)/Cu jointstested ranged up to a maximum of 23.1MPa for joints made with the 4.5-percentTi ABA. The preliminary data on the(SiC/SiC)/1.75-percent-Ti ABA/stain-less-steel and (SiC/SiC)/4.5-percent-TiABA/Cu joints show that the character-istics of the joints are highly predictable— a quality that is desirable for opti-mization of design.

This work was done by Wayne S. Steffier ofHyper-Therm High-Temperature Composites,Inc., for Marshall Space Flight Center.Further information is contained in a TSP(see page 1).MFS-31876

Composite-Material Tanks With Chemically Resistant LinersLiner materials are chosen for compatibility with reactive and/or unstable fluids.Marshall Space Flight Center, Alabama

Lightweight composite-material tankswith chemically resistant liners havebeen developed for storage of chemi-cally reactive and/or unstable fluids —especially hydrogen peroxide. Thesetanks are similar, in some respects, tothe ones described in “LightweightComposite-Material Tanks for Cryo-genic Liquids” (MFS-31379), NASA TechBriefs, Vol. 25, No. 1 (January, 2001),page 58; however, the present tanks arefabricated by a different procedure andthey do not incorporate insulation thatwould be needed to prevent boil-off ofcryogenic fluids.

The manufacture of a tank of thistype begins with the fabrication of areusable multisegmented aluminummandrel in the shape and size of the de-sired interior volume. One or more seg-ments of the mandrel can be aluminumbosses that will be incorporated into thetank as end fittings.

The mandrel is coated with a mold-re-lease material. The mandrel is thenheated to a temperature of about 400 °F(≈200 °C) and coated with a thermo-plastic liner material to the desiredthickness [typically ≈15 mils (≈0.38mm)] by thermal spraying. In the ther-

mal-spraying process, the liner materialin powder form is sprayed and heated tothe melting temperature by a propanetorch and the molten particles land onthe mandrel.

The sprayed liner and mandrel are al-lowed to cool, then the outer surface ofthe liner is chemically and/or mechani-cally etched to enhance bonding of acomposite overwrap. The etched liner iswrapped with multiple layers of anepoxy resin reinforced with graphitefibers; the wrapping can be done eitherby manual application of epoxy-impreg-nated graphite cloth or by winding of

6 NASA Tech Briefs, September 2004

epoxy-impregnated filaments. The en-tire assembly is heated in an autoclave tocure the epoxy. After the curing process,the multisegmented mandrel is disas-sembled and removed from inside, leav-ing the finished tank.

If the tank is to be used for storing hy-drogen peroxide, then the liner materialshould be fluorinated ethylene/propy-lene (FEP), and one or more FEP Oring(s) should be used in the aluminumend fitting(s). This choice of materials isdictated by experimental observationsthat pure aluminum and FEP are theonly materials suitable for long-term

storage of hydrogen peroxide and thatother materials tend to catalyze the de-composition of hydrogen peroxide tooxygen and water.

Other thermoplastic liner materialsthat are suitable for some applicationsinclude nylon 6 and polyethylene. Theprocessing temperatures for nylon 6are lower than those for FEP. Nylon 6is compatible with propane, naturalgas, and other petroleum-based fuels.Polyethylene is compatible with petro-leum-based products and can be usedfor short-term storage of hydrogenperoxide.

This work was done by Thomas K. DeLayof Marshall Space Flight Center. For further information, access the TechnicalSupport Package (TSP) free on-line atwww.techbriefs.com/tsp under the Materi-als category.

This invention is owned by NASA, and apatent application has been filed. Inquiriesconcerning nonexclusive or exclusive licensefor its commercial development should beaddressed to the Patent Counsel, MarshallSpace Flight Center, (256) 544-0021. Referto MFS-31401.

Thermally Conductive Metal-Tube/Carbon-Composite JointsModified solder joints accommodate differential thermal expansion.Lyndon B. Johnson Space Center, Houston, Texas

An improved method of fabricatingjoints between metal and carbon-fiber-based composite materials in light-weight radiators and heat sinks has been devised. Carbon-fiber-based compositematerials have been used in such heat-transfer devices because they offer acombination of high thermal conductiv-ity and low mass density. Metal tubes aretypically used to carry heat-transfer flu-ids to and from such heat-transfer de-

vices. The present fabrication methodhelps to ensure that the joints betweenthe metal tubes and the composite-ma-terial parts in such heat-transfer deviceshave both (1) the relatively high ther-mal conductances needed for efficienttransfer of heat and (2) the flexibilityneeded to accommodate differencesamong thermal expansions of dissimilarmaterials in operation over wide tem-perature ranges.

Techniques used previously to joinmetal tubes with carbon-fiber-basedcomposite parts have included press fit-ting and bonding with epoxy. Both ofthese prior techniques have been foundto yield joints characterized by relativelyhigh thermal resistances.

The present method involves the useof a solder (63 percent Sn, 37 percentPb) to form a highly thermally con-ductive joint between a metal tube anda carbon-fiber-based composite struc-ture. Ordinarily, the large differencesamong the coefficients of thermal ex-pansion of the metal tube, solder, andcarbon-fiber-based composite wouldcause the solder to pull away from thecomposite upon post-fabricationcooldown from the molten state. Inthe present method, the structure ofthe solder is modified (see figure) toenable it to deform readily to accom-modate the differential thermal ex-pansion.

In fabricating the composite-materialstructure, the parts of the carbon fibersadjacent to the hole into which themetal pipe is to be inserted are notcoated with the epoxy or other matrixmaterial. The hole is made wideenough to accommodate the tube plusa layer of low-density nylon netting be-tween the tube and the inner surface ofthe hole. The tube and nylon nettingare inserted in the hole, then the solderis melted around the tube. The omis-sion of coating on the fibers adjacent tothe hole makes it possible for the solderto wick into the spaces between thefibers and form intimate thermal con-

Nylon StrandsSurrounded bySmall Voids in

Solder

FiberDirection

Metal Tube

Solder

Solder Wicked Into Layer of Uncoated Carbon Fiber

Epoxy-Matrix/Carbon-Fiber Composite

Small Gaps between the nylon netting and the solder provide flexibility to accommodate differentialthermal expansion.


tacts with the fibers. Because the solderdoes not wet the nylon, a small voidforms between each nylon strand andthe solder. The thin solder walls thatbound the voids are much more flexi-ble than a solid mass of solder would

be; hence, after solidification, the sol-der can deform to accommodate differ-ential thermal expansion of the variousmaterials present.

This work was done by Robert J. Copelandof TDA Research, Inc., for Johnson Space

Center. For further information, contact: TDA Research, Inc.12345 W. 52nd Ave.Wheat Ridge, CO 80033-1917http://www.tda.com

Refer to MSC-22907.

Improved BN Coatings on SiC Fibers in SiC MatricesOutside debonding would be favored over inside debonding. John H. Glenn Research Center, Cleveland, Ohio

Modifications of BN-based coatingsthat are used as interfacial layers be-tween the fibers and matrices of SiC-fiber/SiC-matrix composite materialshave been investigated to improve thethermomechanical properties of thesematerials. Such interfacial coating layers,which are also known as interphases (notto be confused with “interphase” in thebiological sense), contribute to strengthand fracture toughness of a fiber/matrixcomposite material by providing for lim-ited amounts of fiber/matrix debondingand sliding to absorb some of the energythat would otherwise contribute to thepropagation of cracks.

Heretofore, the debonding and slid-ing have been of a type called “insidedebonding” because they have takenplace predominantly on the inside sur-faces of the BN layers — that is, at the in-

terfaces between the SiC fibers and theinterphases. The modifications cause thedebonding and sliding to include moreof a type, called “outside debonding,”that takes place at the outside surfaces ofthe BN layers — that is, at the interfacesbetween the interphases and the matrix(see figure).

One of the expected advantages ofoutside debonding is that unlike in in-side debonding, the interphases wouldremain on the crack-bridging fibers.The interphases thus remaining shouldafford additional protection against oxi-dation at high temperature and shoulddelay undesired fiber/fiber fusion andembrittlement of the composite mater-ial. A secondary benefit of outsidedebonding is that the interphase/matrixinterfaces could be made more compli-ant than are the fiber/interphase inter-

faces, which necessarily incorporate theroughness of the SiC fibers. By properlyengineering BN interphase layers tofavor outside debonding, it should bepossible, not only to delay embrittle-ment at intermediate temperatures, butalso to reduce the effective interfacialshear strength and increase the failurestrain and toughness of the compositematerial.

Two techniques have been proposedand partially experimentally verified ascandidate means to promote outsidedebonding in state-of-the-art SiC/SiCcomposites. The first technique is oneof application of a weak layer (for exam-ple, a layer of C) to the outer surface ofthe BN interphase. If residual radial ten-sion exists across the interphase(caused, for example, by a thermal-ex-pansion mismatch between the fiber andmatrix), then outside debonding couldoccur during cool down of the compos-ite from its matrix-processing tempera-ture (typically >1,000 °C) to room tem-perature. If the residual tension is notgreat enough, outside debondingshould nevertheless occur as matrixcracks approach the fibers under somestress conditions.

The second technique for promotingoutside debonding is one of heat treat-ment of the composite at a temperatureabove that normally used for processingthe matrix. During the heat treatment,the BN interphase, which is typicallyformed in a porous state at tempera-tures below 1,000 °C, becomes densi-fied by sintering, so that the interphasecontracts away from the SiC matrix.This contraction may cause a gap toform between the BN interphase andSiC matrix, or, at the very least, increasethe residual radial tension at theBN/matrix interface.

In stress-rupture tests in air at a tem-perature of 800 °C, the 100-hour failurestress of state-of-the-art SiC/SiC compos-ite modified to promote outside debond-

Outside Debonding Inside Debonding

1.00mm 1.00mm

20.0µm 10.0µm

BNFiber

BNFiber

BNBN

FiberFiber

Specimens of SiC/SiC Composites that have undergone outside and inside debonding are depicted inscanning electron micrographs at various magnifications.


ing was as much as 50 percent greaterthan that of the corresponding unmodi-fied (inside debonding only) composite.The room-temperature strain to failure ofthe outside-debonding composite wasfound to be 0.5 percent, as compared with0.4 percent for the inside-debondingcomposite, and the ultimate tensile

strength of the outside-debonding com-posite was not less than that of the inside-debonding composite.

This work was done by Gregory N.Morscher, Ramakrishna Bhatt, Hee-MannYun, and James A. DiCarlo of Glenn Re-search Center. Further information is con-tained in 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, MailStop 4-8, 21000 Brookpark Road, Cleveland,Ohio 44135. Refer to LEW-17240-1.


Electronics/Computers

It has been shown that a non-square(NS) 22n+1-ary (where n is a positive in-teger) quadrature amplitude modula-tion [(NS)22n+1-QAM] has inherentmemory that can be exploited to obtaincoding gains. Moreover, it should not benecessary to build new hardware to real-ize these gains.

The present scheme is a product oftheoretical calculations directed towardreducing the computational complexityof decoding coded 22n+1-QAM. In thegeneral case of 22n+1-QAM, the signalconstellation is not square and it is im-possible to have independent in-phase(I) and quadrature-phase (Q) mappingand demapping. However, independentI and Q mapping and demapping aredesirable for reducing the complexity ofcomputing the log likelihood ratio(LLR) between a bit and a received sym-bol (such computations are essential op-erations in iterative decoding). This isbecause in modulation schemes that in-clude independent I and Q mappingand demapping, each bit of a signalpoint is involved in only one-dimen-sional mapping and demapping. As a re-sult, the computation of the LLR isequivalent to that of a one-dimensionalpulse amplitude modulation (PAM) sys-tem. Therefore, it is desirable to find asignal constellation that enables inde-pendent I and Q mapping and demap-ping for 22n+1-QAM.

Careful labeling of each symbol in theconstellation reveals the memory inher-ent in the corresponding modulationscheme. To obtain the signal constellationor (NS)22n+1-QAM, one starts with thesquare constellation for (NS)22n+2-QAM

with independent I-dimension and Q-dimen-sion Gray-code (GC) mapping. That is, eachdimension of the square 22n+2-QAM is anindependent PAM with GC mapping.There are 22n+2 signal points in thesquare 22n+2-QAM constellation. The GClabel of each signal point can be ob-tained by concatenating its I-dimensionGC label with its Q-dimension GC label.If one then deletes every other point ineach dimension, then there remain onlyhalf of the points in each row and half ofthe points in each column. The distancebetween the remaining points in therows and columns are the same. Thetotal number of remaining points is22n+1 and these points form the non-square constellation for (NS)22n+1-QAM.

The labels of the remaining 22n+1

points are the same as in the square 22n+2-QAM constellation. This means that 2n+2bits are used to label each of the 22n+1

points in the (NS)22n+1-QAM constella-tion: n+1 bits for the I-dimension label-ing, and n+1 bits for the Q-dimension la-beling. However, each point in an(NS)22n+1-QAM constellation representsonly 2n+1 bits of information. Hence, the2n+2 bits used for labeling an (NS)22n+1-QAM signal point are not independent.

Close examination has shown that forany signal point in the (NS)22n+1-QAMconstellation, the last bit of its 2n+2 label-ing bits can be viewed as a parity-check bitof the other 2n+1 bits. Therefore, each(NS)22n+1-QAM symbol can be generatedby first encoding the corresponding 2n+1bits with a (2n+2, 2n+1) single-parity-check (SPC) block encoder and thenusing the 2n+2 encoded bits to select oneof the 2n+1 points on the (NS)22n+1-QAM.

The I-dimension position and the Q-dimen-sion position of a signal point on an(NS)22n+1-QAM constellation can be in-dependently determined by the first n+1encoded bits and the remaining n+1 en-coded bits, respectively. The (2n+2, 2n+1)SPC block code can be generated as a re-cursive, systematic, terminated convolu-tional code with two states. In other words,the decomposition of (NS)22n+1-QAMinto a block encoder and a memorylessmodulator leads to a showing that(NS)22n+1-QAM is, by itself a form ofcoded modulation.

When concatenated with a forward-error-correcting (FEC) code (see figure),this decomposition can be applied to ob-tain joint iterative demodulation and de-coding algorithms that exploit the in-herent memory of (NS)22n+1-QAM so asto achieve better coding gains. In addi-tion, because of the independent I andQ mapping of (NS)22n+1-QAM, the de-coding complexity can be reduced tothat of one-dimensional PAM. Moreover,because the signal constellation of(NS)22n+1-QAM is a subset of the square22n+2-QAM constellation, it should bepossible, in practice, to implement(NS)22n+1-QAM by use of 22n+2-QAMequipment already in existence.

Results of some computational simula-tions have shown that with iterative de-modulation and decoding according tothis scheme, coded (NS)8-QAM per-forms 0.5 dB better than does codedstandard 8-QAM and 0.7 dB better thandoes coded 8-ary phase-shift keying(8 PSK) when the FEC code is the(15,11) Hamming code concatenatedwith a rate-1 accumulator code. Othersimulation results show that coded(NS)32-QAM performs 0.25 dB betterthan does coded standard 32-QAM.

This work was done by Lifang Li, DariushDivsalar, and Samuel Dolinar of Caltech forNASA’s Jet Propulsion Laboratory. Fur-ther information is contained in a TSP (seepage 1).

The software used in this innovation isavailable for commercial licensing. Pleasecontact Don Hart of the California Instituteof Technology at (818) 393-3425. Refer toNPO-40308.

Iterative Demodulation and Decoding of Non-Square QAMThe memory inherent in a non-square 22n+1-QAM can be exploited to obtain coding gains.NASA’s Jet Propulsion Laboratory, Pasadena, California

A Non-Square 22n+1-Quadrature Amplitude Modulator would be concatenated with a forward-error-correcting (FEC) encoder. The FEC output bits would be permuted by a random interleaver (π) beforeeach successive group of 2n+1 bits was mapped into an (NS)22n+1-QAM symbol.

SPCEncoder

Data FECEncoder

2n+1 2n+2

Non-Square 22n+1–QAM

2n+1–PAMMapping

2n+1–PAMMapping

n+1 I

QModulatorπ

n+1

Demultiplexer


Measuring Radiation Patterns of Reconfigurable PatchAntennas on WafersTests can be performed relatively inexpensively and without sawing wafers.John H. Glenn Research Center, Cleveland, Ohio

An apparatus and technique havebeen devised for measuring the radia-tion pattern of a microwave patch an-tenna that is one of a number of identi-cal units that have been fabricated in aplanar array on a high-resistivity siliconwafer. The apparatus and technique areintended, more specifically, for applica-tion to such an antenna that includes aDC-controlled microelectromechanicalsystem (MEMS) actuator for switchingthe antenna between two polarizationstates or between two resonance fre-quencies.

Prior to the development of the pre-sent apparatus and technique, patch an-tennas on wafers were tested by tech-niques and equipment that are moresuited to testing of conventional printed-circuit antennas. The techniques in-cluded sawing of the wafers to isolate in-dividual antennas for testing. Theequipment included custom-built testfixtures that included special signallaunchers and transmission-line transi-tions. The present apparatus and tech-nique eliminate the need for sawingwafers and for custom-built test fixtures,thereby making it possible to test anten-nas in less time and at less cost. More-over, in a production setting, elimina-tion of the premature sawing of wafersfor testing reduces loss from breakage,thereby enhancing yield.

The apparatus includes (1) a com-mercial coplanar-waveguide ground-signal-ground radio-frequency (RF)probe, through which microwave exci-tation is applied to a microstrip trans-mission line that is part of the inte-grated circuitry of the patch antennaunder test; (2) DC probes for biasingthe microelectromechanical actuator;(3) a spinning linearly polarized an-tenna for sampling the linearly and cir-cularly polarized radiation from thepatch antenna as a function of anglerelative to the perpendicular to theplane of the wafer; and (4) an auto-matic network analyzer/microwave re-ceiver for measuring the sampled sig-nal. The microwave probe is acommercial unit of the coplanar-wave-guide (CPW) ground-ground-signal-ground type. The microwave and DCprobes (see Figure 1) are installed in a

Wafer

DC Probe

RF Probe

Wafer

DC Probe

RF Probe

Figure 1. RF and DC Probes are applied to the transmission line of one of several identical patch an-tennas on a silicon wafer of 3-in. (7.62-cm) diameter.

Coaxial Rotary Joint

CoaxialDetector

Swinging Plexiglass™ Arm

Motor

Stepper Motor

SwivelableMicroscope

Rotating Linearly Ploarized Pick-up Antenna

RF Probe Station

RF G-S-C Probe

Microwave Absorber

Silicon Wafer With Patch Antennas

Figure 2. The Spinning Open-Ended Rectangular Waveguide samples the radiation from a patch an-tenna on the wafer. The antenna is positioned along an arc by use of the stepping motor.


Low-Cutoff, High-Pass Digital Filtering of Neural SignalsDigital filtering overcomes the drawbacks of resistor-capacitor filtering.NASA’s Jet Propulsion Laboratory, Pasadena, California

The figure depicts the major functionalblocks of a system, now undergoing devel-opment, for conditioning neural signalsacquired by electrodes implanted in abrain. The overall functions to be per-formed by this system can be summarizedas preamplification, multiplexing, digiti-zation, and high-pass filtering.

Other systems under development forrecording neural signals typically containresistor-capacitor analog low-pass filterscharacterized by cutoff frequencies in thevicinity of 100 Hz. In the application forwhich this system is being developed,there is a requirement for a cutoff fre-quency of 5 Hz. Because the resistorsneeded to obtain such a low cutoff fre-quency would be impractically large, itwas decided to perform low-pass filteringby use of digital rather than analog cir-cuitry. In addition, it was decided to time-multiplex the digitized signals from themultiple input channels into a singlestream of data in a single output channel.

The signal in each input channel isfirst processed by a preamplifier having avoltage gain of approximately 50. Em-bedded in each preamplifier is a low-passanti-aliasing filter having a cutoff fre-quency of approximately 10 kHz. Theanti-aliasing filters make it possible tocouple the outputs of the preamplifiersto the input ports of a multiplexer. Theoutput of the multiplexer is a singlestream of time-multiplexed samples ofanalog signals. This stream is processedby a main differential amplifier, the out-put of which is sent to an analog-to-digitalconverter (ADC). The output of the ADCis sent to a digital signal processor (DSP).

One function of the DSP is to digitallyextract the low-frequency component ofthe signal from each channel (the com-ponent that one seeks to filter out) andto store this component in a lookup table[more precisely, a random-access mem-

ory (RAM) configured to implement theelectronic equivalent of a lookup table].Another function of the DSP is to a as-sign a gain vector (also stored in thelookup table) for each preamplifier. Thegain vector for the preamplifier is pre-sented to the main differential amplifierin synchronism with the arrival of the sig-nal from that preamplifier. This ap-proach prevents the saturation of themain differential amplifier and causesthe output signal from every input chan-nel to have optimum strength. Otherfunctions of the DSP include sorting ofsignal spikes, data compression, andpreparation of data for wireless transmis-sion to an external data processor.

The gain of the main differential am-plifier is dynamically adjustable. Fur-thermore, its negative input terminal re-ceives offset signals from the lookuptable via a digital-to-analog converter(DAC) for the purpose of subtractingthe unwanted low-frequency compo-nents of the input signals and therebyperforming high-pass filtering. Initialgain and offset values for each channelare determined empirically and storedin the lookup table in a calibration pro-

cedure. During subsequent operation,the offset and gain uniformity of eachchannel are constantly monitored by useof the combination of the main differ-ential amplifier, ADC, DSP, and lookuptable, and the lookup table is periodi-cally refreshed with updated values ofthe unwanted low-frequency signal com-ponents (offsets) and gains.

This work was done by Mohammad Mo-jarradi, Travis Johnson, Monico Ortiz,Thomas Cunningham, and Richard Ander-sen of Caltech for NASA’s Jet PropulsionLaboratory. Further information is con-tained in a TSP (see page 1).

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

Innovative Technology Assets ManagementJPLMail Stop 202-2334800 Oak Grove DrivePasadena, CA 91109-8099(818) 354-2240E-mail: [email protected] to NPO-30841, volume and number

of this NASA Tech Briefs issue, and thepage number.

This Signal-Conditioning System is designed to be part of a system for monitoring neural electricalsignals. This system implements a low-pass filter having a cutoff frequency of 5 Hz by digital means.

InputChannels

Preamplifiers Multiplexer

DAC RAM

ADC DSP

Main DifferentialAmplifier

+

– Power andWireless-

CommunicationCircuits

Digital Control Subsystem

commercial RF wafer probe stationthat has been modified to accommo-date the rotating sampling antenna.

The sampling antenna (see Figure 2)is an open-ended rectangular wave-guide that is spun by use of a small DCmotor mounted on poly(methyl meth-acrylate) arm. The signal acquired bythe sampling antenna is coupled

through a coaxial rotary joint to a de-tector that is also mounted on the arm.The arm, in turn, is attached to theshaft of a stepping motor, which is usedto position the sampling antenna, inincrements of a few degrees, along anarc that extends from -90° to +90° rela-tive to the perpendicular to the planeof the wafer.

This work was done by Rainee N. Simonsof Glenn Research Center.Further infor-mation 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, CommercialTechnology Office, Attn: Steve Fedor, MailStop 4-8, 21000 Brookpark Road, ClevelandOhio 44135. Refer to LEW-17462.


Software

Further Improvement in3DGRAPE

“3DGRAPE/AL:V2” denotes version 2of the Three-Dimensional Grids AboutAnything by Poisson’s Equation withUpgrades from Ames and Langley com-puter program. The preceding version,3DGRAPE/AL, was described in “Im-proved 3DGRAPE” (ARC-14069) NASATech Briefs, Vol. 21, No. 5 (May 1997),page 66. These programs are so namedbecause they generate volume grids byiteratively solving Poisson’s Equation inthree dimensions. The grids generatedby the various versions of 3DGRAPEhave been used in computational fluiddynamics (CFD). The main novel fea-ture of 3DGRAPE/AL:V2 is the incor-poration of an optional scheme inwhich anisotropic Lagrange-basedtrans-finite interpolation (ALBTFI) iscoupled with exponential decay func-tions to compute and blend interiorsource terms. In the input to3DGRAPE/AL:V2 the user can specifywhether or not to invoke ALBTFI incombination with exponential-decaycontrols, angles, and cell size for con-trolling the character of grid lines. Ofthe known programs that solve ellipticpartial differential equations for gener-ating grids, 3DGRAPE/AL:V2 is theonly code that offers a combination ofspeed and versatility with most optionsfor controlling the densities and othercharacteristics of grids for CFD.

This program was written by Stephen Alterof Langley Research Center. Further infor-mation is contained in a TSP (see page 1).LAR-16415

Ground Support Software forSpaceborne Instrumentation

ION is a system of ground support soft-ware for the ion and neutral mass spec-trometer (INMS) instrument aboard theCassini spacecraft. By incorporatingcommercial off-the-shelf database, Webserver, and Java application components,ION offers considerably more ground-support-service capability than was avail-able previously. A member of the teamthat operates the INMS or a scientistwho uses the data collected by the INMScan gain access to most of the servicesprovided by ION via a standard point-and click hyperlink interface generated

by almost any Web-browser programrunning in almost any operating systemon almost any computer. Data are storedin one central location in a relationaldatabase in a non-proprietary format,are accessible in many combinations andformats, and can be combined with datafrom other instruments and spacecraft.The use of the Java programming lan-guage as a system-interface languageoffers numerous capabilities for ob-ject-oriented programming and formaking the database accessible to par-ticipants using a variety of computerhardware and software.

This program was written by Vincent Ani-cich, Rob Thorpe, Greg Fletcher, HunterWaite, Julia Xu, Erin Walter, Kristie Frick,Greg Farris, Dave Gell, Jufy Furman, ButchCarruth, and John Parejko of Caltech forNASA’s Jet Propulsion Laboratory. Fur-ther information is contained in a TSP (seepage 1).

This software is available for commerciallicensing. Please contact Don Hart of the Cal-ifornia Institute of Technology at (818) 393-3425. Refer to NPO-40282.

MER SPICE InterfaceMER SPICE Interface is a software

module for use in conjunction with theMars Exploration Rover (MER) missionand the SPICE software system of theNavigation and Ancillary Information Fa-cility (NAIF) at NASA’s Jet PropulsionLaboratory. (SPICE is used to acquire,record, and disseminate engineering,navigational, and other ancillary data de-scribing circumstances under which datawere acquired by spaceborne scientific in-struments.) Given a Spacecraft Clockvalue, MER SPICE Interface extractsMER-specific data from SPICE kernels(essentially, raw data files) and calculatesvalues for Planet Day Number, LocalSolar Longitude, Local Solar Elevation,Local Solar Azimuth, and Local SolarTime (UTC). MER SPICE Interface wasadapted from a subroutine, denotedm98SpiceIF written by Payam Zamani,that was intended to calculate SPICE val-ues for the Mars Polar Lander. The maindifference between MER SPICE Interfaceand m98SpiceIf is that MER SPICE Inter-face does not explicitly call CHRONOS, atime-conversion program that is part of alibrary of utility subprograms withinSPICE. Instead, MER SPICE Interfacemimics some portions of the CHRONOS

code, the advantage being that it exe-cutes much faster and can efficiently becalled from a pipeline of events in a par-allel processing environment.

This program was written by Elias Sayfi ofCaltech for NASA’s Jet Propulsion Labo-ratory. Further information is contained ina TSP (see page 1)..


Simulating Operation of a Planetary Rover

Rover Analysis, Modeling, and Simula-tions (ROAMS) is a computer programthat simulates the operation of a roboticvehicle (rover) engaged in explorationof a remote planet. ROAMS is a rover-specific extension of the DARTS andDshell programs, described in priorNASA Tech Briefs articles, which afford ca-pabilities for mathematical modeling ofthe dynamics of a spacecraft as a wholeand of its instruments, actuators, andother subsystems. ROAMS incorporatesmathematical models of kinematics anddynamics of rover mechanical subsys-tems, sensors, interactions with terrain,solar panels and batteries, and onboardnavigation and locomotion-control soft-ware. ROAMS provides a modular simu-lation framework that can be used foranalysis, design, development, testing,and operation of rovers. ROAMS can beused alone for system performance andtrade studies. Alternatively, ROAMS canbe used in an operator-in-the-loop orflight-software closed-loop environment.ROAMS can also be embedded withinother software for use in analysis and de-velopment of algorithms, or for MonteCarlo studies, using a variety of terrainmodels, to generate performance statis-tics. Moreover, taking advantage of real-time features of the underlyingDARTS/Dshell simulation software,ROAMS can also be used for real-timesimulations.

This program was written by AbhinandanJain, Jeng Yen, Garrett Sohl, Robert Steele,and J. Balaram of Caltech for NASA’s JetPropulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).



Analyzing Contents of a Computer Cache

The Cache Contents Estimator (CCE) isa computer program that provides infor-mation on the contents of level-1 cache ofa PowerPC computer. The CCE is config-urable to enable simulation of any proces-sor in the PowerPC family. The need forCCE arises because the contents of level-1caches are not available to either hardwareor software readout mechanisms, yet in-formation on the contents is crucial in thedevelopment of fault-tolerant or highlyavailable computing systems and for realis-tic modeling and prediction of comput-ing-system performance. The CCE com-prises two independent subprograms: (1)the Dynamic Application Address eXtrac-tor (DAAX), which extracts the stream ofaddress references from an applicationprogram undergoing execution and (2)the Cache Simulator (CacheSim), whichmodels the level-1 cache of the processorto be analyzed, by mimicking what thecache controller would do, in response tothe address stream from DAAX. CacheSimgenerates a running estimate of the con-tents of the data and the instruction sub-caches of the level-1 cache, hit/miss ratios,

the percentage of cache that containsvalid or active data, and time-stamped his-tograms of the cache content.

This program was written by John Beahan,Garen Khanoyan, Raphael Some, and LeslieCallum of Caltech for NASA’s Jet Propul-sion Laboratory. Further information iscontained in a TSP (see page 1).This softwareis available for commercial licensing. Pleasecontact Don Hart of the California Instituteof Technology at (818) 393-3425. Refer toNPO-30669.

Discrepancy Reporting Management System

Discrepancy Reporting ManagementSystem (DRMS) is a computer programdesigned for use in the stations of NASA’sDeep Space Network (DSN) to help es-tablish the operational history of equip-ment items; acquire data on the quality ofservice provided to DSN customers; en-able measurement of service perfor-mance; provide early insight into theneed to improve processes, procedures,and interfaces; and enable the tracing ofa data outage to a change in software orhardware. DRMS is a Web-based softwaresystem designed to include a distributed-

database and replication feature toachieve location-specific autonomy whilemaintaining a consistent high quality ofdata. DRMS incorporates commercialWeb and database software. DRMS col-lects, processes, replicates, communicates,and manages information on spacecraftdata discrepancies, equipment resets, andphysical equipment status, and maintainsan internal station log. All discrepancy re-ports (DRs), Master discrepancy reports(MDRs), and Reset data are replicated toa master server at NASA’s Jet PropulsionLaboratory; Master DR data are repli-cated to all the DSN sites; and StationLogs are internal to each of the DSN sitesand are not replicated. Data are validatedaccording to several logical mathematicalcriteria. Queries can be performed on anycombination of data.

This program was written by Tonja M.Cooper of Caltech, James C. Lin of Chase Com-puting International, and Mark L. Chatillonof BAE Systems, Australia, for NASA’s JetPropulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).



Microvalves containingsilicone-rubber seals actu-ated by heating and cool-ing of paraffin have beenproposed for developmentas integral components ofmicrofluidic systems. Incomparison with other mi-crovalves actuated by vari-ous means (electrostatic,electromagnetic, piezo-electric, pneumatic, andothers), the proposedvalves (1) would containsimpler structures thatcould be fabricated atlower cost and (2) could beactuated by simpler (andthus less expensive) con-trol systems.

Each valve according tothe proposal would include a flow chan-nel bounded on one side by a flat sur-face and on the other side by a curvedsurface defined by an arched-cross-sec-tion, elastic seal made of silicone rubber[polydimethylsilane (PDMS)]. The sealwould be sized and shaped so that theelasticity of the PDMS would hold thechannel open except when the seal waspressed down onto the flat surface toclose the channel.

The principle of actuation would ex-ploit the fact that upon melting orfreezing, the volume of a typical paraf-fin increases or decreases, respectively,by about 15 percent. In a valve accord-ing to the proposal, the seal face oppo-site that of the channel would be incontact with a pistonlike plug of paraf-fin. In the case of a valve designed tobe normally open at ambient tempera-ture, one would use a paraffin having amelting temperature above ambient.The seal would be pushed against theflat surface to close the channel byheating the paraffin above its meltingtemperature. In the case of a valve de-signed to be normally closed at ambi-

ent temperature, one would use aparaffin having a melting temperaturebelow ambient. The seal would be al-lowed to spring away from the flat sur-face to open the channel by coolingthe paraffin below its melting tempera-ture. The availability of paraffins thathave melting temperatures from –70 to+80 °C should make it possible to de-velop a variety of normally closed andnormally open valves.

The figure depicts examples of pro-totype normally open and normallyclosed valves according to the proposal.In each valve, an arch cross sectiondefining a channel having dimensionsof the order of tens of micrometerswould be formed in a silicone-rubbersheet about 40 µm thick. The silicone-rubber sheet would be hermeticallysealed to a lower glass plate that woulddefine the sealing surface and to anupper glass plate containing a well. Thewell would be filled with paraffin andcapped with a rigid restraining layer ofepoxy. In the normally open valve, theparaffin would have a melting tempera-ture above ambient (e.g., 40 °C) and

the wall of the well would be coatedwith a layer of titanium that would serveas an electric heater. In the normallyclosed valve, the paraffin would have amelting temperature below ambient(e.g., –5 °C). Instead of a heater in thewell, the normally closed valve wouldinclude a thermoelectric cooler on topof the epoxy cap.

This work was done by Danielle Svelha,Sabrina Feldman, and David Barsic of Cal-tech for NASA’s Jet Propulsion Labora-tory. Further information is contained in aTSP (see page 1).

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

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

Refer to NPO-30519, volume and numberof this NASA Tech Briefs issue, and thepage number.

Normally Open and Normally Closed Microvalves would both exploit the large changes in volume of paraffin thatoccur upon melting and freezing.

Paraffin

Epoxy

Plated-Titanium Wall Heater

SiliconeRubber

Glass

Glass

Glass

Glass

Channel Open

Thermoelectric Cooler

Channel Closed

Channel Closed Channel Open

POWER NOT APPLIED

PLATED-TITANIUMWALL HEATER,

CHANNEL NORMALLYOPEN

THERMOELECTRICCOOLER, CHANNEL

NORMALLY CLOSED

POWER APPLIED

Mechanics

Silicone-Rubber Microvalves Actuated by ParaffinRelative to other microvalves, these would be simpler.NASA’s Jet Propulsion Laboratory, Pasadena, California


Machinery/Automation

Hydraulic Apparatus for Mechanical Testing of NutsAdvantages include mobility and reduced setup time.Lyndon B. Johnson Space Center, Houston, Texas

The figure depicts an apparatus formechanical testing of nuts. In the origi-nal application for which the apparatuswas developed, the nuts are of a frangi-ble type designed for use with py-rotechnic devices in spacecraft applica-tions in which there are requirementsfor rapid, one-time separations of struc-tures that are bolted together. The ap-paratus can also be used to test non-frangible nuts engaged withoutpyrotechnic devices.

This apparatus was developed to re-place prior testing systems that were ex-tremely heavy and immobile and charac-terized by long setup times (of the orderof an hour for each nut to be tested).This apparatus is mobile, and the setupfor each test can now be completed inabout five minutes.

The apparatus can load a nut undertest with a static axial force of as much as6.8 × 105 lb (3.0 MN) and a static momentof as much as 8.5 × 104 lb⋅in. (9.6 × 103

N⋅m) for a predetermined amount oftime. In the case of a test of a frangiblenut, the pyrotechnic devices can be ex-ploded to break the nut while the load isapplied, in which case the breakage ofthe nut relieves the load. The apparatuscan be operated remotely for safety dur-ing an explosive test.

The load-generating portion of theapparatus is driven by low-pressurecompressed air; the remainder of theapparatus is driven by 110-Vac electric-ity. From its source, the compressed airis fed to the apparatus through a regu-lator and a manually operated valve.The regulated compressed air is fed toa pneumatically driven hydraulicpump, which pressurizes oil in a hy-draulic cylinder, thereby causing aload to be applied via a hydraulic nut(not to be confused with the nut undertest). During operation, the hydraulicpressure is correlated with the appliedaxial load, which is verified by use of aload cell.

Prior to operation, one end of a teststud (which could be an ordinary

threaded rod or bolt) is installed in thehydraulic nut. The other end of the teststud passes through a bearing plate; aload cell is slid onto that end, and thenthe nut to be tested is threaded ontothat end and tightened until the nutand load cell press gently against thebearing plate.

The axial load is applied to the nutunder test as the air and hydraulic pres-sures increase. The manually operatedhand valve is closed to isolate the hy-draulic pump to hold the load on thetest article. A second manually oper-ated valve is used to dump the hy-draulic oil back to a reservoir to relievethe load. The maximum axial load islimited by a relief valve on the com-pressed air source; the maximum loadcan be changed by adjusting the settingof this valve.

To set up the apparatus to apply a mo-ment load, one adds a second bearingplate, through which the test stud passeswith a tight fit. Specific loads can be ap-plied to the second bearing plate bytorquing nuts on the all-thread connect-ing the two bearing plates, at a set dis-tance from the center line of the teststud. These loads are verified by use ofload cells. The movement of the secondbearing plate creates a bind with theend of the test stud, thereby giving riseto a moment load applied to the nutunder test.

This work was done by Todd J. Hinkel,Richard J. Dean, Scott C. Hacker, and Dou-glas W. Harrington of Johnson SpaceCenter and Frank Salazar of LockheedMartin. For further information, contactRichard J. Dean at [email protected]. MSC-23159

The Hydraulic Unit Applies a Load to the nut under test via the hydraulic nut and the test stud.

Hydraulic Nut

Bearing Plate

Test Stud

Nut UnderTest Bearing Plate

Load Cell (Axial Load)

Load Cells (Moment Load)


In a proposed advance in friction stirwelding, the torque exerted on theworkpiece by the friction stir pin wouldbe measured and controlled in an effortto measure and control the total heatinput to the workpiece. The total heatinput to the workpiece is an importantparameter of any welding process (fu-sion or friction stir welding). In fusionwelding, measurement and control ofheat input is a difficult problem. How-ever, in friction stir welding, the basicprinciple of operation affords the poten-tial of a straightforward solution: Ne-glecting thermal losses through the pinand the spindle that supports it, the rateof heat input to the workpiece is theproduct of the torque and the speed ofrotation of the friction stir weld pin and,hence, of the spindle. Therefore, if oneacquires and suitably processes data ontorque and rotation and controls thetorque, the rotation, or both, oneshould be able to control the heat inputinto the workpiece.

In conventional practice in frictionstir welding, one uses feedback controlof the spindle motor to maintain a con-stant speed of rotation. According tothe proposal, one would not maintain aconstant speed of rotation: Instead, onewould use feedback control to maintaina constant torque and would measurethe speed of rotation while allowing itto vary. The torque exerted on the

workpiece would be estimated as theproduct of (1) the torque-multiplica-tion ratio of the spindle belt and/orgear drive, (2) the force measured by aload cell mechanically coupled to thespindle motor, and (3) the momentarm of the load cell. Hence, the outputof the load cell would be used as a feed-

back signal for controlling the torque(see figure).

This work was done by Richard Venable,Kevin Colligan, and Alan Knapp of LockheedMartin Corp. for Marshall Space FlightCenter. For further information, contact theNew Technology Representative, Gary Willettat (504) 257-4786. MFS-31834

Manufacturing

Heat Control via Torque Control in Friction Stir WeldingTorque would be controlled and rotation measured to measure and control heat input.Marshall Space Flight Center, Alabama

Amplifier

MotorCurrent

SpindleMotor

Load Cell

ControlSystem

Command Signalto Amplifier

Spindle

Weld LineFriction Stir Weld Pin

Workpiece

TorqueFeedback

The Motor Current Would Be Regulated to maintain constant torque, as part of a scheme to measureand/or control the total heat imparted to the motion of the friction stir weld pin.

A modified electric-arc weldingprocess has been developed for manu-facturing high-quality batches of carbonnanotubes at relatively low cost. Unlikein some other processes for making car-bon nanotubes, metal catalysts are notused and, consequently, it is not neces-sary to perform extensive cleaning andpurification. Also, unlike some otherprocesses, this process is carried out at

atmospheric pressure under a hood in-stead of in a closed, pressurized cham-ber; as a result, the present process canbe implemented more easily.

Although the present welding-basedprocess includes an electric arc, it dif-fers from a prior electric-arc nanotube-production process. The weldingequipment used in this process in-cludes an AC/DC welding power

source with an integral helium-gas de-livery system and circulating water forcooling an assembly that holds one ofthe welding electrodes (in this case,the anode).

The cathode is a hollow carbon (op-tionally, graphite) rod having an outsidediameter of 2 in. (≈5.1 cm) and an in-side diameter of 5/8 in. (≈1.6 cm). Thecathode is partly immersed in a water

Manufacturing High-Quality Carbon Nanotubes at Lower CostThe cost is about 1/20 of that of other processes.Goddard Space Flight Center, Greenbelt, Maryland


bath, such that it protrudes about 2 in.(about 5.1 cm) above the surface of thewater. The bottom end of the cathode isheld underwater by a clamp, to which isconnected the grounding cable of thewelding power source.

The anode is a carbon rod 1/8 in.(≈0.3 cm) in diameter. The assemblythat holds the anode includes a thumb-knob-driven mechanism for controllingthe height of the anode. A small hood isplaced over the anode to direct a flow ofhelium downward from the anode to thecathode during the welding process. Abell-shaped exhaust hood collects thehelium and other gases from theprocess. During the process, as theanode is consumed, the height of the

anode is adjusted to maintain an anode-to-cathode gap of 1 mm.

The arc-welding process is continueduntil the upper end of the anode hasbeen lowered to a specified heightabove the surface of the water bath.The process causes carbon nanotubesto form in the lowest 2.5 cm of theanode. It also causes a deposit reminis-cent of a sandcastle to form on the cath-ode. The nanotube-containing materialis harvested. The cathode and anodecan then be cleaned (or the anode is re-placed, if necessary) and the process re-peated to produce more nanotubes.

Tests have shown that the process re-sults in ≈50-percent yield of carbonnanotubes (mostly of the single-wall

type) of various sizes. Whereas the unitcost of purified single-wall carbon nan-otubes produced by other process isabout $1,000/g in the year 2000, it hasbeen estimated that for the presentprocess, the corresponding cost wouldbe about $10/g.

This work was done by Jeanette M. Bena-vides and Henning Lidecker of GoddardSpace Flight Center. Further information iscontained in a TSP (see page 1).

This invention has been patented by NASA(U.S. Patent No. 6,114,995). Inquiries con-cerning nonexclusive or exclusive license forits commercial development should be ad-dressed to the Patent Counsel, Goddard SpaceFlight Center; (301) 286-7351. Refer to GSC-14601.

Setup for Visual Observation of Carbon-Nanotube Arc ProcessLyndon B. Johnson Space Center, Houston, Texas

A simple optical setup has been de-vised to enable safe viewing of the arcand measurement of the interelectrodegap in a process in which carbon nan-otubes are produced in an arc betweena catalyst-filled carbon anode and agraphite cathode. This setup can beused for visually guided manual posi-tioning of the anode to maintain the in-terelectrode gap at a desired constantvalue, possibly as a low-technology alter-native to the automatic position/voltage

control described in “Automatic Con-trol of Arc Process for Making CarbonNanotubes” (MSC-23134), NASA TechBriefs, Vol. 28, No. 3 (March 2004), page51. The optical setup consists mainly oflenses for projecting an image of the arconto a wall, plus a calibrated grid that ismounted on the wall so that one canmeasure the superimposed image of thearc. To facilitate determination of theend point of the process, the anode isnotched, by use of a file, at the end of

the filled portion that is meant to beconsumed in the process. As the anodeis consumed and the notch comes intoview in the scene projected onto thewall, the process operator switches offthe arc current.

This work was done by Carl D. Scott ofJohnson Space Center and SivaramArepalli of GB Tech Inc. For further informa-tion, contact the Johnson Commercial Technol-ogy Office at (281) 483-3809.MSC-23131


Bio-Medical

Solution Preserves Nucleic Acids in Body-Fluid SpecimensSpecimens can be stored and transported at room temperature.Lyndon B. Johnson Space Center, Houston, Texas

A solution has been formulated topreserve deoxyribonucleic acid (DNA)and ribonucleic acid (RNA) in speci-mens of blood, saliva, and other bodilyfluids. Specimens of this type are col-lected for diagnostic molecular pathol-ogy, which is becoming the method ofchoice for diagnosis of many diseases.The solution makes it possible to storesuch specimens at room temperature,without risk of decomposition, for sub-sequent analysis in a laboratory thatcould be remote from the sampling lo-cation. Thus, the solution could be ameans to bring the benefits of diagnos-tic molecular pathology to geographicregions where refrigeration equipmentand diagnostic laboratories are notavailable.

The table lists the ingredients of thesolution. The functions of the ingredi-ents are the following:• EDTA chelates divalent cations that

are necessary cofactors for nuclease ac-tivity. In so doing, it functionally re-moves these cations and thereby re-tards the action of nucleases. EDTAalso stabilizes the DNA helix.

• Tris serves as a buffering agent, whichis needed because minor contami-nants in an unbuffered solution canexert pronounced effects on pH and

thereby cause spontaneous degrada-tion of DNA.

• SDS is an ionic detergent that inhibitsribonuclease activity. SDS has beenused in some lysis buffers and as a stor-age buffer for RNA after purification.The use of the solution is straightfor-

ward. For example, a sample of saliva iscollected by placing a cotton rollaround in the subject's mouth until itbecomes saturated, then the cotton isplaced in a collection tube. Next, 1.5mL of the solution are injected directly

into the cotton and the tube is cappedfor storage at room temperature. Theeffectiveness of the solution has beendemonstrated in tests on specimens ofsaliva containing herpes simplex virus.In the tests, the viral DNA, as amplifiedby polymerase chain reaction, was de-tected even after storage for 120 days.

This work was done by Duane L. Piersonof Johnson Space Center and Raymond P.Stowe. For further information, contact theJohnson Commercial Technology Office at(281) 483-3809. MSC-22891

The Nucleic Acid Stability Solution (NASS) contains ingredients that perform different roles essentialto the preservation of DNA and RNA in specimens. In the preparation of this solution, the ingredientsare mixed in the indicated quantities (or common multiples thereof), then the solution is sterilized bypassing it through a 0.2-µm filter.

Tris(hydroxymethyl)aminomethane (also known as“Tris” and sold under the trade name Trizma™ Base)

0.12 g 10 mM

Water Free of Deoxyribonuclease and Ribonuclease 99 mL

Total Volume100 mL

Ingredient Weight or Volume of Ingredient

Final Concentration of Ingredient in Solution

Sodium dodecyl sulfate (SDS) 1 g 1 percent

Ethylenediaminetetraacetic acid (EDTA) 0.037 g 1.0 mM

Oligodeoxynucleotide Probes for Detecting Intact CellsCells can be detected, identified, and enumerated via chemiluminescence.Lyndon B. Johnson Space Center, Houston, Texas

A rapid, sensitive test using chemilu-minescent oligodeoxynucleotide probeshas been developed for detecting, iden-tifying, and enumerating intact cells.The test is intended especially for use indetecting and enumerating bacteria andyeasts in potable water.

As in related tests that have been devel-oped recently for similar purposes, theoligodeoxynucleotide probes used in thistest are typically targeted at either single-copy deoxyribonucleic acid (DNA) genes(such as virulence genes) or the multiple

copies (10,000 to 50,000 copies per cell) of16S ribosomal ribonucleic acids (rRNAs).Some of those tests involve radioisotope orfluorescent labeling of the probes for re-porting hybridization of probes to targetnucleic acids. Others of those tests involvelabeling with enzymes plus the use ofchemiluminescent or chromogenic sub-strates to report hybridization via color orthe emission of light, respectively. The pre-sent test is of the last-mentioned type. Thechemiluminescence in the present testcan be detected easily with relatively sim-

ple instrumentation.In developing the present test, the hy-

bridization approach was chosen be-cause hybridization techniques are veryspecific. Hybridization detects stable, in-heritable genetic targets within microor-ganisms. These targets are not depen-dent on products of gene expressionthat can vary with growth conditions orphysiological states of organisms in testsamples. Therefore, unique probes canbe designed to detect and identify spe-cific genera or species of bacteria or


yeast (in terms of rRNA target se-quences) or can be designed to detectand identify virulence genes (genomictarget sequences). Because of the inher-ent specificity of this system, there arefew problems of cross-reactivity.

Hybridization tests are rapid, but hy-bridization tests now available commer-cially lack sensitivity; typically, between106 and 107 cells of the target organismare needed to ensure a reliable test.Consequently, the numbers of targetbacteria in samples are usually ampli-fied by overnight pre-enrichmentgrowth. These tests are usually per-formed in laboratories by skilled techni-cians. The present test was designed toovercome the shortcomings of the com-mercial hybridization tests.

The figure summarizes the majorsteps of the test. It is important to em-phasize that the hybridization processused in this test differs from that ofother hybridization tests in that it doesnot extract target nucleic acids. Thisprocess is based on intact-cell hy-bridization (so-called “in situ hy-bridization”), wherein the intact cellsact as immobilizing agents. The cellsare identified and enumerated by mea-suring the chemiluminescence emit-ted from alkaline phosphatase-probe(AP-probe) hybridization; the chemi-luminescence is detected or measuredby use of photographic film or a lumi-nometer, respectively.

This test provides rapid, simple, andsensitive detection of microorganismsin water. The test is very flexible: spe-cific probes can be developed for al-most any group, genus, and, in manycases, species of microorganisms. The

test can be performed in the field, or ina laboratory, using simple, battery-pow-ered portable instrumentation. The testcan be initiated and completed by non-technical persons. The test format canbe automated easily. Probes for E. coliand the coliform group of bacteria havebeen developed for testing water. Re-sults of a test can be obtained within 8hours. Probes for Vibrio cholerae, Burk-holderia cepacia, Staphylococcus aureus,

Staphylococcus epidermidis, and the Salmo-nella group have also been developed.

This work was done by Reinhardt A.Rosson, Julie Maurina-Brunker, Kim Lang-ley, and Christine M. Pynnonen of Bio-Tech-nical Resources, L. P. for Johnson SpaceCenter. For further information, contact theJohnson Commercial Technology Office at(281) 483-3809.MSC-22663

Intact-Cell Hybridization is performed in a filter cartridge using chemiluminescent oligodeoxynu-cleotide probes to detect target bacteria.

Treat sequentially (in the filter cartridge):

• Treat with 2.5% glutaraldehyde – 30 min at temperature of 4 °C.• Wash with cold phosphate-buffered saline (PBS).• Wash with 90% ethanol/PBS (equal parts by volume).• Wash with cold PBS.• Incubate with Proteinase K (20 µg/ml) for 1 hour at 37 °C.• Wash with Tris/EDTA, pH 8.• Incubate with 0.1 M triethanolamine, pH 8, 10 min.• Incubate with 0.25% acetic anhydride, pH 8, 10 min.• Wash with SSC.• Prehybridize with Plex (or equivalent) solution, 15 to 30 min.• Hybridize with AP-probe (1.5 pmole/mL) in Plex (or equivalent) solution, 4 to 16 hours at stringency temperature.• Incubate twice with Plex Wash II (or equivalent) solution, 5 min. each (stringency washes).

Detect hybridization by light emission (chemiluminescence):

• Fill unit (2.3 mL) with Lumi-Phos™ 530 (or equivalent), incubate 10 min at 37 °C.• Measure light on film (wrap cartridge with aluminum foil with two holes) or with a luminometer.

FilterCartridge

Filter water sample,trapping bacteria inthe filter cartridge.


Physical Sciences

Microwave-Spectral Signatures Would Reveal Concealed ObjectsThis technique should prove superior to conventional ground-probing radar.Lyndon B. Johnson Space Center, Houston, Texas

A proposed technique for locatingconcealed objects (especially small an-tipersonnel land mines) involves the ac-quisition and processing of spectral sig-natures over broad microwave frequencybands. This technique was conceived toovercome the weaknesses of older nar-row-band electromagnetic techniqueslike ground-probing radar and low-fre-quency electromagnetic induction.

Ground-probing radar is susceptibleto false detections and/or interferencecaused by rocks, roots, air pockets, soilinhomogeneities, ice, liquid water, andmiscellaneous buried objects other thanthose sought. Moreover, if the radar fre-quency happens to be one for which thepermittivity of a sought object matchesthe permittivity of the surrounding soilor there is an unfavorable complex-am-plitude addition of the radar reflectionat the receiver, then the object is not de-tected. Low-frequency electromagneticinduction works well for detectingmetallic objects, but the amounts ofmetal in plastic mines are often toosmall to be detectable.

The potential advantage of the pro-posed technique arises from the fact thatwideband spectral signatures generallycontain more relevant information thando narrow-band signals. Consequently,spectral signatures could be used tomake better decisions regarding whetherconcealed objects are present andwhether they are the ones sought. Insome cases, spectral signatures couldprovide information on the depths, sizes,shapes, and compositions of objects.

An apparatus to implement the pro-posed technique (see Figure 1) couldbe assembled from equipment alreadyin common use. Typically, such an ap-paratus would include a radio-fre-quency (RF) transmitter/receiver, abroad-band microwave antenna, and afast personal computer loaded with ap-propriate software. In operation, thecounter would be turned on, the an-tenna would be aimed at the ground orother mass suspected to contain a mineor other sought object, and the operat-ing frequency would be swept over theband of interest.

For success in detection, (1) at least asmall portion of the electromagneticwave radiated by the antenna must pen-etrate the soil or other mass, must im-pinge on the sought object, and must be

either scattered or reflected back to theantenna; and (2) there must be a suit-able frequency-dependent mismatch ofimpedances, as explained next: If, forexample, the object sought were a plas-

Figure 1. Microwave Reflections From the Concealed Object would contribute to the frequency-de-pendent input impedance of the antenna. The impedance would be measured by the network ana-lyzer, and the frequency dependence would be processed to extract information about the concealedobject.

Figure 2. This Plot Is the Fourier Transform of a processed spectral signature, calculated theoreticallyfor the case of a small buried plastic mine.

COMPUTER & SOFTWARE

DifferentiationData

Amplification

Transformation

Interpretation

Displays

RF ELECTRONICS

Frequency-Swept

Transmitter

Frequency-Swept

Receiver

DirectionalCoupler

Plastic Mine or OtherConcealed Object

Soil or OtherMedium

Broad BandAntenna

d1 d1 d3 d4

Time or Distance Argument of Fourier Transform

Fou

rier-

Tra

nsfo

rm A

mpl

itude


tic mine or other dielectric object, thensome microwave energy would pene-trate the object, would undergo one ormore internal reflections, and wouldthen be scattered or reflected back to-ward the antenna. The magnitude andphase of each of these reflections woulddepend on frequency and would con-tribute to the spectral signature of theobject and the surrounding material.The spectral signature would manifestitself as the frequency dependence ofthe input impedance of the antenna.This impedance would be measured bythe computer.

The impedance-vs.-frequency datamust be processed to extract useful in-formation on the location and nature ofthe sought object. One algorithm thatcould be used for this purpose can besummarized as follows:1. Proceeding across the frequency

band, calculate a running average of

the magnitude of input impedance vs.frequency.

2. Compute the difference between themagnitude of impedance and the run-ning average at each frequency.

3. Uniformly digitally amplify the differ-ence data for all frequencies over theband.

4. Compute the Fourier transform of thedifference-vs.-frequency data to ob-tain a plot that is intuitively easy to in-terpret because its abscissa is propor-tional to time and is thus related tosignal-propagation distance and per-mittivity.Figure 2 presents such a plot calculated

theoretically for an apparatus operatingin the frequency band of 1 to 10 GHzwith its antenna aimed toward soil inwhich a plastic mine 3 in. (7.6 cm) in di-ameter and 1-1/2 in. (3.8 cm) thick isburied. The first spectral peak is causedby reflection of the microwave signal

from the antenna input terminal and islocated at d1, which is proportional tothe length of a coaxial cable from thenetwork analyzer to the antenna. Thesecond peak, located at d2, is associatedwith the reflection of the microwave sig-nal at the surface of the ground. Thelargest next two peaks, located at d3 andd4, are attributable to reflection fromthe top and bottom surfaces of themine; thus, d3 and d4 are measures of thedepth of burial of the mine.

This work was done by G. Arndt and P.Ngo of Johnson Space Center, J. R. Carlof Lockheed Martin, and K. Byerly and L.Stolarcyzk.

This invention is owned by NASA, and apatent application has been filed. Inquiriesconcerning nonexclusive or exclusive licensefor its commercial development should be ad-dressed to the Patent Counsel, Johnson SpaceCenter, (281) 483-0837. Refer to MSC-22839.

A digital averaging phasemeter hasbeen built for measuring the differencebetween the phases of the unknown andreference heterodyne signals in a hetero-dyne laser interferometer. This phaseme-ter performs well enough to enable inter-ferometric measurements of distancewith accuracy of the order of 100 pmand with the ability to track distance as itchanges at a speed of as much as 50 cm/s.This phasemeter is unique in that it is asingle, integral system capable of per-forming three major functions that,heretofore, have been performed by sep-arate systems: (1) measurement of thefractional-cycle phase difference, (2)counting of multiple cycles of phasechange, and (3) averaging of phase mea-surements over multiple cycles for im-proved resolution. This phasemeter alsooffers the advantage of making repeatedmeasurements at a high rate: the phase ismeasured on every heterodyne cycle.Thus, for example, in measuring the rel-ative phase of two signals having a het-erodyne frequency of 10 kHz, thephasemeter would accumulate 10,000measurements per second. At this highmeasurement rate, an accurate averagephase determination can be made morequickly than is possible at a lower rate.

Figure 1 schematically depicts a typi-

cal heterodyne laser interferometer inwhich the phasemeter is used. The goalis to measure the change in the length ofthe optical path between two cornercube retroreflectors. Light from a stabi-lized laser is split into two fiber-optic out-puts, denoted P and S, respectively, thatare mutually orthogonally polarized andseparated by a well-defined heterodynefrequency. The two fiber-optic outputs

are fed to a beam launcher that, alongwith the corner-cube retroreflectors, ispart of the interferometer optics. In ad-dition to launching the beams, the beamlauncher immediately diverts and mixesabout 10 percent of the power from thefiber-optic feeds to obtain a referenceheterodyne signal. This signal is de-tected, amplified, and squared to obtaina reference square-wave heterodyne sig-

Laser

BeamLauncher

OpticalFibers

StationaryCorner-CubeRetroreflector

Corner-CubeRetroreflector on Cart

UnknownPhotodiode

ReferencePhotodiode

CableContaining Reference

Heterodyne Signal

CableContaining UnknownHeterodyne Signal

Light Path

Optical System(May contain any number

of reflections)

Cart Sensor

Computer

Phasemeter

HomeInputReferenceInput

UnknownInput

Amplifier, Band-Pass Filter,Sine-to-Square-Wave Converter

Amplifier, Band-Pass Filter,Sine-to-Square-Wave Converter

P

S

Figure 1. A Heterodyne Laser Interferometer is used to measure changes in the length of the opticalpath between the corner-cube retroreflectors. These changes are proportional to changes in the phasedifference between the reference and unknown signals, which are measured by the phasemeter.

Digital Averaging Phasemeter for Heterodyne InterferometryOne instrument performs functions for which separate instruments were previously needed.NASA’s Jet Propulsion Laboratory, Pasadena, California


nal, which is fed to the reference inputterminal of the phasemeter.

The remaining 90 percent of thepower from the fiber-optic feeds of thelight from the two inputs is treated as fol-lows: The P beam is launched towardone corner-cube retroreflector, while theS beam travels to the unknown photodi-ode. The S beam returns to the beamlauncher, passes through it, and contin-ues to the other retroreflector. The Sbeam then returns to the beam launcherwhere it mixes with the P beam, produc-ing the “unknown” heterodyne signal,which is then detected, amplified, and

squared in the same manner as that ofthe reference signal. The resultingsquare-wave is fed to the unknown inputterminal of the phasemeter.

The frequency of the unknown hetero-dyne signal is close to that of the referencesignal: If the optics are motionless, the un-known frequency is exactly the referencefrequency. Motion of the optics gives riseto a Doppler shift in the unknown fre-quency relative to the reference fre-quency. By tracking the relative phases ofthe unknown and reference signals, onetracks the change in the length of the op-tical path between the retroreflectors.

The phasemeter (see Figure 2) tracksthe integer number of cycles and thefractional-cycle portions of the phase dif-ference separately. The integer part ofthe phase difference is taken to equalthe number of positive- or negative-going square-wave level transitions at thereference input minus the number ofsuch transitions at the unknown input.The fractional part of the phase differ-ence is taken to be proportional to thenumber of ticks of a clock of 128-MHzfrequency during the time interval fromthe most recent reference transition tothe next unknown transition.

Home Input

Readout Clock

Integer PhaseCounter Instantaneous

Integer PhaseReadout, 32 Bits

InstantaneousFractionalPhase Readout,16 Bits

SummedFractional PhaseReadout, 32 Bits

Number ofUnknown EdgesDuringSummationReadout (Numberof Summations),23 Bits

Flags, 9 Bits

FractionalPhase at Start ofSummationReadout, 16 Bits

SummedInteger PhaseChangeReadout, 32 Bits

Integer Phase atSummationStart Readout,32 Bits

Integer PhaseCounter

(for Summation)

Reset

Reset

IncrementDecrement

IncrementDecrement

A

A

IntegerCount Latch

IntegerCount Latch

Dat

a B

us

AdderReset

Reset

Reset

Reset

Stop

Start

Stop

Start

Stop

Start

Stop

Start

128-MHz Clock Input

UnknownPhaseInput

ReferencePhaseInput

FractionalPhase Counter

FractionalCount Latch

FractionalCount Latch

Summation-Synchronizing

Clock

StartSummationDelay and

Interval Timer

Stop Summing

Start Summing

Adder

“Number ofUnknowns”

Counter

InstantaneousData Ready Flag

SummedData Ready Flag

Figure 2. In the Phasemeter, the integer-cycle and fractional-cycle parts of the phase difference are measured separately. For greater accuracy, the phaseme-ter can average its measurements over many cycles of the heterodyne signals.


The integer and fractional phase-counter outputs are also fed to accumu-lators to compute the sum of many phasemeasurements over a programmed inter-val. The sum is then used to compute anaverage. The summing interval can bemade to repeat at a fixed frequency, typ-ically in the range between 1 Hz and 1kHz, that is defined by a signal from asummation-synchronizing clock. The av-eraging interval can be programmed to

start any time after the summation-syn-chronizing clock signal and can continuefor any time up to the next such signal.During the summation, each negative-going transition of the unknown signalcauses a phase measurement to besummed into the integer and fractionalphase accumulators. As a result, thenumber of readings in an average equalsthe duration of the summation intervalmultiplied by the unknown heterodyne

frequency; for example, if the hetero-dyne frequency is 10 kHz and the sum-mation interval is 0.1 second, then 1,000measurements are accumulated.

This work was done by Donald Johnson,Robert Spero, Stuart Shaklan, Peter Halver-son, and Andreas Kuhnert of Caltech forNASA’s Jet Propulsion Laboratory. Fur-ther information is contained in a TSP (seepage 1).NPO-30866

Optoelectronic Instrument Monitors pH in a Culture MediumThis instrument is noninvasive and is not significantly affected by biofilm.Lyndon B. Johnson Space Center, Houston, Texas

An optoelectronic instrument moni-tors the pH of an aqueous cell-culturemedium in a perfused rotating-wall-vesselbioreactor. The instrument is designed tosatisfy the following requirements:• It should be able to measure the pH

of the medium continuously with anaccuracy of ±0.1 in the range from6.5 to 7.5.

• It should be noninvasive.• Any material in contact with the cul-

ture medium should be sterilizable aswell as nontoxic to the cells to begrown in the medium.

• The biofilm that inevitably grows onany surface in contact with themedium should not affect the accuracyof the pH measurement.

• It should be possible to obtain accu-rate measurements after only one cali-bration performed prior to a bioreac-tor cell run.

• The instrument should be small andlightweight.The instrument includes a quartz cu-

vette through which the culture mediumflows as it is circulated through thebioreactor. The cuvette is sandwichedbetween light source on one side and aphotodetector on the other side. The

light source comprises a red and a greenlight-emitting diode (LED) that are re-peatedly flashed in alternation with acycle time of 5 s. The responses of thephotodiode to the green and red LEDsare processed electronically to obtain aquantity proportional to the ratio be-tween the amounts of green and redlight transmitted through the medium.

The medium contains some phenolred, which is an organic pH-indicator dye.Phenol red dissociates to a degree that is aknown function of pH and temperature,and its optical absorbance at the wave-length of the green LED (but not at thewavelength of the red LED) varies accord-ingly. Hence, the pH of the medium canbe calculated from the quantity obtainedfrom the photodetector responses, pro-vided that calibration data are available.

During the calibration procedure, thedyed culture medium to be used in thebioreactor is circulated through the cu-vette and the photodetector responsesare processed and recorded while smallamounts of hydrochloric acid are addedto the medium from time to time tomake the pH decrease in small incre-ments through the pH range from 7.5 to6.5. For each set of measurements, the

pH is determined by conventionalmeans. Then the resulting data are fit-ted with a second-order polynomial, thecoefficients of which are thereafter usedto compute the pH as a function of theaforementioned quantity proportionalto the ratio between the amounts ofgreen and red light transmitted.

The cuvette is the only part of the in-strument in contact with the culturemedium. The cuvette can readily besterilized, either separately from or asincorporated into the bioreactor sys-tem, by use of an autoclave or by use ofethylene oxide. Tests have shown thatthe error in the pH measurement bythis instrument does not range beyond±0.1 pH unit, even when a biofilm ispresent. As required, the instrument islightweight (total mass, including elec-tronic circuitry, only 150 g) and compact[overall dimensions of 1.0 by 1.5 by 2.5 in.(approximately 2.5 by 3.8 by 6.4 cm)].

This work was done by Melody M. Andersonand Neal Pellis of Johnson Space Centerand Anthony S. Jeevarajan and Thomas D.Taylor of Wyle Laboratories. For further infor-mation, contact the Johnson Commercial Tech-nology Office at (281) 483-3809.MSC-23107

Imaging of γ-Irradiated Regions of a CrystalElectron-trapping and photorefractive effects are exploited.NASA’s Jet Propulsion Laboratory, Pasadena, California

A holographic technique has been de-vised for generating a visible display ofthe effect of exposure of a photorefrac-tive crystal to γ rays. The technique ex-ploits the space charge that results from

trapping of electrons in defects inducedby γ rays.

The technique involves a three-stageprocess. In the first stage, one writes aholographic pattern in the crystal by use

of the apparatus shown in Figure 1. Alaser beam of 532-nm wavelength is col-limated and split into signal and refer-ence beams by use of a polarizing beamsplitter. On its way to the crystal, the ref-


erence beam goes through a two-dimen-sional optical scanner that contains twopairs of lenses (L1y,L2y and L1x,L2x) andmirrors M1 and M2, which can be ro-tated by use of micrometer drives tomake fine adjustments. The signal beam

is sent through a spatial light mod-ulator that imposes the holo-graphic pattern, then through twoimaging lenses Limg on its way tothe crystal. An aperture is placedat the common focus of lensesLimg to suppress high-order dif-fraction from the spatial lightmodulator. The hologram isformed by interference betweenthe signal and reference beams.

A camera lens focuses an imageof the interior of the crystal ontoa charge-coupled device (CCD). Ifthe crystal is illuminated by only

the reference beam once the hologramhas been formed, then an image of thehologram is formed on the CCD: thisphenomenon is exploited to make visi-ble the pattern of γ irradiation of thecrystal, as described next.

In the second stage of the process, thecrystal is removed from the holographicapparatus and irradiated with γ rays at adose of about 100 krad. In the thirdstage of the process, the crystal is re-mounted in the holographic apparatusin the same position as in the first stageand illuminated with only the referencebeam to obtain the image of the holo-gram as modified by the effect of the γrays. The orientations of M1 and M2 canbe adjusted slightly, if necessary, to max-imize the intensity of the image. Figure 2shows such an image that was formed ina crystal of Fe:LiNbO3.

This work was done by Danut Dragoi,Steven McClure, Allan Johnston, and Tien-Hsin Chao of Caltech for NASA’s JetPropulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).NPO-30622

Figure 1. A Hologram Is Formed in a Crystal to be exposed to γ rays. After exposure to γ rays, the crystal is remounted in this apparatus for reading ofthe hologram.

Laser

Mirror

CCDMirror

Mirror

Spatial LightModulator

Aperture

Collimator

Mirror

Half-WavePlatePolarizing

Beam Splitter

L1y

M2

L2y

L1x L2x

M1

Signal Beam

Limg

Limg

CameraLens

Reference Beam

PhotorefractiveCrystal

Figure 2. This Image Shows the Effect of γ Rays that havepassed through a crystal of Fe:LiNbO3.

Photodiode-Based, Passive Ultraviolet DosimetersOutputs of photodiodes are fed to coulometers.Marshall Space Flight Center, Alabama

Simple, passive instruments have beendeveloped for measuring the exposureof material specimens to vacuum ultravi-olet (VUV) radiation from the Sun.Each instrument contains a silicon pho-todiode and a coulometer. The pho-tocharge generated in the photodiode isstored in the coulometer. The accumu-lated electric charge measured by use ofthe coulometer is assumed to be propor-

tional to the cumulative dose of VUV ra-diation expressed in such convenientunits as equivalent Sun hours (ESH)[defined as the number of hours of ex-posure to sunlight at normal incidence].Intended originally for use aboardspacecraft, these instruments could alsobe adapted to such terrestrial uses asmonitoring the curing of ultraviolet-cur-able epoxies.

Each instrument includes a photodi-ode and a coulometer assemblymounted on an interface plate (seefigure). The photodiode assembly in-cludes an aluminum housing thatholds the photodiode, a poly(tetraflu-oroehylene) cosine receptor, and anarrow-band optical filter. The cosinereceptor ensures that the angular re-sponse of the instrument approxi-


A prototype improved external cavitylaser (ECL) was demonstrated in the sec-ond phase of a continuing effort to de-velop wavelength-agile lasers for fiber-opticcommunications and trace-gas-sensing ap-plications. This laser is designed to offernext-generation performance for incorpo-ration into fiber-optic networks. By elimi-nating several optical components andsimplifying others used in prior designs,the design of this laser reduces costs, mak-

ing lasers of this type very competitive in aprice-sensitive market.

Diode lasers have become enabling de-vices for fiber optic networks because oftheir cost, compactness, and spectralproperties. ECLs built around diodelaser gain elements further enhance ca-pabilities by virtue of their excellentspectral properties with significantly in-creased (relative to prior lasers) wave-length tuning ranges. It is essential to ex-

ploit the increased spectral coverage ofECLs while simultaneously insuring thatthey operate only at precisely definedcommunication channels (wavelengths).Heretofore, this requirement has typi-cally been satisfied through incorpora-tion of add-in optical components that“lock” the ECL output wavelengths tothese specific channels. Such add-incomponents contribute substantially tothe costs of ECL lasers to be used assources for optical communication net-works. Furthermore, the optical align-ment of these components, needed to at-tain the required wavelength precision,is a non-trivial task and can contributesubstantially to production costs.

The design of the present improvedECL differs significantly from the de-signs of prior ECLs. The present designrelies on inherent features of compo-nents already included within an ECL,with slight modifications so that thesecomponents perform their normal func-tions while simultaneously effectinglocking to the required discrete wave-lengths. Hence, add-in optical compo-nents and the associated cost of align-ment can be eliminated.

The figure shows the locking feed-back signal, and the frequency locking

mates the ideal angular response (pro-portional to the cosine of the angle ofincidence). The filter is chosen to passthe ultraviolet wavelength of interestin a specific experiment.

The photodiode is electrically con-nected to the coulometer. The factor ofproportionality between the chargestored in the coulometer and ultravio-let dosage (in units of ESH) is estab-lished, prior to use, in calibration ex-periments that involve the use of lampsand current sources traceable to theNational Institute of Standards andTechnology.

This work was done by Jason A. Vaughnof Marshall Space Flight Center andPerry Gray of Micro Craft, Inc.

This invention is owned by NASA, and apatent application has been filed. For furtherinformation, contact Sammy Nabors, MSFCCommercialization Assistance Lead, at (256)544-5226 or [email protected] to MFS-31316-1.

The Frequency Varies in Steps as a function of the mirror angle. Each step represents locking to theindicated frequency.

0.0194

195

196

197

198

199

0.2 0.6 1.0

Freq

uen

cy, T

Hz

Mirror Angle, Degrees

Lockin

g Feed

back Sig

nal, A

rbitrary U

nits

0.4 0.8 1.2 1.4

200

0.4

0.5

0.6

0.7

0.8

This Simple, Passive Instrument measures the dosage of ultraviolet light in the pass wavelength bandof its filter.

Aluminum Outer Shell

ElectricalConnector

Poly(tetrafluoroethylene)for Electrical insulation

O-Ring Seal Interface Plate

Electrical ConnectorAluminum Housing

Narrow-BandOptical Filter

CosineReceptor

Photodiode

Coulometer

Hole for Connector

Outer Shell Cover

Discrete Wavelength-Locked External Cavity LaserThe laser is locked internally to frequencies of communication channels.John H. Glenn Research Center, Cleveland, Ohio


achieved by use of this signal, as a mir-ror is tilted through a range of angles totune the ECL through 48 channels. Thedata for the frequency plot were ob-tained, simultaneously with the data forthe locking-signal plot, by using a scan-ning Michelson interferometer to pre-cisely determine the ECL wavelength(and, hence, frequency). Given the abil-ity of the Michelson interferometer toobtain highly precise readings, the fre-quency plot can be taken to be a reliableindication of single-mode operation.The discontinuities in the frequencyplot signify the switching of the ECL be-tween channels; in other words, they in-dicate tuning with locking to discretefrequencies. The peaks of the feedback-locking signal correspond to the cen-

ters, or near centers, of the mirror anglescan through the corresponding chan-nels. Thus, it is clear that when the feed-back-locking signal is at a local maxi-mum, the ECL is operating at singlefrequency at or near the middle fre-quency of the selected channel. This isall that is required for precisely lockingthe ECL output wavelength. The lock-ing is achieved without additional exter-nal optical components.

Another aspect of the design of thisECL is a provision for the incorpora-tion of a particularly simple micro-electromechanical system (MEMS)mirror for wavelength tuning. The sim-plified motion of the mirror enablesfacile alignment and rapid tuning,both important in a network source

laser. This ECL is capable of switchingwavelengths across the entire fre-quency band indicated in the figure ina time of less than one millisecond.Other performance characteristics,like the side-mode-suppression ratioand relative-intensity noise, are equalto or better than those of other lasersnow available.

This work was done by Jeffrey S. Pilgrim andJoel A. Silver of Southwest Sciences, Inc.for Glenn Research Center.

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-17313-1.


Books & Reports

Flexible Shields for Protecting SpacecraftAgainst Debris

A report presents the concept ofFlexshield — a class of versatile, light-weight, flexible shields for protectingspacecraft against impacts by small mete-ors and orbiting debris. The Flexshieldconcept incorporates elements of, butgoes beyond, prior spacecraft-shieldingconcepts, including those of Whippleshields and, more recently, multi-shockshields and multi-shock blankets. Ashield of the Flexshield type includesmultiple outer layers (called “bumpers”in the art) made, variously, of advancedceramic and/or polymeric fibers spacedapart from each other by a lightweightfoam. As in prior such shields, thebumpers serve to shock an impinging hy-pervelocity particle, causing it to disinte-grate, vaporize, and spread out over alarger area so that it can be stopped byan innermost layer (back sheet). Theflexibility of the fabric layers and com-pressibility of the foam make it possibleto compress and fold the shield for trans-port, then deploy the shield for use. Theshield can be attached to a spacecraft byuse of snaps, hook-and-pile patches, orother devices. The shield can also con-tain multilayer insulation material, sothat it provides some thermal protectionin addition to mechanical protection.

This work was done by Eric L. Chris-tiansen and Jeanne Lee Crews of JohnsonSpace Center.

This invention is owned by NASA, and apatent application has been filed. Inquiriesconcerning nonexclusive or exclusive licensefor its commercial development should be ad-dressed to the Patent Counsel, Johnson SpaceCenter, (281) 483-0837. Refer to MSC-23314.

Part 2 of a ComputationalStudy of a Drop-Laden Mixing Layer

This second of three reports on acomputational study of a mixing layerladen with evaporating liquid dropspresents the evaluation of Large EddySimulation (LES) models. The LESmodels were evaluated on an existingdatabase that had been generatedusing Direct Numerical Simulation(DNS). The DNS method and the data-base are described in the first report of

this series, “Part 1 of a ComputationalStudy of a Drop-Laden Mixing Layer”(NPO-30719), NASA Tech Briefs, Vol. 28,No.7 (July 2004), page 59. The LESequations, which are derived by apply-ing a spatial filter to the DNS set, gov-ern the evolution of the larger scales ofthe flow and can therefore be solved ona coarser grid. Consistent with the re-duction in grid points, the DNS dropswould be represented by fewer drops,called “computational drops” in theLES context. The LES equations con-tain terms that cannot be directly com-puted on the coarser grid and thatmust instead be modeled. Two types ofmodels are necessary: (1) those for thefiltered source terms representing theeffects of drops on the filtered flowfield and (2) those for the sub-gridscale (SGS) fluxes arising from filter-ing the convective terms in the DNSequations. All of the filtered-source-term models that were developed werefound to overestimate the filteredsource terms. For modeling the SGSfluxes, constant-coefficient Smagorin-sky, gradient, and scale-similarity mod-els were assessed and calibrated on theDNS database. The Smagorinsky modelcorrelated poorly with the SGS fluxes,whereas the gradient and scale-similar-ity models were well correlated with theSGS quantities that they represented.

This work was done by Nora Okong'o andJosette Bellan of Caltech for NASA’s JetPropulsion Laboratory. Further informa-tion is contained in a TSP (see page 1).NPO-30732

Controllable Curved Mirrors Made From Single-Layer EAP Films

A document proposes that light-weight, deployable, large-aperture, con-trollable curved mirrors made of reflec-tively coated thin electroactive-polymer(EAP) films be developed for use inspaceborne microwave and optical sys-tems. In these mirrors, the EAP filmswould serve as both structures and ac-tuators. EAPs that are potentially suit-able for such use include piezoelectric,electrostrictive, ferroelectric, and di-electric polymers. These materials ex-hibit strains proportional to the squaresof applied electric fields. Utilizing thisphenomenon, a curved mirror accord-ing to the proposal could be made from

a flat film, upon which a nonuniformelectrostatic potential (decreasing fromthe center toward the edge) would beimposed to obtain a required curva-ture. The effect would be analogous tothat of an old-fashioned metalworkingpractice in which a flat metal sheet ismade into a bowl by hammering it re-peatedly, the frequency of hammerblows decreasing with distance from thecenter. In operation, the nonuniformelectrostatic potential could be im-posed by use of an electron gun. Calcu-lations have shown that by use of a sin-gle-layer film made of a currentlyavailable EAP, it would be possible tocontrol the focal length of a 2-m-diame-ter mirror from infinity to 1.25 m.

This work was done by Xiaoqi Bao, YosephBar-Cohen, and Stewart Sherrit of Caltech forNASA’s Jet Propulsion Laboratory. Fur-ther information is contained in a TSP (seepage 1).NPO-40275

Demonstration of a PyrotechnicBolt-Retractor System

A paper describes a demonstration ofthe X-38 bolt-retractor system (BRS) ona spacecraft-simulating apparatus,called the Large Mobility Base, inNASA’s Flight Robotics Laboratory(FRL). The BRS design was proven safeby testing in NASA’s Pyrotechnic ShockFacility (PSF) before being demon-strated in the FRL. The paper describesthe BRS, FRL, PSF, and interface hard-ware. Information on the bolt-retractiontime and spacecraft-simulator accelera-tion, and an analysis of forces, are pre-sented. The purpose of the demonstra-tion was to show the capability of theFRL for testing of the use of pyrotech-nics to separate stages of a spacecraft.Although a formal test was not per-formed because of schedule and budgetconstraints, the data in the report showthat the BRS is a successful design con-cept and the FRL is suitable for futureseparation tests.

This work was done by Nick Johnston,Rafiq Ahmed, Craig Garrison, JosephGaines, and Jason Waggoner of MarshallSpace Flight Center. To obtain a copy ofthe paper,”X-38 Bolt Retractor SubsystemSeparation Demonstration,” NASA/TM-2002-212047, September 2002, accesshttp://trs.nis.nasa.gov/archive/00000604.MFS-31874

National Aeronautics andSpace Administration

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