Thirtieth Annual Frequency Control Symposium - IEEE Xplore

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The Thirty-First Annual Frequency Control Symposium is tentatively scheduled for June 1-3, 1977, at the Howard Johnson Hotel, Atlantic City, NJ. Contributors.
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A slight difference in shape between the theoretical surfaces of constant phase and those of the actual mirror also contributed to a shift in resonant frequency [ 7 ] . When this effect was taken into account along with that of (S), experiment and theory agreed quite well, as shown in Fig. 3. SUMMARY Acoustic resonant modes were excited in a Fabry-Perot resonator analogous to those in lasers and beam waveguides. The wavelength of 3 cm was chosen to duplicate a previous microwave experiment [7], and measurements were taken on the same apparatus. The familiar Laguerre-Gaussian modes predicted by approximate beam mode theory were observed, and the resonant frequencies agreed very well t o within the accuracy implied by a first-order perturbation correctionto the approximate theory. In the field of microwaves, the Fabry-Perot resonator is used to achieve very high Q values. Bykov [g] has used capillary waves on the surface of mercury to model fundamental mode oscillations in a two-dimensional open resonator, but to the authors’ knowledge, three-dimensional and/or higher order modes have not been used in acoustics application. The

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absence of any wall losses between mirrors would appear to give this configuration a certain advantage for high Q application. ACKNOWLEDGMENT The authors are grateful to one of thereviewers for pointing the work of Bykov. REFERENCES L. E. Kinsler and A. R. Frey, FundamentalsofAcoustics, New York: John Wiley & Sons, 1962. A . F. Metherell, H. M. A. El-Sum, and L. Larmore, Eds., Acoustic o l f f o l o g r a p h y , New York: Plenum Press, 1969. G. Goubau and F. Schwering, “On the Guided Propagation of Electromagnetic Wave Beams,” IRE Trans. Antennas Propagat. Vol. AP-9, pp. 248-256, May 1961. A. G. Fox and T. Li, “Resonant Modesin a Maser Interferrometer,” Bell Syst. Tech. J., Vol. 40, pp. 453-488, March 1961. G . D. Boyd and H. Kogelnik, “Generalized Confocal Resonator Theory”Be1lSyst. Tech. J.,Vol. 41, pp. 1347-1369, July 1962. H. Kogelnik and T. Li, “Laser Beams and Resonators,” A p p l . O p t . , Vol. 5, pp. 1550-1567, Oct. 1966. C. W. Erickson, “High4rder Modes in a Spherical Fabry-Perot Resonator,”IEEE Trans. MTT, Vol. MTT-23, No. 2, Feb. 1975. V. P. Bykov, High Power Electronics, Vol. 3, pp. 148-153, Nauka, Moscow, 1964, (cited in L. A. Weinstein, Open Resonators and Waveguides, Boulder, Colorado, Golem Press (1969).

Thirtieth Annual Frequency Control Symposium

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HE THIRTIETH Annual Frequency Control Symposium, sponspored by the U S . Army Electronics Command (ECOM) Fort Monmouth, NJ,was held on June 2-4,1976, in Atlantic City, NJ. About 800 participants, from 25 nations on six continents, representing universities, industry, and govemment attended t h s largest symposium devoted to classical and quantum mechanical frequency control and timekeeping. The first day led off with asession on nonlinear stress/ strain phenomena. P. C. Y.Lee and K, M. Wu, Princeton University, described analytically the changes in thicknessshear resonance frequency of circular monoclinic crystal plates subjected to steady in-plane accelerations of arbitrary direction. Good agreement was shown with experiment. The smallness of the effect (order lo-’) belies its importance for high-precision frequency control. Mechanical stress biases set up by thermal shock also produce resonance frequency shifts. This problem was addressed by E. P. EerNisse of Sandia

A. Ballato and J . R. Vig are with the US Army Electronics Technology and Devices Laboratory, US Army Electronics Command, DRSEL-TL-M, Fort Monmouth, NJ 07703. S. Wanuga is with the Electronics Laboratory, General Electric Company, Syracuse, N Y 13201.

Laboratories who showed that for one doubly rotated orientation in quartz, the thermal transient effectvanishes-a valuable finding for the future of fast warmup oscillators. R. B. Stokes and K. M. Lakin, University of Southern California, dealt with finite strain effects on surface acoustic wave (SAW) devices. These areof considerable interest because most epitaxial structures are subjected to temperature-dependent strains which compound the problem of achieving delay stability. Calculations incorporating second- and third-order elastic constants in an extension of Thurston’s theoryagreed well with experiment. D. L. Brownlow of Bell Laboratories closed the session with a discussion of the fracture resistance of synthetic aquartz seed plates, finding that the fracture strength varied with annealing, surface preparation, temperature, and fluid environment. New materials and crystal cutswere the topics of a session in which P. H. Carr, Hanscom AFB, compared variousnew temperature-compensated materials with high piezoelectric coupling. Berlinite and nepheline were two of the promising materials mentioned for bulk and SAW applications. J. Ditaint and R. Lanqon of C.N.E.T., France, reported on the temperature coefficients of doubly rotated lithium tantalate

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plates. Because of the strength of the piezoelectric coupling, the resonance and antiresonance temperature coefficients differ markedly; they found series a of orientations having simultaneously zero temperature coefficients,even a t harmonics, and large values of coupling. The doubly rotated, zero-temperature coefficient locus in quartzwas considered by A. Ballato and G. J. lafrate of ECOM. Along the locus, practical quantities suchas capacitance ratio have been computed, plus their angle gradients, from which manufacturing tolerances can be specified. The zero-temperature coefficient locus in berlinite (AlP04) was also given. Two papers in the session on frequency generation reported on doubly rotated quartz cuts. M. P. Meirs, T. Robinson, and M. B. Bloch, Frequency Electronics, described a stable oscillator for the Pioneer-Venus Program utilizing a fifth harmonic, FC-cut crystal, capable of I p p lo-’ stability under an assortment of environmental variables, including decelerations exceeding 700 g. In the other paper, A. Vulcan and M. B. Bloch, Frequency Electronics, presented resultson the stability of precision oscillators in vibratory environments. It was found that phase noise performance was improved byusing FC-cuts, and that biconvex designs were superior to planoconvex in vibration characteristics. S . Syngellakis and P. C . Y. Lee of Princeton University outlined, in the resonator theory session, an approximate (but very accurate) theory for high-frequency vibrationsof piezoelectric plates. A series expansion of elastic displacement and electric potential in termsof simple thckness modes in avariational principle produces an infinite set of two-dimensional plate equations that are pruned tovarious orders of approximation. Infinite plate dispersion curves, for real and imaginary wavenumbers, were computed for rotated Ycuts of lithium tantalate and compared to the exact three-dimensional results of last year with excellent agreement in the applicable ranges. The vibrations of a biconvex circularA T-cut plate were treated by N. Oura and H. Fukuyo, Tokyo Institute of Technology, and A. Yokoyama, Kumamoto University. It was found that approximating the plateas an oblate spheroid permits a transformation to a Helmholtz equation, the solution of which agrees very well with experiments made by the electrical probe method. In order to shrink thesize of resonators for applications such as wristwatches, the properties of coupled modes are beginning to be explored. Two papers addressed this problem. Y. Oomura of Tokyo Metropolitan University discussed miniature circular disc AT-cut vibrators with diameter/thickness ratios less than five at 1.2 MHz. These used a coupled thickness shear-flexure mode; frequency-temperature reproducibilityis within 3 X Aflatrectangularquartzresonator, also operating in shear-flexure was described by A. E. Zumsteg and P. Suda of the SSIH-Quartz Division of OMEGA. The 4-MHz units were found to have a flatter frequency-temperature curve than usual AT-cuts and stronger attenuation of unwanted modes, resulting in h g h quality factors. Two other papers considered resonators for wristwatches, but dealt with quartz tuning fork designs at 32.768kHz (215 Hz). S . Kanbayashi, S . Okano, K . Hirama, and T. Kudama, Toyo Co., andM.Konno and Y. Tomikawa, Yama-

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gata University, applied the finite element method to analyze tuning fork motion, spurious responses, and mounting factors. Statistical data from productionruns were given for the circuit parameters, aging, shock resistance, and temperature behavior. The authors of the second paper, J. A . Kusters, C. A. Adams, and H. E. Karrer of Hewlett-Packard Co. and R. W. Ward of Litronics Corp., performed a theoretical analysisof resonance in tuning forks, synthesizing a modelusing sections of simple flexure bars suchas +5” X-cut and NT-cuts; correlation with observation was excellent. Experimental fork models were found to exhibit a strong orientational dependence on drive level, with certain crystal orientations showing an anomalous drive level effect at levels less than 0.2 microwatts. Five papers comprised the sessionon filters; twoof these were devoted to monolithic crystal filters, one to a comparison between chargecoupled devices (CCD) and SAWs and two to SAW’S. An analysis of overtone modes in monolithic crystal filters was given by H. F. Tiersten, Rensselaer Polytechnic Institute, for the case of two pole filters with both thicknessshear and thickness-twist coupling directions considered. The influences of piezoelectric stiffening, electrode mass loading and electrical shorting were included in the analysis. A lumped parameter representation of the admittance matrix for the two-port device was also obtained. K. Okuno and T. Watanabe of Nippon Electric Co. reported on a hybrid integrated monolithic crystal filter (HIMF), consisting of thin-film lumped-circuit elements and energy-trapped resonators in integrated structures on a single substrate. As an application, the HIMF can be used in a 100 Mb/s PCM system as a timing pickup filter. D. D. Buss, L. T. Claiborne, C.S. Hartmann, and C. R. Hewes of Texas Instruments Incorporated compared filtering with analog charge-coupled devices and acoustic surfacewave devices. Below 10 MHz, the CCD is capable of many sampleddata or “digital filtering” functions in theanalog domain. Between 10 and 300 MHz, SAWs perform similar functions; both types of devices are capable of time-bandwidth products to lo4. The chirp-Z-transform (CZT), a recently developed technique for performing spectral analysis in the analog domain, can be implemented using CCD’s or SAWs. Both types of implementation were contrasted and compared well with that of a digital FFT. Surface acoustic wave filters for TV applications using ZnOsputtered films were developed byS. Fujishima, H. Ishiyama, A. Inoue, and H. Iekiof Murata Mfg. Co. A glass substrate supports arrays of interdigital electrodes and an overlaying film of rf-sputtered ZnO, highly oriented with C-axis along the surface normal. Film thicknesses of 20 Dm were achieved in three days; the58 MHz filter has a temperature coefficient of -30 ppm/K and low manufacturing cost. A. R. Janus, Hughes Aircraft Company, gave a progress report on theestablishment of a production capability forSAW bandpass and pulse compression filters and tapped delay lines with center frequencies of 100 to 200 MHz on both lithumniobate and ST-cut quartz. E. J. Staples and R. C. Smythe of Piezo Technology Incorporated described the behavior of SAW resonators and coupled resonator filters in termsof twodimensional symmetric and

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antisymmetric modes. They applied aspects of energy trapping and apodization in the design of resonators and showed that as a result of the two dimensional symmetry,SAW resonators may have transverse or in-line mode coupling. Two representative filters reported on were a SAW two-pole resonator having a 1dB insertion loss with typical bandwidth of 0.1% and a four-pole resonator filter, 2-2 poles tandem electrically coupled with an insertion loss of 3 dB and 0.1% bandwidth. Both filters utilized ST-cut quartz and operated at75 MHz. A two-port ST-QuartzSAW Resonator was discussed by W. R. Shreve of Texas Instruments Incorporated. The resonator had a single mode response with an unloaded Q of 20 000. This lowest order mode was coupled by selective apodization of the interdigital transducers. The resonator reflectors were plasma etched grooves onthe surface of the ST-cut quartz.The high Q devices require close control of fabrication processes since variations in groove depths, metallization thickness, etc., can cause resonant frequency shfts that could necessitate post-fabrication frequency tuning. Typical results of two filters operating at fo = 184 MHz for an untuned two-pole filter: insertion loss of 17 dB, 3 dB bandwidth of 17 k H z and out of band rejection 52 dB and a second two-pole filter with a cascaded identical resonator reduced the insertion loss to 7 dB, bandwidth was 40 kHz and out of band rejection of 38 dB. A SAW filter introduced by F. Sandyof Raytheon Research Division makes use of a new geometry in the formof an acoustic ring filter. Four 90” reflecting gratings are located at corners of a rectangular propagation path. IDT’s are placed between opposite pairs of gratings. Because of the geometry and energy propagation, the filter offers bandwidth upto 2% with insertion loss under 3 dB and out-of-band rejection of over 60 dB. Various types of gratings --id filters fabricated on Li Nb03 and ST-cut quartzwere described. J. Schoenwald of Teledyne Incorporated discussed an optical waveguide model for use with SAW resonator designs. The model described the propagation of SAW with regard to transverse boundary conditions. The treatment results in a frequency spectrum of transverse mode resonances associated with each allowed longitudinal mode of the cavity. Resulting analytical design curves and transducer apodization were used to describe the techniques for enhancing a particular mode of the resonator. W. H. Haydl et al. of Institut fur Angewandte Festkorperphysik gave an in-depth report on one-? two-, and three-port SAW resonators using aluminum metallization. They showed electrical tuning results of0.1% using a varactor connected to a “tuning transducer” placed between the grating reflectors. For coupled resonator structures, their device exhibited 80 dB sidelobe suppression. The 0.1% electrical tuning pertains only to the high-coupling piezoelectric materials such as lithium niobate. Investigation of aging effectsin plasma etched SAW resonators was presented by D. T. Bell et al. of Texas Instruments Incorporated. A plasma etched resonator aged in air at 150°C for several months had an aging rate less than 15 ppm/month. The author presented data on processing techniques, such as surface preparation, cleaning, lithography processes, and

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packaging relevant to the aging aspects. Crystals post chemically polished after the standard optical polishing showed a much better aging rate. Data was tabulated for aging rates of devices sealed in dry nitrogen and unsealed in air and compared to activation energies known for bulk devices. R. D. Weglein and 0. W. Otto, Hughes Research Laboratories presented features of a periodic grating oscillator (PGO). The device uses Y-cut quartz and a pair of ion-etched gratings that determines the oscillator frequency as well as the noise characteristics near the carrier. Zero total TCD, (temperature coefficient of delay) is achieved by choosing an appropriate X to Z path length ratio. The spurious-free nature of the oscillator line is due mostly to the saturation characteristics of the feedback amplifier. An X-band exciter was described using a PG0 (97 MHz) and a 100 times solid-state varactor multiplier. L. R. Adkins of Rockwell International reported on the use of a SAW frequency synthesizer that utilizes a simple SAW oscillator which is designed to retain all the comb of frequencies. The advantage of this technique for frequency hopping applications is that a single delay line and feedback loop generates a number of frequencies which are available atall times. MOS/CMOS IC switches having switching times on the order of 10 ns can be used to select the desired frequencies. In the session on resonator design and measurement, three of the papers dealt with the properties of resonators withrectangular electrodes. J . Birch and D. A. Weston of the General Electric Co., Ltd. (England) showed that the incidence of activity dips (bandbreaks) has a systematic dependence on the dimensions and orientation of the rectangular electrodes and on the plateback. J. F. Werner and A. J. Dyer, also of GEC Ltd.: discussed the relationship between plateback,mass loading, and electrode dimensions for resonators with rectangular electrodes operating at fundamental and overtone modes. The dimensioning of rectangular electrodes for the case of a multiple electrode array on a monolithic crystal filterwas discussed by J . H. Sherman, Jr.,of the General ElectricCo. (USA). A laser interferometric technique for measuring the vibrational displacement distribution of the thickness shear modes of A T-cut quartz resonators was discussed byK. Iijima, et al., Yokohama National University. R. E. Newnham and L. E. Cross of the Pennsylvania State University discussed the concepts of secondary ferroic switching and domaindivided piezoelectrics, and suggested that laser-induced twinning in a-quartz can be used to enhance certain modes of motion or to eliminate undesired modes. R. Besson of ENSCM (France) described the fabrication and properties of a new airgap-type resonator. J. J. Gagnepain, also of ENSCM, described the results of fundamental studies on noise in quartz crystal resonators. The design and performance of a new crystal measurement system consisting of an electronically tunable microcircuit admittance bridge and tracking servobridge detector was described by E. Hafner of ECOM and W. J. Riley of GenRad. The frequency and time control requirements of the NAVSTAR/Global Positioning System (GPS) were discussed in a series of four papers. NAVSTARiCPS will, by the mid19803, consist of 24 satellites in synchronous orbit. The

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satellites will send out signals which will permit an unlimited number of properly equipped users to determine their position and velocity in three dimensions, anywhere on earth, dayor night, under all weather conditions, with an estimated position accuracy of 10 meters. Highly precise time control and distribution are essential to NAVSTAR/GPS. F. E. Butterfield of the Aerospace Corp. discussed the operational aspects of the satellite constellation and the specificationson the orbits, clocks, message content, and error budgets. A. J. Van Dierendonck of the General Dynamics Electronics Div. discussed the time requirements. He pointed out that a onenanosecond time error corresponds t o a 30 cm range error. The oscillator and frequency management requirements for a variety of GPS user equipments, such as the manpack, vehicular aircraft, missile, and lower performance/lower cost applications, were discussed by R. A. Maher of Texas Instruments Incorporated. The oscillator requirements for the GPS manpack, including a summary of present high-precision oscillator technology,were presented byJ. Moses of Magnavox. In the session on resonator processing techniques, R . Fischer and L. Schulzke of KVG (W. Germany) described a method of simultaneously plating both sides of carefully mounted and masked resonators which allowsplating directly to frequency. The advantages of the direct plating method over the conventional base plating plus plating to frequency were discussed. R. D. Peters of the General Electric Neutron Devices Dept. presented a progress report on the development of highprecision 5-MHz and 20-MHz fundamental resonators in ceramic flat-pack enclosures. The design of a highly directional nozzle beam type vacuum evaporation source was described by R. P. Andres of Princeton University. The source permits high deposition rates with minimum wastage of electrode materials and can therefore operate for extended periods without requiring frequent opening of the vacuum system to replenish the source. An evaluation of leak testing methods, with emphasis on the helium and radioisotope tracer gas methods, was discussed by R. E. McCullough of Texas Instruments Incorporated. A method of characterizing metal-oxide systems by high-resolution electron spectroscopy, w h c h can be used to study thechemical reactions that take place at the interface between a metal electrode and the quartz crystal, was described by E . J. Scheibner and W. H. Hicklin of the Georgia Institute of Technology. V. E. Bottom of Tyco Crystal Products describeda method of adjusting the frequency of aluminum plated quartz crystal resonators by anodic oxidation. The anodic oxide also serves to stabilize the oxide layer on the aluminum film. H. Fukuyo and N. Oura of the Tokyo Institute of Technology presented the results of studies on the polished layer on quartz plates. They showed that there is an approximately 1008-thick disturbed layer formed by the polishing process which can be removed by a light etch or can be annealed out at high temperature. A method of correcting the angles of cut of quartz plates by etching selected areas so that in the following lapping process the angles shift to the correct values was described by D. Husgen and C. C. Calmes, Jr., of Savoy Electronics. R. L. Filler and J. R. Vig of ECOM described experiments which showed that the bonding technique employed ~

can produce large rotations in the frequency versus temperature characteristics of AT-cut resonators. Apparent angle shifts of up tosix minutes were measured when resonators were reprocessed using different bonding configurations. Eighteen additional papers were presented. These dealt with frequency generation and timekeeping, along with atomic and molecular frequency control. Since these areas are not of immediate interest to most SU readers, we simply list them for completeness.

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A N D TIME-SYNCHRONIZATION, FREQUENCY DISTRIBUTION, AND APPLICATION “Minimum Variance Numerical Methods for Synchronizing Airborne Clocks,” R. J. Kulpinski, MITRE Corporation. “A Heuristic Model of Long-Term Atomic Clock Behavior,” D. B. Percival, US Naval Observatory. “Microwave Frequency Synthesis for Satellite Communications Ground Terminals,” G.Mackiw and G. Wild, RCA. “Phase Synchronization of a Large HF Array by a Local Broadcast Station,” S. H. Taheri, B. D. Steinberg, and D. L. Carlson, University of Pennsylvania. “The Remote Synchronization Technology,” L. J. Rueger, Johns Hopkins University.

A N D MEASUREMENT FREQUENCY GENERATION

1) “Design Considerations in State of the Art Signal Processing and Noise Measurement System,” F . L. Walls, S. R. Stein, J. E. Gray,D. J . Glaze and D. W. Allan, National Bureau of Standards. 2 ) “An Ultra-Stable Low Power 5 MHz Quartz Oscillator Qualified for Space Usage,” J . R. Norton, Johns Hopkins University. 3) “A Miniature High Stability TCXO Using Digital Compensation,” A. Mroch and G. Hykes,Collins Radio Group. 4) “Linearization of Direct FM Voltage Controlled Crystal Oscillators,” S. J. Lipoff, Bell & Howell. 5 ) “System for Automatic Phase Noise Measurement ,” L. Peregrino and D. Ricci, Hewlett-Packard. 6) “An Efficient Hardware Implementation for High Resolution Frequency Synthesis,” B. Bjerde and G. Fisher, General Dynamics.

MOLECULAR FREQUENCY STANDARDS “Velocity Distribution Measurementsof CS Beam Tubes,” D. A. Howe, NationalBureau of Standards. “Performance of a Dual’Beam High Performance Cesium Beam Tube,” G. Seavey, Hewlett Packard. “Measured Performance and Environmental Sensitivities of a Rugged Cesium Beam Frequency Standard,” M. C. Fisher and C. E. Heger, Hewlett Packard. “Precise Frequency Multiplication to the Infrared,” T. G. Blaney and D. J. E. Knight. National Physical Laboratory. “A New Kind of Passively Operating H-Frequency Standard,” F. L.Walls and H. Hellwig, National Bureau of Standards. “NASA Atomic Hydrogen Frequency Standards Program-An Update,” V. S. Reinhardt, D. C. Kaufman, ATOMIC

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W. A. Adams, and J. J.DeLuca, NASAIGoddard Space Flight Center and J. L. Soucy, Bendix Field Engineering Corporation. 7) “AStudytoIdentifyHydrogen Maser FailureModes,” W. B. Bridges, A. N . Chester, J. E. Etter, A. E. Popa, B. L. Walsh, and T. M. Wang, Hughes Research Labs.

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Interested readers may obtainProceedings copies of the Symposium ($8.00) from: Frequency Control Symposium Publications Committee C/OElectronicsIndustriesAssociation 2001 Eye Street, NW Washington, M:20006

The Thirty-First Annual Frequency Control Symposiumis tentatively scheduled for June 1-3, 1977, at the Howard Johnson Hotel, Atlantic City, NJ.

Contributors

Clifford W. Erickson is a native of Duluth,MN He holds BA and M A degrees from Harvard University, and the PhD-degee from the University of Wisconsin, Madison. In 1958-1959 he attended the University of Stockholm, Stockholm, Sweden, on a Rotary Foundation Fellowship. He was a Member of the Technical Staff at Sandia Laboratories where he developed solid state X-ray detectors for studies of nuclear bursts. From 1967 t o 1968 he was a Visiting Scientist at the Institit fur Plasmaphysik, Garching bei Munchen, W. Germany. He joined the Honeywell Corporate Research Center, Bloomington, MN, in 1968, where he has worked in.the areas of electronic flash tubes, gas-filled uv detectors, mass spectrometry of ions formed at high pressure, and recently in the theory and application of open resonators. He is the author of 19 papers and holds four patents. Dr. Erickson is a member of the American Physical Society and the Society of Harvard Engineers and Scientists.

Denis C. Webb (”72) was born in Skowhegan, MA, o n May 12, 1938. He received a B.S.E. degree in engineering physics in 1960, and an M.S. in physics in 1961 from the University of Michigan. From 1961 through 1966, he was employed by the Westinghouse Defense and Space Center in Baltimore, Maryland where he conducted research and development on microwave propagation structures and on YIG magnetostatic wave devices. From 1966 t o 1971 he attended Stanford University, receiving a Ph.D. in applied physics in 1971. His thesis work at Stanford involved development of a scanned acoustical microscope. Following his graduation, he worked at the Physical Electronics YIG tuned Gunn Laboratories in Menlo Park, California, developing oscillators. In 1972 Dr. Webb joined the Microwave Acoustics Group at the Naval Research Laboratory in Washington, DC. His current work is devoted to research and development of acoustic and magnetostatic surface wave devices for signal processing. Dr. Webb is a member of Tau BetaPi.

Yukio Kagawa (SM’75), for a photograph and biography please see page 280 of the July 1976 issue of ~ ~ ~ ~ T R A N S A C T ~ ~ S .

Tatsuo Yamabuchi (S’65-M’67), for a photograph and biographyplease see page 281 of the July 1976 issue of this TRANSACTIONS.

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