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Dec 1986

Volume 80, Issue S1, pp. S1-S128

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back to top Session A. Architectural Acoustics I and Musical Acoustics I: Acoustical Evaluation of Halls for the Performing Arts, Part 1
Invited Papers
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Segerstrom Hall—A review of concept, design process, and results (A)

A. Harold Marshall

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S1-S1 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The recently opened Segerstrom Hall in Orange County, California is a 3000‐seat directed reflection sequence (DRS) hall that responds in a unique asymmetrical way to the competing demands for theater and symphony. This paper reviews the origins of this concept, the design process by which it was realized, and the model study at 1:10 scale carried out in New Zealand. Comparisons between modeled results and final results in the hall will be presented.
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Segerstrom Hall—Evaluation of measurements and design details (A)

Jerald R. Hyde

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S2-S2 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The design of a large multipurpose performing space contrasts the well‐known criteria of theater against the acoustical requirements for symphony and other presentations. With a fan shape of extreme width the only solution for 3000 seats, unique yet workable design solutions are required. The criteria for all uses can push against each other in ways which derive opportunities out of what first might be seen as obstacles. Segerstrom Hall is presented as an example of this creative process. The objective measurement results including early decay time (EDT), sound strength versus position, lateral energy fractions, and early‐to‐late energy ratios will be discussed as they relate to model study results and finally to the subjective experience of the hall itself. Details will be given of test procedures, performance mode variations of the shell and reflector design, and the acoustical curtain system.
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The rest of the Orange County Performing Arts Center (A)

Dennis A. Paoletti

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S2-S2 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Considerable attention has been devoted in recent years at various technical meetings, including the 112th ASA Meeting, to the room acoustics design of the main theater of the Orange County Performing Arts Center in Costa Mesa, CA. In addition to the 3000‐seat multi‐use hall, there are four rehearsal spaces and numerous support facilities. This complex project has required a very large and thorough consulting effort in terms of sound isolation and mechanical‐systems noise and vibration control in addition to room acoustics design. This paper will discuss the overall building complex, details of specific support facilities, and many interesting aspects of the consulting process that have made this project unique.
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Design criteria for acoustical excellence of auditoriums (A)

Paul S. Veneklasen

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S2-S2 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Based on a 25‐year series of highly successful auditoriums, for which the designs drew upon a long background of musical participation and acoustical laboratory research, a summary of guidelines and quantitative achievement criteria is presented. In this paper acoustical factors are extracted from total functional requirements while recognizing that there is extensive interplay. Features are concerned with performers as well as audience. The role of laboratory modeling is stressed. The guidance role of auditorium synthesis over the years is also stressed. Adequate full‐scale verification is compared with current rating schemes.
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Critique of certain concert‐hall design criteria (A)

A. H. Benade

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S2-S2 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Current concert‐hall designs are often seriously unsatisfactory for performers and musically experienced listeners, who tend to pay more attention to the music itself than to the “ambiance” of a hall. Formal experiments dovetail with practical experience to support the idea that the auditory system uses early reflections to compile information on tone, pitch, spatial, and temporal location (as well as loudness) via an extension of the precedence effect. This suggests that the “early reflection” criteria with 60 < t < 80 ms, which were originally proposed before Haas, should be based on t < 30 ms for at least a handful of early reflections to assure a good sampling of (among other things) the radiation patterns of the instruments. Data abound showing poor instrumental recognition when stimuli are recorded under anechoic conditions that give the listener only what the instrument happens to radiate in the direction of the microphone. However, source/listener motions and/or a few close‐in reflectors (with or without instrumental onsets and decays) restore recognizability to recorded sounds. This is consistent with experiments that compare perception of carphone‐presented stimuli with those arising from the statistical sound field of a room. Outlines of such experiments and of practical examples will illustrate and support the views described, and suggest the insecure basis of hall designs guided by undefined “listener preference” data obtained with variously processed versions of music recorded in an anechoic chamber. [Work supported by NSF.]
back to top Session B. Biological Response to Vibration I and Physical Acoustics I: Physical Mechanisms of Biological Effects of Sound and Vibration, Part 1
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Effects of acoustic cavitation under diagnostically relevant conditions (A)

Edwin L. Carstensen

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S3-S3 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Under appropriate conditions, ultrasound is able to produce profound biological effects through its action on microscopic gas bodies in tissues. Clear examples have been found in lower organisms. To determine what this means for mammals will require a better understanding of the basic physical processes and more information about the existence of appropriate gaseous nuclei in mammalian tissues. From the limited information available at the present time, it appears that ultrasound has two qualitatively different modes of action on these bubbles. (1) Continuous wave exposures excited repetitive oscillations of the bubbles and the restraining tissue structures. It appears that this causes intercellular streaming and stresses on the cytoplasmic membrane which may be great enough to cause rupture as well as sublytic effects. (2) Ultrasound applied in very short pulses and at low temporal average intensities produces effects which have the characteristics of transient cavitation. In this case, the gas bodies expand and collapse violently producing mechanical shocks and chemical products of the extremely high temperatures in the compressed phase of the transient cavity. Although it is essential that nuclei of appropriate size be present for transient events to occur, the phenomenon of resonance which is characteristic of stable cavitation is not evident with short isolated pulses. If there are effects of cavitation in mammalian tissues under the low temporal average intensity exposures used in diagnosis, it most probably will come from the latter mechanism. Up to the present time very little effort has been directed to the study of transient cavitation under conditions which may exist within the body.
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Bubble formation in tissues and agar gels during ultrasonic irradiation (A)

Stephen Daniels, Lawrence A. Crum, and Gail R. ter Haar

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S3-S3 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Ultrasound irradiation, used in either continuous or pulsed mode, at a frequency of 0.75 MHz and spatial‐temporal average intensities between 60 and 1000 mW/cm2, has been shown to produce stable gas bubbles in the tissues of experimental animals [S. Daniels and G. R. ter Haar, Proc. Inst. Acoust. 8, 147–154 (1986); G. R. ter Haar, S. Daniels, and K. Morton, IEEE Trans. UFFC‐33, 162–164 (1986)]. Macroscopically visible bubbles are also produced in agar gels during irradiation with ultrasound at the same frequencies and intensities used with experimental animals. The effect on the number of bubbles formed of varying ultrasonic frequency, intensity, pulse length, and duty cycle as well as ambient temperature is similar in the gels to that in animals. Many of the aspects of bubble formation in gels have been explained in a qualitative manner by a theoretical model based on growth of a cavitation nucleus by rectified diffusion. This may provide a useful theoretical basis for the explanation of bubble formation in vivo. [Work supported by MRC (UK), NSF, ONR, NIH, and CRC/MRC Joint Committee program support for the Physics Department, Institute of Cancer Research.]
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In vitro single and multicell bioeffects studies (A)

Morton W. Miller

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S3-S3 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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There have been two broad categories of in vitro bioeffects studies in relation to exposure to ultrasound, postulate testing, and empirical data gathering. Both approaches have led to results, for nonthermal exposure conditions, which are generally consistent with a mechanism involving acoustic cavitation. In general, it is thought to occur in the extracellular fluid, but some evidence is available which suggests an intracellular cavitational mechanism. This postulate needs testing. A large effort has been expended to ascertain whether ultrasound induces sister chromatid exchanges since there are a small number of reported positive effects. None of the reports has been independently confirmed, and attempts at independent confirmation have been negative. [Research supported by PHS.]
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The biological significance of ultrasonically induced cavitation (A)

Mary Dyson, Lawrence A. Crum, and Alan Mortimer

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S4-S4 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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There is now considerable evidence that levels of ultrasound employed clinically can produce cavitation in vitro and, in certain circumstances, in vivo. Transient and prolonged cavitation is potentially damaging, destroying cells locally and inducing chemical changes through free radical production. Although not necessarily lethal, the effects of free radical activity may modify cell activity, particularly if chemical changes are produced in the components of the cell membranes. In contrast, acoustic cavitation of the stable type can have effects which may be of advantage when ultrasound is used as a therapeutic agent, although their production should be avoided in embryonic and fetal tissue; these effects include the enhancement of protein synthesis and cell motility, and could result in the stimulation of repair phenomena by ultrasound. The conditions under which cavitation occurs must be determined so that it can be avoided where advisable and employed where appropriate. [Work supported in part by the Medical Research Council and, through grants to Lawrence A. Crum, by the National Institutes of Health, National Science Foundation and the Office of Naval Research.]
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Ultrasonically induced cavitation in mammals (A)

Leon A. Frizzell and Chong S. Lee

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S4-S4 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The role of cavitation in the production of biological effects in mammals is reviewed with emphasis on recent studies in the mouse neonate. The levels for hind limb paralysis from 1 MHz, continuous wave unfocused ultrasound in the neonatal mouse, within 24 h of birth, have been investigated at 1 and 16 bars ambient pressure and temperature between 10° and 37°C. Above certain intensity levels the exposure duration for paralysis of 50% of specimens exposed increases with increased ambient pressure. Since an increased ambient pressure tends to suppress cavitation, such changes suggest cavitational involvement. Results show that cavitation may be involved in the resultant paralysis above approximately 150 W/cm2 at 10°C, and above approximately 60 W/cm2 at 37°C. This temperature dependence is consistent with a cavitation mechanism. [Work supported by National Institutes of Health.]
Contributed Papers
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Doppler ultrasound pulses can induce SCE In human lymphocytes in vitro (A)

Stanley B. Barnett and Sandra M. Barnstable

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S4-S4 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Human lymphocytes were exposed to an ultrasound pulsing regimen similar to that typically employed in clinical Doppler measurements of fetal blood flow, to determine whether such pulses were able to alter the frequency of sister chromatid exchanges (SCE). A 3.1‐MHz, 1.5‐cm‐diam transducer emitted 5‐ to 50‐cycle pulses in a beam that was directed vertically along the axis of a stationary tube containing the blood suspension. Hydrophone measurements within the tube showed that the beam intensity profile was maintained beyond the free field focal region, thereby ensuring maximum exposure of the contents of the tube. A significant increase in SCE frequency was observed in blood from two random donors exposed to “diagnostic” levels of ultrasound, where the SPTA intensity ranged from 1 to 4 W/cm2. However, a number of further studies on blood from a single (different) donor have failed to show any effect from ultrasound even after an exposure dwell time of 24 h. This extraordinary finding may have some relevance towards explaining some of the controversial reports of SCE induction in human lymphocytes. Research continues to try to identify the mechanisms responsible for this effect.
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The nature of Korotkoff signals (A)

J. E. West, S. Blank, F. B. Muller, B. Cody, G. Harshfield, J. H. Laragh, and T. G. Pickering

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S4-S4 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Analysis of Korotkoff signals (i.e., those signals generated during standard blood pressure measurements) detected under a sphygmomanometer cuff by a foil electret sensor with a frequency range extending below 0.1 Hz reveals three distinct components, K1, K2, and K3. K1 is present above systolic pressure; K2 appears at systolic and vanishes at diastolic pressure; K3 appears between systolic and diastolic pressure and continues to be present below diastolic pressure. K1 and K3 resemble the intra‐arterial pressure waveform. When K3 is calibrated according to the pulse pressure, noninvasive d(K3)/dt determinations correlated well with intra‐arterial dp/dt measurements. Intra‐arterial pressure recordings made with a solid‐state catheter‐tipped manometer distal to the cuff revealed K2 and K3 components. Comparisons of blood pressures derived from K2 with those obtained by the auscultatory (standard) method on 9 normal and 42 hypertensive subjects gave good agreement with minor systematic deviations for both systolic and diastolic values. Estimates of blood pressure using K2 were, however, closer to the intra‐arterial pressure than those obtained with the auscultatory method.
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Measurement of the nonlinear parameter of mixtures to test Apfel's tissue composition model (A)

Erich Carr Everbach and Robert E. Apfel

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S4-S5 (1986); (2 pages)

Online Publication Date: 13 Aug 2005

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Recently a methodology was proposed for predicting tissue composition (percent water, protein, and fat) from measurements of density, sound velocity, and acoustic nonlinearity parameter [R. E. Apfel, J. Acoust. Soc. Am. 79, 148–152 (1986)]. Comparisons of predictions with the measurements of others and with data from handbooks have been encouraging, but a more systematic comparison between theory and experiment was called for. We have established a facility for measuring accurately the sound velocity and nonlinear parameter of liquids and semiliquid substances and we are applying it to the measurement of mixtures in order to test the validity of our composition‐predicting methodology. Eventually we will apply our measurement approach to tissues. Progress on experiment and theory will be presented. [Work supported in part by the Office of Naval Research and by the National Institutes of Health.]
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Response of polymorphonuclear leucocytes (PMNs) to vibration at kilohertz frequencies (A)

W. L. Nyborg, W. L. Beeken, and I. C. Northwood

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S5-S5 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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It has been shown that stable volume oscillations of bubbles in a suspension of biological cells can cause significant change in the cells via small‐scale manifestations of acoustic streaming, radiation force, and radiation torque. These aspects of the acoustic field are simulated, approximately, near small solid objects set into translatory vibration. Except for scale, the phenomena which have been observed at megahertz frequencies are similar to those seen at lower frequencies. In the experiments reported here suspensions of human PMNs, contained in glass capillaries, were exposed to transversely vibrating wires or strips, at frequencies of a few kilohertz, while under view through an optical microscope. As a measure of the potential of the vibrator for producing cellular change, calculations were made of the viscous stress associated with acoustic streaming near the vibrating surface. Among other findings, an increase of cell stickiness was observed at stress levels less than 1 Pa, as were changes of morphology revealed by electron microscopy. Considerable cell destruction occurred at stress levels exceeding 5–10 Pa. [Work supported in part by the NIH.]
back to top Session C: Engineering Acoustics I: Transducer Models
Invited Papers
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Numerical models used in transducer design (A)

Robert E. Montgomery, Clementina M. Ruggiero, and Theodore A. Henriquez

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S5-S5 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Numerical methods currently used to design transducers will be reviewed. The applicability, advantages, and disadvantages of each method will be discussed. Two methods, finite elements and a method for computing acoustic radiation, will be discussed in detail. These two methods will be illustrated by application to a piezoelectric Helmholtz resonator. Computed performance values such as transmitting voltage response, electrical admittance, and normal modes of vibration will be presented and compared to measured values. The presentation will conclude with an overview of needs and future plans.
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Innovative underwater sound transducer designs and their analysis by use of bond graphs (A)

S. Hanish

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S5-S5 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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An innovative technique in modern underwater sound transducer design is to combine conventional transducers with miniature operational networks so as to achieve advanced receiving and transmitting responses for meeting newest design challenges. Operational amplifiers, field‐effect transistors, and microprocessors are a few of the active or passive networks that can be so mated to underwater projectors and hydrophones. For all such electromechanical devices, the newer approach of analysis based on bond graph procedures will be demonstrated. A few examples will be analyzed in detail with the objective of both illustrating the use and advantages of bond graphs, and of unfolding the numerous possibilities for shaping transducer responses to accommodate a new generation of design demands.
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Bond graph modeling for modal dynamics of interacting lumped and distributed systems (A)

Donald L. Margolis

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S5-S6 (1986); (2 pages)

Online Publication Date: 13 Aug 2005

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In many practical engineering systems, it is important to understand the physics of interacting subsystems, some of which lend themselves to lumped representations while others are inherently distributed. The noise and vibration caused by the engine of an automobile is a good example. The engine, the source of the vibrational and acoustical energy, is a lumped system for typical operating speed. However, the engine sits atop the vehicle frame structure, which exhibits modal dynamics. Ultimately, the vibrational energy finds its way to surfaces that radiate acoustic energy to the surroundings. If one were to model this overall system, lumped and distributed dynamic effects would have to be included. Bond graphs are a concise pictorial representation of the energy storage, exchange, and dissipation mechanisms of dynamic engineering systems [R. C. Rosenberg and D.C. Karnopp, Introduction to Physical System Dynamics (McGraw‐Hill, New York, 1983)]. Considerable work has been done in developing bond graph methods for the modal dynamics of distributed systems [D. L. Margolis, “Bond graphs, normal modes, and vehicular structures,” Veh. Syst. Dynam. 7 (1) (1978) and D. L. Margolis, “A survey of bond graph modeling for interacting lumped and distributed systems,” J. Frankin Inst. 319 (1/2) (Jan. 1985)]. The virtues of bond graph modeling are many and space is short; however, once a bond graph model has been constructed, then physical state variables are dictated, and the system can be automatically simulated using a digital computer. This applies to nonlinear as well as linear systems except that the distributed aspects of the overall system must be linear. The paper will develop bond graph modeling for lumped and distributed systems, and the procedure will be demonstrated for realistic systems.
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Waves‐scatter bond graphs for electroacoustic systems (A)

Henry M. Paynter and Ilene J. Busch‐Vishniac

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S6-S6 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Electroacoustics was born as a twin to the telephone 110 years ago. Today electroacoustic transduction involves a sophisticated science and technology. Early in this evolution alternating currents and electrical oscillations were compared to the better‐understood mechanical vibrations, but electro‐technology advanced so rapidly that mechanical systems were soon treated conversely by analogous electrical circuits. Yet because a strict correspondence does not exist at the microscopic and continuum levels, several alternative analogies emerged so that now engineers confront a lack of uniform methodology, particularly when dealing with distributed transducers. Bond graphs were developed to meet just such needs by treating all physical systems as a set of multiport elements richly interconnected by another set of power bonds, which together enforce continuity‐conservation laws for mass, momentum, charge, and energies. Furthermore, to provide self‐consistent signal causality and detailed balances of power dissipation and entropy production, scattering variables can be employed at all ports, and wave variables on all bonds. Such characteristic variables and their methods of use were first introduced by Bernhard Riemann in 1860 for finite amplitude sound waves and later reintroduced in the 1940s for microwave circuitry. Some applications are given of this powerful approach to practical electroacoustical devices and systems.
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Generic models of spatially distributed sensors and actuators (A)

Ilene J. Busch‐Vishniac

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S6-S6 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Traditional models of sensors and actuators typically represent the transducer by a series of interconnected, discrete, lumped elements. Such models are useful because the characteristic behavior of the transducer is described by ordinary differential equations. However, these models are limited to low‐frequency regimes because they contain a finite number of elements. Further, they are not easily adaptable to transducers in which the behavior is explicitly a consequence of the continuum nature of transducing element, such as acoustic horns. Presented here are generic models of transducers in which the continuous nature of the transducer is stressed. The models may be classed into two types: those which apply to transducers in which the coupling between locations occurs only through the input and output ports, and those in which there is mechanical coupling between transducer locations as well. The former case may be modeled using coupled two‐port theory, and the latter using augmented transmission lines. These techniques allow for spatially varying physical parameters, and apply regardless of the transducer type, function, and geometry.
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Analysis of multiply coupled, multimode sonar transducer arrays (A)

Stephen C. Thompson and Michael P. Johnson

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S6-S6 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Sonar transducer element and array performance predictions using linear analysis methods have been usefully performed for over two decades. These analyses were first performed for single degree of freedom (DOF) piston transducers including only the acoustical coupling through the radiating medium. More recently, single DOF transducers including both acoustical and mechanical coupling through their common mounting surface have been analyzed [D. T. Porter, J. Acoust. Soc. Am. Suppl. 1 78, S73 (1985)]. However, many of the transducer types currently under consideration for use in sonar arrays are multiple DOF systems having two or more resonant modes of significance within their operating frequency band. Flextensional and flexural mode transducers, as well as several types of multimode or multiply resonant piston transducer structures, are examples of multiple DOF elements. A general method for the analysis of multiply coupled, multiple DOF transducer arrays will be presented. The equations describing the general case have the same form as those used previously. As a consequence, many of the lessons learned from experience on arrays of single DOF elements can be extended in a straightforward manner. As an example, the concept of velocity control will be explored in different examples of multimode arrays. It will be shown that velocity control can be achieved in only a special class of multimode transducer elements—those having as many control ports (i.e., electrical) as there are structural modes.
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Modeling and design of transducers for electromagnetic generation of acoustics (EMAT) incorporating permeable structures (A)

W. Imaino

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S7-S7 (1986); (1 page) | Cited 1 time

Online Publication Date: 13 Aug 2005

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As a possible means for increasing the electrical to acoustical conversion efficiency as well as enhancing the spatial resolution, we have investigated the performance characteristics of transducers for electromagnetic generation of acoustics (EMATs) that incorporate permeable magnetic structures (permeable EMAT). Since the intent of this investigation is to develop high spatial resolution EMATs for noncontact scanning applications, what we term EMAT microscopy, the basic design guidelines differ somewhat from those employed in the design of more conventional EMATs, as used in pulse‐echo applications, for example. A computer program has been developed, to calculate the magnetic fields, induced currents, and generated forces, of arbitrary candidate designs, taking into strict account the stray fields due to the induced currents in the structure itself, and the anisotropic polarization of the permeable structure. The results of our calculation on even very simple structures show that an enhancement of the electrical to acoustic conversion efficiency and spatial resolution can be achieved, although at the expense of operating bandwidth.
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A fiber‐optic interferometric geophone (A)

D. L. Gardner, Y. Yarber, E. F. Carome, and S. L. Garrett

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S7-S7 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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A fiber‐optic interferometric geophone has been developed which consists of a seismic mass (520 g) supported by two rubber mandrels wound with a single layer of single mode optical fiber. The two mandrel‐wound lengths of optical fiber, each 6.5 m long with reflecting ends, are interconnected via a fiber‐to‐fiber 3‐dB coupler to form a Michelson interferometer. When the case of the sensor is displaced at frequencies above the mass‐spring resonance frequency (i.e., in the mass‐controlled frequency regime), the mass remains approximately at rest while the fiber around one mandrel is compressed and the other is expanded. This geometry has the advantage of not requiring a “reference leg” and providing four times the sensitivity of a single sensor by its “push‐pull” operation and the fact that the light traverses each leg twice due to reflection. Sensitivities of 3500 rad/μ have been measured at frequencies above the mass‐spring resonance, corresponding to an optical leverage factor of 700. [Work supported by the Naval Research Laboratory and the Office of Naval Research.]
back to top Session D. Noise I: Aircraft Noise
Contributed Papers
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On the noise generated in the tip region of airfoils (A)

S. A. McInerny, W. C. Meecham, and P. T. Soderman

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S7-S7 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The generation of noise by turbulence in the tip region of a blunt‐tipped, lifting airfoil was studied. Data were collected on surface and farfield sound pressures in the NASA Ames 2.13 × 3.05 m (7 × 10 ft), subsonic wind tunnel using an NACA 0012 wing section of aspect ratio 2.67, at an angle of attack of 16 deg. The contributions of particular source regions were determined using cross‐correlation techniques on surface and farfield sound pressures. Clipping the recorded signals prior to correlation allowed the isolation of radiated sound levels up to 25 dB below the tunnel background levels within a reasonable record length. The results indicate that in the case of blunt‐tipped airfoils there is a significant noise source in addition to the separated flow under the tip vortex (on the upper wing surface) predicted by other investigators. The characteristics of these two sources of noise are presented and comparison made with existing theories and prediction schemes. [Work supported by NASA Ames Research Center.]
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Airfoil noise in uniform airflow (A)

P. Garcia

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S7-S8 (1986); (2 pages)

Online Publication Date: 13 Aug 2005

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An experimental investigation of the NACA 0012 airfoil noise in uniform flow has been conducted in the anechoic open flow facility CEPRA 19. The purpose is to estimate the trailing edge noise, using the theoretical models developed by Chandiramani [J. Acoust. Soc. Am. 56, 19–29 (1974)] and Howe [BBN Report No. 3679 (1977)]. These models require the knowledge of the spectral content of the turbulent‐boundary‐layer‐induced pressure field, in the vicinity of the trailing edge. The data are obtained from longitudinal and transversal arrays of flush‐mounted pressure sensors, on the airfoil. A simplified theoretical noise prediction is based on the measurement of the turbulent boundary layer pressure spectrum, the convection velocity, and the turbulence transversal integral scale. The comparison between the radiated noise measurement and the simplified prediction is reasonable in the high‐frequency range only. A more general approach allows the prediction of the airfoil‐radiated noise, in the whole frequency domain, and for low frequencies particularly. This general prediction formulation requires the pressure field wavenumber spectrum, induced by the turbulent boundary layer. This wavenumber spectrum is obtained from the transducer array, in contrast with Brook and Hodgson's reconstruction scheme [AIAA Paper No. 80‐0977]. This approach yields a good estimate of the farfield noise. [Work supported by DRET (Direction des Recherches et Études Techniques).]
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Scale model investigation of propeller induced pressures on a fuselage (A)

Werner G. Richarz

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S8-S8 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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In order to optimize sound transmission loss into the interior of an aircraft cabin, the incident pressure field must be known. Heretofore, only rms pressures were considered. It is well known that coupling with flexural waves can occur under certain conditions; thus the phase velocity of the sound field is required. For typical propeller installations, the sound field on an aircraft fuselage is governed by the nearfield of the propeller and the diffracted field. Before the sound reaches the fuselage, it must also propagate through a refracting boundary layer. In order to obtain some insight into this complex problem, a series of scale model tests have been conducted with a 7‐inch propeller placed near a circular fuselage of comparable diameter. The fuselage was instrumented with ten flush‐mounted microphones and could be rotated about its axis of symmetry. The rms pressures and phase velocities are measured at several blade passage frequencies and under simulated flight conditions typical of takeoff, climb, and cruise. The resultant pressure and phase contours are compared with relevant analytical models. [Work supported by the Natural Sciences and Engineering Research Council of Canada.]
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