bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of the sound field fluctuations in the presence of internal waves due to adiabatic mechanism of interaction
Authors: Katsnelson Boris , Badiey Mohsen , Tckhoidze Alexander
Published: September 2012

In the presence of moving nonlinear internal waves character of interaction between sound field and internal waves depends on angle between direction of an acoustic track and wave front of internal waves (mode coupling, horizontal refraction or adiabatic regime) [JASA, vol. (122), pp. 747-760, 2007]. In particular, if this angle is about 15-20 degrees there should be adiabatic mechanism. Adiabatic regime of propagation means that variations of the sound field follow variations of the sound speed profile. In this paper similar situation is considered when wave front of the train of internal waves crosses the acoustic track at the angle about 15 degrees. Theoretical modeling shows specific features of adiabatic fluctuations: variations of shape of waveguide modes, fluctuations of amplitudes (excitation coefficients) of the corresponding modes and phase fluctuations. These fluctuations can be separated in time on dependence on position of the train. Results of modeling are compared with experimental data [shown in accompanying paper, Badiey et al.] and are in good agreement. This work was supported by ONR and RFBR.
Acoustic frequency shifts due to internal tides and nonlinear internal waves
Authors: Turgut Altan , Mignerey Peter C.
Published: September 2012

Significant frequency shifts of acoustic intensity level curves in broadband signal spectrograms were measured in the East China Sea during the summer of 2008. Broadband pulses at 270-330 Hz were transmitted from a fixed source and received at a bottomed horizontal array, located at 33 km range. The acoustic intensity level curves of the received signals indicate regular frequency shifts that are well correlated with the measured internal tides and nonlinear internal waves. Regular frequency shifts due to nonlinear internal waves are observed only when their wave-fronts are nearly parallel to the acoustic propagation path, causing an effective change in the sound speed profile. Similar effects were observed in 3-D numerical simulation results when curved nonlinear internal wave fronts are used. These observations and simulations indicate the potential of monitoring internal tides and nonlinear internal waves using low-frequency acoustic signals when the acoustic source and receiver are strategically placed. [Work supported by the Office of Naval Research.]
Case studies of a method to integrate architectural acoustic and sound systems design
Authors: Siebein Gary W. , Paek Hyun
Published: September 2012

A method to evaluate the integrated architectural acoustic and reinforced sound systems for medium to large size worship and performance spaces using computer modeling of the systems for new facilities and diagnostic impulse response based measurements in existing rooms is presented. Four case studies of varying degrees of design integration of architectural acoustic and sound systems are presented to illustrate the method. Case study 1 is a divisible multi-purpose worship space. The sound system equipment and design was done without considering the acoustical design of the room. It was decided to re-use the existing equipment and adjust the aiming and programming of the system to fit the acoustics and architecture of the room to optimize the balance of natural and reinforced sounds. The second case study covers the design of a theater with a distributed array system to reinforce theatrical and musical sounds on stage. The third case study covers the installation of a new sound system in a large worship space with an organ and a very long reverberation time. The fourth case study covers the diagnostics, architectural and sound system improvements in a unique space for symposia on a college campus.
Naturally you need a sound system
Authors: Dixson Rogers
Published: September 2012

Ignoring Room Acoustics in Audio System design can be just as problematic as ignoring the audio system in designing the acoustics of a space. Contrary to marketing claims by product manufacturers on either side of the design “aisle,” neither system can overcome all of the shortcomings imposed by the poor design of the other. Both elements have to be designed in coordination with each other (as well as in coordination with other systems in the built environment). This can become particularly challenging in multipurpose performance and presentation spaces as there can be multiple audio systems installed in the same space. Sound Reinforcement, Program Playback (particularly multi-channel surround sound) systems are increasingly being installed in performing arts facilities where natural acoustics is a critical element. How these aspects should (and can) be coordinated is discussed in this paper.
Seamless integration of audio visual design into architecture for more successful projects
Authors: Doggett Felicia
Published: September 2012

The integration of audio visual systems into technology-enabled buildings has long been a struggle with the architectural community. In some instances, architects do not want any part of the systems to be visible within the space, like speakers, projectors and equipment racks. In other cases, like digital signage and way-finding technology, the systems are front and center in the room and must be as visible and as user-accessible as possible. Audio visual technology is present in some form in almost every building being constructed today including educational, corporate, houses of worship, legislative, hospitality, sports arenas, healthcare, museums, and retail. Much time is spent not just on the system design, but working with architects on integrating the technology into these built environments, each of which has its own requirements. This presentation focuses on various ways to integrate audio visual technology into buildings for more seamless and successful projects. Balancing the functionality and performance of any audio visual system installation with the aesthetic impact on the space takes experience, creativeness, and a willingness to coordinate with the design team.
Sight and sound: Visual aesthetics of loudspeakers
Authors: Bridgewater Ben , Coffeen Bob , Long Jim
Published: September 2012

Loudspeakers are not only heard but often seen. A sound system’s loudspeakers must be designed to meet the visual expectations of the architect, performers, and owners. A good designer can meet the audio requirements while not offending the architecture of the space. A case study of hidden, obvious, and ugly loudspeakers will be presented.
Soundscape of the North-Eastern Chukchi Sea
Authors: Martin Bruce , Delarue Julien , Hannay David
Published: September 2012

The Chukchi Sea is a dynamic environment that cycles each year from open seas in summer to 100% ice cover in winter. The ice and sea conditions lead to a highly variable acoustic background. In summer the soundscape’s backdrop are wind and wave sounds typical of shallow seas. In the winter, grinding ice sheets can create a cacophony of unusual sounds, some of which can easily be mistaken as being biological in origin. During ice formation and break-up sound levels can increase significantly due to combinations of wind and waves and ice floe collisions. Several marine mammal species move through this environment and their calls sometimes dominate the soundscape. Bearded seals are year-round residents whose calls overwhelm the soundscape in the spring during their mating season. Walrus follow the ice edge and fill their neighbourhoods with grunts, moans and knocks. Seasonal migrants such as bowhead and beluga whales are heard passing through in spring and fall. Summer visitors such as fin, killer, minke and gray whales add to the voices of this environment. Anthropogenic sounds mix into the soundscape during the open water season and are concentrated along the coast lines and in areas of interest for oil and gas exploration. This presentation will provide examples of all these sounds and will show spatial-temporal maps of the sounds distributions based on data from the Chukchi autonomous recording array operated by the Joint Studies Program since 2007.
Seals and sound in a changing Arctic: Ongoing psychoacoustic studies of spotted and ringed seals
Authors: Vitacco Jillian , Reichmuth Colleen , Ghoul Asila , Southall Brandon
Published: September 2012

Arctic environments are changing rapidly as a result of climate warming and industrialization, and as sea ice recedes, activity associated with transportation and oil and gas production increases. Among the many concerns for ice-living seals in the region is the potential for behavioral or auditory effects resulting from noise exposure. Currently there are limited data available concerning the hearing sensitivity of arctic seals - some data exist for harp and ringed seals, while the most comprehensive data are for harbor seals. As the phylogenetic relationships among northern seals are not well resolved, extrapolation across species for management purposes is difficult. To this end, we are working to describe the species-typical hearing of spotted (Phoca largha) and ringed seals (Pusa hispida). Thus far, measurements of the underwater hearing sensitivity of spotted seals show best sensitivity between 3.2–25.6 kHz and peak sensitivity of 51 dB re 1 μPa at 25.6 kHz. Absolute thresholds for airborne tonal signals indicate acute sensitivity of <10 dB re 20 μPa from 0.80–12.8 kHz. Audiometric testing for ringed seals is ongoing, as are critical ratio measurements for both species. These studies will provide valuable insight into how arctic seals perceive acoustic signals, as well as inform management practices for these vulnerable species.
Simultaneous sound production in the bowhead whale Balaena mysticetus—Sexual selection and song complexity
Authors: Tervo Outi M. , Miller Lee A. , Christoffersen Mads F.
Published: September 2012

Different components of bowhead whale Balaena mysticetus song were localized using hydrophone arrays. In 2008 recordings were made using two hydrophones spaced 20–35 m apart. In 2009 a linear GPS synchronized array of four hydrophones with an aperture of ~1400 m was used. The localization results confirm the co-location of the sound sources. The analyses show amplitude modulation of one signal caused by the onset of the second signal, which provides additional evidence of simultaneous sound production. Sound, when used as an indicator of fitness forces the vocalizing animal to improve the quality of its signal to compete with other vocalizing conspecifics. Several methods can be used to improve signal quality and these include 1) large repertoire size, 2) annually/seasonally changing repertoire, 3) broad frequency band, and 4) simultaneous sound production. Bowhead whales show all these features in their acoustic behaviour and we suggest that these complex songs have evolved as the result of sexual selection. Song complexity has been shown to be of importance in the sexual selection of many song bird species implying that sound complexity may be a key factor in the sexual behaviour of bowhead whales.
Acoustic monitoring of belugas (Delphinapterus leucas) in the eastern Chukchi Sea
Authors: Garland Ellen C. , Berchok Catherine , Castellote Manuel
Published: September 2012

Beluga whales (Delphinapterus leucas) are highly vocal animals which make them ideal candidates for passive acoustic monitoring. Alaskan belugas overwinter in the Bering Sea, and in spring, two subpopulations migrate to their predictable summering grounds in the eastern Chukchi and eastern Beaufort Seas. In autumn, these subpopulations complete their annual migration by returning south to the Bering Sea. Additional information is required on the timing and migration routes in spring and autumn to assist in detecting these subpopulations as they transit between the two regions. Preliminary results are presented on the temporal distribution of Alaskan beluga based on acoustic detection (September 2010 to May 2011) from a passive acoustic recorder located 30 miles off Icy Cape, AK, in the eastern Chukchi Sea. Belugas were sporadically detected in autumn from mid-September to the start of December, with a peak in detections in late November. In spring, belugas were detected from mid-April to the end of May, with peaks in early and late May. Within each temporal peak in vocal activity we will investigate the common call types to assist in differentiating migratory streams, and potentially identify each subpopulation as they transit through this inshore area. [Work supported by the National Research Council and Bureau of Ocean Energy Management.]
Pacific walrus vocal repertoire in the northeastern Chukchi Sea: Call type description and relative proportion in time and space
Authors: Mouy Xavier , Delarue Julien , Martin Bruce , Hannay David
Published: September 2012

Pacific walrus are present in the northeastern Chukchi Sea (NCS) from June to October. The study of their sounds has been largely restricted to the knock and bell sounds produced by males during the breeding season and in-air grunts and barks from mother and pups. A passive acoustic monitoring program conducted in the NCS since July 2006 has brought strong evidence that the underwater vocal repertoire of walrus is more diverse. Nine call types (including knocks and bells) and their variants identified over four years of acoustic monitoring will be described. Spectral measurements along with estimates of variability for high signal-to-noise ratio calls will be provided. The relative proportion of each call type across the study area and throughout the season is currently analyzed based on the identification of all calls in samples recorded multiple times per day in 2009 and 2010. Preliminary results suggest that the vocal repertoire of walrus is dominated by grunt-type calls, which is consistent with the NCS herds being mainly composed of females, pups and juveniles. The recurrent presence of knocking sounds indicates that either adult males routinely occur in the study area or that other age and sex classes also produce this call type.
Acoustic focusing flow cytometry
Authors: Kaduchak Gregory , Goddard Gregory R. , Ward Michael D.
Published: September 2012

Acoustic cytometry is a new technology that replaces or partly replaces hydrodynamic focusing of cells or particles in flow cytometry with forces derived from acoustic radiation pressure. The ability to focus cells into a tight line without relying on hydrodynamic forces allows many possibilities outside the scope of conventional flow cytometry. Dilute samples can be processed quickly. Flow velocities can be varied allowing control of particle delivery parameters such as laser interrogation time and volumetric sample input rates. Recently, Life Technologies unveiled a flow cytometer that directs particles into the laser interrogation region using acoustic radiation pressure. In this talk, the application of acoustic cytometry in flow cytometry systems from fundamental principles to details of its implementation will be presented. Data will be shown for both the operational implementation of the acoustic focusing device as well as demonstrating its ability to perform for complex biological assays.
Acoustophoretic cell sorting in microfluidic channels
Authors: Soh Tom H. , Yang Allen
Published: September 2012

In this work, we report the use of ultrasonic acoustophoresis for the label-free separation of viable and non-viable mammalian cells within a microfluidic device. This device exploits the fact that cells that have undergone apoptosis are physically smaller than viable cells, and achieves efficient sorting based on the strong size dependence of acoustic radiation forces in the microchannel. As a model, we have selectively enriched viable MCF-7 breast tumor cells from heterogeneous mixtures of viable and non-viable cells. We found that this mode of separation is gentle on cells, while enabling label-free separation at sample flow-rates of up to 12 mL/hr at a cell density of 106 cells/mL. We have extensively characterized the device and report the effects of piezoelectric voltage and sample flow-rate on device performance, and describe how these parameters can be tuned to optimize recovery, purity or throughput.
Ultrasound standing wave fields for tissue engineering
Authors: Hocking Denise C. , Garvin Kelley A. , Dalecki Diane
Published: September 2012

The spatial organization of cells within native tissues contributes to proper tissue function. Thus, successful engineering of replacement tissues requires methods to control cell location within the engineered tissue. Our studies have focused on utilizing acoustic radiation forces associated with ultrasound standing wave fields (USWF) to rapidly and non-invasively organize cells within 3D collagen gels. We have shown that USWF-induced alignment of fibroblasts into distinct multicellular planar bands increases cell contractility and enhances cell-mediated extracellular matrix reorganization. Additionally, USWF-induced patterning of endothelial cells accelerates the formation of capillary-like sprouts and supports the maturation of sprouts into lumen-containing, vascular networks throughout the volume of the collagen gel. Our recent studies have investigated the influence of various acoustic parameters on the USWF-induced spatial pattern of endothelial cells. The initial density of the USWF-induced cell bands affected both the rate of formation and the morphology of endothelial cell networks, indicating that different USWF-induced endothelial cell patterns can produce morphologically different vascular networks. Design of USWF, by choice of ultrasound frequency or use of multiple transducer geometries, can create more complex cell patterns within hydrogels. Thus, USWF technologies provide a novel approach to pattern large 3D engineered tissues in vitro.
Applications in acoustic manipulation of biological cells in micro-devices
Authors: Ankrett Dyan N. , Glynne-Jones Peter , Hill Martyn
Published: September 2012

Utilizing ultrasonic standing waves in biocompatible micro-fluidic devices, we are able to acoustically manipulate biological cells for a variety of potentially beneficial pharmaceutical, biomedical and environmental applications. Using a device designed to induce sonoporation in the absence of contrast agent micro-bubbles (CA-free sonoporation) we demonstrate both the uptake and efflux of differently sized, membrane impermeable molecules whilst maintaining high cell viability. Crucially we show that the cytotoxic action of several known pharmaceutical agents is significantly increase in porated cells compare with non-porated control cells, suggesting sonoporation-induced facilitated uptake of these agents. We also report on a device that acoustically excites tethered polymer-shelled micro-bubbles to induce micro-streaming around cardiomyocyte membranes in order to mimic myocardial infarction, ischaemia and induction of apoptosis. Initial results from a levitation culture system that continuously perfuses a pellet of ultrasonically suspended chondrocytes are also presented. The pellet geometry allows large numbers of cells to be cultured without developing a necrotic core. Primary chondrocytes and cell lines demonstrated good viability after more than ten days of levitation. Using low power, continuous ultrasonic excitation we have demonstrated significant reductions in biofilm growth in polymer fluid channels potentially increasing the lifespan of in-situ marine sensors.
Acoustic radiation force on a sphere in tissue
Authors: Ilinskii Yurii A. , Zabolotskaya Evgenia A. , Hamilton Mark F.
Published: September 2012

A theory is presented for the acoustic radiation force on a sphere embedded in a soft elastic medium that possesses a shear modulus μ several orders of magnitude smaller than its bulk modulus. Scattering of both compressional and shear waves is taken into account. There is no restriction on the size of the sphere or, apart from axisymmetry, the form of the incident compressional wave. The analysis employs the Piola-Kirchhoff pseudostress tensor and Lagrangian coordinates. In the linear approximation an analytical solution is obtained for the scattered waves. The nonlinear stress and full radiation force are calculated at the next order of approximation. For a small sphere and μ≈0 the classical result for a particle in liquid is recovered. For small but finite shear modulus the radiation force is evaluated for a gas bubble driven at a frequency below resonance. The predicted magnitude of the radiation force on the bubble is found to be less than that in liquid by the factor [1+(4/3)μ/γ P 0]-1, where P 0 is the ambient pressure and γ the ratio of specific heats of the gas. Influence of the scattered shear wave in this limit is negligible. [Work supported by NIH DK070618.]
Dynamic impedance matching for active noise control in a cylindrical waveguide
Authors: Lee Dong Joo , Lee Jae-Wan , Jeon Jae Jin , Seo Young Soo , Ohm Won-Suk
Published: September 2012

In this paper, the feasibility of dynamic impedance matching for noise reduction in a cylindrical waveguide is demonstrated. An active acoustic coating, inserted parallel to the direction of wave propagation, is assumed to dynamically match the acoustic impedance of the incoming wave. The active coating appears as an acoustic branch containing the same fluid, and therefore part of the incoming wave can be diverted to and dissipated in the coating. The performance of the active coating is evaluated using a finite element analysis, where the coating is modeled as a dynamic impedance matching boundary. Simulations reveal that significant reductions in the downstream acoustic pressure can be achieved. Unlike the conventional active techniques that employ phase cancellation, dynamic impedance matching has a number of advantages such as a relatively low power requirement.
On the secondary path of headset active noise cancellation systems
Authors: Xu Buye , Xiao Jinjun , Miller Thomas E. , Wiederholtz Erik , Warren Daniel M. , Zhang Tao
Published: September 2012

Active noise cancellation (ANC) technologies have been successfully applied in headsets to reduce ambient noise in the ear canal. The performance of such a technology depends on the characteristics of the secondary path (SP). In this paper, two different systems are studied: one system utilizes a moving-coil speaker as the secondary source and forms a closed cavity over the ear, while the other one uses a balanced-armature receiver inside the ear canal as the secondary source. The differences in the SP responses of these two systems are investigated both experimentally and theoretically. The implications for designing an effective ANC solution will be discussed based on numerical simulations.
Free-field reciprocity calibration of low-frequency ultrasonic transducers
Authors: Serbyn M. R.
Published: September 2012

Techniques developed for the calibration of electroacoustic transducers provide many practical applications of the principles studied in advanced undergraduate and introductory graduate courses. This communication describes an implementation of the standard method of reciprocity calibration as presented in the popular text, Fundamentals of Acoustics by Kinsler et al. The measurements were performed on inexpensive off-the-shelf transducers designed to operate near 25 kHz and 40 kHz. The anechoic environment consisted of a 2-m3 box lined with absorbing material whose absorption coefficient was measured by the pulse-echo technique. The air density and the speed of sound were calculated using formulas available in the literature. The resulting values of transducer sensitivity (calibration factor) compared well, within 5 -10 %, with the values specified by the vendor. No accuracy statement was available for the transducers under test, not only because of their price, but mainly because no primary calibration services are available in the low ultrasonic range of frequencies, in contrast to the higher, MHz, range. A recent dissertation by N. Bouaoua, discovered in the course of this research, could fill this void should its procedures be adopted by a standards laboratory.
Acoustic supercoupling through a density-near-zero metamaterial channel
Authors: Fleury Romain , Sieck Caleb F. , Haberman Michael R. , Alù Andrea
Published: September 2012

Originally demonstrated with electromagnetic waves, supercoupling describes the extraordinary matched transmission, energy squeezing, and anomalous quasistatic tunneling through narrow channels. This behavior is the result of impedance matching achieved when the effective properties within the channel approach zero. For electromagnetic waves, supercoupling is observed when the electric permittivity in the channel approaches zero. These channels are accordingly known as epsilon-near-zero (ENZ) channels. This work shows that analogous behavior exists in the acoustic domain when the effective density is nearly zero, which can be achieved by tailoring the structure of the channel. Such channels are therefore known as density-near-zero (DNZ) metamaterial channels. Unlike tunneling based on Fabry-Perot resonances, DNZ transmission is independent of channel length and geometry and yields a uniform field along the entire length of the channel. Transmission-line theory is used to describe this peculiar phenomenon and finite element simulations are presented to confirm the unusual transmission properties of the metamaterial channel. It is further shown that acoustic waves may provide a unique possibility of squeezing acoustic energy through arbitrarily small channels in three dimensions, overcoming limitations that arise in the electromagnetic case.
An introduction to the physics of the clarinet for musicians and other non-science majors
Authors: Kausel Wilfried
Published: September 2012

Teaching physics or more generally science related matters to non-science majors requires illustrative comparisons, fascinating application examples, live experiments, multi-medial presentation and simplified representations which can be understood without much background knowledge but which still remain relevant for the taught subject. But first of all, such lectures do require a very dedicated and alert lecturer who is able to captivate his audience by his outstanding presence. Following (some of) these principles a short generally understandable lecture on the acoustics of the clarinet will be given."
The Physics of Music course as an introduction to science
Authors: Ramsey Gordon
Published: September 2012

Our Physics of Music course is an integration of physics and music. We start with the mathematical structure of music, including scales, harmonies and chords. We discuss musical styles and how they differ. After an introduction of physics concepts, including waves, resonances, forces, energy and fluid flow, the physical structure of instruments in the various groups are studied. Connection is made of the instruments and how they reproduce the mathematical nature of music. Finally, venue acoustics are investigated. The course integrates different styles of learning by integrating different learning modes. The classes include lecture/demonstration, discussion, in-class laboratories and a final individual project encompassing many course elements. The constant connection between the physics and the music, along with varied learning techniques, including hands-on experience, provides a motivating approach for non-science majors to experience science in a familiar context.
Acoustics at Berklee College of Music and elsewhere
Authors: Hoover Anthony K.
Published: September 2012

Students in the acoustics class at Berklee College of Music were non-science majors, but the course has done well, spanning over 50 semesters, and a number of those students have continued into graduate school and careers in acoustics. This paper will focus on the design and goals of the class, and will also discuss related experiences of teaching non-scientists in seminars, short courses, courses at other colleges, and the ASA-sponsored Continuing Education short course for architects.
Beats, ratios, and commas: Teaching tuning and temperament to music students
Authors: Carter Stewart , Dostal Jack
Published: September 2012

Undergraduate music students have many preconceived notions about tuning and temperament. For most of them, a piano tuned in equal temperament is perfectly “in tune” and A4 = 440 Hz is the only pitch standard that has ever existed. We find these naïve conceptions about tuning and temperament to be common among our introductory Physics of Music students--music majors, students pursuing majors in the sciences, and other non-science majors. In this paper we describe how we address some of these issues. We teach the mathematical underpinnings of equal, Pythagorean, just, and meantone temperaments, as well as their musical advantages and disadvantages, through the use of live demonstrations and recorded examples. We also describe our future plans to use recorded examples and available local resources—including reproductions of Baroque woodwinds tuned to A4 = 415 Hz and a 1799 organ at A4 = 409 Hz—to give students a broader understanding of historical and modern pitch standards.
Teaching and learning musical acoustics in a "music technology" program
Authors: Maher Robert C.
Published: September 2012

Helping math-averse students to learn musical acoustics can be challenging. Many universities offer a degree program entitled “Music Technology.” While the details of Music Tech programs differ, the general curricular focus includes music theory, electronic and computer music, audio recording and mixing, multimedia production, and computer applications in music composition. Music Tech programs also typically require a “Science of Sound” course that is intended to introduce the physical and mathematical concepts of musical sound and the basic principles of room acoustics. But unlike traditional acoustics students with a physics or engineering background, many students in the music tech programs are unconventional learners who do not tend to have much background in mathematics and the traditional science topics that would be the customary prerequisites for a formal acoustics class. This situation provides an interesting challenge--and a great opportunity--for the instructor to help students learn about acoustics and audio topics while side-stepping the students’ disdain for mathematical formulae. This paper presents one Music Tech lesson example: teaching musical instrument acoustics using a lumped source-filter-coupling model. The learning outcomes are sufficient for the students to understand and implement useful empirical models and simulations.
Measuring brass instruments: A “Physics of Music” lab exercise
Authors: Worland Randy
Published: September 2012

Among the various aspects of brass instruments studied in a Physics of Music class are physical dimensions such as tube length and bore profile. Although textbooks list values for instrument lengths and describe the significance of the cylindrical, conical, and flared sections of tubing, these parameters are not visually obvious in the coiled instrument. A laboratory exercise is described in which students make simple length and diameter measurements of real brass instruments. Plots of tube diameter vs. distance are produced that effectively display what each instrument would look like if straightened out. Students also determine the air paths through valves (which are surprisingly difficult to visualize), and measure the added tubing associated with each valve. Mouthpieces are examined and measured in order to demonstrate the complex set of shapes involved. These hands-on measurements force students to look closely at the component pieces, air paths, and construction details of the instruments. Pedagogically, the use of real instruments in the lab engages students and helps them make connections between the physics of ideal tubes and the design of real brass instruments. Student results and feedback will be described.
Introducing the concept of resonance to non-science majors in a musical acoustics class
Authors: Morrison Andrew
Published: September 2012

Understanding the concept of resonance is one of the most important goals for a student in a musical acoustics course to achieve. In our musical acoustics course students examine the standing wave behavior of simple one-dimensional systems such as stretched strings and pipes with open ends or one closed end. The concept is integral to the discussion of how nearly all musical instrument work, but it is also a difficult concept for many students to understand. In our class, we discuss how looking at the boundary conditions of the systems we examine in class can be applied to predict what the resonant frequencies of the system are.
Ambient noise seismic monitoring of the continuous deformation of the Earth
Authors: Campillo Michel
Published: September 2012

The analogy between the Green function and the long-range correlation of the seismic ambient noise leads to new developments in imaging and monitoring. In the last years this approach allows for high-resolution surface wave tomography, and more recently its potential for body wave imaging was demonstrated. In the same time, the reconstruction of the scattered part of the Green function was analyzed and its possible use to detect slight variations in the medium was confirmed. Ambient noise monitoring allows for a continuous measure of seismic velocity changes related with the tectonic process affecting the lithosphere. I present some examples showing that a change at depth can be monitor with seismic noise records and that those changes are related to the deformation. We analyze in detail the transient deformation on a subduction zone and we discuss the relations between change of seismic velocity, slow slip events and tremors.
Multiple scattering in the spirit of Leslie Foldy
Authors: Martin Paul A.
Published: September 2012

Foldy's name is best known to wave theorists because of his 1945 paper on multiple scattering. This came out of wartime work on sound propagation through bubbly liquids. The paper itself contains a deterministic theory for scattering by a finite number of small objects, and a probabilistic theory for wave propagation through random arrangements of many small scatterers in which a certain closure assumption is invoked. Assumptions of this kind can be said to be unreasonably effective. We describe some of this early work and then review more recent work on a variety of multiple scattering problems.
Characterization of polycrystals by ultrasonic attenuation-to-backscattering ratio measurements
Authors: Li Jia , Rokhlin Stanislav I.
Published: September 2012

Scattering of ultrasonic waves in polycrystalline materials depends on the relative misorientation of the crystallites, their elastic properties and the crystallite size and morphology. Those parameters affect both ultrasonic attenuation and backscattering. In structural material alloys the elastic properties of crystallites and microtextures are often unknown, thus complicating model-based microstructure size determination from ultrasonic measurements. It has been shown by analysis and simulation that the measured attenuation-to-backscattering ratio is independent of the unknown elastic material characteristics and thus may be used advantageously for inverse determination of mictostructural characterization of polycrystalline materials. The method is based on recently developed models for ultrasonic attenuation and backscattering in polycrystals with nonequiaxed grains of general ellipsoidal shape. Using the model approximation an effective size parameter is defined and obtained from the backscattering-to-attenuation ratio measurements. By this method the microstructure size from one side of the sample can be characterized. The method is demonstrated on experimental data for Ti alloy samples with duplex microstructure/microtexture formed by hexagonal alpha crystallites. Volumetric ultrasonic results are compared with direct surface microtexture measurements by orientation image microscopy.
Ultrasonic characterization of polymeric composites containing auxetic inclusions
Authors: Haberman Michael R. , Hook Daniel T. , Klatt Timothy D. , Hewage Trishian A. M. , Alderson Andrew , Alderson Kim L. , Scarpa Fabrizio L.
Published: September 2012

Composite materials are often used as damping treatments or structural materials to mitigate the effects of unwanted vibration and sound. Recent work on materials displaying a negative Poisson’s ratio, known as auxetic materials, indicate that composite materials consisting of a lossy matrix containing auxetic inclusions may lead to improved vibro-acoustic absorption capacity compared to composites containing positive Poisson’s ratio inclusions. This work presents ultrasonic measurements of an epoxy matrix material (Epon E828/D400) containing volume fractions of α-cristobalite inclusions ranging from 5% to 25% by volume. The effective frequency dependent speed of sound and attenuation coefficient of each sample is measured from 1 to 10 MHz using ultrasonic immersion techniques. Ultrasonic test results are compared with Dynamic Mechanical Thermal Analysis and modal damping measurements of stiffness and loss behavior. This material is based upon work supported by the U. S. Army Research Office under grant number W911NF-11-1-0032.
Estimation the mean correlation length of metals by using mode-converted diffuse ultrasonic backscatter model
Authors: Hu Ping , Turner Joseph A.
Published: September 2012

Diffuse ultrasonic backscatter measurements can explain the phenomenon of the scattering at interfaces in heterogeneous materials. The theoretical models of diffuse ultrasonic backscatter for longitudinal (L-L) and shear (T-T) wave scattering within polycrystalline materials have recently been developed. A mean correlation length of metals is successfully calculated from the L-L model at normal incidence in a pulse-echo inspection. Above the first critical angle, mode-conversion scattering occurs when the longitudinal waves are converted to shear waves (L-T) at material grain boundaries. With a similar formalism, a mode-conversion scattering (L-T) model is presented to describe this process. The model is then to fit the experimental response for a pitch-catch transducer configuration and the correlation length is extracted by modifying the beam function. The mean correlation length from the L-T model is in agreement with both the L-L model and the results obtained from optical micrographs. This presentation outlines the theoretical framework and the method to extract the mean correlation length. Mode-converted backscatter removes the influence of the front-wall reflection and may lead to improvements in microstructural characterization and material property evaluation. [Research supported by FRA.]
Detection of inclusions embedded in a polycrystalline medium: A diagrammatic approach
Authors: Koester Lucas W. , Turner Joseph A.
Published: September 2012

Diffuse ultrasonic backscatter techniques are used to evaluate and to quantify polycrystalline microstructure in structural materials including steel, aluminum, and concrete. Modeling of the backscatter received from grain scattering is important for both microstructural characterization and flaw detection. Here, the problem of an inclusion embedded in a polycrystalline background is examined using a diagrammatic approach. Expressions are derived that for the attenuation and diffuse backscatter using a Green’s function approach that incorporates Feynman diagrams for simplicity in the analysis. The resulting equations are solved in the single-scattering limit that couples geometric probabilities and correlation functions such that the impact of the inclusion can be quantified. The effects of frequency, average grain size, polycrystalline properties, inclusion properties and inclusion size are considered. Further work related to inspection with focused beams or immersion type ultrasonic inspections is also presented. This work is anticipated to impact the studies of model-assisted probability and inclusion content quantification in ultrasonic non-destructive evaluation.
Influence of stresses on grain size and attenuation parameters in ultrasonic scattering models
Authors: Kube Christopher M. , Turner Joseph A.
Published: September 2012

Recent findings have shown the dependence of material stresses on the strength of ultrasonic backscatter. The stress dependence arrives when considering the covariance of effective elastic moduli of a medium with a randomly oriented grain structure. In some instances, the change in magnitude of the scattered response due to stress is significant and can be utilized as a technique for NDT stress monitoring. Conversely, ignoring the stress sate could result in significant error when attempting to extract micrsotructural parameters using ultrasonic NDE techniques. This presentation touches on the error generated in estimating the average grain size when using ultrasonic scattering models which include stress dependent backscatter coefficients. Results are given for three scattering modes; longitudinal to longitudinal, shear to shear, and (mode converted) longitudinal to shear under a variety of loading configurations. Furthermore, the stress dependence in the covariance influences common multiple echo attenuation measurements when grain scattering is present. Theoretical attenuation values of the different modes are given for various stress-states. Understanding how stress influences these parameters can potentially improve existing ultrasonic NDT techniques. [Research supported by the Federal Railroad Administration.]
Exact image theory for a three layer medium
Authors: Bhatta Ambika , Thompson Charles , Chandra Kavitha , Mehta Vineet
Published: September 2012

In this work an exact formulation and solution for the image source amplitude in a three layer medium is given. To do so a novel generalization of the Sommerfeld integral is employed. Of particular interest in this paper is the time-domain solution for the impulse response between source and observation points in the middle layer. It is shown that global boundary conditions can be accommodated for multiple reflections from media of having infinite extent. A branch integral formulation of inverse Laplace transform of integral powers of the Fresnel reflection coefficient is given for this case. It is shown that only odd-powers of the branch point argument contribute thereby reducing computational effort required to numerically evaluate the impulse response.
A sonar experiment to study sound propagation through flames
Authors: Abbasi Mustafa Z. , Wilson Preston S. , Ezekoye Ofodike A. , Suits Joelle I.
Published: September 2012

Disorientation is a major cause of firefighter death and injury. When a firefighter is trapped in a structure, there is a small window of time for rescue teams to locate a downed firefighter. We propose an acoustic navigation system based on sonar concepts to augment existing techniques (e.g. thermal imaging cameras). As a first step toward this system, a better understanding of acoustic wave propagation through the fire environment is needed. Therefore, a sonar experiment was developed to measure the distance through a flame. Since information in the literature suggests that transmission loss through fire increases with frequency, a parametric array was used to maintain narrow source directivity while remaining in the low frequency/low attenuation regime. Results of the sonar experiment will be presented for various source functions and flame conditions.
Integral structural health monitoring of helicopter tail booms by guided acoustic waves
Authors: Grill Wolfgang
Published: September 2012

The general principles of structural health monitoring by ultrasonic waves with high resolution monitoring of the time dependence of the transport properties are presented. Reported are essential aspects of the theoretical background together with the results of modeling relating to the developed monitoring scheme and the experimental findings. The presented applications of the developed integral structural health monitoring concentrate on examples involving helicopter tails booms. These include conventional aluminum based bolted frame and stringer constructions as well as fiber compound structural components with foam inlays, in both cases for helicopter tail booms. The presentation includes experimental demonstrations on samples suitable for transport.
Hybrid microcontinuum field approach for intrinsic damage state quantification
Authors: Banerjee Sourav
Published: September 2012

The primary objective of this presentation is to demonstrate a systematic framework for the early stage diagnostics of materials under operation. Defying the conventional route of ‘bottoms-up’ multi-scale modeling approach for material diagnostics, a hybrid ‘top-down’ approach is presented. Structure specific diagnostics and prognostics have become extremely important due to variances in the real life performances of aerospace materials. Structures, structural components and engine components will need individual attention in the near future. Individual attention means that a parallel database must be maintained for each component for on-line digital certification. The ‘digital-twin’ software will have access to structure’s detailed fleet and maintenance records, nondestructive test results, real-time sensory data etc. to certify the materials on-line, but it will need some ‘quantifiable’ parameters. Thus a parameter to quantify the incubation of damage at meso-scale is identified. The intrinsic length scale dependent ‘parameter called ‘damage entropy’ closely resembles the material state due to fatigue, extreme environments, operational hazards or spatio-temporal variability. The proposed quantification process involves physics and statistics based predictive models. In this novel approach ‘micromorphic’ description of material is considered in spatio-temporal non-local sense and the nonlocal features are extracted from the real time signals for damage state quantification.
Mesh-free distributed point source method for modeling guided wave propagation in a viscous fluid layer trapped between two solid plates
Authors: Wada Yuji , Kundu Tribikram , Nakamura Kentaro
Published: September 2012

Distributed Point Source Method (DPSM) is extended to model wave propagation in viscous fluids. Appropriate estimation on attenuation and boundary layer due to fluid viscosity is necessary for the ultrasonic devices that utilize acoustic streaming or ultrasonic levitation. Since the boundary layer is often much thinner than the wavelength, numerical simulations based on the finite element method suffer from large computational cost because very fine mesh is needed to trace the layer. DPSM can efficiently model this problem. The computational cost for modeling the viscous fluid with DPSM is reduced close to the cost of non-viscous fluid analysis. In this paper, equations for DPSM modeling in viscous fluids are derived by decomposing the linearized viscous fluid equations into two components - dilatational and rotational. By considering complex P-wave and S-wave numbers, the sound fields in viscous fluids can be calculated using the same calculation routines used for waves in solids. To verify the calculation precision, a comparison between approximated theory and DPSM generated results for a fundamental ultrasonic field problem is performed. The particle velocity profile parallel to the surface in a viscous fluid between two vibrating plates is calculated. Theoretical results agree well with the DPSM generated results.