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Proceedings of Meetings on Acoustics

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POMA - 162nd Meeting Acoustical Society of America
Conference Location: San Diego, California Conference Date: 31 October - 4 November 2011
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Eavesdropping on coconut rhinoceros beetles, red palm weevils, Asian longhorned beetles, and other invasive travelers

Richard W. Mankin

POMA Volume 14, pp. 010001 (December 2011); (8 pages)

Online Publication Date: December 19, 2011

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As global trade increases, invasive insects inflict increasing economic damage to agriculture and urban landscapes in the United States yearly, despite a sophisticated array of interception methods and quarantine programs designed to exclude their entry. Insects that are hidden inside soil, wood, or stored products are difficult to detect visually but often can be identified acoustically because they produce 3-30-ms, 200-5 000-Hz impulses that are temporally grouped or patterned together in short bursts. Detection and analysis of these sound bursts enables scouts or inspectors to determine that insects are present and sometimes to identify the presence of a particular target species. Here is discussed some of the most successful acoustic methods that have been developed to detect and monitor hidden insect infestations. Acoustic instruments are currently available for use in rapid surveys and for long-term monitoring of infestations. They have been useful particularly for detection of termites, coconut rhinoceros beetles, red palm weevils and Asian longhorned beetles in wood, white grubs and Diaprepes root weevil in soil, and stored product insects. 9 1616
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43.80.Pe Agroacoustics
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The effect of reverberation enhancement on the diffusion of the sound field

Hugh Hopper, David Thompson, and Keith Holland

POMA Volume 14, pp. 015001 (November 2011); (9 pages)

Online Publication Date: November 08, 2011

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Reverberation enhancement is a technology which allows the reverberation time of the room to be increased. It is important to consider the effect of this technology on the other measurable attributes of the room response. The spatial variations of steady state sound pressure level and reverberation time within the room can be used to measure the extent to which the room approximates a diffuse field. A theoretical value of these quantities can be predicted for an ideal diffuse and the ratio between the measured and theoretical values gives a normalised measure of the diffusion of the sound field. This work investigates the changes in these measures when reverberation enhancement is applied to a room. Experimental results have shown that the normalised measures of diffusion increases with the introduction of reverberation enhancement. This implies a reduction in the homogeneity and isotropy of the sound field which may be perceived as a reduction in subjective quality.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Cs Stationary response of rooms to noise; spatial statistics of room response; random testing
43.55.Jz Sound-reinforcement systems for rooms and enclosures
43.55.Ka Computer simulation of acoustics in enclosures, modeling
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On a variable broadband absorption product and acceptable tolerances of reverberation times in halls for amplified music

Niels W. Adelman-Larsen, Eric R. Thompson, and Jens Jørgen Dammerud

POMA Volume 14, pp. 015002 (November 2011); (8 pages)

Online Publication Date: November 30, 2011

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Previous studies have shown that what distinguishes the best from the less well liked halls for pop and rock music is a short reverberation time in the 63, 125 and 250 Hz octave bands. Since a quite long reverberation time in these frequency bands is needed in order to obtain warmth and enough strength at classical music concerts, variable acoustics must address these frequencies in order to obtain desirable acoustics in multipurpose halls. Based on the results of a previous study of Danish rock venues as well as three newly built halls, acceptable tolerances of T30 were investigated. The results suggest that T30 can be at least 1.4 times as long in the 63 Hz octave band as in the 125 Hz band and attain values of +/- 15% at higher frequencies compared to previously determined values. A variable broadband absorption product is also presented. Absorption coefficients are approx. 0.8 in the 125, 250, 500 Hz bands, 0.6 at 1 kHz and decreasing at higher frequencies and in the 63 Hz band when in the ON position. In the OFF position the product attains absorption values between 0.0 and 0.2.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
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Vitruvius and new materiality: practice and theory in the development of an architecture of sound

Lorenzo Beretta

POMA Volume 14, pp. 015003 (December 2011); (15 pages)

Online Publication Date: December 08, 2011

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In architecture, sound is only haphazardly used as an accessory to pre-constituted architectural blocks. To establish the affordability of sound as a material in architectural practice, the paper analyses the social context of today's architecture. Over the centuries, buildings have changed their constituent materials ranging from ceramic to concrete, from wood to glass, from light to vapour. It is argued that Vitruvius' principles of commodity, firmness and delight have led to the generation of 'new and improved' architectures which resembled more to images than liveable places. A renewed interest in the experiential dimension of architecture has changed the way people explore and live space. In sensory architecture, materials are chosen based on the expressive-sensorial qualities and the effects that these have on the user. Technical and technological advances have allowed a controlled manipulation of the ephemeral elements of space, namely water, temperature, light and sound. In particular, it has emerged that through sound digital manipulation it is possible to alter cognition, behaviour, and human interaction leading toward the definition of sound as a material. Sound should no longer be used as an accessory of architectural spaces but, instead, as a material able to give form, volume and shape to architecture.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Fw Auditorium and enclosure design
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Understanding Soundscape as a specific Environmental Experience: Highlighting the importance of context relevance

Itziar Aspuru, Igone Garcia, Karmele Herranz-Pascual, and Ibone Garcia-Borreguero

POMA Volume 14, pp. 015004 (December 2011); (12 pages)

Online Publication Date: December 23, 2011

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A conceptual model about environmental experience is presented to guide soundscape studies. This proposal combines the state of the art and the experience of Tecnalia regarding psychosocial studies which focuses on the relationship between environment and people. The model has been structured around five main elements: person (community), place, activity, previous interaction between person and place, and environmental experience. The environmental experience is understood as a holistic experience not only within that soundscape but also linked to other perceptions, such as landscape, odour, etc. The relevant factors and variables of each main element have been identified to assist us in describing human and social holistic experience in relation to the place, in general, and soundscape (perception) in particular. The main objective of this paper is to analyze conceptually and throughout a field experiment, the relevance of the context, understanding it as the surrounding circumstances of the environmental experience. Hence, a field experiment is presented to analyze the relevance of a context characteristic, namely sound environment on the global environmental experience.
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43.50.Qp Effects of noise on man and society
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.50.Sr Community noise, noise zoning, by-laws, and legislation
43.66.Lj Perceptual effects of sound
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Sound absorption of different green roof systems

Ilaria Pittaluga, Corrado Schenone, and Davide Borelli

POMA Volume 14, pp. 015005 (February 2012); (13 pages)

Online Publication Date: February 01, 2012

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Experimental data on acoustical performances, in particular on sound absorption of several green roof systems were evaluated and discussed. Measurements were performed on samples of three green roof systems, different for maintenance, plant setting and containment criteria, and categorized in extensive green roof (Sample A), semi-intensive green roof (Sample B) and common soil (Sample C). Experimental values of normal incidence acoustic absorption coefficient and acoustic impedance were evaluated for each sample in one-third octave frequency bands from 160 to 1600 Hz by using a standing wave tube. Then, diffusive sound absorption coefficients and normal and diffusive weighted sound absorption coefficients were calculated in the same frequency range. Results show that green roofs provide high sound absorption, mostly if compared with the typical performances of traditional flat roofs. Curves of sound absorption coefficients result strongly dependent on the stratigraphy. Comparison between the different systems performed on the base of weighted sound absorption coefficients shows a better behaviour for the Sample B. Results obtained suggest that green roof technology, in addition to energy and environmental benefits, can contribute to noise control in urban areas by means of high sound absorption performances in relation to the size of the surface area.
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43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
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Estimation of two-dimensional strain rate based on high frame rate ultrasound imaging method

Hong Chen and Jian-yu Lu

POMA Volume 14, pp. 020001 (January 2012); (12 pages)

Online Publication Date: January 13, 2012

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Current SR estimation methods that use speckle tracking technique are based on conventional delay-and-sum (D&S) imaging method with multiple transmissions, which causes skewed image of moving object resulting in inaccurate SR. To overcome the problem, a method to combine high frame rate imaging method (HFR) with speckle tracking technique was proposed. Using only one or a few transmissions for each image; the new method can obtain a snapshot of moving targets, avoiding the skewing problem in D&S method that uses 91 transmissions. Studies, with simulated and experimental echo data respectively, were performed to verify the method. The new method is compared with D&S imaging method also using one transmission so that the skewing problem existing for D&S with multiple transmissions can be avoided. Both plane wave (PW) and limited diffraction beam (LDB) were studied for the HFR imaging method. Results show that the new method has comparable velocity errors and SR accuracy with the D&S method when using one transmission. Moreover, the new method can measure high velocity in application such as blood flow measurement. Using a full view of the heart image, SR can be localized and then estimated.
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43.80.Vj Acoustical medical instrumentation and measurement techniques
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Application of active-learning techniques to enhance student-based learning objectives

Tracianne B. Neilsen and Kent L. Gee

POMA Volume 14, pp. 025001 (January 2012); (11 pages)

Online Publication Date: January 18, 2012

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Research in physics education has indicated that the traditional lecture-style class is not the most efficient way to teach science courses at the university level. Current best-teaching practices focus on creating an active-learning environment and emphasize the students' role in the learning process. Several of the recommended techniques have recently been applied to Brigham Young University's acoustics courses. Adjustments have been built on a foundation of establishing student-based learning outcomes and attempting to align these objectives with assessments and course activities. Improvements have been made to nearly every aspect of the courses including use of class time, assessment materials, and time the students spend out of the classroom. The progress made in bringing two of the courses, specifically an introductory, descriptive acoustics course for a general audience and a junior level introduction to acoustics course for majors, is described. Many of the principles can be similarly applied to acoustics education at other academic levels. Suggestions are made for those seeking to modernize courses at their institutions.
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43.10.Sv Education in acoustics, tutorial papers of interest to acoustics educators
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Modeling and Validation of Magnetostrictive Sound Transducer including Flat Panel

Hae-Jung Park and Young-Woo Park

POMA Volume 14, pp. 030001 (December 2011); (9 pages)

Online Publication Date: December 15, 2011

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This paper contains models of the magnetostrictive actuator and flat panel for the investigation of interaction between them. (1) is a transfer function of magnetostrictive actuator between a displacement Ua and input current I. Ga(s) = Ua (s)/ I (s) = nd / (1 + c/co + sr/co + s2m/co) (1) where, n is number of coil turns, d magnetostrictive constant, c stiffness of prestress spring, co open circuit stiffness, r damping coefficient and $m$ effective mass. (2) is transfer function of a flat panel. Gf(s) = Uf(s)/Ua(s) = - A /(-B+C+D), A = m1k1s2/( m1 s2 + c1s + k), B = m2 s2 + (c1 + c2)s + (k1 + k2), C = (c1s + k1)2/( m1s2 + c1s + k1), D = (c2s + k2)2 /( m3 s2 + (c2 + c3)s + k2 + k3) (2) where, m, c and k are parameters of the actuator and flat panel models, and parameters determined experimentally. The final transfer function of actuator and flat panel is expressed by multiplying Ga(s) and Gf(s). Simulations are performed through commercial program under the conditions applying a white noise to the final transfer function. The simulated and experimental frequency responses are compared.
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43.38.Ct Magnetostrictive transducers
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Development of an Optical Transducer for an Electro-Acoustic Guitar

Seong-Ki Cho and Young-Woo Park

POMA Volume 14, pp. 030002 (December 2011); (6 pages)

Online Publication Date: December 23, 2011

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This paper presents the development of an optical transducer (OT) for an electro-acoustic guitar. Two conceptual designs are proposed: one with one infrared light emitting diode (IR LED) and one photodetector, and the other with two IR LEDs and one photodetector. Both concepts are based on the top-to-bottom structure: IR LED is on the top, and the photodetector is at the bottom. After the preliminary tests, the latter design is selected as the proposed OT. The OT is fabricated on the PCB with proper electronic circuit, and mounted on the guitar. The developed OT is subjected to the performance evaluation with a dedicated measuring device. The performance of the OT is compared with commonly used piezoelectric transducer. Findings are summarized: (1) The output signals from the OT are much higher that those from the piezoelectric transducer in both average and peak-to peak voltages. (2) The noise level from the OT is similar or less than that from the piezoelectric transducer. (3) SNR with the OT is increased by 45% in average, compared with the piezoelectric transducer.
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43.38.Ar Transducing principles, materials, and structures: general
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Electromechanical transduction system design for optimal energy harvesting from ocean waves

Amadou G. Thiam and Allan D. Pierce

POMA Volume 14, pp. 030003 (January 2012); (13 pages)

Online Publication Date: January 26, 2012

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While details of the currently most highly publicized devices for conversion of ocean wave energy to electrical energy are generally not disclosed in the open literature, the authors believe that, for devices not on the coastline, the common transduction mechanism involves electromagnetic induction with conducting wires moving relative to permanent magnets. A general discussion is given of how such a mechanism can be used in this application. The overall analysis of the mechanical system with lumped or distributed masses and elastic elements driven by buoyancy forces associated with incident ocean waves is facilitated, if the transduction system is modeled as linear mechanical dashpots, and the procedures for deriving effective dashpot constants are described. The mechanical analysis suggests that, for waves in a general frequency range, there is an optimal choice for the parameters of the mechanical system, so that the maximum electrical power can be harvested. The optimal energy extracted per wave cycle is invariably much less than the total mechanical energy of the oscillating components of the system. A distinction is made between freely floating systems and systems anchored to the ocean bottom and between systems which are driven near a resonant frequency and those driven substantially below resonance.
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43.38.Ar Transducing principles, materials, and structures: general
43.38.Dv Electromagnetic and electrodynamic transducers
43.40.At Experimental and theoretical studies of vibrating systems
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Reflection reduction by three-dimensional and two-dimensional phononic crystal slabs

Sven M. Ivansson

POMA Volume 14, pp. 030004 (January 2012); (11 pages)

Online Publication Date: January 26, 2012

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A thin rubber coating with scatterer inclusions in a periodic lattice can redistribute sound energy, normally incident on a steel plate in water, in the lateral direction. The scattered energy can be absorbed by the rubber material and the reflection amplitude in the water can be reduced significantly. Coatings with different scatterer material types are here compared: air-filled cavities, high-density inclusions, and high-density inclusions coated by soft silicone rubber (which have attracted much interest in recent phononic crystal research). For each material type, scatterers of spherical (in a doubly periodic lattice) or cylindrical (in a lattice with a single period) shape are considered. Each coating type is optimized by differential evolution, varying a number of material and geometrical parameters to minimize the maximum reflectance within a certain frequency band. The layer multiple-scattering method is used as forward model. Good broad-band reflectance reduction is achieved with cavities (monopole scattering), but even better results are obtained with the coated high-density inclusions (dipole scattering). Combined with mixing scatterers of different sizes, the cylindrical shape, with scatterers in a lattice with a single period, is very powerful. The sensitivity of the performance to different parameters, as well as the incidence angle, is illustrated.
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43.20.Fn Scattering of acoustic waves
43.20.Ks Standing waves, resonance, normal modes
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Ky Structures and materials for absorbing sound in water; propagation in fluid-filled permeable material
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A high-dispersion regime of the zero-order symmetric Lamb wave mode for ultrasonic nondestructive evaluation

Li-Feng Ge

POMA Volume 14, pp. 030005 (January 2012); (9 pages)

Online Publication Date: January 26, 2012

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The zero-order symmetric Lamb wave mode (S0 mode) has been less studied than antisymmetric one (A0 mode). The S0 mode excited by micromachined electrostatic airborne ultrasonic transducers can be used for nondestructive evaluation of multilayer or composite materials, which deserves special attention. The dispersion curve of the S0 mode is investigated in depth and determined accurately by a 3D Plot Method presented previously [Ge, JASA, 126(4):2281 (2009); POMA, 8, 065003 (2011)]. It is revealed that as the product of the transverse wave number and thickness increases from a low limit to infinite the phase velocity of the S0 mode decreases from transverse wave velocity to surface acoustic wave velocity. The low limit determined is 3.46 for Poisson ratio 0.34, and will be 3.31 and 3.05 for 0.28 (Steel) and 0.17 (Silicon), respectively. Also, it is seen that at a small regime over the limit the S0 mode is highly dispersive. Further, an approximate formula to determine the dispersion relation of the regime is derived analytically for the convenience of practical applications. Since the zero-order mode carries more energy than higher-order modes, the high-dispersion regime is significant particularly for ultrasonic nondestructive evaluation. [Work supported by NSFC (60774053)]
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43.25.Dc Nonlinear acoustics of solids
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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Measurement and Propagation of Supersonic Aeroacoustic Noise Sources Using Continuous Scanning Measurement Technologies and the Fast Multipole Boundary Element Method

Michael Y. Yang, Havard Vold, and Partihv Shah

POMA Volume 14, pp. 040001 (December 2011); (14 pages)

Online Publication Date: December 15, 2011

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ATA Engineering has developed a technique that uses a continuous scanning robot to take high-resolution measurements of supersonic jet plumes. The jet noise was modeled using a reduced-order model and propagated to far field microphone locations in the free-field. It is shown that the pressure at these microphones was successfully reconstructed across a range of frequencies. The capability to make predictions when scattering surfaces are present is also demonstrated using the fast multipole boundary element method in VA One. This work was originally designed for supersonic jets, but it can also be used for static firing tests of launch vehicle engines. The measured data could then be used for analytic predictions of the liftoff environment.
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43.20.Fn Scattering of acoustic waves
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.50.Nm Aerodynamic and jet noise
43.50.Yw Instrumentation and techniques for noise measurement and analysis
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Shock Associated Noise Generation in Curved Turbulent Coanda Wall Jets

Caroline Lubert and Richard J. Shafer

POMA Volume 14, pp. 040002 (December 2011); (9 pages)

Online Publication Date: December 15, 2011

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Curved three-dimensional turbulent Coanda wall jets are present in a multitude of natural and engineering applications. The mechanism by which they form a shock-cell structure is poorly understood, as is the accompanying shock-associated noise (SAN) generation. This paper discusses these phenomena from both a modeling and experimental perspective. The Method of Characteristics is used to rewrite the governing hyperbolic partial differential equations as ordinary differential equations, which are then solved numerically using the Euler predictor-corrector method. The effects of complicating factors -- such as radial expansion and streamline curvature -- on the prediction of shock-cell location are then discussed. This paper next compares the theoretical calculations of the shock-wave structure with associated schlieren flow visualization results. Related acoustical measurements are also addressed. In this way, critical flow characteristics for shock-cell formation are identified, and their influence on SAN discussed.
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43.50.Cb Noise spectra, determination of sound power
43.50.Ed Noise generation
43.50.Nm Aerodynamic and jet noise
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Distributed Point Source Method and its Applications in Solving Acoustic Wave Scattering Problems

Ehsan K. Rahani, Taliehossa Hajzargarbashi, and Tribikram Kundu

POMA Volume 14, pp. 045001 (November 2011); (17 pages)

Online Publication Date: November 08, 2011

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A recently developed semi-analytical technique called distributed point source method (DPSM) is used for solving various wave scattering problems. Scattering of focused ultrasonic fields by air bubbles or cavities in solid media is investigated here. Results for both single and multiple cavity geometries are presented. It is investigated when two cavities in close proximity can be distinguished and when it is not possible. The interaction effect between two cavities prohibits simple linear superposition of single cavity solutions to obtain the solution for the two cavities placed in close proximity. Therefore, although some analytical and semi-analytical solutions are available for the single cavity in a focused ultrasonic field, those solutions cannot be simply superimposed for solving the two-cavity problem even in a linear elastic material. The comparison between the ultrasonic energies reflected from two small cavities versus a single big cavity is also investigated.
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43.20.Fn Scattering of acoustic waves
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
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Acoustic microscopy investigation of superconducting materials

Tarek Tahraoui, Salima Debboub, Amar Boudour, and Youcef Boumaiza

POMA Volume 14, pp. 045002 (December 2011); (6 pages)

Online Publication Date: December 19, 2011

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The present work has as subject the study of the acoustic attenuation in some superconductor materials. This study is based on the simulation of the acoustic signal obtained by the reflection acoustic microscope upon the exploration of a coated or uncoated material. The examination of the simulated signal has permitted the determination of the variation of the reflection coefficient with respect to the incidence angle of the exciting acoustic wave. We have also determined the elastic constants, the velocities of different modes of propagation, the acoustic attenuation of the Rayleigh mode as a function of temperature from the reflection coefficient and the acoustic signature.
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43.20.Hq Velocity and attenuation of acoustic waves
43.35.Lq Low-temperature acoustics, sound in liquid helium
43.35.Pt Surface waves in solids and liquids
43.58.Ls Acoustical lenses and microscopes
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Utilization of an acoustic tomography array as a large sonic anemometer/thermometer

Sergey N. Vecherin, Vladimir Ostashev, D. Keith Wilson, and Andrey Grachev

POMA Volume 14, pp. 045003 (January 2012); (16 pages)

Online Publication Date: January 19, 2012

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The temperature, wind velocity, and vertical and horizontal kinematic heat fluxes are important characteristics of the atmospheric surface layer. Point measurements of these meteorological parameters are often not representative due to their horizontal variations. For remote sensing of the area-averaged values of these parameters, we suggest using an acoustic tomography array, such as the one at the Boulder Atmospheric Observatory (BAO). In this approach, the tomography array (with the horizontal size of 80 m by 80 m) is used, in essence, as a large sonic anemometer/thermometer for measurements of the area-averaged, instantaneous values of temperature and wind velocity. The area-averaged horizontal heat flux is then calculated from a time series of the area-averaged temperature and wind velocity. Feasibility of this approach is studied in numerical simulations of the BAO tomography array with the use of the temperature and wind velocity fields obtained with Large Eddy Simulation (LES). The results obtained show that the area-averaged values of temperature, wind velocity, and horizontal heat flux can be estimated with tomographic methods; the area-averaged vertical heat flux might be inferred from the horizontal flux. Preliminary experimental results obtained with the BAO acoustic tomography array show that this remote sensing technique is feasible.
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43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
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A computational model for evaluating the interaural disparities using coincidence detection

Zbynek Bures

POMA Volume 14, pp. 050001 (November 2011); (10 pages)

Online Publication Date: November 08, 2011

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In mammals, spatial hearing is supported by evaluation of two types of binaural disparities, interaural time difference (ITD) and interaural level difference (ILD), that is performed by auditory neurons in the superior olivary complex. Using a complex auditory model which includes a binaural evaluation stage, the output of binaural neurons from medial and lateral superior olive is simulated and quantitatively compared with available experimental data. Both binaural disparities are evaluated using detection of coincidence of spikes arriving from the two channels; in case of ITD, the coincidence of two excitatory spikes is detected, in case of ILD, the coincidence of one excitatory and one inhibitory spike is detected. It is shown that using a physiologically realistic set of parameters, evaluation of both ITD and ILD based on coincidence detection is capable of reproducing the observed neuronal reponses. Furthermore, the model is shown to qualitatively reproduce the justnoticeable differences of ITD depending on frequency and intensity. Supported by projects "Podpora a individualni rozvoj perspektivnich akademickych pracovniku na VSPJ" and M00176 "Elektronicko-biomedicinska kooperace" at the College Of Polytechnics Jihlava, and GACR 309/07/1336 at the AS CR Prague.
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43.64.Bt Models and theories of the auditory system
43.66.Pn Binaural hearing
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Effects of silent interval on human frequency-following responses to voice pitch

Fuh-Cherng Jeng and Ronny P. Warrington

POMA Volume 14, pp. 050002 (November 2011); (8 pages)

Online Publication Date: November 16, 2011

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Human frequency-following responses (FFR) to voice pitch have provided valuable information on how the human brainstem processes speech information. Recordings of the FFR to voice pitch, however, may overlap when insufficient silent intervals are used. To determine the shortest silent interval that can be used with no overlap between adjacent response waveforms, FFRs were recorded from twelve Chinese adults using a wide range of silent intervals. The stimulus token was a Chinese monosyllable with a rising pitch of 117 to 166 Hz and a duration of 250 ms. A high stimulus intensity at 70 dB SPL was used to maximize overlaps in the response waveforms. A total of seven silent intervals, ranging from the full length of the stimulus duration down to approximately half period of the fundamental frequency of the stimulus token, were administered at a random order across participants. Two distinct methods (Hilbert transform and root-mean-square amplitudes) were used to delineate the envelopes and overlaps of the response waveforms. A one-way repeated measures ANOVA was significant (p=0.038) in defining the magnitude of overlaps for the 10 ms pre-stimulus interval. The results indicated the shortest silent interval that could be used without compromising the response is 35-45 ms.
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43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Ri Evoked responses to sounds
43.64.Sj Neural responses to speech
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A direction-selective filter with a rational beam pattern

Dean J. Schmidlin

POMA Volume 14, pp. 055001 (October 2011); (9 pages)

Online Publication Date: October 25, 2011

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Presented in this paper is a direction-selective filter whose beam pattern is a rational function of a direction cosine. First, a plane-wave sinusoidal pressure function is converted from a four-dimensional function to a two-dimensional one by restricting the spatial points to lie on a radial line extending out from the origin in a prescribed look direction. The two-dimensional pressure function is then input into a linear filter characterized by a second-order partial differential equation with constant coefficients. The natural and forced responses are determined from which expressions for the beam pattern of the filter and the time constant of the natural response are found. The beam pattern is the reciprocal of a second-degree polynomial function of the plane wave's direction cosine. It is shown that the frequency range over which the integrity of the beam pattern is maintained is a function of the filter's natural response. An example is presented which illustrates the directivity index that is achievable in contrast to that of a vector or dyadic sensor, both of which have beam patterns that are polynomial functions of a direction cosine.
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43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Gk Space-time signal processing, other than matched field processing
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Improving automatic speech recognition by learning from human errors

Bernd T. Meyer

POMA Volume 14, pp. 060001 (December 2011); (9 pages)

Online Publication Date: December 23, 2011

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This work presents a series of experiments that compare the performance of human speech recognition (HSR) and automatic speech recognition (ASR). The goal of this line of research is to learn from the differences between HSR and ASR, and to use this knowledge to incorporate new signal processing strategies from the human auditory system in automatic classifiers. A database with noisy nonsense utterances is used both for HSR and ASR experiments with focus on the influence of intrinsic variation (arising from changes in speaking rate, effort, and style). A standard ASR system is found to reach human performance level only when the signal-to-noise ratio is increased by 15 dB, which can be seen as the human-machine gap for speech recognition on a sub-lexical level. The sources of intrinsic variation are found to severely degrade phoneme recognition scores both in HSR and in ASR. A comparison of utterances produced at different speaking rates indicates that temporal cues are not optimally exploited in ASR, which results in a strong increase of vowel confusions. Alternative feature extraction methods that take into account temporal and spectro-temporal modulations of speech signals are discussed.
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43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.72.Ja Speech synthesis and synthesis techniques
43.72.Ne Automatic speech recognition systems
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On Rayleigh and Mie scattering

Jerald W. Caruthers

POMA Volume 14, pp. 070001 (November 2011); (13 pages)

Online Publication Date: November 16, 2011

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Scattering described today as "Rayleigh Scattering" represents something that is far short of what Rayleigh actually contributed to the topic in both optics and acoustics. This limited view seems to lie in a few papers in which he truncates series solutions for practical computations, thus leading to scattering of the form , where k is the wavenumber and a is the radius of the sphere and for selected limitations on index of refraction. These approximations led optical scientists to equating "Rayleigh scattering" to little more than "the blue sky." In 1908 Gustav Mie developed a theory for plane-wave scattering from a sphere to which the names "Mie theory" and "Mie scattering" have been indelibly attached to many applications in optics. It is virtually unknown, especially in optics, that Rayleigh actually developed the full theory of plane-wave scattering from a sphere in 1878 (primarily section 334, 2. The Theory of Sound, Macmillan), including original contributions in the concurrently developing mathematics of Bessel functions. The motivation of this presentation is to establish a means of treating weak scattering from bubbles based on their contribution as a distribution of spheres by combining Rayleigh and Mie.
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43.30.Ft Volume scattering
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
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Discrete transparent boundary conditions for parabolic equations

Ronald F. Pannatoni

POMA Volume 14, pp. 070002 (December 2011); (8 pages)

Online Publication Date: December 08, 2011

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There are simple algorithms for constructing transparent boundary conditions (TBC's) for a partial discretization of the basic parabolic equation that is known as a "semi-discrete" parabolic equation. This equation and some of these algorithms are reviewed. Solutions of a semi-discrete parabolic equation in a long rectangular strip subject to TBC's at the long edges of the strip are then considered. These solutions can be computed accurately and efficiently with a pseudospectral method that is based on expansions in Chebyshev polynomials. It is beneficial to combine this method with a conventional split-step FFT solution of a parabolic equation subject to Neumann boundary conditions at the long edges of the strip. This hybrid approach will be called the "decomposition method". It is demonstrated in a computation of radiation modes from the termination of a truncated nonlinear internal gravity wave duct in a shallow ocean area.
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43.20.El Reflection, refraction, diffraction of acoustic waves
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Propagation of coupled modes in three dimensions

Ronald F. Pannatoni

POMA Volume 14, pp. 070003 (December 2011); (8 pages)

Online Publication Date: December 08, 2011

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A time-harmonic acoustic field in an ocean can be represented in terms of local normal modes. This representation may include leaky modes to account for radiation into the bottom. A system of coupled elliptic equations governs the amplitudes of these modes. If there is a primary horizontal direction of propagation, it may be possible to approximate these equations by parabolic equations. The resulting system of coupled parabolic equations can be integrated in the direction of propagation only if a certain linear transformation is nonsingular. This constraint limits the size of the system and the amount of coupling among the modes that are consistent with the parabolic approximations. A method for integrating the coupled parabolic equations numerically is discussed, and it it applied to a problem of three-dimensional propagation and scattering around a conical seamount in a deep ocean.
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43.30.Bp Normal mode propagation of sound in water
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