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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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Influence of impulsive sources on the soundscape of under-ice Arctic marine mammals

Juan Arvelo

POMA Volume 14, pp. 010002 (April 2012); (13 pages)

Online Publication Date: April 03, 2012

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The Arctic Ocean exemplifies the danger in using sound propagation and interaction models without a clear understanding of the physics of the problem or weaknesses inherent in these models. The zone-of-influence for under-ice marine mammals should be expected to differ significantly from that of open-sea organisms. However, increasing the effective sound attenuation, to empirically account for sound interactions with keel drafts, may lead to grossly erroneous conclusions from predictive and forensic studies. Ice elasticity and ridges combine to increase water/ice low-frequency sound penetration enabling long-distance transmission along this liquid-solid interface in the form of an evanescent wave. Consequently, sound pressure and exposure levels near the canopy are significantly higher even when the acoustic wavelength is several times longer than the ice thickness. Therefore, these physical mechanisms should also be taken into account in Arctic environmental impact assessment calculations. For example, it is more efficient for under-ice marine mammals to mitigate exposure to subsequent active sonar events by diving just a few meters deeper under the ice cap rather than increasing range by hundreds of meters. Therefore, some under-ice marine mammals are likely to exhibit a stronger preference towards diving avoidance behavior. Funding provided via UAF sub-award under NOAA Grant NA09NOS4000262.
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43.30.Hw Rough interface scattering
43.30.Vh Active sonar systems
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing
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Automatic detection of vocalizations of the frog Diasporus hylaeformis in audio recordings

Arturo Camacho, Adrián García-Rodríguez, and Federico Bolaños

POMA Volume 14, pp. 010003 (August 2012); (6 pages)

Online Publication Date: August 03, 2012

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A method for the detection of calls of the frog Diasporus hylaeformis (Eleutherodactylidae) in audio recordings is proposed. Unlike most algorithms, which are based for on physical or statistical measures, our algorithm is inspired in biology, specifically in the auditory system of the frog. It attempts to measure the loudness, timbre and pitch of the vocalizations to identify the calls of the focal individual. The first step consists in calculating the loudness of the signal, with the purpose of recognizing the sections where the focal individual's vocalizations are. The second step consists in using timbre to recognize the calls. The last step consists in running a multivariate ANOVA test on pitch and timbre to identify populations of calls, and from there, the focal individual's calls. Our experiments show a precision rate of 99% and a recall rate of 92%. Higher recall rates can be achieved varying certain parameters of the algorithm, but usually with a decrease in precision. Results show that the method is resistant to background noise (including calls of individuals of the same species), microphone-manipulation-induced noise, and human voice. It also adapts well to variations in microphone level over time.
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43.60.Bf Acoustic signal detection and classification, applications to control systems
43.66.Ba Models and theories of auditory processes
43.80.Ev Acoustical measurement methods in biological systems and media
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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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Motion simulation in the environment for auditory research

Braxton B. Boren and Mark Ericson

POMA Volume 14, pp. 015006 (April 2012); (8 pages)

Online Publication Date: April 03, 2012

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Virtual sound source motion has been implemented in the Army Research Laboratory's Environment for Auditory Research, which contains a 57-channel spherical loudspeaker array located in a semi-anechoic chamber. Using the low-latency PortAudio application programming interface from the Psychophysics Toolbox Version 3, 57 channels of streaming audio are dynamically updated in real-time using MATLAB for signal processing. Both Distance-Based Amplitude Panning (DBAP) and Vector Base Amplitude Panning (VBAP) have been implemented in MATLAB for controlling source motion. Sources are defined on a given path, such as a circle, ellipse, or the "dogbone" pattern often used in aviation. Although DBAP works convincingly for virtual sources located on the sphere defined by the loudspeaker array, VBAP is needed to position sources outside the array. Source motion paths are defined parametrically with respect to time, and the playback buffer updates the panned position every 11.5 milliseconds. Based on the source's instantaneous distance, diffuse-field or free-field amplitude attenuation is added in MATLAB as well as air absorption filtering. This virtual sound source method will be used for a variety of audio simulations and auditory experiments.
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43.60.Gk Space-time signal processing, other than matched field processing
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
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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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Acoustic radiation force for rapid detection of particles in biological liquids

Lev A. Ostrovsky, Aba Priev, Victor Ponomarev, and Yechezkel Barenholz

POMA Volume 14, pp. 020002 (March 2012); (11 pages)

Online Publication Date: March 19, 2012

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As known, ultrasonic standing waves can be used to concentrate particles and biological cells into separated bands. Acoustic separation in plane standing waves is limited to particles of few microns and larger. This presentation concerns using acoustic radiation force (RF) produced by cylindrical standing waves, for detection of high-density standing waves in pressure nodes and low-density particles (fat globules) in antinodes. Theoretical calculations show that in a cylindrical ultrasonic resonator RF near the central node can exceed the force at the periphery by about 20 times. In a cylindrical standing wave, RF can induce movement of bacteria with a speed of a few mm/s at frequency of 2 MHz and pressure amplitude of 100 kPa, whereas the speed of bacteria in a plane standing wave does not exceed 0.2 mm/s under the same conditions. The cylindrical standing wave system performance was tested for the E. coli bacteria in water and for a multi-component system containing fat globules and somatic cells in milk. Dilute suspensions of bacteria or fat globules were concentrated by at least two orders of magnitude.
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43.35.Wa Biological effects of ultrasound, ultrasonic tomography
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.80.Ev Acoustical measurement methods in biological systems and media
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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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The effect of musical training on auditory perception

Irene Kannyo and Caroline M. DeLong

POMA Volume 14, pp. 025002 (June 2012); (10 pages)

Online Publication Date: June 22, 2012

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Previous research has shown that musical training affects the type of cues people use to discriminate between auditory stimuli. The current study investigated whether quantity of musical training and musical area of expertise (voice, percussion instrument, non-percussion instrument) affected musical feature perception. Participants with 0-4 years of experience (13 non-musicians), 5-7 years of experience (13 intermediate musicians) and 8 years or more of experience (13 advanced musicians) were presented with pairs of 2.5 s novel music sequences that were identical (no change trials), differed by one musical feature (pitch change, timbre change, or rhythm change), and differed by two musical features (pitch and timbre change, pitch and rhythm change, or timbre and rhythm change). In 64 trials, participants had to report whether they heard a change, as well as classify the specific type of change. Participants in the advanced group (M = 91.2%) and intermediate groups (M = 85.0%) performed significantly better than non-musicians (M = 70.0%). There was no effect of area of musical expertise (voice or instrument) on musical feature change detection. These results suggest that musical training in any area increases the ability to perceive changes in pitch, timbre, and rhythm across unfamiliar auditory sequences.
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43.75.Cd Music perception and cognition
43.75.Zz Analysis, synthesis, and processing of musical sounds
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Acoustical effect of progressive undercutting of percussive aluminum bars

Eric M. Laukkanen and Randy Worland

POMA Volume 14, pp. 025003 (December 2012); (9 pages)

Online Publication Date: December 05, 2012

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Standard vibraphone bars consist of aluminum beams which are traditionally tuned with an arched undercut, for the purpose of aligning the musical overtones harmonically. The acoustical effect of various progressions of undercuts on aluminum bars was studied experimentally and with a finite element computer model. The spectral signature of the aluminum bar was determined with a spectrum analyzer, and the corresponding eigenmodes were imaged with an electronic speckle pattern interferometer. These methods were used to analyze the changes in natural frequencies of the bar as material was removed from various locations. The finite element model was used to verify a set of qualitative rules governing the frequency changes, and as a guide in the design of bars with custom harmonic overtone ratios.
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43.75.Kk Bells, gongs, cymbals, mallet percussion, and similar instruments
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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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Capacity and Statistics of Measured Underwater Acoustic Particle Velocity Channels

Huaihai Guo, Chen Chen, Ali Abdi, Aijun Song, Mohsen Badiey, and Paul Hursky

POMA Volume 14, pp. 030006 (April 2012); (17 pages)

Online Publication Date: April 03, 2012

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Acoustic particle velocity channels can be used for communication in underwater systems [A. Abdi and H. Guo, IEEE Trans. Wireless Communi. 8, 3326-3329, (2009)]. In this paper, the information (Shannon) capacity of underwater acoustic particle velocity channels is studied using measured data. More specifically, the maximum achievable data rates of a compact vector sensor communication receiver and another communication receiver with spatially separated scalar sensors are compared. Some statistics of particle velocity channels such as amplitude distribution and power delay profile are investigated using measured data and proper models are suggested as well. The results are useful for design and simulation of vector sensor underwater communication systems in particle velocity channels.The work is supported in part by the National Science Foundation (NSF), Grant CCF-0830190.
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43.60.Ac Theory of acoustic signal processing
43.60.Cg Statistical properties of signals and noise
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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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Real-ear attenuation of custom-fit earplugs with the communications earplug (CEP)

Elmaree Gordon and Efrem R. Reeves

POMA Volume 14, pp. 040003 (June 2012); (12 pages)

Online Publication Date: June 27, 2012

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Hearing loss is one of the most common occupational injuries in the Department of Defense. Aircrew members are exposed to the continuous noise generated by aircraft and impulsive noise from weapons systems. Even during peacetime, the second most frequent occupational injury for the Armed Services continues to be hearing loss [1]. Pre-formed earplugs do not adequately fit extremely small ear canals, extremely large ear canals, or canals with sharp turns. Custom-fit earplugs may provide a solution for this hard-to-fit population. Fortunately, methodology exists to scan ear impressions to create a digital data set, and transmit this data, via the internet, to a remote manufacturer that will fabricate the custom-fit earplugs. The purpose of this study was to investigate how the attenuation provided by custom-fit earplugs created using the digital scanning technique compared to the attenuation provided by custom-fit earplugs created using the traditional wax-dipped technique when used with the CEP. Results showed that the digitally scanned custom-fit earplugs provide significantly poorer attenuation than the traditional wax-dipped custom-fit earplugs. Comply{trade mark, serif} Canal Tip expandable foam earplugs were also evaluated and the results showed significantly greater attenuation than provided by custom-fit earplugs manufactured by either custom method.
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43.66.Vt Hearing protection
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Theoretical and numerical modelling of a parallel-baffle rectangular duct

Davide Borelli, Corrado Schenone, and Ilaria Pittaluga

POMA Volume 14, pp. 040004 (December 2012); (12 pages)

Online Publication Date: December 04, 2012

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The paper describes the theoretical and numerical analysis of sound attenuation in a parallel-baffle rectangular duct. Insertion losses in a frequency range up to 8000 Hz were predicted by means of a FEM numerical model and by means of analytical models from Sabine and Kurze. The models were then validated in the frequency range from 125 to 8000 Hz by comparing theoretical and numerical results with experimental data obtained in accordance to EN ISO 11691 and EN ISO 7235 standards. The results of the comparison indicate that the behavior of such a dissipative/reactive silencer, with its internal-reflections and energy dissipation phenomena, can be predicted quite well by the FEM model on the whole frequency range. On the contrary, analytical models show little accuracy and such predictions are not always so accurate as design requires; besides, the complexity of the analytical approach tends to limit its application to the common design practice. Overall comparisons suggest that FEM modeling can be an accurate and inexpensive way to predict sound attenuation in parallel-baffle mufflers and fulfill the ever rising needs of proper methods in acoustic design of AC and ventilation plants.
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43.55.Rg Sound transmission through walls and through ducts: theory and measurement
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On the use of prepolarized microphone systems in rocket noise measurements

Troy Taylor, Kent L. Gee, Jarom H. Giraud, Scott D. Sommerfeldt, Jonathan D. Blotter, and Curtis P. Wiederhold

POMA Volume 14, pp. 040005 (December 2012); (13 pages)

Online Publication Date: December 05, 2012

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The acoustic field near large-scale solid rocket motors represents a harsh, high-amplitude noise environment rich with high-bandwidth acoustic shocks. Type-1 prepolarized microphones may be used in these environments with the benefit of reduced cost and measurement because they require only a constant-current supply available in many data acquisition systems. However, there are two potential issues related to microphone response that should be considered. The first is a well-known RC-lowpass filter effect that is associated with using insufficient current to drive long cables with relatively high capacitance. The second has to do with temporary failure of the constant-current supply due to an insufficiently fast response time in representing rapid voltage changes at shocks, which results in spurious, capacitive-like effects in the waveform data that are also manifest as a low-frequency roll-up in the spectrum noise floor. An experiment was conducted to identify under what circumstances these waveform effects arise. Data were measured from a solid rocket motor using several combinations of transducer, cable type, cable length and constant current supply. Results and mitigation methods found from the experiment are discussed. These include increasing the supply current, using low-impedance cables, and selecting microphones with low sensitivities.
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43.25.Vt Intense sound sources
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