bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulations of ultrasound propagation in a spinal structure
Authors: Qiao Shan , Coussios Constantin-C , Cleveland Robin O.
Published: May 2014

Lower back pain is one of the most common health problems in developed countries, the main cause of which is the structure change of the intervertebral disks due to the degeneration. High intensity focused ultrasound (HIFU) can be used to remove the tissue of the degenerate discs through acoustic cavitation, after which injection of a replacement material can restore normal physiological function. The acoustic pressure distribution in and around the disc is important for both efficiency and safety. Ultrasound propagation from two 0.5 MHz focused transducers (placed confocally and oriented at 90 degrees) were simulated using a three-dimensional finite element model (PZFlex, Wiedlinger Associates) for both a homogeneous medium and a bovine spine. The size of computation domain was 64 mm*95 mm*95 mm, with a mesh size of 15 elements per wavelength of the fundamental waveform. Measurements of the pressure field from the two transducers in water were also performed. The simulations in a homogeneous medium agreed with the experimental results, in which a sharp ultrasound focus was observed. However, for the spine, the interference of the vertebral bodies lead to absorption in the bone and a smearing of the focus. [Work supported by EPSRC.]
Can quantitative synthetic aperture vascular elastography predict the stress distribution within the fibrous cap non-invasively
Authors: Huntzicker Steven J. , Doyley Marvin M.
Published: May 2014

An imaging system that can detect and predict the propensity of an atherosclerotic plaque to rupture would reduce stroke. Radial and circumferential strain elastograms can reveal vulnerable regions within the fibrous cap. Circumferential stress imaging could predict the propensity of rupture. However, circumferential stress imaging demands either accurate knowledge of the geometric location of the fibrous cap or high quality strain information. We corroborated this hypothesis by performing studies on simulated vessel phantoms. More precisely, we computed stress elastograms with (1) precise knowledge of the fibrous cap, (2) no knowledge of the fibrous cap, (3) imprecise knowledge of the fibrous cap. We computed stress elastograms with accuracy of 8%, 15%, and 23% from high precision axial and lateral strain elastograms (i.e., 25 dB SNR) when precise, imprecise, and no geometric information was included the stress recovery method. The stress recovery method produced erroneous elastograms at lower noise level (i.e., 15 dB SNR), when no geometric information was included. Similarly, it produced elastograms with accuracy of 13% and 30% when precise and imprecise geometric information was included. The stress imaging method described in this paper performs well enough to warrant further studies with phantoms and ex-vivo samples.
Characterizing collagen microstructure using high frequency ultrasound
Authors: Mercado Karla P. , Helguera María , Hocking Denise C. , Dalecki Diane
Published: May 2014

Collagen is the most abundant extracellular matrix protein in mammals and is widely investigated as a scaffold material for tissue engineering. Collagen provides structural properties for scaffolds and, importantly, the microstructure of collagen can affect key cell behaviors such as cell migration and proliferation. This study investigated the feasibility of using high-frequency quantitative ultrasound to characterize collagen microstructure, namely, collagen fiber density and size, nondestructively. The integrated backscatter coefficient (IBC) was employed as a quantitative ultrasound parameter to characterize collagen microstructure in 3-D engineered hydrogels. To determine the relationship between the IBC and collagen fiber density, hydrogels were fabricated with different collagen concentrations (1–4 mg/mL). Further, collagen hydrogels polymerized at different temperatures (22–37°C) were investigated to determine the relationship between the IBC and collagen microfiber size. The IBC was computed from measurements of the backscattered radio-frequency data collected using a single-element transducer (38-MHz center frequency, 13–47 MHz bandwidth). Parallel studies using second harmonic generation microscopy verified changes in collagen microstructure. Results showed that the IBC increased with increasing collagen concentration and decreasing polymerization temperature. Further, we demonstrated that parametric images of the IBC were useful for assessing spatial variations in collagen microstructure within hydrogels.
Surface roughness and air bubble effects on high-frequency ultrasonic measurements of tissue
Authors: Segura Percy D. , Carter Caitlin , Doyle Timothy E.
Published: May 2014

High-frequency (HF) ultrasound (10–100 MHz) has shown the ability to differentiate between healthy tissue, benign pathologies, and cancer in breast cancer surgical samples. It is hypothesized the sensitivity of HF ultrasound to breast cancer is due to changes in the microscopic structure of the tissue. The objective of this study was to determine the effects of surface roughness and air bubbles on ultrasound results. Since the testing is done with tissue inside a plastic bag, small air bubbles may form between the bag and tissue and interfere with test results. Data were collected on bovine and canine tissues to observe changes in HF readings in various organs and positions within specific tissues. Phantom samples were also created to mimic tissue with irregular surfaces and air bubbles. Samples were sealed into plastic bags, coupled to 50-MHz transducers using glycerin, and tested in pitch-catch and pulse-echo modes. The canine and bovine tissues produced similar results, with peak density trending with tissue heterogeneity. The surface grooves in bovine cardiac tissue also contributed to differences in peak densities. In phantom experiments, bubbles only affected peak density when they were isolated in the sample, but irregular surface structure had a strong effect on peak density.
Acoustic impedance of large orifices in thin plates
Authors: Lee Jongguen , Yi Tongxun , Maxted Katsuo , Syed Asif , Crippa Cameron
Published: May 2014

Acoustic impedance of large orifices (0.5–0.75 in. diameter) in thin plates (0.062 in. thickness) was investigated. This work extended the scope previously studied by Stinson and Shaw [Stinson and Shaw, Acoust. Soc. Am. 77, 2039 (1985)] to orifice diameters that were 32 to 584 times greater than the boundary layer thickness. For a frequency range of 0.3–2.5 kHz, the resistive and reactive components were determined from an impedance tube with six fixed microphones. Sound pressure levels (SPL) were varied from 115 to 145 dB. The transition regime from constant to increasing resistances occurred at higher frequencies for larger diameters. Resistance measurements after the transition regime were in good agreement with Thurston's theory [Thurston, J. Acoust. Soc. Am. 24, 653–656 (1952)] coupled with Morse and Ingard's resistance factor [Morse and Ingard, Theoretical Acoustics (McGraw-Hill, New York, 1969)]. Measured reactances remained constant at magnitudes predicted by Thurston's theory.
Temperature effect on ultrasonic monitoring during a filtration procedure
Authors: Lin Lin
Published: May 2014

Membranes are used extensively for a wide variety of commercial separation applications including those in the water purification, pharmaceutical, and food processing industries. Fouling is a major problem associated with membrane-based liquid separation processes because it can often severely limit process performance. The use of ultrasonic monitoring technique for the characterization of membranes and membrane processes has been widely used by university researchers and industrial groups for a variety of applications including membrane fouling, compaction, formation, defect detection, and morphology characterization. However, during the industrial application, such as desalination procedure, temperature of the feed liquid is not constant. This change of the temperature brings in the concern that whether the change of the ultrasonic signal is caused by the fouling or by the temperature change. This research is focus on to verify the degree of effect of temperature to ultrasonic signal, and provide a method that calibrate the temperature effect for real applications.
Noise induced hearing loss mitigation via planning and engineering
Authors: Fischer Raymond W. , Yankaskas Kurt , Page Chris
Published: May 2014

The US Navy, through an ONR lead effort, is investigating methods and techniques to mitigate hearing loss for the crews and warfighters. Hearing protection is a viable and increasingly popular method of reducing hearing exposure for many ship crew members; however, it has limitations on comfort and low frequency effectiveness, and is often used improperly. Proper naval vessel planning, programmatic changes, and advances in noise control engineering can also have significant impacts by inherently reducing noise exposure through ship design along with the use of passive noise control treatments. These impacts go beyond hearing loss mitigation since they can improve quality of life onboard vessels and provide enhanced warfighter performance. Such approaches also can be made to work in the lower frequency range where hearing protection is not as effective. This paper describes the programmatic and noise control methods being pursued to mitigate and control noise within the US Navy and US Marine Corps. Methodologies to assess the cost impact are also discussed.
Enhanced sound absorption of aluminum foam by the diffuse addition of elastomeric rubbers
Authors: Arroyo Elizabeth , Rayess Nassif , Weaver Jonathan
Published: May 2014

The sound absorption properties of open cell aluminum foams are understood to be significant (Ashby et al.Metal Foams: A Design Guide, 2000) with theoretical models presented in the literature [J. Acoust. Soc. Am. 108, 1697–1709 (2000)]. The pores that exist in metal foams, as artifacts of the manufacturing process, are left unfilled in the vast majority of cases. Work done by the US Navy (US patent 5895726 A) involved filling the voids with phthalonitrile prepolymer, resulting in a marked increase in sound absorption and vibration damping. The work presented here involves adding small amounts of elastomeric rubbers to the metal foam, thereby coating the ligaments of the foam with a thin layer of rubber. The goal is to achieve an increase in sound absorption without the addition of cost and weight. The work involves testing aluminum foam samples of various thicknesses and pore sizes in an impedance tube, with and without the added rubber. A design of experiment model was employed to gauge the effect of the various manufacturing parameters on the sound absorption and to set the stage for a physics-based predictive model.
Investigation of structural intensity applied to carbon composites
Authors: Jaber Mariam , Stoewer Torsten , Bös Joachim , Melz Tobias
Published: May 2014

Structures made from carbon composite materials are rapidly replacing metallic ones in the automotive industry because of their high strength to weight ratio. The goal of this study is to enhance acoustic comfort of cars made from carbon composites by comparing various carbon composites in order to find the most suitable composite in terms of mechanical and dynamic properties. In order to achieve this goal, the structural intensity method was implemented. This method can give information concerning the path of energy propagated through structures and the localization of vibration sources and sinks. The significance of the present research is that it takes into account the effect of the material damping on the dissipation of the energy in a structure. The damping of the composite is presented as a function of its micro and macro mechanical properties, frequency, geometry, and boundary conditions. The damping values were calculated by a 2D analytical multi-scale model based on the laminate theory. The benefit of this research for acoustics is that it demonstrates the effect of material properties on passive control. Consequently, structural energy propagated in carbon composite structures will be reduced and less noise will be radiated.
Experimental research on acoustic agglomeration of fine aerosol particles in the standing-wave tube with abrupt section
Authors: Yun Zhao , Xinwu Zeng , Changchao Gong
Published: May 2014

There is great concern about air pollution caused by fine aerosol particles, which are difficult to be removed by conventional removal system. Acoustic agglomeration is proved to be a promising method for particle control by coagulating the small particles into larger ones. Removal efficiency was grown rapidly as acoustic intensity increased. A standing-wave tube system with abrupt section was designed and built up to generate high intensity sound waves above 160 dB and avoid strong shock waves. Extensive tests were carried out to investigate the acoustic field and removal characteristics of coal-fired inhalation particles. For the development of industrial level system, a high power air-modulated speaker was applied and an insulation plate was used to separate flow induced sound. Separate experiments to determine the difference of plane standing-wave field and high order mode were conducted. The experimental study has demonstrated that agglomeration increases as sound pressure level, mass loading, and exposure time increase. The optimal frequency is around 2400 Hz for attaining integral removal effectiveness. The agglomeration rate is larger (above 86%) as much greater sound level is achieved for the pneumatic source and high order mode. The mechanism and testing system can be used effectively in industrial processes.
Aerodynamic and acoustic analysis of an industrial fan
Authors: Bain Jeremy , Wang Gang , Liu Yi , Wang Percy
Published: May 2014

The efforts to predict noise radiation for an industrial fan using direct computational fluid dynamics (CFD) simulation is presented in this paper. Industry has been using CFD tool to guide fan design in terms of efficiency prediction and improvement. However, the use of CFD tool for aero-dynamic noise prediction is very limited in the past, partly due to the fact that research in aero-acoustics field was not practical for industry application. With the most recent technologies in CFD field and increasing computational power, the industry application of aero-acoustics becomes much more promising. It is demonstrated here that fan tonal noise and broadband noise at low frequencies can be directly predicted using an Overset grid system and high order finite difference schemes with acceptable fidelity.
An experimental investigation on the near-field turbulence and noise for an airfoil with trailing-edge serrations
Authors: Xu Kunbo
Published: May 2014

This study concerns the mechanisms of the turbulent broadband noise reduction for an airfoil with the trailing edge serrations. The turbulence spatio-temporal information were measured with 3D hot-wire and the noise results were acquired with a line array. The experiment is carried out in the Northwestern Polytechnical University low speed open jet wind tunnel on the SD2030 airfoil. λ/h = 0.2. It is showed the spreading rate of the wake and the decay rate of the wake centerline velocity deficit increased with serrated edge compared to the straight edge, shedding vortex peaks appeared in the wake, and the three components of velocity changed differently with serrated trailing edge. Serrated trailing edge structure could reduce the radiated noise was proofed by noise results.
Necessity as the mother of innovation: Adapting noise control practice to very different set of mechanical system design approaches in an age of low energy designs
Authors: Pfeiffer Scott D.
Published: May 2014

The shift in Mechanical Systems design to natural ventilation, dedicated outside air systems, variable refrigerant flow, and the return to radiant systems all present new challenges in low-noise systems. Case studies of current projects explore the sound isolation impact of natural ventilation, the benefits of reduced air quantity in dedicated outside air, the distributed noise issues in variable refrigerant flow, and the limitations of radiant systems as they apply in performing arts and noise critical spaces.
Readily available noise control for residences in Boston
Authors: Timmerman Nancy S.
Published: May 2014

Urban residential noise control may involve high-end interior finishes, insufficient noise reduction between neighbors (in a same building), or interior/exterior noise reduction for mechanical equipment or transportation where the distances are small or non-existent. Three residences in Boston's South End, where the author is a consultant (and resident), will be discussed. The area consists of brownstones built in the mid-nineteenth century, with granite foundations, masonry facades, and common brick walls. Treatments were used which were acceptable to the “users”—neighbors on both sides of the fence.
Singing in the wind; noise from railings on coastal and high-rise residential construction
Authors: Cunefare Kenneth
Published: May 2014

Beach-front and high-rise residential buildings are commonly exposed to sustained high winds. Balcony railings with long spans and identical pickets on uniform spacing may be driven into extremely high amplitude synchronous motion due to phase and frequency locked vortex shedding. The railing motion can excite structural vibration in floor slabs which can propagate into units and produce undesirable tone-rich noise within the units, noise that stands out well above the wind noise that also propagates into the units. Solution of this problem requires breaking the physical phenomena that induce the railing motion, including blanking off the railings; stiffening the railings; and breaking the symmetry of the individual pickets. The problem may be further complicated by questions of who should pay for the remediation of the problem, and the costs associated with remediating numerous units, particularly on high-rise developments. Increased awareness during the design phase of the potential for this problem may reduce the need for post-construction controls.
What do teachers think about noise in the classroom?
Authors: Jaramillo Ana M. , Ermann Michael G. , Miller Patrick
Published: May 2014

Surveys were sent to 396 Orlando-area elementary school teachers to gauge their subjective evaluation of noise in their classroom, and their general attitudes toward classroom noise. The 87 responses were correlated with the types of mechanical systems in their respective schools: (1) fan and compressor in room, (2) fan in room and remote compressor, or (3) remote fan and remote compressor. Results were also compared to the results of a previous study of the same 73 schools that linked school mechanical system type with student achievement. While teachers were more likely to be annoyed by noise in the schools with the noisiest types of mechanical systems, they were still less likely to be annoyed than the research might suggest—and when teachers did express annoyance, it was more likely to be centered around the kind of distracting noise generated by other children in adjacent corridors than by mechanical system noise.
Relationship between air infiltration and acoustic leakage of building enclosures
Authors: Muehleisen Ralph T. , Tatara Eric , Bethke Brett
Published: May 2014

Air infiltration, the uncontrolled leakage of air into buildings through the enclosure from pressure differences across it, accounts for a significant fraction of the heating energy in cold weather climates. Measurement and control of this infiltration is a necessary part of reducing the energy and carbon footprint of both current and newly constructed buildings. The most popular method of measuring infiltration, whole building pressurization, is limited to small buildings with fully constructed enclosures, which makes it an impractical method for measuring infiltration on medium to large buildings or small buildings still under construction. Acoustic methods, which allow for the measurement of infiltration of building sections and incomplete enclosures, have been proposed as an alternative to whole building pressurization. These new methods show great promise in extending infiltration measurement to many more buildings, but links between the acoustic leakage characteristics and the infiltration characteristics of typical enclosures are required. In this paper, the relationship between the acoustic leakage and the air infiltration through typical building envelope cracks is investigated. [This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.]
Hemi-anechoic chamber qualification and comparison of room qualification standards
Authors: Davidson Madeline A.
Published: May 2014

The hemi-anechoic chamber at the Trane Laboratory in La Crosse, Wisconsin, is commonly used for acoustic testing of machinery and equipment. As required by standards, it must periodically be qualified. Sound measurements taken in a hemi-anechoic facility often depend on the assumption that the chamber is essentially free-field. To verify that the room is sufficiently anechoic, the procedures in ANSI/ASA Standard S12.55-2012/ISO 3745:2012 and ISO Standard 26101-2012 are followed. One challenge of a room qualification is finding adequate sound sources. Sources used in the qualification procedure must be Omni-directional, so directionality measurements must be taken to prove that a source is suitable for the room qualification procedure. The specific qualification procedure described in this paper involved two sound sources—a compression driver and a 6 in. × 9 in. speaker. In addition, the particular method described in this paper involves a temporary plywood floor and six microphone traverse paths extending out from the center of the chamber. This approach to qualifying a facility is expected to define what part of the room is adequately anechoic. This paper will describe the results obtained when following each of these standards.
Sound absorption of parallel arrangement of multiple micro-perforated panel absorbers at oblique incidence
Authors: Wang Chunqi , Huang Lixi , Zhang Yumin
Published: May 2014

Many efforts have been made to enhance the sound absorption performance of micro-perforated panel (MPP) absorbers. Among them, one straightforward approach is to arrange multiple MPP absorbers of different frequency characteristics in parallel so as to combine different frequency bands together, hence an MPP absorber array. In previous study, the parallel absorption mechanism is identified to be contributed by three factors: (i) the strong local resonance absorption, (ii) the supplementary absorption by non-resonating absorbers, and (iii) the change of environmental impedance conditions; and the local resonance absorption mechanism accounts for the increased equivalent acoustic resistance of the MPP. This study seeks to examine how the MPP absorber array performs at oblique incidence and in diffuse field. One major concern here is how the incidence angle of the sound waves affects the parallel absorption mechanism. In this study, a finite element model is developed to simulate the acoustic performance of an infinitely large MPP absorber array. Numerical results show that the sound absorption coefficients of the MPP absorber array may change noticeably as the incidence angle varies. The diffuse field sound absorption coefficients of a prototype specimen are measured in a reverberation room and compared with the numerical predictions.
Research on the flow resistance of acoustic materials—Takes Concert Hall at Gulangyu Music School in Xiamen as an Example
Authors: Wang Peng , Yan Xiang , Shuai Lu W. , Song Gang , Liang Yan
Published: May 2014

Different kinds of acoustic materials are used in a concert hall design, which has different functions such as diffusing, reflecting, or absorbing. The cushion of chairs in concert halls usually uses porous sound-absorbing material, whose absorbing attributes are mainly determined by its flow resistance. In the design of Concert Hall at Gulangyu Music School in Xiamen, we measured the flow resistance of materials, trying to acquire the best sound-absorbing attributes by adjusting the flow resistance, and also tested the material samples’ absorbing coefficients in reverberation room. In a nutshell, measuring and analyzing flow resistance is an advanced method in acoustic design, which could help acousticians decide the most suitable absorbing attributes of chairs, and acquire the best sound quality.
The effective sound speed approximation and its implications for en-route propagation
Authors: Sparrow Victor , Poulain Kieran , Romond Rachel
Published: May 2014

The effective sound speed approximation is widely used in underwater and outdoor sound propagation using common models such as ray tracing, the parabolic equation, and wavenumber integration methods such as the fast field program. It is also used in popular specialized propagation methods such as NORD2000 and the Hybrid Propagation Model (HPM). Long ago when the effective sound speed approximation was first introduced, its shortcomings were understood. But over the years, a common knowledge of those shortcomings has waned. The purpose of this talk is to remind everyone that for certain situations the effective sound speed approximation is not appropriate. One of those instances is for the propagation of sound from aircraft cruising at en-route altitudes when wind is present. This is one situation where the effective sound speed approximation can lead to substantially incorrect sound level predictions on the ground. [Work supported by the FAA. The opinions, conclusions, and recommendations in this material are those of the authors and do not necessarily reflect the views of FAA Center of Excellence sponsoring organizations.]
Large eddy simulation of surface pressure fluctuations generated by elevated gusts
Authors: Cain Jericho , Raspet Richard , Otte Martin
Published: May 2014

A surface monitoring system that can detect turbulence aloft would benefit wind turbine damage prevention, aircraft safety, and would be a new probe to study the atmospheric boundary layer. Previous research indicated that elevated velocity events may trigger pressure fluctuations on the ground. If that is true, it should be possible to monitor elevated wind gusts by measuring these pressure fluctuations. The goal of this project was to develop a ground based detection method that monitors pressure fluctuations on the ground for indicators that a gust event may be taking place at higher altitudes. Using gust data generated with a convective boundary layer large eddy simulation, cross-correlation analysis between the time evolution of the frequency content corresponding to elevated wind gusts and the pressure on the ground below were investigated. Several common features of the pressures caused by elevated gusts were identified. These features were used to develop a tracking program that monitors fast moving high amplitude pressure fluctuations and to design a ground based pressure sensing array. The array design and tracking software was used to identify several new gust events within the simulated atmosphere.
Spatial coherence function for a wideband acoustic signal
Authors: Cain Jericho , Collier Sandra , Ostashev Vladimir , Wilson D. Keith
Published: May 2014

Atmospheric turbulence has a significant impact on acoustic propagation. It is necessary to account for this impact in order to study noise propagation, sound localization, and for the development of new remote sensing methods. A solution to a set of recently derived closed form equations for the spatial coherence function of a broadband acoustic pulse propagating in a turbulent atmosphere without refraction and with spatial fluctuations in the wind and temperature fields is presented. Typical regimes of the atmospheric boundary layer are explored.
The high-order parabolic equation to solve propagation problems in aeroacoustics
Authors: Malbéqui Patrice
Published: May 2014

The parabolic equation (PE) has proved its capability to deal with the long range sound propagation in the atmosphere. It also represents an attractive alternative to the ray model to handle duct propagation in high frequencies, for the noise radiated by the nacelle of aero-engines. It was recently shown that the High-Order Parabolic Equation (HOPE), based on a Padé expansion with an order of 5, significantly increases the aperture angle of propagation compared to the standard and the Wide-Angle PEs, allowing prediction close to cut-off frequency of the duct. This paper concerns the propagation using the HOPE in heterogeneous flows, including boundary layers above a wall and in shear layers. The thickness of the boundary layer is about dozens of centimeters while outside it, the Mach number reaches 0.5. The boundary layer effects are investigated showing the refraction effects on a range propagation of 30 m, up to 4 kHz. In the shear layer, discontinuities in the directivity patterns occur significant differences of the directivity patterns occur. Comparisons with the Euler solutions are considered, establishing the domain of application of the HOPE on a set of flow configurations, including beyond its theoretical limits. [Work supported by Airbus-France.]
Behavioral explorations of cochlear gain reduction
Authors: Strickland Elizabeth A. , Roverud Elin , DeRoy Milvae Kristina
Published: May 2014

Physiological measures have shown that the medial olivocochlear reflex (MOCR) decreases the gain of the cochlear active process in response to ipsilateral or contralateral sound. As a first step to determining its role in human hearing in different environments, our lab has used psychoacoustical techniques to look for evidence of the MOCR in behavioral results. Well-known forward masking techniques that are thought to measure frequency selectivity and the input/output function at the level of the cochlea have been modified so that the stimuli (masker and signal) are short enough that they should not evoke the MOCR. With this paradigm, a longer sound (a precursor) can be presented before these stimuli to evoke the MOCR. The amount of threshold shift caused by the precursor depends on its duration and its frequency relative to the signal in a way that supports the hypothesis that the precursor has reduced the gain of the cochlear active process. The magnitude and time course of gain reduction measured across our studies will be discussed. The results support the hypothesis that one role of the MOCR may be to adjust the dynamic range of hearing in noise. [Work supported by NIH(NIDCD)R01 DC008327, T32 DC000030-21, and Purdue Research Foundation.]
Time-course of recovery from the effects of a notched-noise on the ear-canal pressure at different frequencies
Authors: Walsh Kyle P. , Wojtczak Magdalena
Published: May 2014

Different methods for estimating the effect of the medial olivocochlear reflex (MOCR) on stimulus-frequency otoacoustic emissions (SFOAEs) in humans appear to yield different estimates of the time-course of recovery from the effect. However, it is uncertain whether the observed differences in recovery times were due to differences in the methods used to extract the changes in SFOAEs, due to the fact that different feedback-based reflexes—MOCR or the middle ear muscle reflex (MEMR)—were activated, or due to the dependence of recovery from the activated reflex on the probe frequency. In this study, the ear-canal pressure was measured for continuous probes with frequencies of 1, 2, 4, and 6 kHz, in the presence and absence of an ipsilateral notched-noise elicitor. Changes in the magnitude and phase of the ear-canal pressure were extracted to estimate recovery times from the effects of the elicitor. The results showed that the recovery time increased with increasing probe frequency—from about 380 ms at 1 kHz to about 1500 ms at 6 kHz, on average. The measurements also were repeated for each of the probe frequencies paired with a simultaneous 500-Hz tone to examine the role of the MEMR. [Work supported by NIH grant R01DC010374.]
Causality and scattering from cylindrical shells
Authors: McDaniel James G.
Published: May 2014

Acoustic scattering from a cylindrical shell is required to be causal, so that the incident wave must precede the scattered wave that it creates. In the frequency domain, this statement may be explored by forming a frequency-dependent complex-valued reflection coefficient that relates the scattered wave to the incident wave. The real and imaginary parts of the reflection coefficient must therefore satisfy Hilbert Transform relations that involve integrals over frequency. As a result, one may find the real part of the reflection coefficient given only its imaginary part over a frequency range, and vice-versa. The reflection coefficient is not required to be minimum phase and rarely is minimum phase, so the causality condition cannot be used directly to estimate the phase of the reflection coefficient from its magnitude. However, the effective impedance associated with the reflection coefficient is required to be minimum phase. An approach is presented for using these relations to estimate the phase of a reflection coefficient given only its magnitude. Examples are presented that illustrate these relationships for cylindrical shells.
Measurement of spectral resolution and listening effort in people with cochlear implants
Authors: Winn Matthew , Litovsky Ruth Y. , Edwards Jan R.
Published: May 2014

Cochlear implants (CIs) provide notably poor spectral resolution, which poses significant challenges for speech understanding, and places greater demands on listening effort. We evaluated a CI stimulation strategy designed to improve spectral resolution by measuring its impact on listening effort (as quantified by pupil dilation, which is considered to be a reliable index of cognitive load). Specifically, we investigated dichotic interleaved processing channels (where odd channels are active in one ear, and even channels are active in the contralateral ear). We used a sentence listening and repetition task where listeners alternated between their everyday clinical CI configurations and the interleaved channel strategy, to test which offered better resolution and demanded less effort. Methods and analyses stemmed from previous experiments confirming that spectral resolution has a systematic impact on listening effort in individuals with normal hearing. Pupil dilation measures were generally consistent with speech perception (r2 = 0.48, p < 0.001), suggesting that spectral resolution plays an important role in listening effort for listeners with CIs. When using interleaved channels, both speech perception performance and pupillary responses were variable across individuals, underscoring the need for individualized measurement for CI listeners rather than group analysis, in the pursuit of better clinical fitting.
The effect of background noise on intelligibility of adults and children with dysphonia
Authors: Ishikawa Keiko , Powell Maria , Phero Heidi , de Alarcon Alessandro , Khosla Sid M. , Boyce Suzanne , Kelchner Lisa
Published: May 2014

A majority of patients with dysphonia report reduced intelligibility in their daily communication environments. Laryngeal pathology often causes abnormal vibration and incomplete closure of the vocal folds, resulting in increased noise and decreased harmonic power in the speech signal. These acoustic consequences likely make dysphonic speech more difficult to understand, particularly in the presence of background noise. The study tested two hypotheses: (1) intelligibility of dysphonic speech is more negatively affected by background noise than that of normal speech, and (2) listener ratings of intelligibility will correlate with clinical measures of dysphonia. One hundred twenty speech samples were collected from 6 adults and 4 children with normal voice and 6 adults and 4 children with varying degrees of dysphonia. Each sample consisted of a short phrase or sentence and was characterized by two acoustic measures commonly associated with degree of dysphonia: cepstral peak prominence (CPP) and harmonic to noise ratio (HNR). Samples were combined with three levels of “cafeteria” noise ( + 0 dB SNR, + 5 dB SNR, and no noise) and then subjected to a speech perception experiment with 60 normal listeners. This project is ongoing. Preliminary results support hypothesis 1; additional findings related to hypothesis 2 will also be discussed.
Two-dimensional slant filters for beam steering
Authors: Schmidlin Dean J.
Published: May 2014

The concept of a two-dimensional digital “slant” filter is introduced. If the input and output of the slant filter are represented by matrices whose row and column indices denote discrete time and discrete space, respectively, then each diagonal of the output matrix is equal to the linear convolution of the corresponding diagonal of the input matrix with a common one-dimensional sequence. This sequence may be considered as the impulse response of a one-dimensional shift-invariant filter. The transfer function of the slant filter has the form H(z1,z2) = G(z1z2) where G(z) is the transfer function of the one-dimensional filter. It is shown that the slant filter is capable of forming and steering a beam using pressure samples from a linear array. The output of the beamformer is equal to the last column of the output matrix of the slant filter. One interesting feature is the possibility that two beamformers can have the same beamwidth but steer the beam to different angles. Another is that though the slant filter is two-dimensional, it can be designed by utilizing well-developed one-dimensional techniques. An example is presented to illustrate the theoretical concepts.
Compressive acoustic imaging with metamaterials
Authors: Xie Yangbo , Tsai Tsung-Han , Brady David J. , Cummer Steven A.
Published: May 2014

Compressive imaging has brought revolutionary design methodologies to imaging systems. By shuffling and multiplexing the object information space, the imaging system compresses data on the physical layer and enables employing fewer sensors and acquiring less data than traditional isomorphic mapping imaging systems. Recently metamaterials have been investigated for designing compressive imager. Metamaterials are engineered materials with properties that are usually unattainable in nature. Acoustic metamaterials can possess highly anisotropy, strongly dispersion, negative dynamic density, or bulk modulus, and they open up new possibilities of wave-matter interaction and signal modulation. In this work, we designed, fabricated, and tested a metamaterial-based single detector, 360 degree field of view compressive acoustic imager. Local resonator arrays are design to resonate randomly in both spatial and spectrum dimensions to favor compressive imaging task. The presented experimental results show that with only about 60 measured values, the imager is able to reconstruct a scene of more than 1000 sampling points in space, achieving a compression ratio of about 20:1. Multiple static and moving target imaging task were performed with this low cost, single detector, non-mechanical scanning compressive imager. Our work paves the way for designing metamaterials based compressive acoustic imaging system.
Evaluation of a high-order Ambisonics decoder for irregular loudspeaker arrays through reproduced field measurements
Authors: Trevino Lopez Jorge A. , Okamoto Takuma , Iwaya Yukio , Sakamoto Shuichi , Suzuki Yo-iti
Published: May 2014

High-order Ambisonics (HOA) is a sound field reproduction technique that defines a scalable and system-independent encoding of spatial sound information. Decoding of HOA signals for reproduction using loudspeaker arrays can be a difficult task if the angular spacing between adjacent loudspeakers, as observed from the listening position, is not uniform. In this research, one of such systems is considered: a 157-channel irregular loudspeaker array. The array is used to reproduce simple HOA-encoded sound fields. Three HOA decoding methods are evaluated: two conventional ones and a recently proposed decoder designed for irregular loudspeaker arrays. Reproduction accuracy is compared by directly measuring the sound pressure around the listening position, the so-called sweet spot. Coarse-resolution sound field measurements give an approximate size for the listening region generated by the different methods. In addition, dummy head recordings are used to evaluate interaural level and phase differences. The results are used to estimate the accuracy of the system when presenting spatial sound. This study shows the importance of selecting a proper decoding method to reproduce HOA with irregular loudspeaker arrays. This is emphasized by the use of an actual loudspeakers system instead of a computer simulation, a common shortcoming of previous studies.
Coherent vector sensor processing for autonomous underwater glider networks
Authors: Nichols Brendan , Martin James , Sabra Karim , Trivett David , Smith Kevin B.
Published: May 2014

A distributed array of autonomous underwater gliders, each fitted with a vector sensor measuring acoustic pressure and velocity, form an autonomous sensor network theoretically capable of detecting and tracking objects in an ocean environment. However, uncertainties in sensor positions impede the ability of this glider network to perform optimally. Our work aims to compare the performance of coherent and incoherent processing for acoustic source localization using an array of underwater gliders. Data used in the study were obtained from numerical simulations as well as experimental data collected using the research vessel as a source for localization purposes. By estimating the vessel position with a single glider’s data (incoherent) and comparing to the location estimated with both gliders’ data (coherent), it was determined that location estimation accuracy could be improved using coherent processing, provided the gliders’ positions could be measured with sufficient precision. The results of this study could potentially aid the design and navigation strategies of future glider networks with a large number of elements.
Spatial correlation of the acoustic vector field of the surface noise in three-dimensional ocean environments
Authors: Huang Yiwang , Guo Junyuan
Published: May 2014

Spatial correlation of ocean ambient noise is a classical and attractive topic in ocean acoustics. Usually acoustic particle velocity can be formulated by the gradient of sound pressure. But due to the complexity of the sound pressure in range-dependent environments, the velocities of the surface noise are too difficult to be solved by this way. Fortunately, by taking advantage of the exchangeability of partial derivative and integral operation, a new derivation was proposed and a vector model for the surface-generated noise in three-dimensional ocean environments was developed directly from the correlation function of sound pressure. As a model verification, spatial correlation of the acoustic vector field of the surface noise in a range-independent environment was derived, and the identical correlation functions were given compared with the literature. After then, the surface noise in a range-dependent environment was considered with a rigid bottom hypothesis. The effects on the correlation taken by the bottom sloping and medium absorption were analyzed numerically.
Some effects of room acoustics and background noise on assistive listening systems and devices
Authors: Mapp Peter
Published: May 2014

Approximately 10–14% of the general population (United States and Northern Europe) suffer from a noticeable degree of hearing loss and would benefit from some form of hearing assistance or deaf aid. However, many hearing aids do not provide a suitable level of intelligibility when used in large reverberant or noisy spaces and rooms. The paper investigates the acoustic and speech intelligibility requirements for Assistive Listening Systems that may be used separately or in conjunction with a hearing aid to improve the potential intelligibility of the received speech signal. A number of microphone pick-up scenarios have been investigated and are reported in terms of their potential intelligibility and sound quality performance. The results of testing carried out in a number of rooms and venues are presented, mainly in terms of the resultant Speech Transmission Index (STI). The paper concludes by providing a number of recommendations and guidelines for successful microphone placement and introduces a novel technique for establishing useful talker sound radiation and hence microphone target aiming.
An approach for estimating noise induced hearing loss because of indoor and outdoor environment noise factors in healthcare facilities
Authors: Kocyigit Filiz B.
Published: May 2014

This paper investigates a number of healthcare centers from University Medical Schools and State Hospitals, Baskent University Medical School and Private Research Hospitals, and the State Hospital. The sound levels present in these centers were compared with number international as well as Turkish standards. Research was carried out in the following way: First, physicians and nurses were surveyed by means of a questionnaire. Then, the hospital buildings were examined in terms of their architectural design features. Lastly, sound levels were measured in the consequent spaces where questionnaires were also conducted. In addition, noise in hospitals can be detrimental as it helps to present their environment as quiet and peaceful. WHO provides guidelines for hospitals in this respect in its Guidelines for Community Noise published in 1995 (4). ANSI S12.2, recommends a maximum Room Criterions Curves (NCC) value ranging on the room type, and a maximum Noise Criteria Balanced (NCB) value ranging. A document issued by the Environmental Protection Agency (EPA) summarizing significant community noise studies provides recommendations in terms of the Ld&n (day-night sound pressure level). The Institute of Turkish Standards (TSE) is also working on this subject and the first national standard about ambient at Table 11.
The science of underwater sound: Education, communication, and outreach
Authors: Scowcroft Gail , Vigness-Raposa Kathleen J.
Published: May 2014

As a complex scientific topic, underwater sound can be challenging for scientists to discuss and effectively communicate with non-science audiences. Educational audiences span formal K-16 classrooms to museum and aquarium visitors. The science of sound is often included in upper middle school physical sciences curricula, high school physics classes, and undergraduate and graduate university courses, which can take advantage of calculus to support student understanding. Communicating with the media presents other challenges: pressing or immediate deadlines; a need to deliver eye-catching, flashy pieces that capture reader attention; and a general lack of fundamental knowledge of underwater sound by readers. Scientists must be proactive in their engagement with media to ensure good fundamental science is communicated and to increase useful stories about new developments in underwater sound research. Regulators and other decision-makers are also pressed for time when contemplating a topic, yet they need the most up-to-date scientific findings to support their decision-making. This talk will provide an overview of the challenges that ocean acoustic specialists face when trying to communicate the results of their research and meet the needs of diverse audiences. In addition, strategies and possible solutions will be discussed.