bluuebunny/crossref_metadata_2025 huggingface dataset:
New equipment for the measurements of flow resistivity and porosity of open cell ceramic and metal foams
Authors: Jados Benjamin , Muehleisen Ralph T.
Published: May 2008

Two of the most important measurements in the acoustic analysis of porous media are the flow resistivity and porosity. To reduce the errors in the measurements of these parameters, new instruments have been developed, which incorporate recent technological advances. The new equipment helps to streamline the user experience and improve the confidence of the results. The current design includes the use of LabVIEW and COMSOL Multiphysics software, the use of thermal press-fit sample holders, and the use of low differential pressure transducers. The new instruments were used to study the flow resistivity and porosity of various pore sizes of open cell ceramic and metal foams. Data are presented with accompanying errors, as well as a discussion of the shortcomings and possible improvements of the measurement system.
The Biot Type II wave in the fluid and matrix of soils
Authors: Sabatier James M. , McNeill Chris
Published: May 2008

When an acoustic wave is incident on the surface of the porous ground energy is coupled into the soil matrix and fluid. To investigate the depth dependence of the Type I and II waves from the ground surface, the ground is modeled as a semi-infinite air-filled poroelastic medium. Using a modified form of Biot-Stoll theory the magnitude and phase of the matrix velocity and fluid pressure caused by the two possible dilatational waves are determined. Traditionally speaking the type I (fast) wave is the nondispersive wave traveling in the solid, and the type II (slow) wave is dispersive and travels primarily in the fluid (air). Previous experiments have shown the possibility that the type II wave travels in the solid near the surface and influences the measured matrix velocity and fluid pressure. Calculations have been done showing that near the surface of the ground the type II wave actually does have a large effect on the particle velocity of the matrix. After the first few centimeters the type II wave is completely attenuated and the type I wave is responsible for the displacement and pressure in the medium
Anisotropy effects on the acoustical properties of porous materials
Authors: Dazel Olivier , Allard Jean François , Boeckx Laurens , Geebelen Nathalie , Khurana Poonam , Lauriks Walter
Published: May 2008

Porous materials are now widely used in noise control for their acoustic properties in sound absorption and transmission. These properties are function of the internal porous medium structure. Generally, most of the models assume that the porous medium is isotropic. Mineral wools (as well as some foams) clearly present an anisotropic structure. This communication is concerned with the adaptation of recent works on isotropic materials to the case of anisotropic porous materials. The general theory will be exposed for sound absorbing materials with anisotropic acoustical and mechanical parameters. The case of transverse isotropic materials (with fibers organized in planes running parallels one to each other) will then be detailed in particular in the case when the plane of fibers is not the same than the normal plane of the sample. The influence on the acoustical properties anisotropic porous materials will then be presented. Illustrations are then provided with measurements performed on wools and it will be shown that the rigidity coefficients of a sample can be evaluated at audible frequencies from measurements in particular from the speed of the Rayleigh wave in different directions.
Optimal sound absorbing and manufacturable two-dimensional, hexagonal-like porous structure
Authors: Perrot Camille , Chevillotte Fabien , Panneton Raymond
Published: May 2008

Results from a numerical study examining micro-macro relations linking local geometry parameters to sound absorption properties are presented. For an hexagonal structure of solid fibers, the porosity φ, the thermal characteristic length Λ', the static viscous permeability ko, the tortuosity α∞, the viscous characteristic length Λ, and the sound absorption coefficient are computed. Numerical solutions of the steady Stokes and electrical equations are employed to provide ko, α∞, and Λ. Hybrid estimates based on direct numerical evaluation of porosity φ, Λ', ko, α∞, Λ and the analytical model derived by Johnson, Champoux, and Allard are used to relate varying (i) throat size, (ii) pore size, and (iii) fibers cross-section shapes to the sound absorption spectrum. The result of this paper tends to demonstrate the important effect of throat size in the sound absorption level, cell size in the sound absorption frequency selectivity, fibers cross-section shape in the porous material weight reduction. In a hexagonal porous structure with solid fibers, the sound absorption level will tend to be maximized with a 48 ± 10 μm throat size corresponding to an intermediate resistivity, a 13 ± 8 μm fiber radius associated with small pores, and convex triangular cross-section shape fibers allowing weight reduction.
Ultrasonic behaviour of high pressure air filled porous media
Authors: Griffiths Stephane , Ayrault Christophe
Published: May 2008

This paper deals with the acoustic behaviour of porous media when the saturating fluid is high pressured. These observations are performed by ultrasonic transmission through a porous sample with variations of the static pressure of the saturating fluid. In order to characterize high damping materials, measurements are performed for high static pressure (up to 18 bars). It is shown that the behaviour of transmission coefficient and speed with pressure follow the Biot's theory. Moreover, measurements are strongly dependant on temperature, which is not visible in modelizations with Biot's model, although this parameter is taken into account in thermodynamical parameters. It is therefore assumed that mechanical characteristics vary with temperature and pressure. An estimation of mechanical parameters is then performed by minimization between the Biot's model and experimental data. First results, obtained in suitable cases for which measurements quality is good and minimization process converges correctly, show that mechanical parameters follow the evolution with frequency described by Pritz at low frequencies. Further researches are still necessary to determine dependance to temperature.
Automatic characterisation of ground surfaces from in situ measurements
Authors: Dutilleux Guillaume , Ecotiere David
Published: May 2008

The study of long term acoustic performance of road pavements requires to access the evolution of the intrinsic parameters of these surfaces, such as resistivity or tortuosity. In long range sound propagation as well, it is well known that ground absorption is time varying. The understanding of this variation is an important issue. In both application cases, nondestructive measurement methods are required. The present contribution focuses on the 2-parameter model by Delany and Bazley for outdoor surfaces and the 4-parameter one by Hamet-Berengier for porous road pavements. It is shown that for both models the absorption coefficient spectrum obtained by an ISO 13472-1 compliant measurement contains enough data for the automatic identification. For the 2-parameter model the identification is based on a suitable cost function. The complexity of the function is low enough for a resolution by exhaustive search. It turns out that, for a large set of soft ground samples, the cost function is convex. Therefore the resolution can be done quite efficiently by classical gradient descent methods. Regarding the 4-parameter model, although the cost function is no longer convex, the resolution can be performed using a global optimization tool, like an evolutionary algorithm.
Sound absorbing properties of materials made of rubber crumbs
Authors: Asdrubali Francesco , D'Alessandro Francesco , Schiavoni Samuele
Published: May 2008

Recycled tyre granules can be used for manufacturing acoustic insulating and absorbing materials, with applications in buildings and road barriers. Therefore, the production of these materials is a valid alternative to the disposal into landfill or incineration of used tyres. This paper presents the results of sound absorbing coefficient measurements of several samples manufactured at the Acoustics Laboratory of the University of Perugia. The sound absorbing panels were produced by mixing rubber crumbs and an adequate binder in a proper proportion and then by compacting the obtained mix. The methodology used to evaluate coefficient of absorption coefficient is indicated in ISO 10534-2 standard, thanks to an impedance tube. The influence on the absorption performance of granules size, binder concentration, thickness and compaction ratio of the samples was investigated and an optimization process was carried out, in order to produce a sample with satisfying acoustical performances.
Analysis of bandpass spectra of phononic defect-mode waveguides based on mode coupling between point defects
Authors: Miyashita Toyokatsu
Published: May 2008

Pass bands of defect-mode waveguides fabricated in sonic/phononic crystals have desirable characteristics for their practical applications to acoustic bandpass filters. Their mechanism is considered to originate in mode-coupling characteristics of point defects, a chain of which composes a defect-mode waveguide. Especially, mode confinement in each point defect or their mode coupling is found to decide the flatness of the pass band. For example, with a relatively strong mode confinement, the transmission of the pass band swings between 0 and -16 dB with frequency, although the transmission outside the pass band remains still typically at -50 dB. On the contrary with a moderate mode confinement, the transmission remains fairly flat only with a swing of 2 dB. We have obtained these characteristics not only by an elastic FDTD method but also by acoustic experiments. These have been investigated theoretically and experimentally based on analyses of the mode coupling between point defects. Two sonic/phononic crystals are considered; one is composed of acrylic-resin cylinders in air, and the other steel cylinders in water.
Combined seismic, radar, and induction sensor for landmine detection
Authors: Scott Waymond R. , Kim Kangwook , Larson Gregg D. , Gurbuz Ali C. , McClellan James H.
Published: May 2008

An experimental system to collect co-located ground penetrating radar (GPR), electromagnetic induction (EMI), and seismic data was developed to investigate possibilities of using the sensors in a cooperative manner and to investigate the benefits of the fusion of the sensors. These sensors were chosen because they can sense a wide range of physical properties. The seismic sensor is sensitive to the differences between the mechanical properties of a landmine and the soil while the GPR is sensitive to the dielectric properties, and the EMI sensor is sensitive to the conductivity. In the experiments, a range of mines and clutter objects were buried at various depths in a sandbox. Multiple burial scenarios were investigated with a variety of antipersonnel and antitank mines and typical clutter objects. The GPR makes use of modified resistive-vee antennas. The EMI sensor collects broadband data so that the relaxation spectra of the buried targets can be used to aid discrimination. The system uses electrodynamic shakers to generate seismic waves, and a radar is used to measure the displacement of the surface caused by the seismic waves. The responses of each of these sensors to the buried targets will be shown. [Work supported by ARO.]
Hysteresis effects in nonlinear acoustic landmine detection
Authors: Korman Murray S.
Published: May 2008

In nonlinear acoustic landmine detection the vibration interaction of the top-plate of the buried plastic landmine with the adjacent soil is a subject of interest due to the strong nonlinear coupling. Using airborne sound excitation (in buried plastic anti-tank inert VS 1.6 and VS 2.2 landmine experiments) tuning curve behavior and generation of combination frequencies from two-tone tests were similar to the mesoscopic/nanoscale nonlinear elastic behavior observed in geomaterials like sandstone [J. Acoust. Soc. Am. 116, 3354-3369 (2004)]. Tuning curve measurements near resonance for increased acoustic amplitude (exhibiting softening) can be explained if hysteresis effects (characteristic of mesoscopic nonlinearity) are considered. The backbone curve (peak amplitude vs. corresponding resonant frequency from a family of tuning curves) exhibits mostly linear behavior for “off target” soil surface vibration measurements of a soil layer resonating over a rigid boundary. Backbone curves for “on target” measurements exhibit significantly more bending and curvature when a soil layer resonates over the compliant top-plate of the landmine. An oscillator with hysteresis modeled by a distribution of parallel spring elements each with a different threshold slip condition seems to describe the “off target” behavior, while a single bilinear hysteresis element describes the “on target” results. [Support by USNA.]
Fast acoustic landmine detection using multiple beam laser Doppler vibrometry
Authors: Aranchuk Vyacheslav , Sabatier James M. , Burgett Richard D.
Published: May 2008

An acoustic method of buried landmine detection consisting of excitation of the ground using airborne sound or seismic waves in the frequency range from about 50 Hz to 1000 Hz, and obtaining a velocity image of the ground surface with a laser Doppler vibrometer (LDV) has been developed and successfully tested in the laboratory and field experiments. The presence of a buried landmine can be detected by an abnormality in the velocity image. Initially, the scanning single-beam LDV created a velocity image of the ground through point-by-point measurements, which resulted in a long measurement time. To reduce this measurement time, a multiple beam LDV having 16 beams configured in a linear array was developed and successfully used in field experiments. To further reduce the time of measurement, a full-field LDV capable of making 256 vibration measurements in parallel on the target, configured as 16x16 square array of points equally separated in x- and y-directions has been recently developed. The system is capable of creating a two-dimensional vibrational velocity image of the ground surface in the time defined by the required frequency resolution. The parallel measurement makes the system a unique tool to measure transient vibrations.
Review of a model for the response of a buried landmine to an airborne acoustic signal
Authors: Velea Doru , Waxler Roger , Sabatier James M.
Published: May 2008

Buried landmines can be found acoustically by insonifying the ground and detecting a contrast between the vibratory motion of the ground surface directly above the mine and a short distance away from the mine. Experiments have revealed a short-ranged spatial response and a frequency response that peaks around 100-200 Hz for anti-tank mines. The peak is believed to be a response to mechanical resonances of the mine itself. A model was developed to explain these experimental observations and to predict how the mine's resonance is influenced by the surrounding soil. In the model the soil was assumed to be an effective fluid while the mine was modeled as a right cylinder with a compliant top. The response of the top of the mine was modeled by an impedance condition. Predictions of the model are presented and compared with the phenomena observed in the field.
Cleaning of semiconductor substrates by controlled cavitation
Authors: Holsteyns Frank , Lippert Alexander , Lechner Florian , Otto Andrea , Nowak Till , Mettin Robert , Doinikov Alexander A. , Okorn-Schmidt Harald
Published: May 2008

The continuing downscaling of device geometries in the semiconductor industry is driving the requirements for both process and contamination control. Historically, the physical and the chemical processes required for contamination control were evolutionarily scaled with device geometry. However, today's tailored wet-chemical cleaning approaches must strive to meet stringent requirements to assure a minimal material loss and no damage to extremely fragile structures. While chemical solutions exist for the control of molecular-organic and metallic ion contamination, the physico-chemical solutions for the removal of nanosized particulate contamination to critical diameters below 20 nm are still undetermined. Therefore, the potential and the limitations of megasonic cleaning, which is mainly based on cavitation, are carefully balanced and a detailed understanding of the ongoing physical mechanisms is necessary to maintain a stable window of operation. The relevant active mechanisms present in such a cavitation driven cleaning process, will depend in great part on the characteristics of the applied sound field; that is to say on frequency, amplitude and uniformity and also on the properties of the cleaning liquid, i.e., the level of gasification, temperature, surface tension, and many others. Different techniques in conjunction with simulations and modeling are under development to improve the design of a novel cleaning tool that can address the challenges.
Using megasonic agitation to extend chemical cleaning for nanotechnology device production
Authors: Franklin Cole
Published: May 2008

Aqueous and solvent chemicals are widely used in the semiconductor industry and as the technology nodes shrink device makers are working to extend these cleaning fluids to the next technology node. Internal data shows megasonic agitation can enhance polymer removal without complete dissolution for both aqueous and solvent chemicals. Data has shown solvents and semi-aqueous solutions show better selectivity with advanced material stacks over aqueous solution. It has been established that megasonic energy can enhance particle removal from semiconductor devices during cleaning processes. However, applied megasonic energy can also damage sensitive semiconductor devices during cleaning, especially in aqueous solutions. Aqueous fluids appear to promote much more damage for the same applied megasonic power than do most solvents. We show that some solvents have a higher threshold for cavitation than deionized water mixes. Since device manufacturers are working to extend their current cleaning chemicals to the 65 and 45 nm pilot production and research nodes, we studied several ways to accomplish this goal for aqueous or solvent chemicals. Described here we apply a methods to predict the damage of nanostructures by various liquids using signal analysis to better understand the mechanical that promotes improved control of cleaning without damage.
Cinephotographic observations of particle removal from a surface by acoustic cavitation
Authors: Crum Lawrence A. , Bailey Michael R. , Canney Michael S. , Chen Hong , Matula Thomas , McInnes Christopher
Published: May 2008

It is commonly believed that ultrasonic cleaners remove particles from a surface through acoustic cavitation, presumably in which a pulsating bubble interacts directly with the particle. We are unaware of any direct evidence of this interaction. Recently, however, we have used a high-speed movie camera to observe the removal of biofilm attached to a solid surface during exposure to a cavitation field. The biofilm consisted of Streptococcus mutans, a common oral bacterium, grown on a glass slide and observed under magnification to be both thinly coating the glass surface and clustered in larger colonies. The cavitation field was created by an UltreoTM toothbrush which combines both vibrating bristles and an ultrasound transducer with waveguide, operating at a frequency of 324 kHz. When the waveguide was immersed in water containing bubbles from an ultrasound contrast agent (OptisonTM), visual observations could be made with the naked eye of biofilm removal. With high-speed cinephotography, it was possible to observe bacteria removal by the direct interaction of a cavitation bubble (cloud) and the colony. These observations will be presented along with our interpretations of the data. [Work supported in part by UltreoTM, Inc.]
Influence of noise type, degree of comodulation and interaural phase difference on the combined monaural and binaural masking release
Authors: Epp Bastian , Verhey Jesko
Published: May 2008

Several masking experiments have shown that the auditory system is able to use coherent envelope fluctuations of the masker across frequency within one ear as well as differences in interaural disparity between signal and masker to enhance signal detection. The two effects associated with these abilities are comodulation masking release (CMR) and binaural masking level difference (BMLD). The aim of the present study was to investigate the combination of CMR and BMLD. Thresholds of a sinusoidal signal were measured in a flanking band paradigm, i.e., in the presence of several narrowband noise maskers, (i) for two noise types (Gaussian and multiplied noise), (ii) various degrees of comodulation, and (iii) various interaural phase differences (IPD) of the signal. Thresholds decreased as the signal IPD increased and decreased as the masker comodulation increased. For both noise types, the maximum CMR was about 10 dB and the maximum BMLD was about 14 dB. Thresholds where monaural and binaural cues were present showed an addition of the single effects, i.e., a maximum masking release of 24 dB. A simplified model of the auditory system assuming a serial alignment of the across-frequency and the binaural processing stages is able to reproduce the dataset.
Contributions of the brainstem and below to auditory scene analysis
Authors: Winter Ian M.
Published: May 2008

We are increasingly aware of the cues the auditory system uses in the segregation and fusion of auditory objects, however, we have very little evidence for how, or where, these cues are extracted in the auditory pathway. Here I will show how the inner ear and cochlear nucleus contribute to three classical auditory scene analysis phenomena. In the first, grouping by common onset; adaptation, lateral suppression, and recovery from suppression all play a role. In the second phemonenon, a sequential streaming task, commonly referred to as ABA, the contributing low-level mechanisms are frequency tuning and neural adaptation. Finally, in the third phenomenon, comodulation masking release, which describes the seemingly paradoxical situation whereby the detection of a masked signal is improved by the addition of coherently modulated energy remote from the signal frequency, lateral suppression is an important mediator. Taken together these studies suggest that neurophysiological processes at, or before, the level of the cochlear nucleus make an important contribution to auditory scene analysis.
Identifying auditory events at a cocktail party: Principles of temporal integration and stream segregation
Authors: Sussman Elyse
Published: May 2008

The question of how sequential sound elements are grouped into meaningful percepts has been within the focus of researchers for decades. This talk takes a new perspective by addressing how within-stream temporal integration occurs in the context of a cocktail party. In a noisy environment, the ability to identify specific events depends upon multiple processes: the overall segregation of sounds into streams as well as the within-stream integration of sequential sounds into meaningful units. This talk presents two studies that address the interaction of these two complex processes. Event-related potentials were used to determine effects of timing (Experiment 1) and of attention (Experiment 2) on the perception of within-stream sound events in multistream environments. Experiment 1 shows that within-stream temporal integration of sequential elements uses previously segregated streams as input. Experiment 2 shows that attention can override stimulus-driven processing biases to facilitate task demands. These results demonstrate different time courses for segregation of sounds into separate streams and for integration of sound elements into within-stream units. Thus, the findings suggest that different neural mechanisms interact in the perceptual organization of sequential sound elements.
Object formation versus object selection
Authors: Shinn-Cunningham Barbara
Published: May 2008

Auditory scene analysis is intricately linked to our ability to understand one acoustic source amidst competing sources. However, studies of selective attention often fail to distinguish between the roles of object formation (estimating the spectro-temporal content of a particular auditory object) and object selection (determining which object will be the focus of attention) in performance. Part of the difficulty in trying to disentangle these effects is that they are intimately related. However, listeners in a selective attention task often report sound elements that are similar in a sound dimension they know is task irrelevant when trying to selectively attend to a different sound attribute (e.g., location, pitch, intensity, timbre). Such results suggest a model of selective attention in which the focus of attention is an auditory object that is formed through interactions between automatic grouping processes and top-down selection. A conceptual model of these interactions will be presented along with data in support of this framework. [Work supported by AFOSR and ONR.]
Perceptual dynamics of auditory streaming and its neural correlates
Authors: Kashino Makio , Kondo Hirohito M. , Okada Minae
Published: May 2008

Prolonged listening to a repeated sequence consisting of low and high tones produces spontaneous transitions in the perceptual state between a single coherent stream and two segregated streams. The dissociation between constant physical stimulation and fluctuating perceptual experience in auditory streaming provides a compelling means for studying how auditory percepts are formed in the brain. First, we psychophysically examined the nature of such perceptual transitions in various frequency differences (Δf) between low and high tones. After the initial buildup of streaming, perceptual transitions occurred frequently even at the Δfs that were previously thought to produce a stable percept, and the dominant perceptual state changed depending on Δf. Next, we explored brain activities correlated with the perceptual transitions using functional magnetic resonance imaging (fMRI). An event- related analysis revealed that the auditory cortex and thalamus were activated at the timing of perceptual transitions. The response onset of the activity in the auditory cortex was earlier than that in the thalamus for the transition from dominant to non-dominant percepts, and later for the transition from non- dominant to dominant percepts. These results imply that the interaction of the auditory cortex and thalamus plays a crucial role for perceptual transitions in auditory streaming.
Neural cross-correlation metrics to quantify envelope and fine-structure coding in auditory-nerve responses
Authors: Heinz Michael , Swaminathan Jayaganesh
Published: May 2008

Fundamental questions about the relative perceptual importance of envelope and fine structure are often addressed using specialized acoustic stimuli, such as temporal-fine-structure speech or auditory chimaeras. Interpretation of these perceptual studies assumes envelope and fine structure can be isolated at the output of the cochlea. Narrowband cochlear filtering constrains the ability to isolate fine structure from envelope; however, envelope recovery from fine structure has been difficult to evaluate physiologically. Separate neural cross-correlation coefficients (CCCs) for envelope and fine-structure were developed based on shuffled auto- and cross-correlograms. Neural CCCs have a wide dynamic range for both within-fiber, cross-stimulus and cross-fiber, within-stimulus correlations based on both model and recorded spike-train data from auditory-nerve fibers. Results provide physiological evidence consistent with perceptual findings that envelope recovery is reduced as the number of analysis bands increases, but is not completely eliminated for 8- and 16-band conditions. Neural CCCs were also used to evaluate across-fiber temporal coding, which has been implicated in the difficulties that hearing-impaired listeners have in understanding speech in complex acoustic backgrounds. Results demonstrate the potential of these neural CCC metrics to quantitatively evaluate a wide range of perceptually significant temporal coding issues relevant to normal and impaired hearing. Supported by NIH-NIDCD.
Transmission of temporal fine structure by a penetrating auditory nerve implant
Authors: Middlebrooks John C. , Snyder Russell L.
Published: May 2008

We are quantifying the transmission of temporal fine structure from a penetrating auditory nerve electrode array to the inferior colliculus (IC) in anesthetized cats. We stimulate with biphasic electrical pulse trains and determine the maximum pulse rate eliciting phase-locked activity. Many IC neurons showed significant phase locking to rates as high as 600 pulses per second (pps) when the nerve was stimulated with the penetrating array, whereas phase locking reached only 300 pps when stimulated with a conventional intrascalar cochlear implant. Phase locking to rates >300 pps was found primarily among IC units with characteristic frequencies (CFs) <2 kHz. Such low frequency fibers are not stimulated selectively by conventional intrascalar cochlear implant. We selectively stimulated apical fibers by placing ball electrodes on the apical spiral lamina. Activation of these balls selectively stimulated low-CF IC neurons. These neurons phase locked to 600 pps. Based on these results, we conclude that transmission of temporal information from a penetrating intraneural electrode array is superior to that obtained with a conventional cochlear implant but only insofar as the intraneural electrodes provide more selective access to low-CF pathways. Supported by NIDCD NO1-DC-5-0005.
Localization and mesoscopics in structures and rooms I
Authors: Weaver Richard
Published: May 2008

Diffuse field methods such as reverberation room acoustics and statistical energy analysis predict wave energy flow in complex structures. They are predicated on an incorrect assumption of incoherence. The consequent failures of otherwise successful theories are occasionally striking. The most noteworthy among these are related to Anderson - and other kinds of - localization. Residual coherence manifests also in time-reversal invariance and Green's function retrieval in field-field correlations. It is sometimes possible in special cases to make ad hoc corrections to the diffuse field theories. It would be preferable, however, to augment them with more a fundamental quantitative theory applicable to a wide variety of systems. This talk reviews mesoscopic phenomena such as weak Anderson localization, modal echoes, Anderson localization, Thouless localization, and Greens function retrieval. It sets out the phenomena and concepts behind the new theory to be presented in “Localization and Mesoscopics in Structures and Rooms II” at a later session.
Periodic assembly of multicoupled beams: Wave propagation and natural modes
Authors: Gosse Guillaume , Pezerat Charles , Bessac François
Published: May 2008

The present work is concerned with the vibrations of a discrete multi-coupled periodic system. It lies within a larger study on the vibroacoustic behaviour of a heat exchanger. These structures are usually made of a succession of huge number of identical parallel fins (around 600 per meter) connected by tubes conveying the coolant fluid. By now their behaviour can not be calculated using FE model. As a first step, the periodicity principles are applied on a simpler structure, i.e.. an assembly of identical beams linked by several damped springs. The basic unit is symmetric and composed of one flexural beam with several springs on each side. Using the Floquet-Bloch's theorem and the works of Denys Mead (receptance matrix), it is possible to completely describe the whole structure behaviour (natural modes, response) only from the vibroacoustic knowledge of the basic unit. This has be done analytically and the results were confirmed by a (very time consuming) FE model calculation. The study of the basic unit can also give valuable information on the physical phenomena governing the transmission from one unit to the next, and then the propagation in the whole structure.
General absorbing boundary for acoustic and elastic waves
Authors: Duhamel Denis
Published: May 2008

In the finite element computation of unbounded acoustic problems, the domains must be of finite size and artificial absorbing conditions have to be introduced in order to avoid reflections at the truncated boundary. This communication proposes a new method in the frequency domain to generate efficient absorbing boundary conditions without the need to consider high order derivatives on the boundary. Moreover the approach is quite general and can consider media with mean flow or be applied to structural vibrations. It needs the knowledge of the dynamic stiffness matrix of only one element which can be obtained from any finite element software. The final result is an impedance condition linking the forces and displacements on the boundary which is determined numerically from a wave analysis of one element of the media. Using this impedance condition a finite element problem can be solved by standard methods. This is then applied to study some examples for 2D standard acoustic, acoustic problems with mean flow and vibrations of plates.
Measurement of SEA damping loss factor for complex structures
Authors: Bolduc Maxime , Atalla Noureddine
Published: May 2008

Statistical Energy Analysis has become extremely popular in the transportation industry. As a prediction tool, it offers appealing advantages such as its wide frequency range and short computational time, which conventional methods do not offer. Critical parameter in every SEA model, the damping characteristics of the subsystems must be determined by way of experimentations. A variety of different techniques of measuring the damping loss factor were developed. These techniques can be divided into three main groups: (i) method based on the identification of modal damping by curve-fitting frequency response function, (ii) decay techniques based on-determination of the reverberation time and, (iii) steady-state techniques involving measurements of power input method much closely related to the definition of SEA since its starting point is the power balance. This work presents an experimental study of these techniques for various structures such as flat metallic panels, aircraft side walls (ribbed curved panels) and sandwich-composite panels in both low and high damping configurations (additions of damping materials, sound packages in both single wall and double wall configurations, mounting effects, ...). In particular, a critical discussion is made on the implementation, advantages and drawbacks of each method regarding its use in SEA modeling of complex structures.
Transmission loss of a panel with tuned vibration absorbers
Authors: Howard Carl Q.
Published: May 2008

The transmission loss of a rectangular panel with numerous discrete tuned vibration absorbers is investigated both theoretically and experimentally. The 49 tuned vibration absorbers have a linear distribution of resonance frequencies and were arranged in grid pattern on the rectangular plate. The transmission loss of the plate was measured between two reverberation chambers and was compared with theoretical predictions. In addition, theoretical predictions and experimental measurements were conducted on a similar system where each vibration absorber was replaced with the equivalent mass of the absorber. The numerical computations were conducted on a distributed computing network comprising 200 desktop computers. The results indicate the improvement in sound transmission loss that can be achieved, greater than merely increasing the thickness of the panel (mass law), and also provides a data set for comparison with predictions involving the use of fuzzy-structure theory.
Sound radiation induced force vibration of submerged and fluid filled multilayered spherical shell
Authors: Malakooti Sadeq , Hasheminejad Seyyed M. , Mohammadi Nader
Published: May 2008

Nowadays sound radiation from spherical shells is attracted for aviation industry. In this paper, the general approach is presented for predicting a coupled fluid solid interaction problem. Therefore, a fully elasticity solution is applied in conjunction with laminated shell model for considering of the sound field over the shell. For each plies the elasticity coefficients are assumed to be constant. The main objectives of this work are investigating the influence of internal and external acoustic mediums and also radially inhomogeneity on acoustic performance of the spherical shell. Numerical results are presented for a three layered spherical shell. For each excitation frequency, sound pressure over zenith angle in polar coordinate is plotted. Also pressure levels against excitation frequency for resonance spectroscopy are investigated.
Application of guided flexural waves in immersed plates to aquatic propulsion of mono-hull marine vessels
Authors: Krylov Victor V. , Porteous Ewan
Published: May 2008

The present paper describes the results of the experimental investigation of a small-scale mono-hull model boat propelled by a localised flexural wave propagating along the plate of finite width forming the boat's keel. Forward propulsion of the boat was achieved through flexural wave propagation in the opposite direction, which is similar to the aquatic propulsion used in nature by stingrays. The model boat under consideration underwent a series of tests both in a Perspex water tank and in the experimental pool. In particular, the forward velocity of the boat has been measured for different frequencies and amplitudes of the flexural wave. The highest velocity achieved was 32 cm/s. The thrust and propulsive efficiency have been measured as well. The obtained value of the propulsive efficiency in the optimum regime was 51%. This indicates that efficiency of this type of aquatic propulsion is comparable to that of dolphins and sharks (around 75%) and to that of a traditional propeller (around 70%). In contrast to a propeller though, the wavelike aquatic propulsion has the following advantages: it does not generate underwater noise and it is safe for people and marine animals.
Multi-bay double panel system with heterogeneous blanket treatment: A comparison between theory and experiment
Authors: Idrisi Kamal , Johnson Marty , Toso Alessandro
Published: May 2008

This study is part of an effort to improve the low frequency performance of acoustic blankets used to reduce the noise inside aircraft cabins. This is achieved by embedding small masses inside the poro-elastic layer such that they act like distributed mass spring damper systems. These mass-spring-damper systems can then be designed to reduce the sound transmission through the double panel system at low frequencies where traditional poro-elastic materials have little effect. A mathematical model of a multi-bay double panel system with frames, stringers, an acoustic cavity and porous/mass layer was developed using impedance and mobility methods (IMM). The multi-bay double panel system includes four skin pockets with four HG blankets of different dimensions such that the interaction between the panels can be analyzed. The predicted responses of the source and receiver panel due to a point force are validated with experimental measurements. The results indicate that proper tuning of the mass insertions can improve the broadband noise reduction below 500 Hz with less than 10% added mass without losing the performance of the acoustic foam at high frequencies.
Active noise control at a moving location in a modally dense three-dimensional sound field using virtual sensing
Authors: Moreau Danielle J. , Cazzolato Ben S. , Zander Anthony C.
Published: May 2008

Local active noise control systems generate a zone of quiet at the physical error sensor using secondary sources to cancel the acoustic pressure at the sensor location. The resulting zone of quiet is generally limited in size and as such, placement of the physical error sensor at the location of desired attenuation is required, which is often inconvenient. Virtual acoustic sensors overcome this by projecting the zone of quiet away from the physical error sensor to a remote location. While virtual acoustic sensors have shown potential to improve the performance of local active noise control systems, it is, however, likely that the desired location of maximum attenuation is not spatially fixed. The work described here presents a virtual sensing method capable of tracking a desired location in a modally dense three-dimensional sound field. The developed algorithm has been experimentally verified in a three-dimensional enclosure and the experimental results are presented.
Damage detection in composite laminates using coin-tap method
Authors: Kim Sung Joon
Published: May 2008

The "coin-tap" test has the ability to indicate damage in a composite structural element due to a localized change of stiffness. The change in vibration signature may be detected by ear or more precisely by measurement of the dynamic contact force. It has been shown that the characteristics of radiated sound from a structure during a tap are changed by the presence of defect beneath the surface of the composite structure. For structurally radiated noise, the sound field is directly coupled to the structural motion. Therefore, impact response analysis should be computed. In this study, the radiated sound induced by impact is obtained by solving the Rayleigh integral equation. Experimental results for the delaminated composite structure are presented and correlations between analytical predictions and measured data are shown. It is shown that the sound based tap test is useful and practical diagnostic tool for detecting localized delamination in composite laminates
Interaction of a pair of complex dynamical systems under impact conditions
Authors: Vignola Joseph F. , Judge John A. , McCoy John
Published: May 2008

An important class of complex dynamical systems has members that are comprised of a dominant simple system, made complex by attaching a large number of significantly less massive subsystems. The response of such systems to a simple forcing that acts on the dominant system has received considerable attention. A simple forcing is understood here to be represented by a time series that has very limited support when represented in either temporal or spectral space. Little attention has be paid to the response of such systems to a complex forcing, understood to be one represented by a time series that has extended support when represented in both temporal and spectral spaces. In the reported study, the interaction of two systems drawn from the described class, under impact conditions are investigated. Significantly, the action of each system on the other during the time interval of their contact is represented by an interaction force that is complex in the sense described. The investigation is accomplished via numerical simulation, physical experiments and analysis.
A Portable robot audition software system for multiple simultaneous speech signals
Authors: Okuno Hiroshi G. , Yamamoto Shunichi , Nakadai Kazuhiro , Valin Jean-Marc , Ogata Tetsuya , Komatani Kazunori
Published: May 2008

Since a robot is deployed in various kinds of environments, the robot audition system should work with minimum prior information on environments to localize, separate and recognize utterances by multiple simultaneous talkers. For example, it should not assume either the number of speakers, the location of speakers for sound source separation (SSS), or specially tuned acoustic model for automatic speech recognition (ASR). We developed a portable robot audition that uses eight microphones installed on the surface of robot's body such as Honda ASIMO, and SIG-2 and Robovie-R2 at Kyoto University with different microphone configurations. The system integrates SSS and ASR by using the Missing-Feature Theory. For SSS, we use Geometric Source Separation (GSS) [Parra 2002] and multichannel post-filter [Cohen 2002] to separate each utterance. Since separated speech signals are distorted due to interfering talkers and sound source separation, multichannel post-filter enhanced speech signals. At this process, we create a missing feature mask that specifies which acoustic features are reliable in time-frequency domain. Multiband Julius [Nishimura 2004], a missing-feature-theory based ASR, uses this mask to avoid the influence of unreliable features in recognizing such distorted speech signals. The system demonstrated a waitress that accepts meal orders placed by three actual human talkers and a voice "Rock-Scissors-Paper" game referee that decides who wins the game.
Inter- and intra-speaker variation: some methodological consequences for sociophonetic research
Authors: Docherty Gerard J. , Foulkes Paul
Published: May 2008

In recent years there has been a rapidly growing awareness of the importance of sociophonetic variation for advancing models of speech production, perception and learning. Meanwhile within sociolinguistic research there has been an equally rapidly evolving recognition that full accounts of the social marking functions of speech communication require greater focus on the manner in which individuals deploy phonetic resources variably as a reflection of the fluid identities which they project across the diverse interactions which they participate in. The aim of this talk is to explore some of the methodological consequences of these developments. We explore the ways in which an approach to sociophonetic variation which rightly focuses on how it plays out in the performance of individual speakers can be reconciled with the development of models of speech production and perception which to date have typically been driven by what is found to be common across individual speakers/listeners and much less by those factors which differentiate them.
Sociophonetic methods for studying substratal effects and new dialect formation
Authors: Thomas Erik R.
Published: May 2008

Studies of substratal effects in the formation of new language varieties have seldom combined both acoustic sophistication and the examination of a broad suite of pronunciation features. This study provides an example of how such work can be conducted. The study focuses on Pearsall, Texas, a community in southern Texas in which Mexican Americans have formed an established community for four generations and exhibit a shift from Spanish dominance to English dominance. A variety of segmental and prosodic variables are examined, both for different generations of Mexican Americans and for Anglo speakers of the contact dialect, and the variables are compared statistically. Results show that some Spanish interference features are discarded, while others take on a life of their own as markers of Mexican American identity.