bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and theoretical investigations of focusing of ultrasonic waves by two-dimensional flat phononic crystals
Authors: Sukhovich Alexey , Page John H. , Merheb Bassam , Vasseur Jérôme , Deymier Pierre
Published: May 2008

We compare experimental and theoretical results demonstrating focusing of sound fields emitted by subwavelength sources using two-dimensional flat phononic crystals. Our phononic crystals are made of stainless steel rods assembled in a triangular crystal lattice and immersed in a liquid. Focusing is achieved due to negative refraction of ultrasonic waves propagating through the crystal, which is realized at the frequencies corresponding to the 2nd band, where the group velocity and wave vector are antiparallel. High quality images are obtained experimentally with a methanol-filled phononic crystal surrounded by water, in which the source and detecting transducers are located. Excellent resolution approaching the diffraction limit is achieved for the frequency at which the equifrequency contours inside the crystal match those in water. Our experimental results are compared with theoretical predictions by the Finite Difference Time Domain (FDTD) method. Good agreement is observed for the width of the focal spot in the direction parallel to the crystal surface, while along the perpendicular direction, we find experimentally that the focal spot is narrower and closer to the crystal surface than in the theoretical predictions.
A Transient Grating approach to elastic wave and thermal propagation in a 2D free-standing micrometric phononic crystal
Authors: Malfanti Iacopo , Torre Renato , Bartolini Paolo , Taschin Andrea , Vita Francesco , Simoni Francesco
Published: May 2008

We investigate the phonon propagation in a 2D phononic crystal (with typical dimensions on the micrometric scale) by means of a transient grating (TG) heterodyne detected experiment. In a TG experiment both a temperature and a density grating are induced by means of optical techniques. The relaxation dynamics of the induced grating are then monitored live-time over 6 temporal decades with a probe beam. Our sample is a freestanding 100 micrometer thick polymer matrix with empty rods (filled with gas) arranged in a triangular lattice. Evidence of the presence of two different bulk wave acoustic modes are experimentally found. The excited acoustic modes show a correlation with the orientation of the sample with respect to the induced grating wave vector, while the thermal properties show a significant dependence on the magnitude of the induced grating wave vector.
Thermal shifting of phononic bandgaps in barium strontium titanate-based structures
Authors: Jim Kwok Lung , Leung Chi Wah , Choy Chung Loong , Chan Helen L. W.
Published: May 2008

Phononic crystals, which are structures with periodic variations of density and/or sound velocities, can exhibit phononic bandgaps where propagation of acoustic waves is forbidden. The ability of phononic crystals to manipulate sound, in a similar manner which photonic crystal control light, makes them particularly useful for applications such as acoustic filters or very efficient waveguides. Since the positions of the phononic bandgaps depend solely on the densities and the sound velocities of the constituent materials, it is expected that a modulation in the densities and/or sound velocities of the constituent materials would result in a phononic bandgap shift. It is known that ferroelectric ceramic, such as barium strontium titanate (BST), will undergo a ferroelectric-to-paraelectric phase transition across the Curie temperature. During the phase transition, there is a large variation in the sound velocities of BST which result in a shift of the phononic bandgaps. In this work, we calculated the phononic bandstructures of BST-based structures by the plane-wave expansion method and showed that the phononic bandgaps can be shifted thermally.
Nondiffractive propagation of sound in sonic crystals
Authors: Perez-Arjona Isabel , Sánchez-Morcillo Victor , Espinosa Víctor , Staliunas Kestutis , Redondo Javier
Published: May 2008

In this work we present the study of the nondiffractive propagation regime of ultrasonic waves in a two-dimensional periodic acoustic media (sonic crystal) both from the theoretical and the experimental point of view. An analytical treatment of this regime sonic wave propagation is presented, which allows evaluating the parameters of the nondiffractive regime, just as the minimum size of the nondiffractively propagating acoustic beam. Experimentally, we report on the first experimental demonstration of the subdiffractive propagation (self-collimation) of an ultrasound beam in a sonic crystal formed by steel cylinders in water. The experimental measurements show a good agreement with the theoretical predictions, where the effect of the finite size of the crystal was also considered. The preliminary results on self-collimation of sound in three-dimensional sonic crystal, in progress at the present moment, will be also presented.
In-situ measurement of interface permeability
Authors: Lin Lin , Peterson Michael , Greenberg Alan , McCool Benjamin
Published: May 2008

Permeability of a porous interface is important for many areas of research and technology ranging from transport of nutrients in marine sediments to produce separations in bio-pharmaceuticals. Biot theory has shown that porous materials are able to support the propagation of two longitudinal waves: fast and slow wave. By measuring the propagation threshold of the slow longitudinal wave when the wave number is higher than the critical wave number kcr, we can obtain the intrinsic permeability of a porous interface. The ability to sense permeability change due to differences in pore size and fluid viscosity is demonstrated. The measurement is compared to an exact solution for kcr as well as previously published analytical solutions. This technique for measuring permeability has been shown in a model material and can now be extended to a wide range of materials of scientific and technical importance.
Influence of sound absorption on close proximity noise of porous pavement
Authors: Paje S. E. , Bueno Moises , Viñuela Urbano , Terán Fernando
Published: May 2008

The main objective of this research is to correlate sound absorption of a new bituminous porous pavement (air void content 21%) with the close proximity noise. Different core samples were taken from a porous road surface. The normal incidence sound absorption spectra were measured for these samples using the two-microphone impedance tube. Noise levels close to the tire/pavement contact patch were measured continuously in a geo-referenced way, when the test vehicle was rolling. The emission properties of the porous surface as a function of vehicles speed are analyzed in the acoustic frequency range showing different behaviors for the relationships between noise levels and speed. An abrupt variation in the relationship between the coefficient B and frequencies below 1 kHz was observed (Lcp=A+Ḃlog(V)). This feature could be highly influenced by sound absorption mechanism, particularly noticeable for a non-clogged porous surface with a high content of air voids.
Physico-chemical properties and ultrasonic characterization of calcium phosphate ceramics
Authors: Predoi Daniela , Derible Serge , Duflo Hugues , Predoi Mihai Valentin M. , Petre Cristian Catalin
Published: May 2008

Calcium phosphate compounds have been studied for biomedical applications due to their chemical and structural similarity to the mineral phase of bone and tooth. The composition, physical and chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparation conditions and sometimes it resulted into non- stoichiometric calcium deficient hydroxyapathite (Hap) powders. The present paper refers to calcinations of calcium phosphate ceramics at 800 and 1000oC. The effect of heat treatment were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential thermal analysis (DTA) and thermal gravimetric analysis (TGA). FTIR spectra showed the presence of various PO43- and OH-groups present in the powders. Powders compacted and sintered at 800 and 1000oC showed an increase in density. The main objective of the paper is a comparison of the results obtained by the previous methods to those obtained using the ultrasonic air-coupling technique. Modulated ultrasonic signals of 500 kHz central frequency have been transmitted through the calcium phosphate ceramics specimens. Correlation between signals allowed some conclusions concerning density, porosity and preparation temperature influence on these specimens. These comparisons and correlation of methods, allow a better characterisation of such important materials
The theoretical analyse of the surface acoustic waves propagated on the surface of the bulk materials with subsurface defect
Authors: Xu Xiaodong , Ding Ran , Glorieux Christ , Liu Xiaojun
Published: May 2008

A theoretical model based on finite element method is used to analyse the properties of surface acoustic wave (SAW) propagated on the surface of the bulk materials with subsurface defect. The simulation results reveal the modes conversion between SAW and Lamb wave at the border of the defect and explain the diffusion properties of SAW propagated on the bulk material with subsurface defect. The modes conversion and wave reflection at the border of the defect are theoretically explained why there are a lot of riffles after the SAW passed through Al sample with circle subsurface defect, which detected by laser ultrasonic method. The relationships between the wavelength of wave and the physical state of the defect in the bulk material are also fully described in theoretical simulation.
Stroboscopic White Light Interferometry for Dynamic Characterization of Capacitive Pressure Sensors
Authors: Kassamakov Ivan , Hanhijärvi Kalle , Aaltonen Juha , Sainiemi Lauri , Grigoras Kestutis , Franssila Sami , Kärkkäinen Anu , Hæggström Edward
Published: May 2008

Scanning white light interferometry (SWLI) is a well-established method for accurate static out-of-plane 3-D profiling of micromechanical devices. Periodic displacement can be measured using stroboscopic illumination synchronized to an arbitrary phase angle of the sample oscillation. We modified an existing SWLI setup for dynamic MEMS characterization. A two-channel function generator drives the sample and the stroboscopic illumination, and controls the inter-channel phase. A phosphorous white light LED or single-color LED is used as light source. Currently our shortest stroboscopic pulse is 50 ns. We measured the out-of-plane displacement of a thermal microbridge fabricated on SOI wafer with 20 nm accuracy. The microbridge was driven with sinusoidal and square wave signals (1 Hz - 960 Hz). The stroboscopic duty cycles were 0.1% - 5%. We also characterize the vibration modes of the membrane of a capacitive pressure sensor. Stroboscopic SWLI is useful for nanoscale profile measurements of periodic oscillations.
Laser-generated narrow-band ultrasonic wave for detection of subsurface defect
Authors: Ding Ran , Xu Xiaodong
Published: May 2008

Laser ultrasonics employs laser beams to excite ultrasound. Spatial and/or temporal modulated intensity of laser on the surface of the specimen (aluminum) can serve to narrow the band of the generated ultrasound around the desired central frequency and meanwhile obtains higher signal-noise ratio. In the present work, we use Computer Generated Holograms (CGHs) to spatial-modulate the laser beam. CGHs provide flexibility of adjustment of the intensity profile of the laser on the specimen and the online reconstruction of CGHs by digital and electronic devices helps to reduce the complexity of the experimental system and is promising in detection of subsurface defect and depth profiling as the surface acoustic waves penetrate into the solids a depth proportional to the wavelength. Discussion was carried out between experimental results and a theoretical model which based on finite element analysis.
Application of nonlinear laser photoacoustic technique to crack detection
Authors: Zakrzewski Jacek , Chigarev Nikolay , Tournat Vincent , Mounier Denis , Gusev Vitali
Published: May 2008

Nonlinear acoustics is a promising method for non-destructive testing (NDT) as it allows to improve the sensitivity and contrast of defects detection. The application of contactless laser photoacoustic technique for the tasks of nonlinear acoustics looks very promising. Meanwhile, real examples of industrial systems using nonlinear photoacoustics are still absent. In this work nonlinear photoacoustic response of artificially prepared cracks has been studied. Acoustic vibrations have been excited through the loASAHGRcal heating caused by the absorption of a focused beam of visible or near-infrared laser radiation. Several methods have been applied for the detection of surface displacement including piezo-transducers, air-coupled transducers and optical laser interferometry. It has been shown, that nonlinear acoustic response increases drastically when both pump and probe points are localized near the crack. For this reason, the last two methods allowing local probing look very promising. Two dimensional scans of generation and detection points on the sample surface could be used to obtain the images of crack at new spectral components induced by crack nonlinearity. The goal of this work is to find optimal methods of the excitation and detection of nonlinear photoacoustic response of the crack. It should make the technique attractive for the industrial applications.
Looking for shear waves in glass forming liquids
Authors: Pezeril Thomas , Klieber Christoph , Andrieu Stephane , Nelson Keith
Published: May 2008

The ability of the generation of picosecond shear acoustic pulses in solids using ultrashort optical pulses have been employed to look for high frequency shear waves in glass forming liquids. As a transducer we used a canted iron thin film deposited on a glass substrate. The strong shear efficiency of generation provided by this kind of samples allowed the study of several glass forming liquids. As a first try, we have detected shear brillouin scattering in m-toludine at 100K, that is below the glass transition temperature, at a frequency of 9 GHz. Then, we observed shear waves propagating at room temperature in glycerol at frequencies below 50 GHz.
Scattering of a buried circular membrane imbedded in a rigid substrate in a layered fluid waveguide
Authors: Mattingly Michelle B. , Buchanan James L. , Malek-Madani Reza , Korman Murray S.
Published: May 2008

A study of mathematical modeling of the buried landmine detection problem involves wave propagation in a layered waveguide in the presence of a flush mount buried circular target. In this study, emphasis is placed on acoustic to seismic coupling of an airborne CW point source located over an iso-velocity fluid layer. The top plate of the buried landmine is modeled as a circular elastic membrane stretched flush over a cylindrical cavity in a rigid substrate beneath the fluid layer. The finite fluid layer affords a manageable study of the modal resonances in the waveguide system with and without the target. The Helmholtz equation is solved in the atmospheric layer using cylindrical coordinates and a point source. The homogeneous Helmholtz equation is used in the fluid layer. Green's function techniques involving vibrations of the membrane are incorporated into the boundary conditions. Results of the closed form normal mode solution will be presented in a MATLAB™ user interface; describing the effects of frequency, depth, density, sound, absorption, including radius and elastic parameters of the membrane. Comparison of the results (involving the fluid surface particle velocity profiles across the target) will be made with experiments reported in the literature to evaluate its usefulness.
Numerical simulations of resonant granular layers
Authors: Turner Joseph A. , Bobaru Florin , Rattanadit Kitti
Published: May 2008

A coupled Discrete Element Method-Finite Element Method (DEM-FEM) model is developed and implemented for simulating the dynamic response of a dry granular layer on top of an elastic beam. The implementation is first validated against the quasi-static results for spherical particles which are compared with well-bonded effective-medium models. In the dynamic regime however, the effective-medium analytical result differs from experimental values in terms of the dependence of particle size. The simulations developed are used to understand the discrepancy between the theory and the experiments. The first resonance of the system is examined with respect to particle size using a variety of particle sizes and a frequency sweep input. The particle size dependence observed experimentally is reproduced in the simulations only through inclusion of cohesive forces between the particles. Rolling resistance and friction between particle is shown to be of minor importance. This new modeling tool offers promise for understanding the dynamic interactions of granular materials. [Work supported by ARL]
Low-frequency acoustoelasticity in glass beads saturated with water using a nonlinear wave-coupling technique
Authors: Renaud Guillaume , Callé Samuel , Remenieras Jean-Pierre , Defontaine Marielle
Published: May 2008

To study "non-classical" acoustical nonlinearities in cracked materials, we developed a nonlinear (NL) wave coupling technique. Propagation velocity and amplitude of short high-frequency (HF, 600 kHz) bursts are modulated as result of nonlinear interaction with a low-frequency (LF, 3 kHz) wave. Time Of Flight Modulation (TOFM) is indeed related to both elasticity and density variations. Because high acoustic nonlinearities in glass beads have been reported, we applied our technique to glass beads with different diameters (hundreds micrometers). A small container is filled up with glass beads saturated with water and placed below the LF source. The large HF to LF ratio (200) and the small sample size (6 cm) compared to the LF wavelength in water (50 cm) allow: 1) to measure instantaneous Time Of Flight Modulation (TOFM) and attenuation as functions of the instantaneous LF pressure, 2) to consider the LF pressure field a quasi-static hydrostatic variation of the ambient pressure in the medium. The LF pressure amplitude in water is approximately 10 kPa. Different TOFM and NL attenuation behaviors in tension and in compression, as well as different hysteresis patterns, are observed. The influence of the LF pressure amplitude is discussed.
Sound in a linear array of magnetic spheres
Authors: Ruiz-Suarez J. Carlos , Malloggi Florent , Carvente Osvaldo , Cruz-Damas Jose , Pacheco Felipe
Published: May 2008

We study the propagation of sound in a chain of strongly magnetized spheres. The strong dipole-dipole magnetic force allows us to hold the chain in different positions to evaluate the effect gravity produces on sound transmission. This strong cohesion permits us also to insert in the chain a periodical array of impurities and study the effect this array has in the transmission. A well defined gap of frequencies, where no sound propagation exists, is observed. We investigate as well square lattices, and look into the effects dipole anisotropy causes to sound propagation. Finally, we study the effects produced by vacancies.
Linear and non linear acoustic waves in macroscopically inhomogeneous unconsolidated granular crystals
Authors: Merkel Aurélien , Jacob Xavier , Tournat Vincent , Gusev Vitali
Published: May 2008

Ordered unconsolidated structure of spherical beads in the absence of external loading except the gravity field constitutes a macroscopically inhomogeneous and strongly nonlinear phononic crystal. We report the experimental and theoretical investigation of linear and nonlinear acoustic phenomena in these granular crystals of finite thickness along the gravity direction. In particular the dependence of the resonance frequencies on the thickness of the crystal (the number of layers) is evaluated. The linear transmission of acoustic waves from the bottom to the free surface of the granular crystal exhibits complicated features. It is compared to the linear transmission through the same structure but with a macroscopically homogeneous static stress. Some frequency regions of the acoustic response function are shown to be insensitive to the transition from an inhomogeneous static stress (gravity induced) to a homogeneous one (additional external load). The nonlinear acoustic phenomena of resonance frequency shift and resonance curve broadening with increasing amplitude of acoustic oscillations are observed. It allows to measure the nonlinear parameters of the crystal for different amounts of layers, accounting for the absolute particle velocity amplitude detected at the free surface with a laser vibrometer. Corresponding theoretical models describing the acoustic eigenmodes in macroscopically homogeneous and inhomogeneous granular crystals are developed.
Treatment of the asymptotic behaviour of the piezolectric Green's function for finite element/boundary element analysis of surface waveguides
Authors: Ballandras Sylvain , Lenczner Michel , Larroche Thierry
Published: May 2008

The simulation of surface waveguides has been dramatically improved by the combination of analytic description of piezoelectric materials using surface Green's function and numerical approaches sur as plane wave expansion, finite diffrence, finite element, etc. A lot of work has been dedicated to treat the singularities of such Green's function generally derived in the spectral domain. An interesting approach consists in using the Green's function which relates the surface stresses to the displacements which is particularly well-suited for mixed finite element/boundary element formulations. This Green's function does not exhibit any pole but presents an asymptotic behavior which tends to infinity along increasing wavenumber values, which prevents the computation of its Fourier transform. In this work, we show how this difficulty can be overcome and we propose a formulation in which the Green's function is factorized in order to change its asymptotic behaviour to a form allowing for Fourier transform computation for non periodic problems and an analytic treatment of its asymptotic behaviour for the simulation of periodic structures. Examples are provided to show the interest of the proposed approach in terms of computation delays and precision.
Auditory capture in a spatial cueing task
Authors: Van Der Hoeven Marieke , Bronkhorst Adelbert W.
Published: May 2008

This study examined how an auditory non-informative spatial cue influences detection and localization of auditory targets. In a go-no go task subjects attended a centrally placed loudspeaker surrounded by 6 other loudspeakers and were asked to respond only to centre targets. The cue came from one of the loudspeakers and preceded the target tone with an SOA of 100 or 400 ms. A baseline condition with a spatially diffuse cue was included, using out-of-phase presentation through two loudspeakers. Results show that, compared to the baseline, cues shortened reaction times at small cue-target angles (up to 7°) and increased them at larger angles. At the shortest SOA, the reaction time difference was up to 80 ms. Furthermore, cueing seems to have no effect on sound localization: false alarms were normally distributed around the hits. These findings demonstrate that strong auditory capture effects occur that depend on cue-target distance.
A binaural advantage in the subjective modulation transfer function with simple impulse responses
Authors: Thompson Eric R. , Dau Torsten
Published: May 2008

The speech transmission index (STI) has been a popular method for predicting speech intelligibility in rooms. It is based on the magnitude of the modulation transfer function, which can be derived from the impulse response of the room and the background noise levels. However, it does not take into account that humans listen with two ears. There can be large interaural phase differences in the modulation transfer functions, which can create detectable interaural level difference fluctuations. Measurements were made to determine whether these interaural modulation phase differences can be used to enhance the detectability of sinusoidal intensity modulations imposed on a broadband noise carrier and then convolved with simple, dichotic impulse responses. The results show that there can be a significant advantage to listening with two ears over listening with just one. Some further investigations were made to determine whether this advantage in signal detection can also be used as an advantage for speech intelligibility.
Loudspeaker sound quality: comparison of assessment procedures
Authors: Koehl Vincent , Paquier Mathieu
Published: May 2008

In listening tests involving different loudspeakers and aimed at assessing the sound quality of these sound-reproducing systems, the level is generally adjusted to compensate for differences in sensitivity. The loudness sensation must be alike for each system under test. Because of the non-stationary nature of the musical signals used as test material in loudspeaker ratings, loudness assessment by using the current models (Zwicker, Mooreœ) remains slightly inaccurate. In practice, loudness is often equalized by ear by the experimenter. This study deals with the comparison of various test procedures. The first experiment was a paired comparison of loudspeakers where short-duration stimuli were presented to listeners for preference ratings. In the second experiment, the same listeners were allowed to switch, at any time, from one loudspeaker to another one so that the proposed stimuli were longer. In both experiments the loudness was equalized by the experimenter. However, under normal listening conditions, the listener is usually free to adjust by himself the reproduction level. At last, in a third experiment, the listeners had the opportunity, at any time, to not only to switch from one system to another one, but also to adjust the loudness of the stimuli.
Study of the perceptive space linked to dashboard tapping sounds
Authors: Montignies Francois , Parizet Etienne
Published: May 2008

It was observed that dashboard tapping sounds can be produced by customers exploring static vehicles. To master the perceived quality of the dashboard, a global sound design process has thus been engaged. The specific aim of the present study was to identify the acoustical and technological characteristics being major determinants in the discrimination of the sounds and in the evaluation of the sound sources. 47 sounds were used for a perceptive test in laboratory. They were recorded in 22 vehicles by hand-tapping on different dashboard parts. In a same session, each subject performed 3 different tasks: categorisation (free sorting of sounds), description (free verbalisations) and evaluation (the score of a freely selected prototype was attributed to the whole group). Data analysis took advantage of the combination of various multidimensional analysis techniques, already used in psychoacoustics or sensory analysis. This low-cost methodology allowed us to describe a wide range of product samples with complementary psychological data. Results will help us to propose a sound metric which represent the evaluation of dashboard quality evoked by the sound. Furthermore, they give first hypotheses for the technological variables that could be decisive in the design process.
Pitch-based streaming of vowel sequences, speech-in-speech segregation, and frequency selectivity
Authors: Gaudrain Etienne , Grimault Nicolas , Healy Eric W. , Béra Jean-Christophe
Published: May 2008

Simultaneous and sequential segregation are described as the base mechanisms for auditory scene analysis and are likely to be involved in concurrent speech segregation. However, speech-in-noise perception has been found to be uncorrelated to simultaneous segregation, but related to pure-tone fusion threshold. This study aimed to clarify the relationship between pitch-based speech-in-speech segregation, pitch-based streaming and frequency selectivity. Twenty-five listeners with close to normal hearing were involved. Auditory filter widths were derived from a notched-noise method. Speech-in-speech perception was measured using words presented in a time reversed single talker background, with various pitch differences between target and masker. The streaming performance was measured using an objective order-naming task on vowel sequences. The results showed a correlation between frequency selectivity and performance in speech-in-speech perception suggesting that intelligibility relies on simultaneous masking. A correlation was also found between the effect of pitch on speech-in-speech perception and the effect of pitch on streaming performance. However, no correlation was found between streaming and frequency selectivity. These latter results suggest that pitch-based segregation probably relies on pitch discrimination which is only weakly correlated to frequency selectivity.
Simulation of an electro-acoustic implant (EAS) with a hybrid vocoder
Authors: Seldran Fabien , Truy Eric , Gallégo Stéphane , Berger-Vachon Christian , Collet Lionel , Thai-Van Hung
Published: May 2008

Electroacoustic stimulation (EAS) is indicated for hearing impaired patients with enough residual hearing in low frequencies and severe hearing loss in high frequencies. We aimed at simulating the speech intelligibility provided by EAS with a hybrid vocoder model. The French Fournier word set was used in this study. We therefore tested several parameters on 24 normal hearing adults. First, the boundary between acoustic and electric stimulation frequency areas (Fc) was taken at 500, 707, 1000 and 1414Hz. Second, we assessed the effect of electrical stimulation channel numbers (1 to 4). Third, we tested the effect of background noise with a cocktail party noise at -6, 0 and +6 dB SNR. It appeared that the 3 electrical channels & 707 Hz Fc condition produced normal-hearing-like results (at least in quiet). In noisy auditory scene, 4 electrical channels & 500 Hz Fc could produce fair speech intelligibility. [Work supported by CNRS, Lyon1 University and Medel].
Temporal weighting in loudness judgments of time-varying sounds containing a gradual change in level
Authors: Oberfeld Daniel
Published: May 2008

Two experiments studied how listeners weight the level information from different portions of a noise consisting of ten temporal segments, the levels of which were sampled independently from a normal distribution. If a gradual increase in level ("fade-in") is imposed on the first few segments in such a sound, temporal weights in global loudness judgments in a one-interval paradigm show a delayed primacy effect [Oberfeld and Plank, Fortschritte der Akustik - DAGA2005, 227-228 (2005)]. The maximum weight is assigned to the first segment presented at the full level, while the weights assigned to the fade-in segments are close to zero. In Experiment 1, a similar pattern of weights was observed in a two-interval paradigm. Thus, listeners do not use intensity information from the fade-in segments even when making within-trial comparisons. In Experiment 2, the first three segments gradually decreased rather than increased in level (i.e., the first segment had the highest level). Listeners gave near exclusive weight to the first segment. The results are compatible with a tendency to assign greater weight to loud elements [Lutfi and Jesteadt, J. Acoust. Soc. Am. 120, 3853-3860 (2006)] rather than with segmentation of the noise into a "gradually changing" and a "stable" part.
Resolution improvement of beamformers using spherical microphone array
Authors: Pascal Jean-Claude , Li Jing-Fang
Published: May 2008

Spherical microphone array has been studied for various applications. In enclosed space, spherical array eliminates forward-backward grating lobes occurring in two-dimensional arrays. Beamforming and spherical harmonic decomposition are both used to map the distribution of source strength. The two approaches show similar performance at frequencies where the upper spherical harmonic order equals the product of the wave number and sphere radius. However, at lower frequencies, processing using spherical harmonics maintains the same directivity while the spatial resolution for delay-and-sum beamformer deteriorates. It has been shown that the scattering of sound by a rigid sphere improves the directivity of the same open sphere microphone beamformer, by increasing the path length travelled by incident sound. This paper concerns focused beamformer using rigid and open sphere. The concept of statistically optimized array processing (SOAP) is applied to adapt to a particular interior geometry, considering the scattered field in case of rigid sphere. The regularization process makes it possible to use a model of partially coherent sound field in the enclosed space. A deconvolution post-processing based on the knowledge of the actual steering vector leads to an efficient and robust solution to improve considerably the resolution of the source strength distribution.
A boundary element method for near-field acoustical holography in bounded noisy environment
Authors: Langrenne Christophe , Melon Manuel , Garcia Alexandre
Published: May 2008

This paper presents a boundary element method to recover free field conditions from noisy bounded space situations. The proposed approach is based on the Helmholtz integral formulation and requires the knowledge of double layer pressure fields on two parallel closed surfaces surrounding the source. First, the outgoing and ingoing pressure fields are separated. Then, the incident field scattered by the tested source is subtracted from the outgoing field to estimate the pressure field which would have been radiated in free field. The method had been numerically tested and an experimental example is given here. The source is a rectangular box with seven loudspeakers mounted on it driven by bandwith limited white noise. The source is put at 0.4 m from the ground of a semi-anechoïc room. The ground plays a disturbant role because it produces secondary sources. The results show the effectiveness of the method particularly at frequencies where stationary waves between the ground and the underside of the box exist.
Noise source characterisation using patch impedance technique
Authors: Pavić G , Totaro Nicolas
Published: May 2008

A novel approach of an environment-independent sound source characterisation is discussed. The source is defined via a suitable enveloping interface surface by its blocked sound pressure and its surface impedance. Both the blocked pressure and the impedance are discretised using the averaging patch concept. Such a definition avoids singularity of point acoustic impedance and is suitable for numerical as well as experimental implementation. The characterisation of a source by the patch concept allows for the acoustical sub-structuring, which in turn enables the prediction of the sound field created by the source coupled to an arbitrary environment. Numerical simulations are presented which demonstrate the feasibility of the approach. It is hoped that the proposed approach can serve as a universal tool for noise synthesis of complex equipment incorporating noise sources.
Experimental feasibility of in-duct sound source reconstruction
Authors: Bravo Teresa , Maury Cédric
Published: May 2008

Due to the expected air transport growth and stringent environmental regulations, there is a strong need to develop noise reduction techniques at acceptable cost in the aeronautical sector. A sound characterisation of the aero-acoustic sources in the nacelle acoustic duct problem plays a crucial role. In this study, it is shown how the liners optimized impedances strongly depend on the noise source characteristics under both tonal and broadband excitation conditions, and in the latter case, for varying degree of correlations between the random source strengths. The limitations for source identification methods, such as pointwise model-based inverse techniques, have been studied. These methods are able to provide reliable models of equivalent sound sources from a limited number of in-duct measurements, but require a priori knowledge of the source location. The performance of such techniques are compared with two different approaches, namely the use of focussed in-duct beamforming techniques to locate the unknown sources, and a decomposition of the assumed source strengths into angular Fourier series for both the location and the determination of the source amplitudes. Experimental results are presented for the location and the reconstruction of the particle velocity spectrum of wall-mounted compression drivers from in-duct measurements.
Radiation efficiency of natural modes of plates with beam stiffeners
Authors: Rousounelos Andreas , Walsh Stephen J. , Krylov Victor V.
Published: May 2008

In this paper, the radiation efficiency of the natural modes of finite plates with attached beams is considered. Firstly, the scattering of flexural waves, by the beams and the boundaries, in the plate is considered. The reflection and transmission coefficients along with the near-field coefficients of the beam are used to calculate the vibration field of the plate, by taking into account an infinite number of reflections from the boundaries. A wavenumber transform of the vibration velocity field is used to calculate the sound power and the radiation efficiency. Numerical results are presented, for a number of attached beams, and show that the beams introduce ripples in the radiation efficiency curve, below a certain frequency. The amplitude of the ripples is controlled by the mass and the torsional stiffness of the attached beams whereas the stiffness of the beam has little influence. The results are compared with measurements of the radiation efficiency of plates with attached beams.
Virtual statistical energy analysis for vibroacoustic industrial prediction
Authors: Borello Gérard , Gagliardini Laurent , Thenail Denis
Published: May 2008

In the mid-frequency range (200-2000 Hz), difficulty is encountered when modeling car body vibroacoustic interactions, mainly due to the complexity of automotive design. Analytical Statistical Energy Analysis (ASEA) is efficient to bring to the fore regions of interest regarding NVH design but was proven to be accurate only above 2000 Hz. To overcome ASEA limitations at lower frequencies, Virtual SEA (VSEA) technique was introduced to translate the dynamic information contained in a finite element (FE) model into an SEA model. Any FE model, whatever its complexity, can thus be processed thanks to an automatic sub-structuring algorithm and a built-in VSEA modal synthesis solver, fast leading to robust numerical SEA model. VSEA also addresses structure-borne noise problems by coupling structural VSEA subsystems to analytical acoustic subsystems through a virtual wave number. Investigation of damping and trim treatment effects on mixed acoustic and structural subsystems are thus possible. While reviewing VSEA theory, industrial application cases will be presented.
Effect of boundary restraints on sound radiation
Authors: Li Wen
Published: May 2008

This study is focused on the effect of boundary restraints on the sound radiation from a rectangular plate. The modal and acoustic characteristics of square plates are studied for different restraining stiffnesses and configurations. It is shown that the modes of the restrained plates can be considerably different from those for the familar simply supported boundary condition, so are the corresponding modal radiation efficiencies. The proposed method generally applies to the plates elastically restrained along any edge(s) and for any stiffness values. The acoustic calculations are also valid for any acoustic wavenumber, instead of only for some extreme acoustic/structural wavenumbers as in other investigations.
High-speed electronic speckle pattern interferometry of a struck flat plate
Authors: Moore Thomas , Zietlow Daniel , Gorman Christopher
Published: May 2008

An electronic speckle pattern interferometer capable of imaging 33,000 frames per second has been used to study the transient motion of a flat plate which was struck at a point near the edge. Multiple interferograms, each with an exposure time of 25 microseconds, were combined to construct a video of the plate motion that can be used for both qualitative and quantitative analysis. The interferograms reveal the expected evolution of the bending waves created when a thin circular plate is struck near the edge; however, anomalous displacement of the surface of the plate is also observed. This unusual displacement of the surface takes the form of a transverse wave that precedes the motion directly attributable to the normal propagation of the initial bending wave.
Optimizing the Dynamic Behaviour of a Large Portal Robot
Authors: Koenig Christian R. , Kochmann Markus , Ohlendorf Jan , Müller Dieter H. , Thoben K.-D.
Published: May 2008

The object under investigation in this work is a portal robot used for the production of large fibre reinforced structures. The achieved product quality and the production speed of the device are influenced by the vibration and the damping behaviour of the system. The required process time is determined by kinematic parameters, i.e. speed and acceleration of the system and the dead time required for the vibration level to decay to a threshold level given by the required precision of process. In the first step, a Design of Experiments is used in order to identify the ideal combination of acceleration and speed. At this optimum, the sum of the drive time and the dead time reaches a minimum for a given precision. In the second step, an experimental Modal Analysis is performed in order to identify the potential for an optimization of the structure.
Evaluation of hand-transmitted vibration exposure on basis of a questionnaire
Authors: Pääkkönen Rauno , Sauni Riitta , Uitti Jukka , Toppila Esko
Published: May 2008

We made a survey to see if metal workers had symptoms caused by vibration. The vibration exposure over lifetime was also asked. The cumulative HAV dose was calculated as a HAV index determined on the basis of the questionnaire, in which jobs, tools and active work time (hours/day, days/week, moths/year) had been requested. An index, I, describing the total HAV exposure was determined by I= a8h2 x y x d, where I = cumulative exposure index (m2ad/s4), y = exposure time in years (a), and d = annual exposure time in days. The exposure of metal workers varied 1-5 m/s2, and the average was 2.4 m/s2. The limit value of European directive 5 m/s2 is not usually exceeded. However, there is a wide unaccuracy area that needs to be cleared one way or another. We also connected symptoms and exposure on statistical level. The total exposure times did not differ significantly in these groups, but, when the daily HAV exposure was taken into account in the calculation of the cumulative index, the difference was statistically significant.
Left parietal activation during the production of pointing in several modalities: prosodic focus, syntactic extraction, digital- and ocular- pointing
Authors: Loevenbruck Hélène , Vilain Coriandre , Carota Francesca , Baciu Monica , Abry Christian , Lamalle Laurent , Pichat Cédric , Segebarth Christoph
Published: May 2008

Deixis, or pointing, is the ability to draw the viewer/listener's attention to an object, a person, a direction or an event. Pointing is gradually acquired by children, first with the eyes, then with the finger, then with intonation and finally with syntax. The crucial role of digital pointing in language acquisition suggests that all modalities of pointing may share a common cerebral network. An fMRI study of the production of multimodal pointing was carried out on 15 subjects. Subjects were scanned during the execution of index finger pointing gestures, eye pointing gestures, prosodic pointing (focus) and syntactic pointing (extraction). The results of a random effect group analysis show that the left superior parietal lobule (BA 7) was activated in all three digital, ocular and prosodic pointing but not in syntactic pointing. These results indicate that pointing in different modalities may recruit the left superior parietal lobule, with ocular pointing more anterior than prosodic pointing, itself more anterior than digital pointing. A grammaticalisation process is suggested to explain the lack of parietal activation in syntactic pointing.
Acoustic cues to the voicing contrast in coda stops in the speech of 2-year-olds learning American English
Authors: Hanson Helen M. , Shattuck-Hufnagel Stefanie
Published: May 2008

Developing a model of how children acquire the phonological feature contrasts and phonetic cues of their adult speech community requires a detailed understanding of how production changes during development. Earlier studies based on listening provided an initial estimate of these patterns; recent instrumental studies of the acoustic and articulatory details of production during development have revealed some surprises, including covert contrasts between distinctive feature categories (e.g., Scobbie et al., 1996) and of incomplete acquisition of adult feature-cue patterns (Imbrie, 2005), which can be difficult for adults to hear. Few instrumental studies, however, have focused on the child's cue patterns for coda consonants (although see Song and Demuth, in press). Our study of cues to the feature [voice] for coda stops used quantitative acoustic analyses of tokens from the Imbrie corpus of 2-year-old speech to compare child productions with those of their adult caretakers. Results show that a) many children produce a noisy region at the end of the vowel for voiceless codas (in duck, cup) but a long strong voice bar during closure for voiced codas (in bug, tub), and b) these cues may be exaggerated versions of the feature cues of their adult caretakers.
Compensatory tongue patterns in glossectomy patients
Authors: Murano Emi , Stone Maureen , Liu Xiaofeng , Zhuo Jiachen , Salama Andrew , Gullapalli Rao , Ord Robert , Prince Jerry
Published: May 2008

To examine the effects of glossectomy surgery on tongue deformation strategies, a unique combination of data was used, including internal tongue strain patterns from tagged-cine-MRI and detailed muscle architecture from high-resolution MR images. Two glossectomy patient groups were studied and compared to normal controls. They differed in the type of reconstruction after cancer excision: primary closure or reconstruction with forearm flap. All patients included in this study had the same tumor type (Squamous Cell Carcinoma), size (T1 and T2) and location (unilateral mid-third of oral tongue). The tongue developed distinct deformation strategies that move the remaining tongue tissue, the flap and the scar tissue. Compensatory patterns such as pivot points and areas of rigidity will be shown and discussed. These appear to be compensatory strategies to optimize speech output after surgery. This presentation is based on viewing the tongue as a muscular hydrostat, which provides the basis for hypotheses about the formation and release of areas of rigidity within the tongue. The rigidity might be a way to simplify sound-specific strategies for moving the tongue and controlling changes in its shape in normal and patient subjects. Supported by NIH K99DC009279, and R01DC01758 from the NIDCD.