bluuebunny/crossref_metadata_2025 huggingface dataset:
Array gain degradation due to nearby bubbles
Authors: Culver Richard Lee , Trujillo Mario F.
Published: May 2008

Signal-to-noise ratio (SNR) is signal power divided by noise power, usually expressed in dB (SNR = 20*log10(Psig/Pnoise). Array gain (AG) is the increase in SNR at an array output relative to that at a single element. AG assumes spatially-compact signals embedded in spatially-diffuse noise or interference. When the array is steered in the direction of a signal, AG is maximum when the signal is fully coherent across the array (i.e. the signals add in phase for all elements) while the noise or interference is incoherent across the array (i.e. adds with random phase). For an acoustic array operating in the ocean, we would like to understand the degree to which nearby bubbles degrade AG. Scattering by bubbles represents interference at the array. Bubble attenuation can also degrades array performance by attenuating the signal of interest, but that is separate from AG degradation. Previously we applied the single scattering approximation of Ishimaru (1977, Chap. 6) and found that scattering from bubbles very close to the array can generate correlated interference, thereby decreasing AG. Here we validate the theory using in-water measurements of AG as the distance of from the array to the bubbles varies. Work sponsored by Office of Naval Research, Code 321 Undersea Signal Processing.
Standard-target method of calibrating active sonars: principles, applications, benefits
Authors: Foote Kenneth G.
Published: May 2008

The standard-target method of calibrating active sonar involves suspending a target at a known position in a sonar beam, insonifying it with a known signal, measuring the scattered pressure field, and relating this to the scattering properties of the target. These properties are known a priori for standard targets, rendering the calibration primary. Repetition of the procedure for different relative sonar-target positions can enable determination of directional and nearfield characteristics. Following a review of standard-target calibration principles, the method is illustrated for both narrowband and broadband scientific echo sounders and multibeam sonars, with operating frequencies in the range 18-3200 kHz. Applications to sidescan sonar and to low-frequency parametric sonars and other mid-frequency sonars in the nominal range 1-10 kHz have not yet been developed, but are evidently feasible given preliminary standard-target designs, which are described. In every case, the standard targets are of a proven manageable size, with immersion weight less than 200 N. Benefits of standard-target calibration, including accuracy, operational convenience, and cost-effectiveness, among others, are emphasized. The method, which is useful for both quantitative and qualitative imaging applications, extends to borehole acoustic sensors and medical ultrasonic devices.
Theoretical justification of a coherent forward model for subbottom profiler data inversion
Authors: Rakotonarivo Sandrine , Legris Michel , Desmare Rozenn , Jean Frédéric
Published: May 2008

Subbottom profiling systems measure and identify sediment layers that exist below the sediment/water interface. Nowadays, very-high resolution chirp profilers provide calibrated wideband signals which may enable quantitative seabed characterisation. In literature, sediment classification is based on attenuation and reflectivity estimation and backscattering models used for the inversion consider plane wave propagation through layered homogeneous attenuated bottom. But this bottom modelling may be in contradiction with the emitted spherical front wave and core samples observations which point out a heterogeneous structure of marine subbottom. Therefore, impacts of profiler features, geometry measurement and subbottom structure (layering, attenuation, rugosity, and volumetric inhomogeneity) on backscattering signal are all reviewed in this paper. This analysis shows that classical model of wave coherent propagation through layered homogeneous attenuated media offers the best compromise between its accuracy and inversion possibility, if bottom heterogeneities are insignificant (Rayleigh scatterers). For bigger heterogeneities (Rayleigh parameter close to unity), coherent backscattering still prevails though wave propagation is affected by scattering. In this case, the same coherent forward model is used with modified reflectivity and transmission coefficients. Then, sensitiviy and inversion possibility of the coherent bottom backscattering model are discussed.
The modelling of vibration transmission through plate/beam structures typical of lightweight buildings
Authors: Galbrun Laurent
Published: May 2008

Vibration transmission through plate/beam structures typical of lightweight buildings is examined in this paper. Modelling difficulties are analysed and related to the several modelling choices available, including connection type, beam modelling, modal properties and material properties. A number of key experiments carried out on structures made of one or more parallel plates attached to a single beam are discussed, and the applicability and limitations of fundamental theories are identified through the use of Statistical Energy Analysis (SEA) models. It is shown that the interrelation between the various modelling factors can lead to complex models. The systems for which existing models can be used are identified, as well as those for which more complex models need to be developed.
A simplified approach to impact sound insulation rating without using a tapping machine
Authors: Li Ming , Dodd George
Published: May 2008

The aim of this study is to investigate a simplified approach for obtaining ratings of impact insulation of floors which requires only airborne sound measurements and correction factors depending on the particular type of floor finish. One third octave frequency-dependent correction factors have been obtained by processing published results of both airborne and impact insulation on floors. The uncertainty of predicted Ln,w values using correction factors shows a good agreement with ISO recommended limits. The proposed technique has value in reducing the cost and effort for field insulation measurements. Further work is underway to refine the method and to extend the range of constructions for which we have correction factor.
Some practical aspects of the prediction of structure-borne sound caused by house-hold equipment
Authors: Gerretsen Eddy
Published: May 2008

Sound levels in rooms due to service equipment in the building can be an important reason for disturbance and more so in light weight building structures. Though the recently published draft standard prEN 12354-5 gives a framework for the prediction of the structure-borne sound as caused by this type of sources, there is still a lot to be studied and developed. That is certainly the case for light weight building structures. Some possibilities to simplify the indicated models have been studied and experimental data has been gathered for house hold equipment, taking a washing machine as an example, applied both in a 'heavy' and in a 'light weight' building. Various possibilities to apply substitution methods to characterise such a source as structure-borne sound source have been tried and compared.
Biosonar model for obtaining fine target structure in complex targets
Authors: Buck John R.
Published: May 2008

Bats use echolocation to discriminate targets with multiple glints in which the glints are much closer together in time than the integration time of the bat auditory system. This indicates the bats cannot be using purely time-domain processing to image the target. It is likely that the bats exploit cues such as spectral peaks and notches due to the interference between the glints at specific frequencies. However, these interference patterns quickly grow complicated as the number of glints increases. The cepstrum is a signal processing algorithm designed to identify these interference intervals. We previously demonstrated that simple two-glint targets can be accurately resolved using a time-varying version of the cepstrum, or cepstrogram. This talk will present an algorithm for interpreting the evolution of cepstral peaks across a target with many glints to estimate the inter-glint intervals. This algorithm has the desirable quality of processing the data causally as it is received, and thus is possible to implement in real time. The performance of the algorithm will be evaluated using experimental data from an ultrasonic bat simulator. [Work supported by US Office of Naval Research]
Dynamic tracking of free-swimming whale groups using digital acoustic recording tags
Authors: White Charles , Miller James H. , Potty Gopu R. , Johnson Mark
Published: May 2008

Understanding the group behavior of free-swimming whales is critical to the management and conservation of many whale species. Moreover, understanding how whales coordinate their activities could serve as a model for improving the communication and navigation systems of underwater robots and autonomous underwater vehicles (AUVs). One method for studying the group behavior of free-swimming whales involves simultaneously attaching acoustic recording tags to multiple animals within a close-swimming conspecific group. Acoustic recording tags can sample an animal's acoustic environment simultaneously with other physical parameters such as diving depth and acceleration. In this paper, methods are presented for dynamically tracking whales that vocalize regularly such as odontocetes using the DTAG, a digital acoustic recording tag developed by the Woods Hole Oceanographic Institution. A trilateration model is reviewed for tracking groups of whales that include three or more tagged whales using time of flight data and results are given from applying this model to a novel data set of three simultaneously diving and cross-audible short-finned pilot whales (Globicephala macrorhyncus). A new model is subsequently proposed for tracking whale groups that include only two tagged whales using a generalization of multilateration and data captured by stereo DTAGs.
Wide-area geoacoustic inversion using distant ship noise
Authors: Turgut Altan
Published: May 2008

Broadband (50-500 Hz) noise data from fast-traveling surface ships in the vicinity of a VLA and a bottomed HLA are used to estimate the geoacoustic properties on the New Jersey Shelf. Matched-field inversion of geometric and geoacoustic parameters are presented by using twenty days of ship noise data, collected during the RAGS03 winter experiment. Noise data from different ships at different ranges provided robust geoacoustic inversions for both VLA and bottomed HLA data. Acoustic propagation tracks are determined from the HLA beamforming results and a 3-D geoacoustic parameter map is constructed. The constructed geoacoustic parameter map shows good agreement with the results from chirp sonar inversion and acoustic probe measurements, indicating silty seafloor sediments on the outer-shelf area and sandy sediments on the inner-shelf area. Efficiency of the 3-D geoacoustic inversion and extension to range-dependent inversions at longer ranges are also discussed. [Work supported by ONR.]
Doppler Geo-Spectroscopy in the Makai Experiment
Authors: Barclay David R. , Buckingham Michael
Published: May 2008

Using data collected during the 2005 Makai experiment, acoustic parameters of a coral-sand seabed were obtained using the Doppler spectroscopy inversion technique. A light aircraft was used as a low frequency (80 - 400 Hz) sound source over an isovelocity shallow water channel. A microphone near the ocean surface and a hydrophone near the seabed were used to record the Doppler spreading of each harmonic of the aircraft's engine and propeller. In the water column, spectral peaks with the greatest up and down Doppler shifts are associated with the shallow equivalent rays of normal modes. The least mean squares (LMS) adaptive filter was used to track and enhance the frequency of these propagating modes. The inversion relies on a full wave number spectral model of a moving source in a three-layer waveguide. The Doppler shifted modes in the water column are observed in the data and simulated in the model. The comparison of the two, in symphony with the aircraft's signal in the air, returns the geoacoustic parameters of the seabed. The inversion was performed on numerous over-flights and the results were averaged to show statistical confidence. Work supported by ONR.
Geo-acoustic inversion with adaptive beamformed data
Authors: Stotts Steven A. , Koch Robert A.
Published: May 2008

Geo-acoustic inversion with matched field replicas constructed by adaptive techniques lacks robustness, because localizations with such techniques are sensitive to model mismatch [Soares, Jesus, and Coelho, J. Acoust. Soc. Am. 122, 3391-3404 (2007)]. Instead of adapting the matched field weights, inversion with adaptive beam-formed (ABF) plane wave sub-aperture data produces accurate source localizations for ships of opportunity [Stotts and Hawkins, J. Acoust. Soc. Am. 118, 1857 (2005)]. Model inputs to the matched-field cost function are evaluated at sub-aperture phase centers in this approach. The main purpose of this talk is to demonstrate the robustness and accuracy of solutions obtained from geo-acoustic inversion using plane wave ABF data. Improvements over either single element or conventional plane wave beam-formed (CBF) sub-aperture data for geo-acoustic inversions and simultaneous geo-acoustic inversions/source localizations using a source of opportunity in real data containing interferers will be demonstrated.
Elastic waves in human kidney stones: Shear dominates spall in shock wave lithotripsy
Authors: Cleveland Robin O. , Luo Haibiao , Williams James C.
Published: May 2008

We investigated the role of shear waves and spall in the fragmentation of human kidney stones. Seven human kidney stones, approximately 5 mm in diameter, were scanned with micro computed tomography to obtain a 3D representation that was imported into an elastic wave code. The code was initialized with a lithotripsy waveform and the evolution of stresses and strains was tracked through space and time. The evolution of the principal stress indicated that reflection from the distal surface of the stone (spallation) did not induce large tensile stresses (<40 MPa) due to the curved geometry of the proximal and distal surfaces. Instead as the shock wave in the fluid passed the mid-section of the stone there was efficient coupling into shear waves which then propagated into the interior of the stone and generated the largest regions of high tensile stress (>60 MPa). The results indicate that for the human stones studied here shear waves generated at the stone periphery are more important than spall in generating high tensile stress. These data suggest that the focal width of a lithotripter needs to be larger than the stone in order to generate large stresses. [Work supported by NIH DK43881 and DK59933].
Damage potential of single-bubble collapse in shockwave lithotripsy
Authors: Johnsen Eric , Colonius Tim
Published: May 2008

In shockwave lithotripsy, the combined effect of focused shockwaves and cavitation pulverizes kidney stones. Although cavitation is known to play an important role in stone comminution, the underlying mechanism is not fully understood. The goal of the present study is to quantify the potential damage caused by Rayleigh collapse (RC) and shock-induced collapse (SIC) of a single bubble near a stone. A high-order accurate, quasi-conservative, shock- and interface-capturing scheme [E. Johnsen and T. Colonius, J. Comput. Phys. 2006] is employed to simulate both phenomena. A high-speed re-entrant jet forms during the collapse and hits the distal side of the bubble, thereby generating a water-hammer pressure wave. A high pressure is measured along the stone surface upon the impact of this wave, thus providing potential for erosion. In SIC, this pressure may reach 1 GPa and bubbles within approximately 15 initial radii generate a pressure higher than the incoming pulse. In addition, by using the present results as time-dependent boundary conditions for an elastic wave propagation code, it is shown that a tension large enough to lead to failure may be achieved within small stones or fragments. This work is supported by NIH grant PO1 DK043881 and ONR Grant N00014-06-1-0730.
Acoustic signals from gold nanoparticles irradiated with pulsed lasers
Authors: Ungureanu Constantin , Van Weperen Tamara , Sijl Jeroen , Rayavarapu Raja , Manohar Srirang , Versluis Michel , Van Leeuwen Ton G.
Published: May 2008

Photoacoustic imaging is a new imaging technique, which enables imaging of living tissue with high resolution. The technique analyses ultrasound pulses generated when absorbing structures in tissue are irradiated with pulsed light. Due to the phenomenon of plasmon resonance gold nanoparticles possess high optical absorption coefficients which makes them potential contrast agents in photoacoustics. Further, the heat generated around these particles when irradiated with pulsed light can lead to nonlinear effects including bubble formation. The acoustic signals produced by gold nanoparticles in the linear thermoelastic and non-linear regimes are expected to have specific acoustic signatures. In this study, we investigate the acoustic signals generated by two sets of gold spheres having 25 nm and 60 nm diameter irradiated by laser pulses with increasing incident fluence rates. We identify and discuss the differences in acoustic signals belonging to the thermoelastic expansion regime and the non-linear regime. Finally, the experimental results are compared with different theoretical models available in literature.
Simulating Sonic Scanner responses in an interactive Web-based High Performance Computing environment
Authors: Polyakov Valery , Valero Henri-Pierre , Omeragic Dzevat , Kocian Raymond L. , Habashy Tarek M. , Pabon Jahir
Published: May 2008

Sonic Scanner logging tool collects a wealth of data about the geological formation. The drawback of this is that we are now discovering new features on the acoustic logs that have never been observed before; only rigorous modeling can help properly interpret the data. Invariably, it is difficult to learn quickly how to run a modeling code, set the parameters properly, and be able to detect possible errors in the input. In addition, complex modeling requires high power computing resources, which are not always easily accessible the user. To address these problems we developed a multi-tier Web-based log modeling environment where the Sonic Scanner simulator is easily accessible from the common Web browser. The user builds the model in an intuitive AJAX-like interface and submits the simulation to a remote High Performance Cluster. The computed waveforms are played back in the browser using Scalable Vector Graphics in a variety of customizable displays. The Web application is easily available to any user with an Internet access. In addition, a programmatically accessible Web service is available to application developers who desire to build their own interpretation applications using the Sonic Scanner simulator engine.
Listener-oriented motor control: Comparing evidence from speech and singing
Authors: Lindblom Björn
Published: May 2008

Singing and speech make different use of the vocal tract but work in similar ways with respect to how sound production is controlled. A principle that they share is: output-oriented control. This mode of organization implies that the task of the motor system is defined in terms of the desired properties of the output sound, rather than in terms of motor processes. This claim is strongly supported by Johan Sundberg's experimental work on singing and by 'compensatory articulation' and 'hyper-speech', phenomena that remind us that, for speech, output-directed control is also readily acknowledged. Our comparative review of singin and speech will be placed in the context of the current debate on the 'invariance' and true nature of phonetic units: 'articulatory gestures' or 'auditory goals'?
Noise reduction of freight wagons achieved by LL-blocks implementation: Last investigations and results from IPG and NICOBB projects
Authors: Létourneaux Fabien , Peen Jasper , Meunier Nicolas , Jansen Erwin H. , Cremezi-Charlet Cora
Published: May 2008

The high noise emission levels of freight wagons during rolling are mainly due to uneven wheel treads produced during the braking sequences when the vehicle is equipped with cast iron blocks. This has lead to the development of two types of composite brake shoes (K- and LL-blocks), which are far less aggressive to the wheel.It has been demonstrated that K-blocks achieve a noise reduction of about 10 dB but they are mainly dedicated, at term, to the new vehicles as their friction coefficient is very different to the cast iron one. LL-blocks are on the contrary especially designed for retrofit vehicles and do not require major modifications of the braking equipment. But as they were only very recently made available by the manufacturers due to difficulties in their development, noise efficiency of LL-blocks products is not well-established. This paper focuses on the noise reduction and noise emission values of freight vehicles equipped with LL-blocks. It aims at presenting on-going studies on this topic and at providing reliable and accurate results from different measurement campaigns carried out on a TSI reference track. This work is the result of a collaboration between the UIC project NICOBB and the Dutch Noise Innovation Programme.
A study on regularization parameter choice in Near-field Acoustical Holography
Authors: Gomes Jesper
Published: May 2008

Regularization plays an important role in Near-field Acoustical Holography (NAH), and choosing the right amount of regularization is crucial in order to get a meaningful solution. An automated method such as the L-curve or Generalized Cross-Validation (GCV) is often used in NAH to choose a regularization parameter. These parameter choice methods (PCMs) are attractive, since they require no a priori knowledge about the noise. However, there seems to be no clear understanding of when one PCM is better than the other. This paper presents comparisons of three PCMs: GCV, L-curve and Normalized Cumulative Periodogram (NCP). The latter method is new within NAH and it is based on the Fourier transform of the residual vector. The methods are used in connection with three NAH methods: Statistically Optimized Near-field Acoustical Holography (SONAH), the Inverse Boundary Element Method (IBEM), and the Equivalent Source Method (ESM). All combinations of the PCMs and the NAH methods are investigated using simulated measurements with different types of noise added to the input. Finally, the comparisons are carried out for a practical experiment. This aim of this work is to create a better understanding of which mechanisms that affect the performance of the different PCMs.
Cyclic Sound Intensity and Source separation from NAH measurements on a Diesel engine
Authors: Lafon Brice , Antoni Jerome
Published: May 2008

Noise source separation and acoustic imaging are two research fields of interest in car industry. For this, RENAULT (French car manufacturer) and the University of Technology of Compiègne (UTC, France) are conducting an original study aiming to couple these fields to solve in an efficient way engine NVH problems. Previously, in the first part of this study, combustion noise separation on Diesel engine radiation was implemented from classical sound intensity measurements. The separation, based on Wiener filtering, was performed by taking advantage from the cyclostationary property of engine signals. The second part, presented here, aims to overcome the main shortcoming of the method: time-consuming measurements. Our method is then applied to Near-field Acoustic Holography that is faster and more adapted to an industrial context. Source separation is implemented to complete global radiation maps by specific-source radiation maps such as combustion and other sources radiating in low frequencies since NAH performs rather in low frequencies. Furthermore, the exploitation of cyclostationarity enables to define a cyclic sound intensity (an instantaneous intensity estimated during an average engine cycle). Then, radiation movies can be set to allow a precise location of a specific radiation emergence in space, in frequency and in crankshaft angle.
Fast and Slow Dynamics in Damaged Materials: Correlation to Acoustic Emission
Authors: Bentahar Mourad , Marec Anne , El Guerjouma Rachid , Thomas Jean-Hugh
Published: May 2008

Results are reported of the study of anomalous nonlinear fast dynamics (FD) and slow dynamics (SD) in damaged solids. Experimental observations characterizing FD and SD may be used to detect and eventually characterize induced damage of structural components. Here, we analyze the evolution of the non-linear dynamic behaviour of two polymer-based composites of different reinforcing elements as Sheet Moulding Compound (SMC) and Polymer Concrete (PC) as a function of their gradual damage. More particularly, non-linear FD and SD parameters (time and frequency shift) have been found to be very sensitive to damage creation and evolution for both materials. Besides,acoustic emission monitoring was performed and allowed to calculate the elastic energy released by SMC and PC at every damage stage. Interesting logarithm-like evolution of the followed non-linear parameters as a function of the calculated energy is found. A classification of the collected acoustic emission signals is proposed to understand the contribution of the different damage mechanisms to the evolution of the non-linear behaviour.
Determination of symmetry relations between higher order material constants for the study of nonlinear acoustic properties of piezoelectric crystals of any symmetry class
Authors: Declercq Nico F.
Published: May 2008

Each crystal is invariant under a given point symmetry operation. This results in relations between the different material property constants, such as second order elastic constants, second order piezoelectric constants and second order dielectric constants. Those relations are well reported in text books for the linear behavior of crystals. When nonlinear effects are studied, higher order constants play a significant role and their symmetry relations have only been reported in the literature for a limited number of crystal classes. The problem with higher order constants is that it is rather complicated and very time consuming to study the symmetry relations. This paper presents a newly developed semi-automatic computer program that is able to handle any kind of symmetry relation. Results are reported for all the different crystal classes for the higher order constants, i.e. third order elastic constants, third order piezoelectric constants, third order dielectric constants and electrostrictive constants. The results are important for the study of nonlinear properties of crystals and composites and will ease the experimental quantitative determination of all linear and nonlinear material constants of crystals.
An ultrasonic anemometer for Mars
Authors: Wilson Colin , Davis Lee A. , Hutchins David , Towner Martin C.
Published: May 2008

Ultrasonic anemometers are often used for studies of 3-D atmospheric turbulence on Earth, due to their robust calibration and fast operation (>10 Hz). The same qualities make ultrasonic anemometry attractive for use on Mars, where similar atmospheric turbulence is found. The low density of Martian atmosphere - a hundredth that of the Earth's - is problematic, because of the large acoustic impedance mismatch between the atmosphere and piezoelectric transducers. One solution to this problem is to use piezoelectric transducers with a hornlike resonator bonded to their front surface. Another solution is to use a capacitive membrane transducer instead. We report on performance of various ultrasonic transducers in carbon dioxide Martian pressures, and present an instrument design capable of meeting the stringent mass, power, and environmental requirements of the European ExoMars lander.
Experimental and Numerical Investigation of the Acoustic Response of Multi-slit Bunsen Burners
Authors: De Goey Philip , Kornilov Victor , Rook Ronald , Ten Thije Boonkkamp Jan
Published: May 2008

Acoustic resonances in combustion systems like central heating boilers prohibit further technological advances in these systems. The design and construction is obstructed by acoustic problems because they are largely misunderstood, in spite of our increase in knowledge over the last decades. The flame often acts as an active element in the acoustic field, because the flame transfer function of acoustic waves has a large amplitude at low frequencies. Current models of the phase of the flame transfer function of Bunsen-type flames, based on kinematic behavior of the flame dynamics, completely miss the experimentally observed phase, unless the measured flow field is used in the model. In the current paper we analyze numerical results of the flame dynamics, flow field and flame transfer function found with a 2D detailed numerical model of the flow and structure of the flame on a multiple-slit burner. The model is validated with experiments of the flame dynamics (using chemiluminescence), flow dynamics (using PIV) and flame transfer function (using OH luminescence for the heat release fluctuations and heated wire probe for the acoustic distortions) on exactly the same configuration. A very good agreement is found which indicates the importance of predicting all the influences of the flow on the flame and vise-versa.
Particle deposit formation during filtration characterisation using ultrasonic waves
Authors: Laux Didier , Blasco Hugues , Ferrandis Jean-Yves , Mendret Julie , Guigui Christelle , Cabassud Corinne , Schmitz Philippe
Published: May 2008

Membranes filtration processes are widely used because of their ability to remove particles, colloidal species and micro-organisms from different liquids feeds. However an inherent process limitation is the membrane fouling due to deposition of suspended matter during filtration. Therefore the understanding of formation and transport properties of particle deposit responsible for membrane fouling is a necessary step to optimize membrane processes. These deposits are non homogeneous, highly porous and very thin (less than 500 μm). Thus, it is necessary to obtain local information in order to analyze and model the basic mechanisms involved in deposit formation and then to further predict process operation. As local parameters such as cake thickness and porosity are hardly reachable with conventional techniques, we propose in this paper the use of an ultrasonic echographic method. In a first step this method is validated on deposits of small glass balls. We show that the porosity and thickness of the deposit is in good agreement with theory. Then, the ultrasonic technique has been adapted on a filtration cell in order to give in line results during filtration. First results are presented and discussed.
Single-sided air-coupled ultrasonic NDT of thick plates
Authors: Delrue Steven , Lust Pieter , Deveugele Jurgen , Blomme Erik , Bou Matar Olivier , Van Den Abeele Koen
Published: May 2008

Non-contact air-coupled ultrasonic inspection using single sided access to the material offers interesting possibilities for the development of ultrasonic in-line NDT-systems. This contribution reports observations and simulations obtained from a single-sided air-coupled pitch-catch configuration. The feasibility of the technique is demonstrated with respect to artificial defects in aluminium samples. Depending on the configuration it is possible to establish one or more ultrasonic images of the defect, their number and relative position containing information about the location and depth of the defect. The experiments are simulated using a spectral solution obtained within Comsol, and compared with a full 2D Finite Difference Time Domain simulation and a ray tracing (shadow) approach. The simulations allow simple prediction of the response images in more complicated experimental conditions.
Model-based reconstruction methods of NDT ultrasonic array data
Authors: Calmon Pierre , Iakovleva Ekaterina , Fidahoussen Alex , Ribay Guillemette
Published: May 2008

Ultrasonic array techniques are more and more used in NDT applications because of their flexibility and of their adaptability to complex configurations. In addition they can provide richer data than conventional methods. An optimal exploitation of such data in the aim of localizing and characterizing the detected flaws requires the application of imaging and reconstruction techniques based on a direct modeling of the propagation of ultrasound from the transmitter to the receiver. The quantitative models for the propagation which are available in the CIVA software platform developed at CEA-LIST allow such direct modelling in parts of possibly complex geometries and materials. Different array data reconstruction methods based on the exploitation of these direct models have been studied and implemented in the plat-form. Thus, in this communication we present in particular algorithms derived of synthetic focusing approach. These algorithms exploit the time of flight identification and can be apply to any set of array data. We also present a reconstruction method based on the post-processing of the transfert matrix of the array and the application of MUSIC algorithm. We show and discuss results obtained with these methods both on simulated and experimental data.
Simulation of noise barrier insertion loss using the boundary element method
Authors: Waubke Holger , Kreuzer Wolfgang , Chen Zhensheng
Published: May 2008

Within a project of the European Commission "Calm Tracks & Routes" the performances of different styles of noise barriers were investigated. Additionally new methods for increasing the absorption were investigated. A central theme was to investigate the mitigation of curved walls with high absorption coefficients, because studies made before the project gave the hint that noise barriers curved away from the source should give satisfying insertion loss. Due to the curvature the view in the landscape is hindered to a lesser degree compared to straight noise barriers. The investigation of the noise barriers was done by boundary element methods. An absorptive model for grassland was added and implemented into Green's functions. Due to the existence of smeared sources the application of the fast multipole method was not possible and the simulations were limited to the two-dimensional case. It became obvious that the distance of the source is important for the mitigation of curved noise barriers with respect to straight ones. Therefore different wall types and source positions were investigated. The results of the numerical simulation were compared to measurements in situ and in a large anechoic chamber.
An efficient distributed BEM solver for acoustic and vibroacoustic analyses on a standard PC network
Authors: Di Francescantonio Paolo
Published: May 2008

An efficient BEM approach that permit to solve large acoustic and vibroacoustic problems distributing analyses on a standard PC network is presented. The high efficiency is based on a mix of elements including: 1) A proprietary and high efficient communication and synchronization library (not MPI) 2) A Multi Domain Approach for reducing memory requirements and solution time 3) Efficient iterative solvers The proprietary communication / synchronization library permits to take full advantage of recent multi core PC, enabling to set up clusters with a large number of computing units with a reduced number of PC. A "distributed memory" approach permit to have available the sum of all the PCs RAM, ensuring the possibility to solve large and huge problems that cannot be faced with standard approaches. The Multi Domain approach permit to further reduce the memory requirements, while preserving all the required flexibility in terms of boundary condition and coupling with structural modes. Examples will be showed of large an huge analyses in different application fields including purely acoustics, and fully coupled structural-acoustic analyses.
A hybrid SEA/image sources approach for the prediction of the insertion loss of enclosures
Authors: Sgard Franck C. , Nelisse Hugues , Atalla Noureddine , Amedin Celse Kafui , Oddo Rémy
Published: May 2008

Enclosures are a classical solution to reduce the sound exposure of workers to the noise radiated by machinery. Their acoustic design can be achieved with the help of predictive tools based on simple analytical tools or sophisticated numerical deterministic models. However, there is no simple and fast tool allowing to account for the complexity of the enclosure configuration, capable of better simulating the non-diffuse nature of the field inside the enclosure and covering the typical frequency range [100Hz; 5000Hz]. This paper presents the development of such a tool for the prediction of the acoustic performance of enclosures. It is based on a hybrid model: the statistical energy analysis (SEA) for the sound transmission across the various elements of the enclosure and the method of image sources for the sound field inside the enclosure. The approach is validated by comparing calculation and experimental results carried out in a semi-anechoic room on rectangular and L-shape enclosures for several inner source locations. The effect of an opening is also investigated. The comparisons between the models and the experimental results show a good agreement for most of the tested configurations.
Temporal organization of prosodic and segmental features in spoken Japanese
Authors: Fujisaki Hiroya , Ohno Sumio
Published: May 2008

It is apparent that prosodic and segmental features of speech must be temporally coordinated in order to produce a consistent and meaningful message. The precise mechanism for the coordination, however, has not been clear. The present study looks into this problem in the case of word accent in spoken Japanese. The speech material consisted of utterances of Japanese words that were identical in the word accent type, in the number of morae, in vowel constituents, but were different in consonantal constituents (including a 'null' consonant) at a certain intervocalic position. As for the prosodic features, the fundamental frequency contours were analyzed using the command-response model, and the onset and the offset of the extracted accent command were used as indices of prosodic timing. As for the segmental features, the formant frequency trajectories of the vowels were analyzed using another command-response model, which allowed extraction of the onset of the articulatory command for a vowel nucleus as an index of segmental timing. Comparison of the timings of these commands provides a means for quantitative analysis of the relationship between segmental and prosodic features of speech, and leads to an understanding of the underlying mechanism for their temporal coordination.
Second language rhythm and rhythm metrics
Authors: Ferjan Naja , Ross Tristie , Arvaniti Amalia
Published: May 2008

Several metrics that reflect the variability of vocalic and consonantal intervals in speech have been shown to successfully discriminate between the rhythm of first and second language (L2) speakers producing short sentences of a given language. Here we elicited running read speech from native speakers of English, German and Italian speaking English. We hypothesized that the scores of German L2 speakers would be closer to the scores of native English speakers, since both English and German are stress-timed, and that the scores of Italian L2 speakers would exhibit greater differences from native English scores, since Italian is stress-timed. Our results show instead that the scores of some German speakers are less close to those of the native English speakers than the scores of some Italian speakers, a difference that cannot be attributed to fluency, proficiency level, or length of exposure to English. It is possible that these results reflect over-compensation of some sort by some L2 speakers, though a more likely explanation is that the popular metrics used to quantify speech rhythm may be unreliable or at least not sufficiently robust to be used with L2 data. Reasons why this may be so for L2 speech in particular are discussed.
Influences of language typical speech rate on the perception of speech rhythm
Authors: Dellwo Volker
Published: May 2008

Human listeners can distinguish languages of different rhythmic classes (e.g. stress- and syllable-timed languages). The present study investigated the role of speech rate in this process. In experiment I, speech rate measurements (syllables/second) of read speech were performed in two stress-timed (English, German) and two syllable-timed languages (French, Italian). The results revealed that speech rate distinguishes as reliable between rhythmic class as previously proposed correlates of speech rhythm (%V, VarcoC and nPVI). For a perceptual task (experiment II) sentences from French and German were delexicalized by turning consonantal intervals into white noise and vocalic intervals into complex periodic tones. 18 listeners rated the regularity of the noise-tone sequences on a 13 point scale. The results revealed that listeners rated French stimuli as significantly more regular than English stimuli. It was further shown that the rate of noise-tone sequences was the best predictor for the regularity rating (faster sequences were perceived as more regular) compared to standard rhythm measures (%V, VarcoC and nPVI). Both experiments together show that a) syllable-timed languages are produced faster than stress-timed languages and b) listeners' perception of speech rhythm is highly influenced by these rate differences.
A longitudinal study on vocal aging - Changes in F0, jitter, shimmer and glottal noise
Authors: Kasuya Hideki , Yoshida Hajime , Mori Hiroki , Kido Hiroshi
Published: May 2008

A longitudinal study on vocal aging was conducted for voicing source parameters: fundamental frequency (F0), jitter (period perturbation quotient, PPQ), shimmer (amplitude perturbation quotient, APQ) and glottal noise (normalized noise energy in a high frequency band, NNEb). Acoustic analyses were made on the sustained phonations of the Japanese vowel /a/ of 20 males and 38 females with no laryngeal disease, which were recorded once every year over periods ranging from 11 to 19 years. The acoustic parameters measured were subjected to statistical regression analysis, where the longitudinal change of the parameters was evaluated by the t-test. Two males (10%) and 12 females (32%) showed significant falling in F0 (P<0.05) but no significant rising was observed. Five males (25%) and 12 females (32%) displayed a significant increase in APQ (P<0.05), whereas only six females (16%) and no male revealed significant changes in PPQ (P<0.05). Increase in NNEb was significant for seven males (35%) and 14 females (37%) (P<0.05). We conclude that 1) F0 falling is a more emblematic tendency of female vocal aging than male, 2) shimmer is a more observable indication of vocal aging than jitter, and 3) glottal noise in a high frequency region tends to increase with age.
Calibration of broadband sonar systems using multiple standard targets
Authors: Atkins Philip , Francis David T. , Foote Kenneth G.
Published: May 2008

A seven-octave active sonar system spanning the nominal frequency range 25-3200 kHz was deployed in Norwegian waters for the purpose of measuring the acoustic scattering characteristics of a range of marine organisms. This system transmitted linear frequency-modulated (LFM) signals in order to achieve good range resolution and to obtain spectral information on resolved targets. Total system performance was variously measured in situ and ex situ, depending on the particular octave band, using standard-target spheres. This enabled the frequency response of the entire system to be determined and the sidelobe level of the matched-filter receiver to be reduced. The effects of the deep nulls encountered in the backscattered spectrum of target spheres were partially reduced by using a string of up to six spheres of different sizes and material properties. Typical results will be presented showing that such calibration procedures are sensitive the relative alignment of the sonar-target and to sound-speed profile changes over the length of the string. [This work originated with EU RTD support through contract MAS3-CT95-0031.]
Multibeam sonar calibration techniques
Authors: De Moustier Christian , Kraft Barbara J. , McGillicuddy Glenn
Published: May 2008

The acoustic calibration facility at the University of New Hampshire's Chase Ocean Engineering Laboratory has been used to calibrate several transducer arrays from multibeam sonars that operate at 100 kHz and above. In each case, we mount the transducer array on a rotating colum and measure the array's transmit and receive characteristics with a reference transducers leased from the Naval Undersea Warfare Center, Newport RI. Our rotation angles are known to within 0.2° and our acoustic calibration measurements are repeatable to within 0.5 dB. After adjusting for measured impedance mismatches between the elements of the array, we determine the actual element separation as the ratio of physical spacing over acoustic wavelength, and we use this result to estimate the beam pointing accuracy of the sonar. The beamforming gain is then estimated for all beam directions from broadside to the full range of steering angles used by the sonar. This work is motivated by research efforts to obtain calibrated acoustic backscatter measurements from multibeam echo-sounder that are used for seafloor characterization applications or for detection and identification of targets in the water column.
Real time sound field visualization in the near field, far field and at absorbing surfaces
Authors: De Bree Hans-Elias , Tijs Emiel , Basten Tom
Published: May 2008

The Microflown is a small sensor that is capable of measuring the acoustic particle velocity. In combination with a small pressure microphone it is possible to measure the complete sound field. If the sound field close to an acoustic material is measured it make sense to measure the particle velocity normal to the surface and the sound pressure. With this, the acoustic impedance and absorption can be measured in real time, and with a high spatial resolution. If the sound field of a sound radiating object is measured, the sound field can be obtained directly. Three applications include: direct acoustic camera, that is the real time display of the sound field (velocity, pressure, intensity). Holography that is the pressure, velocity reconstruction on the surface based on the measured sound field (and other places). And cabin interior noise mapping, that is the visualization of the interior noise perceived on a certain location. With three dimensional sound probes (sound pressure and particle velocity in three dimensions), sources in the free field can be found for both bearings as distance. Most recent developments are presented.