bluuebunny/crossref_metadata_2025 huggingface dataset:
Aeroacoustics of axial propeller: Applying to an acoustic wind tunnel and optimization of an axial propeller for cooling system
Authors: Dupont Y.
Published: July 2002

A simplified model is more convenient to predict design parameter effects on operating characteristics and radiated noise of a propeller. Thus, the aeroacoustic design software, decivent, is used for subsonic axial flow fan, mounted as well in reduced systems like cooling systems as in greater structures like test wind tunnel. For a given flow rate and with the blades specified in cylindrical sections, the total pressure and torque are provided by the following computations: (i) outlet velocity triangle by solving radial balance, (ii) lift coefficient by a conformal transformation, and (iii) lift and drag forces, evaluated with considerations of laminar or turbulent boundary layer stall. The outlet relative velocity and force fields allow one to compute the radiated noise whose components are (i) loading noise, computed by Lighthill’s model, and (ii) broadband noise computed by Fukano’s model. Correlations with tests show the validity of this methodology. This software, weak customer in computational duration, may be connected with an optimization software which, after some hundred iterations, allows one to exhibit the best compromise. Two propellers design by these means will be presented: one for a preliminary plan of an acoustic wind tunnel, and one for a cooling system.
Intensive narrow-band noise of oscillating circular gas jet
Authors: Semenov Andrew G. , Rimsky-Korsakov V. Andrew
Published: July 2002

Self-sustained oscillations of a jet issuing from a circular nozzle in an impedance plane into unbounded space or interacting with various obstacles, such as a parallel plane or a coaxial rigid circle, are analyzed. In the problem statement region of the circular jet inner boundary, alternative deflection during self-interaction or interaction with obstacles is considered as an axisymmetric monopole (volume) source of axial sound waves inside the jet cylinder directed to the jet root. By means of the corresponding 1-D boundary value problem solution, Nyquist stability criteria are derived for oscillations inside the cylindrical volume bounded by jet boundaries. Conditions favorable for jet boundary axially symmetric self-sustained oscillations excitation are found and their relations to the problem basic parameters are predicted, both for subsonic and supersonic jet cases. The proposed method could be used in various practical jet-obstacle interaction noise-generation problem analyses.
Sound scattering by Gauss beam from cylindrical objects
Authors: Oboznenko I. L. , Oboznenko E. I. , Genis Vladimir I.
Published: July 2002

Practically, when diagnosing vessels by focusing array, the vessel is radiated not by the plane wave, but a time-limited beam. Here one can see the results of theoretical and experimental research of Gauss beam sound scattering from cylindrical objects with wave resistance different from the medium. Well-known results of sound scattering on cylinders with limited sizes are wrong in reality, because of limiting the vertical size of the cylinder. In fact, all the objects, including the cylinder, are radiated by a nonconcentrated beam, like a Gauss beam. Theoretical and experimental results of Gauss beam scattering in the band of parameter α=a/w (where a-cylinder radius; w-Gauss beam width on e−1 range) from 10−6 (quasiplane wave) to 100 (super-narrow beam) show, that a scattered wave spectrum changes very substantially. This point needs caution, and immediately changes classic results for the plane wave. Also, the sound beam echo-signal spectrum in the reverse direction gives one the ability to classify and to differ objects as ‘‘more soft’’ or ‘‘more hard’’ with respect to medium (for wave resistance it differs up to 5%–10% from medium). This permits the classification of cylindrical foreign inclusions or defects of little vessels like post-, precapillaries.
Complex poles of Lamb waves propagating along anisotropic and absorbing fluid-loaded plates
Authors: Deschamps Marc , Poncelet Olivier
Published: July 2002

This work presents theoretical and experimental investigations on Lamb wave generation along anisotropic immersed plates. The structure of these guided waves is strongly dependent on the nature of the source (transient source, bounded beam...). An incident plane wave for which the signal is time-limited is considered, and leads to transient Lamb waves mathematically defined by complex frequencies. These frequencies are the poles of the reflection/transmission coefficients of the fluid-loaded plates. This point of view, recently developed for isotropic plates, is completely different from the classic approach in terms of leaky Lamb waves, which are harmonic waves. New interesting results are then obtained for the NDT of thin anisotropic plates: the dispersion curves calculated for complex frequencies are very different from those calculated for real frequencies (harmonic waves). Moreover, some modes have a negative imaginary part of the frequency that implies transient phenomena increasing with time. The waveforms of the reflected signals are obtained and explained by the calculation of a contour integral in the complex frequency plane. The roles of anisotropy and absorbing effects are discussed.
Modal scattering from orifices
Authors: Horner Jane L. , Petersson Björn A. T. , Lyons Richard
Published: July 2002

When considering a sound wave traveling through a circular orifice in a rigid baffle, both the reflected and scattered field have to be established on the incident side of the orifice. Previous investigations have used Hankel transforms to establish the amplitudes of these two waves. This study concentrates on the coupling of the modes in the scattered and reflected fields, with the object of the investigation being to determine if a modal approach may be taken to describe the reflected sound fields from such an orifice. Results are shown in the form of the modal contributions to the integrand which must be used to obtain the scattered field.
Quality assessment of adherent and fusion-welded joints in silicon wafers by nonlinear ultrasound
Authors: Wegner A. , Koka A. , Hirsekorn S. , Arnold W.
Published: July 2002

The interest in fusion-welded silicon wafers has increased recently because of their excellent electrical and mechanical properties. Typical applications are in acceleration and pressure sensors. The interface of room temperature bonded wafers contains a physically adsorbed water layer. Bond temperatures higher than 373 K cause a reduction of the adsorbed water by diffusion and thus an increase in bond strength. If electronical components are protected by surrounding silicon wafers, the joining temperature must not be higher than 673 K. The bond strength of the interface essentially defines the reliability of the components. Therefore, a nondestructive method to evaluate the bond quality is required. Binding forces are nonlinear and cause a nonlinear modulation of transmitted or reflected ultrasonic waves. Inhomogeneities in bond strength of an interface can be imaged by the local ultrasonic amplitudes of the insonified frequency and of its higher harmonics measured interferometrically in transmission. A quantitative evaluation of the image data yields information about the variations in bond strength and the size of delaminations and of weakly bonded areas. This paper presents experimental and theoretical investigations of the interface of bonded silicon wafers exploiting the nonlinear transmission of ultrasound. The data are compared to destructive tests.
One-bit time reversal through high-order multiple scattering media
Authors: Derode Arnaud , Tourin Arnaud , Fink Mathias
Published: July 2002

A time-reversal mirror (TRM) is an adaptative device that can focus an ultrasonic wave through an inhomogeneous medium. In a typical experiment, a pointlike source transmits a pulse that propagates through the medium. The distorted wavefronts are recorded by a 128-tranducer array. The 128 signals are digitized over 8 bits, stored in a memory, time reversed, and retransmitted by the array through the medium: the resulting wave converges onto the source, despite the inhomogeneities. In the presence of high-order multiple scattering, the TRM still works and takes advantage of it to refocus a pulse with a finer spatial resolution than in a homogeneous medium. Moreover, it is shown that the TRM is still able to focus a wave even if the recorded scattered wave is encoded over 1 bit, only its sign being used. Reducing the number from 8 bits to 1 does not appear to change the lateral resolution; the signal-to-noise ratio is a little higher. Thus the 1-bit TRM appears to be a very robust and low-cost focusing device. Experiments were carried out in a water tank through a random collection of 2400 parallel steel rods.
Characterization of time-reversed elastic waves in ergodic billiards
Authors: de Rosny Julien , Draeger Carsten , Fink Mathias
Published: July 2002

One year ago, this laboratory showed experimentally and numerically that an elastic wave can be time reversed in a highly reflecting cavity with a single pointlike source [Draeger and Fink, J. Acoust. Soc. Am. 101, 3090(A) (1997)]. This is possible because the cavity is low dissipative and its shape is ergodic. Now the properties of this experiment are better understood. Clearly, two parameters are involved. The first one (T) is the beginning of the time reversal window; the second one is its duration ΔT. The lowest value of T which gives an isotropic focusing is the ‘‘angular mixing time;’’ it may be related to the ergodicity time. There is another characteristic time: beyond a certain limit, increasing ΔT does not improve the quality of focusing any longer. This ‘‘saturation time’’ is very dependent on the initial pulse length; it is analogous to the Heisenberg time. Also, the difference beteween the perfect theoretical time reversal and the experimental one is explained.
Investigation of the process of self-demodulation of acoustic waves in the river sand
Authors: Nazarov Veniamin E. , Zaitsev Vladimir Yu. , Kolpakov Andrey B.
Published: July 2002

Experimental investigation and theoretical description of nonlinear self-demodulation of a pulsed high-frequency acoustic wave and propagation of the secondary low-frequency acoustic pulses in dry and water-saturated sand are carried out. The dependence of the propagation time of the video pulses upon the initial static pressure and the relation of the duration and the form of the secondary pulses with the form of the envelope of the initial high-frequency wave were studied. In order to describe the observed dependences, nonlinear equations of state for the considered grain media were suggested. Using the equations, analytical expressions for the demodulated pulse forms were derived. On the basis of matching the theoretical predictions and experimental data, linear and nonlinear acoustic parameters of the sand are determined. The obtained results may be applied to analysis of seismic signals and used for development of seismoacoustic sensing methods, primarily for diagnostic applications of nonlinear effects.
Anomalously high elastic nonlinearity and frequency-independent Q-factor as complementary properties of microinhomogeneous solids
Authors: Zaitsev Vladimir
Published: July 2002

During the last few decades, a wide class of media demonstrating anomalously high elastic nonlinearity was experimentally revealed (e.g., rocks, grainy materials, concretes). Their nonlinear parameters often exceeded those of homogeneous liquids and solids by several orders of magnitude, whereas linear elastic properties remained ‘‘normal.’’ Just the same, materials often possess an almost frequency-independent Q-factor, which also is quite different from homogeneous liquids. These acoustical peculiarities may be evidently attributed to the influence of structural microinhomogeneities (e.g., cracks, grains, etc.) typical of the mentioned media. Recently, a few physical models describing nonlinearity of grainy and crack-containing materials were proposed, while the description of the dissipation (almost frequency-independent Q-factor) still is restricted to phenomenological models. The report presents a rather demonstrative model of microinhomogeneous solids, which allows for explanation of the mentioned facts. It follows naturally that the microinhomogeneities may not cause significant change of linear elasticity, whereas a sharp increase of elastic nonlinearity and occurrence of the frequency-independent Q-factor appear to be complementary manifestations of the same microstructure. The model readily allows one to relate medium structural features with its elastic and dissipative properties. [Work supported partially by RFBR and Academic Board of KUL.] a)Permanent address: Inst. of Appl. Phys. RAS, 46 Uljanova St., Nizhny Novgorod, 603600, Russia.
‘‘Acoustical modeling’’ according to the theory of the common networks—Taking into account nonlinear effects
Authors: Huebelt Joern , Sarradj Ennes
Published: July 2002

One method to model the electroacoustical transducer consists of describing its basic system components using lumped elements according to the theory of the common networks. In the past this technique has been widely used. However, the validity of the underlying simplifications has to be proofed in particular cases. The modeling of the acoustic behavior of a signal horn shall demonstrate the efficiency of this method. In a first step, a linear model in the frequency domain was established. It turned out that for a more exact simulation, the consideration of nonlinear effects is necessary. Due to the extension to nonlinear components, the analysis of the system has to be carried out in the time domain. The model provides the possibility to include the results of the FEM analysis or the BEM analysis, for those system parts which cannot be reduced to lumped elements. Moreover, it enables a relatively fast and inexpensive examination of the system characteristics compared to the FEM or the BEM analysis and can be easily adapted to similar horn types.
The cavitation collapse on a sub-ns time scale
Authors: Gompf B. , Pecha R. , Eisenmenger W.
Published: July 2002

A single sonoluminescing air bubble trapped in the pressure maximum of a resonant sound field in water is an ideal model system to investigate the end phase of the cavitation collapse. The dynamics of these single bubbles can be characterized with Mie-scattering. In earlier experiments, the scattered light was detected with photomultiplier tubes (PMT) where the time resolution is limited by the response of the PMT and no spatial resolution is possible. Using a streak camera, the scattered light can be recorded with high spatial and temporal resolution. The streak images show that at the minimum radius the scattered light intensity is not only a function of R(t) anymore, and the changes in the refractive indices inside the bubble and in the highly compressed water surrounding the bubble have to be considered. Together with the width and intensity of the emitted light pulses, the results represent a complete data set for the end phase of the bubble collapse.
Molecular dynamics approach for a sonoluminescing bubble
Authors: Metten Burkhard , Kurz Thomas , Lauterborn Werner
Published: July 2002

Up to now the numerical calculations for the converging shock or compression wave model of sonoluminescence have been based primarily on continuum methods. Here an alternative approach by molecular dynamics simulation is shown to be feasible with today’s computer memory and speed. Both approaches are compared. Results of the simulations are presented for the scaling behavior with the number of particles, for different boundary conditions (spherical and ellipsoidal bubbles) and for one and more species in the bubble. The dependence of the light intensity and pulse duration on the sphericity of the bubble is discussed. [Work supported by the Graduiertenkolleg Stroemungsinstabilitäten und Turbulenz.]
Attack transients of free reed organ pipes
Authors: Braasch Jonas , Ahrens Christian
Published: July 2002

Free reed pipes in organs have fallen out of favor, because they were reputated to have a sluggish attack transient. To test this theory, the starting transients of the ‘‘Klarinette 8 ft’’ pipes were measured on the new Klais organ in the Auditorium Maximum, Bochum. Further measurements to determine the role of the wind pressure were done on the wind chest of the Klais workshop in Bonn. The transients of the free reed pipes were compared to those of bound reed pipes and diapason pipes (measured on the same organ). As the results show, the attack transient of the free reed pipes was indeed slower than that of bound reed pipes, but on the same order of that of diapason pipes. However, in contrast to the free reed pipes, diapason pipes have a noticeable broadband noise preceding the sound. In addition, there is a delay between the onset of the first-order harmonic and the onset of the higher-order harmonic in the starting transient of the free reed pipe. This effect is not usually found in the transient of diapason pipes.
A computer program for optimization of brass instruments. Part I. Concept, implementation
Authors: Kausel Wilfried , Anglmayer Paul , Widholm Gregor
Published: July 2002

Computer optimization is used to improve characteristics of real world systems. Different strategies are known and have successfully been applied in areas like filter design, circuit synthesis, layout, etc. Common to all optimization methods is the need for mathematical models and target functions evaluating to a single number, reflecting the sum on all deficiencies depending on variables to be varied. In a brass instrument optimizer these variables are representing physical dimensions which later on can be changed by the instrument maker (e.g., by inserting sleeves or modifying the bore). In the target function, differences between actual and desired characteristics like intonation or responsiveness are calculated, weighted, and added. Because these characteristics can only be derived from the instrument’s calculated input impedance, physical modeling is required. Systematically and algorithmically, the optimizer approaches the best possible instrument step by step, varying optimization variables. It is directed by the result and tendency of the target function which is evaluated after each step. The brass instrument optimization program introduced here makes computer optimization available for musical instrument manufacturers. Much expert knowledge like defining target functions, specifying optimization variables, and modeling instruments are hidden from the user, making the tool easy enough to work with.
Predicting the joint annoyance of multiple noise sources
Authors: Berglund Birgitta , Nilsson Mats E.
Published: July 2002

Noise annoyance is always linked to a complex of environmental noises (noise emission) even if source-specific annoyance is possible to report. Therefore, there is a lack of agreement between total or joint annoyance predicted from source emissions and the actual annoyance reported under field conditions. Models developed from laboratory experiments are commonly pure mathematical constructs based on simple energy summation of totally overlapping sound, whereas the field conditions require yet undeveloped mathematical models that account for perceptual-cognitive integration processes. To be successful in predicting joint annoyance of multiple noise sources, it is necessary that the integration of information derived from noise emission(s) is modeled, rather than simply to sum mathematically noise-source emissions. Important factors for perceptual-cognitive integration processes are kinds of noise sources, their levels, time pattern of joint emissions, discernibility of sounds, and the role these play in the soundscape. Existing models can to varying degree accommodate these factors, but it seems necessary that new models particularly take into account the time pattern of joint emissions as well as the role of sounds in (perceived) soundscapes.
ANSI S12.13: Using audiometric data variability to assess hearing conservation success or failure
Authors: Royster Julia D. , Royster Larry H.
Published: July 2002

In 1991, draft standard ANSI S12.13 was published, offering methods for using the variability in audiometric data as an indicator of the effectiveness of hearing conservation programs (HCPs) in protecting noise-exposed personnel from occupational hearing loss. In contrast to methods which require many years of data before hearing thresholds of noise-exposed groups may be compared to control groups, ANSI S12.13 methods may be applied to as few as two successive audiograms. If high variability is found between successive audiograms, it may be due either to unreliable testing (a problem in itself) or to inadequate protection from noise, allowing a temporary and eventually permanent threshold shift to occur. In either case, the evaluator is alerted that the HCP is ineffective. Identifying poor audiometry prevents erroneous decisions from being made based on bad data, both for individuals and for groups. This information enables the evaluator to make needed improvements to the HCP. Examples of analyses will be shown to illustrate patterns of results indicating both procedural problems and insufficient protection. Experience with ANSI S12.13 confirms the value of two simple procedures.
Research strategies for evaluating effectiveness of industrial hearing loss prevention programs (HLLP)
Authors: Prince Mary M. , Franks John R. , Merry Carol , Colligan Michael
Published: July 2002

NIOSH recommends that hearing loss prevention programs (HLPPs) be implemented for all workers whose unprotected 8-h TWA exposures equal or exceed 85 dB and that the programs include at least the following components: (1) initial and annual audits of procedures, (2) noise exposure assessment, (3) engineering and administrative control of noise exposures, (4) audiometric surveillance and evaluation, (5) use of hearing protectors (for exposures >85 dB, regardless of duration), (6) education and motivation, (7) recordkeeping, and (8) program evaluation. All components except program evaluation and routine in-hour audits are generally discussed in the Occupational Safety and Health Administration (OSHA) Hearing Conservation Amendment (HCA). This paper presents research approaches for systematically evaluating OSHA-mandated hearing conservation programs. The intent of such research is to (a) develop methods for evaluating hearing conservation programs that can be used across several industrial sectors and (b) identify ways in which ‘‘hearing conservation’’ can effectively become ‘‘hearing prevention’’ programs. General approaches are presented for each program element and data collection issues are discussed with specific examples of how various methods can been used for program evaluation. The goal of such research strategies is to identify the best predictors of program effectiveness.
Computational analysis of a thermoacoustic refrigerator
Authors: Schneider Thomas , Klein Rupert , Besnoin Etienne , Knio Omar M.
Published: July 2002

The velocity and temperature fields in an idealized, parallel-plate, thermoacoustic refrigerator are analyzed using a low-Mach-number computational approach. Two-dimensional unsteady calculations of the flow field in the neighborhood of the stack and heat exchangers are performed using: (a) a semi-implicit, finite-volume, Godunov-type, compressible flow solver, and (b) a vorticity-based scheme for stratified flows. The first model is used to address the limiting case of plates with vanishingly small thickness, while the second model is used to analyze finite blockage effects. The predictions of both models are compared to each other and are used to study the effect of heat exchanger properties on the thermal performance of the device. [The work of T.S. and R.K. is supported by DFG. The work of E.B. and O.M.K. is supported by the Office of Naval Research.]
Acoustic images at the nanometer scale—Why and how?
Authors: Kulik Andrew , Dupas Emmanuel , Oulevey Frederic , Gourdon Delphine , Burnham Nancy , Gremaud Gerard
Published: July 2002

For years, researchers have attempted super-resolution acoustical images. Using a subwavelength detector one can map acoustical fields with a spatial resolution determined by the size of the detector. A breakthrough approach is to use an atomic force microscope (AFM) in order to detect ultrasound. The lateral resolutions that have been achieved by various groups are better than 50 nm. Different methods are in use to generate and detect the signal. Three main setups have been developed: (i) Contact-mode medium-frequency (typically 500 kHz) low-amplitude methods (SLAM), (ii) ‘‘mechanical diode’’ high-frequency (typically 5 MHz) high-amplitude pulsed setups (UFM), and (iii) contact-mode high-frequency (typically 5–400 MHz) methods using mixing of two ultrasonic waves through the nonlinearity of the tip–sample interaction. All three systems map different properties of the sample and have advantages and disadvantages. An overview of these methods will be illustrated by images and measurements.
Material characterization using micro-machined air transducers
Authors: Khuri-Yakub Butrus T. , Degertekin F. Levent , Hansen Sean T. , Irani Neville R.
Published: July 2002

This paper presents the application of micro-machined ultrasonic air transducers (MUT) to material characterization. The transducers are made of thin membrane capacitors with very thin vacuum gaps. A system analysis that details the design of the transducers and the transmitter and receiver electronics to deliver over a 100-dB dynamic range while operating in the 1–5-MHz range is presented. The transducers and electronics system are used both in pulse–echo and pitch–catch modes to evaluate materials. In transmission and reflection, the system is used to image defects in carbon epoxy composites. Transducers are designed, using Lamb wave theoretical calculations, to excite selected Lamb wave modes in composite and other materials. The transducers are then used to characterize the composites with respect to defect detection (via Lamb wave velocity changes) and material characterization (via slowness curve inversion).
Time-domain ultrasound diffraction tomography
Authors: Mast T. Douglas
Published: July 2002

A quantitative ultrasonic imaging method employing time-domain scattering data is presented. This method provides tomographic images of inhomogeneous media using scattering measurements made on a surface surrounding the medium of interest, e.g., on a circle for two-dimensional problems or on a sphere for three-dimensional problems. These scattering data are used to construct a time-domain analog of the far-field scattering operator. Images of compressibility variations are then reconstructed using a coherent combination of the far-field scattered waveforms, delayed and summed in a manner that numerically focuses on the unknown medium. This approach is closely related to synthetic aperture imaging; however, unlike conventional synthetic-aperture methods, the present method provides quantitative reconstructions of compressibility variations, analogous to frequency-compunded filtered backpropagation images weighted by the spectrum of the incident wave. Example reconstructions, obtained using synthetic data for two-dimensional scattering of wideband pulses, show that the time-domain reconstruction method can provide image quality superior to single-frequency reconstructions for objects of size and contrast relevant to medical imaging problems such as ultrasonic mammography. Reconstructions also illustrate the dependence of image quality on the number of incident-wave insonifications and on the range of scattering angles available for measurements.
Vocal qualities that singers can control but often limit
Authors: Titze Ingo R.
Published: July 2002

In singing, there is sometimes a conflict between maximizing the size and consistency of the voice and maximizing the number of distinct qualities that can be utilized. Most vocalists can voluntarily change vocal register (from chest to fry, falsetto, and in some cases whistle), vocal ring (from resonant to fluty), vocal tightness (from normal to breathy or pressed), and vocal roughness. But classical singers, for whom electronic amplification is often not an option, limit the use of the full scope of these qualities. Falsetto register which involves only part of the vocal fold in vibration, is used sparingly because it doesn’t balance with chest voice in terms of loudness. The same can be said for breathy voice, produced with a wider glottis. Some vocal qualities are not used because they are spectrally unbalanced, and rough voice is often rejected because it suggests lack of refinement and harmonic purity. With amplification, many of the restrictions on vocal quality are removed. [Work supported by Grant No. P60 DC00976 from the National Institute on Deafness and Other Communication Disorders.]
An interdisciplinary study on railway and road traffic noise: Annoyance differences
Authors: Schreckenberg Dirk , Schuemer-Kohrs Anke , Schuemer Rudolf , Griefahn Barbara , Moehler Ulrich
Published: July 2002

An interdisciplinary study was made to compare the annoyance responses to railway noise and to road traffic noise. Acoustical measurements were taken in eight areas to assess the noise levels caused by railway and road traffic noise. Road traffic noise was predominant in four of the eight areas and railway noise in the other four areas. A total of 1600 residents were interviewed. The data allow the individuals’ annoyance responses to be related to the individual noise levels for each of the two sources. Some preliminary results of the not yet completed study with regard to the relative annoyance by the two sources are described. The general annoyance (24 h, by day and at night) is less for railway than for road traffic noise at equal noise levels. Also, the disturbances at night attributed to railway noise are less than those attributed to road traffic noise. In the daytime, the difference in the disturbance between railway and road traffic noise depends on the disturbance aspect considered: With regard to communication, there is a greater annoyance attributed to railway than to road traffic noise. With regard to outdoor recreation, road traffic noise is more disturbing than railway noise.
Energy source superposition technique for solving two-dimensional acoustic problems
Authors: Herrin David W. , Seybert Andrew F.
Published: July 2002

An energy source superposition technique has been developed to determine sound energy and intensity. Using this method, the intensity along the boundary is approximated by superimposing energy sources placed outside the acoustic domain. The unknown amplitudes of these sources are found using a linear least squares, then these energy sources may be superimposed to approximate the sound energy. Several tests were performed to evaluate the approach. First, it was demonstrated that the energy sources could be superimposed if the interference pattern between propagating waves was neglected. This was demonstrated for plane waves, cylindrical waves, and spherical waves. Two-dimensional energy results were then compared for the few cases where a closed form solution could be obtained like the pulsating cylinder and the one-dimensional duct. Finally, results were compared to acoustic boundary element solutions with good agreement. [Work supported by the University of Kentucky Center for Computational Sciences.]
An impedance coating formulation for a coupled structural acoustics code
Authors: Mathews Ian C. , Jeans Richard A.
Published: July 2002

In the automotive and aerospace industries as well as the underwater acoustics defense applications the addition of coatings to modify the response of the vibrating structure is commonplace. The surface of the structure is therefore separated from the surrounding fluid by this coating. Traditionally, the coating is modeled using continuum or thick-shell-type finite elements. Difficulties arise if the Poisson ratio for such a coating is close to one-half. In the approach presented in this paper, it is proposed to model the behavior of these coatings by a 2×2 coupling matrix relating the normal velocity and pressure on each side of the coating. The impedance relationships developed for such coatings are local, complex, and maybe frequency dependent. A second approach for modeling a coating is also detailed and validated. In this approach the coating is assumed to behave on any point on the surface as an infinite plane layer of compressible fluid. For this approach to be valid, the thickness of the coating must be negligible with respect to the acoustic wavelength in the exterior fluid. The analytical solutions developed for validating both proposed methods will also be derived in this paper.
Model and experiments of multiple acoustical scattering from small obstacles
Authors: Schickert Martin , Ermert Helmut
Published: July 2002

A self-consistent model is presented to calculate acoustical scattering of waves from many discrete obstacles, including multiple scattering. The model provides a formulation for incorporating single scattering Green’s functions into a multiple scattering solution using auxiliary sources. Geometry and material parameters of the scatterers in the ensemble may be different, and are arbitrary as long as each single scattering solution is known. In restricting the number of auxiliary sources the model is approximate, yet it is empirically shown to work in a quantitative manner for scatterers of ka up to about one, where k is the wave number of the background medium and a is half of the cross section of a scatterer. To ease experimental verification, a two-dimensional setup is considered where obstacles are circular cylinders of infinite length. The model is tested against experimental data gathered from ultrasonic experiments in a water tank. Ensembles of two to ten strong scattering cylinders were used, their radius being chosen such that ka =3D 0.5 at the mean frequency of the transducers. Numerical and experimental results are compared in time and frequency domain and show quantitative agreement in all investigated arrangements. Results of a numerical experiment including 50 different cylinders are also shown.
A time-domain numerical model for the acoustic scattering from rigid or elastic targets
Authors: El-Ghaouty Ahmed , Dubus Bertrand , Lavie Antoine
Published: July 2002

In order to predict the backscattered echoes from immersed targets, a numerical model based on the space–time Helmholtz–Kirchhoff integral formulation (HKIF) is developed in the EQI code. Two different schemes are implemented for the space–time discretization: a classical finite-element discretization in space and finite difference discretization in time (FEM/FDM) and a space–time finite-element discretization (FEM/FEM). The computed results are provided for the test case of a rigid sphere. Two well-known spurious effects of the discretized HKIF are described: (i) the existence of an instability which grows exponentially as time progresses and (ii) the inaccuracy of the results in the shadow zone. The origin of these effects and the relative performance of the FEM/FDM and FEM/FEM methods are discussed. Finally, the coupling with a finite-element structural model (ATILA code) and its effect on the instability are also presented.
Ultrasonic field analysis by numerical quadruple integration with repeated trapezoidal rule
Authors: Imamura Tohru
Published: July 2002

To compute the ultrasonic field by the square flat transducers, numerical quadruple integration is being carried out with repeated trapezoidal rule. The medium of ultrasonic propagation is supposed to be isotropic and nonabsorptive. Only the longitudinal wave is being treated, which follows the Huygens principle. The sound pressure, the particle velocity, and the specific acoustic impedance, which is the quotient of the sound pressure by the particle velocity, are all obtained. Using the repeated trapezoidal rule with automatic interval halving, how results are converged is investigated. The computed resuls are surveyed numerically for each single, double, triple, and quadruple integration. These results are used for the higher-fold numerical multiple integrations. By this method, the effect of tilt for the receiving square flat transducer to the similar transmitting transducer is obtained, which seems very difficult to analyze by using the axial symmetry of the ultrasonic field [T. Imamura, J. Acoust. Soc. Am. 103, 3041(A) (1998)].
Hydrophone calibration at the UK National Physical Laboratory: From primary standards to dissemination
Authors: Zeqiri Bajram
Published: July 2002

Ultrasonic hydrophones continue to play a pivotal role in assessing the safety of medical ultrasonic equipment. International and national standards require measurements of the acoustic fields generated by this type of equipment to be made using hydrophones of specified properties such as bandwidth, spatial resolution, etc. A critical property of the hydrophone is the absolute calibration of its receive sensitivity and its ultimate traceability to national standards of measurement. At NPL, the primary standard laser interferometer has been in operation for over 10 years, providing this traceability for the majority of hydrophones currently used worldwide. This presentation will give an outline description of the interferometer, describing how the primary standard is disseminated to the user community through secondary standard hydrophones using a nonlinear intercomparison method. A number of key results related to the long-term stability of reference hydrophones will be presented. The paper will then concentrate on recent developments in the application of the interferometer which have sought to increase its working frequency range up to 60 MHz.
Two-dimensional hydrophone arrays: Measurement methods for the new millenium
Authors: Hurrell A. M. , Duck F. A.
Published: July 2002

As the boundaries of knowledge of ultrasound systems are extended, the limitations of current measurement systems are exposed. To meet the challenge posed by ever more demanding standards of measurement, Precision Acoustics has designed and manufactured an innovative two-dimensional hydrophone array—the Acoustic Imager. Calibration data for the Acoustic Imager is presented, and it has been shown to have a higher sensitivity than a polymer probe or membrane type hydrophones of the same diameter (0.2 mm). This is achieved while maintaining a frequency response flat enough to meet the requirements of an IEC866 class A device over the frequency range 1–20 MHz. The experimental results presented, from the characterization of both linear and nonlinear ultrasonic fields, demonstrate the advantages of hydrophone arrays for ultrasonic field measurements (e.g., reduced scan times, minimization of phase errors). Demonstrative examples are also provided to display the data postprocessing capabilities of the Acoustic Imager in the assessment of the acoustic parameters used to describe medical ultrasound fields.
Optical measurement of wide bandwidth ultrasound fields
Authors: Pitts Todd A. , Greenleaf James F.
Published: July 2002

A technique for measuring instantaneous three-dimensional pressure in a wideband ultrasound pulse is presented. A collimated laser pulse impinges on the ultrasound field, and the optical intensity in a diffraction plane subsequent to this scattering event is imaged onto a CCD camera and stored. Timing is controlled precisely, allowing the acousto-optic interaction to occur at the same point in the temporal evolution of the sound field each time the experiment is performed. After interaction with the ultrasound pulse, the optical phase is approximately proportional to the ray sum of instantaneous pressure in the pulse (taken in the direction of optical propagation). Optical phase immediately subsequent to passage through the ultrasound pulse is computed from recorded optical intensity via a phase retrieval algorithm. The experiment is performed at several angles as the ultrasound transducer is rotated about an axis normal to the optical axis of the imaging system. Tomographic reconstruction algorithms are applied to the retrieved optical phase data, computing pressure at all points in the ultrasound pulse. The resulting pulse may be propagated forward or backward in time under a source-free model. Reconstructions of the field from a 2.5-MHz array transducer compare well with hydrophone measurements.
Methods of beam divergence corrections on broadband direct contact ultrasonic technique
Authors: Kruger Silvio E. , Charlier Jacques , Rebello Joao M. A.
Published: July 2002

The separation of intrinsic attenuation and velocity parameters from extrinsic factors is a complex task in nondestructive ultrasonic characterization of materials. The effect of the ultrasonic beam divergence due to finite source is discussed both theoretically and experimentally in this work. The objective is to evaluate different techniques of attenuation and velocity measurements with beam divergence corrections on direct contact configuration. Both amplitude and phase spectra for signals generated and detected by commercial NDE broadband transducers are to be corrected. The effectiveness of each technique is evaluated with different transducers and sample geometry. The results show that a smaller effective transducer diameter than the nominal must be assumed in theoretical corrections [P. H. Rogers and A. L. Van Buren, J. Acoust. Soc. Am. 55, 724–728 (1974)] and that the experimental determination of calibration correction for a particular transducer by a reference sample can be a good alternative.
Elastic and viscoelastic characterization by Brillouin spectroscopy
Authors: Daniele Fioretto
Published: July 2002

Brillouin light scattering has been widely used in the last years to investigate the elastic and viscoelastic properties of both films and bulk samples. This has been possible thanks to the development of a new class of high-contrast Fabry–Perot interferometers, which permit the detection of the weak light signal scattered by surface and bulk phonons. A brief review on measurements performed in metallic, semiconductor and organic thin films is reported and connections between experimental data and physical parameters of the medium are discussed. The results of the viscoelastic characterization of supercooled liquids are also reported, giving information on the dynamics of disordered systems close to the glass transition.
Evaluation technique for spectra of complex Young’s moduli
Authors: Bossemeyer H. G.
Published: July 2002

For a proper design of acoustic absorbers, detailed information about temperature- and frequency-dependent elastic moduli of absorber materials is essential. Dynamic Young’s modulus data depicted in a complex plane determine whether a material is thermo-rheological simple or not. However, even if all data points fit well to a single curve, suggesting simple behavior, severe systematic errors can be involved. A new evaluation technique which relies on well-known visco-elastic material models is introduced to detect systematic errors and to obtain more reliable modulus spectra.
Shock wave characteristics in liquids and extracorporal lithotripsy
Authors: Eisenmenger Wolfgang
Published: July 2002

Reliable determinations of shock wave parameters such as risetime, pulse width, and positive and negative pressure amplitudes are prerequisites for a study and comparison of different stone destruction mechanisms in lithotripsy. In comparing stone destruction mechanisms, it is found that the fiber-optic probe hydrophone is ideally suited for reliable shock-wave measurements, especially also in the negative pulse range. Different stone destruction mechanisms as a direct action of the shock wave penetrating into the stone, the sound soft reflection, i.e., the Hopkinson effect, the importance of cavitation, and finally the action of evanescent waves in the stone caused by the passing pressure wave in the liquid are discussed in their dependence on shock wave parameters. The results are compared with experiment.
Acoustic time-reversal experiments in the nonlinear regime
Authors: Tanter Mickaël , Thomas Jean-Louis , Coulouvrat François , Fink Mathias
Published: July 2002

Until now, time-reversal mirrors (TRM) were only used in a low power regime for which nonlinearities can be neglected. Here, their behavior is investigated in a higher power regime compelling nonlinearities to be taken into account. If one considers the acoustic wave equation in a weakly nonlinear medium, the time-reversal invariance holds. Thus, Burger’s equation is invariant when time and direction of propagation are simultaneously reversed. In a nonlinear medium, the shape of a sinusoid changes continuously during propagation as energy is transferred to harmonics. The inverse process would take place after reflection on a TRM. This property holds as long as the shock distance is not reached, otherwise the shock discontinuity implies an irreversible change of the entropy and the time-reversal invariance is broken. These results are confirmed by a finite differences simulation of Burger’s equation. However, experiments are very difficult to carry out because of the limited bandwidth of transducers. Nevertheless, for 1-D problems and an antisymmetric wave packet, a time reversal is equivalent to a reflection on a pressure release interface. This trick has been used to conduct an experiment giving qualitative good agreements with the simulation. a)Also at Lab. de Modélisation en Mécanique, Univ. Paris VI, CNRS UMR 7607, 4 place jussieu, F75252 Paris Cedex 05, France.
Honoring the contributions of Reinier Plomp in psychoacoustics
Authors: Moore Brian C. J.
Published: July 2002

Reinier Plomp has had a huge impact on the field of psychoacoustics of a period of 40 years. Many of this papers have become regarded as ‘‘classical.’’ His studies on the ‘‘science of science’’ led to the conclusion that the number of published papers cited more than 25 times is a good indicator of an author’s scientific impact. Seven out of the first ten of Plomp’s publications (and 27 in total) satisfy this criterion, which is a remarkable achievement. This lecture briefly reviews some of the most highly cited of Plomp’s papers, concentrating on temporal integration at threshold, the rate of decay of auditory sensation, the ability to ‘‘hear out’’ partials in complex tones, the perception of the pitch of complex tones, and tonal consonance and the critical bandwidth. Many of the concepts introduced in these papers were novel at the time, but are now widely accepted. His data have stood the test of time. I, and many others, are grateful to him for the clarity of his writing, the breadth of his conception, his ability to identify key problems, and his role as ‘‘Promoter’’ of many fine Ph.D. students.
Speech perception: Ideas and concepts initiated by Reinier Plomp
Authors: Houtgast Tammo
Published: July 2002

In the late 1960s, a central issue in the research group on speech and hearing at TNO, headed by Reinier Plomp, was the relation between the perceptual and physical characteristics of sound. One impressive example concerned the research on vowel sounds, conducted together with Louis Pols. By adapting novel approaches for studying supra-threshold phenomena (triadic comparison of stimuli, Kruskal’s multi-dimensional scaling technique), the perceptual differences among vowel sounds could be visualized in a two- or three-dimensional representation of vowel points. This representation appeared to be in excellent agreement with a physical configuration of the vowel points, based on one-third-octave band analysis of the vowel sounds. It is conceptually only a small step from these isolated steady-state vowels, corresponding to points in a multi-dimensional space, to running speech resulting in a trace within that space. The spectral distances between successive points in such a speech trace reflect the rate-of-change in the speech signal as perceived by a listener. This framework of thinking, i.e., the perceptual relevance of projecting speech in the spectral domain, did lay at the roots of our later work on the development of objective measures for quantifying speech intelligibility.