bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of degradation of intensity, time, or frequency content on speech intelligibility for normal-hearing and hearing-impaired listeners
Authors: van Schijndel Nicolle H. , Houtgast Tammo , Festen Joost M.
Published: July 2002

Many hearing-impaired listeners suffer from distorted auditory processing capabilities. This study examines which aspects of auditory coding (i.e., intensity, time, or frequency) are distorted and how this affects speech perception. The distortion-sensitivity model is used: The effect of distorted auditory coding of a speech signal is simulated by an artificial distortion, and the sensitivity of speech intelligibility to this artificial distortion is compared for normal-hearing and hearing-impaired listeners. Stimuli (speech plus noise) are wavelet coded using a complex sinusoidal carrier with a Gaussian envelope (14 octave bandwidth). Intensity information is distorted by multiplying the modulus of each wavelet coefficient by a random factor. Temporal and spectral information are distorted by randomly shifting the wavelet positions along the temporal or spectral axis, respectively. Measured were (1) detection thresholds for each type of distortion, and (2) speech-reception thresholds for various degrees of distortion. For spectral distortion, hearing-impaired listeners showed increased detection thresholds and were also less sensitive to the distortion with respect to speech perception. For intensity and temporal distortion, this was not observed. Results indicate that a distorted coding of spectral information may be an important factor underlying reduced speech intelligibility for the hearing impaired.
Mode isolation: A new algorithm for modal parameter identification
Authors: Drexel Michael V. , Ginsberg Jerry H.
Published: July 2002

Multiple degree of freedom (MDOF) algorithms are the dominant methods for extracting modal parameters from measured data. These methods are founded on the notion that because the response of a linear dynamic system is the sum of many modal contributions, the extraction technique must deal with all of the modal parameters in a simultaneous fashion. The Mode Isolation Algorithm (MIA) described here is a frequency domain formulation that takes an alternative viewpoint. It extracts the modal parameters of each mode in an iterative search, and then refines the estimation of each mode by isolating its effect from the other modal contributions. The first iteration estimates modes in a hierarchy of their dominance. As each mode is estimated, its contribution is subtracted from the data set, until all that remains is noise. The second and subsequent iterations subtract the current estimates for all other modes to identify the properties of the mode under consideration. The various operations are described in detail, and then illustrated using data from a four-degree-of-freedom system that was previously used to assess the Eigensystem Realization Algorithm (ERA) and Enhanced ERA. Eigenvalues and mode shapes are compared for each algorithm. Another example analyzes simulated data for a cantilever beam with three suspended one-degree-of-freedom subsystems, in which the parameters are adjusted to bring two natural frequencies into close proximity. The results suggest that MIA is more accurate, and more robust in the treatment of noisy data, than either ERA version, and that it is able to identify modes whose bandwidth is comparable to the difference of adjacent natural frequencies.
A power conservation approach to predict the spatial variation of the cross-sectionally averaged mean-square pressure in reverberant enclosures
Authors: Franzoni Linda P.
Published: July 2002

Although it is commonly assumed that broadband mean-square pressure levels are spatially uniform in reverberant enclosures, there is a gradual spatial variation, especially if the room is long in one direction, and/or the acoustic absorption is not applied uniformly to the enclosure boundaries. An equation for predicting the average cross-sectional sound pressure levels in a lightly damped enclosure with absorption is derived based on conservation of acoustic power. The derivation involves a one-dimensional boundary value problem, the solution of which is an estimate of the average sound pressure level at cross-sections in the interior. In its simplicity, the resulting formula is reminiscent of the classical Sabine formulation; however, this prediction contains a spatially varying function that depends upon the distribution of absorption (side-wall versus end-wall). The formula is demonstrated on a model problem consisting of a rectangular acoustic enclosure with a source on one end-wall, absorption on the opposing end-wall, and a combination of hard and absorbing side-walls. Comparisons with an exact numerical simulation show that the prediction works well for a wide range of absorption levels and provides an improvement over classical diffuse field theory, where the levels are assumed to be spatially uniform. A formula for the volume-averaged, broadband, mean-square pressure (a modified Sabine formula) is also derived and shown to give excellent agreement with the numerical simulations.
Electrokinetic transduction of slow waves in porous media
Authors: Block Gareth , Chotiros Nicholas P.
Published: July 2002

One candidate for modeling wave propagation in ocean sediments is Biot theory. It predicts two kinds of compressional waves: a fast wave, described by in-phase motion of the pore fluid and porous solid structure, and a slow wave, described by out-of-phase motion. Slow wave motion is heavily damped and has been difficult to measure directly using acoustic transducers. An electrokinetic (EK) transduction technique for studying slow waves is being developed which takes into account the surface chemistry of the grains and pore fluid salinity. EK measurements are advantageous because they are linked directly to out-of-phase, relative motion between the pore fluid and grain structure. EK transmission occurs when an applied voltage drives ionic (and thus fluidic) currents in an electrolyte-saturated material. Conversely, EK reception is possible when fluid electrolyte motion in this material creates a measurable streaming potential. Progress on the experimental apparatus and theoretical model for the EK transmission case will be reported. [Work supported by ONR, Ocean Acoustics.]
Ray shooting, eigenray search, and complex resonances for submerged structures
Authors: Lu I-Tai , Yao Y. Q.
Published: July 2002

The general theory of a ray-mode approach for time-harmonic responses and a wavefront-resonant approach for transient responses of submerged structures [I-T. Lu, J. Acoust. Soc. Am. 99, 114–132 (1996)] is applied to a prototype structure consisting of a cylindrical pipe, hemispherical endcaps, a bulkhead, and a rib. The acoustic scattering returns are synthesized systematically in terms of angular spectra of surface modes of the structural elements where bookkeeping of various spectral objects such as ray, collective ray, modes, ray mode, resonance, etc. can be maintained. Ray shooting and eigenray searching procedures for the guided modes of structural elements are derived. An approximate solution for the resonances of the global submerged structure is also obtained. Numerical examples of typical ray trajectories of these guided modes, travel times of wavefronts, and complex frequencies of resonances are presented.
Development of distortion product emissions in the gerbil: “Filter” response and signal delay
Authors: Mills David M. , Rubel Edwin W
Published: July 2002

Amplitude and phase responses of distortion product otoacoustic emissions as a function of stimulus frequency ratio were measured for frequencies between 2 and 48 kHz, in Mongolian gerbils (Meriones unguiculates) aged 15 to 30 days after birth. After baseline measurements, furosemide was administered to distinguish active from passive emissions. At all ages, structure in the form of multiple peaks was observed in the amplitude responses of specific odd-order emissions. This structure depended on the emission frequency, not the stimulus frequency ratio, and did not generally depend on the stimulus amplitude. Nor was it dependent on the functioning of the cochlear amplifier: At moderate stimulus levels, the observed emission distribution simply shifted to lower amplitudes when the cochlear amplifier was made temporarily dysfunctional by furosemide injection. The center frequencies and widths of the peaks in the amplitude response did not generally change with age, except that the relative amplitudes of the higher-frequency peaks were increased in younger animals. At 2 kHz, however, the distribution showed other evidence of maturation, with the frequency of maximum emission moving downward with age. The phase responses yielded estimates of the round trip signal (group or traveling wave) delay. At a given frequency, the active signal delay typically decreased substantially with increasing stimulus level. However, there was a rapid variation in delay as the stimulus level passed the normal active–passive crossover level. At stimulus levels measured relative to the active–passive crossover level, i.e., either 20 or 30 dB lower, the active signal delay decreased only slightly with age. Overall, both filter response and signal delay characteristics were found to be essentially mature near the onset of hearing.
Internal friction and boundary conditions in lossy fluid seabeds
Authors: Deane Grant B.
Published: July 2002

There are two distinct mechanisms associated with compressional wave absorption in lossy media, internal relaxation and internal friction. For the special case of propagation in an homogeneous, unbounded medium, both mechanisms can be modeled by adopting the convention of a complex sound speed and are, in this sense, equivalent. For the more realistic case of propagation in a stratified medium, the convention of complex sound speed does not give a correct description for losses which modify the linearized equation of motion, such as internal friction. In the presence of boundaries, internal friction can be modeled by the introduction of a complex quiescent density in addition to complex sound speed. Propagation models which use complex sound speed only in the presence of boundaries make the tacit assumption that seafloor losses are caused by internal relaxations only. A solution is developed for propagation in a lossy Pekeris channel where absorption in the lower fluid is caused by internal friction. The example that has been considered yields a sound level 3 dB less than the standard description over a 50-km path.
Response of a two-layer compliant slab to inviscid incompressible fluid flow
Authors: Evrensel Cahit A. , Zhou Li , Khan Md. Raquib U.
Published: July 2002

In this study, the dynamics of two-dimensional wave trains at the interface between a two-layer viscoelastic coating and flow of an inviscid fluid is examined theoretically. The objective is to understand the interaction mechanism between the two media better, and to explore the effects of different geometric and material properties on this mechanism. Each layer of coating is treated as an infinite, elastic, or viscoelastic solid of finite thickness, bonded to each other. The flow is modeled by the potential theory. The two media, two-layer slab and the fluid, are coupled through stress and velocity, normal to the surface of the slab. Two layers of the slab are assumed to be bonded to each other. The proposed mathematical model is used to predict the appearance of unstable surface waves of the coating. A few dimensionless parameters are identified. The model predicts that the instabilities initiate in the form of standing waves for the viscoelastic coating while the speed of the unstable waves at the interface of the elastic coating and the fluid is relatively high.
Response to “Comments on ‘Elastic wave radiation and diffraction of a piston source’ ” [J. Acoust. Soc. Am. 101, 2374 (1997)]
Authors: Tang X. M. , Toksoz M. N. , Cheng C. H.
Published: July 2002

The authors respond to the comments of Wang and Du.
An error intensity spectral filtering method for active control of broadband structural intensity
Authors: Swanson David C. , Gentry Cassandra A. , Hayek Sabih I. , Sommerfeldt Scott D.
Published: July 2002

The implementation of structural intensity measurement using an accelerometer array allows active attenuation of broadband frequency vibration using a modified filtered-x algorithm. In this work, a multi-input channel accelerometer error filter outputs a single channel error signal proportional to the propagating power. The filter is specified in the frequency domain as a transfer function from a model of bending waves in a finite beam. Integrity of the beam model and active control simulations is verified by monitoring an acceleration in the far field. The best overall performance is achieved when the error sensor array is in the far field of the primary and adaptive control force actuators. Broadband application of the intensity error technique in physical model-based simulations showed 15- to 25-dB attenuation except at a few isolated frequencies. These preliminary simulation results support new approaches to active stuctural control through error sensor array processing.
Modeling low-frequency reverberation near the Mid-Atlantic Ridge and comparison with ARSRP data
Authors: Caruthers Jerald W. , Yoerger E. J. , Novarini J. C.
Published: July 2002

The Acoustic Reverberation Special Research Program (ARSRP) of the Office of Naval Research conducted low-frequency acoustic reverberation experiments just west of the Mid-Atlantic Ridge in 1993. Analyses of these data are supported by a bathymetric survey that produced nearly full-coverage bathymetry gridded to a resolution of 200×200 m. At this scale direct-path reverberation data has been successfully modeled using Lambert’s law applied to the local grazing angle determined from the high-resolution bathymetry. The analysis suggests that there could be a slightly weaker dependence on grazing angle than sine squared. The good agreement of this simple model with data shows that, for this region, two-dimensional seafloor morphology at the proper scale determines the ability to predict reverberation. For a model, such as Lambert’s law, that glosses over the details of seafloor microroughness or texture at the scale the acoustic wavelength (λ=6 m), the seafloor morphology scale that is critical is shown to be an order of magnitude or two greater than an acoustic wavelength. An average Lambert coefficient for the region is between −14 and −17 dB, but it is less than −20 dB for deeply sedimented areas and around −12 dB for rugged exposed rock areas.
Coupled-amplitude approach to solving the Helmholtz equation
Authors: Dacol Dalcio K.
Published: July 2002

The coupled-amplitude technique for solving the Helmholtz equation has been developed in the context of coupled normal modes by researchers working in a variety of wave propagation problems. In this article it is shown that this approach is not dependent on modal expansions and first-order differential equations in range for the coupled amplitudes are derived without invoking normal-mode expansions. The relationship of this exact transformation to the parabolic approximation is analyzed and numerical methods for solving the coupled-amplitude equations are discussed. The usual range-stepping algorithms used to obtain an approximate solution to the Helmholtz equation are based on the parabolic approximation and restricted to the forward propagating component of the solution. A complete solution of the Helmholtz equation in an inhomogeneous medium must also include backpropagating waves, that is, waves scattered towards the source by inhomogeneities. The inclusion of such effects in a numerically feasible full-wave approach to acoustic propagation is a problem of continual interest in the acoustics of inhomogeneous media and in ocean acoustics. The method discussed in this article addresses this difficult problem.
A study on robust utterance verification for connected digits recognition
Authors: Rahim Mazin G. , Lee Chin-Hui , Juang Biing-Hwang
Published: July 2002

Utterance verification represents a key technology in the design of a user-friendly speech recognition system. One essential element when designing such a system is the ability to maintain a uniform performance over a wide range of acoustic conditions. An acoustic mismatch between training and testing conditions often results in an undesirable performance degradation. This paper addresses the issue of robustness in utterance verification of a speech recognition system. Two techniques, namely signal bias removal (SBR) and on-line adaptation, are studied. The SBR algorithm is used to deal with global mismatch conditions caused by handset and channel differences. The on-line adaptation algorithm is used to adjust verification threshold at runtime for achieving a desirable trade-off between false rejection and false alarm in new test conditions. Various on-line adaptation schemes are investigated. We show that both supervised or unsupervised adaptation can effectively adjust the verification threshold to achieve a desirable performance trade-off irrespective of the initial setting of the threshold. We report on connected digit recognition/verification results for matched and mismatched training and testing conditions. At a 5% digit string rejection rate, the proposed robust utterance verification system gives a reduction in string error rate between 32% and 35% over the conventional system, while still correctly rejects over 99.9% of nonvocabulary utterances.
Direct laboratory measurement of forward scattering by individual fish
Authors: Ding Li
Published: July 2002

Acoustic backscatter has been widely used to detect and quantify fish. However, other types of information can also be exploited for this purpose. One is acoustic signals scattered by fish in the forward direction. This paper describes a novel laboratory experiment aimed at direct measurement of forward scattering by individual fish. A copper sphere is first used to test the measurement concept and establish experimental procedures. Then forward scattering by fish, in both the dorsal aspect and side aspect, is measured against the incident angle of sound, and simultaneous measurements of backscatter are also made. The results indicate that the forward scattering of individual fish is significantly stronger than the backscattering: At or near normal incidence, the forward scattering is 14–17 dB stronger. It is also found that the forward scattering varies with the incident angle of sound to a much less extent than the backscattering. These features could prove to be the advantages of using forward scatter for detection and quantification of fish. How to make the best use of forward-scattered signals remains to be exploited.
Automatic integrated analysis of jaw and lip movement in speech production
Authors: Borghese Nunzio Alberto , Ferrigno Giancarlo , Redolfi Marco , Pedotti Antonio
Published: July 2002

A noninvasive methodology for studying the kinematics of speech production is presented. It is based on the tracking of very small and light passive markers attached to the subjects’ face. Using a pair of TV cameras, the 3-D markers’ positions are computed in real time, at a subpixel accuracy, by a dedicated hardware. From these data, the time course of a set of parameters which describe lip and jaw movement is computed; in addition, a semiautomatic procedure that identifies the exact onset and offset of the investigated sequences has been developed. To compare the results over different productions, a time normalization procedure based on a continuous inverse Fourier transform has been implemented.
The representation of concurrent vowels in the cat anesthetized ventral cochlear nucleus: Evidence for a periodicity-tagged spectral representation
Authors: Keilson Suzanne E. , Richards Virginia M. , Wyman Bradley T. , Young Eric D.
Published: July 2002

Chopper units of the ventral cochlear nucleus (VCN) provide a rate representation of stimulus spectrum and a temporal representation of fundamental frequency (F0). This dual representation may be useful in segregating competing speech sounds, where differences in F0 are a cue. Responses to the vowel portion of concurrently presented pairs of syllables /bV∫/ with different F0’s (88, 98, and 112 Hz) were studied in the VCN of anesthetized cats; 11 English vowels were used for V. Vowels were chosen so that one had a formant frequency just above the unit’s best frequency (BF) and the other had a formant just below BF. By changing the stimulus sampling rate, formant peaks were shifted relative to the unit’s BF, producing a range of stimuli, varying in the relative power of the two vowels within the unit’s tuning curve. Results show that units’ discharge rates reflect the energy within their tuning curves and the relative synchronization of units’ responses to the two F0’s favors the dominant vowel. A method of segregating two vowels is provided in which relative synchronization to the F0’s is used to apportion discharge rate between the vowels. Best results were obtained in chopper units, although primarylike units showed similar behavior.
Incorporating phonetic properties in hidden Markov models for speech recognition
Authors: Sitaram Ramachandrula N. V. , Sreenivas Thippur
Published: July 2002

In this paper the incorporation of important phonetic properties into hidden Markov models (HMM) is studied. Phones have characteristic properties such as unique temporal structure, context sensitive behavior and specific duration, etc. New HMMs which incorporate the above properties with additional degrees of freedom to the standard HMM states are proposed. The use of each of the phonetic property for speech recognition is demonstrated using the new HMMs. All the algorithms required for using these new models in various applications of speech recognition have been presented. Experimental comparison with the standard discrete HMM for a speaker-independent continuous speech phone recognition task show that consistent improvement is achieved by the new models.
Space–time far-field representation of Green’s functions for cross-plane shear waves in general transversely isotropic media
Authors: Spies Martin
Published: July 2002

For transversely isotropic materials like fiber composites, but also unidirectionally grain-structured austenitic steels, the elastodynamic dyadic and triadic Green’s functions for the pure shear (SH) wave mode are given in the space–time domain. The first stage of the derivation is performed in a way similar to the derivation of these functions in the form of their 2D space–time spectral representations [M. Spies, J. Acoust. Soc. Am. 96, 1144–1157 (1994)]. In the present study, the inverse Fourier integrations are performed using a far-field approximation. The resulting expressions appear in a coordinate-free form and contain the orientation of the material’s fiber axis as an additional parameter. Thus the results are particularly useful for extension to the case of layered material. Numerical evaluation is performed for a unidirectional composite material for several orientations. Since the application of the SH-wave type bears considerable potential in nondestructive testing, the results presented in this article may find some application within this framework.
Reconstruction of the velocity and density in a stratified acoustic half-space using a short-pulse point source
Authors: Cao Jiasu , He Sailing
Published: July 2002

The reconstruction of the velocity and density in a stratified half-space using the reflection data generated by a short-pulse point source is considered. Transverse spatial Hankel transform is applied to the transient reflected and incident pressures on the surface. The reflection kernel in the Hankel-transformed space is obtained through a deconvolution. The time-domain Green function approach based on the wave splitting is then used to reconstruct the parameters. This time-domain approach to the inverse problem is exact and noniterative. Numerical results for some synthetical examples are presented to illustrate the Hankel transform, deconvolution, and the reconstruction. The finite-difference time-domain method is used to generate the transient reflection data in the physical space in a numerical simulation. The reconstruction using obliquely incident plane waves is also considered in an Appendix.
On the eigenfrequency of a gas bubble in a liquid
Authors: Leander Johan L.
Published: July 2002

This investigation concerns free linear gas bubble oscillations in liquids. Of prime interest is the eigenfrequency, and in particular its real part, here named as the transient frequency. The conceptual difference between the more frequently consulted resonance frequency and the transient frequency is first addressed by means of the classical mechanical oscillator. Next, bubble pulsations in liquids are discussed and an existing model is used for the gas–liquid interaction from which an approximate expression for the eigenfrequency is derived. A rationale for the approximate evaluation of the functions modeling the thermal processes is suggested which is independent of the frequency content of any possible pressure excitation. Moreover, compressibility effects are not approximated in the derivation presented here. The quantitative difference between the adiabatic resonance frequency and the derived estimate of the transient frequency is found to be of significance for small bubbles. Finally, the similarity between a standard mechanical oscillator and a bubble in a liquid for the case of liquid-compressibility effects only is discussed.
Jovian acoustic matched-field processing
Authors: Collins Michael D. , McDonald B. Edward , Kuperman W. A. , Siegmann William L.
Published: July 2002

Evidence of waves has been observed in Hubble Space Telescope (HST) images of the Comet Shoemaker–Levy 9 impact sites [H. B. Hammel et al., “HST imaging of atmospheric phenomena created by the impact of Comet Shoemaker–Levy 9,” Science 267, 1288–1296 (1995)]. The radius of a ring that appears near the fragment G impact site is consistent with an acoustic wave and increases with time. This feature cannot be explained in terms of a naive plane-wave model because it appears to expand at a rate that is slower than the speed associated with its radius. This behavior can be explained in terms of multipath propagation in the sound channel. According to this hypothesis, acoustic waves corresponding to different group speeds followed paths that passed in and out of the relatively thin debris layer in which the feature appears. Matched-field processing for the depth of the source indicates that the fragment G explosion must have occurred deep in the water clouds if the ring indeed corresponds to an acoustic wave.
Side drift of aerosols in two-dimensional resonant acoustic levitators
Authors: Dain Y.
Published: July 2002

The periodic structure of dispersed particle distributions in a quickly oscillating plane sonic field has been the object of many classical investigations. It is well-known that particles dispersed in a standing one-dimensional sonic wave tend to concentrate either at nodes or at anti-nodes of the fluid velocity. If the amplitude of oscillations is sufficiently small, such that no shock waves can develop, the interaction of a two-dimensional sonic mode with particles in a resonant chamber is analyzed. The chamber considered is bounded by two parallel cylindrical mirrors, which enable the existence of the “bouncing ball” mode concentrated in the neighborhood of the minimal diameter connecting the mirrors centers. If the size of the diameter exceeds the sonic wavelength, the mode magnitude decays rapidly away from the diameter. The domain is filled with fluid, which contains spherical particles. The quantitative theoretical description of the phenomenon of steady forces acting on dispersed particles in the chamber is achieved. The chamber boundary mirrors cause dispersed particles to move in a direction transverse to the diameter, where the “bouncing ball” mode is concentrated. It is shown that in addition to the well-known one-dimensional particle motion along the diameter toward the velocity nodes or anti-nodes, there exists a side drift, which depends on the fluid-to-particle density ratio, the “bouncing ball” mode frequency and the radii of curvature of the resonator’s mirrors.
Study of woodwind-like systems through nonlinear differential equations. Part II. Real geometry
Authors: Barjau Ana , Gibiat Vincent
Published: July 2002

In a previous paper [Barjau et al., J. Acoust. Soc. Am. 102, 3023–3031 (1997)], a differential formulation has been used to study the stability and bifurcations in geometrically simple woodwindlike systems. For general bore geometries, such differential formulation can be obtained by representing the system through a lumped equivalent mechanical model whose parameters are extracted from a real impedance curve on which a modal analysis has been performed. The present procedure is then applied to a particular case and several time-domain simulations are carried out in order to both assess the validity of the systematically developed procedure and explore the possible system behaviors far from the threshold of oscillation.
Double wave of Stoneley type on the interface of a stratified fluid layer and an elastic solid half-space
Authors: Alenitsyn A.
Published: July 2002

Sound propagation from a point time-harmonic source in a stratified water layer lying over an elastic solid half-space is investigated. It is assumed that the sound speed in the layer is less than the shear speed in the solid bottom, and that it increases with the depth. Numerical examples are given which show that the dependence of the wave field on the range between the source and the receiver can sharply change the character under rather small variations of the frequency. Namely, for some particular frequencies, the sound amplitude shows a periodical dependence on the range, while for other frequencies there is no periodicity. A theoretical explanation of this phenomenon is given in a mathematical development using the normal modes theory and high-frequency asymptotic approximations. The dispersion phase curves are found to have “quasi-intersections,” i.e., small domains where two adjacent curves almost intersect. The corresponding frequencies are called the “specific” frequencies. For any nonspecific frequency, there is one interface Stoneley (=Scholte) mode, whilst for each specific frequency there are two modes of the Stoneley type with close phase velocities. The periodicity of the field is a result of interference in the two Stoneley modes.
A multiresolution analysis of scattering by a pair of local regions of complex heterogeneity
Authors: Steinberg Ben Zion , McCoy John J.
Published: July 2002

The scattering by a pair of spatially disjoint local regions of complex (multiscale) stiffness heterogeneity in an unbounded thin linearly elastic plate is investigated. Issues of the mutual interaction of the spatially disjoint scatterers and its manifestation within a homogenized, or effective, formulation governing large scale response fields are the focus. It is shown analytically and numerically that while one must incorporate scatterer/scatterer coupling for estimating the large scale response field, one can neglect this coupling in estimating the effective measures for describing the scatterers.
Specific characteristics of ultrasound contrast agents
Authors: De Jong Nico , Frinking Peter
Published: July 2002

Ultrasound contrast agents possess acoustical characteristics which differ from the surrounding medium. Specific signatures of the agent, consisting of free or encapsulated gas bubbles, will improve the discrimination between the blood containing the agent and the tissue. One of the specific signatures is the initiation of a volume pulsation when the ultrasound wave hits a free or encapsulated gas bubble. Depending on the magnitude of the ultrasound wave the pulsation will be linear to the applied pressure or nonlinear to the applied pressure. Nonlinear vibration can be split into stationary (harmonic) and transient (power) scattering. Besides the nonlinear vibration (harmonics), specific characteristics include enhanced scattering as a function of the acoustic amplitude, transient scattering which is very useful for measuring flow, LOC (loss of correlation) imaging, and the persistence as a function of ambient parameters like pressure and temperature. Recently, a 2-D echomachine has been adapted for imaging of the nonlinear vibration of contrast agents and further developments in both hardware and software will be advantageous for the many specific characteristics of these agents.
Bubble dynamics of ultrasound contrast agents
Authors: Averkiou Michalakis A. , Bruce Matthew F. , Powers Jeffry E.
Published: July 2002

The bubble dynamics involved with microbubble contrast agents under insonification is investigated. The acoustic field of an ATL HDI-3000 diagnostic ultrasound system in a contrast specific harmonic imaging mode is reviewed first, and its major features that are related with microbubble behavior are discussed. Issues relating to sound attenuation, mechanical index, and bubble destruction are addressed. The nonlinear oscillatory behavior of contrast microbubbles is modeled with the Gilmore equation. The acoustic pressure field of a short pulse utilized in harmonic imaging is measured with a hydrophone and used as the driving pressure of the Gilmore model. Radius-time [R(t)] and bubble wall velocity-time [U(t)] curves are shown. Frequency domain analysis of U(t) indicates transient resonance characteristics in both the fundamental and second harmonic components that are somewhat different from what one would expect with a continuous-wave steady-state response. The times for complete solution of microbubbles in water are calculated and correlated to observations seen in ultrasound images with contrast agents. Radio frequency (rf) data of scattered pulses from contrast agent microbubbles in an in-vitro experiment were collected with a phased array. This data is used to support and explain the contrast microbubble behavior.
Shear wave excitation in a rubberlike medium by focused shock pulse
Authors: Pishchal’nikov Yury A. , Andreev Valery G. , Rudenko Oleg V. , Sapozhnikov Oleg A. , Sarvazyan Armen P.
Published: July 2002

Ultrasonic excitation of shear waves is important for elasticity imaging of biological tissue. In the shear wave elasticity imaging shear strain is remotely induced in tissue by the radiation force of focused modulated ultrasound. Previous study has shown that tone bursts of millisecond duration at megahertz frequencies with intensities and exposures typical for diagnostic ultrasound may induce bulk radiation force of the order of 0.01 N/cm3 and shear displacements of the order of 10 μ. In this work, new nonlinear mechanisms are discussed that provide detectable shear displacements by means of single submicrosecond pulses. Two new possibilities are discussed. Significantly enhanced radiation force and greater shear displacement can be produced in tissue by single acoustic videopulse with nonzero momentum. Another possibility is based on the enhanced nonlinear absorption which occurs after the shock is formed in the temporal profile of the pulse. Nonlinear mathematical models describing the process of generation of shear waves using single pulses are developed. Experimentally, single focused pulses are excited by high-power laser radiation inside an optoacoustic cell. Shear displacements are detected in a sample of gel using optical scattering. Results of modeling and experiments are in good agreement. [Work supported by CRDF and RFBR.]
Structural vibration mode imaging using photorefractive holography
Authors: Telschow K. L. , Deason V. A.
Published: July 2002

Photorefractive processing of optical interference offers a noncontacting optical method for vibration detection that forms an optical ‘‘lock-in’’ amplifier. Multiwave mixing with synchronous detection allows measurement of both the vibration amplitude and phase of a vibrating surface directly as a function of the excitation frequency. Narrow bandwidth detection with flat frequency response can be achieved at frequencies above the photorefractive response (∼100 Hz). A minimum detectable displacement amplitude of a few picometers has been demonstrated for a point measurement, with the possibility of further improvement. The method can also be configured to provide full-field imaging of resonant vibrational modes of materials with various microstructures and shapes. Both specularly and diffusely reflecting surfaces can be accommodated. Results will be presented showing the noncontacting imaging capabilities for vibrational spectral analysis of structures and characterization of material properties that these sensors provide for smart systems. [Work suported by the U.S. Department of Energy.]
Transient behavior of acoustic gyrometers
Authors: Dupire Philippa , Bruneau Michel
Published: July 2002

Acoustic gyrometry was developed during the past 15 years as a new miniaturized or low-cost technology. The operation of acoustic gyrometers employs acoustic fields inside fluid-filled resonant cavities to determine angular velocities. Until now, research efforts and design methodology have concentrated both on trapezoidal miniaturized gyros (etched on silicon chips) as well as on cylindrical gyros designed using classical techniques. These approaches are restricted to the frequency domain, which involves only the steady Coriolis effect. Nowadays, the need for a time domain solution for inertial effects on acoustic fields clearly arises when dealing with applications involving strong variations of the rotation rates. This paper aims at providing such advances in ‘‘inertial-acoustic’’ theory and modeling. The discussion covers cylindrical gyros because the presence of an unsteady rotational velocity gradient (with respect to the radial coordinate) of a gas in a cylindrical cavity adds one of the most important features both in the basic physics underlying ‘‘inertial-acoustic’’ transient processes and in the behavior of the gyros. In conclusion, only some new requirements, which have to be taken into account in the design of acoustic gyros, will be addressed as a discussion of the transient behavior in detail is beyond the scope of this paper. [Work supported by DRET-DGA.]
Toxin and gene transfer into cells by extracorporeal shock waves
Authors: Delius M. , Lauer U.
Published: July 2002

Shock wave application to cells in vitro causes a transient increase of the permeability of the cell membrane which does not lead to cell death. It was hypothesized that shock waves might be a new method of transferring therapeutic agents directly into cells. To test this, biological effects resulting from the acoustical transfer of proteins and nucleic acids into cells were examined. Protein transfer was examined with the ribosome inactivating proteins gelonin and saporin which inhibit the cellular protein synthesis. Dose response curves were established with three tumor cell lines in the presence and absence of shock waves. Compared to the controls, shock waves enhanced the action of gelonin and saporin from 300 to 40 000 fold. In vivo experiments with an animal tumor model established that acoustic transfer of these agents into cells also occurred in vivo. Gene transfer by shock waves was examined in a number of cell lines by plasmid vectors carrying standard reporter genes. Transfer succeeded in many cases yet the transduction efficiency was lower than with other established methods of gene transfer. In summary shock wave permeabilization is a new method for tumour therapy and gene transfer.
Electroacoustics and standards
Authors: Rasmussen Gunnar
Published: July 2002

Standardization within electroacoustics has been of great importance for the development of sound measuring instrumentation. The sound level meters are used to build up a homogeneous database, which in turn is used as a foundation for the measurement standards. Based on the database, regulation and legislation of noise exposure, noise control, product labeling, etc., may take place. The development of standards for sound level meters, measurement microphones, and calibration techniques has led to big improvements. The development of standards for intensity instrumentation and measurements will hopefully lead to similar improvements in developing the instrumentation and practical use in the daily work of the practitioners. The revision of the standards is important. They should hopefully lead to improvements for the manufacturer and for the users. The revisions should take into account the technical development and the expanded use of instrumentation in the acoustical and mechanical field. The ability to measure small changes in emitted intensity by critical sources is important for research in noise control. The measurement of sound-pressure level in the outdoor environment is not well treated in the standards, although it is an area where the legislation is most restrictive regarding noise exposure, because it influences the largest parts of the population. Examples and proposals will be given.
Diagnosis of noise sources from high-speed trains using the microphone-array technique
Authors: Barsikow B.
Published: July 2002

To reduce noise radiated by high-speed trains, abatement at the source is becoming increasingly important. Techniques for accomplishing this task require an exact knowledge of the individual sources involved and their reduction potential. During the past several years, a number of sound-generating components on ICE trains operated by the DB AG (German Railway) have been investigated by the akustikk-data Engineering Office. Microphone arrays provide a useful technology for investigating noise radiated by individual sources. Among the arrays used for recent measurements are the horizontal and vertical interspersed line arrays as well as X-shaped arrays. Examples measured by each of these instruments are shown. Results of these measurements with arrays yield the strength of each source and their speed exponents. In addition, narrow-band analysis of the sound is possible because the effects of the Doppler shift are not present. With this information, the importance of each source to the total radiated noise can be estimated. Examples of such results are given for rolling noise as well as for components emitting aerodynamic noise. For both types of sources, the effectiveness of various abatement measures is discussed.
Identification of moving acoustic sources from the pass-by noise
Authors: Lim Byoung-Duk , Kim Deok-Ki
Published: July 2002

The identification of a moving noise source such as a transportation system is usually difficult at high speed since microphones attached to the moving noise source may induce a high level of aerodynamic noise, while the measurement using a fixed microphone suffers from the distortion of the source characteristics due to its motion. In this study a time domain technique based on the finite difference method and regularization is developed for the recovery of the stationary source characteristics from the distorted signal measured at a fixed point. The sources are assumed to be point sources with stationary frequency characteristics, and move along a line at a constant subsonic speed. In the previous work of the present authors recovery of the stationary source signal from a point source requires the information about time origin. For multiple sources it is impossible to set a single time origin that a source signal recovery method using multiple time origins are developed. In the numerical simulations the effects of estimation errors in the parameters, such as the speed of source, time origin, and background noise level, are investigated and the results show the usefulness of this method.
The acoustical impact of local railway lines
Authors: Pronello Cristina
Published: July 2002

Local railway lines serve a regional traffic. They have few users since the service offered presents insufficient quality standards. These lines could have more users and they could become metropolitan connections by adopting new vehicles which are faster and more modern. This study has dealt with the current acoustical impact that they produce. Therefore, a number of acoustical measurements have been made along a local railway line. They have been carried out by varying the speed of the trains at a fixed measuring distance of 7.5 m and by varying the measuring distance with a single train speed. The obtained results have shown that current trains produce in the average a greater acoustical impact when compared to modern trains. This has been observed even at slow speeds and with reduced train lengths. Measurements made on a new train, that should soon start its service on the line, have shown that there would be no increase of the produced acoustical level, even with increased speeds. As a consequence, it may be concluded that the current service on the analyzed line could be enhanced by increasing the train speed and the number of runs, maintaining an equivalent daily analogous to the one currently guaranteed.
Prediction system for rotor–stator interaction noise generation, propagation, and optimization of acoustic liners
Authors: Lu Yadong , Hu Zongan , Cui Jiya
Published: July 2002

Based upon the acoustic mode matches between the source modes and propagating modes, this paper applies the flexible tolerance optimization method to optimize the acoustic parameters (impedance), geometric structure parameters, such as open area ratio, cavity depth, and hole diameter, and operating condition parameters, such as blade passing frequency. The optimum values of the design variables are determined when the in-duct sound suppression approaches the maximum. It can be derived from the optimum results that the emphasis of the engineering optimization design of the perforated plate honeycomb structure should be placed on the optimum choice of the open area ratio and cavity depth. Some other referential criteria for the engineering design of the multi-linings are also provided. Thus, the theoretical prediction system for rotor–stator interaction noise generation and in-duct propagation and optimization of acoustic liners has been developed in this paper. By means of this prediction system, the acoustically multi-sectioned treatments can be theoretically designed for the suppression of rotor–stator interaction noise with discrete frequency, in advance of the beginning of the practical engineering design of acoustic liners.
Vibrations of a film with arrays of point masses
Authors: Handa Takato , Piacsek Andy , Yu Roger
Published: July 2002

As a result of the Bloch theory, the eigenstates of an electron in a strictly periodic potential are extended and the eigenenergy levels form allowed energy bands separated by forbidden gaps. Very recently there has been a great deal of excitement in the physics community concerning the extension of the idea to electromagnetic and acoustic waves. The three-dimensional (3-D) photonic band material with a periodically varying dielectric constant has been found. The frequency band structure of a rectangle thin film with arrays of point masses on it interests us. It is assumed that the film is supported by a frame so that at the boundaries, the vibration vanishes. By taking advantage of this zero-boundary condition, a double sine wave expansion was used to transform the 2-D wave equation into a matrix equation. Up to 12 000 eigenvalues and eigenfunctions can be obtained accurately. A number of point mass configurations (or arrangements) were studied and their frequency structure provides rich insight into the physics of the system. In this report, the calculated frequency band structure of the system and the wave functions will be discussed.