bluuebunny/crossref_metadata_2025 huggingface dataset:
Active control design for acoustic radiation using mixed-norm optimization
Authors: Cox David E. , Henry James K. , Clark Robert L.
Published: July 2002

The interpretation of system norms is important in the design of optimal control laws. The infinity-norm allows for stability analysis even when the design model contains errors or uncertainties. H∞ robust control design makes use of this property. In many physical situations the two-norm can be related to system energy and is a more meaningful measure of performance. This is the basis of control designs such as LQR/LQG. Traditionally, optimal control laws are designed with respect to one of these norms. New methods in solving linear matrix inequalities (LMIs), however, make it possible to directly solve optimization problems whose cost functions involve a mixture of norms. In this work linear matrix inequalities are used to design controllers which suppress acoustic radiation from a driven plate. Specifically, a rectangular aluminum plate is instrumented with four piezoelectric sensoriactuators which provide both sensing and actuation. A laser Doppler velocimeter is used to measure velocity of the plate over a grid of points. Radiation filters predict far field acoustic power from the velocity measurements and are used for the design of optimal control laws. Both experimental and simulated results are presented which show the benefit of mixed norm control design made possible using LMIs.
A study of vowel production in persons with dysphagia
Authors: DiMaggio Joanne L. , Bell-Berti Fredericka
Published: July 2002

Dysphagia refers to disorders of any stage(s) of swallowing (oral preparatory, oral, pharyngeal, and esophageal). Dysfunctions in any of the first three stages result from problems in the use of the oral and/or pharyngeal musculature, which is also the musculature of speech articulation. Thus one would expect a correlation between dysphagia and dysarthria. However, clinical observation have led to the impression that it is possible to have dysphagia without obvious dysarthria. Thus in this study, formant frequency measures of the vowels of three groups of subjects: persons with dysphagia and mild dysarthria; persons with dysphagia and moderate-to-severe dysarthria; and age matched normal subjects are examined. The speech sample contains the hVd items used by G. E. Peterson and H. L. Barney [J. Acoust. Soc. Am. 24, 175–184 (1952)], as well as additional CVCs in which the initial and final consonants are varied, to examine their effects on vowel productions by these subjects. [Work supported by St. John’s University.]
Perception of synthetic vowels by cochlear implant recipients
Authors: Hawks John W. , Fourakis Marios S.
Published: July 2002

Adult recipients of cochlear implants (Nucleus and Clarion) provided identifications and confidence ratings for two sets of 465 vowel-like tokens which were synthesized with two fundamental frequency (F0) contours representative of a typical male voice and female voice. Formant combinations used for the stimulus sets sampled a large range encompassing all nonretroflex vowels of American English. Subjects assigned each token to one of ten American English vowel qualities or to a category indicating it was not one of the ten, and rated their confidence of identification on a five-point scale. Various perceptual maps were constructed from these responses based on number of agreements per token, most often used ID category per token, and average ratings. These maps will be compared with similar maps derived from normal hearing subjects. Comparison and discussion will address general differences in perceptual vowel spaces and rating patterns between the subject groups, as well as specific differences related to the two different F0 contours. Within the implanted subject group, the effects of implant processor type and electrode mapping differences on perception will be explored.
Modified LPC resynthesis for controlling speech stimulus discriminability
Authors: Protopapas Athanassios
Published: July 2002

Phonetically ambiguous speech stimuli are needed in many experimental situations, and various editing and splicing methods have been devised to construct them, sometimes with results of questionable naturalness. A resynthesis procedure based on Linear Predictive Coding (LPC) is presented here whereby interpolation of vocal tract equivalent model parameters (log area ratio coefficients) ensures vocal tract compatible, perceptually ambiguous results. An important extension of this method is also presented: Extrapolation along the same line, defined by the points corresponding to a minimal pair, leads to ‘‘exaggerated’’ speech stimuli that differ from each other more than the original (natural) recordings and, acoustically, in much the same way; e.g., critical formant transition differences are automatically enhanced by increased frequency range and peak amplitude. Such stimuli are potentially very useful in perceptual training of language-learning impaired children and of second-language learners who cannot discriminate certain non-native contrasts. Examples of ambiguous and exaggerated stimuli are shown along with perceptual (categorization and discrimination) performance of English and Japanese speakers for stimuli synthesized along (and beyond) an /r/–/l/ continuum. Preliminary training results indicate that such exaggerated stimuli are useful in making second language contrasts distinctive.
Practical prediction techniques for sound diffusers
Authors: Cox Trevor J.
Published: July 2002

In recent decades accurate methods for predicting the diffraction and scattering from diffusing surfaces have been developed. This paper will review the methods that are available based on the Helmholtz–Kirchhoff integral equation. The application of various accurate boundary element methods to a variety of diffusing surfaces such as Schroeder diffusers and simple reflectors will be presented. In addition, a review of more approximate, but faster, techniques will be given. Many modern diffusers, such as Schroeder diffusers and some optimized surfaces, rely on these approximate prediction methods in their design. The implications of using approximate methods to diffuser design and application will be discussed.
Perspectives on uncertainty, tolerance, and precision in outdoor sound measurements
Authors: Putnam Robert
Published: July 2002

Outdoor acoustical surveys typically involve greater variations in sound levels than indoor or laboratory measurements, whether the object is the determination of ambient statistical information, or the characterization of outdoor noise sources, such as for regulatory compliance purposes. Historical usage of each of the terms uncertainty, tolerance, and precision has been inconsistent and often vague, which leads to misunderstanding among all parties concerned with the definition of sound levels. The value we have come to refer to as uncertainty in outdoor sound measurements usually includes tolerance and precision. The field of acoustics is making progress in standardizing the definitions and uses of these, often misused, terms. This paper will discuss the perspectives of ISO, ANSI, ASME, and ASTM toward these terms, especially in light of recent standardization efforts. The use of the term tolerance, it will be recommended, should properly be a narrow one, as it is presently given in ASME Performance Test Codes. This paper will summarize concise definitions and recommendations for standard usage, together with classification of the constituent elements of each term, in order to promote consistency within the acoustical community, thereby helping to insure improved clarity on the subject among all concerned parties.
Summary of USAF sonic boom research
Authors: Downing Micah , Cook Brenda
Published: July 2002

This presentation summarizes the sonic boom research performed and sponsored by the U.S. Air Force during the 80s and 90s. The U.S. Air Force has funded research for sonic boom measurements and computer modeling as well as its effects on humans, animals, and structures. The primary motivation has been to better understand the potential impacts that supersonic operations have on the environment so that any adverse impact can be minimized while maintaining operational readiness. The developments and the findings from the projects will be highlighted along with a discussion about future research goals.
Effects of simulated N-waves on the auditory brainstem response of three species of pinnipeds
Authors: Bowles Ann E. , Wolski Larry , Berg Erik
Published: July 2002

Pinnipeds (seals and sea lions) on breeding beaches and hauling areas can be exposed to sonic booms from existing and planned civilian supersonic aircraft. Although carpet booms do not produce detectable threshold shifts in humans, the available anatomical information is not adequate to extrapolate models for humans to pinnipeds. Therefore, rehabilitated stranded California sea lions (Zalophus californianus), harbor seals (Phoca vitulina), and elephant seals (Mirounga angustirostris) were exposed to simulated N-waves with levels up to 6 psf and rise times as low as 0.4 ms. The auditory brainstem response (ABR) was used to estimate auditory sensitivity before and after exposure. The test signals were broadband clicks, and tone pips at 2 and 8 kHz. Level of the least detectable ABR waveform was used to estimate best sensitivity, while latencies to the major peaks of the waveform were used to monitor recovery rates. Latency shifts (2 ms) that recovered over the course of a 2-h post-exposure monitoring period were found in some individuals, but these did not correspond to a change in least detectable ABR for any animal. [Work supported by NASA Contract NAS1-20101.]
Spectrographic measurement of instantaneous frequency and the time-dependent weighted average instantaneous frequency
Authors: Loughlin Patrick J.
Published: July 2002

Instantaneous frequency (IF) is an important signal characteristic arising in many fields. It is a concept intimately linked to time–frequency analysis, where it can be obtained from a time–frequency distribution (TFD) as the first conditional moment in frequency, suggesting that the IF is the average frequency at each time. However, this interpretation is questionable, since it is well known that the IF often ranges beyond the spectral support of the signal. In addition, to obtain the IF from a spectrogram (which is one possible TFD), a very wideband—and thus severely spectrally distorted—spectrogram must be used. More reasonable bandwidths are investigated, and, in particular, give the conditions by which the first conditional moment of a spectrogram can indeed be interpreted as the average frequency at each time. Under these conditions, namely when the spectrogram bandwidth is less than the frequency separation of the signal components in the time–frequency plane, the spectrogram yields not the usual IF, but a time-dependent weighted average instantaneous frequency (WAIF) of the signal. Also, while the IF and WAIF are generally different, sometimes they are the same (in particular, when there is symmetry in the time–frequency spectrum of the signal); in that case, the first conditional spectral moments of both wideband and narrow band spectrograms are the same and interpretable as the average frequency at each time.
An improved state-space method for coupled fluid–structure interaction analysis
Authors: Cunefare Kenneth A. , De Rosa Sergio
Published: July 2002

This paper presents an improved state-space method for incorporating fluid–structure interaction into structural acoustic analyses. Giordano and Koopmann [J. A. Giordano and G. H. Koopmann, “State-space boundary element-finite element coupling for fluid–structure interaction analysis,” J. Acoust. Soc. Am. 98, 363–372 (1995)] introduced a state-space approach for the coupled analysis of fluid-loaded structures. Giordano’s method employed a third-order interpolation of the fluid impedance, coupled with state-space formalism, permitting the direct eigenvalue analysis of the coupled system, and thereby yielding the fluid-loaded modes and natural frequencies. This is in contrast to the common technique of sweeping through a range of frequencies so as to identify the natural frequencies and mode shapes. The original state-space approach yielded system matrices of order 4N, where N is the number of degrees of freedom in the underlying model. Where Giordano’s method employed an interpolation based on surface velocity, the work presented in this paper uses an interpolation based on surface displacement. This simple modification to the method yields a system order of 3N, with concomitant reduction in the required computational effort, storage, etc. We further present a method to assess the validity of the resonances obtained through this approximation technique. The method is demonstrated here for an infinite 1-D panel in a baffle, using the surface variational principle and the method of assumed modes to develop the coupled fluid–structure problem. This structure and the analysis methods are not fundamental to the state-space development, and are used solely as vehicles to demonstrate the new formulation.
Lateralization of a moving auditory image: Interrelation of interaural time and intensity differences
Authors: Altman Jacob A. , Variaguina Olga V. , Nikitin Nikolay I. , Radionova Elena A.
Published: July 2002

Lateralization of moving fused auditory images (FAIs) was studied under dichotic stimulation, with FAI movement from the right and left ears to midline. The movement was produced by the gradual change of interaural time delay (from ±630 to 0 μs) in a binaurally presented click train in which a constant interaural intensity difference (IID) between ±13 dB was also imposed. The task of the subjects was to show with her/his finger the point on the head surface where the FAI trajectory’s ending or starting points were perceived. With IID change within ±13 dB, the FAI movement trajectory shifted toward the ear receiving the more intense stimulus. The length of the movement trajectory shortened with IID increase. Functions relating the value of perceived lateral position (Y) of the movement trajectory’s ending and starting points to IID value (X) were nearly linear: Y=AX+B. These functions differed in their characteristics whether the movement was to the right versus to the left of midline. They also differed from analogous functions for stationary FAI. At IID=0 the FAI movement trajectory’s endpoint was shifted from midline in the direction of movement. Equivalence ratio for IID and ITD were estimated to be 51 and 29 μs/dB respectively for the trajectory’s starting and ending points. The IID factor could be several times as effective in moving FAI lateralization as the ITD factor.
PZT5 spherical hydrophone simulation using a coupled FE-BE method
Authors: Jarng Soon S.
Published: July 2002

This paper describes the application of a coupled finite-element–boundary element method to obtain the steady-state response of a hydrophone. The particular structure considered is a flooded piezoelectric spherical shell. The hydrophone is three-dimensionally simulated to transduce an incident plane acoustic pressure onto the outer surface of the sonar spherical shell to electrical potentials on inner and outer surfaces of the shell. The acoustic field formed from the scattered sound pressure is also simulated. In addition, the displacement of the shell caused by the externally incident acoustic pressure is shown in temporal motion. The frequency response of the PZT5 spherical shell is also shown in comparison with theoretical expectation. The coupled FE-BE method is described in detail. [This study was granted by STEPI (Science & Technology Policy Institute) Korea, as 1998 international program of co-work of research between Korea and the United Kingdom. The fortran program of the present work was run by a super computer (Cray C90) operated at SERI (now ETRI), Korea.]
Real time auralization with EASE 3.0
Authors: Ahnert Wolfgang
Published: July 2002

The new EASE 3.0 for Windows combines advanced features of the DOS-based system EASE 2.1 with the known ones of the Auralization package EARS 1.1. In case of the DOS-based system, one has to use additional hardware to convolve the calculated impulse responses with the head-related transfer functions and eventually with the dry tests signal. After calculation of the corresponding impulse response one can listen now in EASE 3.0 to the convolved binaural signal by use of just a normal sound card. Additionally, with a duplex sound card one can enter CD signals directly and, after a transient time of 50 ms to 2 s (depending on the computer parameters and the sample rate of the signal), one can obtain the auralized results. Another option allows one to calculate the direct sound sequence of used speaker signals in realtime also and then to use the auralization routine to check echo occurrence or correct localization of sound sources. The convolution algorithm used in EASE 3.0 is patent pending and was created in cooperation with LAKE/Australia. In a project still under construction, the measured results have been compared with auralization results obtained by physical scale model measurements. Both results will be demonstrated.
Considerations about the influence of traffic noise in the design of new hospitals
Authors: Medeiros Eduardo Bauzer , de Azevedo Camelier Ivan
Published: July 2002

The main origin of noise disturbance in new hospitals located inside densely populated areas can usually be associated with vehicular traffic. However, the effect of this disturbance is often not fully appreciated. Compliance with standard legislation limits is often considered to be a satisfactory design criterion. In fact, even moderately higher noise levels can introduce physiological changes, which may have a decisive influence on the convalescence of a hospital patient. The present work associates some of the information which is available on the effects of patients subjected to different noise levels with considerations about hospital and the associated access roads design. Field measurements carried out in the vicinity of typical existing and planned hospitals are also described and associated with the local traffic conditions. Finally, a few practical guidelines are laid, considering a rest situation of a hospital under construction near an important access road. The objective is to establish a set of acoustic design guidelines for hospitals and the surrounding areas, particularly the road system, aiming at a more efficient convalescence period for the patients.
Acoustic data preprocessing in the TOMOLAB/OCTOPUS project
Authors: Didier Mauuary , Faure Bernard
Published: July 2002

This paper presents the acoustic data preprocessing task in the TOMOLAB graphic interface tool. TOMOLAB is a goal of the OCTOPUS project, under the MAST III program of the European Community. Data preprocessing consists in transforming raw tomographic data into compressed/correlated peaklike data. It is the first step before time delay estimation, time delay identification, and time delay inversion. The complete data processing must perform matched filtering, multisequence averaging, Doppler/phase compensation, and mooring motion correction. A synthetic view is given of several technical choices that integrate these tasks, jointly or successively. This work is based on internal studies and existing pieces of literature. The Hadamard transform, the Fourier matched filtering, fast Doppler processing, phase estimation/correction algorithm, delay shifting in the time or Fourier domain, data format and sampling are discussed. Efficient data processing has to account for the computing speed, the compression ratio, and achievable accuracy of delay estimation.
Matched-peak tomography
Authors: Skarsoulis E. K.
Published: July 2002

A new approach is presented for the inversion of travel-time data in ocean acoustic tomography. Using model relations between sound-speed and arrival-time perturbations about a set of background states, arrival times and associated model errors are calculated on a fine grid of model states discretizing the parameter space. Each model state can explain (identify) a number of observed peaks in a particular reception laying within the uncertainty intervals of the corresponding predicted arrival times. The model states that explain the maximum number of observed peaks are considered as the more likely parametric descriptions of the reception; these model states can be described in terms of mean values and variances providing a statistical answer (matched-peak solution) to the inversion problem. An advantage of the proposed approach is that there is no need for initialization of the inversion procedure, i.e., no need for additional hydrographic information. Furthermore, the matched-peak solution for each reception is independent of the previous reception identification/inversion results. The method was applied to nine-month-long tomography data from the Thetis-2 experiment in the western Mediterranean sea. [Work partially supported by EU/MAST.]
On the simultaneous estimation of current and sound velocity structure in the ocean, using matched-field processing
Authors: Taroudakis Michael , Markaki Maria
Published: July 2002

A matched-field processing method for the simultaneous estimation of ocean current velocity structure and sound speed profiles, based on reciprocal transmissions of cw or broadband acoustic signals between two locations in the water column, is presented and discussed. For each transmission, a single source and a vertical array of hydrophones are used. The current velocity is introduced as an additional unknown in the inverse problem, through the concept of the ‘‘effective sound speed,’’ being the sum of the actual sound speed and the projection of the current velocity on a vertical plane, defined by the sound source and the receiver. The work is mainly focused on the study of the effect of variations of the current velocity on the various processors proposed for the matched-field inversions and on the inversion procedure itself, under the assumption that neither the actual position of the source receiver system nor the actual sound velocity structure are known. Using synthetic data, it is demonstrated that the results of inversion for the current velocity are reliable, under some limitations posed by the degree of uncertainty for the other unknown parameters. [Work supported by INTAS-RFBR.]
An ocean acoustic tomography experiment in the central Labrador Sea—First results
Authors: Kindler Detlef , Send Uwe
Published: July 2002

First results of an ongoing acoustic tomography experiment will be presented. Since August 1996 a mooring array consisting of four tomography transceivers (400 Hz), redeployed in the summers of 1997 and 1998, has been measuring acoustic travel times over distances of typically 170–300 km in the central Labrador Sea. The purpose of such measurements is to estimate time series of horizontally integrated properties like ocean heat content and vertical temperature stratification by inverting travel times into sound speeds and hence into heat contents and temperatures. These large-scale properties will be used to study the interannual variability of ocean heat budget and water masses formed in close connection to deep convection and the ensuing renewal of Labrador Sea Water (LSW) [R. A. Clarke and J. C. Gascard, J. Phys. Oceanogr. 13, 1764–1778 (1983)]. The variability during winter results from destabilization of the water column near the ocean surface caused by atmospheric cooling, subsequent mixing down to 1000–2000 m, and the following restratification of the convection area. The investigations are focused on the upper 2000 m of the water column, which are well insonified by several trackable ray paths with enough acoustic energy to be processed. [Work supported by Deutsche Forschungsgemeinschaft.]
Stiffness of strings: Significance in musical acoustics
Authors: Lieber Edgar
Published: July 2002

In a linear differential equation of a vibrating string there is a link representing stiffness of the string. In nonlinear theory, string stiffness has not yet been taken into consideration. The author has completed this by means of the Lagrange II method and presents essential results. The significance of string stiffness is different for the different groups of instruments. Pianos have remarkably stiff strings. This is inevitable and also necessary because stiffness participates essentially in forming vividness of sound. The well-known ‘‘stretched octaves’’ and also the typical tuning curve are caused by this. For plucked strings, stiffness forms character of sound, together with choice of plucking spot on string and with corpus. For bowed strings, it is preferable to have strings, with minor stiffness, because the interaction of bow/string is better. The effects of jitter and rippling (supplement of sound with statistic noise effects) are better formed by less stiff strings. For wound strings, minor stiffness is possible with cores of filament structure. Theory and examples will be discussed. a)Present address: Erich Ohser Str. 10, D-08525 Plauen, Germany.
Interaction between resonators and fluid motion in ducts
Authors: Ronneberger Dirk
Published: July 2002

Each time one is confronted with unwanted narrow-band noise which propagates along a duct, it suggests itself to make use of resonators in the suppression of this noise. However, resonators may be highly sensitive to superimposed mean flow: Detuning and drastic decay of the quality factor is encountered in many cases, nevertheless, also the contrary may happen, namely the increase of the acoustic energy in the resonator. This may result in self-excited oscillations or in the amplification of the incident sound. The paper gives a review of these phenomena, and it will focus on the physical effects behind these phenomena. Simple models that are based on the governing physical effects have been developed and are compared to experimental results with different configurations of resonators in flow ducts. In the case of sound amplification the amplitude of the organized motion of the fluid may become very high so that the nonlinearity of the interaction with the mean flow becomes significant. The state of knowledge and the open questions in this respect will be addressed as well.
On the exact solution of the acoustic wave equation in a parabolic velocity profile in a hard-walled duct
Authors: Campos L. M. B. C. , Oliveira J. M. G. S.
Published: July 2002

The exact solution of the acoustic wave equation in a parabolic shear flow profile is obtained; the only exact solution given in the literature [Goldstein and Rice (1963); Jones (1977), (1978); Scott (1979); Koutsoyannis (1980)] is for a linear velocity profile, and the solution for the exponential shear flow is given elsewhere [Campos and Serrão (1998)]. The wave equation has three singularities, like the Gaussian hypergeometric equation, but it is of an extended type, since the singularity at infinity is irregular (all three singularities of the Gaussian hypergeometric equation are regular). The other two singularities of the present equation are regular, and one lies at the axis of the duct, and the other at the dicritical layers, where the Doppler-shifted frequency vanishes. The critical layers do not exist (they lie outside the duct) for longitudinal wave vector antiparallel to the mean flow (case I), i.e., propagation upstream in a local frame of reference. In the opposite case of longitudinal wave vector parallel to the mean flow (case II) there are three subcases, depending on whether the Doppler-shifted frequency on the axis of the duct is: (case II A) positive, i.e., critical layers are at imaginary ‘‘distance;’’ (case II B) zero, i.e., the critical layer lies on the axis of the duct: (case II C) negative, i.e., two critical layers exist in the duct. In all cases (I, II A, II B, II C) it is possible to obtain the exact acoustic field over the whole flow region by expanding around the singularities and matching solutions. Since the acoustic wave equation in a shear flow does not lead to a Sturm–Liouville problem, the eigenfunctions need not be orthogonal or complete. There is a single set of natural frequencies and normal modes in cases I, II A, and II B, but not in case II C; in the latter case, where two critical layers lie in the flow, they may separate three sets of eigenvalues/eigenfunctions, in the regions between by the critical layers and the walls.
Matching formant frequencies of complex sounds on different fundamentals
Authors: Darwin C. J. , Dissard Pascal
Published: July 2002

In order to explore the ability of listeners to match formant frequencies in periodic sounds that differ in their fundamental frequency (F0), listeners adjusted the frequency of one formant of periodically excited one- or two-formant sounds to match the timbre of a similar target sound that could have either the same or a different F0. Variability of matching (s.d. of matches within each listener) was low when matching sounds were on the same F0. Variability increased when matching sounds had different F0s. However, this increase was larger for sounds with resolved harmonics than for those with unresolved harmonics. This difference may reflect the perceptual cost of estimating the spectral envelope (and formant frequency) from the excitation pattern. [Work supported by EPSRC Grant No. GR/L03422.]
Evidence of a dissociation between the mechanisms governing the perceptual grouping of spectral components and the computation of low pitch
Authors: Roberts Brian , Brunstrom Jeffrey M.
Published: July 2002

The perceptual fusion of harmonically related partials is often assumed to result from the operation of a template mechanism that is responsible for computing low pitch. This dual-role hypothesis has been tested using frequency-shifted complexes. These sounds are inharmonic, but preserve a regular spectral pattern of equal component spacing. Stimuli had a nominal fundamental (F0) frequency of 200 Hz (roving range ±20%), and were frequency shifted either by 25.0% or 37.5%. Three consecutive components (6–8) were removed and replaced with a sinusoidal probe, located at one of a set of regularly spaced positions spanning the gap. On any trial, subjects heard a complex tone followed by an adjustable pure tone in a continuous loop. Subjects were well able to match the pitch of the probe unless it corresponded with a position predicted by the spectral pattern of the complex. In contrast, hit rates were not depressed for probes positioned at integer multiples of the F0(s) corresponding to the low pitch(es) of the complex, which were predicted from previous data [Patterson, J. Acoust. Soc. Am. 53, 1565–1572 (1973)]. The findings suggest that separate mechanisms are responsible for the computation of low pitch and for the perceptual grouping of partials.
Bulk viscidity model in acoustics of bubbly water-saturated soil
Authors: Shreiber Isaac
Published: July 2002

Recent experimental studies of acoustic wave propagation in water-saturated soil showed that the shock wave structure in the medium is similar to acoustic waves in bubbly liquids; namely, shock waves in the medium have an oscillating profile and strong attenuation of amplitude. The main physical reasons preventing the generalization of bubbly liquid acoustics in this case are that bubble expansion in unlimited space differs from bubble expansion in porous media, and the most delicate moment of this generalization is how to define the mixture pressure, what the mixture pressure is, and how it corresponds to pressure in the bubbles and relates to bubble dynamics. The goal of this communication is to show how to generalize the bubbly liquid acoustics in the water–bubbles–sand case with the help of the cell-model approach. The cell model is used for the Rayleigh equation derivation for a single bubble dynamics in a porous medium, and the governing equations for nonlinear acoustic waves are derived. The obtained canonical equations can explain some experimental data of three-phase media acoustics.
Localized modes of oscillating structures which lie on the bottom
Authors: Abramian Andrei
Published: July 2002

The phenomenon of wave localization in hydroelastic systems leads to the strength concentration of radiation fields. The linear method considers the process of localization to be the formation of nonpropagation waves (trapped modes phenomenon). The presence of such waves in the total wave packet points to the existance of mixed natural spectrum of differential operators describing the behavior of hydroelastic systems. The problem of liquid and oscillating structure interaction caused by the trapped modes phenomenon has been solved (membranes, dies, plates and different liquid models). The areas of wave localization have been determined. These areas depend on both the parameters of oscillating structures and the liquid waveguide parameters (the linear dimensions of the channel filled with liquid; the height from the bottom to the liquid surface; the liquid density gradient according to the height, etc.). Necessary and sufficient conditions for the low-frequency trapped modes and the high-frequency trapped modes have been found. The wave localization in nonlinear elastic structures interacting with liquid has been studied. Cases of weak and strong nonlinearity have been investigated. It has been shown that the slightly decreasing tail is added to nonlinear localized modes depending on the frequency of linear localized modes. The tail is caused by the interaction of the mode’s continuous spectrum and the localized modes.
Variation of frequency with blowing pressure for an air-driven free reed
Authors: Cottingham James P. , Reed Christopher H. , Busha Michael
Published: July 2002

In free reed instruments, an approximately linear decrease of playing frequency with increasing blowing pressure is normally observed. Laboratory measurements on harmonium-type reeds from an American reed organ have shown additionally that at very low pressure there is a small region of increasing frequency with increasing blowing pressure, and at extremely high blowing pressures, the frequency of reed vibration increases rapidly with increasing pressure. Measurements of growth and damping rates confirm the previously reported result [A. O. St. Hilaire, T. A. Wilson, and G. S. Beavers, J. Fluid Mech. 49, 805–815 (1971)] that at low air-flow rates aerodynamic forces add to the mechanical damping of the vibrating reed, but at higher flow rates, the aerodynamic forces contribute negative damping, resulting in self-sustained oscillations. Measurements of reed damping or growth rates have been made over a wide pressure range. Incorporation of these values along with other appropriate parameters in Fletcher’s model of reed vibration [N. H. Fletcher, Acustica 43, 63–72 (1979)] permit theoretical calculation of the variation in frequency with pressure for the air-driven free reed. The results of these calculations agree well with experimental data.
Application of the surface variational principle in coupled fluid-structure interaction analysis
Authors: Cunefare Kenneth A.
Published: July 2002

The surface variational principle (SVP) provides a unique tool for the investigation of coupled fluid-structure interactions, particularly on axisymmetric structures. The implementation of the SVP considered here uses basis functions that span the entire wetted surface of an object of interest. If the same or similar basis functions are used to model the structural dynamic response, the result is an analysis tool that can provide detailed insight into the coupling of fluid and structural motion across a broad range of scales. Further, since the method is grounded on a Ritz-expansion and a variational approach, the convergence behavior of the method is known and may be used to assess the accuracy of the results. In this manner, the SVP has been used to investigate the influence of feature representation within structural acoustic models, to investigate the feasibility of bounding the structural response to a perturbation in structural detail, and to investigate the controlling mechanisms for the coupling of exterior sound fields to interior fields through finite elastic cylinders. This paper introduces the coupled SVP method, reviews the advantages and disadvantages of the numerical implementation of the SVP, and presents some of the insights this method has provided.
Ultrasonic power measurement by means of radiation force
Authors: Beissner K.
Published: July 2002

The time-average acoustic power emitted by an ultrasonic source transducer is one of the key values characterizing the strength of ultrasonic fields. According to both fundamental IEC Standards dealing with the acoustic output of medical devices, namely that of diagnostic devices (IEC 61157) and that of therapeutic devices (IEC 61689), the ultrasonic power is to be measured and declared. The measurement method considered to be the most reliable one and recommended in IEC 61161 is that using a radiation force balance. In the present paper, various radiation force balance designs are discussed and compared. It is shown that the correctness of the results depends mainly on the acoustic properties of the target. One way of checking the performance of the radiation force balance is to use a translation stage with a computer-controlled step motor, which allows high-resolution variation of the transducer/target distance. The results of international intercomparisons of ultrasonic power measurements using continuous-wave reference transducers as well as a commercial, pulsed diagnostic instrument are presented and discussed.
An international comparison of transducer surface vibration distribution determination
Authors: Bangash M. A. , Molkenstruck W. , Reibold R. , Chivers R. C.
Published: July 2002

A lack of knowledge of the detailed behavior of the actual transducers used in a particular application can provide an indeterminate limitation on the sensitivity or the accuracy of the measurements being made. In principle, knowledge of the distribution of the surface vibration of the transducer permits the irradiating field at any point in the region of interest to be determined. Previous reports of surface vibration distribution determination have suffered from a lack of verification. The present work reports measurements made on four transducers (two with ceramic elements and two with PVdF elements of an approximate diameter of 10 mm at frequencies between 2.25 and 3.0 MHz) using two independent techniques. Measurements were made of the fields in transverse planes at four different distances from each transducer. The PTB measurements employed optical diffraction tomography while those from Guildford used scanned miniature (0.25- or 0.5-mm-diam PVdF) hydrophones to measure both amplitude and phase. Excellent agreement was found between the measurements from the two techniques, including absolute pressure levels, confirming that the vibration distribution of a transmitting transducer can be reliably determined although it requires great technical care and, at present, is time consuming.
Wideband calibration of PVDF hydrophones by an electromagnetic hydrophone using theoretical spectra of overtones
Authors: Filipczynski Leszek , Kujawska Tamara , Wojcik Janusz
Published: July 2002

PVDF hydrophones are limited in their frequency band, thus distorting measured pulses. For nonlinear effects, caused by propagation of ultrasonic pulses with finite amplitudes, the frequency characteristics are of particular importance. One can correct those distortions knowing the sensitivity characteristics of the hydrophone. To find the sensitivity of the PVDF hydrophone, focused pressure pulses were at first measured by themselves and compared with those measured by the electromagnetic hydrophone (EMH) at low source pressure (linear propagation conditions). So due to the narrow frequency band, one avoided frequency distortions in the EMH, where the absolute pressure was obtained from only two measurements: electrical and magnetic. To discover the sensitivity frequency characteristics, a wideband pulse spectrum of overtones (at known high source pressure) was obtained. Multiplying the theoretical spectrum by the expected sensitivity characteristics, to match theoretical and measured spectra, one obtained the true frequency characteristics. Finally, the averaging effect occurring on the surface of the sensitive electrode of the PVDF hydrophone was computed and eliminated, to obtain the sensitivity for the incident plane wave. For determination of theoretical pressure pulses and their spectra, a special numerical code was elaborated, based on numerical solutions of the nonlinear wave propagation.
Characterization of ultrasonic contact transducers using a Michelson interferometer
Authors: Hurley Donna C. , Lerch Terence P.
Published: July 2002

Accurate measurements of velocity, attenuation, and other ultrasonic properties of materials involve diffraction corrections that can significantly alter the measured values. Although diffraction calculations require knowledge of the transducer’s effective radius, this parameter is difficult to determine precisely for contact transducers. Here, an experimental method to quantitatively characterize longitudinal contact transducers is presented. Narrowband (toneburst) electronics excite the transducer, and a Michelson interferometer measures the out-of-plane displacements on the sample’s opposite side. With a resolution of approximately 10 μm, this optical technique allows transverse spatial scans of the displacement field to be obtained. Furthermore, the on-axis position may be located with the interferometer and the transducer excitation frequency varied. The frequency dependence of the on-axis amplitude is measured using a sample whose thickness is approximately half the nearfield distance at the transducer’s center frequency. The shape of the transverse scans and the observed minimum in the frequency dependence permit the transducer’s effective radius to be calculated. Measurements are presented for transducers in the 1- to 10-MHz range with nominal radii between 2.5 and 6.4 mm. The results are compared to a numerical diffraction model to evaluate the accuracy and precision of this approach.
Measurement of elastic properties of GaAs with laser-generated surface acoustic waves
Authors: Flannery C. M. , Chilla E. , Fröhlich H.-J.
Published: July 2002

Surface acoustic wave (SAW) velocities were measured as a function of angle on both GaAs (001) and GaAs (111) crystal cuts. Surface acoustic wave packets were generated by a pulsed nitrogen laser beam focused into a line shape on the sample surface. The SAWs were detected by a PVDF foil with steel wedge transducer at different propagating distances. The system was automated to measure SAW velocity at a range of angles, and thus produces a velocity-angle (or slowness) curve. From the slowness curve the three independent elastic constants may be derived. The SAW velocity measurement setup is presented and aspects of the propagation of SAW modes for different cuts and angles are discussed. The accuracy of the elastic constants derived from SAW measurements on both cuts is examined, and other detected acoustic wave modes are discussed with regard to their origin and suitability for elastic constant measurement.
Elastic nonlinearity and damage detection in quasibrittle materials using single mode nonlinear resonant ultrasound spectroscopy (SIMONRUS)
Authors: Van Den Abeele Koen
Published: July 2002

A promising tool for NDT of quasibrittle materials has been developed and applied in the field of damage detection. The technique focuses on the acoustic nonlinear response of the material’s resonance modes when driven at small wave amplitudes. A diagnostic method was constructed to quantify the acoustic nonlinearity of homogenous and isotropic samples in bench-top resonance experiments. The analysis of the data is supported by a phenomenological model based on the Preisach model of hysteresis. Six material parameters—two linear and four nonlinear—can be extracted from a simple set of amplitude-dependent resonance experiments, and completely define the material state of the sample. The characterization procedure is applied to damage detection in slate plates. Linear and nonlinear parameters were measured for progressive fatigue induced by cyclic mechanical loading. A rapid increase of the nonlinear parameters was observed early in the loading process and only a small to modest variation of the linear parameters. Near failure, the nonlinear coefficient deduced from the softening of the modulus increased by a factor of 1000. Similar observations were made when analyzing the second and third harmonics. Presently, linear and nonlinear behavior of slate exposed to natural and accelerated hygrothermal aging is being monitored.
Phase-conjugated ultrasonic beams of finite amplitude
Authors: Brysev A. P. , Bunkin F. V. , Krutyansky L. M. , Preobrazhensky V. L. , Stakhovsky A. D. , Pyl’nov Yu. V. , Cunningham K. B. , Younghouse S. J. , Hamilton M. F.
Published: July 2002

Generation of intense, phase-conjugated ultrasonic beams by a single active magnetic element in a supercritical parametric mode has been demonstrated experimentally and theoretically. Specifically, phase conjugation with amplification greater than 80 dB, producing intensities of several hundred W/cm2 at MHz frequencies, is accomplished via parametric electromagnetic pumping of magnetoelastic solids. Reversal of the sound field incident on the conjugator has been confirmed by observation of the self-targeting of beams on scattering sites in water [Usp. Fiz. Nauk 168, 877–890 (1998) (in Russian)]. The large amplification provided by the conjugator leads to nonlinear distortion and shock formation in the conjugate field. These nonlinear effects are studied experimentally with measurements based on light diffraction for conjugated beams in water having intensities of 2 W/cm2 and frequencies near 5 MHz. Numerical simulations corresponding to experimental conditions take into account absorption, diffraction, nonlinearity, and the finite size of the conjugator. The simulations reveal the presence of shocks, yet accurate reversal of the incident field despite the strong waveform distortion [Phys. Acoust. (in press (1998)]. Potential applications of this technololgy are discussed. [Work supported by RFBR (Grants 96-02-17301, 98-02-16761), CRDF (Project RE1-270), and ONR.]
Nonlinear profiles and spectra transformation in going from vibrating piston to traveling wave
Authors: Andreev Valeri G. , Rudenko Oleg V.
Published: July 2002

The effects of nonlinear relation between the radiating surface motion law and the traveling wave profile are studied. These effects are significant in the neighbor of the source for the vibration velocities compared with a sound speed. The source was modeled as a nonlinear vibrating system, namely, as a piston excited by external force and loaded by the medium. The temporal profiles and harmonics amplitudes of waves radiated by the piston at harmonic, wide-band (pulsed) and noise excitation are calculated. The effects of dynamic (regular) and stochastic wave generation are compared, and characteristic features of spectral transformation for these two cases are analyzed. Special attention is paid to the difference between the boundary nonlinear phenomena considered here and bulk effects due to nonlinear elastic properties of a medium. A possibility of observing such phenomena for the radiation of high intensity waves into the bubbly liquid is discussed. [Work supported by CRDF and RFBR.]
Multi-frequency plane, nonlinear, and dissipative waves for arbitrary distances
Authors: Hedberg Claes M.
Published: July 2002

A solution for multi-frequency plane waves propagating through a dissipative and nonlinear medium is presented. It originates from the well-known Mendousse solution, a ratio between Bessel function series, for a pure sinusiodal wave. The solution is exact. The only limitation, which is inherited from the Mendousse solution, is the slow convergence of the series when the nonlinearity is very large compared to the dissipation. Otherwise, any frequencies, amplitudes, and phases can be introduced in the original wave and the solution is valid for any propagated distance. Results for some multi-frequency signals are presented.