bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical study of sound field radiated from a circular duct with an open end
Authors: Zhu Zhichi , Zhou Anqi , Huang Dongtao , Guo Qing
Published: July 2002

A dispersion-relation-preserving (DRP) scheme for computational acoustics has been developed in recent years. This scheme is of high accuracy and can preserve the original dispersion relations of governing equations so that a good global acoustic solution can be ensured. However, the scheme is usually not only very complex but also problem dependent. In this paper, a unified DRP scheme for both internal and boundary points is developed for solving the sound field radiated from a circular duct with an open end. This unified DRP scheme is further applied to obtain the sound fields numerically in three different cases, namely, without flow and flange, without flow but with flange, and with flow and flange. In addition, relevant reflection efficiencies are also predicted at various Helmholtz numbers. Satisfactory comparisons of the predicted reflection efficiencies with data from other studies are illustrated. It is also shown that the numerical method with the DRP scheme presented in the paper is successful.
Influence of airflow on sound propagation in a curved tunnel
Authors: Imaizumi Hiroyuki , Isei Takehiro
Published: July 2002

Measurements were made to examine influences of airflow on propagation attenuation of sound in a curved tunnel. The speed of airflow varied in width direction of the cross section of tunnel, and the values were from around 1 to 3 m/s. Sound attenuation upwind was less than that downwind at high frequencies up to the receivers that are in sight of the source. The tendency agrees with sound attenuation measured in a straight tunnel with airflow [H. Imaizumi et al., J. JSSE 31, 228–239 (1992)]. Difference of the attenuation gradually became small in the same frequency region at receivers that are out of sight from the source. Numerical calculations by means of a ray tracing method were applied to propagation attenuation of sound in a curved two-dimensional plane. Transmission losses of sound energy calculated only from reflection times of the sound rays on the inner wall were compared under each propagation condition. The transmission loss downwind was larger than upwind up to the receivers that are in sight, while the difference of both became small at the further receivers due to the rapid increase of the reflection times of rays. The calculation results qualitatively agree with the experimental measurements.
Performance measurements of a thermoacoustic refrigerator driven at high amplitudes
Authors: Poese Matthew E. , Garrett Steven L.
Published: July 2002

Since the power density in a thermoacoustic device is proportional to the square of the acoustic Mach number, there is strong motivation to design thermoacoustic refrigerators to operate at larger pressure amplitudes. Measurements will be reported of a modified version of the space thermoacoustic refrigerator (STAR) [Garrett et al., ‘‘Thermoacoustic refrigerator for space applications,’’ J. Thermophysics Heat Transfer 7, 595–599 (1993)] driven at pressure amplitudes two to three times as large as reported in 1993. The results of these measurements will be compared to both a DeltaE computer model of the low-amplitude (linear) performance and one that includes turbulent flow in the duct regions of the device. An overview of the instrumentation, including a measurement of exhaust heat with an absolute accuracy of 65 mW, will also be presented. [Work supported by Office of Naval Research.]
Extended performance measurements for SETAC
Authors: Grant Anat , Garrett Steven L.
Published: July 2002

The Shipboard Electronics ThermoAcoustic Cooler (SETAC) was built at the Naval Postgraduate School in Monterey, CA. In a demonstration at sea aboard the U.S.S. Deyo in April 1995, SETAC was used to provide 419 watts of useful cooling power across a stack temperature difference Thot−Tcold=30 °C with an acoustic input power of 227 watts. New data spanning a wider range of temperature difference and heat load will be presented and compared to a DeltaE model. [Work supported by the Office of Naval Research.]
Modeling in 3D of directional radiation of curved woodwind instruments
Authors: Causse Rene E. , Lheureux Carole
Published: July 2002

In a previous presentation [Causse et al., J. Acoust. Soc. Am. 100(4), Pt. 2, 2812 (1996)], the directional pattern of some instruments of the woodwind family was modeled and compared. These instruments, oboe, clarinet, and flute, were chosen for their straight tube and for the fact that the simplification that the holes of the lattice are aligned and oriented in the same direction did not introduce big errors. A second class of instruments of this family are instruments with curved tubes, for example the bassoon, the bass clarinet, or the alto saxophone. The original model was modified to take into account the curves but also the real orientation of the holes. The far-field radiated pressure was calculated at a constant radius on a sphere enclosing the instrument. The main difficulty with this model is expressing the directivity of each opening (holes and bell) in the same coordinate system. In the cases where this leads to excessive calculation, some simplifications are proposed. Model results were compared with experimental measurements of actual instruments. Comparisons of the directional radiation between these instruments and also with straight ones will be presented. Implications for the perception of these instruments will be discussed.
Reaction to combined sources of noise may depend on the respondents’ interpretation of the questions
Authors: Job R. F. Soames
Published: July 2002

Reaction to multiple sources of noise has proven difficult to explain. The unexpected results of assessment of total reaction to noise may not arise from inadequate integration within the subject nor from complexities of the perception of the noise. This abstract suggests that responses to questions regarding reaction to combined sources may reflect the subjects’ interpretation of the relevant questions. Requests for reaction to the total noise load may be interpreted as requesting total reaction to the two sources, or average reaction to the two sources, or total or average reaction to the total noise environment. The consequences of such interpretations by the subjects are not easily predicted. Predictions would be influenced by: whether reaction is a unipolar negative scale versus a bipolar scale from negative to positive; whether the combined reaction is an average or a total; and whether the average or total should include consideration of the times for which each noise is not present. Finally, it should be noted that different subjects may interpret the same question in different ways in relation to these alternatives. Examples of the role of these variables are identified, and a set of models of reaction based on the various alternatives proposed.
Combined qualitative and quantitative measurements to evaluate noises from combined sources
Authors: Schulte-Fortkamp Brigitte
Published: July 2002

Previous studies on assessing combined noises have shown the rating of environmental noises from combined sources as a very complex and difficult task. Disturbance and annoyance caused by the influence of noises require in their complexity an adequate procedure of evaluation. There are different theories to explain those rating results of an overall noise situation which is almost rated lower than the most annoying single source. If sounds are synergistic, the criteria and kinds of sources have to be found which are dominant for the person who assesses the noises. In traditional laboratory studies the context is faded out by the evaluation process, while the context effects in field studies play a decisive role and the evaluation of annoyance caused by noise allows the consideration of different factors in a situation where noises are combined. In a current socio- and psychoacoustical field study the process of assessing the noises and the noises as well are precisely described in interviews and acoustical diaries. In another combined procedure of qualitative-explorative and objective-standardized measurements in a laboratory setting specific noise components causing annoyance and disturbance have been identified. The special methodical procedure and results will be presented.
Characterization of an urban area’s acoustical comfort
Authors: Beaumont Jacques , Barlet Aline , Louwrse Christophe , Semidor Catherine
Published: July 2002

In this paper a global method to characterize acoustic comfort in urban areas is presented. This method takes into account the relationships between urban forms (shapes, sizes, and material surfaces), the opinions of town-users, and noise descriptors. These descriptors are deduced from a method based on time automatic detection threshold to classify four types of noise. This system allows the study of sound situation in a self-contained way over a long period (several hours). The influence of building design is estimated according to the visualization of the evolution of these descriptors in 2D and 3D maps all over the studied area. The first results show that noise levels fit well with the architectural characteristics of the buildings (facade irregularities, materials,...). To validate this method, experiments were conducted on a Bordeaux central district. The effects of an urban area’s morphology on listeners’ noise perception are analyzed from investigations carried out with people living or working in the tested site. The aim of this work is to develop a decision-assisting tool in the acoustic design of urban areas. Environmental considerations, such as noise, must be included in urban planning not only to avoid disturbance, but to provide better satisfaction in living in the city.
Matrix theory of elastic resonance scattering
Authors: Choi Myoung S. , Cheong Yong M.
Published: July 2002

A fundamental matrix theory is developed for the exact isolation (in both magnitude and phase) of resonance amplitudes contained in the elastic field scattered by a penetrable target. Similarities and differences between this matrix theory and the classical resonance scattering theory [L. Flax, L. R. Dragonette, and H. Uberall, J. Acoust. Soc. Am. 63, 723–731 (1978)] are discussed. The matrix theory is then applied to cylindrical and spherical fluid-filled cavities, and analytical expressions for the resonance amplitudes are derived. In the vicinity of resonance frequencies, the resonance amplitude expressions have forms similar to the Breit–Wigner formula. In order to check the validity of the matrix theory, numerical calculations are performed for a cylindrical water-filled cavity in an aluminum medium. Resonance spectra of the cavity are presented for some partial waves and their characteristics are also discussed.
Raman–Nath diffraction caused at the focal point of a concave type transducer
Authors: Watanabe Y. , Miyaki H. , Fujita K.
Published: July 2002

To estimate the intensity of sound pressure in the vicinity of the focal point of a concave type transducer, Raman–Nath diffraction caused at the focal point of a concave type transducer is theoretically and experimen- tally discussed. Sound field, near the focal point, including the acoustic nonlinearity, is theoretically calculated by using the KZK equation. Light intensity of zeroth order Raman–Nath diffraction is also calculated as a function of the sound pressure at the focal point. In the high intensive sound region, it is found that the acoustic nonlinearity makes the light intensity curve disappear at the local peaks. The He–Ne laser whose beam spot diameter is 1.2 mm is supplied as a light source. Light intensities of the zeroth-order Raman–Nath diffraction caused at the focal point are observed by changing the driving voltage of the transducer. The experimentally obtained graph shows the relatively same pattern compared with the theoretically calculated one. The sound pressure at the focal point is estimated by fitting those two results. It is confirmed that the sound pressure estimated by the optical method shows good agreements with the estimated one by the hydrophone measurements.
Frequency-dependent saturation in inner hair cell responses
Authors: Cheatham M. A. , Dallos P.
Published: July 2002

Inner hair cell (IHC) recordings are made in guinea pig from cochlear turns 2, 3, and 4 where best frequencies (BF) are approximately 4000, 1000, and 250 Hz, respectively. Input–output functions for the ac receptor potential are measured for inputs at, below, and above the BF of each recording location. Although all responses saturate at high intensities, the response magnitude at which saturation occurs depends on stimulus frequency. For example, in turn 2 more linear responses are observed below BF while in turn 4 a different pattern emerges. At this apical recording site, which responds preferentially to very low frequencies, IHCs exhibit more linear behavior above BF. In other words, response magnitude at saturation exceeds that measured for inputs at and below the BF of the cell. The reasons for this dependence on BF are evaluated by comparing input–output functions for ac responses recorded intracellularly from IHCs and extracellularly from the organ of Corti fluid space. [Work supported by Grant No. 5 R01 DC00089, National Institute on Deafness and Other Communication Disorders, National Institutes of Health.]
Signal detection theoretic analysis of auditory processing: Phase uncertainty and multiple channel integration
Authors: Gresham Lisa C. , Collins Leslie M.
Published: July 2002

Traditionally, psychophysical data has been predicted either by constructing models of the peripheral auditory system or by using signal detection theory. The resulting theoretical detection performance is often substantially greater than experimental results and has been explained by adding ‘‘internal noise’’ to the system in a somewhat ad hoc manner. An integrated approach combining both a physiologically based auditory model and classical signal detection theory has been shown to produce more accurate predictions of experimental data. The discrepancy that still exists may be due, in part, to the two unrealistic assumptions that the system is deterministic and that a single channel with the highest signal-to-noise ratio determines detection performance. The work presented here investigates the impact of phase uncertainty and multiple channel integration on predicted detection performance. More accurate predictions of experimental data are obtained, particularly after the first two stages of the auditory model, when phase uncertainty is added to the auditory input signal and the resulting output signals are analyzed using the integrated approach. Integrating information across multiple channels increases the predicted performance, albeit not substantially, suggesting that the single-channel approximation is not a significant source of discrepancy between theoretical and experimental results. [Work supported by NIH.]
Optimization procedures for strain sensing in active structural acoustic control
Authors: Masson Patrice , Berry Alain
Published: July 2002

Many active structural acoustic control strategies which are based on the minimization of the radiated acoustic power are defined in the wave number domain to exploit the fact that only supersonic structural wave number components are radiating sound. Discrete sensors are more appropriate for this purpose as they allow the ability to distinguish between the structural components on two-dimensional structures. However, the use of such sensors may require extensive real-time computation, as the displacement field has to be reconstructed from the strain field in order to compute the radiated acoustic power. Two approaches are herein proposed to optimize the calculation of the radiated acoustic power. The first one allows the calculation of the radiated power directly from the strain field, without requiring any reconstruction of the displacement field. The second approach is directed toward the optimization of the radiated power calculation by using a wavelet transform of the displacement field, thus avoiding the Fourier transform and the integration of the radiating components. Experimental control results are presented using different types of strain sensors mounted on a simply supported beam. It is shown that in that case, a significant gain in computation time can be obtained using the proposed approaches without sacrificing the control performances.
Measurements and modeling of the transient acoustic field at impacted plates
Authors: Chaigne Antoine , Lambourg Christophe , Schedin Staffan
Published: July 2002

A comparison between measured and simulated transient acoustic fields generated by thin impacted plates is reported. The plate is modeled by using finite difference methods and the radiated pressure is obtained by solving the Rayleigh integral [Ch. Lambourg and A. Chaigne, J. Acoust. Soc. Am. 101(A) (1997)]. The results are evaluated in the form of the spatial pressure distribution at instants short after the excitation. Experimentally, a lead bullet (0.5 g, 100 m/s) is fired towards a cantilever steel plate (300×30×1 mm). The duration of the impact is estimated by using a high-speed camera that can register several million frames per second. An interferometric comparison of the change in optical path length of two holographic recordings, captured before and shortly after the impact, gives a 2-D projection of the acoustic field. A double-pulsed ruby laser, emitting light pulses of short duration (30 ns), is used as light source [S. Schedin, A. O. Waahlin, and P. Gren, J. Acoust. Soc. Am 99, 700–705 (1996)]. A high degree of similarity is observed between measured and simulated sound field, except in the close vicinity of the impact point. It is presumed that the discrepancies are due to nonlinear effects which are not included in the model.
Comparison between DyWT- and EGG-based estimation of glottal closure instant for speech signal
Authors: Seok Jongwon , Son Youngho , Bae Keunsung
Published: July 2002

Recently, wavelet transform has found many applications. Mallat has shown that, with a proper choice of wavelet function, the local maxima of wavelet transformed signal indicate the position of the signal sharp variation points. Since the glottal closure causes sharp changes in the derivative of air flow in the glottis and transient in the speech signal, wavelet analysis can be used for detection of glottal closure instant (GCI) from the speech signal. It is known that the point of maximum negative value in a differentiated EGG signal agrees well with the closing time of the vocal folds. Due to the limited practical utility of the EGG signal, however, a speech-only-based GCI detection method is still needed. In this paper, GCI detection algorithm based on the dyadic wavelet transform (DyWT) is proposed and experimental results are shown. Using the EGG signal as a reference, experimental results are analyzed and discussed for evaluation of its performance. Preliminary experimental results show that DyWT-based GCI detection method has some speaker dependency and wavelet transformed speech signal at scale 4 gives more reliable GCI information than that of others. [This work has been partially supported by a grant from Korea Science and Engineering Foundation (KOSEF 971-0917- 103-2).]
Acoustic propagation in the ocean surf zone
Authors: Means Steven L. , Heitmeyer Richard M. , Wales Stephen C. , Hayward Thomas J. , Livingston Ellen S. , Schindall Jeffrey A.
Published: July 2002

Broadband acoustic propagation measurements were conducted during the SandyDuck’97 experiment to provide a means of interpreting noise data taken both within and outside of the surf zone. The source was located outside of the nominal surf zone region at a distance of 470 m from the shore in 6 m of water. The receivers were spaced at 6-m intervals 45 to 183 m offshore in 1 to 3 m of water. Both the source and the receivers were located along a line orthogonal to the shore. The cw line sets were transmitted to obtain a description of the temporal fluctuations in the narrowband propagation induced by the temporal variability of the medium, the surface, and the entrained bubble distribution, as a function of range and frequency. The cw pulses and biphase-modulated PR sequences were transmitted to obtain a description of the spatial and temporal variability of the multipath structure. Measurements show significant time variations even under low surf conditions. The measured results are interpreted through simulations obtained using a FEPE propagation model with near-concurrent estimates of the bathymetry and geoacoustic parameters derived by Fabre and Wilson [IEEE J. Ocean. Eng. 22, 434–444 (1997)]. [Work supported by ONR.]
Wind-generated acoustic spectral effects in the surf zone in the presence and absence of rainfall at Duck, North Carolina
Authors: Proni John R. , Wilkerson John C.
Published: July 2002

Observations of wind-induced effects upon concurrently measured rainfall-generated spectra in the surf zone off Duck, North Carolina were made in November, 1992. Rapid changes in wind speed from about 5 m/s to 14 m/s were accompanied by a frequency-dependent reduction in rainfall spectral level. The reduction initiated at about 50 kHz (the highest frequency recorded) and progressed to lower frequencies with time. When the wind burst diminished, spectral levels increased. Rainfall rate was monitored using conventional rain gauges so that rainfall rate change effects could be distinguished from wind change effects in the measured acoustical spectra. The general surf-noise spectrum level changes were also observed to be affected by wind speed changes.
Acoustic observations of suspended sediments in the Changjiang Estuary
Authors: Zhang Shuying
Published: July 2002

An acoustic backscatter instrument of dual frequencies (0.5 and 1.5 MHz) was developed for suspended sediment measurements and for sediment transport studies. The instrument measures the vertical concentration profiles of suspended sediments with a temporal resolution of 1 s and a spatial (depth) resolution of 10 cm for 0.5 MHz or 2 cm for 1.5 MHz. The data of backscattered acoustic energy are sampled at a rate of 75 kHz for a 450-s burst each time, so each burst comprises 450 vertical profiles. Coincidentally, six calibration points for the water column are taken through water sampling. Further data processing for each burst, such as compensation for sound transmission losses, in situ calibration of acoustic scattering intensity to real concentration of suspended sediments, and ensemble averaging over adjustable time–depth sizes permits three-dimensional concentration profiles to be derived. To increase the accuracy of concentration measurement, a multisegment procedure to form an appropriate compensation and calibration curve is applied. Through observations at the Changjiang Estuary four patterns of vertical suspension profiles are identified at flood and ebb tides. In addition, lutoclines and interfacial waves within the near-bed high concentration suspensions are revealed.
Numerical simulations of tissue heating created by high-intensity focused ultrasound
Authors: Curra Francesco P. , Kaczkowski Peter , Mourad Pierre D. , Crum Lawrence A. , Khokhlova Vera A.
Published: July 2002

Modeling of high-intensity focused ultrasound (HIFU) propagation and heating effects in tissue has usually been studied under the assumption of linear acoustics. Nevertheless, nonlinear propagation can lead to important differences in heat deposition depending on the degree of nonlinearity achieved in a HIFU field. To be presented are calculations of the spatial patterns of acoustic intensity (I) and heat generation [H=−(∂/∂z+1/r∂/∂r)I for strongly nonlinear acoustic waves and H=2αI for weakly nonlinear acoustic waves, where α is acoustic absorption] associated with focused weakly and strongly nonlinear acoustic wave propagation in biological tissue. The propagation is modeled using a KZK equation method with special attention to correct modeling of shock generation and biologically relevant attenuation, as well as using initializing data based on existing designs of transducers for acoustic hemostasis. The heat generation term forces the ‘‘bio-heat’’ equation, which predicts the generation, movement, and dissipation of heat within biological tissue. The tissue model contains blood flow in an artery or vein and is perfused by a capillary bed. For this talk the differences in spatial patterns of acoustic intensity created by weakly and strongly nonlinear CW 1-Mhz acoustic wave propagation are shown. How those differences translate into differences in heat generation and therefore bioeffect within biological tissue are then demonstrated. [Work sponsored by DARPA.]
Occlusion of blood vessels using high-intensity focused ultrasound
Authors: Vaezy Shahram , Martin Roy , Kaczkowski Peter , Keilman George , Carter Steve , Caps Michael , Mourad Pierre , Crum Lawrence
Published: July 2002

Vascular injury may result from both trauma and invasive medical procedures. High-intensity focused ultrasound (HIFU) was used to occlude surgically exposed blood vessels of anesthetized rabbits, as a mechanism of hemostasis applicable to vascular injury. A HIFU transducer, with a spherically curved aperture area of 6.34 cm2, a focal length of 4 cm, and a frequency of 3.3 MHz, was used. The transducer was equipped with a conical housing filled with water, providing a coupling medium to the vessels. Femoral arteries and veins were occluded after a HIFU treatment of approximately 30–60 s, at a focal intensity of 3000 W/cm2. The vessels were severed after the treatment to confirm complete occlusion. No bleeding was observed. Gross and microscopic examination of the vessels revealed two major mechanisms of occlusion, dissection of the vessel wall and shrinkage of the vessel. In the dissection mechanism, a flap of the inner wall of the vessel peeled as a result of the HIFU treatment and caused a blockage of the blood flow, while in the shrinkage mechanism a mechanical constriction of the vessel lumen caused the blockage. HIFU may provide a valuable method for hemostasis of injured vessels by treating a region of the blood vessel, proximal to the hemorrhaging site.
Occlusion of blood flow by high-intensity focused ultrasound
Authors: Rivens Ian , Rowland Ian , ter Haar Gail , Denbow Mark , Fisk Nicholas
Published: July 2002

This work investigates the possiblity of occluding blood flow (in vivo) using high-intensity focused ultrasound surgery (FUS). Such an effect could be used, for example, in the noninvasive treatment of foetal dysfunctions. A high-power 1.7-MHz, 150-mm focal length, piezoelectric transducer was used to expose rat femoral vessels to a free field I−SP=4660 W cm−2 for 2 s under terminal anaesthesia. Initially, eight separate exposures were used. Later experiments were aimed at determining an optimal single exposure to produce flow occlusion. Before and after exposure, magnetic resonance FISP 3-D angiograms (MRA) with submillimeter spatial resolution were acquired using a Siemens Vision MR System (1.5T) and extremity coil. In all animals, MRA showed reduced blood flow both in the treated region and distal to it. The results of single-dose optimization will be discussed. The ability to curtail blood flow using FUS allows the possibility of treating Foeto-Foetal Transfusion Syndrome by occluding the placental shunt vessels responsible for vascular inbalance in identical twins. Currently available interventional treatments (surgery or intrauterine laser therapy) have significant mortality and morbidity. The FUS has the advantage of being noninvasive. [Work was funded by the UK Medical Research Council.]
Concept of biological focal field and its importance in tissue resection with high-intensity focused ultrasound
Authors: Wang Zhi B. , Wu Feng , Wang Zhi L. , Liu Chuan
Published: July 2002

Many studies showed that in vitro the size and shape of the necrosed tissue volume generated by high-intensity focused ultrasound (HIFU) were dependent upon the transducer size and radius of curvature, operating frequency, input power, pulse duration, and delay time between each pulse. In this research the shape and size of necrosed tissue volume produced by HIFU with 1.6-MHz focused transducer were carefully checked and compared in rabbits and pigs. This volume was generated by a single exposure or focal planes. It was shown that with the same therapeutic parameters, HIFU can selectively necrose one region of liver in vivo. However, its shape and size differed between in vitro and in vivo. These changes implied that the necrosed tissue volume in vivo depended upon not only HIFU conditions, but also the structure, function, and movement of target tissue. In contrast with the physical focal region, necrosed tissue volume in vivo could also be termed the biological focal field of HIFU. Theoretically, it resembled more closely the living tissue damaged by HIFU. In order to avoid the side effects, it is important to set up the data about biological focal fields of different organs in tissue resection with HIFU.
Control of particles in a standing wave field using ultrasonic vibration
Authors: Nomura Shinfuku , Murakami Kouichi , Yoshikawa Yukinori , Ochi Junji
Published: July 2002

In order to control the motion of micromachines by acoustic power, the behavior of particles falling in several liquids with a standing wave field was studied experimentally. A PZT transducer with a frequency of 28 kHz was fixed to the bottom of a cylinder. Several small tubes were inserted in this cylinder, and glass particles with a diameter of about 1.5–3.5 mm were dropped in these tubes, respectively. Since cavitation bubbles are observed by applying ultrasonic vibration to a liquid, cavitation intensity as estimated from the erosion loss of an aluminum sheet was measured to investigate the effect of cavitation generation on the radiation pressure. Cavitation intensity in degassed water was weaker than that in ion-exchanged water; however, the decrease in velocity of the glass particles by applying ultrasonic vibration exhibited the greatest deceleration in the degassed water. Ultrasonic power effectively acts on a particle as a radiation force when cavitation does not occur and there is almost no damping of the ultrasonic wave. When varying the tube diameter, as the ratio of the diameter of tube to the particle diameter increased, so did the deceleration. All particles were levitated by the ultrasonic radiation force in a ratio of more than 0.6.
The multicomponent composition of the low acoustic impedance matching layer for the ultrasonic transducer operating in the air
Authors: Gudra Tadeusz
Published: July 2002

Piezoceramic transducers with matching layers are usually used to generate an ultrasonic wave in the air within the frequency range above 100 kHz. The paper presents a new material composition of low acoustic impedance named ITAKOM, whose acoustic characteristics makes it applicable as a matching medium between a piezoelectric transducer and a gas medium in a wide range of frequencies. Porosity is the common feature of all the lowest acoustic impedance materials. The results of the studies of different material compositions show that pore diameters and their percentage in the composite volume have greater importance than the composite make-up and render possible the elaboration of a composite material whose parameters can be defined by the percentage interdependence of components. Due to the comparatively wide range of density and wave velocity materials of acoustic impedance ranging from 0.2 −1×106 Pa⋅s/m can be produced. An example of an application of this material to construct the focusing ultrasonic transducer operating in the air at the frequency f=1.3 MHz in the setup of phase sensitive scanning acoustic microscopy as well as the results of object measurements are presented in the ultrasonic journal [Gudra et al., Ultrasonics 34, 711–719 (1996)].
The discovery of natural classes by non-native listeners
Authors: Kingston John , Moreton Elliott
Published: July 2002

Using natural disyllabic stimuli, English speakers were trained to sort one, two, or three pairs of German nonlow rounded vowels into two cat-egories, then a new pair was added and their ability to sort it into the same categories was tested. Each pair contrasted in [high], [tense], and [back]. Category membership was determined by only one of these features. Three-pair training provided enough information to tell which one; two-pair narrowed it down to two possibilities; one-pair left it open. Listeners in three experiments using different pairs of test vowels sorted the test vowels significantly better as the number of training pairs increased. This suggests they were inducing feature-based natural classes. The rival exemplar model of Nosofsky [J. Exp. Psych.: Gen. 115, 39–57 (1986)] would say that while more pairs bring more phonetic variety, they also exemplify more robustly the dimensions along which the categories differ phonetically, and thereby shift attentional weight to those dimensions. Similar experiments will pit these two hypotheses against one another with training pairs which contrast only in the feature that defines the sort categories. If listeners are using feature-based natural classes, their performance should not improve with more training pairs; if they are using exemplars, it should. [Work supported by NIH.]
The Journal of the Acoustical Society of America and other technical journals of the future—a new multimedia format?
Authors: Raichel Daniel R.
Published: July 2002

The Journal of the Acoustical Society of America (JASA) is now available in two formats—the traditional printed issue and the CD-ROM. However, CD-ROMs are in the early process of being displaced by the newer, more powerful DVDs which feature a capacity of approximately 2.8 GB per disk side rather than the 650 MB standard for each CD-ROM. CD-ROMs, however, will not immediately be rendered obsolete by the use of a current DVD player since the latter is backward compatible for CD-ROM playback. However, even in the CD-ROM format, a technical journal can take on new aspects of multimedia, which were hitherto unavailable or impracticable in printed media. The greatly enhanced capacity of the DVD disk provides even greater opportunities for extended expositions. Animation scenes, photographs, extended databases which would not have otherwise been included in a printed article, dynamic plots, sound effects, virtual reality scenes which permit one to ‘‘visit’’ laboratory sites or ‘‘witness’’ the topical phenomena, and even computer programs and entire reproductions of cited references can be incorporated in an article slated for publication on the new multimedia disks or on future storage devices.
Limitations on adiabatic normal modes in range-varying environments
Authors: Mignerey Peter C.
Published: July 2002

Curvilinear coordinates are used to extend adiabatic normal modes to weak range-dependent environments including those with sloping bottoms. Reciprocal vertical wave numbers of a reference mode provide the coordinate scale factors. This approach is valid for negligible horizontal derivatives of intermodal vertical-wave number ratios. Large gradients in the bottom impedance make these ratios large, implying significant mode coupling in oceanic regions spanning both soft and hard terrains. Additionally, a large number of eigenvalues are needed to compute adiabatic normal-mode solutions for high-resolution acoustic fields. The direct solution of eigenvalue problems on a fine grid is often prohibitive. Alternatively, the eigenvalues may be interpolated to the fine grid. This approach usually requires extrapolation toward edges across which the horizontal wave number becomes imaginary at mode cutoff. One choice for an interpolation function is the integrated reciprocal vertical wave number. This function, proportional to water depth, is smooth and real throughout the cutoff region, while causing the horizontal wave number to vanish along the cutoff line. [Work supported by the Office of Naval Research and partially by DOD High Performance Computing facilities at NRL.]
Variation in acoustically measured abundance from repeated surveys of an isolated herring population
Authors: Huse I. , Ostrowski M.
Published: July 2002

An isolated population of herring was surveyed acoustically a total of 18 times while wintering in a fjord in northern Norway. Total abundance and variograms were computed for each survey. Three-dimensional distribution graphs are presented. The results are discussed in terms of total variation of acoustic survey estimates.
Quantification of myocardial blood flow using ultrasound-induced destruction of microbubbles administered as a constant venous infusion
Authors: Kaul Sanjiv
Published: July 2002

It was hypothesized that if microbubbles are administered as a continuous infusion, then destroying them in the myocardium and measuring their myocardial reappearance rate at steady state will provide a measure of mean myocardial microbubble velocity. Conversely, measuring their myocardial concentration will provide an assessment of microvascular cross-sectional area (CSA). Myocardial blood flow (MBF) can then be calculated from the product of the two. Accordingly, experiments were performed in 21 dogs where MBF was altered mechanically or pharmacologically in the absence or presence of coronary stenosis. Microbubbles were delivered as a constant infusion, and two-dimensional ultrasound was performed using different PI. The myocardial video intensity (VI) versus PI plots were fitted to an exponential function: y=A(1−e−βτ), where A is the plateau VI reflecting the microvascular CSA, and β reflects the rate of rise of VI and hence, microbubble velocity. Excellent correlations were found between flow and β, as well as the product of A and β. It is concluded that MBF can be quantified by destroying microbubbles with ultrasound during a venous infusion.
Targeted acoustic contrast agents: New opportunities for ultrasound in medical diagnosis and therapy
Authors: Lanza Gregory M. , Wallace Kirk D. , Trousil Rebecca L. , Miller James G. , Rose James H. , Gaffney Patrick J. , Abendschein Dana R. , Hall Christopher S. , Scott Michael J. , Lorenz Christine A. , Fuhrhop Ralph , Wickline Samuel A.
Published: July 2002

For 30 years, medical professionals have sought the ‘‘magic bullet’’ which would allow sensitive detection of disease and facilitate localized administration of potent chemotherapeutic agents without systemic toxicities. Ligand targeted ultrasonic contrast agents have the potential to improve diagnostic sensitivity, port drugs to specific pathologic tissues, and provide dosimetry of the delivered therapeutics. The authors have recently developed a ligand directed, lipid encapsulated perfluorocarbon emulsion particle (250-nm diameter). These particles, when bound to biological surfaces, strikingly increase the acoustic reflectivity, although the particles have low inherent echogenicity. Contrast enhancement of the reflectivity of blood thrombi, fibrin clots, and nitrocellulose membranes has been tentatively explained by a transmission line model. Intravenous injection of the perfluorocarbon emulsion particles has localized and acoustically enhanced remote thrombi which were otherwise difficult to detect. The contrast agent has a 1-h circulatory half-life which greatly facilitates successful systemic targeting. The small particle size of these emulsions affords access to tiny capillary beds and vascular endothelial disruptions such as those following angioplasty. Collectively, these studies suggest perfluorocarbon contrast agents can target molecular epitopes within and proximate to the systemic circulation. These agents are creating new and exciting opportunities for ultrasound in medical diagnosis and therapy.
Characterization of ultrasound-contrast agents by short-burst excitation
Authors: Kripfgans Oliver D. , Fowlkes J. Brian , Carson Paul L.
Published: July 2002

A two-frequency method has been adapted to the use of short ultrasonic bursts for the determination of bubble size. The advantage of a burst method is threefold. The overall energy transfer into the volume of interest is smaller as compared to cw. Second, it allows simple methods for improving spatial resolution. Finally, only one transducer will eventually be required in a pulse-echo mode. The experimental setup is designed to fully compensate for transducer characteristics and sample artifacts such as attenuation through window material and contrast agent solution. This leads to a constant sound pressure exposure for contrast agent in the focal volume. The data acquisition employs the frequency tracking procedure where spectra for narrow-band excition are analyzed for fundamental, second harmonic, and sidebands. A technique of nonconstant imaging frequency is used to avoid ambiguities due to coincidences between higher harmonics of the fundamental and multiples of the sideband frequencies. Measurements with shell-encapsulated microbubbles showed the behavior demonstrated by previous cw methods. Higher harmonics as well as sidebands were present due to the nonlinear dynamics of the contrast agents. [This work was supported in part by USPHS Grant Nos. RO1 DK42290 and 1RO1 HL54201.]
Low-frequency circuit noise in hearing aids
Authors: Rawool Vishakha W.
Published: July 2002

Some hearing impaired listeners complain about the circuit noise in hearing aids. This is specially true for individuals with high-frequency hearing impairments who have normal hearing in the lower frequencies. In this investigation, the equivalent input noise levels were measured in several different hearing aids: linear, wide dynamic range compression, high-level compression, programmable, and digital aids. For the linear, programmable, and digital aids the measurements were made with two types of frequency responses. One was suitable for a flat moderate hearing impairment and another for a high-frequency hearing impairment. For the linear and compression aids, the noise levels were measured by using two different volume control settings. All the measurements were made by using 11 different special purpose average frequencies ranging from 200 to 5000 Hz. The results suggest generally higher circuit noise in the lower frequencies in all the hearing aids. Changes in volume control settings showed no differences in noise levels. For the programmable aids, the flat versus high-frequency configurations yielded similar noise levels. For the linear and digital aids, the high-frequency configuration yielded higher noise levels in the lower frequencies when compared to the flat configurations.
On the intentional use of instrument characteristics in contemporary classical compositions
Authors: Hettergott Alexandra
Published: July 2002

Compositional intention is likewise subjected to the (mechanical) instruments’ sound characteristics and technical possibilities, for instance, the possibility to produce impulsive or stationary sounds, to form (pedaled) chord clusters, or to microtonally retune pitch during performance. These differing techniques may additionally allow several (intended) psychoacoustical effects, as a changing fluctuation (beatings, roughness) or pitch strength, which also have a strong impact on timbre: so in the latter case the pitches’ varying distinctiveness may be combined with a ‘‘metallic,’’ ‘‘plastic,’’ or ‘‘wooden’’ sound coloring. Consequently, in composing the decision for strings, either struck (piano, also prepared), bowed (violin, microtonally tuned), or plucked (harpsichord), for flue, reed (organ), or free-reed (mouth organ) pipes, etc., is also subjected to (a priori) intentional reflections aimed on the very (new) sound experience imagined. By means of music and score examples [W. Rihm, J. Cage, G. Scelsi, G. Ligeti, O. Messiaen, T. Hosokawa] as well as spectra and spectrograms the paper sheds some light on the composers’ sounding and purposeful use of the mechanical instruments’ possibilities in sound production in order to get (close to) the corresponding aesthetics of expression intended.
An automated apparatus for measuring sound speeds in hazardous gases
Authors: Hurly John J.
Published: July 2002

Our laboratory has developed an automated apparatus for measuring the sound speed in hazardous gases such as those used in processing semiconductors. The sound speed is deduced from measurements of the acoustic resonance frequencies of a gas-filled, cylindrical cavity. After the cavity is calibrated with argon, the uncertainty in the sound speed is less than 0.01%. The u(P,T) data span the temperature and pressure ranges 200–475 K and 100–1500 kPa. From the measured sound speeds we derive the ideal gas heat capacities from the zero-pressure intercepts with a typical uncertainty of only 0.1%. The virial equation of state is also deduced from u(P,T) providing the temperature-dependent density virial coefficients. In comparisons with Burnett measurements, we find that the densities calculated with the derived virial equation of state have uncertainties of less than 0.1% in density. Some recent measurements in SF6, CF6, and C2F6 will be used to illustrate the systems capabilities. Work in progress on BCl3 will also be discussed.
Ultrasonic methods for the on-line real-time characterization of mixing in multiphase systems
Authors: Bond Leonard J. , Matthiesen Hans
Published: July 2002

There is currently an increasing interest in developing ultrasonics to provide data that can be used for both process monitoring and control. These developments are being driven by the need to better understand the fluid dynamics and multiphase media interaction phenomena encountered. This is needed to give insights into the process and quantitative data for use in models. This paper will report results obtained through the analysis of dynamic B-scan and digital ultrasonic A-scan data, which are being used for the characterization of mixing in multiphase systems. Results obtained with a model system of sugar mixing into water, under a variety of conditions, will be presented. The insights that are given into the mixing process through the use of a B-scan system will be shown on video. The processes being used to extract data from (I) B-scan images and (II) rf (time-amplitude traces) measured with A-scan systems, to enable the implementation of a mixing index will be reported. Particular attention will focus on the issues of measurement scale and characterization of inhomogeneity. Data will be compared with theoretical model results for ultrasonic properties of homogeneous systems, in particular for suspensions, colloidal systems, and reactions including phase changes.
Water jets and a self-focusing shock pulse source
Authors: Mortimer Bruce J. P. , Skews Beric W.
Published: July 2002

The interaction of a liquid pressure pulse with a liquid–air boundary can produce surface deformation and water jet eruption if the incident pressures are high enough. This is important when analyzing damage mechanisms in lithotripsy and in our efforts to produce pulsed water jets [Mortimer and Skews, J. Acoust. Soc. Am. 100, 3548–3553 (1996)]. High-pressure pulses can be generated by either using focusing lens refraction and convergent reflectors, or using self-focusing sources. In this work experimental results using an electromagnetic shock wave source (EMAS) and a new self-focusing source (FEMAS) as discussed. A high-speed digital camera was used to study the water jet production. It was found to consist of two regions; first a high-speed initial jet and second a slower cumulative jet due to the hydrodynamic flow initiated by the source. Results for the FEMAS show a contained cumulative jet as opposed to an unstable jet observed with the EMAS. These results indicate that the device concentrates its on-axis pressure and velocity, a result confirmed by our pressure measurements. However, the operation of the FEMAS was also found to be rather complex in behavior. [Work supported by the Foundation for Research Development.]