bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound localization in the median sagittal plane by hearing impaired listeners
Authors: Rakerd Brad , Vander Velde Timothy J. , Hartmann William Morris
Published: October 2005

Previously, it was reported that listeners with substantial high-frequency hearing loss have difficulty localizing sounds in the median sagittal plane [Vander Velde etal., 1812(A) (1993)]. When asked to localize broadband noise, they performed near chance level on an elevation task and somewhat better, but far below normal, on a task that required that they distinguish between sources to the front, overhead, and rear. In the present study, these experiments were repeated with new subjects (n=16), and with the following variations, each introduced to encourage improved performance. (1) Low-frequency components of the noise stimulus were filtered out to preclude the masking of more informative high-frequency components. (2) The difficulty level of the elevation task was eased. (3) Subjects were tested while wearing their hearing aids. Each of these changes helped a few individuals, typically in small ways, but none produced statistically significant improvement for the group overall (p≳0.05). Together, these results point up a significant localization problem for individuals with high-frequency hearing loss of the sort that commonly accompanies aging. The results also support the theory that spectral cues are of the greatest importance for median plane localization. [Work supported by NIDCD.]
On the use of acoustical holography for the determination of intensity in structures
Authors: Romano Anthony J. , Williams Earl G. , DelVecchio Charles G.
Published: October 2005

An overview of the methods for determining structural intensity from information obtained using near-field acoustical holography (NAH) is presented. Toward these ends, a presentation of the theoretical basis and practical methodologies involved in NAH is given, as well as a brief restatement of the structural intensity formulation appropriate for thin shells and plates. A method for obtaining the unknown displacement and stress components from a knowledge of surface pressure and normal velocity is discussed, and these methods are applied to experimental data obtained for the particular cases of a point-driven, fluid-loaded rectangular plate and cylindrical shell. A movie will be presented which displays the instantaneous structural intensity corresponding to the situations previously outlined. a)Also at Sachs/Freeman Associates, Inc., 1401 McCormick Dr., Landover, MD 20785.
Broadband control of multi-mode power flow in beams using wave vector sensors
Authors: Gibbs G. P. , Bronzel M. , Fuller C. R. , Blotter J. D. , Montgomery D. E. , West R. L.
Published: October 2005

Recent work has demonstrated the use of wave filtering techniques to estimate traveling waves in the time domain. These techniques use PVDF surface mounted sensors in conjunction with a digital filter network to estimate the traveling flexural and extensional waves in beams for band-limited spectra. The traveling wave estimates are proportional to the power flow in the beam, and thus can be used as the cost function of an active control system. In this paper, experimental results are presented which demonstrate the broad band active control of flexural and extensional power flow in beams using surface mounted piezoceramic control actuators, surface mounted PVDF wave vector filters, and a TMS320C30 based adaptive controller. The results demonstrate flexural and extensional power flow attenuations of 5 to 20 dB for band-limited excitation. Independent verification of the total beam response before and after control (three dimensional) is found via a technique called experimental spatial dynamics modeling (ESDM). Velocity measurements from a scanning laser vibrometer are processed using the ESDM technique to produce a full 3-D velocity response field. These data can be further reduced using a method termed experimental spatial structural intensity (ESSI) to determine the complex intensity over the beam. Contour plots are presented showing flexural and extensional power flow in the beam for both uncontrolled and controlled cases. [Work supported by NASA Langley Research Center.]
Laser interferometry for structural acoustics
Authors: Berthelot Yves H. , Jarzynski Jacek , Kil Hyun-Gwon , Wills Lance , Yang Ming
Published: October 2005

Laser interferometry offers the possibility of measuring in real time instantaneous surface velocities in the μm/s range by noninvasive measurements. It can also be used to measure the three components of the surface vector velocity at several points simultaneously and, therefore, it is a promising way of measuring structural intensity and power flow in arbitrarily complex structures under laboratory conditions. Three different laser interferometric probes are currently being used at Georgia Tech for research in structural acoustics. The advantages and disadvantages of each system will be discussed within the context of structural intensity measurements. [Work supported by the Office of Naval Research, Code 332 SM.]
Measurement of structural intensity
Authors: Rasmussen Gunnar
Published: October 2005

The modeling of structural behavior leads to simplified models of very often complex structures. To get a better understanding of the energy flow inside and out of the structures, the development of measurement methods is very important. Dynamic movements are associated with vibratory and acoustic energy dissipation. If the surface area is large compared to an acoustic wavelength, acoustic intensity is a good indicator of dynamic activity. If the area is small compared to a wavelength at the frequencies in question, surface measurements using the vibratory motion on the structure surface may be a good indicator. By transfer of energy between structural parts, point power measurements should be applied. Measurements may be carried out using acoustical techniques for determination of structure borne energy. The acoustical transducers used must be able to measure correctly in very reactive environments. A proper calibrated intensity probe will offer a noncontact measurement of an area, which may be small or large depending on wavelength for measurement of vectors caused by dispersed waves. The use of two accelerometers or an accelerometer and a force transducer may also be useful for detection of energy flow in a structure. Acoustic calibration of intensity probes has been improved to meet standard requirements. Calibration of accelerometers and force transducers is carried out by substitution measurements against a third transducer. Measurements on structures has found many practical applications.
Numerical investigation of error mechanisms in near-field acoustic holography (NAH)
Authors: Carroll Gerard P.
Published: October 2005

Near-field acoustic holography (NAH) has been validated in precisely controlled laboratory conditions for small scale models. The practical validity of the approach in nonlaboratory settings for larger scale models, where increased background noise, inexact sensor positioning, and other environmental contaminants are likely, needs to be established. In this paper, the effect of these error mechanisms on the accuracy of cylindrical near-field acoustic holography are investigated numerically. This is accomplished using simulated hologram plane pressure data obtained from surface pressure and velocity results. The surface pressure and velocity are obtained using FEM/BEM calculations (SARA) for a ribbed cylindrical model. The simulated hologram plane data are obtained from the SARA results using a numerical implementation (Gaussian quadrature) of the Helmholtz integral. The errors in the holographic reconstructions associated with background noise, sensor placement, and other error mechanisms are revealed by comparing the holographically reconstructed results with the original SARA results. Since the ribbed cylindrical model under investigation is quite detailed, this approach is a good test of the ability of NAH to appropriately reproduce the complex surface behavior. [Work supported by ONR.]
Energy partitioning in a truss structure
Authors: Machens Kai-Ulrich , Dyer Ira
Published: October 2005

MIT is investigating both theoretically and experimentally wave propagation in truss structures. Experiments were conducted to measure energy partitioning in flexural, longitudinal, and torsional vibrations of specific truss members. The truss consists of 109 aluminum struts assembled via 35 joints to form a regular structure of 11 cells connected in series. A complete numerical analysis [Y. P. Guo, 3291(A) (1994)] finds that energy equilibria among different wave types can be expected, the ratios of which are dependent upon the distinct classes of struts making up the truss. This was tested by simultaneous measurement of the transfer functions at various locations along the axis of each strut considered. The truss was excited by broadband white noise (5-kHz baseband) at one end of the truss. Wave number processing extracts two complex wave amplitudes, each associated with traveling waves propagating in opposite directions. Thus the spectral energy content of the strut is known and is compared to others in the same class. In addition, struts of other classes are measured to discuss issues related to equipartition of energy, pass/stop bands and natural damping of complex branched structures.
On the use of quadratic boundary elements for sensitivity analyses
Authors: Cunefare Kenneth A.
Published: October 2005

The use of the acoustic boundary element method is gaining widespread acceptance. As the BEM matures, new uses for it are being developed, including its incorporation into design optimization and active noise control algorithms. The use of quadratic shape functions in the BEM formulation provides certain benefits with regard to modeling and surface representation. However, these popular elements do pose challenges when acoustic sensitivity information is desired of the formulation, such as is used in optimization and active noise control. The difficulty arises from the implications of a positive change in a nodal value (e.g., surface normal velocity), and the net change over the balance of the element. Corner nodes will yield a net negative change, while mid-side nodes will yield a net positive change, both for positive nodal change. This presentation demonstrates that the use of quadratic elements requires careful treatment as a consequence of this behavior, and that element-based, rather than node-based, sensitivities are most appropriate with this element.
Vibration studies of joints in structures
Authors: Kim S. K. , Prasad M. G.
Published: October 2005

Joints are used extensively in connected structures which are part of machine systems. Joints introduce discontinuity in structures which not only disturb the energy flow but are also possible locations of failure. Thus it is necessary to characterize the joints to determine their rigidity. A joint can be characterized in terms of the energy reflection coefficient and impedance. This study presents both analytical and experimental work on vibration characterization of joints. The analytical work is based on both classical and finite-element methods. The experimental work is based on the two sensor method for impedance measurements. The vibration behavior of a joint is studied in terms of reflection coefficient and impedance. The joints considered are bolted joints in specimen structures such as cantilever beams. Good results are obtained which supports the application of such studies in design and diagnostics of structural joints. [Work supported by Daewoo Motor Company, Seoul, Korea.]
Vibrational power flow through adhesively bonded beams
Authors: Wu Qunli , Hong Yiren , Lim M. K.
Published: October 2005

A theoretical and experimental study of power flow through adhesive lap-joint beams was carried out in this paper. The mathematical model of power flow in the beams was developed by treating the joint as a sandwich structure. The power flow analysis for different joint parameters was performed. The relationship between the joint parameters and the power flow was investigated. The power flow measurement system was calibrated in a stepped beam with known reflection coefficient of the step, and then the measurements were carried out on aluminum beams with epoxy bonded joints. The measured results agreed well with the theoretical prediction. The termination effects on the power flow measurement are discussed.
Access to phonological structure in listening to speech
Authors: Fowler Carol A.
Published: October 2005

In a direct-realist theory of speech perception, listeners are in immediate (in the sense of unmediated) contact with the phonological units of their language when they use structure in acoustic speech signals as information for its causal source—phonological gestures of the vocal tract. In the theory, phonological categories include, minimally, the sets of motor-equivalent articulatory movements producible by a synergy of the vocal-tract, each set, thereby, counting as a token of the same phonological gesture for producer/perceivers of speech. Maximally, categories include a set of similar gestures that members of a language community do not distinguish. Categories, thus, are defined gesturally, not acoustically, as for example, research on prototypes in speech have been interpreted as suggesting. Striking behaviors of listeners that index their extraction of information about phonetic gestures from the acoustic speech signal is their parsing of acoustic signals. A literature review suggests that listeners do not hear such unitary acoustic dimensions as fundamental frequency or duration as unitary. Rather, they parse each dimension into its distinct, converging gestural cause. Complementarily, listeners use as information for a phonological unit the constellation of diverse acoustic consequences of the units gestural realization. [Work supported by NICHD.]
Undoing place assimilation
Authors: Lahiri Aditi
Published: October 2005

Phonological variation in the form of different phonetic shapes of words pose a challenge for theories of speech perception and language comprehension. Postlexical phonological processes like assimilation and deletion frequently cause the phonetic shape of a word to change in a given phonological context. Such processes can easily lead to the creation of nonwords. In a sentence like ‘‘I detest green bananas,’’ the word green may well be pronounced as [grim] in the context of a following [b]. Listeners, however, apparently have no problems in parsing and identifying the word correctly in ongoing speech. How is the linguistic system organized such that it can accept the sequence [grim] as the word green? In this talk, competing theoretical accounts dealing with such variation will be presented. An account which assumes a highly abstract lexical representation will be presented. This account assumes that the central component of the linguistic system is the lexicon which contains, among other things, a dictionary of uninflected words with their phonological forms, semantic properties, and syntactic properties of various sorts. The phonological form is assumed to have a highly abstract representation on the basis of which the listener accepts or rejects phonetic variance. In addition, a recent hypothesis will be argued against that assumes an on-line process of phonological inference and an abstract representation will be presented to deal with phonetic variation. The data to support the hypothesis comes from German assimilation processes.
On the internal perceptual structure of phonological features: The [voice] distinction
Authors: Diehl Randy L. , Castleman Wendy A. , Kingston John
Published: October 2005

Apart from phonological features and their individual phonetic correlates, an intermediate level of structure apparently exists in which subsets of phonetic properties form perceptually coherent units, referred to here as ‘‘integrated perceptual properties.’’ The mapping between each successive level of structure is arguably many-to-one, elevating both redundancy and distinctiveness at the level of phonological features. For the distinctive feature [voice], a main integrated perceptual property corresponding to the [+voice] value is the presence of low-frequency energy during or near the consonant, which may be further analyzed into at least three phonetically distinct subproperties: voicing during the consonant constriction, a low F1 near the constriction, and a low F0 in the same region. Two predictions follow if these three subproperties contribute to a single integrated perceptual property. One is that the effects on [voice] judgments of varying either a low F1 or F0 should pattern in similar ways for a given utterance position and stress pattern; this prediction was confirmed. The second prediction is that two stimuli in which separate subproperties of the low-frequency property are positively correlated (i.e., they are either both present or both absent) will be more distinguishable than two stimuli in which the subproperties are negatively correlated; though not yet confirmed for the pairing of F1 with F0, this prediction was confirmed for pairings of F1 or F0 with constriction voicing.
Speech perception as a pattern recognition
Authors: Nearey Terrance M.
Published: October 2005

Phonetics involves three domains of events: (1) acoustic/auditory, (2) articulatory/gestural, and (3) symbolic/phonological. Theories of perception hold different views about the relationships among these domains. Auditorists (e.g., Kingston and Diehl) emphasize a strong (i.e., simple, direct) relation between (1) and (3). Gesturalists (e.g., Liberman and Mattingly) propose a strong relation between (2) and (3). Advocates of double-strong theory (e.g., Blumstein and Stevens) propose strong relations of both (1) and (2) to (3). Difficulties with all these theories will be discussed. An alternative, ‘‘double-weak’’ theory will be described and evidence supporting it will be presented. This approach views speech production and perception as distinct but cooperative systems. This view accepts the gesturalist contention that the acoustic mapping if phonological units is modified by context in ways that are important to perception. However, it also contends that the accommodation of contextual effects in perception is limited and highly stylized. Assuming a concomitant stylization of gestural patterns in production, relatively simple pattern-recognition strategies in perception may suffice for successful communication.
Determination of sea ice processes using geophone arrays
Authors: Stein Peter J. , Euerle Steven E.
Published: October 2005

Similar to land-based geophysics, seismoacoustic techniques are necessary to study sea ice mechanics. Most ice fracturing can only be detected via the elastic/acoustic waves which radiate. One of the best means of determining the spatially averaged mechanical properties is through probing the ice with elastic waves. Here the results are described from two separate experiments in which large (order 1-km aperture) arrays of triaxial geophones were deployed to study the sea ice mechanical properties via the elastic waves which propagate in the ice. The first test was conducted on ‘‘clean’’ first-year shore-fast ice off the coast of Resolute Bay Canada in Spring 1992. The second was a winter-over system deployed on multiyear ice during the Fall 1993 SIMI field operation in the Beaufort Sea (subsequently recovered in March 1994). Additionally, during SIMI an automated ‘‘hammer blow’’ source was deployed which impacted the ice every 7 h. Various signal processing and data analysis techniques for studying sea ice processes such as ice growth and thermal fracturing will be described. Results will be presented along with comparisons between first-year and multiyear ice. [Work supported by ONR.]
Seismo-acoustic remote sensing and inversion of sea ice fracture events
Authors: Schmidt H. , Dudko Y. , von der Heydt K. , Scheer E. K.
Published: October 2005

A new, layered seismo-acoustic remote sensing concept was developed and applied during the SIMI field experiments in the Beaufort Sea in the Fall of 1993 and the Spring of 1994. A large-aperture, 32-element, horizontal hydrophone array was used to record the acoustic emission from ice events. Using real-time array processing, maps of the seismic activity of the ice cover out to a range of 2 to 3 km were continuously generated. Once an active zone was detected, clusters of five 3-axis geophones and a single hydrophone were deployed in the active zone for near-field recording of the seismo-acoustic emission. The data were transmitted back to the main camp via a wireless local area network, and recorded on tape. During the Spring experiment data were recorded continuously on the hydrophone array for 4 weeks, and several deployments of the geophone clusters were performed in the vicinity of active ice mechanical processes such as ridge building, finger rafting, and floe fracturing. In addition, the clusters were deployed on specimens used for artificial fracturing experiments. The layered remote sensing concept is described, and examples are given of the seismo-acoustic emission produced by the different types of ice events. Finally, the matched-field fracture plane analysis of the seismic data is described.
Acoustic and seismic measurement of ice processes
Authors: Farmer David M. , Xie Yunbo
Published: October 2005

As sea ice responds to environmental forcing, it deforms leading to the storage of strain energy. When mechanical failure occurs, most of this energy is dissipated through fracturing, but a small portion radiates as seismic and acoustic waves. These waves provide useful signals for sensing the failure process in the ice. In a recent ice mechanics experiment conducted north of Prudhoe Bay (SIMI ’94), a large number of ice failure events were observed using geophone and hydrophone arrays. Preliminary results are presented, including a large-scale tensile fracture test and naturally occurring sounds near a closing lead. For the artificial fracture, the acoustic signals allow determination of cracking rate, fracture advance, and crack propagation velocities. The overall crack propagation speed is estimated to be of order 50 m s−1; maximum cracking activities occur prior to peak loading. In the second data set, the naturally occurring stick-slip process was observed as two ice sheets moved against each other in a closing lead. A wide range of frequencies can occur simultaneously representing different components of the sliding and slipping mechanisms.
A study of the evolution of under-ice fresh water layer during summer melt phase in the Arctic
Authors: Rajan Subramaniam D. , Laible Henry , Tucker Walter B.
Published: October 2005

In the Arctic, the entire snow cover and a significant part of the ice melt during the summer months. The melt water, which is at about 0 °C, reaches the underside of the ice where it overlies much colder and denser saline water and forms under-ice melt ponds. It has been suggested that these under-ice melt ponds can play a significant role in heat flux through the ice. The changes in acoustic propagation in a region very close to the bottom of the ice using data collected during a multiseason cross-hole tomography experiment conducted in the Arctic are presented. Since acoustic propagation is dependent on the properties of the medium, the changes in acoustic propagation to the changes in the characteristics of the medium are related. Further an investigation is made as to whether these changes correspond to those observed by Martin and Kauffman [J. Fluid Mech. (1974)] in a laboratory experiment conducted to study the development of under-ice melt ponds. [Work supported by ONR.]
Seismoacoustic ultrasonic modeling characterization of sea ice processes
Authors: Chamuel Jacques R.
Published: October 2005

Sea ice processes affect the elastic properties, structure, and boundaries of the ice cover, and change the composition and acoustic properties of the top water layer underneath the ice. Upward refraction in the water creates substantial interaction between underwater acoustic waves and the ice cover influencing long-range low-frequency propagation. In order to develop a basic understanding of sea ice processes, it is essential to characterize seismoacoustic phenomena associated with sea ice growth, melting, refreezing, cracking, ridging, and rafting. Controlled laboratory experiments were conducted to study diverse transient liquid/solid seismoacoustic wave phenomena. Examples from scaled ultrasonic modeling results are presented characterizing near-grazing Scholte wave backscattering from trenches at liquid/solid interfaces, effective attenuation of flexural waves from horizontal refraction, seismic profiling from 45° oblique boreholes, viscous waves in ice suspensions, variability of shear wave speed in sea ice cores, edge wave propagation along truncated and range-dependent apex angle wedges, focused multiple scattering, and finger-rafting. The findings provide physical insight into high-latitude seismoacoustic oceanography and contribute to the interpretation of Arctic field data. [Work supported by ONR.]
Ice activities during the AREA 88 experiment. II. Noise events recorded on geophones
Authors: Yang T. C.
Published: October 2005

During the AREA 88 experiment (Spring of 1988), an ice camp was deployed on an ice floe in the general neighborhood of 78 N and 55 W in the central Arctic. The ice floe became active on and off for a period of days. Many of the noise events were recorded on a planar array of geophones. The response of three-axis geophones were used to analyze the forcing mechanism of the noise events by comparing the geophone response to the ice activities with that generated by man, i.e., hammer blows. Specifically, frequency-wave-number analysis was used to sort out the longitudinal, shear, and flexural waves in the geophone data. While the examples shown here indicate that floe bumping/rubbing was the likely cause for the very-low-frequency noise signals analyzed, long-term accumulative geophone data indicate vertical forcing was the dominant source for ice generated noise.
Acoustic scattering in an elastic medium as it relates to sea ice and the determination of effective moduli
Authors: Laible Henry A. , Rajan Subramaniam D.
Published: October 2005

The scattering of sound in ice is a complex problem which depends upon the material properties of the ice as well as the frequency of the sound source. Because of the complexity of the problem, a simplified approach to acoustic wave scattering is taken. The ice is modeled as a two-phase medium in which fluid-filled cylindrical cavities (brine channels) are embedded in an attenuating elastic matrix. An analytical solution is obtained for the acoustic scattering of longitudinal waves from an infinitely long cylinder. The solution is extended for low-ka wave propagation in order to determine effective moduli (Lamé parameters and density) and effective wave speeds. An experiment is conducted in the lab to determine the scattering cross section versus angle for a single cylindrical scatterer for frequencies of 160 and 200 kHz. In addition, effective moduli are determined as a function of cavity concentration. The experimental and theoretical results are presented. [Work supported by ONR.]
Temporal evolution of compressional wave speed in sea ice
Authors: Rajan Subramaniam D.
Published: October 2005

A year-long cross-hole tomography experiment was conducted in sea ice during 1992 to 1993. The analysis of the data is presented and the variations in the compressional wave speed structure in sea ice with season are investigated and related to the changes that are predicted by thermodynamic model. [Work supported by ONR.]
Effects of absorption placement on interior noise levels—A theoretical study
Authors: Labrozzi Danielle S. , Franzoni Linda P.
Published: October 2005

The effect of the spatial distribution of absorbing surfaces on the sound field in enclosures is investigated. For a given overall level of absorption, the difference between distributing the absorption uniformly or localizing it in a single region is studied. Attention is focused on the high-frequency range having wavelengths small compared to the enclosure dimensions, but either large or small compared to the absorptive region. The distribution of mean-square pressure in a bandwidth is studied to ascertain the degree of uniformity throughout the enclosure, and particularly in the vicinity of the absorbing region. Of special interest is the effect of absorption on intensification zones, which are the regions near boundaries where there is a high degree of spatial correlation between modes. Depending upon the amount of absorption, the center frequency wavelength and/or the dimensions of the absorber are used to determine the size of nonuniform regions in the enclosure. The study is conducted using classical modal analysis. The results provide physical insight into the behavior of acoustic fields in enclosures.
Visualization of acoustic scattering in a three-dimensional enclosure
Authors: Isler Sylvia K. , Harpanahalli Vardhani , Thompson Charles
Published: October 2005

Frequently the results of time-varying computer simulations of acoustic behavior in built environments are difficult to analyze due the multidimensional nature of the numerical results. Graphical displays of acoustic data have been effective in remedying this problem. A technique for visualizing the time evolution of a sound pressure field within an enclosure due to a source located in the enclosure is presented. The numerical technique for computing the pressure distribution within the enclosure employs the method of images. Padé approximants are used to take into consideration the effects of sound scattering under high-contrast conditions. The graphical representation of the enclosure is created as follows. The walls of the enclosure and objects contained therein are rendered with the standard radiosity method. The graphical display of the interaction of the pressure field with the enclosure and its contents was accomplished by rendering each volume element in the field according to the pressure magnitude. The presentation will include a sequence of images depicting the time evolution of the pressure field in the enclosure.
Design and construction of an academic acoustics laboratory at CCNY on a limited budget
Authors: Musora Samuel , Raichel Daniel R. , Jiji Latif , Abdulla-Altaii Karim
Published: October 2005

Establishing an acoustics laboratory from the start on limited funds ($50 K) for the purpose of training engineering students constitutes a formidable task that requires careful planning and design. Cost considerations limit the size of an anechoic chamber, but fortunately a commercially ready unit was found available for the price of $15 K and with a cutoff frequency of 125 Hz. A reverberation chamber could be constructed in-house with the incorporation of a reflective door which is also available commercially. The preferred minimum room volume of 7062 ft3 results in a cut-off frequency of 125 Hz. In the selection of instrumentation, advantage was taken of the ready availability of task-specific circuit boards which can be inserted into microcomputers which can then serve as FFT analyzers and signals generators. Other equipment include a Class 1 sound level meter kit, a number of extremely low-priced SLMs, audio amplifiers, monitor speakers, measurement microphones, and an X-Y plotter. Also, the available space was reconfigured to minimize outside interference and to maximize the ease of facility usage.
Acoustic absorptivity of direct acoustic rate feedback control
Authors: Cole Daniel G. , Saunders William R.
Published: October 2005

The fixed-gain feedback methods often provide the only means of limiting transient noise and excessive sound pressures due to unmeasurable, incoherent disturbances. The use of direct acoustic rate feedback (DARFB) to control an enclosure’s reverberant energy has the benefit over other feedback methods of larger stability margins and improved stability robustness. It also provides a means for achieving acceptable sound pressure levels in locations and environments which are not suited to surface treatments of sound absorbing materials. The effect of DARFB on the growth and decay of sound in enclosures is investigated and the change in the reverberation time of a sound field is discussed for active absorption using single and multiple controllers. Various models for the dynamics of sound growth are used and are shown to provide equivalent or similar results. Effective Sabine absorption coefficients are shown for active absorption and are compared with sound absorbing materials. The effectiveness of transducer placement is also discussed with respect to active absorption and the closed-loop reverberation time. Numerical examples of acoustic absorption are given for a rectangular enclosure.
A novel active control approach for aircraft interior noise
Authors: Houston Brian H. , Marcus Martin H.
Published: October 2005

The results of numerical experiments carried out to study the broadband structural acoustics of an aircraft-like shell under point excitation have been previously reported. The dominant mechanisms that lead to the enhancement of interior acoustic levels are resonances in the structure (both in the endcap and cylinder wall) forcing high interior acoustic levels as well as structural-borne energy coupling into ‘‘rigid wall’’ cavity resonances. Wave-number domain analysis reveals the evidence of free waves on the cylinder modified by finite length effects, flexural Bloch waves, and coupling to the cavity resonances. In this paper, results are presented of active control simulations that employ novel control approaches that are wave-number-domain based. These results also show that global access to low-order interior modes is obtained through simple actuation schemes and that minimization of some of the more dominant interior modes is achieved by the application of simple constraints to the structure.
Active control of acoustic impedance with a multi-element system
Authors: Houston Brian H. , Photiadis Douglas M. , Bucaro J. A. , Corsaro Robert D. , Kraus Larry A.
Published: October 2005

The use of active control of acoustic impedance is of general interest due to a variety of potential defense and civilian applications. These include control systems to minimize aircraft and rocket payload section interior acoustic levels. Control of impedance at a boundary is one of the most challenging in active control due to the collocation of sensors and actuators (implicit in this is feedback control). Some of the technical issues include—the selection of the appropriate physical control law, the degree of inter-connectivity (local versus global control), device linearity, component and processor delays, system identification, nonminimal phase-zero constraints the coupling matrix, and performance versus robustness tradeoffs. Recently, new active boundary control (ABC) experiments were carried out at NRL’s Laboratory for Structural Acoustics on a 15-tile array system. The results of these experiments will be discussed with a focus on the application of H∞ control engineering techniques and the physics involved.
Estimating perceptual distributions for endpoint stimuli
Authors: Schouten M. E. H. , van Hessen A. J.
Published: October 2005

Rather than to assume that all stimuli on a continuum give rise to perceptual distributions that are Gaussian and equal, it is sometimes desirable to determine these distributions more directly, for example when the stimuli are speech sounds. This can be done by means of (absolute) identification or (non-numerical) magnitude estimation. A problem with such methods is that the apparent distributions obtained with them become skewed as the stimuli approach either end of the continuum. An attempt was made to recover the underlying distributions by extending the response range by three stimulus steps beyond the continuum endpoints, both for intensity and for stop consonants. The resulting distributions were fitted by means of Gaussian functions, so that a direct measure of d’ in these tasks was obtained. It is assumed that in tasks other than identification or magnitude estimation, the widths of the distributions change, but that their means are unaffected.
The equation of diffusion applied to energy density of vibrating beams
Authors: Djimadoum Myriam , Guyader Jean Louis
Published: October 2005

Inspired by precedent studies on the possibility of writing simple differential equations governing the evolution of vibratory energy density [D. J. Nefske and S. H. Sung, Trans. ASME 111, 94–100 (1989)], and equation of diffusion and its related conditions at discontinuities have been developed for an energetic quantity Ω in the case of flexural waves propagating in beams, where Ω represents the space-averaged far-field part of the displacement autospectrum, is proportional to energy density, but does not need extra time averaging. Several assumptions based on frequency and space averaging allow writing energetic conditions at discontinuities and defining a complete formalism for monodimensional problems. The procedure is applied to two coupled Euler Bernoulli beams: Ω is numerically in very good agreement with ‘‘exact’’ space and frequency-averaged far-field results and so the conditions at discontinuities are validated. Knowing that Ω allows for the ability to obtain an approximation of the energy flow in the beams and so gives an idea of how the energy propagates in the structure. These good results are encouraging, but the generalization of the procedure to plates is not trivial and requires further assumptions.
Measurement of the flexural wave power transmission and reflection coefficients of joints using wave-number domain methods
Authors: Unglenieks Robert J. , Bernhard Robert J.
Published: October 2005

Recently, a number of investigators have proposed so-called energy flow analysis techniques to allow engineers to perform high-frequency structural vibration studies of coupled structural elements. One key parameter required for this analysis is the power transmission and reflection coefficients of the joints that couple structural elements. A wave-number domain technique has been developed which uses a spatial fast Fourier transform to transform velocity data obtained in the spatial/frequency domain into the wave-number/frequency domain. The resulting wave-number domain spectrum allows estimation of energy flow segregated into right and left traveling components. Using the segregated energy flows for all of the structural elements coupled at a joint, it is possible to estimate the power transmission and reflection coefficients of the joint. A ladder frame structural system is analyzed to determine the flexural wave power transmission and reflection coefficients of ell- and tee-joints that comprise the structure. The structure is forced so that only flexural and longitudinal waves are excited. A scanning laser Doppler vibrometer is used to collect the flexural wave velocity data. The estimates of the joint coefficients are presented and compared to the analytical values for rigid joints.
Magnetic field studies of the superconducting transition in (La1−xSrx)2CuO4 single crystal by ultrasonic measurements
Authors: McKenna M. J. , Zhang Hong , Sarma Bimal K. , Levy Moises , Kimura T. , Kishio K. , Kitazawa K.
Published: October 2005

The temperature dependence of the ultrasonic attenuation and the relative sound velocity were measured in a single crystal of (La1−xSrx)2CuO4 (x=0.075, nominal) with dimensions of about 4×4×4 mm3, in a temperature range of 4.2 to 50 K. The superconducting transition of this sample measured by ac susceptibility is at 36.6 K. The frequency of longitudinal sound waves propagating along the c axis was extended up to 305 MHz. The attenuation shows two peaks, one at about 27 K and the other at around 36.7 K, while the sound velocity exhibits softenings of about 20 and 80 ppm at the corresponding temperatures, respectively. Magnetic fields of 11 KOe were applied in the a-b plane to study the effects of the field on both the temperatures and the heights of these features in attenuation and velocity. The results, combined with the frequency dependences of these features, suggest that the transition at 36.7 K may possibly be produced by both a structural transition and the superconducting transition. In addition, results on the temperature dependence of the attenuation upon cooling in magnetic fields will be presented. [Work supported by the Office of Naval Research.]
Pressure and cavitation measurements of an intra-arterial angioplasty device
Authors: Makin Inder Raj S. , Everbach E. Carr
Published: October 2005

Variation of the acoustic field radiated from a low-frequency (22.5 kHz) catheterlike angioplasty device in a relatively large (600 L) tank of water was presented earlier [I. R. S. Makin and E. C. Everbach, 2855(A) (1994)]. The normal volume of the human torso or the human limb into which the ultrasonic wire is inserted during therapy cannot be treated, however, as an infinite medium for the 66.6-mm wavelength (calculated for water) due to the wire source. Therefore the sound field of the device was investigated in a liquid-filled Plexiglasregistered cylinder (200-mm diameter, 350-mm height) to simulate anthropometric dimensions. Measurement of pressures along the axis of the cylinder for the wire source positioned axially at one end of the cylinder shows a marked standing wave pattern even up to an axial range of 250 mm. Such strong standing waves could potentially exist far away from the probe tip invivo. In addition, the occurrence of cavitation at the tip of the wire was confirmed using a 20-MHz passive cavitation detection technique.
Temperature rise generated by diagnostic ultrasound in a transcranial phantom
Authors: Wu Junru , Cubberley Frances , Gormley Gerard , Szabo Thomas L.
Published: October 2005

Temperature rises generated by diagnostic ultrasound from a commercial system (Sonos 1000 Hewlett–Packard) in a transcranial phantom that consists of human temporal bone and tissue-mimicking material are measured. Significant temperature rises were found at the external and internal temporal bone surfaces.. The experimental results are compared with Cranial Thermal Indices (TIC) developed by American Institute of Ultrasound in Medicine and National Electrical Manufacturers association in 1992 for various modes. For all the modes compared, TIC underestimated temperature rise at the external temporal bone surface. The differences between the data and temperature rises predicted by TIC can be attributed to transducer surface heating. [Work supported by Hewlett–Packard Co.]
Numerical anomalies in the Rayleigh–Ritz method for calculating the normal mode vibrations of arbitrarily shaped elastic solids
Authors: Spoor P. S. , Maynard J. D.
Published: October 2005

A matrix implementation of the Rayleigh–Ritz variational method was used by Demarest [H. H. Demarest, 768] to make the first successful calculation of the eigenfrequencies and eigenmodes of an isotropic elastic cube, and was later generalized by Ohno [I. Ohno, J. Phys. Earth 57, 355] and Visscher [W. M. Visscher etal., 2154–2162 (1991)] to apply to solids of arbitrary shape and elastic symmetry. This became the core of a new method of elastic constant determination based on measurements of the normal mode spectra of elastic parallelepipeds and spheres, called resonant ultrasound spectroscopy (RUS). In theory, one should be able to use Rayleigh–Ritz to determine the effect of imperfect parallelepipeds (due to small errors in sample preparation) on the accuracy of RUS. It has been discovered, however, that the method may not converge properly for many relevant cases, producing spurious results. A variety of examples, including comparisons with low-order approximations, will be discussed. [Work supported by NSF Grant DMR-9000549 and by the Office of Naval Research.]
Ultrasonic characterization of the quality of an epoxy resin
Authors: Faiz B. , Moudden A. , Décultot D. , Maze G.
Published: October 2005

A pulse ultrasonic technique has been developed to study the quality of the liquid/solid transformation of an epoxy resin made up of two components (resin and hardener). The epoxy resin is in a tank with parallel faces. A reflection technique allows the measurement of the phase velocity, the attenuation, and the acoustical impedance. The first and second parameters give an average state of the resin hardening in the thickness. The temporal evolution of the last parameter allows an evaluation of the state of the resin at the interface resin/tank wall. These experiments have been achieved for different proportions of the hardener. The velocity and the attenuation increase at first and then stabilize after a time which is as short as the hardener concentration is high. The experiment shows that 10% of the hardener is the optimum value and that 20% of it produces a vitreous transition. The experimental results also show that the acoustical impedance stabilizes after a time longer than the one observed for the velocity and the attenuation. The velocity and the attenuation are significant parameters of the optimum value of the hardener concentration. The acoustical impedance is the significant parameter of the bond quality.
Polarimetric fiber-optic ultrasonic sensor for the nondestructive evaluation of materials
Authors: Zhou Chonghua , Letcher Stephen V. , Narendran N.
Published: October 2005

A fiber-optic polarimetric interferometer has been used as an ultrasonic sensor in a feasibility study of flaw detection and nondestructive evaluation of materials. The sensor is based on acoustic modulation of the birefringence of a polarization-maintaining fiber. The small size of the fiber and the ability to embed it in materials provide significant advantages over conventional transducers. When the fiber and sample are both immersed in water, sample thickness and flaw location, size, and orientation have been evaluated. The fiber has also been embedded in a Plexiglas specimen and has shown the potential to locate internal flaws. [Work supported, in part, by NSF.]
Numerical investigations of double-Helmholtz resonators and duct-end effects
Authors: Mehl James B.
Published: October 2005

The acoustic fields and eigenfrequencies of double Helmholtz resonators (Greenspan viscometers) have been investigated using a boundary-integral-equation technique. The resonator geometry consists of a circular duct connected at both ends to concentric cylindrical cavities. Comparisons of the numerically determined fields with analytic expressions based on a Green’s function expansion establish the high accuracy of the method. The acoustic flow near the duct-cavity orifices has the expected singular behavior at the edge of the duct orifice. The associated duct-end inertance corresponds to a length correction of approximately 0.82 times the duct radii, slightly smaller than the classical formulas of Rayleigh and Ingard [ 1037–1061 (1953)], which are based on an assumed uniform (piston) flow within the orifice. Numerical integrations of the square of the tangential particle velocity over the walls of the duct and the cavity wall surrounding the orifice have been used to estimate the orifice resistance. This quantity was found to correspond to a resistance effective length of approximately 0.79 times the viscous penetration length, a result of importance in the modeling of Greenspan viscometers. [Work supported by the Office of Naval Research.]