bluuebunny/crossref_metadata_2025 huggingface dataset:
Designing piezoceramic actuators and motors
Authors: Garcia Ephraim
Published: July 2002

Piezoelectric actuators have high energy densities and are capable of producing high force, high bandwidth output. However, they lack the stroke required by many practical applications. Solid-state mechanisms have been designed that utilize flexure hinges to efficiently amplify the stroke of a piezoelectric stack element up to five times. The designs avoid the losses encountered in traditional hinge joints, which are primarily due to tolerance problems, and they minimize losses due to material strain. The mechanisms have been successfully employed in micropositioners for several different applications, including mirror positioners for wavefront compensation and proof mass actuators for vibration suppression. Piezoceramic actuators have also been employed in very high stroke mechanisms: linear and rotary motors. These motors fall into two classes, the ultrasonic motors and the quasistatic type motors. The ultrasonic motors, such as the traveling wave motor, must run at very high frequencies, usually at the resonance frequency of the stator. The quasistatic type motors, such as the inchworm motors, are able to run at low frequencies, but also can be operated at resonance to achieve higher speeds. Both inchworm motors and ultrasonic motors have been successfully demonstrated as prototype devices.
Acoustic resonance spectroscopy for the water pollution detection
Authors: Oishi Tetsuro
Published: July 2002

A resonator is investigated using acoustic resonance spectroscopy for use in sensing pollutants in water. This work was partially funded and supported by the STrategic Envirotechnology Partnership (STEP) through the Advanced Technology Center at the University of Massachusetts—Dartmouth. The transmitter and receiver are coupled externally to the wall of the cavity. The transmitter generates the sound using a swept frequency source. The receiver on the opposite side of the wall of the cavity can detect the transmitted signal. The acoustic properties of liquids such as velocity and attenuation can be calculated from the observed spectrum signal. A small amount of chemicals in water can change those acoustic properties of water. Experiments using several different kinds of chemicals are described to demonstrate the possibilities of this technique for the water pollution detection.
Relation of backward masking and frequency discrimination to reading and language among 5- to 12-year-old children
Authors: Saunders Gabrielle H. , Protopapas Athanassios , Cangiano Gaston R. , Salz Talya , Cerles Lin F.
Published: July 2002

Psychoacoustic adaptive threshold estimation procedures were implemented as ‘‘computer games’’ to measure, with no experimenter intervention, backward detection masking and frequency discrimination in 54 children aged 5–12 years. Assessments of the subjects’ pure-tone hearing thresholds (52 normal), language abilities (CELF-3; 2 below average), and reading skills (Woodcock Reading Mastery; none below average) were also made. Thresholds were successfully obtained for detection of a 20-ms 1-kHz tone followed immediately by a 300-ms bandpass (600–1400 Hz) noise masker (46 children); for frequency discrimination of 250-ms tones in the 800- to 1200-Hz range (41 children); and for discrimination of 20-ms tones at 900 and 1100 Hz, each followed by a 300-ms bandpass noise masker at an adaptively varied ISI (27 children). Success at obtaining a valid threshold was not related to the child’s age, although the frequency discrimination thresholds were. Receptive language ability was significantly correlated with backward masking; reading skills were significantly correlated with frequency discrimination. Related findings have been reported for adult poor readers [Protopapas et al., J. Acoust. Soc. Am. 102, 3188 (1997)] and specifically language impaired children [Wright et al., Nature 387, 176–178 (1997)], consistent with an auditory processing deficit hypothesis in reading and language impairments.
Estimation of far-field acoustic power radiation from vibrating plates
Authors: Rahman Khalilur , Mandal Nirmal Kumar , Uddin Wahhaj
Published: July 2002

The total average acoustic power radiation from one side of a rectangular flat plate, vibrating in its natural modes under a mixed boundary condition of one end simply supported, while the other three are fixed, has been estimated. The radiation efficiency of the plate with same end conditions has also been found for verifying the method of the present study by comparison with those established in literature. Numerical results on the acoustic power radiation by the plate have been obtained for various mode orders, aspect ratios, and thickness ratios. The characteristic beam functions developed by Warburton have been used for representing the vibration modes of the rectangular flat plate. At low mode orders, the power radiation from the plate is observed to increase with the increase of mode orders. But at the higher-mode orders, the acoustic power radiation is observed to fluctuate, maintaining nearly the same average magnitude. With further increased mode orders, the waviness is reduced gradually. The variation of acoustic power radiation for two different materials has been studied. It is observed that at low mode orders, a steel plate radiates more acoustic power than that of the plastic plate but at high mode, the reverse is true.
Transient boundary integral solution for arbitrarily shaped thin shells
Authors: Vartiainen Markku J.
Published: July 2002

The transient acoustic wave from thin, arbitrarily shaped three-dimensional surfaces is computed using the boundary integral equation method. Helmholtz’ equation of retarded potentials is discretized by spatial and temporal, quadratically varying, conforming elements. When the body interior collapses into a thin shell, the resulting equation set from the ordinary integral equation becomes underdetermined. Therefore, the normal derivative has been taken, which, due to the hard body boundary condition, cancels the self term and leads to an equation of the Fredholm second kind. In this, the potential difference between the two sides of the surface is a variable instead of the potential itself. In the presentation a collocation solution method for the equation is shown, and a numerical computation algorithm reviewed. By comparing solutions with those obtained from the ordinary retarded potential equation, the approach is shown to have good accuracy when applied to closed bodies such as a sphere and a cone-sphere. The method for thin shells is verified with frequency domain solutions for certain shapes where exact far-field solutions are available. The solutions in the frequency domain have been extracted from the transient ones by Fourier deconvolution.
Dissipation and the resolution of nonuniqueness in structural dynamics
Authors: McCoy John J.
Published: July 2002

The inverse problem of determining the causative forces acting at multiple point-ports of a structural element, based on motion data at these same ports, is nonuniquely posed at isolated critical frequencies for which the determinant of the mobility matrix vanishes. This nonuniqueness is resolved in the presence of a dissipation that removes the critical frequencies from the axis of real numbers. Demonstrated is that the resolution is achieved at the price of a prediction that is unduly sensitive to any uncertainty in the description of the dissipation mechanism. The demonstration is provided through a small parameter, asymptotic representation of the solution of the inverse problem, which obtains in the presence of a weak dissipation. This representation, which is achieved via a rescaling of the inverse problem solution, shows a unique description of the limit point result, provided the limit process is specified. The nonuniqueness that applies to the idealized formulation that one obtains for dissipation free systems is thus seen to reflect a physics of different limit processes resulting in different predictions at the limit point.
Determination of the stochasticity of the excitation function of speech
Authors: He Chuang , Zweig George
Published: July 2002

The frequency above which the excitation function of a voiced vowel becomes essentially stochastic is determined. It varies with speaker and stress. Knowledge of this transition frequency can be used to develop better spectral subtraction denoising algorithms, where different methods of spectral estimation are used above and below this frequency. In addition, whenever speech is (1) unvoiced, or voiced with constant pitch, and (2) the convolution of an excitation function with another function, a normalized variance of the spectral estimate of speech can be defined which equals the normalized variance of the spectral estimate of the excitation function. This normalized variance measures the frequency dependence of the relative strengths of the stochastic and deterministic components present in the excitation function. As expected, for voiced vowels the normalized variance is small at low frequencies, confirming that the excitation function is largely deterministic. At high frequencies the normalized variance is large and the excitation function is primarily stochastic. Therefore, voiced vowels are whispered at high frequencies. [Work supported by DOE applied mathematics program and DARPA information technology office.]
Active noise reduction for cellular and PCS handsets
Authors: Zuniga Michael A.
Published: July 2002

The effectiveness of active noise reduction (ANR) technology in Prototype cellular and PCS handsets has been investigated by developing prototype terminals with both feedback and feedforward control approaches. In contrast to ANR headsets, which present a relatively stable and favorable earpiece (i.e., receiver-error-microphone) transfer function (TF) to the ANR control system, an even greater challenge is faced in applying ANR to cellular/PCS handsets where the corresponding TF varies with positioning of the earpiece about the ear. As a first step in the investigation, a practical cellular/PCS handset earpiece, suitable for ANR, but with reduced position variability in the earpiece TF, has been developed using a lumped parameter, equivalent circuit model of the earpiece–ear system. Experimental results are presented for the new earpiece design tested against different users’ ears and against several acoustic load impedances. As the next step in the investigation, both feedback and fixed feedforward ANR control algorithms were implemented on a low-latency programmable ASIC developed specifically for ANR applications. The ANR performance results are presented for both feedback and feedforward designs tested against a range of users and also as measured against a B&K 4195 ‘‘leaky’’ coupler.
Commercial active noise control solutions for aircraft—A variety of approaches
Authors: Miller Lane , Norris Mark , Rossetti Dino
Published: July 2002

Today’s aerospace market is placing increasing emphasis on reducing noise and vibration to enhance passenger comfort. Lord offers high-performance active solutions for aircraft noise problems with its NVX active systems. There are currently over 50 Lord NVXTM Active Systems flying on a variety of aircraft around the world. These systems include active isolations sytems for the Cessna Citation X business jet, a pylon active structural control system for DC9 aircraft, and speaker-based active noise control systems for corporate turboprops. While the systems share many commonalties, they represent a variety of different approaches to the individual noise problems of these aircraft. Each of these problems requires a solution optimally designed for the application. During the presentation, the system components and general operation will be discussed. The benefits and limitations of these approaches will also be covered. How each system was optimized for its specific application will also be discussed. Numerous noise and vibration performance measurements will be presented. Further, the robustness and reliability of the various systems will be addressed.
A comparison of ANR headset performance for loopshaping and H∞ control system design
Authors: Vaudrey Michael A. , Cole Daniel G. , Saunders William R.
Published: July 2002

Active noise reduction (ANR) has been widely accepted as a critical component in circumaural hearing protectors and communication headsets for many commercial and military applications. That is because ANR headsets provide the end-user with at-ear noise suppression that is more effective than passive configurations alone can offer. In the past few years, there have been significant advances in this technology area. These are largely related to attempts to transition from traditional analog control hardware to digital implementations. One benefit of digital controller design is the ease of constructing optimal and robust compensators. The traditional approach in designing feedback ANR headsets is usually ‘‘loopshaping,’’ which is a somewhat heuristic design method. The desire for further improvements in feedback ANR headset performance is leading engineers toward more analytical approaches for controller design, including the robust techniques of H∞. This presentation compares and contrasts loopshaping and optimal controller design for the single-input, single-output disturbance rejection problem. A controls engineer experienced in loopshaping design techniques and a controls engineer experienced in optimal controller design techniques compare results for an ANR headset design. Constraints are placed on bandwidth, actuator force, and system design. It is shown that the loopshaping design can perform as good as or better than the optimal control solution for the given constraints.
Nonuniform acoustic localization: Decay of the incoherent impulse response
Authors: Smith Eric
Published: July 2002

Acoustic localization in random-scattering media is a consequence of backscatter enhancement in the regime of strong scattering. In statistically uniform, conservative media, idealized localization is predicted to lead, above a critical frequency, to eternal trapping of wave energy within the bulk, and decoupling of interior, strongly scattered wave solutions from any propagating spectrum exterior to the strong-scattering region. Small-size correlations show a diffusive transient approach to the later, stationary noise spectrum. It is shown here that strong but nonuniform scattering leads to ‘‘almost-localization,’’ producing scattered solutions that are weakly coupled to a propagating spectrum in the manner of resonances. Such states produce an exponential, rather than diffusive, decay tail in the incoherent late-time impulse response, with a time constant predicted to exhibit universal scaling with frequency for smooth nonuniformity. The predicted relation agrees well with a long-known scaling regime in earthquake-seismic coda, which has been attributed to multiple scatter. Preliminary evidence is presented for similar exponential decay in impulse reflections from saturated sand, suggesting a similar multiple-scattering origin. [Work supported by the Office of Naval Research, Code 321OA.]
Matched-field inversion for geoacoustic uncertainty distributions
Authors: Dosso Stan E.
Published: July 2002

Determining seabed geoacoustic properties from ocean acoustic field measurements represents a nonlinear, nonunique inverse problem with no direct solution. Matched-field inversion methods provide a practical approach to this problem based on searching a multidimensional parameter space for the geoacoustic model that minimizes the mismatch between measured and modeled acoustic fields. Since the parameter space can be large with many local minima, global search algorithms such as simulated annealing or genetic algorithms are typically employed. In addition to determining the single best-fit solution, these search methods have also been applied to compile a posteriori distributions of model parameters in an attempt to assess the range of acceptable solutions. However, to date, the definition of what constitutes an acceptable model has been arbitrary with no connection to the uncertainties of the data being inverted. This paper describes an inversion scheme based on sampling the parameter space to compile a distribution of models with mismatch values that are statistically consistent with the noise on the measured acoustic fields. The sampling is carried out using a highly efficient hybrid search algorithm which combines fast simulated annealing and the downhill simplex method.
Predicting the combined effect of model mismatch and noise in matched-field inversion
Authors: Kessel Ronald T.
Published: July 2002

Matched-field inversion undertakes to match the sound-field of a distant source recorded by a hydrophone array with the predictions of a computer model, the best-match model being the best estimate of the overall propagation scenario (source position and environmental parameters). However, the match is never perfect because the model is an ideal (hence mismatched) approximation of the real environment, and because background noise affects the quality of the received signal. Here it is shown how model mismatch and noise together degrade the correlation between the modeled and measured field using the Bartlett processor. Model mismatch is included by analysis of the normal modes of sound propagation, assuming the adiabatic mode approximation for weakly range-dependent media. The result is a fairly simple predictor of the Bartlett correlation expected in practice given estimates of the SNR and model mismatch—the mismatch being cast either in terms of realistic uncertainties for model parameters, or more simply by a single figure of merit quantifying the mean effect of mismatch through its influence on the modes.
Multiscale estimation of bottom properties
Authors: Rajan Subramaniam D.
Published: July 2002

In shallow water areas, the ocean bottom plays an important role in the propagation of acoustic energy. It is therefore important to be able to determine the bottom acoustic properties with adequate resolution and accuracy. Further, if the bottom model is to be capable of predicting the field over a range of frequencies, the model has to be extracted from broadband data. The possibility of obtaining the bottom properties at different scales of resolution is explored. Scaling functions derived from wavelets are used as the basis functions for estimating the bottom properties. Modal inverse method and the multifrequency data acquired during the Hudson Canyon experiment are used for this study.
High-resolution geoacoustic inversion from wide-angle seismic reflection measurements
Authors: Osler John C. , Holland Charles W.
Published: July 2002

Using wide-angle reflections from sub-bottom layers and an analytical inversion, high-resolution geoacoustic models comprised of interval velocities and layer thickness are obtained. The inversion uses the ray-parameter method of Bryan [J. Acoust. Soc. Am. 68, 1403–1408 (1980)]; the solution for a given layer is independent of the overlying layers and applicable when the water depth is less than the horizontal source–receiver offset. It has been tested using synthetically generated wide angle reflection hyperbolae and found to be robust for water depth/layer thickness ratios as high as 150, including cases with multiple layers and low velocity zones. The experimental geometry consists of a surface-towed impulsive source and a fixed receiver that is moored above the seabed. Experiments have been conducted at several shallow water sites in the Northern Tyrrhenian Sea, Malta Channel, and Gulf of Cadiz. The resulting geoacoustic models form the base from which more complicated models (including velocity gradients, densities, and attenuations) are constructed, for example, by frequency domain modeling of bottom loss data measured with the same experimental geometry. The time domain processing and analysis techniques will be discussed and inversion results will be shown along with seismic reflection profiles.
Low-frequency acoustic emissions of a plunging water jet. Part I. Experiment
Authors: Berger Thomas K. , Hahn Thomas R. , Buckingham Michael J.
Published: July 2002

Low-frequency acoustic emissions of bubble clouds entrained by a continuous fresh water jet were experimentally studied. Bubble clouds penetrating 10–20 cm deep into a 160-cm deep pool of fresh water were generated and dispersed by an impinging water stream of 1.6 mm diameter and velocities of up to 10 m/s. The sound field was recorded with small hydrophones at various positions close to the cloud as well as directly in the plume. At frequencies below 1 kHz the power spectral density exhibited a strong resonance structure. The observed resonance frequencies scale with the jet velocity as well as the air volume flux but are largely independent of the details of the air entrainment (e.g., nozzle geometry). Reference measurements in a much larger body of fresh water, a natural lake, are shown to exhibit the same resonances, indicating that wall reflections in the tank do not influence the values of the resonance frequencies. All observations are consistent with an interpretation of the bubble plume as a resonant cavity with a sound speed much smaller than in the surrounding medium.
Does eye color correlate with susceptibility to noise-induced hearing loss?
Authors: Royster Julia D. , Royster Larry H.
Published: July 2002

Several authors over the last 30 years have suggested an association between eye color and susceptibility to both temporary threshold shift (TTS) from noise and noise-induced permanent threshold shift (NIPTS). Pigmentation in the iris is related to the concentration of melanin in the stria vascularis of the cochlea. In earlier research the potential link between susceptibility and pigmentation was not firmly established or explained. More recently, investigators M.-L. Barrenas and P.-A. Hellstrom [Ear Hearing 17, 63–68 (1996)] have suggested possible physiological mechanisms for the effect. This paper summarizes the available literature and provides new data from hearing conservation program audiograms of employees in a large industrial site, compared for groups divided by gender, race, and eye color.
Susceptibility to hearing loss: Physiological, physical, behavioral and probabilistic factors
Authors: Price G. Richard
Published: July 2002

The problem of susceptibility to hearing loss is important from both scientific and legal perspectives. In developing and validating a mathematical model of the ear to predict auditory hazard [Price and Kalb, J. Acoust. Soc. Am. 100, 2674 (1996)] it has become critical to identify the sources of variance in hearing loss data. In turn, the model has provided the capacity for insight into processes that are operative. For very intense sounds, losses are virtually instantaneous and both the physical characteristics of the ear and the details of the moment matter. Physiological characteristics such as small ear canals, thick ear drums, active middle ear muscles and narrow annular ligaments promote less loss. Physical details such as the azimuth of the source and the head-related transfer function are also important. Behavioral patterns are critical too—the near-sighted risk-taker may hammer much closer to the unprotected ear than the far-sighted hearing conservationist. And last, the probabilistic details of the impulse itself can be critical. For example, gunfire impulses with the same peak pressures and durations, from the same weapon, may nevertheless differ by a factor of 5 in their predicted effect, due to the details of turbulent flow.
The effect of mean flow/source motion on sound pressure fields with absorption
Authors: Kelly Jeffrey J.
Published: July 2002

The sound field for a moving source can be described in either a source-fixed or space-fixed reference frame. Noise source modules for prediction codes are usually formulated in the source frame since this simplifies the boundary conditions associated with the acoustic field. Also, this allows consideration of a distributed source, which is important for Doppler effects. For community noise studies, noise metrics are computed in a ground based coordinate system. In principle, the problem can be formulated and a solution sought in either frame of reference. Once the problem is solved in a particular reference frame, coordinate transformations allow the pressure field to be expressed in different reference frames. In this study, the problem is formulated in a source-fixed frame. By using Fourier transforms and separation of variables, a solution is determined in the source frame. Directivity patterns are constructed for a cylindrical radiator, which show the influence of Mach number, frequency and displacement pattern on the radiated sound field. The far-field acoustic relations are transformed to emission coordinates that depict what is observed from a space-fixed (ground) reference frame. Effects of mean flow/forward flight on absorption due to viscosity are also presented.
Sound propagation over a large wedge: A comparison between the geometrical theory of diffraction and the parabolic approximation
Authors: Robertson John S.
Published: July 2002

Low-frequency propagation over wedges, hills, and barriers is an important problem with many applications. Two different propagation models are used to compare the sound field generated by a steady single-frequency source in front of, over, and behind a large, rigid, v-shaped wedge. Predictions along the boundary made with both models at several frequencies are compared and found to be in excellent agreement. The results provide additional evidence that the parabolic approximation is able to account accurately for propagation effects caused by terrain irregularities.
Spatial and temporal characteristics of acoustic Bessel Bullets by modal decomposition
Authors: Stepanishen Peter R.
Published: July 2002

Acoustic Bessel Bullets (BB) are defined to be a class of bandlimited transient localized waves which maintain their spatially dependent shape and time history as they propagate in free space. An analytical approach is presented to investigate the space-time characteristics of such wave fields which are generated from finite circular planar apertures with radially symmetric space-time noncausal source distributions. The approach is based on a modal decomposition of the space-time planar source distribution which is combined with a generalized space-time impulse response method to determine the field. Numerical results are presented to illustrate the general space-time characteristics of the modal decomposition of the source distributions, the generalized impulse responses and the associated acoustic BB fields.
Elastic wave scattering from a sphere
Authors: Sessarego Jean-Pierre , Sageloli Jean , Guillermin Régine , Überall Herbert
Published: July 2002

Theoretical and experimental studies of the scattering of compressional waves from an elastic sphere imbedded in an isotropic elastic medium have been carried out by the authors; the experiments were performed with impulsive signals. Both monostatic and bistatic scattering amplitudes were obtained. From the calculated resonances exhibited in the individual normal-mode scattering amplitudes, phase-velocity dispersion curves for the circumferential waves excited on the sphere by the scattering process were obtained. The observed scattered pulses exhibit quantitatively the propagation of these circumferential waves and of the radiation shed by them, which becomes very clearly evident in a comparison of (180 deg) monostatic, and of bistatic scattering at 90 deg. Very good agreement is found between the measured pulse shapes, and those obtained by theoretical calculations, but the main result is the verification of the circumferential-wave mechanism of scattering.
Structural acoustics and active constrained layer damping (ACLD) of an aircraft fuselage section
Authors: Herdic Peter C. , Baz Amr M. , Houston Brian H. , Marcus Martin H.
Published: July 2002

Active structural acoustic control of an aircraft fuselage section is demonstrated using active constrained layer damping (ACLD), where both interior acoustic levels and surface vibrations are reduced. The uncontrolled response of the fuselage is evaluated under several different physical forcing functions by performing dense spatially sampled broadband (10–1000 Hz) measurements of surface velocity and interior pressure. One of these forcing functions is a point force applied to the stiffener skeletal structure. This response reveals rich structural acoustics, exciting broad wave numbers and local resonances, both of which excite the interior acoustics. This case is further investigated using a finite/infinite element model of the fuselage section and the interior/exterior fluid. Twelve ACLD patches are strategically positioned on the fuselage to target control of the offending modes. Each patch is constructed of a passive viscoelastic layer and an active piezo film; these patches are lightweight and inexpensive, which makes this technique practical in-flight and attractive to commercial industry. Good performance is achieved under a point force disturbance using simple minimization control laws. Reported are the structural acoustics that are observed from these high spatially sampled measurements along with the results of the control experiments. a)Also with SFA, Inc., Landover, MD.
Parametric time-frequency estimation of prosthetic heart valve sounds
Authors: Perkins D. E. , Thomas G. H. , Clark G. A.
Published: July 2002

Prosthetic heart valves have been responsible for extending the life spans and improving the quality of life of many people with serious heart conditions. Even though the heart valves are extremely reliable, eventually they are susceptible to the long-term fatigue and structural failure effects expected for mechanical devices operating over long periods of time. In this paper the application of parametric time-frequency estimation techniques to acoustic measurement of prosthetic heart valve under test in an anechoic tank is described. The analysis reveals interesting signatures when comparing fractured to normal valve sounds. The emphasis is on the application of recursive parametric techniques to ‘‘track’’ changes in the propagating sounds as it is captured by an omnidirectional hydrophone.
Study on verifying technology of rms detector characteristics of sound level meters
Authors: Zhang Mingduo
Published: July 2002

Current standards have defined the methods to verify the rms (root-mean-square) detector characteristic of sound level meters. When using these methods, there will be a systematic error in the measuring results. The results then cannot accurately express the error in the rms detector characteristic of a sound level meter. The reason for this is that the effect of the difference between the frequency-weighting characteristics of the sound level meter to be inspected and that of the standard system is ignored. So, an erroneous judgment may be made. Aiming at this problem, this paper contains some theoretical analysis and quantitative calculation in detail. An improved verifying method is put forward.
Studies on the conversion of near-grazing underwater ultrasonic waves in a sandy seafloor
Authors: Chamuel Jacques R.
Published: July 2002

Ultrasonic modeling results are presented supporting the hypothesis given by the author [J. R. Chamuel, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, submitted Letter 10 April 1998] explaining the anomalous ultrasonic slow wave observed in water-saturated sand [N. P. Chotiros, J. Acoust. Soc. Am. 97, 199–214 (1995)] using a layered elastic model. The rapid increase of the shear wave velocity of sand with depth causes the conversion of near-grazing underwater acoustic waves into multiple coupled shear and compressional waves. Physical insight into the physical mechanisms is obtained from the refraction/conversion of broadband transient shear and compressional waves penetrating a layered solid with a low shear wave velocity. Polycarbonate/Plexiglas and wax/polycarbonate layered models were utilized. PP, PS, SP, and SS wave components were detected in the lower solid simulating the multiple features present in the anomalous acoustic sand data. In the effectively layered water/sand model, an underwater acoustic wave incident beyond the compressional wave critical angle is partially converted into a shear wave in the sand which is reconverted into a compressional wave appearing as an anomalous slow wave when detected by a buried receiver. [Work supported by ONR.]
Analysis of broadband reverberant fields in terms of time-averaged energy and intensity variables using a boundary element formulation
Authors: Bliss Donald B. , Franzoni Linda P.
Published: July 2002

In practice, reverberant sound fields often exhibit significant spatial variation in time-averaged sound pressure level and intensity. In this theory for steady-state, high-frequency, broadband, diffuse sound fields, the enclosure boundaries are replaced by a continuous distribution of broadband uncorrelated sources, each of which provides a constituent field expressed in terms of time-averaged energy and intensity variables. Superposition of these fields leads to the overall time-averaged acoustic energy and intensity as a function of position. Boundary conditions for radiating and absorbing surfaces are also recast in terms of energy and intensity variables. The use of these averaged variables, which vary slowly in space, allows direct and efficient calculation of important sound field characteristics. The approach is implemented as a boundary element formulation for efficient evaluation of the pressure and intensity fields in enclosures. Application of the method is illustrated by the solution of model problems, which are also solved by classical means for comparison. The approach is much more efficient than a full frequency-dependent calculation, but it also provides more detailed information than is available from other simple theories. An application is the analysis of moderately absorptive enclosures, such as vehicle interiors.
Propagation of sonic booms through a water fog
Authors: Xu Y.
Published: July 2002

Sonic boom propagation in a quiet, water–fog atmosphere is investigated. An evolutional equation that governs the development of sonic boom is derived. The interaction between sonic boom shock and droplet spectrum in fog (due to vaporization and liquefaction) is considered. The effect of nonlinearity, attenuation, and dispersion due to multiple relaxation and viscosity are also taken into account. A computer code is developed to solve the evolutional equation. From the numerical solutions of the equation, it is found that not only the relaxation and heat conduction increase the nonlinear distortion, but the droplet spectrum in fog greatly influences the development of sonic boom. The change of droplet spectrum affects the rise time of N wave and even causes sonic boom shock to degenerate to a series of waves.
An approach for modeling spot-welded joints in an energy finite element formulation
Authors: Zhao Xi , Vlahopoulos Nickolas , Allen Thomas
Published: July 2002

An emerging simulation technology is the energy finite element analysis (EFEA) [P. Cho, ‘‘Energy Flow Analysis of Coupled Structures,’’ Ph.D. dissertation, Purdue University, 1993; O. M. Bouthier and R. J. Bernhard, ‘‘Models of space averaged energetics of plates,’’ AIAA J. 30(3) (March 1992)]. In order for this method to be applicable to automotive structures it is important that it be suitable for modeling spot-welded joints. This work presents a development effort in computing the energy transmitted through spot-welded joints, and utilizing the information in an EFEA formulation. It is based on principles utilized for deriving coupling loss factors for statistical energy analysis (SEA) from conventional finite element models [C. Simmons, ‘‘Structure-borne sound transmission through plate junctions and estimates of SEA coupling loss factors using the finite element method,’’ J. Sound Vib. 144(2), 215–227 (1991)]. There are two components to the new development: (i) Deriving numerically information about the energy ratio between spot-welded members. (ii) Incorporating information for the energy transferred between members in the EFEA analysis. Technical information and comparison of numerical results to test data will be presented. [Work supported by Automated Analysis Corp. and Ford Motor Co.]
The acoustic generation of internal flow and rotation of levitated fluid particles
Authors: Trinh Eugene H. , Chung Sang K.
Published: July 2002

The detailed motions of levitated fluid particles in response to acoustic fields have become a topic of renewed interest because of the potential application of containerless processing techniques to a number of fundamental studies in heat or mass transfer and crystal growth. In these situations, acoustic fields are generally used to generate internal circulation to boost the transport rates, or to control the rotational motion of a levitated solution droplet. Two instances where such effects have been discovered and are being exploited will be discussed. The first case involves millimeter-size gas or vapor bubbles ultrasonically trapped in a resonant liquid cell and displaying vigorous internal circulation due to the excitation of high-frequency capillary waves at their interface. The second example deals with the drive of rotational motion of levitated droplets in ambient air and the effects of viscosity on this coupling. The results indicate that acoustic streaming flows are responsible for the generation of this controlled torque. [Work sponsored by NASA.]
Whole blood clarification in an ultrasonic standing wave
Authors: Cousins Caroline M. , Higgins Susan E. , Limaye Medha S. , Hawkes Jeremy J. , Coakley W. Terence , Holownia Peter , Price Christopher P.
Published: July 2002

There has been interest for a number of years in the possibility of separating, for transfusion proposes, blood cells from the suspending plasma in ultrasonic standing waves. On a much smaller scale, there has also been interest in separating cells and plasma so that the latter can be analyzed in single or multiple sample systems. Cells in whole blood occupy about 45% of the suspension volume. It has been shown with a number of different cell types, e.g., yeast and bacteria, that concentrations of this order are not as efficiently harvested by ultrasound as lower concentrations. Removal of cells from 2–5 ml whole blood volumes has been examined here in standing wave fields from plane or tubular transducers. The tubular transducers were driven at frequencies from 0.66 to 3.4 MHz. A range of frequencies, sonication pulsing regimes, and power levels have been established that result in cell separation efficiencies in excess of 99.5% in 5 min under conditions where cavitation has been avoided. The technique is now being applied to the blood of increasing numbers of volunteer donors to establish confidence in the ability to clarify plasma without cell damage. [Work supported by BBSRC and EU.]
Particle filtration by a combination of ultrasound standing waves and laminar flow
Authors: Hawkes Jeremy J. , Cousins Caroline , Coakley W. Terence , Keay Peter J.
Published: July 2002

Radiation forces in ultrasonic standing waves move suspended particles to half-wavelength separations, thus creating concentrated bands of particles separated by cleared medium. Continuous flow filters of one-half wavelength acoustic pathlength (0.25 mm, 3-MHz frequency) are described here in which particles concentrate on the central axis of the flow chamber. This concentration is maintained downstream in a novel laminar flow expansion section where the concentrated particles and clarified suspending phase are removed at separate outlets. The expanded downstream laminar section facilitates the engineering and positioning of efficient removal ports. Filter construction provides observation windows for monitoring of band integrity either parallel or at 90 degrees to the transducer face. The short acoustic pathlength in the present systems allows particle separations at frequencies significantly higher than previously employed in single half-wavelength systems, thus permitting exploitation of higher acoustic pressures without generating order-disrupting cavitation. Results for clarification of polystyrene latex particles, under flow conditions where particles typically spend <1 s in the field, are in excess of 98% and 70% for 9- and 1-μm-diam particles, respectively. [Work supported by BBSRC and EU.]
Single-cavitation bubble luminescence after fs-laser-induced breakdown in water
Authors: Schenke Cordt , Kurz Thomas , Lauterborn Werner
Published: July 2002

The use of ultrashort, intense laser pulses to induce an optical breakdown has both advantages and disadvantages. One of the most important advantages is the possibility to create cavitation bubbles with a much smaller size than by use of nanosecond pulses. By this, the parameter range of single cavitation bubble luminescence (SCBL) studies can be extended. The dynamics and luminescence of the created bubbles were investigated. Due to self-focusing, the initially formed plasma has a cylindrical shape, which leads to elongated cavitation bubbles. The observed dynamics of the bubbles seems to indicate the formation of two jets penetrating the bubble while collapsing. For the first time, luminescence of bubbles created this way is observed. It seems to arise from the collapse of microbubbles which are created by self-focusing in the prefocal region.
Acoustic bubble traps
Authors: Geisler Reinhard , Kurz Thomas , Lauterborn Werner
Published: July 2002

A small, oscillating bubble in a liquid can be trapped in the antinode of an acoustic standing wave field. Bubble stability is required for the study of single-bubble sonoluminescence (SBSL). The properties of the acoustic resonator are essential for the stable trapping of sonoluminescing bubbles. Its acoustic modes were measured by means of holographic interferometry and hydrophones. Flasks of different geometries (spherical, cylindrical, rectangular, ovoid) were investigated as well as different acoustic modes. Higher harmonic modes were used to trap several single, stable sonoluminescencent bubbles within one acoustic resonator (few bubble sonoluminescence, FBSL). This opens up the possibility to study bubble–bubble interactions (secondary Bjerknes forces).
Vapor cavitation zone formation in a water layer
Authors: Shreiber Isaac
Published: July 2002

This paper deals with a model for the formation of a vapor bubble cavitation zone within a water layer due to a rarefied wave propagating in the water layer. The water in the layer is close to the saturation line (subheated). Models are presented for vapor cavitation zone development, pressure field formation, and the phenomenon of coalescence. The specific feature of the cavitation is a reflected rarefied wave; the growing and floating bubbles generate the swelling of the entire bulk of water; the coalescing and floating bubbles can uplift the water layer and splash it. The gas cavitation phenomenon and a de-aeration technology are also discussed and the Epshtein model for cavitation was developed. The Epshtein model assumes that the essence of water cavitation is the solved gas diffusion into the bubble germs providing for their growth. The peculiarity of the problem is the bubbles get into a periodic acoustic wave and they grow under the rectified diffusion process activity. These large bubbles can escape the cavitating layer.
Stick–slip oscillations: Dynamics of friction and surface roughness
Authors: Bengisu M. T. , Akay Adnan
Published: July 2002

While its classical model is relatively simple, friction actually depends on both the interface properties of interacting surfaces and on the dynamics of the system containing them. At a microscopic level, the true contact area changes as the surfaces move relative to each other. Thus at a macroscopic level, total friction and normal forces are time-dependent phenomena. This paper introduces a more detailed friction model, one that explicitly considers deformation of and adhesion between surface asperities. Using probabilistic surface models for two nominally flat surfaces, the stick–slip model sums adhesive and deformative forces over all asperities. Two features distinguish this approach from more traditional analyses: (i) Roughness distributions of the two interacting surfaces are considered to be independent, (ii) Intersurface contacts occur at both asperity peaks, as in previous models, and on their slopes. Slope contacts, in particular, are important because these oblique interactions produce motion normal to the plane of sliding. Building the model begins by analyzing local friction forces as composites of resistance to elastic deformation and shear resistance arising from adhesion between asperity surfaces. By extending the expressions obtained for normal and tangential friction forces over the macroscopic surfaces, the model then describes the stick–slip behavior frequently observed in dynamic systems and permits simulating a rigid body on a moving platform. Numerical results for several surface and system parameters illustrate both time-dependent and time-averaged frictional forces. These analyses also show that, although total averaged friction remains constant with respect to sliding velocity for the cases considered, the relatively small deformation component exhibits resonancelike behavior at certain speeds. Stick–slip occurs only within a narrow range around these critical speeds of a system. External damping can prevent stick–slip motion, and both deformative and adhesive frictional forces must be present for it to occur at all.
Static friction threshold effects on hysteresis and frequency spectra in rocks
Authors: Kadish Abraham
Published: July 2002

Static friction in rocks is modeled as a threshold phenomenon. An inverse problem in ground motion is analyzed for propagation in a medium with an arbitrary number of fractures at which static friction thresholds determine the onset of slippage. It is shown that seismic source dynamics inferred from surface motion is unique. This result is used to show that the threshold property of static friction is not a mechanism for hysteresis in rocks. The coda for the surface motion is shown, in the case of a single fracture and a deep source of finite duration, to be either a periodic function in time, or to asymptote in time to such a function, depending on an algebraic relation between ground and fracture parameters. The fundamental period of the coda is independent of the source time series and is equal to four times the signal transit time between the single fracture and ground surface. Only odd harmonics of the fundamental frequency are present in a Fourier series of these periodic functions.
Analysis of acousto-ultrasonic characteristics for an isotropic thin plate
Authors: Liu T. , Liew K. M. , Kitipornchai S. , Wang G.
Published: July 2002

For the purpose of understanding and improving the acousto-ultrasonic (AU) technique, the AU characteristics for an isotropic plate is investigated in this paper. Unlike the previous wave tracing method, a spectral analysis approach is presented, which can take into account the effects of the transducers’ characteristics. Using this approach and introducing the point source/point receiver assumption, the input–output frequency spectrum relationships for the cases of one transmitter/one receiver and one transmitter/multiple receivers coupled to an isotropic thin plate are expressed in explicit forms. Based on this, a wave scattering parameter to bridge two different sensing types of the receiving transducers is presented, and a new type stress wave parameter for the AU technique is developed, which eliminates the influence of the complex mechanic-electron transduction characteristics of the receivers and also separates to some extent the effects of some other external factors such as transducer masses and locations. Finally, some numerical simulations are carried out and conclusions drawn concerning the AU technique.