bluuebunny/crossref_metadata_2025 huggingface dataset:
Active flow control using MEMS actuators to reduce fan noise
Authors: Feng Jinwei , Rao Nikhil , Burdisso Ricardo A. , Ng Wing F.
Published: July 2002

Active flow control is employed for wake filling in the upstream guide vanes of a fan stage to reduce the unsteady pressure on the downstream rotor blades. Micro-electro-mechanical systems (MEMS)-based micro- valves are used to control precisely the amount of blowing air used to energize the low velocity wake fluid coming off the trailing edge of the stationary blades. A multichannel feedback proportional-integral-and-derivative controller is used to provide the control signals to the microvalves to optimize the blowing air needed to obtain uniform wake filling along the span of the guide vanes. An experiment is conducted using a small-scale turbofan simulator in an anechoic chamber to monitor the fan noise reduction due to wake filling. The error signals used for the controller were the pressure differences between a Pitot probe placed in the freestream flow and Pitot probes placed in the wakes of the guide vanes. Results indicate noise reduction of 10 dB at the blade-passing frequency tone and 2–5 dB at the harmonics. In addition, the controller is able to track the change in flow conditions due to transients of the turbofan simulator speed, thus demonstrating the successful implementation of the active flow control to minimize fan noise. [Work supported by AFSOR and NASA.]
Revisiting analysis by synthesis
Authors: Bunnell Timothy , Eberhardt Silvio
Published: July 2002

Analysis by synthesis (AbS)—analyzing a speech signal by determining parameters for its synthesis—has been visited by investigators for several decades, but this approach has not resulted in commonly used speech acoustic analysis tools. The most prominent reasons for this are the substantial computational demands of AbS and the availability of fast analysis methods like LPC that are ‘‘good enough’’ in most cases. However, the availability of substantially more powerful, yet inexpensive, computers and the need for analysis methods that work well in all cases prompted this revisit to the use of AbS. To that end, an AbS program was developed that performs a pitch synchronous fit of formant synthesis parameters to acoustic speech signals. This program, called GASP, uses the Levenberg–Marquardt method to adjust synthesis parameters to achieve an accurate approximation to the input speech spectrum for each analysis epoch. At present, GASP fits five formants and one antiresonance along with corresponding bandwidths and two source parameters (amplitude and spectral slope). The talk will illustrate advantages and some disadvantages of the GASP approach, and describe an extension of GASP that incorporates temporal as well as spectral constraints on parameter fitting. [Work supported by Nemours Research Programs and NIH.]
Spectral analysis of esophageal speech
Authors: Lu Jinlin , Nakamura Satoshi , Shikano Kiyohiro
Published: July 2002

Esophageal speech is widely used by larynegetomized people. The purpose of this paper is to show the spectral characteristics of esophageal speech and to investigate the effect of the spectral component in the higher-frequency region from the viewpoint of speech quality. In order to obtain accurate spectral characteristics of esophageal speech which is perturbed both in period and amplitude, the STRAIGHT method [Kawahara et al., ICASSP-97, 1303–1306 (1997)] was used partly, and some other processes were added into it. The results from sustained Japanese five vowels, which were produced by seven esophageal and seven normal adult speakers, indicate that (1) spectral tilt of each of the esophageal vowels is larger than that of the normal vowels, (2) the energies in the higher-frequency region of esophageal speech are systematically larger than those of the normal speech. A paired comparison approach was used to evaluate the resynthesized speech which is obtained from a synthesizer based on an RK-source model [Klatt et al., J. Acoust. Soc. Am 87, 820–857 (1990)] and the original prosodical parameters. When the energy in the higher-frequency region was attenuated at some values, then the resynthesized speech was preferred more by the listeners.
Comparing alternate representations of acoustic properties in vowel perception
Authors: Nearey Terrance M. , Kiefte Michael , Hillenbrand James H.
Published: July 2002

Hillenbrand and Nearey [submitted; see J. Acoust. Soc. Am. 100, 2688(A) (1996)] have shown that listeners’ identification of vowels can be well predicted using a two-target, formant-based feature set. However, their analysis also suggests that other factors affect the perception of vowels in natural /hVd/ syllables. Various methods have been proposed for the representation of acoustic cues to vowel quality. This work will compare several alternate methods of characterizing short-time spectra, including cosine series [Zahorian and Jagharghi, J. Acoust. Soc. Am. 94, 1966–1982 (1993)] and Gaussian mixtures [Zolfaghari and Robinson, Proc. 4th Intl. Conf. Spoken Lang. Proc., 1229–1332 (1996)], as well as more traditional envelope-peak (formant) based analyses. Alternate methods of sampling or summarizing time-series of such parametric representations will also be explored. To what extent can other representations improve predictions of listeners’ behavior? Using cross-validation techniques, alternative methods will be evaluated on the acoustic and perceptual data of Hillenbrand et al. [J. Acoust. Soc. Am. 97, 3099–3111 (1995)] based on more than 1500 /hVd/ syllables, as well as on perceptual data for vowels resynthesized from measurements of the subset of those stimuli studied by Hillenbrand and Nearey (1996).
Coupling to SH as a loss mechanism in shallow-water acoustic propagation
Authors: Soukup Darin J. , Odom Robert I. , Park Jeffrey
Published: July 2002

Since horizontally polarized shear waves (SH) are polarized normal to the propagation and polarization direction of a bottom interacting shallow-water acoustic signal, they are generally not considered as a loss mechanism. However, most marine sediments are anisotropic to some degree as a result of the bedding process with a symmetry axis normal to the bedding planes. Particle motions of compressional (P), vertically polarized shear waves (SV), and SH waves are no longer independent. Dispersion calculations show that the quasi-P-SV and quasi-SH mode branches attract and repel as the symmetry axis is rotated. For certain ranges of the symmetry axis angle, the phase velocities of the quasi-P-SV and quasi-SH approach each other. Coupled-mode computations have been performed, which indicate that energy can be efficiently redistributed among modes with both P-SV and SH components in the bottom. The coupling is induced by range dependence in the waveguide, and energy is distributed among all propagating modes. This is in contrast to propagation in TI and isotropic bottoms for which the range-dependent mode coupling is more strongly nearest neighbor. Loss to the quasi-SH should be considered when modeling propagation in shallow water with an anisotropic bottom. [Work supported by ONR.]
Telesonar channel estimation and adaptation
Authors: Rice Joseph , Shockley Richard , Green Dale , Proakis John , Stojanovic Milica
Published: July 2002

Sound is the best form of energy for broadcasting communication signals in the ocean. However, the physical channel is impaired by nonwhite noise, frequency-selective absorption, a refractive medium, a sloping seafloor, a dynamic sea-surface, and scattering at the boundaries. Temporal variability of these influences and motion of the link terminals introduce fluctuations in the received signal and noise fields. These oceanographic and geometric factors produce measurable effects on underwater acoustic communication systems. The relevant direct measures of these channel effects include multipath spreading, Doppler shifts and spreading, coherence time, and noise statistics. Measuring and understanding these effects support optimization of both modulation and demodulation parameters. Such channel adaptation strategies enhance quality of service for the communication link. Theory, simulation, and ocean experiment illustrate link improvements. [Work funded by ONR 32, the SSC-SD Independent Research Program, and the Navy SBIR Program.]
Information theoretic/chaotic sonar signal processing
Authors: Quazi Azizul H. , Katz Richard A.
Published: July 2002

Dynamical systems generate complex signals. Very often, traditional sonar signal processing in both the time domain and frequency domain are not adequate enough to characterize the complex dynamics of underwater sources that generate, radiate and/or reflect sonar signals. Recent advances in signal processing are aimed at capitalizing on the inherent complexities in a signal structure by applying information theoretic/chaotic processing analysis tools to reveal signal dynamics, otherwise unseen when traditional (linear) signal processing methods are applied. Here examples are presented of periodicities (i.e., limit cycles), quasi-periodicites (2-torus and n-torus motion) and nonperiodic (chaotic) motion as applied to signals-of-interest in underwater acoustic applications. It is demonstrated how nonlinear diagnostic tools, when appropriately applied to underwater acoustic time series measurements, can be used for extracting new information about system dynamics.
Frequency response measurement with composed audio test signal
Authors: Maletic Mladen , Domitrovic Hrvoje , Djurek Ivan
Published: July 2002

The composed audio test signal (CATS) is formed by mixing three mutually independent composed saw signals (CSSs). The CSS sequences are a special type of pseudorandom signal. The CATS closely follows the characteristics of natural signals, and its behavior is controlled by the well-defined and configurable parameters. The amplitude probability density function of the CATS follows Gaussian distribution. Furthermore, second and third CSS sequences are generated using the perturbated parameters of the first one. Pseudorandom noise can have a spectrum and amplitude distribution similar to that of white noise. The CATS methods employ efficient cross correlation between input and output to recover the periodic impulse response (PIR) of the system being measured. The PIR can be considered as the impulse response only if the CATSs period equals or exceeds the duration of the system impulse response. The frequency response can then be found by taking the discrete Fourier transform of the impulse response. The CATS can be used as a test signal with two-channel analyzers. The averaged cross spectrum is divided by the averaged autospectrum of the input channel to obtain the frequency response.
An Internet-oriented system for acoustic measurements of sound fields
Authors: Sakurai Masatugu , Aizawa Shinichi , Ando Yoichi
Published: July 2002

A new diagnostic system was developed, based on the model of the auditory-brain system. The system, including the AD and DA converters, works on the PC for Windows, thus there is no need for special additional devices. Further, the system is available on the Internet, where a user can obtain further information about the system, and utilize it easily in practice by downloading a demonstration program. After obtaining the binaural impulse responses, four orthogonal factors, including the SPL, the initial time delay gap between the direct sound and the first reflection, the subsequent reverberation time, and the IACC are analyzed. Then, these factors may be used for the calculation of the scale values of both global and individual subjective preference. In addition, two more factors, τIACC and WIACC, in the interaural cross-correlation function are figured out for evaluating the image shift or balance of sound fields and the apparent source width (ASW), respectively. Also, the effective duration of ACF, τe, and fine structures of autocorrelation function of sound signals, including the value of first maximum, φ1, and its delay time, τ1, are analyzed. This system may be utilized for automatic control of sound fields by electroacoustic systems also.
Modification of chamber resonance through active mass control
Authors: Martin James S. , Rogers Peter H.
Published: July 2002

A traveling wave chamber was constructed for the controlled insonification of rodents in order to test the physiological effects of intense underwater low-frequency sound. In initial testing, this chamber exhibited a sharp resonance in the band of interest. This resonance was found to be dictated by the mass of the piston driver and the stiffness of the chamber’s contents. The presence of the resonance significantly reduced the operational bandwidth of the chamber. Conventional approaches to shifting the resonance out of the band of interest by directly altering piston mass and/or armature stiffness were found to be impossible. An open-loop active control system was devised which utilized piston-mounted accelerometers and summed their output with the drive signal prior to a power amplifier. Since the driver is well characterized as a force transducer, the result of this control scheme is that the piston mimics a significantly lighter structure with no reduction in the actual piston mass. The operational bandwidth of the chamber was increased with a minimum of additional hardware and negligible additional power consumption. Loop gain can be limited by stability limits imposed by the phase response of the power amplifier. This scheme may also have applications in transducer design.
Characterization of quiet areas: Subjective evaluation and sound-level indices
Authors: Botteldooren Dick B. , Decloedt Saskia , Bruyneel Jürgen
Published: July 2002

In densely populated regions, a government may decide to conserve quiet areas within reach of the average population. To characterize such areas, long-term exposure measures and typical limits have to be decided upon. Since the main goal of the silent area is to provide repose for Man, a subjective evaluation of silence may also be envisaged. In this paper, subjective evaluation of silence and sound-level measurements obtained in two related, but independent studies of open area are compared. Thorough statistical analyses lead to the conclusion that statistical noise levels with larger index (LA95 to LA50) are best suited to predict subjective silence. Critical levels are obtained. They lead to over 80% correct classification for both studies. Reported disturbance, on the other hand, seems correlated to events, but does not have a strong influence on the global rating of silence.
The application of SODAR and RASS configurations in operational meteorology
Authors: Engelbart D.
Published: July 2002

In operational meteorology, the recent improvements in scale resolution as well as physical parametrizations of numerical weather prediction models imply the demand of improvements in its measured data base, i.e., in measuring systems. Compared with the classical aerological sounding by radiosondes, supplying data of meteorological standard parameters twice per day, active remote-sensing systems like SODAR and RASS are able to increase both time resolution and vertical resolution considerably depending on system configuration. By using pure acoustical sounding a SODAR allows the derivation of vertical profiles of the 3-D wind vector, whereas integrated systems like SODAR and RASS or windprofiler and RASS are able to supply temperature profiles as well. A crucial point regarding assimilation of operationally measured data into numerical models is described by data quality. A second general point is focused on the availability of remotely sensed data. Generally, in operational meteorology acoustic remote sensing may aid in three major tasks, i.e., data supply of operational numerical models, improvement of physical parametrizations by supplying validation data and monitoring of complex parameters, e.g., boundary-layer height. As an example for model validation the presentation finally will show some results of SODAR- and RASS-derived flux profiles in comparison to high-resolution model results.
Coupled-phase model for the acoustical properties of granular materials
Authors: Attenborough Keith , Umnova Olga
Published: July 2002

The external flow approach has been used to predict acoustical properties of granular materials, assuming the constituent particles are identical and spherical. Analytical expressions for steady-state permeability, high-frequency limit of tortuosity, and characteristic viscous dimension have been derived using the Kuwabara cell model to allow for hydrodynamic interactions between the particles. Good agreement between theoretical and experimental [E. Charlaix, A. P. Kushnick, and J. P. Stokes, Phys. Rev. Lett. 61, 1595–1598 (1988)] results has been demonstrated for stacked glass beads. A new similarity relationship between complex density and compressibility has been derived. It is analogous to that obtained earlier for materials with straight cylindrical pores [M. R. Stinson and Y. Champoux, J. Acoust. Soc. Am. 91, 685–695 (1992)]. In addition to hydrodynamic interactions between particles, thermal interactions have been considered using the ‘‘mirror approximation’’ [Y. Hemar and N. Hermann, J. Phys. II France 7, 637–647 (1997)]. The characteristic impedance of the stacked glass beads layer has been calculated using this relationship and is shown to be in good agreement with measured values and the predictions of pore-based models. [Work supported by EPSRC.]
Acoustic scintillations induced by atmospheric turbulence, as imaged with a large planar vertical microphone array
Authors: Wilson D. Keith , Tate Calandra R. , Swanson David C. , Reichard Karl M.
Published: July 2002

A planar vertical array of 32 microphones (eight elements in the vertical direction, and four in the horizontal; overall dimensions approximately 6 by 3 m) was constructed on agricultural land near the Pennsylvania State University. Several data sets having 20-min duration were collected, for atmospheric states including windy daytime conditions and still nighttime conditions. The received signals due to a source 770 m distant from the array were processed to form a time-varying virtual image of the source. During the daytime, the source image undergoes dramatic scintillations and fluctuations in its apparent position. The nighttime image is quite stable, and the vertical dependence of the microphone signals suggests that the sound energy propagates as well-defined modes. Cross coherence between the microphones, as a function of vertical and horizontal separation, is also discussed.
The high-power acoustical warning systems
Authors: Somek Branko , Fajt Sinisa , Domitrovic Hrvoje
Published: July 2002

The high-power acoustical warning and informing systems are necessary for various aims. Mostly these systems work in open space, particularly in urban areas (towns, villages, river valleys). The useful coverage depends upon used transducers-emitters and installed electrical power. Almost all such systems have omnidirectional coverage, i.e., equal acoustical energy is radiated in all directions. The environmental conditions (air temperature and humidity, strength and direction of wind, etc.) and miscellaneous barriers (buildings, land configuration, trees) have an influence on the sound propagation for warning and informing systems. The other important point is that these systems are also used for spoken messages, not only for alarm. The computer simulation was done which takes all these parameters into account, and enables calculation of needed acoustical and electrical parameters.
Perceptual learning in the discrimination of interaural time differences
Authors: Kawashima Takayuki , Kashino Makio , Sato Takao
Published: July 2002

Experiments were conducted to clarify whether spatial resolution improves with practice. Four adult subjects were involved in measuring a discrimination threshold in interaural time difference (ITD) discrimination tasks. The threshold was measured using adaptive, 2-alternative, forced-choice procedure. The subjects were pretested with 500-Hz pure tones which have ±300 (plus meaning that the right channel signal leads) or 0 μs ITDs. Then two subjects were repeatedly tested for 9 days (about 80 min per day) at 300 μs ITD and the others at −300 μs ITD, with feedback to their responses. Following the practice period they were tested at ±300 and 0 μs ITDs again (post-test). At the trained ITDs, the spatial resolution improved throughout practice period, and the threshold declined from 81 to 39 μs on average between pretest and post-test. At untrained ITDs, on the other hand, the resolution did not improve between two tests. The improvement was maintained even 74 days after the post-test. These results suggest that the spatial resolution based on ITD improves with practice, and the improvement occurs locally in a certain ITD region, at least within 300 μs around the trained ITD.
Estimate of the radiated acoustical power using strain sensing
Authors: Berger Helmut
Published: July 2002

In common active structural acoustic control systems, the acoustical feedback signal is obtained from error microphones placed in the far field of the vibrating structure. Using strain sensors on the surface, the need for far-field acoustic sensors is eliminated, which is advantageous in practical applications where no microphones can be used. An estimate of the radiated acoustic power from a vibrating plate by the use of on-plate PVDF sensors is discussed. Since the number and the location of the sensors directly affect the quality of the radiation information, the influence of various sensor arrangements is investigated. For this purpose, a clamped rectangular plate is considered which is excited at four discrete frequencies in such a way that four modes contribute effectively to sound radiation. Since the vibrational behavior is well known, the required number of PVDF sensors may be reduced, which speeds up the computation of the radiated acoustic power during the adaptation process. It will be shown that the analytical results agree well with experimental data.
A new piezoelectric active noise reduction earplug
Authors: Bauer Raoul , Hamery Pascal J. F. , Lotton Pierrick , Dancer Armand L.
Published: July 2002

This paper describes the electroacoustic components of a new active noise reduction (ANR) earplug device. Compared to a helmet, an earplug offers a better passive attenuation at low frequencies. Moreover, reducing dimensions of the acoustic cavity minimizes problems of resonance and acoustic delays, and allows active attenuation at higher frequencies (up to about 2 kHz). However, the microphone and the loudspeaker which are inserted into the earplug yield specific requirements (dimensions, output pressure, ...). The microphone used is a commercially available Electret. The loudspeaker is specially designed for this application. It consists of a cylindrical piezoelectric ceramic loaded with a thin fluid air. This laterally radiating loudspeaker provides a high-volume flow compared to its dimensions. Prototypes with ceramics of different properties have been tested. A classic model of equivalent circuit based on electromechanical analogies has been adapted to describe their behavior. Theoretical and experimental frequency responses of the earplug in cavities, artificial and real ears will be presented. Lastly, several examples of simulation of the active attenuation that can be obtained with the earplug together with a numerical ANR filter designed by ISL will be mentioned. a)Also at Laboratoire d’Acoustique de l’Université du Maine, Avenue Olivier Messiaen 72085 Le Mans Cedex 9, France.
Magnetostrictive actuation and digital variable structure control for active noise and vibration cancellation
Authors: Greenough R. D. , Smith R. J. , Wilkinson A. J. , Jenner A. G.
Published: July 2002

Magnetostrictive actuators are ideally suited to active suppression of noise and vibration because of their low-frequency response, low-voltage operation, and high-load-bearing capability. In developing a system for active control, it was recognized that a strategy was important to contend with the nonlinear, hysterectic, and load-dependent behavior of the actuators. Consequently, digital variable structure control (DVSC) was selected, a method which has been successfully implemented in the laboratory and is now being employed and developed for practical applications. It has been demonstrated that with DVSC and a controller sample rate of 4 kHz, 32 dB of cancellation can be achieved at ∼5 Hz. However, recent developments have increased the sample rate to ∼8 kHz. Operation of the controller hardware with a simulated load has shown it capable of cancelling a vibration level of 0.001g2/Hz0.5 up to 150 Hz. Experiments with the uprated controller have achieved cancellation levels of 40 dB in practice. In servo mode, the controller clearly demonstrates its ability to contend with the nonlinear properties of magnetorestrictive actuators working under load. The system is presently being investigated for use in, for example, aircraft structures and industrial machines.
Does ‘‘one hundred fifty-five’’ mean 155 or 100,55 or 100,50,5?
Authors: Bickley Corine , Nord Lennart
Published: July 2002

The goal of this study is to determine what are the acoustic cues, if any, that differentiate the spoken phrase that means 155 from one that means 100,55 or others for 150,5 or 1,155 or 100,50,5. The motivation for this study comes from an issue that arose in designing a speech-user interface—that is, a user interface controlled by a user’s speech via a speech recognizer. Users of a speech-user interface for programs that require numerical input (engineering design systems, accounting packages, etc.) need to speak sequences of numbers such as 100,50,5 (for example, to specify a three-dimensional coordinate location) as well as 100,55 (for a two-dimensional coordinate location). In this study, speakers produced utterances of one-, two-, and three-number sequences in two languages: Swedish and English. These productions were analyzed acoustically in terms of fundamental frequency, syllable duration, and amplitude. Listeners identified for each production whether the speaker intended to specify one, two, or three numbers, and which numbers. The results of the acoustic analyses will be presented and discussed with respect to the listener judgments. [Work supported in part by EC-TIDE Grant No. ENABL DE 3206.]
Vowel-dependent VOT variation: An experimental study
Authors: Chang Steve S. , Ohala John J. , Hansson Gunnar , James Benjamin , Lewis Julie , Liaw Lily , Urban Margaret , Yu Alan , Van Bik Kenneth
Published: July 2002

That the VOT of voiceless stops is typically longer before high, close vowels and shorter before low, open ones is well documented. The hypothesis was tested that high vowels engender longer VOT because they offer greater resistance to the air escaping from the mouth (thereby delaying the transglottal pressure differential required for voicing). A correlation was sought between oral pressure decay (OPD) and VOT. Acoustic and aerodynamic data were collected from a male native speaker of American English uttering 12 nonsense words of the type atí, atà in isolation ten times. Pressure data was sampled by inserting a tube into the subject’s pharyngeal cavity via the nose. The VOT was measured from the release of the burst to the onset of the first periodic cycle. The OPD was defined as the time required for oral pressure to decrease from the peak to a fixed low threshold. The OPD and VOT measurements displayed a significant, linear correlation, indicating that VOT and vowel height are indeed mechanically linked. Moreover, tokens with voiceless stops preceding sonorants, e.g., atwà, akjà, yielded the longest VOTs since sonorants have narrower constrictions, resulting in longer OPDs.
Speaking rate effects on vowel identification in natural sentence contexts
Authors: Berman Adam M. , Neville Jonathan S. , Gottfried Terry L.
Published: July 2002

Previous research [T. L. Gottfried, J. L. Miller, and P. E. Payton, Phonetica 47, 155–172 (1990)] has indicated for synthetic speech that vowel identification changes according to the speaking rate of the sentence context, even when the vowel contrast is specified experimentally only by spectral differences. This study tests listeners’ identification of /i/ vs /I / in stimulus continua created by altering formant values and durations of the target syllables ‘‘beat’’ and ‘‘bit’’ in naturally produced sentences. These targets were spoken in two sentence frames, one spoken at a moderate rate of speech and the other compressed to twice the speaking rate. Longer syllable durations significantly shifted the boundary of the spectral continuum, so that there were more ‘‘beat’’ responses as compared to shorter durations. However, unlike what was found for synthetic vowel series, there was no significant effect of sentence rate on the number of ‘‘beat’’ responses. Reasons for this different outcome, and the relevance of these findings for theories of rate normalization, are discussed. [Work supported by Lawrence University Faculty Grant.]
Cavitation bubbles’ motions under ultrasound
Authors: Laborde Jean-Luc
Published: July 2002

Propagation of power ultrasound (from 20 to 800 kHz) through a liquid initiates acoustic cavitation. Inceptions and germs grow into bubbles which collapse, possibly giving rise to extreme conditions of temperature and pressure (assessed to be up to 10 000 K and 500 atm). For instance, these conditions greatly enhance chemical reactions. A high-speed film shot at 500 fps clearly identifies stable and transient cavitation and shows bubble population phenomena. Clouds of bubbles grow up to ten times their emergence size during 15 ms, and move at velocity around 50 cm/s. Mathematical modeling is performed as a new approach to predict where active bubbles are and how intense cavitation is. A calculation based on fluid dynamics equations is undertaken, as CFD codes have shown great interest because they provide not only the pressure field but also velocity and temperature fields. Two phase flows (liquid-bubbles) could be modeled. Nonlinearities arising from the dissipation of the acoustic wave are computed and lead to the calculation of the acoustic streaming. This result gives a better knowledge of bubbles’ behavior. The comparison with photographs, a high-speed film, and particle image velocity show good agreement with simulations.
The ubiquitous FLEXBARTM transducer element for low-frequency, broadband high-power sonar projector arrays
Authors: Fitzgerald James W.
Published: July 2002

The piezoceramic FLEXBARTM, a modified free-free flexure bar, is a sonar projector element of extraordinary versatility and superior performance. It represents a cost-effective, mature transducer technology that is uniquely suitable for projectors of virtually any configuration; viz., planar, cylindrical, spherical, or conformal. Piezoceramic FLEXBARTM projectors have been designed to operate at frequencies from ∼250 Hz to ∼5 kHz, with source levels and beam patterns only constrained by the available power and the allowable array envelope. In conjunction with pressure-equalizing oil-filled internal cavities, FLEXBARTM projectors are operational to essentially any depth. For example, REFLEXDUCERTM model RFD-420/A, a cylindrical array comprised of 32 FLEXBARTMs, and incorporated into a housing 20 cm D×40 cm H, has the following performance characteristics: resonant frequency to f0≂2000 Hz; quality factor Qm≂3; bandwidth B/W≂670 Hz (−3 dB); source level SL≂210 dB//μPa/m; electric power in Pwr(e)≂12 500 W; acoustic power out Pwr(a)≂8125; electro-acoustic efficiency ηea≂65%. The unit, including an internal 1:5 step-up transformer with a tuned secondary, weights approximately 66 kg so that its effective acoustic power-to-weight ratio is ≂120 W/kg (≂55 W/lb). A conformal submarine-sail design is shown covering a bandwidth of 1–5 kHz at a source level of SL≂245 dB//μPa/m, with steerable midband vertical beam patterns of θv≂10 degrees (−3 dB) and steerable horizontal patterns of θh≂5 degrees (−3 dB).
Comparing two different principles of parametric F0 modeling
Authors: Möhler Gregor
Published: July 2002

A number of data-based approaches to intonation modeling represent F0 movements using continuous parameters [P. Taylor, Proc. ESCA/IEEE Workshop on Speech Synthesis, Monhonk, NY (1994), pp. 175–178; G. Möhler, Ph.D. Thesis, University of Stuttgart, Stuttgart, Germany, 1998]. This is contradictory to most intonation theories, which suggest that intonation can be modeled with a set of distinct phonological entities that are phonetically realized as F0 movements (e.g., J. Pierrehumbert, Ph.D. Thesis, MIT, Cambridge, MA, 1980). This principle has rarely been incorporated into data-based intonation modeling. In this study two data-based intonation models are compared following the two principles described above. The models are trained on the male speaker of the German news corpus. The first approach uses an F0 parametrization with six continuous parametric intonation event (PaIntE) parameters. These parameters are derived by approximating the F0 curve with an appropriate model function. In the second model, a vector quantization (VQ) is applied to the PaIntE parametrization, resulting in a number of distinct F0 shapes. CART trees are used for predicting both the PaIntE parameters and the VQ code words from a set of features derived from the respective utterance. The intonation quality was assessed and it was found that the VQ model has advantages over the PaIntE model, because the curve as a whole can be predicted, rather than individual parameters. Furthermore, phonetic analysis can be based on the basic shapes represented in the code book.
Love waves in nonclassical micropolar piezoelectricity
Authors: Vieru Dumitru , Ciumasu Silvia G.
Published: July 2002

The basic equations of the linear theory of the micropolar piezoelectricity with polarization gradient have been derived in the paper ‘‘Polarization gradient in micropolar piezoelectricity,’’ presented at IMSE’98, 10–13 August 1998, Michigan Tech, Houghton, MI. In the case of the two-dimensional problem, the fundamental system of differential equations is split up into two independent systems. The second type of the two-dimensional problem is considered. In this paper, electromechanicallycoupled Love waves are studied in the case of propagation along an isotropic, micropolar, dielectric layer attached to an isotropic, purely micropolar half-space.
Ultrasonic waves birefringence in wood-based composite panels
Authors: Bucur Voichita , Garros Simone
Published: July 2002

The aim of this research is to study the ultrasonic waves birefringence in three wood-based composite panels, chipboards, oriented strandboards, and medium-density fiberboards, for the characterization of their global elastic and structural properties. Shear waves of 1 MHz were used to study the ultrasonic birefringence and to determine the shear terms of the stiffness matrix. As a complement for anisotropic behavior panel study, longitudinal waves of the same frequency were used to determine the corresponding terms of the stiffness matrix. Shear wave birefringence is the highest in the transversal anisotropic plane of the panels. Textural anisotropy was observed at the scale of the skin and core. Data related to the local characterization of the skin and core of the panels by x-ray microdensitometric technique revealed that, generally, the profile of the panel is symmetric and the skin density is higher than the core density. The nondestructive estimation of the birefringence of ultrasonic waves is a useful tool for further evaluation of panel performance related to their structural integrity and bond performance.
Surface acoustic wave sensors for the detection of gases and for biological applications
Authors: von Schikfus Manfred
Published: July 2002

The presence of organic or inorganic chemical species can be detected by their reaction with a suitable reagent. In acoustic sensors where the sensor reagent is immobilized on the device, the associated mass increase is detected by a change of the propagation characteristics of an acoustic wave. Acoustic surface wave (SAW) devices promise an advantage over the commonly used quartz oscillators because of their inherent higher sensitivity associated with their high operating frequency of up to several hundred MHz. Until now SAW devices have not found widespread application, mainly because of handling difficulties associated with the necessity to mount these devices on sockets and to connect them electrically with bonding wires. In this contribution, techniques will be presented to overcome problems associated with the operation of SAW sensors in aggressive liquids or in gases at elevated temperatures. A new type of SAW device has been developed in which no ohmic electrical contacts are required. Instead, electrical connection between the device and the electronic circuitry is achieved by inductive coupling. In this way, operation and preparation of the devices is considerably eased. Data will be presented on immunosensing in buffer solutions, and on gas sensing at temperatures up to 500 °C.
Broadband 3-D high spatial density structural response measurements of a pair of framed air-loaded cylinders of differing internal complexity
Authors: Vignola Joseph F. , Photiadis Douglas M. , Houston Brian H.
Published: July 2002

The presence of internal structure can greatly alter the acoustic behavior of elastic structures. The effect of a large number of internal oscillators on the vibrational response of an air-loaded framed cylindrical shell has been examined experimentally. This examination included the construction of two shells of the same design, one of which has 880 attached oscillators. Spatially dense (200 axial points by 80 azimuthal =16 000 points) 3-D laser Doppler vibrometer measurements have been collected for both of these structures for the case of broadband radial point excitation. Comparisons made between these two visually identical structures reveal dramatic differences. These include a modification of the participation factors between the three displacement polarizations and strong spatial confinement of the vibration response due to complexity. These results are presented together with a discussion of mechanisms which may account for these observations. [Work sponsored by ONR.]
Test of various sound transducer systems for the use in ANC-systems and several applications of the ANC-system NANCY®
Authors: St. Deus Dr. , Schatz W.
Published: July 2002

With the introduction of ANC technologies, sound transducers have been increasingly applied in industrial fields. as well. In most cases, sound generators are set up through loudspeaker systems known from audio applications. Thus they are constructed to satisfy requirements of volume and quality (frequency response, distortion factor) while playing speech and music. This is different than applications of ANC systems in industrial environments. The following features are mainly required: (1) production of high sound pressure, especially for low frequencies (down to 30 Hz and less); (2) resistance against high temperatures (up to 700 °C) and aggressive environments (high environment pressure or vacuum); (3) compact design; (4) long operating life (min. 1 year); and (5) directional effect (preferably unidirectional, sound downward). Currently, criteria as above are increasingly determining further developments of sound transducer systems. With respect to that, various sound transducer systems were tested in a lab channel with the ANC system NANCY®. The results are stated here. In addition several examples of use of the ANC system NANCY® are presented.
Strategy policy of ISO/TC43 ‘‘Acoustics’’
Authors: Brinkmann Klaus
Published: July 2002

The scope of ISO Technical Committee 43 ‘‘Acoustics,’’ together with its Subcommittees ‘‘Noise’’ and ‘‘Building Acoustics’’ comprises standardization in the whole field of acoustics, i.e., the measurement of sound, its generation, transmission, and reception as well as its effects on Man and the environment. Close liaison is maintained with related international and regional standardization committees, especially IEC/TC 29, which is responsible for electroacoustic standards. ISO standards elaborated by TC 43 are equally addressed to a variety of parties, such as industry, regulatory authorities, trade and consumer groups, research institutes, testing laboratories and consulting engineers, health and safety inspectors, audiologists, and communication experts. Representatives of these groups from 24 different countries contribute actively to its work. More than 120 standards have been published so far and the present program of work includes nearly 80 projects for new or revised standards. In the past few years, major emphasis was laid on the measurement of machinery noise and the measurement and rating of sound insulation in buildings and of building products, both in the context of recent regional legislation. Fields like environmental noise, transport noise, noise prediction, and simplified measurement methods for building acoustics are considered to be future priority areas.
A generalized modal impulse response and Fourier transform approach to investigate acoustic transient Bessel beams and Bessel bullets
Authors: Stepanishen Peter R.
Published: July 2002

A generalized modal space–time impulse response and Fourier transform approach is developed to investigate the general properties of transient Bessel beam (TBB) fields which are generated using planar circular apertures. The approach is based on a modal decomposition of the aperture source distributions which are required to generate the space–time TBB fields. Numerical results are presented to illustrate the general space–time properties of the modal impulse responses and the modal source functions. The on-axis far field for the finite aperture is shown to be simply related to the lowest order term in the modal expansion. The space–time properties of the acoustic field for a particular type of band-limited TBB field which is designated as an acoustic Bessel bullet (BB) are then investigated. Some numerical results are presented to illustrate the space–time properties of acoustic BB fields generated from an infinite aperture. Analogous on-axis harmonic results from a finite aperture are presented. These latter results clearly indicate that the higher-order modes exhibit spatial rates of decay which are greater than the inverse range decay for the lowest order mode.
Acoustic-impulse spectroscopy in Cu–Zn alloys
Authors: Hsu Rebekah Min-Fang , Wur Ching-Shuei , Jan Chang-Shew
Published: July 2002

An electro-optical design was developed as the impulse spectrometer to identify the composition of the binary Cu–Zn alloys. The acoustic emission (AE) of Cu–Zn alloys was investigated using the Michelson interferometer as the detector. AE signals were detected from the impulse method with a one-dimensional simplified model. It is reported that the Cu component percentage in the family of the Cu–Zn alloys could be related to the bandwidth of frequency spectrum. Therefore, their composition can be recognized by observing the AE information in dynamics.
On the lowest radial frequencies of a rigid-walled narrow toroidal duct
Authors: Gottlieb H. P. W.
Published: July 2002

For a rigid-walled toroidal duct of rectangular cross section, narrow in the radial direction, the lowest radial characteristic frequency approximation appears to form a sequence proportional to the angular wave number integer [C. C. Lawrenson, L. D. Lafleur, and F. D. Shields, “The solution for the propagation of sound in a toroidal waveguide with driven walls (the acoustitron),” J. Acoust. Soc. Am. 103, 1253–1260 (1998)]. By use of properties of Bessel functions, a more accurate higher-order formula for these frequencies is presented which, moreover, shows that there is, in fact, some deviation from the strict harmonicity.
Analysis, testing, and control of a reverberant sound field within the fuselage of a business jet
Authors: Clark Robert L. , Gibbs Gary P.
Published: July 2002

The objective of this project was to develop a speaker-based active control system capable of dissipating reverberant acoustic energy within the fuselage of a typical business jet aircraft. A ground-based fuselage was utilized as the test-bed for the work conducted in this project. Typical aircraft fuselage trim was installed to more accurately reflect the acoustic properties of a flight-ready aircraft. Speaker locations were selected based upon the acoustic modal characteristics of the fuselage and practical considerations concerning available space in the walls of the trim. Preliminary control experiments involving single-input, single-output, feedback loops resulted in a very localized zone of quiet which yielded no global effects. Multi-input, multi-output feedback control with a distributed array of eight pairs of transducers weighted (spatially) to emphasize energy dissipation of select acoustic modes resulted in as much as 6 dB of global attenuation at acoustic resonances corresponding to the second and third acoustic modes (46 and 71 Hz, respectively) of the enclosure. While objective results were very promising, subjective evaluation of the enclosure resulted in an inaudible difference in the sound field before and after closing the loop on the control system.
Studies of acousto-electrically levitated drop and particle clusters and arrays
Authors: Apfel Robert E. , Zheng Yibing , Tian Yuren
Published: July 2002

Research into the behavior of clusters and arrays of fluid or solid particles is made possible by acousto-electric levitation in air and charging of “seed” droplets (10–30 μm in diameter) which come together in 2-D clusters (with up to 300 droplets). Such clusters condense into larger drops (e.g., 50–300 μm) which form uniformly spaced 2-D arrays of monodispersed drops. Similar behavior has been observed for charged solid particles. This research has applications to studies of drop evaporation, combustion, nucleation, and materials synthesis.
The role of F1 in the perception of voice onset time and voice offset time
Authors: Pind Jörgen
Published: July 2002

An important speech cue is that of voice onset time (VOT), a cue for the perception of voicing and aspiration in word-initial stops. Preaspiration, an [h]-like sound between a vowel and the following stop, can be cued by voice offset time, a cue which in most respects mirrors VOT. In Icelandic VOffT is much more sensitive to the duration of the preceding vowel than is VOT to the duration of the following vowel. This has been explained by noting that preaspiration can only follow a phonemically short vowel. Lengthening of the vowel, either by changing its duration or by moving the spectrum towards that appropriate for a long vowel, will thus demand a longer VOffT to cue preaspiration. An experiment is reported showing that this greater effect that vowel quantity has on the perception of VOffT than on the perception of VOT cannot be explained by the effect of F1 frequency at vowel offset.