bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of ultrasonic exposure fields
Authors: Christman C. L. , Stratmeyer M. E.
Published: October 2005

Acoustic field parameters were measured and calculated for an automatic-scan ultrasonic exposure apparatus designed for biological effects studies that has been previously reported. Free far-field pressure profiles of disk transducers resonant at 1.0 MHz were obtained under conditions using a hydrophone calibrated by a pendulum consisting of a stainless steel sphere on a bifilar suspension. Typical total acoustic power measurements using a radiation force balance technique agreed within ±10% of the integrated intensity profiles. An efficient computer program was used to calculate the pressure distribution for a baffled piston by means of an existing Fourier transform approach. These theoretical intensity profiles agreed well with the actual data. Several scans directly behind holders used to expose both biological solutions and cell suspensions showed disruption of the normal free-field pattern. Scans also demonstrated differences in the acoustic coupling to mice for various preparation methods prior to ultrasound exposure.
Suppression of ambient noise in bone-conduction microphones for speech communication
Authors: Sebesta G. J. , Hofer A. , Carlisle R. W.
Published: October 2005

A microphone sensitive to vibrations of the head is useful in applications where it is necessary to leave the face of the user unencumbered. Such a transducer operates on the inertia principle, with the inner and outer surfaces operating in phase. It has some sensitivity as an air-conduction microphone, and when used in free space it has a figure-eight response pattern. To suppress airborne noise and to leave it sensitive exclusively to bone-conduction vibrations impinging on the inner surface, it is necessary to convert the transducer into a cardioid-type device. The inner surface is to be sensitive to vibrations, and airborne sound is to be neutralized as much as possible. In a microphone described in this paper, the transducer is suspended by a highly compliant member in a housing which attenuates airborne sound, with optimum exclusion of high frequencies. Low-frequency airborne sound is neutralized by impressing it equally upon the inner and outer surfaces of the transducer. The over-all suppression of noise permits good speech transmission in a noise field up to 85 dB. By the use of an outer acoustic enclosure this has been experimentally increased to 115 dB.
Some recent developments in audio teleconferencing technology
Authors: Kumar A. , Arndt H. , Botros R.
Published: October 2005

The recent concern about energy resources and conservation has generated new interest in the area of teleconferencing. Audio teleconferencing has been found to satisfy most of the needs of the conferees in accomplishing various tasks. The various acoustic, hardware, and general system dimensions and their relation to the user involved in the act of audio teleconferencing are discussed in this paper. The results of the effort directed towards the determination of the acoustic characteristics of the conference room environment and assessment of the suitability to audio teleconferencing are presented. The initial attempts at the design of a portable, free-standing audio conferencing terminal as well as the study of the interaction between the system and the participants are detailed. The need for integrated research that addresses itself to the problem in the areas of acoustic environment, quality of audio signal transmitted and reproduced, and the various means of conference augmentation is emphasized. The future plans of research in this area are outlined and some preliminary results are discussed.
Low-frequency pressure-gradient sensor
Authors: Mongiovi M. P.
Published: October 2005

An acoustic sensor for use in an underwater environment with possible deep sea applications is described. It is suitable for the detection of low-frequency signals in the 10–1000-Hz range. Its directional characteristics yield a voltage response proportional to the cosine of the angle of the incident acoustic signal. An analytical model was developed to calculate the receiving response of the sensor. Several sensors differing in material and physical dimensions were constructed and tested while encapsulated in a number of different materials. These tests included receiving responses, directivity patterns, acceleration, and phase responses. Actual receiving responses were compared then with the responses predicted by the analytical model. Reasonable agreement between the two was found.
Performance of small arrays of flexural disk transducers
Authors: Walker W. F.
Published: October 2005

Trilaminar disk elements of small aperture (a = 34 mm) have been used in compact four- and six-element arrays for 2.4-kHz resonant frequency projectors with improved performance over single balanced pair (two-element) projectors of larger (a = 54 mm) elemental aperture. Several configurations of these arrays have been tested, and the results are compared to predicted values and to the larger two-element transducer. Benefits in performance are gained by improved radiation resistance and reduced radiation mass through array interaction and by the simultaneous reduction of the mechanical mass of the elements. Furthermore, the electrical impedance is reduced by the increased electrical capacity of the total array. An omnidirectional array with no dimension of the structure exceeding 110 mm performs untuned with a source level (Ss) of 141.0 dB re 1 μPa when normalized to 1 m and 1 V. The mechanical quality factor is 3.0 (untuned), and the electroacoustic efficiency is about 0.7. When series tuned, these arrays have shown bandwidths greater than 1500 Hz between −3 dB points.
Operation of a condenser microphone as the terminal element of a half-wavelength transmission line in an AM carrier system
Authors: Zuckerwar Allan J.
Published: October 2005

In some applications a condenser microphone, situated in a hostile (e.g., high-temperature) environment, must be separated from its supporting electronics by means of a relatively long cable. Operating the cable as a half-wavelength transmission line serves to annul the effects of cable capacitance but leads to a substantial reduction in system sensitivity. Several cables, approximately 25 ft long and ranging in characteristic impedance from 50–300 Ω, have been tested in a prototype AM carrier system. The carrier frequency was adjusted to tune the system within the interval 7 to 50 MHz, corresponding to one-half wavelength up to three full wavelengths along the line. It was found that a high characteristic impedance, as well as low cable losses, is essential to minimize the attenuation due to the cable. In the best case the reduction in sensitivity due to cable losses was limited to 15 dB. [Supported by NASA.]
Modeling surface-acoustic-wave electromagnetic transducers
Authors: Szabo T. L. , Sethares J. C. , Frost H. M.
Published: October 2005

An equivalent-circuit model for noncontact surface-wave electromagnetic Lorentz-force transducers has been developed from expressions describing the dynamic magnetic fields surrounding a transducer meander array of conductors. Both electrical and acoustical properties of the transducer are included in the model and agree well with experimental measurements. Simple shunt capacitive matching improved the double transduction efficiency by 13 dB for a pair of transducers fabricated from multiconductor flat cable whereas series matching had a negligible effect. Included in the model is a new loss term, the eddy-current resistance, that depends both on the gap between the transducer and metal sample and the conductivity of the sample. The excellent reproducibility and predictable frequency response characteristics of these devices should prove useful especially in nondestructive evaluation applications.
Model study of a Doppler wind monitor receiver bunker
Authors: Finch R. D. , Nagarkar B. N.
Published: October 2005

The receiver of an acoustic doppler wind measurement system has been modelled to study beam patterns at various angles of inclination of the scattered signal. The system studied was a parabolic reflector with off-axis focusing action. The model was constructed to be one-tenth full scale. It was demonstrated that the receiving beam could be steered in both the vertical and transverse directions by placing microphones at various focal positions. Positioning of the bunker side walls did not appear to be critical. The earthworks around the full-sized emplacement appeared to have no significant effect on the beam pattern. It is also demonstrated that some acoustical lining on the walls of the bunker is essential, and various configurations of treatment were studied. [Work supported by NOAA and FAA.]
Acoustic shadowing of ground-level microphones during static jet-engine acoustic tests
Authors: Walker David Q.
Published: October 2005

For ground run-up acoustic testing of jet aircraft engines, microphones may be located close to the ground level to eliminate the acoustic interference effects at the far-field microphones caused by the presence of the reflecting ground plane. However, microphones in this position are particularly sensitive to acoustic shadowing caused by wind and temperature gradients in the acoustic test arena. Examples of acoustic and meteorological data taken during full-scale engine tests, together with acoustic ray-tracing analyses, are used to describe the sensitivity of the ground-level microphones to acoustic shadowing. In addition, the permissible meteorological conditions for the successful application of the ground-level measurement technique are defined as a function of source to receiver distance. [Work supported by NASA Lewis Research Center under Contract NAS3-15570 with the Boeing Commercial Airplane Company.]
Criteria for building-equipment noise control
Authors: Cavanaugh W. I.
Published: October 2005

The cost and complexity of building equipment has progressively increased as more sophisticated techniques for controlling the thermal and general architectural environment evolve. An unavoidable byproduct of most systems for moving and conditioning air, or for moving people (elevators) etc., is noise. While initially building occupants accepted sometimes uncomfortably high noise levels as a necessary evil that went with a new convenience, an almost universal attitude toward quiet operation of building equipment has arrived. Decisions on how much quieting, and by whom, ultimately involve the goals or criteria for acceptable noise levels. Acceptable limits vary with the activities in the usually diverse spaces involved. This paper reviews experience with the selection and application of criteria for building equipment noise. The NC (and more recently PNC) noise criteria curves introduced by Beranek in 1957 are widely used for acoustical performance specifications, particularly for generally steady noises. While “quiet” operation is always the objective, “silent” operation of some building equipment systems may result in a condition as objectionable as excessively high noise levels. Some case histories of building equipment noise are reviewed to illustrate how criteria have been applied and assessed toward satisfying typical building occupants.
Prediction of aircraft interior noise
Authors: Howlett James T. , Morales David A.
Published: October 2005

At the present time, predictions of aircraft interior noise depend heavily on empirical correction factors derived from previous flight measurements. However, to design for acceptable interior noise levels and to optimize acoustic treatments, analytical techniques which do not depend on empirical data are needed. This paper describes a research program which involves evaluating current interior-noise prediction methods, conducting basic research on noise transmission through aircraft structure and structural panels, and incorporating the latest improvements in noise prediction techniques into a computerized prediction method. An existing analytical program (developed by Cockburn and Jolly in 1968) forms the basis of some modal analysis work which will be described. The accuracy of this modal analysis technique for predicting low-frequency, coupled acoustic-structural natural frequencies will be presented along with trends indicating the effects of varying parameters such as fuselage length and diameter. The paper will include the latest results of this work and will discuss the relationship between these results and the ultimate objective: an accurate analytical technique for predicting aircraft interior noise.
Sources and characteristics of interior noise in general aviation aircraft
Authors: Jha S. K. , Catherines J. J.
Published: October 2005

A field study has been conducted to examine the interior noise characteristics of a general aviation aircraft. The noise environment that is encountered in flight as well as the variation of noise with speed and altitude of the flight is described. It is shown that the noise consists of very high level, low frequency components, and its intensity is determined primarily by the components in the frequency range below 2000 Hz. Noise analyses to identify the sources of noise suggest that among the many conceivable sources, the engine and the propeller are the two dominant sources. The relative importance of these two sources is described. In addition to the flight measurements, interior noise measurements have been made on aircraft operating under stationary condition on the ground. A comparison of the noise data in flight with those on the ground indicates that there are some differences in the spectral characteristics for these two conditions. Another part of this study involved measuring the acoustic field around the aircraft both in near-field and far-field conditions. Data will be presented to describe the variation of sound pressure levels around the aircraft in 10-ft increments up to 50 ft during constant-rpm operation. During this ground study, accelerometers were mounted on various aircraft components such as engine, engine frame, interior floor, etc. and the resultant vibration characteristics will be compared with the interior noise spectral characteristics.
Ventilation-louver sound transmission-loss test results
Authors: Teplitzky Allan M. , Carlson John P.
Published: October 2005

Indoor machinery installations, air conditioning equipment, and transformer vaults may need louvers to permit required air flows. These louvers may be significant paths for sound that is radiated into the surrounding community. Previous investigators reported field measurements on metal louvers. In this study, a series of laboratory sound transmission-loss tests (ASTM E90-70) were performed on various types of metal and masonry louver systems. Masonry louvers included experimental configurations of resonant cavity blocks and concrete grill screens. Metal louvers tested included “V”-shaped and 45° blades. Louvers were tested to quantitatively determine the effects of blinding the “line-of-sight,” forming a labyrinth, or double set of louvers separated by an air space between. Test results are discussed. As expected, mostly all of the louvers tested provided relatively little attenuation at low frequencies. Attenuation generally improved by disruption of the line-of-sight through the louvers.
Two lecture demonstrations in acoustics using an overhead (transparancy) projector
Authors: Apfel Robert E.
Published: October 2005

When lecturing to a large audience it is often desirable to enlarge a small demonstration. A closed circuit TV system is often helpful, but there are many instances in which a simple transparancy projector can be used to greater advantage. For instance, the famous Chladni plate experiment in which the modal vibration patterns of a plate are visualized by the patterns taken by fine-grain sand when the edge of the plate is bowed can be modified by using double thickness window glass over a transparancy projector. The plate is supported from the sides, and colored Christmas glitter traces the modal patterns when the plate is bowed. Another demonstration emphasizes by analogy the importance of the size of a body compared to the acoustic wavelength. A glass baking dish is partially filled with glycerin and a large number of plastic balls are floated on the surface. A bar (3–4 in. in length) is manually moved back and forth. For low frequencies the particles slosh around the bar; at higher frequencies they do not have time to move around the bar and are “compressed” and “rarefied” in front of the bar. This, of course, goes on while the dish is on the overhead projector. These demonstrations will be performed.
Some favorite demonstrations in musical acoustics
Authors: Rossing Thomas D.
Published: October 2005

If any teacher has doubts about the pedagogical value of demonstration experiments, compare the student remark “I remember that you told us” with the remark “I remember that you told us.” It is especially important in courses in musical acoustics to demonstrate, as well as to describe, the phenomena of sound. A number of lecture demonstrations will be described and some will be demonstrated.
Lecture demonstrations in sound
Authors: Elder S. A. , Pinkston E. R. , Smithson J. R.
Published: October 2005

Over the past several years the Naval Academy Physics Department has developed a series of lecture demonstrations in sound to be shown to undergraduate physics students. A selection of these demonstrations will be shown.
Ambient illumination, personality, and annoyance response to noise
Authors: Shigehisa T. , Gunn W. J.
Published: October 2005

Annoyance response to nine spectrally treated aircraft noise was measured at three sound levels by magnitude estimation under three levels of illumination (2.69, 21.53, 129.17 1 m m−2, achromatic). Treatment included two degrees of energy reduction at octave bands centered at 315,800, 1600, and 4000 Hz. Subjects judged 27 stimuli, while engaged in a television-viewing task. Results showed that personality correlates of annoyance disappear when illumination becomes brighter. Under dim illumination, there is a positive correlation between annoyance and the EPI E- and N-scale scores, at the lesser energy reduction at 315 Hz at the highest sound level (r = +0.444 for E, +0.492 for N, df = 22, p<0.05, two-tailed tests). This indicates that the more extroverted the subject, and the more neurotic the subject, the greater the annoyance when the light is dim. Furthermore, there is a negative correlation (p<0.05) between annoyance and L-scale score, under dim (r = −0.439), moderate (r = −0.436), and bright (r = −0.475) illumination, regardless of amount of energy reduction at 800 and 4000 Hz. This suggests that the more intelligent the subject, the greater the annoyance when the light is dim, moderate, or bright.
Passenger ride quality within a noise and vibration environment
Authors: Dempsey Thomas K. , Leatherwood Jack D. , Drezek Arlene
Published: October 2005

The subjective response to noise and vibration stimuli was studied in a ride quality simulator to determine the importance of these two stimuli (or their interaction) in the prediction of passenger ride quality. Subjects used category scales to rate noise comfort, vibration comfort, noise and vibration comfort, and overall comfort in an effort to evaluate parametric arrangements of noise and vibration. The noise stimuli were composed of octave frequency bands centered at 125, 250, 1000, and 2000 Hz, each presented at 70, 75, 80, and 85 dBA. The vertical vibration stimuli were 5-Hz-bandwidth random vibrations centered at 3, 5, 7, and 9 Hz, each presented at 0.03, 0.06, 0.09, and 0.12g rms. Analyses were directed at (1) a determination of the subject's ability to separate noise and vibration as contributors to discomfort, (2) an assessment of the physical measures of noise and vibration (and certain demographic factors) that optimize ride quality prediction in this type of multifactor environment, (3) an evaluation of the relative contribution of noise and vibration to passenger ride quality, and (4) development of information as to the “most appropriate” subjective scale for future assessments of ride quality in a noise and vibration environment.
Measurement and protection of the hearing of industrial populations
Authors: Berger E. H. , Royster L. H. , Thomas W. G. , Wood T. J.
Published: October 2005

In the past years the relationship of industrial noise exposure to hearing loss has considerable attention. The hearing loss resulting from such noise exposure is currently being evaluated as a result of a study partially funded by the Rockefeller Foundation. This study is concerned with all aspects of industrial hearing loss and the measurement thereof. Topics that will be covered include: (1) selection of an appropriate non-(industrial)-noise exposed population and an analysis of the resulting baseline hearing levels; (2) limitations of industrial audiometric testing; (3) audiometric biological cheeks; (4) protection afforded by a properly administered hearing conservation program; and (5) industrial hearing loss resulting from on-the-job exposure to steady state noise. [Work partially supported by a Rockefeller Foundation Grant.]
Observed temporal summation effects for lingual vibrotactile threshold measurements
Authors: Telage Kal M. , Fucci Donald J. , Blackmon Robert
Published: October 2005

Investigations using mechanical stimulation to measure lingual threshold sensitivity have resulted in conflicting assumptions concerning the nature of underlying neural transducers. A basic question concerns whether or not exteroceptive touch receptors in the lingual surface summate energy in response to displacement of tissues. This study tested the hypothesis that these receptors would demonstrate temporal summation as a function of pulse duration time. The stimulus unit included an audio oscillator, frequency counter, electronic switch, interval timer, amplifier, and electromagnetic vibrator. The measurement unit consisted of an accelerometer, cathode follower, microphone amplifier, and vacuum-tube volt-meter. Vibrotactile lingual thresholds for 250 Hz were obtained for four groups of normal speaking adult subjects using respective pulse duration times of 50, 100, 200, and 400 msec. Peak values were recorded in millivolts and converted to dB re one micron rms. Temporal summation was observed up to 200 msec reaching an asymptote around 400 msec. Findings supported the position that tactile transducers in mucous tissues respond to vibratory displacements in the same ways as pressure receptors in other cutaneous tissues.
Audibility of group delay distortions
Authors: Blauert J. , Laws P.
Published: October 2005

We report upon exemplary measurements of group-delay distortions as induced into electroacoustical transmission by the fact that earphones and loudspeakers are not necessarily minimum phase systems. Additional psychoacoustical tests showed that the measured distortions are on the order of the limit of perceptibility or exceed this limit. The limit of perceptibility of group-delay distortions depends strongly upon the kind of signal, the shape of the group-delay curve, and the state of training of the subjects. For short sound pulses and group-delay distortions as produced by second-order all-pass filters we found in diotic presentation, with one all-pass at frequencies between 1 and 4 kHz, a limit of group-delay perceptibility between 1 and 2 msec for untrained subjects and 0.4 msec for trained subjects. Further experiments with up to 20 all-pass filters showed that for group-delay curves with multiple maxima and minima the limit of perceptibility has a value of about 0.6 msec (peak to valley) for trained subjects.
Uniqueness of articulations determined from acoustic data
Authors: Rice Lloyd , Ladefoged Peter
Published: October 2005

What is the minimum set of acoustic data that determines a unique shape of the vocal tract? This depends in part on the degree of accuracy with which the vocal tract shape is to be specified (the number of points on the surface of the vocal tract that are determined), in part on the kind of acoustic data (whether both frequencies and bandwidths of the formants are known), and in part on the constraints that are imposed on the possible shapes of the vocal tract, so that only potentially observable shapes are considered. We assume that the degree of accuracy required involves specifying 18 points along the vocal tract, and that the articulatory constraints are those that have been observed in non-nasalized vowels. We then show the extent to which we can determine the shape of the vocal tract, given only two or three formant frequencies and no bandwidth information.
Nonuniform normalization of formant data
Authors: Fant G.
Published: October 2005

A survey of female-male differences in vowel-formant frequencies in six languages reveals vowel category and formant number specific trends which have been adopted as a basis for speaker or speaker-category normalization. As in the uniform method described by Nordstrom and Lindblom [“A normalization procedure for vowel formant data,” paper 212, International Congress of Phonetic Sciences, Leeds, 1975] the procedure starts with measuring the speaker's average F3 in his most open vowels. This F3a is related to a reference F3r close to 2500 Hz to produce a scale factor k = (F3a/F3r − 1) 100%. The correction factors in percent to be applied to the subject's formant data are now a fraction k/17 of the universal average female-male percentage differences k1, k2, and k3 for F1, F2, and F3, respectively. The vowel category specific k1, k2, and k3 are interpolated from vectors within F2 versus F1 and F3 versus F1 graphs. For a better match to children's voices the speaker's k is maximized to 24% in the formula above and a constant of k-24 is added to the scale factors. The nonuniform method, when applied to a pool of formant data from both female and male subjects, has been found to reduce the female-male variance to about half of that remaining after the simple uniform method of Nordstrom and Lindblom. The origin of the nonuniform vowel and formant specific female-male differences is discussed. These are paralleled by tenor-bass formant relations, as found by Cleveland [T. Cleveland (unpublished)].
Vowel harmony in Montreal French (II)
Authors: Yaeger Malcah
Published: October 2005

In examining the systematic coarticulatory influence of a vowel on the vowel which precedes it, these hypotheses have been tested: (1) harmonic coarticulation can, for this language system, move only in one direction/in either direction; (2) harmonic coarticulation is a systematic phonemic/systematic phonetic phenomenon. The difference is visible when phonetic realization of phonological units overlaps a great deal. In this case either vowels vary in accordance with the mean F2 of the phonological unit which succeeds them, or in direct relation as the F2 of a following vowel varies (independently of whether this variation accords with phonological boundaries) the F2 of the preceding vowel will vary. We hope to show that the coarticulatory influence of one vowel on the next is unidirectional and that it is a phonetic coarticulatory influence. The data consists of conversational-style interviews made by the Sankoff-Cedergren Project in Montreal. Contrasts will be made between the patterns displayed by Montreal vernacular speakers and the pattern of the most conservative speaker in the corpus.
Temporal planning and the voicing contrast
Authors: Lisker L.
Published: October 2005

Assuming that a phonetic transcription of a speech event is to at least a first approximation its phonetic description, the segmental nature of the transcription may be understood to assert that, if two or more features shift their values “between” two segments, then these shifts occur simultaneously. Physical data indicate that articulatory shifts thought to occur in synchrony may be out of phase by amounts that are not negligible as compared with the durations ascribed to entire segments. Whether such phase variations are subject to the speaker's control in any direct way, or whether they reflect certain physiological constraints on the speech apparatus, is still to be settled to everyone's satisfaction. Moreover the same question is appropriately raised with respect to shifts that are apparently very precisely synchronized, i.e., involving tolerances of a few tens of milliseconds. An interesting case involves the precise timing relation between supraglottal and laryngeal gestures in stop-vowel and vowel-stop sequences. In the former this timing relation is variable, yielding distinct stop categories, and this variation is presumably under speaker control. In the latter there appears to be less variability in the timing of closure and extinction of glottal tone. Instead, there is significant variability in vowel duration, ascribable to properties of the following stop. The present paper presents data reporting on the durational relations among prevocalic stops, vowels, and post-vocalic stops in one- and two-syllable nonsense words. The utterances measured were produced by a single speaker under conditions designed to minimize variability, so that obtained measures of variation might serve as baseline values to be compared with segment duration data from less restricted speech samples.
Detection and quantification of fish populations by ultrasonic echo ranging
Authors: Thorne R. E.
Published: October 2005

The discovery that fish schools could be detected by ultrasonic echo ranging led to early utilization of hydroacoustic equipment by fisherman and fisheries scientists. However, the full potential of ultrasonic echo ranging for quantitative fisheries investigations has only recently begun to be realized. At the University of Washington a concerted effort to develop and apply hydroacoustic methods in the study of fish populations was initiated in the late 1960's. Investigations have been conducted on the relationship between echo intensity and fish abundance and on scattering characteristics of fish targets. Equipment and techniques which were developed as part of this research are now being applied by fisheries managers on several fish stocks in the northeastern Pacific and in scientific investigations of the role of fish in both freshwater and marine ecosystems. [Work supported by Sea Grant and IDOE.]
Bioacoustic location of a thermal front in the Arlantic Ocean near Cape Hatteras
Authors: Magnuson John J. , Brandt Stephen B. , Clay Clarence S.
Published: October 2005

High resolution echo-sounding measurements of biological scatterers were made across a thermal front between the cold Virginian and warm Gulf Stream water masses. Here the front is nearly east-west. The distribution of many cold water species extended southward to the front. The warm water species in the Gulf Stream extended northward but not beyond the front. The thermal front resembles an ecotone with relatively high fish abundance and diversity. There was a high concentration of scatterers along the front. Mid-water trawls caught Anchoa (6 cm) and Estrumeus (10 cm) on the front. Acoustic measurements were made with Simrad EK 120 (frequency 120 kHz and ping duration 10−4 sec). The data were recorded on magnetic tape and analyzed in the laboratory. Acoustic estimates of fish abundance correlated closely with trawl catches and the location of the thermal front. [Supported by National Science Foundation and National Oceanic and Atmospheric Administration, Office of Sea Grant.]
Ultrasonic spectral analyses of ocular tissues
Authors: Lizzi F. L. , Laviola M. A. , Franzen L. , Coleman D. J.
Published: October 2005

Spectrum analysis is performed on signals obtained from a wideband ultrasonic system used in clinical ophthalmic examinations. Clinical data has been cataloged to form the nucleus of a digital data library to assist in delineating characteristic spectral features of specific pathologies. The spectral analysis system analyzes gated r-f echoes from tissue segments selected with the assistance of simultaneous A- and B-mode displays. On-line averaging of spectra obtained along parallel illumination paths is provided to yield the average backscatter power spectra of tissues with heterogeneous, random interior structure. These spectra are digitized and compensated for system absolute-gain and frequency characteristics. The shapes and absolute levels of compensated spectra are being examined to evaluate their diagnostic utility. Vitreous hemorrhages are found to exhibit spectra that increase as the fourth power of frequency as would be expected for a distribution of Rayleigh scatters. Some tumors have displayed spectral resonances indicative of an ordered spatial structure. Membranous tissues (e.g., detached retinas) produce scaloped spectral patterns that can be used to deduce membrane thickness. [Work supported by NIH.]
Attenuation and velocity in normal brain
Authors: Kremkau F. W. , McGraw C. P. , Barnes R. W.
Published: October 2005

Attenuation and propagation velocity at 1, 3, and 5 MHz were measured in vitro at six anatomic sites in seven normal human brains obtained at autopsy. Piezoelectric transducer method gave attenuation values about 50% higher than radiation force method. Age at death for adults (20–72 yrs) was not a significant variable. A three-day-old infant brain, however, showed attenuation about one third that for adult. Formalin fixing increases attenuation by about 30% and reduces velocity by less than 1%. Five-day aging of unfixed tissue reduces attenuation by about 20%. White matter has higher attenuation (which is also a stronger function of frequency) than gray or mixed matter. Attenuation is a negative function of temperature. The magnitude of temperature coefficient or attenuation is greater for lower temperatures or higher frequencies. Velocity vs temperature curves exhibit a minimum at about 15°C. These observations indicate that for attenuation and velocity measurements in normal brain in the 1 to 5 MHz range, temperature must be closely controlled, and aging and fixing of tissue must be taken into account when analysing attenuation data. [Work supported by NINCDS.]
Tissue characterization using spectral analysis of ultrasonic waveforms
Authors: Jones J. P. , Holasek E. , Purnell E. W.
Published: October 2005

Many types of tissues can be uniquely classified in terms of their acoustical properties and changes in their acoustical properties can be correlated with specific pathological states. For example, the ultrasonic absorption and scattering characteristics of tissue seem to provide a useful basis for tissue differentiation. Since these properties are strongly frequency dependent, spectral analysis is suggested as a preferred measurement procedure. To present spectral information in a clinically useful way, we have developed a technique for incorporating spectral characteristics into a B-scan ultrasonogram. The technique yields a single cross-section echo record which is formed from a composite of data obtained from three scans at different frequency bands, each separately recorded through a different color filter. The signal from a wide-band transducer is divided into three separate frequency bands and the response recorded on a single color photograph with the primary colors of light representing the three component frequencies. Experiments with physical models demonstrate a good correlation between this two-dimensional display of spectral information and a true spectral analysis. Preliminary clinical trials have discovered characteristic color patterns associated with a malignant melanoma. [Work supported by NIH.]
Ultrasonic indentation of plastics and bioeffects applications
Authors: Frost H. M.
Published: October 2005

New results with an ultrasonic indenter system for soft plastics indicate that refinements in bioeffects studies involving vibrating objects acting on biological tissue are feasible. Resonant frequency changes are digitally recorded with time for the 90 kHz, self-excited sample-vibrator system. These changes characterize both the contact area and the changing viscoelastic properties of the sample and correlate well with the photoelastic strain data. Typical data are presented on video tape. A regime exists where the time-averaged acoustic force F is proportional to the indenter vibration amplitude u0 : F = Ku0. The empirical constant K of 9 × 108 dyn/cm agrees well with the value 8 × 108 dyn/cm calculated from Hertzian contact theory and is apparently insensitive to the small temperature rises of sound absorption. Potential applications in tissue-indenter studies include reproducible acoustic and static contact conditions and measurable changes in mechanical properties. A novel test for glaucoma is also proposed. [Work supported by NIH and Hood Interdisciplinary Fellowship.]
Measuring mechanical structure of tissue from scattered ultrasonic signals
Authors: Burger J. E.
Published: October 2005

Ultrasonic B-scans obtained clinically of many different kinds of tissue show random clutter originating from within their boundaries. This clutter is generally due to backscatter from scattering centers within the tissue and associated with its mechanical structure. The mechanical structures of different tissues are different, and so the spatial distributions of the scattering centers are expected to be different also. The spectral density in wavenumber of the scattering centers distributed along an axis is proposed as a basis for differential tissue diagnosis by ultrasound. This signature of the randomly distributed ultrasonic scattering centers is found to be a function of frequency, scattering angle, and axis orientation. The analytical results are based on the definition of the scattering strength at a point in the tissue as the scattered pressure measured at a unit distance from the point, per unit volume and pressure of the interrogating signal. The results show how the signature is calculated from experimentally measurable quantities. These quantities include the energy spectral densities of the interrogating ultrasonic signal and of the scattered ultrasonic signals received at different scattering angles. The different signatures of quasiperiodic and diffuse tissues are qualitatively described.
Expression for the effect of arbitrary temperature and mean flow profiles on the speed of sound in a duct
Authors: Robertson Baldwin
Published: October 2005

The wavenumber for the fundamental mode in a uniform duct with arbitrary cross section of area A is shown to be k = ±(w2A∫dAc2)12 − wA∫Vc2 dA, when the frequency w/2p is well below cutoff. This is valid for an arbitrary transverse variation in the temperature and hence in the local sound speed c, up to first order in c1/c0, where c = c0 + c1 and c0 = const. It is also valid for an arbitrary transverse variation in the mean longitudinal velocity V, up to first order in V/c. For an ideal gas, c2 = yP/p, where y is a constant, P is the pressure (assumed constant) and p is the density (which varies with temperature). Hence the first term contains only the average density, and the second only the average mass flow rate. Correction terms will be presented.
Nature of the eigenvalue problem for rectangular ducts with uniform flow
Authors: Kraft R. E.
Published: October 2005

The soft-wall acoustic boundary condition in a rectangular duct with uniform mean flow leads to a transcendental equation for the complex eigenvalues. Numerical schemes to determine the sequence of eigenvalues have, in the past, been subject to frequent-convergence problems leading to double or missed eigenvalues. Accuracy of the eigenvalue determination is critical to the operation of modal analysis suppression prediction programs. The causes of these convergence problems are examined in terms of contour maps of the eigenvalue—admittance relationship. A method for minimizing the convergence problems using a special initial value estimation subroutine is presented. Irregular cases which still fail to converge are considered by examination of the contour distortion of the modal mappings caused by the effects of flow. The effects of flow on optimum modal attenuation rates is considered, as are applications of the method to cylindrical duct geometry.
Interactive graphic system for the analysis of acoustic pulses
Authors: Steele D. W. , Jones L. K. , Sullivan F. J. M.
Published: October 2005

A computer-based system has been developed to allow a user to process, interact with, and summarize properties of large quantities of pulsed acoustic signals. Using a computer-driven graphics display, the user may search through any of a number of stored signals, looking at the signal itself or a processed version of the signal. Displays which present both the time signal along with power spectra can be selected. Using knob-controlled cursors, markers may be placed on the signal for future reference. Other operator interactions include know control for signal position and slew rate, variable frame step rate, signal scale changes, and specification of processing type. Data storage and retrieval is accomplished with a large minicomputer while signal processing is performed in a high-speed array-processing computer. The software developed for this system includes a FORTRAN-callable interactive graphics package and a FORTRAN-callable array-processing library. Also included are future application software, including creation of new displays and specification of new types of signal processing, to be written in FORTRAN.
Acoustic signature inspection of railroad wheels
Authors: Finch R. D. , Nagy K.
Published: October 2005

Two preliminary tests of an acoustic-signature inspection system for finding defective railroad wheels are described. In one test, comparison with a standard signature was used and a wheel with a plate crack and three wheels with thermal cracks of various sizes were found. In the second test, comparison of signatures of wheels at either end of a given axle was used and one wheel with a shattered rim and one with a large thermal crack were found.
Solid lens collimator for near-field calibration
Authors: Folds D. L.
Published: October 2005

Acoustic measurements with near-field arrays which simulate far-field conditions have been used in the past at frequencies less than 20 kHz primarily due to the difficulties of fabricating multielement transparent arrays at high frequencies. In this paper a solid lens operating as the acoustic equivalent of an optical collimator is used to produce planar waves. The acoustic collimator employs a single transducer element placed at the focal point of an acoustic lens. Amplitude shading which is required to control the diffraction rings at the edge of the field can be accomplished by proper selection of the attenuation coefficient of the lens material. Also, the directivity of the single transducer element can be designed to achieve appropriate shading of the lens aperture. This paper describes collimator lens design considerations and experimental results obtained with lens collimators in the frequency range 200–1200 kHz. Far-field results and those obtained with the collimator are compared.
Design of near-field calibration arrays
Authors: Van Buren A. L.
Published: October 2005

The determination of the far-field acoustic radiation from large-aperture transducers requires great distances if the measurements are made in the far-field. The difficulty in obtaining a homogeneous medium large enough to house such measurements has encouraged efforts to determine the far-field radiation from measurements in the near-field. One successful method which resulted from these efforts is based on the Trott near-field calibration array (NFCA) concept. This paper discusses the design of NFCA's. The NFCA reciprocity principle that is the basis for the NFCA is examined. A numerical procedure that is based on this reciprocity principle is described for use in designing NFCA's with arbitrary array configuration and operating conditions. Applications of this technique to the design of a hexagonal planar NFCA, a cylindrical NFCA, and a steered rectangular planar NFCA are presented. Included are experimental results.
Precision acousto-optic calibration of ultrasonic transducers
Authors: Cook B. D. , Berlinghieri J. C.
Published: October 2005

Precision determination of the power radiated by an ultrasonic transducer must account for the structure of the near-field. A new procedure which does not requite modeling of the sound field is presented. Optical data acquired from passing parallel light through the sound field is processed using a Fourier transform projection theorem to construct a description of energy flow in a spatial frequency domain. The radiated power is then calculated from the values in this domain.
A case for simple highway-noise models
Authors: Plotkin Kenneth J.
Published: October 2005

In recent years, prediction of noise from existing and proposed highways has become a major problem. In addition to “real,” or design, situations (which can range from a single building site to entire counties), there is a need for general highway-noise prediction as part of a general national strategy for noise reduction. Accordingly, a number of highway-noise models have been developed. These exhibit various degrees of complexity in both noise metrics computed and in the kinds of good geometry handled. For development of noise contours around existing highways, it is generally more satisfactory to predict noise levels (supported by some measurements) than to conduct a program of measurements alone. This paper addresses the question of how complex a highway-noise model needs to be. For predictions in design situations, the question is far from trivial, beginning with the noise metric desired. Leq is quite simple to compute, with straight lanes becoming line sources. Any metrics based on higher statistical moments of the temporal distribution (such as L10, LNP) are much more difficult to compute, and often require questionable approximations. For most cases, it is concluded that it is preferable to compute Leq, and use widely available empirical relations to compute other required metrics (e.g., L10) from this. Do special configurations occur often enough to warrant their inclusion in a general highway model? Since the ultimate purpose of highway noise prediction is to evaluate community impact, the uncertainty of community response must be considered when including complex refinements into a model. Finally, if others are to use a model, the user format must be carefully considered. A model which is complex to use is just as impractical as one which uses excessive computer time.
Measurement and diagnosis of locomotive noise
Authors: Remington Paul J. , Rudd Michael J.
Published: October 2005

Measurements of the noise generated by an SD40-2 diesel electric locomotive are described. The noise was measured in three types of moving tests: with the locomotive passing a 6-microphone array while under maximum power acceleration, while simulating the pulling of a train, and while coasting by unpowered. Stationary noise measurements were made at 16-microphone positions around the locomotive while the locomotive was attached to a load cell. The moving tests show that at the lower throttle settings, wheel/rail noise may be an important contributor to the overall locomotive noise signature even at low speeds. At throttle 8, wheel/rail noise does not become a significant source until speeds in excess of 50 mph are reached. At throttle 8 and at speeds below 50 mph, noise spectra measured opposite the moving locomotive are quite comparable to noise spectra measured opposite the stationary locomotive. Diagnostic tests to determine the contribution of the various sources in the locomotive to the overall noise were performed at seven locations on one side of the locomotive. Engine exhaust, engine intake, engine/generator, radiator cooling fans, dynamic brake fans, traction motor blowers, dust bin blower compressor, and structureborne noise have all been identified. [Work supported by the U.S. Department of Transportation.]