The Journal of the Acoustical Society of America

Published by Acoustical Society of America

Online ISSN: 1520-8524


Print ISSN: 0001-4966


Low-frequency (
  • Article

August 2013


223 Reads






The purpose of this study was to examine whether low frequency (<100 kHz), low intensity (<100 mW/cm(2), spatial peak temporal peak) ultrasound can be an effective treatment of venous stasis ulcers, which affect 500 000 patients annually costing over $1 billion per year. Twenty subjects were treated with either 20 or 100 kHz ultrasound for between 15 and 45 min per session for a maximum of four treatments. Healing was monitored by changes in wound area. Additionally, two in vitro studies were conducted using fibroblasts exposed to 20 kHz ultrasound to confirm the ultrasound's effects on proliferation and cellular metabolism. Subjects receiving 20 kHz ultrasound for 15 min showed statistically faster (p < 0.03) rate of wound closure. All five of these subjects fully healed by the fourth treatment session. The in vitro results indicated that 20 kHz ultrasound at 100 mW/cm(2) caused an average of 32% increased metabolism (p < 0.05) and 40% increased cell proliferation (p < 0.01) after 24 h when compared to the control, non-treated cells. Although statistically limited, this work supports the notion that low-intensity, low-frequency ultrasound is beneficial for treating venous ulcers.

Various applications of active field control

October 2011


37 Reads

Several types of various active field control (AFC) applications are discussed, while referring to representative projects for each application. (1) Realization of acoustics in a huge hall to classical music program, E.g., Tokyo International Forum: This venue is a multi-purpose hall with approximately 5000 seats. AFC achieves "loudness" and "reverberance" equivalent to those of a hall with 2500 seats or fewer. (2) Compensation of acoustics on stage without rigid shell using the electro-acoustic method. E.g., High school auditoriums: In these renovation projects, AFC achieves "acoustical support" for performer on stage and "uniformity" throughout the auditorium from the stage to the audience area, etc. (3) Improvement of the acoustics under the balcony in auditoria. E.g., Experiments on a full-scale model and the school auditorium. The system is a non-regenerative system, and the loudspeakers, located at positions corresponding to measurement points across the balcony, recreate the reflecting sound from above the balcony area, which otherwise fail to reach to the listeners under the balcony. The results of the experiment show that the system is significantly better for all tests to the use of no system and that the system is superior to a standard PA (delay system).

Real-time active control of structural energy density and structural power flow.

March 2010


68 Reads

Structural energy density and structural power flow have long been used as metrics in the active control of vibrating structures. The greater portion of this previous work has focused on frequency-domain methods which incorporate assumptions about the relative contributions of near-field and far-field energy components. This paper describes the implementation of filtered-x-based time-domain control schemes which utilize 9- and 13-accelerometer arrays to estimate and control structural energy density and structural power flow, respectively. Experiments were performed on a clamped steel plate excited and controlled by various combinations of loudspeakers and electrodynamic shakers in a frequency range from 25 to 100 Hz. Analog circuitry was used to estimate spatial derivatives and reduce channel count. The development of control laws incorporating the effects of the analog circuitry is presented. Control attentuation results are given, sensor placement is discussed, and implementation challenges are addressed. [This work is supported by NSF Grant 0826554.].

Comparison of primary and secondary calibrations of infrasound microphones from 0.01 to 20 Hz

November 2013


107 Reads

Secondary calibration of microphones at infrasonic frequencies by comparison to a reference pressure transducer in a piston-driven chamber is straightforward as long as the two transducers can be located much closer than a wavelength or a correction for their separation can be determined accurately. If the response of the reference transducer is flat to zero frequency, the reference can be calibrated statically. For comparison calibration, the uncertainty is dominated by the uncertainty in the reference. In this investigation, a calibration chamber that is normally used for comparison calibration has been analyzed for primary calibration. In the primary mode, the calibration depends on chamber dimensions, piston displacement, temperature, barometric pressure, leak rate, and a thermo-viscous acoustic model. The primary and secondary calibrations are performed simultaneously; however, the two calibration modes produce almost entirely independent response estimates of both magnitude and phase. The calibrations extend well below the nominal low-frequency roll-off of the microphone and allow identification of the characteristics of the pressure-equalization leak. In addition to the linear analysis, the effects of nonlinearity and convection are explored.

FIG. 1. Diagram of the data acquisition system. 
FIG. 2. Schematic diagram showing the transducer in the propagation medium, and the effective volume of scatterers in the second medium. 
FIG. 3. Measurements of the attenuation coefficients from each of the polystyrene sphere specimens. Error bars denote standard deviations. The black squares, open circles, and black triangles denote measurements made with transducers having nominal center frequencies of 10, 25, and 50 MHz, respectively. 
Frequency dependence of acoustic backscatter from 5 to 65 MHz (0.06
  • Article
  • Full-text available

September 1996


394 Reads

Attenuation and compensated backscatter from suspensions of random distributions of polystyrene beads in agarose are reported across a broad, continuous range of frequencies including frequencies which are currently of interest in the emerging fields of acoustic backscatter microscopy and intravascular imaging. Data are reported over the range of ka from 0.06 to 4, where k is the magnitude of the ultrasonic wave vector and a is the radius of the beads. The attenuation coefficient exhibits a linear dependence on frequency for ka < < 1 and more complex behaviour at larger values of ka. The measured frequency dependence of the compensated backscatter was consistent with the frequency dependence of the differential backscatter cross section for a single polystyrene sphere throughout the range of ka investigated.

Evidence for a common scale O(0.1) m that controls seabed scattering and reverberation in shallow water

May 2013


26 Reads

Analysis of the spectral content of long-range reverberation yields two observations. First, there is a remarkably similar scale, O(0.1)m, between three diverse continental shelf regions. This is surprising given general understanding of the complexity and diversity of geologic processes. Second, there is strong evidence that the scale is associated with heterogeneities within the sediment. Thus, sediment volume scattering, not interface scattering, controls long-range reverberation from a few hundred Hertz to several kilohertz. This is also unexpected given that at long-ranges the vertical grazing angles are less than the critical angle, and hence, the penetration of the acoustic field into the sub-bottom is expected to be modest. The consistency of the scale, O(0.1)m, suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings. Neither the feature nor mechanism is known at this time. Several hypotheses will be presented. [Work supported by ONR Ocean Acoustics.].

FIG. 2. Block diagram of the transmitting and listening systems.
The study area, showing the test harbor seal in position at the underwater listening station, and the nontest animal with the other trainer; (a) top view and (b) side view, both to scale.
Underwater detection of tonal signals between 0.125 and 100 kHz by harbor seals (Phoca vitulina)

March 2009


382 Reads

The underwater hearing sensitivities of two 1-year-old female harbor seals were quantified in a pool built for acoustic research, using a behavioral psychoacoustic technique. The animals were trained to respond when they detected an acoustic signal and not to respond when they did not (go/no-go response). Pure tones (0.125-0.25 kHz) and narrowband frequency modulated (tonal) signals (center frequencies 0.5-100 kHz) of 900 ms duration were tested. Thresholds at each frequency were measured using the up-down staircase method and defined as the stimulus level resulting in a 50% detection rate. The audiograms of the two seals did not differ statistically: both plots showed the typical mammalian U-shape, but with a wide and flat bottom. Maximum sensitivity (54 dB re 1 microPa, rms) occurred at 1 kHz. The frequency range of best hearing (within 10 dB of maximum sensitivity) was from 0.5 to 40 kHz (6(1/3) octaves). Higher hearing thresholds (indicating poorer sensitivity) were observed below 1 and above 40 kHz. Thresholds below 4 kHz were lower than those previously described for harbor seals, which demonstrates the importance of using quiet facilities, built specifically for acoustic research, for hearing studies in marine mammals. The results suggest that under unmasked conditions many anthropogenic noise sources and sounds from conspecifics are audible to harbor seals at greater ranges than formerly believed.

In vitro measurement of the frequency-dependent attenuation in cancellous bone between 0.2 and 2 MHz

September 2000


366 Reads

Our goal was to evaluate the frequency dependence of the ultrasonic attenuation coefficient in cancellous bone. Estimates were obtained in immersion, using a substitution method in the through-transmit mode, by scanning 14 human bone specimens (calcaneus). Measurements were performed with three pairs of focused transducers with a center frequency of 0.5, 1.0, and 2.25 MHz, respectively in order to cover an extended frequency bandwidth (0.2-1.7 MHz). When the experimental attenuation coefficient values were modeled with a nonlinear power fit alpha(f)=alpha0 +alpha(I)f(n), the attenuation coefficient was found to increase as f(1.09+/-0.3) over the measurement bandwidth. However, a substantial variation of the exponent n (0.4-2.2) within specimens and also between specimens was observed. The acoustical parameters were compared to bone mineral density. A highly significant relationship was noted between alpha1 and BMD (r2= 0.75, p< 10(-4)). No correlation was found between n and BMD. Several attenuation mechanisms are discussed as well as the potential impact these results may have in in vivo quantitative measurements.

Frequency-dependent attenuation and backscatter coefficients in bovine trabecular bone from 0.2 to 1.2 MHz

January 2012


47 Reads

The frequency-dependent attenuation and backscatter coefficients were measured in 25 bovine femoral trabecular bone samples from 0.2 to 1.2 MHz. When the average attenuation coefficient was fitted to a nonlinear power law α(f)=α(0)+α(1)f(n), the exponent n was found to be 1.65. In contrast, the average backscatter coefficient was fitted to a power law η(f)=η(1)f(n) and the exponent n was measured as 3.25. The apparent bone density was significantly correlated with the parameter α(1) (0.2-0.7 MHz: r = 0.852, 0.6-1.2 MHz: r = 0.832) as well as the backscatter coefficient (0.5 MHz: r = 0.751, 1.0 MHz: r = 0.808).

FIG. 2. Block diagram of the signal generation and listening systems.
FIG. 4. The average hearing thresholds of the two seals in the present study for 0.2-40 kHz signals with durations between 0.5 and 5000 ms depending on the frequency. FIG. 5. The relationship between the number of cycles in a pulse and the mean increase in the hearing thresholds in the two female harbor seals for pure tones of 0.2 b, 1 , 4 , 16 , 32 , and 40 kHz. The dashed line represents the mean trend of the threshold increase with decreasing number of cycles threshold increase dB = 36.90− 12.77 logcycles.
The study area, showing one harbor seal in position for testing at the underwater listening station, and the non-test animal waiting with its trainer: (a) top view and (b) side view (both to scale).
The relationship between signal duration and mean 50% detection thresholds (dB re    1   μ Pa   , rms) in the two female harbor seals [(○) seal 1 and (●) seal 2] for pure tones of (a) 0.2, (b) 1, (c) 4, (d) 16, (e) 32, and (f) 40 kHz (for details see Table I). The curves give the least-squares fits of the mean data to the exponential model [Eq. 5 in Plomp and Bouman, 1959]; the arrows indicate the shortest tones that were used to fit the model. For each frequency the time constant of integration     ( τ )     is calculated.
Block diagram of the signal generation and listening systems.
The effect of signal duration on the underwater hearing thresholds of two harbor seals (Phoca vitulina) for single tonal signals between 0.2 and 40 kHz

February 2010


318 Reads

The underwater hearing sensitivities of two 2-year-old female harbor seals were quantified in a pool built for acoustic research by using a behavioral psycho-acoustic technique. The animals were trained only to respond when they detected an acoustic signal ("go/no-go" response). Detection thresholds were obtained for pure tone signals (frequencies: 0.2-40 kHz; durations: 0.5-5000 ms, depending on the frequency; 59 frequency-duration combinations). Detection thresholds were quantified by varying the signal amplitude by the 1-up, 1-down staircase method, and were defined as the stimulus levels, resulting in a 50% detection rate. The hearing thresholds of the two seals were similar for all frequencies except for 40 kHz, for which the thresholds differed by, on average, 3.7 dB. There was an inverse relationship between the time constant (tau), derived from an exponential model of temporal integration, and the frequency [log(tau)=2.86-0.94 log(f);tau in ms and f in kHz]. Similarly, the thresholds increased when the pulse was shorter than approximately 780 cycles (independent of the frequency). For pulses shorter than the integration time, the thresholds increased by 9-16 dB per decade reduction in the duration or number of cycles in the pulse. The results of this study suggest that most published hearing thresholds <or=1 kHz for harbor seals are probably not absolute, as they were derived from signals with durations shorter than the time constants for those frequencies.

Discomfort from sinusoidal oscillation in the roll and lateral. axes at frequencies between 0.2 and 1.6 Hz

June 2007


95 Reads

Discomfort caused by low frequency lateral and roll oscillations is often predicted from lateral acceleration in the plane of the seat, irrespective of whether it comes from horizontal motion or a component of gravity arising from roll. This study investigated discomfort from lateral and roll oscillation and whether acceleration in the plane of a seat predicts discomfort. Twelve subjects, sitting with and without backrest, used magnitude estimation to judge sinusoidal oscillations in the roll and lateral axes at ten frequencies between 0.2 and 1.6 Hz at magnitudes between 0.063 and 0.63 m s(-2) root mean square. The rate of growth of vibration discomfort with increasing magnitude reduced with increasing frequency, so the frequency-dependence of discomfort varied with magnitude. Acceleration in the plane of the seat predicted discomfort from both lateral and roll oscillation at frequencies less than 0.4 Hz. At higher frequencies, acceleration produced by roll oscillation resulted in greater discomfort than the same acceleration produced by lateral oscillation. At frequencies greater than 0.4 Hz, a full height backrest increased discomfort with both lateral and roll oscillation. The prediction of discomfort caused by low frequency lateral and roll oscillation requires that both components are measured and assessed according to their separate effects.

FIG. 1. The study area, showing the test harbor seal in position at the underwater listening station; ͑ a ͒ top view and ͑ b ͒ side view, both to scale. 
FIG. 2. Block diagram of the transmitting and listening systems. 
FIG. 3. ͑ a ͒ Power averaged background noise level in the pool in dB re 1 ␮ Pa 2 / Hz ͑ derived from 1/3-octave band levels; n = 5 ͒ and the self-noise 
Underwater hearing sensitivity of harbor seals (Phoca vitulina) for narrow noise bands between 0.2 and 80 kHz

August 2009


592 Reads

The underwater hearing sensitivities of two 1.5-year-old female harbor seals were quantified in a quiet pool built specifically for acoustic research, by using a behavioral psychoacoustic technique. The animals were trained to respond when they detected an acoustic signal and not to respond when they did not ("go/no-go" response). Fourteen narrowband noise signals (1/3-octave bands but with some energy in adjacent bands), at 1/3-octave center frequencies of 0.2-80 kHz, and of 900 ms duration, were tested. Thresholds at each frequency were measured using the up-down staircase method and defined as the stimulus level resulting in a 50% detection rate. Between 0.5 and 40 kHz, the thresholds corresponded to a 1/3-octave band noise level of approximately 60 dB re 1 microPa (SD+/-3.0 dB). At lower frequencies, the thresholds increased to 66 dB re 1 microPa and at 80 kHz the thresholds rose to 114 dB re 1 microPa. The 1/3-octave noise band thresholds of the two seals did not differ from each other, or from the narrowband frequency-modulated tone thresholds at the same frequencies obtained a few months before for the same animals. These hearing threshold values can be used to calculate detection ranges of underwater calls and anthropogenic noises by harbor seals.

The effect of signal duration on the underwater detection thresholds of a harbor porpoise (Phocoena phocoena) for single frequency-modulated tonal signals between 0.25 and 160 kHz

November 2010


747 Reads

The underwater hearing sensitivity of a young male harbor porpoise for tonal signals of various signal durations was quantified by using a behavioral psychophysical technique. The animal was trained to respond only when it detected an acoustic signal. Fifty percent detection thresholds were obtained for tonal signals (15 frequencies between 0.25-160 kHz, durations 0.5-5000 ms depending on the frequency; 134 frequency-duration combinations in total). Detection thresholds were quantified by varying signal amplitude by the 1-up 1-down staircase method. The hearing thresholds increased when the signal duration fell below the time constant of integration. The time constants, derived from an exponential model of integration [Plomp and Bouman, J. Acoust. Soc. Am. 31, 749-758 (1959)], varied from 629 ms at 2 kHz to 39 ms at 64 kHz. The integration times of the porpoises were similar to those of other mammals including humans, even though the porpoise is a marine mammal and a hearing specialist. The results enable more accurate estimations of the distances at which porpoises can detect short-duration environmental tonal signals. The audiogram thresholds presented by Kastelein et al. [J. Acoust. Soc. Am. 112, 334-344 (2002)], after correction for the frequency bandwidth of the FM signals, are similar to the results of the present study for signals of 1500 ms duration. Harbor porpoise hearing is more sensitive between 2 and 10 kHz, and less sensitive above 10 kHz, than formerly believed.

Level discrimination as a function of level for tones from 0.25 to 16 kHz

June 1987


61 Reads

Difference limens for level (delta L in dB = 20 log [(p + delta p)/p], where p is pressure) were measured as a function of level for tones at 0.25, 0.5, 1, 2, 4, 8, 10, 12, 14, and 16 kHz. At each frequency, test levels encompassed the range from near threshold to 95 dB SPL in steps of 10 dB or smaller. The stimulus duration was 500 ms and the interstimulus interval was 250 ms. An adaptive two-alternative forced-choice procedure with feedback was used. Results for six normal listeners show individual differences among listeners, but the general trends seen in the average data clearly are present in the individual data and show the following. First, the delta Ls at all but the highest frequencies are generally smaller at high levels than at low levels. Second, the delta Ls at equal SPLs are largely independent of frequency up to about 4 kHz, but increase with frequency above 4 kHz. Third, at 8 and 10 kHz, the delta Ls are clearly nonmonotonic functions of level, showing consistent deterioration in the mid-level delta Ls relative to the low- and high-level delta Ls. The present data are discussed qualitatively in terms of current models of level discrimination.

Active control of multimodal tonal noise propagated in acircular duct with axial subsonic mean flow up to M=0.3

June 2008


43 Reads

As new generation of aircraft engine with lower blade passing frequency appeared in the 1990's, the fan tones radiated from the inlets had become one of the dominant source of sound. Efforts have then been made to develop active noise control. Encouraging results have been obtained but the physical limitation of the fan tones reduction have not been clearly determined, owing mainly to the complexity of the experimental rigs. This paper present an experimental investigation of the control of multimodal tonal noise propagated in circular duct in presence of a mean flow (M</=0.3). A laboratory wind tunnel has been implemented for this purpose. Two limiting factors for the sound reduction are underlined: (i) the degradation of the secondary transfer matrix conditioning as the number of propagating modes increases in the duct and (ii) the degradation of the hypothesis of the time-invariance of the system to control as the flow velocity is increased. The effect of those limiting factors on the control efficiency are evaluated.

FIG. 1. Schematic diagram of the experimental setup for ultrasonic measurements in through-transmission geometry. 
FIG. 2. ͑ a ͒ Temporal signals and ͑ b ͒ pressure spectra measured with and without the sediment in the acoustic path for the pair of 0.5 MHz transducers. 
FIG. 3. ͑ a ͒ Temporal signals and ͑ b ͒ pressure spectra measured with and without the sediment in the acoustic path for the pair of 1.0 MHz transducers. 
FIG. 5. Experimental and theoretical velocity shifts plotted as a function of frequency for the fast longitudinal wave in the water-saturated sandy sediment and in the glass-grain composite. 
Frequency dependencies of phase velocity and attenuation coefficient in a water-saturated sandy sediment from 0.3 to 1.0 MHz

June 2007


470 Reads

The frequency-dependent phase velocity and attenuation coefficient for the fast longitudinal wave in a water-saturated sandy sediment were measured over the frequency range from 0.3 to 1.0 MHz. The experimental data of phase velocity exhibited the significant negative dispersion, with the mean rate of decline of 120 +/- 20 m/s/MHz. The Biot model predicted the approximately nondispersive phase velocity and the grain-shearing (GS) model exhibited the slightly positive dispersion. In contrast, the predictions of the multiple scattering models for the negative dispersion in the glass-grain composite were in general agreement with the experimental data for the water-saturated sandy sediment measured here. The experimental data of attenuation coefficient was found to increase nonlinearly with frequency from 0.3 to 1.0 MHz. However, both the Biot and the GS models yielded the attenuation coefficient increasing almost linearly with frequency. The total attenuation coefficient given by the algebraic sum of absorption and scattering components showed a reasonable agreement with the experimental data for overall frequencies. This study suggests that the scattering is the principal mechanism responsible for the variations of phase velocity and attenuation coefficient with frequency in water-saturated sandy sediments at high frequencies.

The study facility, showing a harbor porpoise in position at the listening station: (a) top view, and (b) side view, both to scale. Also shown is the swimming path during a trial.
(a) The mean background noise level in the pool (Leq method), sea state 0, and the masking noise levels (spectrum levels shown as ●) in which the porpoises had to detect the tonal signals. Also shown is the self-noise of the recording system. (b) The mean CRs (based on 50% DTs) of the harbor porpoises 01 (◼) and 02 (○) in the present study. Each data point represents the mean of around 90 reversal pairs. (c) The mean CRs of the two harbor porpoises of the present study for the 19 tonal signals (solid line). Also shown are CRs of bottlenose dolphins (gray circles,  Johnson, 1968a ; ◻,  Au and Moore, 1990 ), a beluga (●,  Johnson et al., 1989 ), a false killer whale (△,  Thomas et al., 1990 ), and another harbor porpoise (▲,  Kastelein and Wensveen, 2008 ).
Critical ratios in harbor porpoises (Phocoena phocoena) for tonal signals between 0.315 and 150 kHz in random Gaussian white noise

October 2009


277 Reads

A psychoacoustic behavioral technique was used to determine the critical ratios (CRs) of two harbor porpoises for tonal signals with frequencies between 0.315 and 150 kHz, in random Gaussian white noise. The masked 50% detection hearing thresholds were measured using a "go/no-go" response paradigm and an up-down staircase psychometric method. CRs were determined at one masking noise level for each test frequency and were similar in both animals. For signals between 0.315 and 4 kHz, the CRs were relatively constant at around 18 dB. Between 4 and 150 kHz the CR increased gradually from 18 to 39 dB ( approximately 3.3 dB/octave). Generally harbor porpoises can detect tonal signals in Gaussian white noise slightly better than most odontocetes tested so far. By combining the mean CRs found in the present study with the spectrum level of the background noise levels at sea, the basic audiogram, and the directivity index, the detection threshold levels of harbor porpoises for tonal signals in various sea states can be calculated.

Influence of the filling fluid on frequency-dependent velocity and attenuation in cancellous bones between 0.35 and 2.5 MHz

December 2009


63 Reads

The paper is focused on experiments on human cancellous bones filled with different fluids with the goal of evaluating their contribution to velocity dispersion, absorption, and scattering mechanisms. The specimens were measured first filled with marrow and subsequently, after marrow removal, with water and alcohol. No significant influence of the fluids was evidenced on the attenuation coefficient. Given the absence of impact of viscosity of the saturating fluid, the authors hypothesized that the source of attenuation is associated with viscoelastic absorption in the solid trabeculae and with scattering. Alteration of scattering obtained by changing the acoustic impedance mismatch between the fluid (alcohol vs water) and the trabeculae was reflected neither in the attenuation nor in its slope. This led the authors to suggest that longitudinal-to-shear scattering together with absorption in the solid phase are candidates as main sources for the attenuation. The differences in velocity values indicate that the elastic properties of the fluid are main determinants of the phase velocity. This finding is particularly significant in the context of /in vivo/ measurements, because it demonstrates that the subject-dependent properties of marrow may partly explain the inter-subject variability of speed of sound values.

Otoacoustic emissions evoked by 0.5 kHz tone bursts

June 2009


47 Reads

The aim of this research is to extend previous studies of the time-frequency features of otoacoustic emissions (OAEs) using information about the properties of the signals at low frequencies. Responses to 0.5 kHz tone bursts were compared to OAEs that were evoked by click stimuli and by 1, 2, and 4 kHz tone burst stimuli. The OAEs were measured using 20 and 30 ms intervals between stimuli. The analysis revealed no differences in the time-frequency properties of 1, 2, and 4 kHz bursts measured using these two different acquisition windows. However, at 0.5 kHz the latency of the response was affected significantly if a shorter time window was used. This was caused by the fact that the response reached a maximum after an average time of 15.4 ms, and lasted a few milliseconds longer. Therefore, for this particular stimulus, the use of a 30 ms time window seems more appropriate. In addition, as an example of the possible application of low-frequency OAEs, signals were measured in patients suffering from partial deafness, characterized by steep audiograms with normal thresholds up to 0.5 kHz and almost total deafness above this frequency. Although no response to clicks was observed in these subjects, the use of 0.5 kHz tone bursts did produce OAEs.

FIG. 6. Syringodium filiforme. Comparison of image-and acoustic-based biomass measurements as a function of the number of leaves and rhizomes in the resonator. The vertical axis is total volume fraction V i / V tot i = leaves or rhizomes. The error bars are described in the text. FIG. 7. Halodule wrightii. Comparison of image-and acoustic-based biomass measurements as a function of the number of leaves and rhizomes in the resonator. The vertical axis is total volume fraction V i / V tot i = leaves or rhizomes. The error bars are described in the text.
Thalassia testudinum. Comparison of image- and acoustic-based biomass measurements as a function of the number of leaves (a) and rhizomes (b) in the resonator. The vertical axis is total volume fraction      V i  /  V  tot      (    i = leaves    or rhizomes). The error bars are described in the text.
Laboratory investigation of the acoustic response of seagrass tissue in the frequency band 0.5-2.5 kHz

May 2009


552 Reads

Previous in situ investigations of seagrass have revealed acoustic phenomena that depend on plant density, tissue gas content, and free bubbles produced by photosynthetic activity, but corresponding predictive models that could be used to optimize acoustic remote sensing, shallow water sonar, and mine hunting applications have not appeared. To begin to address this deficiency, low frequency (0.5-2.5 kHz) acoustic laboratory experiments were conducted on three freshly collected Texas Gulf Coast seagrass species. A one-dimensional acoustic resonator technique was used to assess the biomass and effective acoustic properties of the leaves and rhizomes of Thalassia testudinum (turtle grass), Syringodium filiforme (manatee grass), and Halodule wrightii (shoal grass). Independent biomass and gas content estimates were obtained via microscopic cross-section imagery. The acoustic results were compared to model predictions based on Wood's equation for a two-phase medium. The effective sound speed in the plant-filled resonator was strongly dependent on plant biomass, but the Wood's equation model (based on tissue gas content alone) could not predict the effective sound speed for the low irradiance conditions of the experiment, in which no free bubbles were generated by photosynthesis. The results corroborate previously published results obtained in situ for another seagrass species, Posidonia oceanica.

Correlations between acoustic properties and bone density in bovine cancellous bone from 0.5 to 2 MHz

June 2003


372 Reads

Correlations between acoustic properties and bone density were investigated in the 12 defatted bovine cancellous bone specimens in vitro. Speed of sound (SOS) and broadband ultrasonic attenuation (BUA) were measured in three different frequency bandwidths from 0.5 to 2 MHz using three matched pairs of transducers with the center frequencies of 1, 2.25, and 3.5 MHz. The relative orientation between ultrasonic beam and bone specimen was the mediolateral (ML) direction of the bovine tibia. SOS shows significant linear positive correlation with apparent density for all three pairs of transducers. However, BUA shows relatively weak correlation with apparent density. SOS and BUA are only weakly correlated with each other. The linear combination of SOS and BUA in a multiple regression model leads to a significant improvement in predicting apparent density. The correlations among SOS, BUA, and bone density can be effectively and clearly represented in the three-dimensional space by the multiple regression model. These results suggest that the frequency range up to 1.5 MHz and the multiple regression model in the three-dimensional space can be useful in the osteoporosis diagnosis.

Geoacoustic inversion in the frequency range 0.8-1.6 kHz with drifting sparse arrays during MREA/BP'07 experiment

June 2008


66 Reads

In order to evaluate properly the acoustic propagation characteristics in shallow water environments, it is well established that appropriate knowledge of the acoustic properties of the seabottom is required. In the last decade, full-field geoacoustic inversion techniques have been demonstrated to provide adequate methodologies to assess those properties. However, several of the developed techniques may suffer a lack of adequacy to the design of low-frequency active sonar systems (LFAS) for which the assessment of seabottom characteristics are drawn. For instance most matched-field inversion techniques demonstrated so far use acoustical signals at much lower frequencies than those of the sonar. Furthermore, some of the techniques may be difficult to be handled in an "operationally relevant context" since they are based on relatively complex designed systems such as highly instrumented vertical line arrays spanning the whole water column. In this paper, we investigate the potential of medium-frequency acoustical signals (0.8-1.6 kHz) received at several ranges on a field of drifting sparse arrays, eventually reduced to a couple of hydrophones, for spatially-coherent geoacoustic inversion purposes. The experimental datasets of the Maritime Rapid Environmental Assessment MREABP'07 sea trial south of Elba Island in the Mediterranean Sea are used to support this study.

A system for evaluating auditory function from 8000--20 000 Hz

January 1980


53 Reads

A system for the measurement of auditory function from 8000--20 000 Hz is described. This system introduces advances in: (a) maximum power output, (b) signal fidelity, and (c) transducer characteristics. Two case studies are presented to illustrate the clinical information gained from the measurement of high-frequency auditory sensitivity, which is not readily apparent in conventional threshold assessment.

The effects of noise upon human hearing sensitivity from 8000 to 20 000 Hz

June 1981


80 Reads

High-frequency (8 to 20 kHz) hearing sensitivity was compared in thirty-six, 20 to 29-year-old military veterans with histories of steady-state or impulsive noise exposure. Threshold shifts were prominent for the steady-state noise subjects from 13 to 20 kHz. Mean thresholds from 8 through 12 kHz were maximally 20 dB poorer than a sample of young adult normals. Audiometric configurations for this group were generally smooth and symmetrical above 8000 Hz. For the impulsive noise group, substantial shifts in sensitivity were seen from 2 to 20 kHz and the high-frequency audiometric configurations were often jagged and/or asymmetrical. The variability of subjects in this group was greater than that seen in the steady-state noise exposed sample. Several case studies are presented to illustrate these characteristics. Measurement of auditory sensitivity from 8 to 20 kHz extends the mapping of basal cochlear function, providing information which often is not predictable from conventional audiometric measurement. This additional information provides for more comprehensive inter- and intra-subject comparison of the degree and extent of threshold changes present.

Comparison of the properties of tonpilz transducers fabricated with < 001 > fiber-textured lead magnesium niobate-lead titanate ceramic and single crystals

November 2009


44 Reads

Tonpilz transducers are fabricated from 001 fiber-textured 0.72Pb(Mg(1/3)Nb(2/3))O(3)-0.28PbTiO(3) (PMN-28PT) ceramics, obtained by the templated grain growth process, and PMN-28PT ceramic and Bridgman grown single crystals of the same composition. In-water characterization of single element transducers shows higher source levels, higher in-water coupling, and more usable bandwidth for the 81 vol % textured PMN-28PT device than for the ceramic PMN-28PT element. The 81 vol % textured PMN-28PT tonpilz element measured under large signals shows linearity in sound pressure levels up to 0.23 MV/m drive field but undergoes a phase transition due to a lowered transition temperature from the SrTiO(3) template particles. Although the textured ceramic performs well in this application, it could be further improved with compositional tailoring to raise the transition temperature and better processing to improve the texture quality. With these improvements textured piezoelectric ceramics will be viable options for medical ultrasound, actuators, and sonar applications because of their ease of processing, compositional homogeneity, and potentially lower cost than single crystal.

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