Acoustic Saturation Research Articles

Rainforest birds avoid biotic signal masking only in cases of high acoustic saturation

Rainforest birds avoid biotic signal masking only in cases of high acoustic saturation

On the non-linear behaviour of ultrasonic air-borne phased arrays

Air-coupled phased arrays are an increasing area of academic and industrial interest. Their application to acoustic levitation and mid-air haptics relies on high amplitude focussed fields capable of generating very high acoustic pressures (e.g. >150 dB SPL). At these elevated pressures non-linear propagation effects can become significant, for example: the generation of harmonic frequencies, waveform asymmetry and acoustic saturation. In this work the basics of non-linear acoustics are presented with emphasis on energy loss mechanisms. Experimental work shows non-linearities as a function of focussing distance and driving amplitude. Large 2D microphone scans normal and tangential to the acoustic axis are carried out. Comparisons to linear models are made as well as modification to saturation equations developed for water-coupled fields. It is shown that saturation losses can become significant at elevated transducer amplitudes and focal distances. Metrics such as the waveform asymmetry, total harmonic distortion and energy loss are used to show the onset and magnitude of non-linearities. The volumetric experimental data shows how the fundamental and harmonic fields can differ in amplitude sufficiently such that harmonic amplitudes can exceed the fundamental. Suggestions are made on how to identify non-linearities and their general effect on air-coupled arrays and their applications.

Seismic-Derived Rock True Resistivity (R) Revisited. Part I: Reformulation Of Combined Gassmann – Shaly Sand Models

The last decade has observed frantic efforts by geoscientists to extract as much information as possible from seismic data. From the traditional role of establishing subsurface structural geometry, seismic processing and interpretations have evolved into an ever increasing role in providing rock physical properties such as acoustic impedance (AI) and porosity (0). The more common use of 3-D seismic surveys, in both exploration and development stages, have fur- ther underlined the role of seismic data as provider of inter-well rock property data. Further developments in the petrophysics-related seismic interpretation have also shown efforts to ex- tract information related to contents of formation rocks. From the widely acknowledged brightspot analysis for detecting presence of gas-bearing porous rocks in the last decades of the 20 century to the later efforts to extract information regarding fluid saturation in reservoir. Actually, as early as in mid- 1960s have scientists started to investigate the relations between acoustic signals and fluid saturation (e.g King, 1966; Domenico, 1976; Gregory, 1976). However, due to the fact that the then commonly used of 2-D seismic was considered as having insuf- ficient resolution for any practical uses in the field, the efforts remained mainly for academic purposes only. Rapid developments in technology of 3-D seis- mic survey and processing, as well as its more com- mon use at present have prompted attentions back to the investigations aimed at extracting fluid saturation information from seismie data. In 1990s have Widarsono and Saptono (1997) started a series of investigation through laboratory measurements and modeling using core samples. This was followed by more works not only at laboratory level but at larger levels of well and field scales (e.g. Widarsono Saptono, 2000a, 2000b, and 2001; and Widarsono et al, 2002a, 2000b). Other investigators (e.g. Furre Brevik, 2000; Wu, 2000; Zhu et al, 2000; and more recently Wu et al, 2005) have also devoted some works to achieving the same goal. Other paths of development have incorporated other supporting tech- niques such as non-linear regression (e.g.Balch et al, 1998) and artificial neural network (e.g. Poupon Ingram, 1999; Oldenziel et al, 2000).From various investigations using seismic waves as the sole data for fluid saturation extraction, short- comings were soon felt in the form of 'narrow bands' of acoustic signals (ie P-wave velocity, V, and acoustic impedance, AI) that are influenced by varia- tions in fluid saturation. In other words, V, and AI are not too influenced by variation in fluid saturation. This reduces the effectiveness of seismic-derived V and Al as fluid saturation indicators. Efforts were then devoted to link V, and AI to other parameters such as rock true resistivity (R), a parameter known to be very sensitive to variation in fluid saturation. Widarsono and Saptono (2003, 2004) provide laboratory verifications and first field trial with some degree of succes. However, certain assump- tions (i.e. constant/uniform porosity) in the theoreti- cal formulation were still adopted in the above works, which in turn reduced the validity of the resulting formula produced and used. In this paper, the first part of a three-part work, is devoted to reformulating the combination of Gassmann theory and shaly sand water saturation models of Poupon and Hossin. These are to replace the shale-free Archie model used in the above works, which is considered as invalid for most field uses. With this reformulation, it is hoped that a more robust model/formula of resistivity as a function of acoustic impedance (R, = fAI)) is achieved, hence a more reliable resistivity could be extracted from seismic- derived acoustic impedance. Summarily, the objectives of the works a part of them presented in this paper are - To establish a model/method to obtain formation rock true resistivity (R) from seismic-derived acoustic impedance (AI), and To provide correction/modification onto previous works reported in Widarsono Saptono (2003, 2004).

David Blackstock and the physics of nonlinear sound beams

In the 1970s, David Blackstock and his students and colleagues examined nonlinear sound beams both theoretically and experimentally. Two noteworthy articles in JASA resulted from this research, one by Shooter, Muir and Blackstock (1974) and another by Lockwood, Muir and Blackstock (1973). Of particular interest was the generation of highly directive radiation at harmonics of the source frequency that at moderate source levels decreased in beamwidth with harmonic order. Additional sidelobes were also observed in the harmonics. The main lobe in both the fundamental and the harmonics eventually broadened with increasing source level as shock waves were formed. Eventually finite-amplitude absorption became significant, acoustic saturation set in, and the medium did not permit further increase in amplitude. David’s application of weak-shock theory to model this process was validated by underwater acoustic experiments at the Applied Research Laboratories Lake Travis Test Station involving transducers driven at high intensities, at several hundred kilohertz, with waveforms and beams measured at ranges of several hundred meters. The results provided guidance for many applications, ranging from audio frequency tools in ocean acoustics to ultrasonic biomedical instruments now used worldwide in diagnostic and therapeutic applications. [Work supported by ARL:UT.]

David T. Blackstock: Scholar, teacher, mentor, and gentleman

David T. Blackstock was born in Austin, Texas in 1930. After earning B.S. and M.S. degrees in physics at University of Texas at Austin he spent two years at Wright-Patterson Air Force Base, where he developed an interest in acoustics working under Henning von Gierke on hearing protection. He then joined F. V. Hunt’s group at Harvard University and earned a Ph.D. in applied physics in 1960 with a doctoral thesis in nonlinear acoustics, ultimately his lifelong passion. Following three years at General Dynamics and seven years at University of Rochester, David returned to UT in 1970 to join its Applied Research Laboratories, and in 1987 he became Professor of Mechanical Engineering. Among David’s legacies is his formulation of a convenient framework for implementing weak-shock theory. Combining analytical, computational, and experimental approaches, he proceeded to investigate acoustic saturation, finite-amplitude noise, suppression of sound by sound, parametric array in air, sonic boom, therapeutic ultrasound, and other fundamental problems in nonlinear acoustics. David was widely known as an exceptionally caring man, whether bringing Soviet scientists and their research to the attention of the West, teaching and mentoring graduate students, or through extensive service in the ASA and International Commission for Acoustics.

Two-phase pore-fluid distribution in fractured media: acoustic wave velocity vs saturation

The acoustic wave velocity varies with fluid saturation and pore-fluid distribution. We use a P-wave source and the staggered grid finite-difference method, with second-order accuracy in time and eighth-order accuracy in space, to simulate the acoustic wave field in a fractured medium that is saturated with a two-phase pore fluid (gas & water). Further, we analyze the variation of acoustic wave velocity with saturation for different pore-fluid distribution modes. The numerical simulation method is simple and yields accurate results.

Using soundscapes to detect variable degrees of human influence on tropical forests in Papua New Guinea.

There is global concern about tropical forest degradation, in part, because of the associated loss of biodiversity. Communities and indigenous people play a fundamental role in tropical forest management and are often efficient at preventing forest degradation. However, monitoring changes in biodiversity due to degradation, especially at a scale appropriate to local tropical forest management, is plagued by difficulties, including the need for expert training, inconsistencies across observers, and lack of baseline or reference data. We used a new biodiversity remote-sensing technology, the recording of soundscapes, to test whether the acoustic saturation of a tropical forest in Papua New Guinea decreases as land-use intensity by the communities that manage the forest increases. We sampled soundscapes continuously for 24 hours at 34 sites in different land-use zones of 3 communities. Land-use zones where forest cover was fully retained had significantly higher soundscape saturation during peak acoustic activity times (i.e., dawn and dusk chorus) compared with land-use types with fragmented forest cover. We conclude that, in Papua New Guinea, the relatively simple measure of soundscape saturation may provide a cheap, objective, reproducible, and effective tool for monitoring tropical forest deviation from an intact state, particularly if it is used to detect the presence of intact dawn and dusk choruses.

Shock formation and nonlinear saturation effects in the ultrasound field of a diagnostic curvilinear probe.

Newer imaging and therapeutic ultrasound technologies may benefit from in situ pressure levels higher than conventional diagnostic ultrasound. One example is the recently developed use of ultrasonic radiation force to move kidney stones and residual fragments out of the urinary collecting system. A commercial diagnostic 2.3 MHz C5-2 array probe has been used to deliver the acoustic pushing pulses. The probe is a curvilinear array comprising 128 elements equally spaced along a convex cylindrical surface. The effectiveness of the treatment can be increased by using higher transducer output to provide a stronger pushing force; however nonlinear acoustic saturation can be a limiting factor. In this work nonlinear propagation effects were analyzed for the C5-2 transducer using a combined measurement and modeling approach. Simulations were based on the three-dimensional Westervelt equation with the boundary condition set to match low power measurements of the acoustic pressure field. Nonlinear focal waveforms simulated for different numbers of operating elements of the array at several output power levels were compared to fiber-optic hydrophone measurements and were found to be in good agreement. It was shown that saturation effects do limit the acoustic pressure in the focal region of a diagnostic imaging probe.

Predicting Reservoir Performance Using the Elastic Properties of Well Logs in Fabi Field, Niger Delta Basin in Nigeria

In recent times, characterization of reservoir using elastic properties of the well logs is limited to discrimination of reservoir fluids and lithologies which do not precisely reflect reservoir characteristics. In this study, we propose a robust approach that uses the well log derived attributes to predict the effects of the production related changes and performance levels of the reservoirs. First, the elastic attributes were generated from the well logs using the transform menu of the E-log program. The appropriate pairs of the attributes were cross-plotted and color overlay of the most robust attributes established. The cross-plot of Lambda-Rho versus Mu-Rho revealed the gas charged sand, brine charged sand and streak of shale in HD5000 reservoir. The color overlay of the lambda-Rho showed very high degree of brine saturation and very low gas saturation. The cross plot of velocity ratio versus P-impedance in HD8000 reservoir revealed hydrocarbon charged sand which was associated with very low velocity ratio, acoustic impedance values and brine saturation. The color overlay of acoustic impedance showed very high hydrocarbon saturation and low brine saturation. The cross plot of Mu-rho versus density at HD9000 reservoir also revealed the hydrocarbon charged sand (very low-density values) and brine charged sand. The color overlay of density revealed relatively high hydrocarbon and low brine saturation. The high brine saturation in the reservoirs probably resulted from increase in formation water due to production and steam injection program which is an indication of reservoir depletion. However, the results indicate that HD8000 and HD9000 reservoirs are still active for more hydrocarbon production while HD5000 reservoir is not.

Estimation of reservoir fluid saturation from seismic data: amplitude analysis and impedance inversion as a function of noise

SUMMARY Noise in seismic data can create significant challenges for the integration of 4D information into seismic history matching procedures. Impedances derived from a seismic inversion are usually compared to impedances provided by the coupling between a fluid flow and a petro-elastic model. The problem is that uncertainties associated with noise in seismic data are rarely carried though all the seismic inversion steps. And the noise in seismic data can alter the correlation between acoustic impedance and fluid saturation, resulting in erroneous estimates of reservoir properties. We hypothesize that the amplitude domain could be a better option than the impedance domain for seismic history matching, considering seismic noise. To verify this hypothesis we analyse amplitude and impedance changes as a function of water saturation and seismic noise. We demonstrate that the noise in seismic data causes higher variations on seismic inversion results than on amplitudes. A cross-domain comparison suggests that these impedance variations can be as high as their values derived from the seismic baseline survey. These results indicate that matching time-lapse seismic and fluid flow data in the amplitude domain may be more reliable than using the impedance domain - in the presence of strong seismic noise. Errors in seismic data, such as noise, need to be considered when undertaking seismic history matching, and proper uncertainty analysis is required for accurate reservoir predictions.

Nonlinear acoustics and the Acoustical Society of America

The modern era of nonlinear underwater acoustics had its roots in a remarkable session at the 57th ASA meeting at Providence RI in June, 1960, chaired by Westervelt, of Brown University, who also presented his remarkable new theory of the parametric acoustic array. This conceptual “device” enables highly directive low frequency sound to be created from the nonlinear interaction of two high frequency radiations of high directivity, which was confirmed in a model- tank study paper in this session by Brown Univ. Professor Robert Beyer and student Bellin. JASA has been the major worldwide forum for publications in nonlinear underwater acoustics, ever since, with much of the U.S. work done at the Navy Underwater Sound Laboratory and its successor, the Naval Underwater Systems Center, as well as the Applied Research Laboratories of the University of Texas at Austin. Topics have included parametric arrays, the nonlinear generation of harmonic radiations and transients, acoustic saturation, nonlinear transmitting and receiving sonar and imaging, and many practical applications to underwater sound and acoustical oceanography. Current and/or developing applications include underwater communications, backscattering measurements, penetration of narrow beams into sediments, sub-bottom profiling, and fish school quantification and classification. These and other topics are reviewed and recent implementations are described. [Work supported by ARL:UT Austin.]

Nonlinear Effects in Ultrasound Fields of Diagnostic-type Transducers Used for Kidney Stone Propulsion: Characterization in Water.

Newer imaging and therapeutic ultrasound technologies require higher in situ pressure levels compared to conventional diagnostic values. One example is the recently developed use of focused ultrasonic radiation force to move kidney stones and residual fragments out of the urinary collecting system. A commercial diagnostic 2.3 MHz C5-2 array probe is used to deliver the acoustic pushing pulses. The probe comprises 128 elements equally spaced at the 55 mm long convex cylindrical surface with 38 mm radius of curvature. The efficacy of the treatment can be increased by using higher transducer output to provide stronger pushing force; however, nonlinear acoustic saturation effect can be a limiting factor. In this work nonlinear propagation effects were analyzed for the C5-2 transducer using a combined measurement and modeling approach. Simulations were based on the 3D Westervelt equation; the boundary condition was set to match low power pressure beam scans. Focal waveforms simulated for increased output power levels were compared with the fiber-optic hydrophone measurements and were found in good agreement. It was shown that saturation effects do limit the acoustic pressure in the focal region of the transducer. This work has application to standard diagnostic probes and imaging.

Inversión geoestadística conjunta de datos sísmicos y electromagnéticos

Three-dimensional numerical models are key tools for reservoir characterization and management. In order to decrease the uncertainty associated with these models, it is essential the integration of all the available data within the geo-modeling workflow. Geostatistical seismic inversion has proven its ability to integrate well-log data and seismic reflection data to infer reliable subsurface elastic models. Recently, the use of electromagnetic data is being used to infer the spatial distribution of the subsurface pore fluid distribution. We present a new iterative geostatistical methodology that is able to jointly invert seismic reflection and electromagnetic data for petro-elastic models, i.e. water saturation, porosity and acoustic impedance. The proposed approach is based on a genetic algorithm that works as a global optimizer to converge the iterative methodology and uses stochastic sequential simulation as the perturbation technique of the model parameter space. A calibrated rock physics model acts as the link between the elastic properties derived from the seismic reflection data and the petrophysical properties derived from the inverted resistivity models. The geostatistical joint inversion of seismic and electromagnetic data was successfully tested and implemented in a synthetic dataset, Stanford VI-E. The inverted petro-elastic models of acoustic impedance, porosity and water saturation agree with the real three-dimensional petro-elastic models in both large- and small- scale details.

Nonlinear saturation effects in ultrasound fields of diagnostic-type transducers used for kidney stone propulsion

A novel therapeutic application of ultrasound for repositioning kidney stones is being developed. The method uses acoustic radiation force to expel mm-sized stones or to dislodge even larger obstructing stones. A standard diagnostic 2.3 MHz C5-2 array probe has been used to generate pushing acoustic pulses. The probe comprises 128 elements equally spaced at the 55 mm long convex cylindrical surface with 41.2 mm radius of curvature. The efficacy of the treatment can be increased by using higher transducer output to provide stronger pushing force; however, nonlinear acoustic saturation effect can be a limiting factor. In this work, nonlinear propagation effects were analyzed for the C5-2 transducer using a combined measurement and modeling approach. Simulations were based on the 3D Westervelt equation; the boundary condition was set to match low power measurements. Focal waveforms simulated for several output power levels were compared with the fiber-optic hydrophone measurements and were found in good agreement. It was shown that saturation effects do limit the acoustic pressure in the focal region of the transducer. This work has application to standard diagnostic probes and imaging. [Work supported by RSF 14-12-00974, NIH EB007643, DK43881 and DK092197, and NSBRI through NASA NCC 9-58.]

Low-temperature thermal conductances of amorphous dielectric microbridges in the diffusive to ballistic transition

Through a lossy acoustic-wave model we explore the effect of inelastic scattering on the low-temperature thermal conductances of amorphous dielectric microbridges in the diffusive to ballistic transition. The model gives not only the thermal flux as a function of geometry and temperature, but also the temperature distribution of the internal degrees of freedom that constitute the loss, which in turn can be used for calculating noise. The approach leads to powerful conceptual insights and provides a numerical framework for analyzing experimental data. Si${}_{x}$N${}_{y}$ tends to behave ballistically at low frequencies and diffusively at high frequencies, and when integrated over all frequency, the diffusive to ballistic transition becomes apparent at lengths of around a few hundred microns. It is possible to include flux-dependent acoustic loss, which leads to counterintuitive thermal behavior. A sample can behave diffusively when measured using a small temperature difference, but ballistically when measured using a large temperature difference. There is compelling circumstantial evidence that the effects of acoustic saturation have been seen, but not explicitly recognized, on many occasions.

Tissue non-linearity

The propagation of acoustic waves is a fundamentally non-linear process, and only waves with infinitesimally small amplitudes may be described by linear expressions. In practice, all ultrasound propagation is associated with a progressive distortion in the acoustic waveform and the generation of frequency harmonics. At the frequencies and amplitudes used for medical diagnostic scanning, the waveform distortion can result in the formation of acoustic shocks, excess deposition of energy, and acoustic saturation. These effects occur most strongly when ultrasound propagates within liquids with comparatively low acoustic attenuation, such as water, amniotic fluid, or urine. Attenuation by soft tissues limits but does not extinguish these non-linear effects. Harmonics may be used to create tissue harmonic images. These offer improvements over conventional B-mode images in spatial resolution and, more significantly, in the suppression of acoustic clutter and side-lobe artefacts. The quantity B/A has promise as a parameter for tissue characterization, but methods for imaging B/A have shown only limited success. Standard methods for the prediction of tissue in-situ exposure from acoustic measurements in water, whether for regulatory purposes, for safety assessment, or for planning therapeutic regimes, may be in error because of unaccounted non-linear losses. Biological effects mechanisms are altered by finite-amplitude effects.

High‐powered parametric acoustic array in air.

MIT Lincoln Laboratory has developed a prototype high‐powered parametric acoustic array (HPPAA) for standoff acoustic excitation in several applications. Parametric arrays offer a highly directional, narrow beam mechanism to deliver sound in air to desired targets typically within a 100 m range. However, a difficult challenge arises in generating sufficient sound power at difference‐frequencies below 1000 Hz at a range which can be critical for many target types. An important objective of the HPPAA design maximizes the difference‐frequency pressure amplitude at range by maximizing the end‐fire array length established by the PAA. The design optimizes the trade‐offs between the three characteristic lengths that control the resultant end‐fire array length including the pump or carrier wave attenuation, PAA aperture, and acoustic saturation of air. In field demonstrations, the HPPAA generated a carrier wave pressure power approximately 155 dB re‐20‐microPa one meter from the PAA face while generating a 300 Hz difference‐frequency SPL of 90 dB re‐20‐microPa 8 meters from the PAA. These sound pressure levels at a few hundred hertz may enable safe standoff excitation and detection of buried landmines and may be useful in standoff nondestructive testing (NDT) damage detection and imaging of structures.

Prediction of cavitating flow noise by direct numerical simulation

In this study, a direct numerical simulation procedure for the cavitating flow noise is presented. The compressible Navier–Stokes equations are written for the two-phase fluid, employing a density-based homogeneous equilibrium model with a linearly-combined equation of state. To resolve the linear and non-linear waves in the cavitating flow, a sixth-order compact central scheme is utilized with the selective spatial filtering technique. The present cavitation model and numerical methods are validated for two benchmark problems: linear wave convection and acoustic saturation in a bubbly flow. The cavitating flow noise is then computed for a 2D circular cylinder flow at Reynolds number based on a cylinder diameter, 200 and cavitation numbers, σ = 0.7 – 2 . It is observed that, at cavitation numbers σ = 1 and 0.7, the cavitating flow and noise characteristics are significantly changed by the shock waves due to the coherent collapse of the cloud cavitation in the wake. To verify the present direct simulation and further analyze the sources of cavitation noise, an acoustic analogy based on a classical theory of Fitzpatrik and Strasberg is derived. The far-field noise predicted by direct simulation is well compared with that of acoustic analogy, and it also confirms the f - 2 decaying rate in the spectrum, as predicted by the model of Fitzpatrik and Strasberg with the Rayleigh–Plesset equation.

Anharmonic acoustic resonators in miniature thermoacoustic cooler

In optimizing miniature thermoacoustic coolers for high cooling power density, the acoustic resonator has to be able to sustain very high amplitude acoustic oscillation at the resonant frequency of the driver in order to pump heat up a temperature gradient. Nonlinear effects in cylindrical-shaped resonators lead to acoustic saturation; acoustic energy is dissipated in higher harmonics, thus limiting the intensity of the fundamental mode. To overcome this limitation, noncylindrical resonators were studied here. Conical, exponential, and halfcosine shapes were used. They produce high-amplitude sound waves with essentially no shock waves. Such resonators were chosen here to operate at around 4 kHz, the resonant frequency of the piezoelectric driver. They are easily adapted to the miniature refrigerator. Moreover, they provide an impedance match, which is shape dependent, between the driver and the resonator. Tests at sound intensity levels up to 170 dB show essentially no distortion of the acoustic waveform. Results of their performance will be discussed. [Work supported by ONR and the State of Utah.]

Clayton H. Allen’s discovery of nonlinear acoustic saturation

In 1950 Clayton H. Allen (1918–2004) discovered nonlinear acoustic saturation. His Penn State doctoral thesis, ‘‘Finite Amplitude Distortion in a Spherically Diverging Sound Wave in Air,’’ is about experiments on intense sound produced by a 12.2-cm diameter baffled piston vibrating at 14.6 kHz. At r=3.8 cm (the next-to-last nearfield peak) the maximum SPL produced was 161 dB (re 20 μPa). The farfield began at about 50 cm. Measurements were made of the fundamental and 2nd–6th harmonics out to r=200 cm. His received level versus source level curves at r=200 cm show the now familiar plateau that is reached as nonlinear effects limit the achievable SPL for a given distance at a given frequency. Clay’s discovery is quite remarkable because (1) it was totally unexpected and (2) it came long before any theoretical predictions of the phenomenon were developed. Alas, however, the work was never published except in the Army Signal Corps report from Penn State, ‘‘Atmospheric Physics and Sound Propagation, Final Report for Period July 1, 1945 to May 20, 1950,’’ and in two papers presented orally at the Penn State ASA Meeting in June 1950. As a result, Clay’s remarkable work has gone unappreciated for many years. This presentation is dedicated to his memory.