Average Sound Speed Research Articles

1Pb5-6 Relation between statistical properties of sound speed distribution and average sound speed estimation

1Pb5-6 Relation between statistical properties of sound speed distribution and average sound speed estimation

Breast Density Assessment in Young Women with Ultrasound based on Speed of Sound: Influence of the Menstrual Cycle.

To investigate changes in breast density (BD) during the menstrual cycle in young women in comparison to inter-breast and -segment changes as well as reproducibility of a novel Speed-of-Sound (SoS) Ultrasound (US) method.SoS-US uses a conventional US system with a reflector and a software add-on to quantify SoS in the retro-mammillary, inner and outer segments of both breasts. Twenty healthy women (18–40 years) with regular menstrual cycles were scanned twice with two weeks in-between. Three of these were additionally measured twice per week for 25 days. Average SoS (m/s) and ΔSoS (segment-variation SoS; m/s) were measured. Variations between follicular and luteal phases and changes over the four-week period were assessed. Inter-examiner and inter-reader agreements were also evaluated. Variances between cycle phases, examiners and readers were compared.No significant SoS difference was observed between follicular and luteal phases for the twenty women (P = .126), and between all different days for the three more frequently measured women (P = .892). Inter-reader (ICC = 0.999) and inter-examiner (ICC = 0.990) agreements were high. The SoS variance due to menstrual variations was not significantly larger than the inter-examiner uncertainty (P = .461). Inter-reader variations were significantly smaller than menstrual and examiner variations (P < .001).SoS-US showed high inter-examiner and inter-reader reproducibility. The alterations during the menstrual cycles were not significantly larger than the confidence interval of measurements.

Properties of Dislocation Drag from Phonon Wind at Ambient Conditions.

It is well known that, under plastic deformation, dislocations are not only created but also move through the crystal, and their mobility is impeded by their interaction with the crystal structure. At high stress and temperature, this “drag” is dominated by phonon wind, i.e., phonons scattering off dislocations. Employing the semi-isotropic approach discussed in detail in a previous paper (J. Phys. Chem. Solids 2019, 124, 24–35), we discuss here the approximate functional dependence of dislocation drag B on dislocation velocity in various regimes between a few percent of transverse sound speed and (where is the effective average transverse sound speed of the polycrystal). In doing so, we find an effective functional form for dislocation drag for different slip systems and dislocation characters at fixed (room) temperature and low pressure.

Acoustic remote sensing for source localization and atmospheric tomography: Applications of the cross-correlation Green's function retrieval method.

In this work, the application of the cross-correlation Green's function retrieval method for source localization and atmospheric acoustic tomography is presented. Open field experimental measurements of an acoustic source, with an impulsive waveform, are conducted for the evaluation of an array system. Of particular interest are the source localization and sound speed estimation capabilities of the array system. The cross-correlation delay-and-sum beamformer is used to estimate source directivity and sound speed. This beamformer inherently employs the cross-correlation Green's function retrieval method between a pair of receivers. The beamforming results adequately identify the various source directions as well as the scatterers along the propagation path. Reasonable sound speed estimates are obtained at the peak frequency of the retrieved Green's functions. In the case of atmospheric acoustic tomography, the estimated sound speed from the array system can serve as an average background sound speed in a tomographic inversion algorithm. Utilizing a tomographic inversion algorithm with radial basis functions and the estimated sound speed, the reconstruction of temperature and wind velocity profiles are demonstrated.

A Bayesian approach to a passive range estimation method of underwater sound source in shallow water waveguide

In this paper, a matched mode processing method is used to estimate the range of underwater sound source in shallow water, in which the replica field is calculated with the P and Q normal mode model. In this normal mode model, the replica field is described with the bottom phase shift coefficient, the sea depth and the average sound speed profile. The influence caused by the uncertainty of environment parameters, on the accuracy of range estimation is discussed with Bayesian approximation. Bayesian approximation is a good way to estimate the unknown parameters based on probability of data. The Gaussian distribution model and Markov Chain Monte Carlo method are used in this paper for calculating the posterior probability density. The effect of the uncertainty or error of environment parameters to the ranging result is obtained. The practicality of the ranging method is raised significantly. The procedure and the discussed results are given.

Sound Propagation in Shallow Water with an Inhomogeneous GAS-Saturated Bottom

We present the methods and results of numerical experiments studying the low-frequency sound propagation in one of the areas of the Arctic shelf with a randomly inhomogeneous gas-saturated bottom. The characteristics of the upper layer of bottom sedimentary rocks (sediments) used in calculations were obtained during a 3D seismic survey and trial drilling of the seafloor. We demonstrate the possibilities of substituting in numerical simulation a real bottom with a fluid homogeneous half-space where the effective value of the sound speed is equal to the average sound speed in the bottom, with averaging along the sound propagation path to a sediment depth of 0.6 wavelength in the bottom. An original technique is proposed for estimating the sound speed propagation in an upper inhomogeneous sediment layer. The technique is based on measurements of acoustic wave attenuation in water during waveguide propagation.

Sound speed profile calculations for the Northern Gulf of Mexico

Many sound speed calculations for the Gulf of Mexico use an average sound speed over the entire Gulf. In a variety of applications, such as localization or tracking of marine mammals, a more precise sound speed profile is helpful to make more accurate calculations. Using a reasonable approximation to Del Grosso’s equation, the sound speed profile may be computed as a function of temperature, pressure, and salinity. The Littoral Acoustic Demonstration Center—Gulf Ecological Monitoring and Modeling (LADC-GEMM) project collected underwater acoustic data in the northern Gulf of Mexico during the summer of 2015 using Environmental Acoustic Recording Systems (EARS), returning to sites previously surveyed by LADC. Oceanographic data were also collected at those sites and can be used for more accurate sound speed profiles at the specific locations and specific times of the acoustic data recordings, increasing the accuracy of subsequent calculations such as real-time tracking and other applications. Sound speed profiles for sites in the northern Gulf of Mexico will be presented. [This research was made possible by a grant from The Gulf of Mexico Research Initiative. Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org.]

A passive range method of underwater source based on single hydrophone

Aiming at the passive impulse wideband source range problem in shallow water waveguides, a passive source range method with single hydrophone which is applied to the shallow water waveguide with a bottom of liquid semi-infinite space is presented in this paper by combining the group delay theory and warping transformation. The receive signal is composed of several normal modes, and each mode represents many characteristics of the waveguide environment. Warping transformation is a good tool which can achieve the separation and extraction of normal modes from the received signal, and it is also an unitary and reversible transformation, so the warped signal of each normal mode can be recovered completely. The dispersion curves of normal modes can be extracted by warping transformation, and the relation between arrival time and frequency of each order normal mode can also be calculated, and then the time delay of arriving hydrophone between arbitrary two different normal modes is obtained. According to the group delay theory, different order normal mode has different arrival time at the same frequency, and the arrival time of normal mode is determined at its group speed when the distance between the source and hydrophone is certain. So the propagation range can be estimated when the time delay and the slow group speed difference between two different normal modes are known. When the waveguide environmental parameters are known, the slow group speed difference of arbitrary two normal modes can be calculated by KRAKEN. However, when the bottom parameters are unknown, the bottom reflection phase shift parameter is an important parameter describing the acoustic parameters of the bottom, and it contains nearly all the bottom information, what is more, the bottom reflection phase shift parameter is also a parameter that can be extracted by some experimental data easily. When the depth and the average sound speed of the water column are known, the slow group speed difference between two order normal modes can be represented by the seafloor phase shift parameter. Therefore, the source range can be represented by the bottom reflection phase shift parameter, the sea depth and the mean sound speed in the waveguide, and under this condition, the source location can be estimated by one single hydrophone. The effectiveness and accuracy of the method are proved by the numerical simulation results and sea experimental data processing, in which the signals are both received by a single hydrophone. The sea experimental data contain linear frequency modulation impulse source signal and explosion sound source signal, and the mean relative error of range estimation is less than 10%.

Treating patients with mild adolescent idiopathic scoliosis using scoliosis-specific exercises

Objective To explore the effect of scoliosis-specific exercises (SSE) on patients with mild adolescent idiopathic scoliosis (AIS). Methods Thirty patients with mild AIS were assigned to a control group (n=10) or an SSE group (n=20). The control group received routine health education, while the SSE group completed a 60-minute set of SSE 2 to 3 times a week for 12 weeks. The angle of trunk rotation (ATR), maximum Cobb angle and angle of vertebral rotation (AVR) were recorded. Bone strength parameters including the speed of sound (SOS), Z-score and percentile distal radius were measured. Surface electromyography (sEMG) was performed for the erector spinae muscle. In addition, forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were measured and compared with the predicted values (FVC/pred% and FEV1pred%). A falling index (FI) and quality of life (QOL) were measured. Results Compared with before the treatment, the average maximum Cobb angle in the control group increased significantly after the lessons, but there was no significant difference in any of the other measures, including QOL. For the control group the activation rate of the concave side of the apex level erector spinae was significantly lower than on the convex side both before and after the lessons. The SSE group showed no significant improvement in their average ATR, maximum Cobb angle, AVR or FI results, but their average SOS, Z-score and percentile of the distal radius, FVC, FEV1 and motor function improved significantly after the treatment. Before the treatment the activation rate of their concave side was also lower than on the convex side, but after the treatment there was no significant difference between them on average. Conclusion Early SSE can prevent further deformation, promote bone strength, improve lung function reduce the difference in the motor control of the bilateral erector spinae muscles among patients with mild AIS. It can promote a better quality of life and is worth applying in clinical practice. Key words: Adolescent idiopathic scoliosis; Scoliosis; Exercise; Rehabilitation

Real-time monitoring of coastal current and throughflow by ocean acoustical tomography with a time reversal responder

The conventional Coastal Acoustic Tomography (CAT) system works in a controlled timing of sound transmission from acoustic stations surrounding an observation site. Data received in each station are sent to an integrated data center via communication network and a real-time mapping of current and sound speed is realized. In a new time reversal mirror CAT system (TRM-CAT) proposed, data received at a few land stations by time reversal responders gather all data transferred to the data center. The SNR of received signals is increased and the cost of field experiment is reduced. The TRM-CAT consists of two types of station, land and response stations. The land station is a conventional CAT station that sends coded signals to the response station and receives time reversal signals released. The response station work as a responder, which does not transmit any acoustic signals, until a signals coming from the land station are recorded in a memory, and then reconstructed as a time reversal data to transmit toward the land station at a pre-determined timing. One-way travel time and travel time difference are determined by a matched filter with codes. As a results, the average sound speed and flow velocity can be calculated in land stations. The TRM-CAT is designed and the system simulation is presented. Application to monitoring volume and heat transports through straits and rivers in real time is planned now. Finally, the TRM-CAT serves as a cost effective system for real-time mapping of velocity structures in the coastal sea.

A Comparative Study of Moored/Point and Acoustic Tomography/Integral Observations of Sound Speed in Fram Strait Using Objective Mapping Techniques

AbstractEstimation of the exchange of seawater of various properties between the Arctic and North Atlantic Oceans presents a challenging observational problem. The strong current systems within Fram Strait induce recirculations and a turbulent ocean environment dominated by mesoscale variations of 4–10-km scale. By employing a simple parameterized model for mesoscale variability within Fram Strait, the authors examine the ability of a line array of closely spaced moorings and an acoustic tomography line to measure the average sound speed, a proxy variable for ocean temperature or heat content. Objective maps are employed to quantify the uncertainties resulting from the different measurement approaches. While measurements by a mooring line and tomography result in similar uncertainties in estimations of range- and depth-averaged sound speed, the combination of the two approaches gives uncertainties 3 times smaller. The two measurements are sufficiently different as to be complementary; one measurement provides resolution for the aspects of the temperature section that the other misses. The parameterized model and its assumptions as to the magnitudes and scales of variability were tested by application to a hydrographic section across Fram Strait measured in 2011. This study supports the deployment of the 2013–16 Arctic Ocean under Melting Ice (UNDER-ICE) network of tomographic transceivers spanning the ongoing moored array line across Fram Strait. Optimal estimation for this ocean environment may require combining disparate data types as constraints on a numerical ocean model using data assimilation.

Passive impulsive source range estimation based on warping operator in shallow water

An approach to passive impulsive source range estimation in shallow water is proposed. The approach is based on warping transformation of the energy density function of the received signal. Because of the influence of the sea bottom, it is difficult to find a warping operator adapted to the dispersion characteristics of modes in shallow water. Even though the modes can be separated from each other by using the warping operator adapted to the ideal waveguide, it is impossible to obtain the analytic solutions of the characteristic frequencies, while the energy density function of the received signal is not affected by the sea bottom. Like the received signal and the autocorrelation function of the signal, the frequency spectrum of the warped energy density function of the received signal also owns invariable frequency features. These characteristic frequencies equal the difference in the cut-off frequency between two modes in ideal waveguide, which are easy to calculate with the knowledge of the depth and the average sound speed of the water. What is more, the warping operator transforms mode pairs in energy density function with the same mode number difference into one monotone, which means one characteristic frequency is not unique for one mode pair. In shallow water, the acoustic field is typically composed of a group of modes with close mode numbers. Therefore, the smaller the mode number difference, the more the mode pairs, and the higher the spectral peak of the corresponding monotone is. When the source range is unknown, the approximate relation formula between the extracted characteristic frequency in a supposed source range and the real characteristic frequency is derived, based on which a fast passive source range estimation method is proposed. The proposed method successfully avoids using the guide source and the calculation of replica field, which is necessary in existing passive range estimation algorithms. And applying warping operator to the energy density function of the received signal makes it easy to obtain the analytic solutions of the characteristic frequencies, which is impossible in previous researches. The method is successfully applied to the Yellow Sea impulsive signal data collected by a single hydrophone in November 2011. The mean relative error of range estimation is less than 8%.

Concentration measurement of yeast suspensions using high frequency ultrasound backscattering

This work proposes the use of an ultrasound based technique to measure the concentration of yeasts in liquid suspension. This measurement was achieved by the detection and quantification of ultrasonic echoes backscattered by the cells. More specifically, the technique was applied to the detection and quantification of Saccharomyces cerevisiae. A theoretical approach was proposed to get the average density and sound speed of the yeasts, which were found to be 1116kg/m3 and 1679m/s, respectively. These parameters were needed to model the waves backscattered by each single cell. A pulse-echo arrangement working around 50MHz, being able to detect echoes from single yeasts was used to characterize experimentally yeast solutions from 102 to 107cells/ml. The Non-negative Matrix Factorization denoising technique was applied for data analysis. This technique required a previous learning of the spectral patterns of the echoes reflected from yeasts in solution and the base noise from the liquid medium. Comparison between pulse correlation (without denoising) and theoretical and experimental pattern learning was made to select the best signal processing. A linear relation between ultrasound output and concentration was obtained with correlation coefficient R2=0.996 for the experimental learning. Concentrations from 104 to 107cells/ml were detected above the base noise. These results show the viability of using the ultrasound backscattering technique to detect yeasts and measure their concentration in liquid cultures, improving the sensitivity obtained using spectrophotometric methods by one order of magnitude.

Study of bone strength in patients with adolescent idiopathic scoliosis

Objective To investigate the bone strength of adolescent idiopathic scoliosis (AIS) patients. Methods A total of 68 AIS patients and 20 healthy subjects were recruited. Speed of sound (SOS), Z-score and percentile of distal radius of normal subjects and AIS patients were measured using the quantitative ultrasound. Results Compared with normal controls, AIS had significantly lower average SOS, Z value and percentile. No significant difference was found among different curve patterns and gender of AIS patients. There was a positive correlation between SOS and age in AIS patients. However, there was no correlation between SOS and maximal Cobb angle in AIS patients. Conclusions AIS patients have lower bone strength generally. The bone strength has a positive correlation with the age, but no correlation with the curve pattern and gender in AIS patients. Key words: Adolescent; Idiopathic; Scoliosis; Bone strength

Frequency domain ultrasound waveform tomography: breast imaging using a ring transducer

Application of the frequency domain acoustic wave equation on data acquired from ultrasound tomography scans is shown to yield high resolution sound speed images on the order of the wavelength of the highest reconstructed frequency. Using a signal bandwidth of 0.4–1 MHz and an average sound speed of 1500 m s−1, the resolution is approximately 1.5 mm. The quantitative sound speed values and morphology provided by these images have the potential to inform diagnosis and classification of breast disease. In this study, we present the formalism, practical application, and in vivo results of waveform tomography applied to breast data gathered by two different ultrasound tomography scanners that utilize ring transducers. The formalism includes a review of frequency domain modeling of the wave equation using finite difference operators as well as a review of the gradient descent method for the iterative reconstruction scheme. It is shown that the practical application of waveform tomography requires an accurate starting model, careful data processing, and a method to gradually incorporate higher frequency information into the sound speed reconstruction. Following these steps resulted in high resolution quantitative sound speed images of the breast. These images show marked improvement relative to commonly used ray tomography reconstruction methods. The robustness of the method is demonstrated by obtaining similar results from two different ultrasound tomography devices. We also compare our method to MRI to demonstrate concordant findings. The clinical data used in this work was obtained from a HIPAA compliant clinical study (IRB 040912M1F).

Is the Intrahepatic Sound Speed an Indicator of the Fat Content of the Liver in Children?

Can the sonographically estimated intrahepatic sound speed give hints on the hepatic fat content in children? In 75 children and adolescents the intrahepatic sound speed was estimated during routine sonography of the liver as a result of an image reconstruction algorithm. It was correlated with weight, age, size, and body mass index (BMI) oft he children, respectively. The average hepatic sound speed in children of normal weight was 1 566 m/s (standard deviation (STD) 29 m/s, in overweight or obese children it was 1 501 m/s (STD 22 m/s), and in obese children it was 1 497 ms (STD 24 m/s). The strongest correlation was found between sound speed and BMI of the children, respectively. The difference of sound speed in normal weighing subjects and overweight/obese children was statistically significant. There is a good correlation between the estimated intrahepatic sound speed and the fat content of the liver. Further examinations are encouraged.

Localization for broadband source by a single vector sensor in shallow water

The physical meaning of array invariant is the absolute traveling time of different modal from a source to a receiver under the average sound speed. It can be gotten by the derivative of the arriving time against the corresponding cosecant function of elevation angle for each modal, which can be used for the passive source localization. A vector sensor can be seen as a small volumetric array. It has its capability of elevation angle determination to describe the multi-modal propagation and the single-modal dispersion in shallow water, which may imply a chance to get the array invariant for the source localization. Here, we take advantage of the dispersion based short time Fourier transform and warping transform techniques for the time-frequency analysis of vector sensor signals. This technique can improve acoustic normal mode identification and thereby extract the modal data more accurately for array invariant determination. The idea had been effectively validated during the experiment that took place in ...

Parallel strip waveguide for ultrasonic flow measurement in harsh environments.

Wetted ultrasonic transit time flow meters typically consist of one or more pairs of transducers, containing piezoelectric elements, which alternate between transmitting and detecting an ultrasonic pulse. Typical piezoelectric materials and the adhesives used to attach the piezoelectric element in such devices can be damaged by hostile environments, such as extreme temperature, potentially limiting possible applications of ultrasonic flow measurement techniques. We have investigated a design for a flow meter with an integrated thermal buffer waveguide consisting of five parallel stainless steel strips. These, in addition to thermal protection, may function as a transducer array, with the possibility of steering the emitted field. Because the buffer strips used in the transducer assembly are thin, one might expect Lamb-like guided waves to propagate along it. However, the finite width of the strips has a significant effect on the propagation characteristics of the guided waves. In this work, the effect of the waveguide's small rectangular cross-section has been studied. Additionally, we have examined the effect of thermal gradients on the average sound speed and dispersion characteristics of such strip waveguides. We also suggest modifications to the plate geometry, which can alter both the frequency content and the shape of the transmitted pulse, potentially giving a better signal to use in flow measurement.

A Monte Carlo experiment for measuring acoustic properties of macroalgae living tissue.

A methodology is developed to measure ex situ ultrasonic velocity of submerged aquatic vegetation tissue, in particular, macroalgae, in a nondestructive and efficient manner. An entire thallus is submerged in artificial seawater-filled tank through which many ultrasonic pulse-echo measurements are recorded while thallus parts are randomly displaced. Average sound speed of tissue is estimated from normal fit to extracted travel times given measured total volume fraction of tissue and travel time in water alone. For species Ecklonia radiata the resulting values for sound speed 1573.4 ± 4.8 m s(-1) and adiabatic compressibility 3.134 ×10(-10) ± 1.34 ×10(-11) Pa(-1) at 18 °C agree with more laborious and destructive methods.

Measurement of acoustic material properties of macroalgae (Ecklonia radiata)

Temperate macroalgal forests are among the most productive ecosystems in the world. Acoustic propagation measurements have been used to monitor primary production over broad spatial scales (101–103m) in seagrass meadows, and work is in development to assess the application of acoustics for measuring aggregate production in kelp beds and forests. In addition, scientific echosounders have been used routinely for mapping these benthic habitats and, in some cases, identify dominant species. Further advances in these areas require the development of species-specific acoustic models. However there is little knowledge of the acoustic properties of macroalgae, in part because measuring sound speed in large macroalgae is challenging due to their complex morphology. In this study four different methods are developed and trialled to determine the intrinsic sound speed of Ecklonia radiata tissue based on measurement of the time of flight of an ultrasonic pulse, while compressibility is calculated from density measurements. Direct methods involved lengths of stipe and tightly packed stacks of macroalgae blade tissue. Indirect methods focused on an entire intact macroalga submerged in seawater, and a homogenate solution containing seawater and blended blade tissue. Blade tissue showed a density contrast (relative to seawater) of 1.23 and a sound speed contrast of 1.0374 for the stacks. The homogenate solution gave a sound speed contrast of 1.0424. Stipe tissue density and sound speed were lower. Density contrast was 1.04 and sound speed contrasts were 1.0179 (SD=0.0025) and 1.0064 (SD=0.0032) depending on the sample. Whole macroalgae had age- and size-dependent densities with an average density contrast of 1.11 (SD=0.09) and showed an average sound speed of 1572.8m/s (17.8°C) and contrast of 1.0404 (SD=0.0139). Compressibility was higher in stipe than blade tissue, with 3.924e-10Pa−1 and 3.982e-10Pa−1 for stipes and 3.209e-10Pa−1 and 3.180e-10Pa−1 for blade in stacks and homogenate respectively. The results show that E. radiata sound speed and density are higher, and compressibility lower, than that of seawater. This is likely related to high concentrations of alginate, and other structural and storage carbohydrates in the macroalgae, and thus may vary seasonally. The differences between tissue types found for all properties reflect the morphology and anatomy of this macroalga, with tightly condensed chloroplast cells in blade tissue and loosely packed structural cells in the stipe. This research provides essential input parameters to numerical models that will enhance acoustic habitat mapping and allow the development of acoustic inverse methods. This may enable the estimation of aggregate primary production over large spatial scales in temperate kelp habitats, thus informing their future management.