Structure Of Acoustic Field Research Articles

Manipulation of Gaseous Ions with Acoustic Fields at Atmospheric Pressure.

The ability to controllably move gaseous ions is an essential aspect of ion-based spectrometry (e.g., mass spectrometry and ion mobility spectrometry) as well as materials processing. At higher pressures, ion motion is largely governed by diffusion and multiple collisions with neutral gas molecules. Thus, high-pressure ion optics based on electrostatics require large fields, radio frequency drives, complicated geometries, and/or partially transmissive grids that become contaminated. Here, we demonstrate that low-power standing acoustic waves can be used to guide, block, focus, and separate beams of ions akin to electrostatic ion optics. Ions preferentially travel through the static-pressure regions ("nodes") while neutral gas does not appear to be impacted by the acoustic field structure and continues along a straight trajectory. This acoustic ion manipulation (AIM) approach has broad implications for ion manipulation techniques at high pressure, while expanding our fundamental understanding of the behavior of ions in gases.

Bottom Multi-Parameter Bayesian Inversion Based on an Acoustic Backscattering Model

The geoacoustic and physical properties of the bottom, as well as spatial distribution, are crucial factors in analyzing the underwater acoustic field structure and establishing a geoacoustic model. Acoustic inversion has been widely used as an economical and effective method to obtain multi-parameters of the bottom. Compared with traditional inversion methods based on acoustic propagation models, acoustic backscattering models are more suitable for multi-parameter inversion, because they contain more bottom information. In this study, a Bayesian inversion method based on an acoustic backscattering model is proposed to obtain bottom multi-parameters, including geoacoustic parameters (the sound speed and loss parameter), partial physical parameters of the sediment, and statistical parameters of the seafloor roughness and sediment heterogeneity. The bottom was viewed as a kind of fluid medium. A high-frequency backscattering model based on fluid theory was adopted as the forward model to fit the scattering strength between the model prediction and the measured data. The Bayesian inversion method was used to obtain the posterior probability density (PPD) of the inversion parameters. Parameter estimation, uncertainty, and correlation were acquired by calculating the maximum a posterior (MAP), the mean values, the one-dimensional marginal distributions of the PPD, and the covariance matrix. Finally, the high-frequency bottom backscattering strength from the Quinault Range site was employed for inversion tests. The estimated values and uncertainties of various bottom parameters are presented and compared with the directly measured bottom parameters. The comparison results demonstrate that the method proposed herein can be used to estimate the sediment/water sound speed ratio, the sediment/water density ratio, and the spectral exponent of the roughness spectrum effectively and reliably.

Bayesian geoacoustic inversion in shallow water with vertical coherence of ship-radiated noise

Spatial structure of underwater acoustic field depends strongly on the geoacoustic properties of the seabed. The geoacoustic parameters can be estimated using the spatial coherence dominated by a single broadband source. In this paper, geoacoustic inversion of a shallow water environment is carried out using the vertical coherence of ship-radiated noise at a close range. Data were measured in an experiment in the South China Sea, and the vertical coherence is extracted from a single hydrophone pair in the vertical line array. The closest point of the passing research ship approach is determined first, and then the broadband coherence curves are extracted as the input for the inversion algorithm. Due to the lack of an appropriate parametrization, the trans-dimensional inversion method combined with the auto-regressive error model is adopted in this paper. The inversion results show that the sound speed is the most sensitive, followed by the density, and then the attenuation coefficient is the least sensitive, which is consistent with previous works. The data error hypothesis is verified via a posterior examinations.

Ultrasound frequency effect on soybean protein: Acoustic field simulation, extraction rate and structure

This study endeavored to develop a method to evaluate the effect of ultrasound frequency on soybean protein extraction. In the ultrasonic frequencies range from 20 to 52 kHz, 28, 35, and 45 kHz were predicted to be the resonance frequencies in the ultrasound-assisted extraction (UAE) process of soybean protein by simulating the acoustic field distribution. The absolute sound pressure and the relative standard deviation could be well-coordinated via frequency regulation. The extraction experiment of soybean protein showed that the extraction rate was improved significantly (p < 0.05) with the aid of ultrasound. The extraction effect was optimal at 28 kHz and the extraction rate was improved to 73.35 g/100 g from 46.09 g/100 g of control under the same condition. The structure of the extracted protein was analyzed by the spectrum to further explore the mechanism of the effect of ultrasonic frequency. Spectral analysis showed that 20, 28, and 35 kHz had a significant influence on the structure of protein molecules. Therefore, acoustic field simulation can be used as one effective method for selecting ultrasonic frequency, which could help to optimize equipment and improve efficiency.

Linear and nonlinear Bayesian localization in ocean acoustics

Ocean-acoustic localization can be considered an inverse problem that involves estimating model parameters that specify the location of one or more acoustic sources and/or receivers based on fitting measured acoustic data, which can include observable quantities such as travel times, travel-time differences, modal dispersion, or acoustic-field structure. In a Bayesian inversion approach, data and prior information are used to compute the posterior probability density (PPD) of the model parameters, providing uncertainty analysis that quantifies the information content of the problem. The Bayesian formulation provides the generality to treat all uncertain parameters (e.g., both source and receiver locations, environmental properties, clock drifts) as unknowns subject to appropriate levels of prior information. Marginalizing over nuisance parameters can improve localization accuracy or at least account for parameter uncertainties in the localization uncertainty. Some Bayesian localization problems can be solved efficiently using linearization and iteration, with closed-form approximations for the PPD. In other cases, nonlinear (numerical) methods such as Markov-chain Monte Carlo sampling or trans-dimensional inversion are required. This talk will illustrate these concepts with a series of examples including array-element localization for moored and towed arrays, tracking autonomous underwater vehicles at a test range, marine-mammal localization, and multi-source matched-field localization

The Influence of Intratermocline Eddies on Sound Propagation in the Deep Part of the Sea of Japan

The results of stochastic modeling of the influence of positive and negative intratermocline eddies (lenses) on the spatiotemporal structure of acoustic fields in the deep part of the Sea of Japan are presented. The lens shape was modeled by an ellipse. The lens center and the emitter were located on the axis of the underwater sound channel. The vertical distribution of the acoustic field inside the lens was studied at various ranges in front of the center, in the center and behind the center of the lens, as well as at ranges of 40 and 100 km. A negative lens focuses the ray paths on the axis of underwater sound channel at all ranges. A positive lens has a defocusing effect, yet with an increase in range it decreases significantly. The impulse response of the propagation channel was studied on the underwater acoustic channel axis at the ranges of 40 and 100 km. The maxima of impulse response during the passage of the sound emitter through the negative lens shift in time towards increasing, and when passing through the positive lens – towards decreasing with respect to the impulse response of the propagation channel in the absence of lenses.

An Autonomous Combined Receiving Acoustic System Based on a Three-Component Vector Receiver and a Hydrophone

A hydroacoustic autonomous receiving system that uses a combined receiver has been developed for carrying out investigations of the vector−scalar structure of acoustic fields under shallow water conditions with a submersion depth as large as 100 m. The acoustic fields are investigated by measuring the acoustic pressure and three orthogonal components of oscillatory acceleration using sensors with a sensitivity of 150−180 μV/Pa. In addition, data on the spatial position of the system from the orientation and depth sensors are synchronously recorded and, together with the data from acoustic channels, are saved to an SD card.

Formation Characteristics of the Zonal Structure of Acoustic Fields in the Deep Part of the Sea of Japan

The results of modeling the effects of stochastic levels of sound speed on formation of the zonal structure of acoustic fields for the hydrologic and acoustic environment of the deep part of the Sea of Japan. Numerical experiment involved calculation of the vertical structure of acoustic fields at the ranges from 20 to 120 km with discontinuity equal to 50 m in beam zooming for the set values of random component of sound speed field. In accordance with calculation, analytical correlations of changing coordinates of the closest and the furthest borderlines of the first three convergence zones at emitter depth depending on the level of random component of sound speed field were determined. Changes in borderlines of convergence zones occur in accordance with linear law; this said, the closest borderlines shift towards the emitter and the furthest borderlines – away from it. The obtained results of analyzing changes in structure of vertical distribution of acoustic field at the borderlines of convergence zones can be applied for engineering the systems of underwater monitoring for detection of local disruptions of acoustic velocity field of various nature against natural stochastic parameters of water environment in the deep part of the Sea of Japan.

Regional Variability of Influence of Small-Scale Sound-Speed Fluctuation Levels on the Acoustic Fields Formation in the Ocean

The results presented herein are the research findings about the influence of small-scale inhomogeneity’s in water environment on the structure of acoustic fields for hydrological and acoustical conditions that are typical for the Atlantic and Pacific Oceans. Small-scale sound-speed fluctuations were modeled by adding a stochastic perturbation to the deterministic mean profile. Quantitative experiment was conducted to determine the dynamics of changes in the first three convergence zones at the depths of emission source in relation to the random componentry in the sound-speed field. Analytical dependences of increasing widths of upper convergence zones on the level of the random componentry in the sound-speed field were determined based on the results of quantitative experiment. With increasing stochasticity levels, the width of convergence zones increases in accordance with linear law, and the absolute increments grow with the increase of convergence zone number. When the values of a random componentry in the sound-speed field are fixed, the absolute increment of width of the upper convergence zones in the Atlantic Ocean is higher than in the Pacific Ocean. This said, the gradient of a smooth profile of the sound velocity by depth above the axis of hydroacoustic channel is higher in the Atlantic Ocean. Consequently, the absolute increments of width of the convergence zones depend not only on the levels of stochasticity parameters of water environment, yet, also, on the gradient size of smooth profile of the sound speed at depths above the axis of hydroacoustic channel.

Features of the Invariant of the Spatial–Frequency Interference Structure of Acoustic Fields in Oceanic Waveguides

The paper considers the regular patterns that can be manifested in the behavior of the invariant of the spatial–frequency interference structure of an acoustic field in oceanic waveguides that are homogeneous and inhomogeneous along a track. Using the WKB and adiabatic approximations, an analytic expression is obtained for the invariant that, when certain conditions are fulfilled, reduces to the well-known classical expression independent of the mode numbers, their parity, or the emission frequency. It has been established that the approximate classical expression for the invariant correctly describes the slope of interference lines only in ranges of variation in the grazing angles of modes where the dependence of the cycle length of their corresponding Brillouin waves on the ray parameter is quite smooth and monotonic. The paper studies the formation of the spatial–frequency interference structure of an acoustic field propagating from a shallowwater isovelocity waveguide to a relatively deep-water waveguide with a near-surface sound channel.

The effect of the small-scale variability of sound velocity on the zonal structure of acoustic fields in oceanic waveguides

The effect of the small-scale variability of sound velocity on the zonal structure of acoustic fields in oceanic waveguides

Peculiarities of the Formation of the Interference Structure of Scalar-Vector Acoustic Fields on the Shelf of the Sea of Japan

The results of experimental study of the spatial structure of the scalar-vector acoustic field formed during towing of a tone low-frequency emitter over the shelf of the Sea of Japan are discussed. The experiment was accomplished by towing the source of a tone signal with a frequency of 134 Hz at a depth of 20 m over various acoustic tracks at distances up to 10 km from an integrated receiving system consisting of a receiver of acoustic pressure and three orthogonal components of the acoustic pressure gradient. Special attention has been focused on study of the interference structure of the scalar and vector fields with provision of the technical reliability of the method and the results of the experiment under controlled hydrological conditions. We discuss the quantitative characteristics and peculiarities of the interference formation along tracks that differ in depth. The unique results of comparing the horizontal and vertical components of the fields are most interesting of all. They allowed us to reveal the existence of eddy structures in the acoustic field of the source over several tracks. We analyze the possibility of practical application of the results of our research.

On measurement of acoustic pulse arrival angles using a vertical array

We consider a recently developed method to analyze the angular structure of pulsed acoustic fields in an underwater sound channel. The method is based on the Husimi transform that allows us to approximately link a wave field with the corresponding ray arrivals. The advantage of the method lies in the possibility of its practical realization by a vertical hydrophone array crossing only a small part of the oceanic depth. The main aim of the present work is to find the optimal parameter values of the array that ensure good angular accuracy and sufficient reliability of the algorithm to calculate the arrival angles. Broadband pulses with central frequencies of 80 and 240 Hz are considered. It is shown that an array with a length of several hundred meters allows measuring the angular spectrum with an accuracy of up to 1 degree. The angular resolution is lowered with an increase of the sound wavelength due to the fundamental limitations imposed by the uncertainty relation.

Ultrasound field structure simulation in acousto-optic cells with acoustic beam reflection

Some part of the acousto-optic devices fabricated from various crystals applies acoustic wave reflection from one of the crystal facets to arouse the wave with characteristics needed. The acoustic wave is at first aroused by piezoelectric transducer. It propagates along some direction and reflects from the acousto-optic cell face. The face orientation gives the possibility to obtain desired acoustic wave after the reflection. The reflection may be accompanied by the change of the acoustic mode type. The reflection process affects the acoustic beam structure causing the redistribution of acoustic energy inside the beam and the inclination of wave fronts. In this research the influence of acoustic beam reflection on the acoustoc field structure in the quasi-collinear acousto-optic cells fabricated from the tellurium dioxide crystal is examined and compared with acoustic beam reflection in collinear acousto-optic cell fabricated from the calcium molybdate crystal. Tellurium dioxide crystal has extremely strong acoustic anisotropy while calcium molybdate may be considered as acoustically isotropic media. The examined problem is solved using the original method when the media acoustic anisotropy influence on every component of ultrasound beam angular spectrum is taken into account. The presented research has also the applied importance as acoustic field structure influence on the acousto-optic devices characteristics. [This research was supported by the RSF grant №14-22-0042.]

Acoustic field structure simulation in quasi-collinear acousto-optic cells with ultrasound beam reflection

Ultrasound wave reflection from one of the crystal faces is the convenient way to arouse the acoustic beam with a desired propagation direction in acousto-optic cells with collinear and quasi-collinear interaction geometries. The reflection process effects on the ultrasound field amplitude and phase structure. The method to simulate the reflected finite ultrasound beam structure in the case of acoustically anisotropic media is presented in this paper. The investigation is carried on the example of two quasi-collinear acousto-optic cells fabricated on the base of tellurium dioxide crystal. The cells have special geometry that allows to obtain extremely long acousto-optic interaction length and to achieve unprecedented spectral resolution. The influence of reflection process in the acousto-optic diffraction characteristics was also examined.

Features of the energy structure of acoustic fields in the ocean with two-dimensional random inhomogeneities

The paper is devoted to the analytic study and numerical simulation of mid-frequency acoustic signal propagation in a two-dimensional inhomogeneous random shallow-water medium. The study was carried out by the cross section method (local modes). We present original theoretical estimates for the behavior of the average acoustic field intensity and show that at different distances, the features of propagation loss behavior are determined by the intensity of fluctuations and their horizontal scale and depend on the initial regular parameters, such as the emission frequency and size of sound losses in the bottom. We establish analytically that for the considered waveguide and sound frequency parameters, mode coupling effect has a local character and weakly influences the statistics. We establish that the specific form of the spatial spectrum of sound velocity inhomogeneities for the statistical patterns of the field intensity is insignificant during observations in the range of shallow-water distances of practical interest.

Investigation of acoustic beam reflection influence on the collinear acousto-optic interaction characteristics

Significant part of acousto-optic devices apply the acoustic beam reflection to arouse the desired type of acoustic mode propagating along the required direction in crystal. The influence of acoustic beam reflection process on the ultrasound field structure in the acousto-optic cell and the collinear acousto-optic diffraction characteristics is examined in this paper. The investigation is carried on the example of the collinear acousto-optic filter fabricated on the base of calcium molybdate crystal. It is shown that the reflection process changes the acoustic field structure and affects the acousto-optic filter transmission function shape and diffraction efficiency.

Array gain of conventional beamformer affected by structure of acoustic field in continental slope area

Conventional beamforming (CBF) is an important processing step in underwater array signal processing. Previous researches have shown that the sound field structure as manifested by amplitude nonhomogeneity and wave-front corrugation can reduce the array gain of CBF. The acoustic environment of the continental shelf slope area is very complex. For an underwater acoustic array in this area, the amplitude and phase of the received signals will be distortional seriously. Recently, the acoustic field correlation has been the focus of research on the array gain relations with the underwater acoustic filed. However, the attenuation of acoustic field correlation is not the only factor that induces the array gain to decline, and the analyses of the array gain in the shallow water based on normal-mode model are not applicable to the continental slope area. In this paper, the array gain relations with the structure of acoustic field in continental slop area are investigated based on the theory of underwater acoustic signal propagation. The effects of acoustic field on the signal and noise gains are considered respectively. The analytic expressions of the array gain of CBF in an isotropic noise field are derived from the primal definition of array gain, which indicates that acoustic field correlation and transmission loss in continental slope are the intrinsic factors that affect the array gain of CBF. A horizontal uniform linear array (ULA) with a wide aperture receiving signals from a source in the deep water region is considered in the upslope propagation condition. The RAM program is utilized in the numerical simulations to generate the sound field of this specific environment with given parameters. The array gains, the ATLs and the horizontal longitudinal correlation coefficients of the acoustic field corresponding to three different locations are compared. Conclusions can be drawn as follows. 1) The array gain of CBF is determined by acoustic field correlation and the acoustic average transmission loss (ATL), and its maximum is less than 10lg M as the signal waveform distortion. 2) when the ATLs corresponding to hydrophones at two different receiving locations are similar, the correlation of acoustic filed is higher, and the array gain of CBF is larger. 3) When the ATLs corresponding to hydrophones at two different receiving locations are greatly different, the relation between the array gain of CBF and the acoustic filed correlation is no longer positive. The simulation results verify the array gain of CBF relations with the acoustic filed correlation and the transmission loss in the continental slope area.

Study on Piston Slap Induced Liner Cavitation

Liner cavitation induced by piston slap in a diesel engine is caused by water pressure fluctuation when the pressure of coolant falls below saturated vapor pressure. Cavitation erosion of cylinder liners is thought to be generated by the impulsive pressure or jet flow impingement following the collapse of cavitation bubbles. In this study, a numerical method to predict the water pressure fluctuation in water coolant passage induced by piston slap impact force is developed. In complimentary impact vibration experiments, high frequency components of the water pressure fluctuation can be seen just after the pressure reaches the saturated vapor pressure level or less. These high frequency components seem to show the occurrence of cavitation. A finite element acoustic model of the water coolant passage in an actual engine block is created and its validity is confirmed by the acoustic vibration tests in air. Then, the coupled vibration characteristics of the water acoustic field and engine block structure are determined, and water pressure waveform induced by piston slap is predicted.

Study on the interference structure of vector acoustic field in shallow water

The application of vector sensors is closely associated with the characteristics of vector acoustic field in shallow water, whose study is the foundation for target detection, positioning, and classification. Beginning from Normal Mode theory, theoretical studies are presented about the amplitude of different components of vector acoustic field involving the pressure, horizontal and vertical particle velocity, as well as the phase relation between the pressure and the vertical particle velocity. The main factors considered here are the source depth and the range relative to the vector sensor. These interference structures were observed during the experiment that took place in July of 2013 in South China Sea of nearly 90m depth. The results indicated that the interference structures of vector acoustic field are not only influenced by the sound speed profile but also by seabed parameters including stratification depth and its corresponding acoustic properties. Moreover, the phase relation between the pressure and vertical particle velocity is remarkably impact by these parameters. [Work supported by the National 863 Project (No. 2011AA090502) and Defense Industrial Technology Development Program (B2420132004).]