Acoustic Scattering Research Articles

Underwater Acoustic Scattering from Multiple Ice Balls at the Ice–Water Interface

Underwater Acoustic Scattering from Multiple Ice Balls at the Ice–Water Interface

Acoustic Scattering From Rough Bubbly Ocean Surface Based on SSA and EMM

Acoustic Scattering From Rough Bubbly Ocean Surface Based on SSA and EMM

A Hybrid Finite Element Method – Kirchhoff Approximation Method for Modeling Acoustic Scattering from an Underwater Vehicle Model with Alberich Coatings with Periodic Internal Cavities

Anechoic tiles can significantly reduce the echo intensity of underwater vehicles, thereby increasing the difficulty of detecting such vehicles. However, the computational efficiency of conventional methods such as the finite element method (FEM) and the boundary element method (BEM) has its limitations. A fast hybrid method for modeling acoustic scattering from underwater vehicles with anechoic tiles with periodic internal cavities, is developed by combining the Kirchhoff approximation (KA) and FEM. The accuracy and rapidity of the KA method were validated by FEM. According to the actual situation, the reflection coefficients of rubber materials with two different structures under rigid backing are simulated by FEM. Using the KA method, the acoustic scattering characteristics of the underwater vehicle with anechoic tiles are obtained by inputting the reflection coefficients and the target’s geometric grid. Experiments on the monostatic target strength (TS) in the frequency range of 1 to 20 kHz and time domain echo characteristics of acoustic scattering on a benchmark scale model with anechoic tiles are conducted. The research results indicate that the TS values and echo characteristic curves of the KA solutions closely approximate the experimental results, which verifies the accuracy of the KA method in calculating the TS and echo characteristics of underwater vehicles with anechoic tiles.

Mathematics-Informed Neural Network for Acoustic Scattering by Parallel Plates

This paper proposes a mathematics-informed neural network (MINN) approach for resolving the long-term challenge in wave scattering modeling. The central innovation lies in integrating Cauchy–Riemann equations into machine learning architectures. By incorporating Cauchy integrals and boundary conditions, the neural network successfully learns to numerically produce matrix kernel factorization for Wiener–Hopf analytical models. To validate and demonstrate the approach, a benchmark case of wave scattering from parallel hard–soft plates is studied by comparing the machine learning results with the available analytical solutions. The proposed MINN approach could provide a new route to extensively enhance the theoretical modeling capability for several wave scattering and fluid mechanics problems. The code can be found at https://github.com/lscapku/MINN.

Highlight Model of Underwater Target Acoustic Scattering in the Bistatic System

<p>A highlight model for the target signal in the bistatic system is proposed based on the calculation results of the acoustic field, which means that the target can be equivalent to several highlights according to certain characteristics of the target when calculating the scattering acoustic field. The parameters of the highlight model were given based on the calculation results. Two sets of experiments on the highlight model of the bistatic system were conducted with a fixed transmitter and a target, one being the receiver rotating around the target, and the other being the target rotating around itself at different receiver angles. The comparison of multi angle pseudo color images through experiments and theoretical simulations shows that the scattering highlight model can describe the scattering characteristics of the target to a certain extent. Only geometric highlights were simulated in this article, and it can be foreseen that bistatic system highlight model of scattering waves can be accurately described with a full understanding of the target.</p> <p> </p>

An Efficient Method for Solving Problems of Acoustic Scattering on Three-Dimensional Transparent Structures

The article contains a study of methods for solving integral equations in the context of acoustic problems. The methodology considered is applied to describe acoustic wave propagation and scattering. Efficient discretization methods are used together with iterative methods to solve the operator equations, including an apparatus for fast multiplication of the resulting post-discretization Toeplitz matrices by a vector using the fast Fourier transform. The theoretical analysis of the proposed numerical algorithm demonstrates its efficiency in terms of the required number of arithmetic operations and the memory footprint of the computing system. The presented numerical simulation demonstrates the possibility of solving the problem of acoustic wave propagation in transparent media using the proposed methods. A visualization of the obtained solutions for a practical problem with a high level of discretization of the solution volume domain is also presented.

Parametric study of blind-label acoustic subwavelength imaging

There is a long-existing tradeoff between the imaging resolution and the penetration depth in imaging systems caused by the diffraction limit. We developed a “blind label” approach to tackle this problem, which significantly improves the practicality of acoustic subwavelength imaging in biomedical ultrasound imaging, non-destructive testing, and other acoustic sensing and communication applications. The “blind labels” in our system refer to randomly distributed acoustic scatterers with deep-subwavelength sizes whose exact locations and trajectories are not necessary information in image reconstruction. Our imaging framework is composed of two parts: (1) spatial mixing: a physical process that converts the originally evanescent components in the scattered waves from the object to propagating components that can reach the far-field detector and (2) computational reconstruction. In this talk, we will mainly report our quantitative investigation of the system parameters’ impact on the performance of the blind-label subwavelength imaging system, providing guidance to future system setups in various applications.

Acoustic Scattering Characteristics and Geometric Parameter Prediction for Underwater Multiple Targets Arranged in a Linear Pattern

The construction of wind farm pilings, submarine pipelines, and underwater submarines involves multiple cylinders. However, there is currently a lack of economic research on predicting the mechanism and characteristics of mutual coupling of acoustic scattering from multiple cylindrical targets. This study investigates the mechanism and prediction method of acoustic scattering for the structural distribution characteristics of underwater multi-cylindrical targets. A model of a multi-cylindrical target’s two-dimensional acoustic field was established using the finite element method. Numerical calculations were then carried out to elucidate the scattering characteristics of the frequency–angle spectrum in far-field omnidirectional scattering. The simulation of echoes in the time domain explains how echoes propagate and interact with each other, and provides formulas for calculating interference and resonance frequencies. The frequency calculation formula extracts key features from the spectrum, providing a basis for predicting the characteristics of multi-cylindrical targets in terms of scale and spatial position. Measurement experiments were conducted on a double-cylindrical target in a water tank, and the theoretical calculations and experimental data were used to estimate the target’s radius and distance. The actual layout confirms the accuracy of the interference and resonance frequency prediction formulas. This study offers a valuable solution for refined feature extraction and spatial estimation of underwater targets.

Diel Vertical Migrators Respond to Short‐Term Upwelling Events

AbstractPelagic organisms inhabiting coastal upwelling regions face a high risk of advection away from the nearshore productive habitat, potentially leading to mortality. We explored how animals remain in a productive yet highly advective environment in the Northern California Current System using the cabled observatory system located off the Oregon coast. Acoustic scatterers consistent with swimbladder‐bearing fish were only present during the downwelling season as these animals avoided the cold waters associated with strong upwelling conditions in summer and fall. Fish responded to short‐term upwelling events by increasing the frequency of diel vertical migration. Throughout the study, their vertical positions corresponded to the depth of minimum cross‐shelf transport, providing a mechanism for retention. The observed behavioral response highlights the importance of studying ecological processes at short timescales and the abilities of pelagic organisms to control their horizontal distributions through fine‐tuned diel vertical migration in response to upwelling.

A New Class of Uniformly Stable Time-Domain Foldy–Lax Models for Scattering by Small Particles. Acoustic Sound-Soft Scattering by Circles

A New Class of Uniformly Stable Time-Domain Foldy–Lax Models for Scattering by Small Particles. Acoustic Sound-Soft Scattering by Circles

An acoustic investigation of the near-surface turbulence on Mars.

The Perseverance rover is carrying out an original acoustic experiment on Mars: the SuperCam microphone records the spherical acoustic waves generated by laser sparks at distances from 2 m to more than 8 m. These N-shaped acoustic waves scatter from the multiple local heterogeneities of the turbulent atmosphere. Therefore, large and random fluctuations of sound travel time and intensity develop as the waves cross the medium. The variances of the travel times and the scintillation index (normalized variance of the sound intensity) are studied within the mathematical formalism of the propagation of spherical acoustic waves through thermal turbulence to infer statistical properties of the Mars atmospheric temperature fluctuation field. The comparison with the theory is made by simplifying assumptions that do not include wind fluctuations and diffraction effects. Two Earth years (about one Martian year) of observations acquired during the maximum convective period (10:00-14:00 Mars local time) show a good agreement between the dataset and the formalism: the travel time variance diverges from the linear Chernov solution exactly where the density of occurrence of the first caustic reaches its maximum. Moreover, on average, waves travel faster than the mean speed of sound due to a fast path effect, which is also observed on Earth. To account for the distribution of turbulent eddies, several power spectra are tested and the best match to observation is obtained with a generalized von Karman spectrum with a shallower slope than the Kolmogorov cascade, ϕ(k)∝(1+k2L2)-4/3. It is associated with an outer scale of turbulence, L, of 11 cm at 2 m above the surface and a standard deviation of 6 K over 9 s for the temperature. These near-surface atmospheric properties are consistent with a weak to moderate wave scattering regime around noon with little saturation. Overall, this study presents an innovative and promising methodology to probe the near-surface atmospheric turbulence on Mars.

Fredholm Integral Equation for Problems of Acoustic Scattering by Three-Dimensional Transparent Structures

We consider the differential and integral statements of problems of acoustic scattering by three-dimensional bounded transparent structures described by an integral equation. The results of the numerical solution of the integral equation describing the class of problems under consideration are presented. A theorem on existence and uniqueness of the solution is proved.

Hermite-scan imaging for differentiating glioblastoma from normal brain: Simulations and ex vivo studies for applications in intra-operative tumor identificationa).

Hermite-scan (H-scan) imaging is a tissue characterization technique based on the analysis of raw ultrasound radio frequency (RF) echoes. It matches the RF echoes to Gaussian-weighted Hermite polynomials of various orders to extract information related to scatterer diameter. It provides a color map of large and small scatterers in the red and blue H-scan image channels, respectively. H-scan has been previously reported for characterizing breast, pancreatic, and thyroid tumors. The present work evaluated H-scan imaging to differentiate glioblastoma tumors from normal brain tissue ex vivo. First, we conducted 2-D numerical simulations using the k-wave toolbox to assess the performance of parameters derived from H-scan images of acoustic scatterers (15-150 μm diameters) and concentrations (0.2%-1% w/v). We found that the parameter intensity-weighted percentage of red (IWPR) was sensitive to changes in scatterer diameters independent of concentration. Next, we assessed the feasibility of using the IWPR parameter for differentiating glioblastoma and normal brain tissues (n = 11 samples per group). The IWPR parameter estimates for normal tissue (44.1% ± 1.4%) were significantly different (p < 0.0001) from those for glioblastoma (36.2% ± 0.65%). These findings advance the development of H-scan imaging for potential use in differentiating glioblastoma tumors from normal brain tissue during resection surgery.

Modulation Mechanism of Acoustic Scattering in Underwater Corner Reflectors with Acoustic Metasurfaces

Modulation Mechanism of Acoustic Scattering in Underwater Corner Reflectors with Acoustic Metasurfaces

A Method to Determine Bubble Distribution in Liquid Using Data of Inverse Acoustical Scattering

Abstract Information on bubble distributions in liquids is required for various applications. Employment of inverse acoustic scattering is the usual path to determine these distributions. This path is based on solving a Fredholm first kind integral equation leading to an ill-posed mathematical problem. The usual regularization methods for such a problem are quite complex and require introduction of some tuning parameters. Meanwhile, as shown in this paper, another method works well for media, where acoustic waves propagate with the small losses. This method is based on extraction of a singular Cauchy integral in the above-mentioned equation and of the further inversion of this integral. Such a regularization via inversion is a simple operation that gives numerically stable solutions. Here this regularization is described, verified using the method of manufactured solutions and validated with the well-known already published experimental data.

A Method for Enhancing the Acoustic Scattering Characteristics of Underwater Acoustic Corner Reflectors in Vacuum Cavities

To alleviate the problem of unsatisfactory target strength and scattering stability of an underwater corner reflector, a method to enhance the acoustic scattering characteristics using a vacuum cavity as an acoustic reflecting layer is proposed. According to the principle of acoustic impedance mismatch of a water-reflecting layer, a vacuum cavity corner reflector is designed to take advantage of the property that sound waves cannot propagate under vacuum conditions. The acoustic vacuum reflecting layer has a theoretical acoustic reflecting coefficient of one. Comparative analyses are carried out with the single-layer metal corner reflector in terms of frequency and angle of incidence. For the concave structure of the underwater corner reflector, the structural finite element software ANSYS combined with the acoustic analysis software SYSNOISE is used to simulate and analyse the acoustic scattering characteristics, and the consistency of the simulation calculations and experimental data is verified through the pool experiments for typical cases. The results show that under the same reflection area, the vacuum cavity underwater corner reflector has large scattering intensity, good antiacoustic performance, no obvious frequency characteristics, and good decoupling effects. The target echo intensity value can be increased by 2 dB for better scattering stability. The overall weight is reduced by about 20 kg, with considerable engineering practicality, proving that the true cavity corner reflector is an ideal underwater acoustic counter-acoustic device.

Acoustic cloning

Cloning refers to producing copies of objects that cannot be distinguished from the original based on their behavior or response. Here, we present a general methodology to clone objects that scatter acoustic waves and demonstrate it experimentally. We acquire digital twins and bring them back to life—a simple two-step process. First, we place the scattering object in a circular receiver aperture and insonify it from the outside using simple speakers. From the recorded data, which may be reverberative, we retrieve the object's scattering Green's functions for radiation conditions using a technique called multi-dimensional deconvolution. This process recovers the temporal and spatial bandwidth and removes the scattering interactions with the boundaries of the experimentation domain, if present. In the second step, the acoustic scatterer is removed and reconstructed holographically using the acquired scattering Green's functions. The hologram scatters arbitrary incident wavefields in real-time exactly like the original object. Low-latency feedback enables reproducing all orders of wave interactions between physical scatterers and the numerical hologram. The two-step process is demonstrated by cloning several rigid scatterers in a two-dimensional acoustic waveguide. Applications range from fully realistic digital scattering models to efficient meta-material experimentation. [Work supported by SNSF grant 197182.]

Reciprocity, passivity, and causality in fully coupled acousto-electrodynamic media

Multiple-scattering homogenization procedures in acoustics and electromagnetics have shown that subwavelength asymmetries and lattice effects in metamaterials give rise to bianisotropy, the tensorial coupling of two constitutive relations. Asymmetric piezoelectric scatters in the quasi-electrostatic regime have recently been shown to couple the electric field to the bianisotropic elastodynamic relations, yielding an additional, emergent property termed electro-momentum coupling. To facilitate the study of scatterers responsible for electro-momentum coupling, Wallen et al. [Proc. Mtgs. Acoust. 46, 065002 (2022)] and Lee et al. [J. Appl. Phys. 132, 125108 (2022)] abandoned the quasi-electrostatic approximation in favor of a simultaneously acoustic and electrodynamic scatterer. We previously used a multiple-scattering homogenization procedure to show that a collection of such scatterers gives rise to constitutive relations that fully couple acoustics and electrodynamics. Now, we derive bounds on these fully coupled relations due to reciprocity, passivity, and causality. These results recover known bianisotropic and piezoelectric bounds and reveal that the imaginary parts of the additional electro-momentum and magneto-momentum coupling coefficients vanish in lossless, reciprocal, and passive media. The bounds also verify that the constitutive relations derived by our homogenization procedure satisfy reciprocity, passivity, and causality. [Work supported by DARPA and ARL:UT McKinney Fellowship in Acoustics.]

Direct measurements of gas flux at seep sites using a broadband split-beam echosounder

Measurement of methane gas flux from oceanic seep sites is challenging, given the ephemeral nature and the heterogeneous spatial distribution of seeps. Acoustic systems offer a solution, as they make synoptic measurements of the water column, and the gas bubbles are strong acoustic scatterers. Here, we present a method to directly estimate gas flux using a calibrated broadband split-beam echosounder. The vertical range resolution of the broadband system facilitates discrimination of individual bubbles in the acoustic record. By comparing measurements of bubble target strength to an analytical scattering model, bubble radii can be directly measured from the acoustic data. Concurrently, split-aperture processing allows for the precise tracking of bubbles as they rise from the seafloor for measurement of bubble rise velocity. Together, the observations of bubble radius and rise velocity offer a measure of gas flux, requiring nothing more than a vessel transiting over a seep site. Application of this method to seep data collected on the East Siberian Arctic Shelf shows good agreement between resulting measurements of bubble radii (0.68–8.40 mm) with those made using optical sensors, and bubble rise velocities (4–36 cm/s) are consistent with published measurements and models. Extrapolating from single bubbles measurements, our estimates of regional methane flux (2.9 × 104 kg/year) suggest that carbon emissions in this region may be lower than previously believed.

Blind-label acoustic subwavelength imaging

There is a long-existing tradeoff between the imaging resolution and the penetration depth in acoustic imaging caused by the diffraction limit. Most of the existing subwavelength imaging approaches that address this trade-off require exogenous “labels,” such as metamaterials or contrast agents, to be deposited close to the objects. Those labels need to either remain static or be tracked precisely during imaging, therefore, are extremely restrictive in practical applications. This talk will present our recent work on a “blind label” approach for acoustic subwavelength imaging. The “blind labels” are randomly distributed acoustic scatterers with deep-subwavelength sizes whose exact locations and trajectories are unknown. A hardware/software co-design framework is developed that is composed of two parts: 1) spatial mixing: a physical process that converts the originally evanescent components in the scattered waves from the object to propagating components that can reach the far-field detector; 2) computational image reconstruction. Our experiments both in air at KHz frequency range and in water at MHz frequency range achieved multi-fold resolution enhancement. The proposed “blind-label” approach relaxes the restrictions of depositing controlled labels close to the object, therefore significantly improving the practicality of acoustic subwavelength imaging in acoustic sensing, imaging, and communication applications.