bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic radiation force and torque on an object near a penetrable interface or impedance boundary
Authors: Simon Blake E. , Hamilton Mark F.
Published: April 2023

An analytical approach for calculating radiation force and torque on a sphere or spheroid near a rigid or pressure release boundary due to an arbitrary incident acoustic field was developed recently by the authors [Proc. Meet. Acoust. 48, 045004 (2022)]. In that approach, the linear scattering problem is solved using the method of images along with expansions of the acoustic fields in spherical or spheroidal wave functions. The expansion coefficients can then be substituted into an existing expression to obtain the radiation force and torque on the object. In the present work, the aforementioned theory is extended to include penetrable interfaces and impedance boundaries using an approximation of the interfacial boundary conditions. For fluid-fluid interfaces, the object can be placed on either side of the interface with respect to the incident field. This approximate analytical approach is computationally efficient and compares well with the results from an independent finite element model. In addition, an experiment was conducted with a plastic sphere submerged in water and positioned near a boundary. Results from the experiment are discussed in relation to the analytical model. [BES is supported by the ARL:UT Chester M. McKinney Graduate Fellowship in Acoustics.]
Extraction and manipulation of hydrocarbon droplets by ultrasound radiation
Authors: Lirette Robert , Mobley Joel
Published: April 2023

Acoustic tweezers are a method of using sound radiation forces to trap and manipulate objects. Previously, we demonstrated an acoustic tweezer capable of first creating the objects, droplets of CCl4 from a reservoir, before trapping and manipulating them. We achieved this using a single transducer whose field was modified by a low-profile fraxicon (Fresnel axicon) lens exhibiting specific near-field trapping zones and far-field Bessel beam behavior which enable the trapping process. Here, we extend the method to include another class of fluids, complex hydrocarbons, using conventional SAE30 motor oil in water. Furthermore, with the higher power levels used in this study we demonstrate the discovery of a second trapping region in the field generated by our transducer. The non-contact extraction and manipulation of organic and hydrocarbon fluid samples could have significant biological and environmental applications where a container would contaminate, destroy, or otherwise change the samples under investigation.
Acoustophoresis under multiple simultaneous frequencies
Authors: Rear David B. , Feke Donald L.
Published: April 2023

The manipulation of suspended particles using ultrasonic fields remains an active area of research due to the many potential applications of acoustophoresis. While prior research has focused primarily on the acoustophoretic behavior of particles in response to an acoustic field of a single wavelength, relatively little work has been done to study the acoustophoretic behavior of subject to two or more concurrent frequencies of sound. The presence of multiple concurrent, resonant frequencies can lead to more complicated particle behavior spatially across the chamber than the simple node/anti-node attraction/repulsion behavior present in single-frequency chambers. In this study, we investigate the behavior of spherical particles (both single phase and core-shell) in multi-frequency chambers in both the Rayleigh (long wavelength) limit and cases where the particle size is the same order of magnitude as the wavelength of the background field. A mathematical description of the phenomena is developed in terms of the ratios of the pressure amplitudes for the individual background frequencies, including the criteria for continuously moveable nodes. Attention will also be paid to the implications of more than one simultaneous frequency on the motion of particles undergoing a change in size.
Accurate determination of elastic anisotropy to detect internal microstructures using resonant ultrasound spectroscopy
Authors: Maiorov Boris , Munroe Tannor , Peria William K. , Mizzi Christopher A.
Published: April 2023

Elastic constants are of great significance, because they are fundamental thermodynamic susceptibilities that connect directly to thermodynamics and electronic structure, as well as to mechanical properties. Resonant ultrasound spectroscopy (RUS) measures non-destructively all fundamental elastic properties by determining the natural frequencies at which a 3D object resonates when is mechanically excited (normal modes). By using an inversion scheme, it is possible to extract the entire elastic tensor of a material with extreme sensitivity in a single frequency sweep using only one, small sample. This makes RUS particularly advantageous to study physical properties of low-symmetry single crystals and textured bulk materials. I will present recent RUS measurement examples of its applications to thermodynamic and materials science problems. I will focus on the effect of texture in elastic constants as a result of mechanical or growth processes and the robustness of results obtained by RUS. In materials such as aluminum that is often considered isotropic but shows clear anisotropy when it is extruded, or 3D printed. Similar but much larger effect is found in additive manufactured stainless steel where the growth process leads to a large anisotropy with a softening of 40%–50% along the build direction.
Relaxing free boundary conditions in resonant ultrasound spectroscopy for extreme environments
Authors: Mizzi Christopher A. , Munroe Tannor , Maiorov Boris
Published: April 2023

Elastic constants are thermodynamic susceptibilities, which provide symmetry-resolved insight into phase transitions and material anisotropy. Therefore, their importance spans basic to applied science and engineering. Resonant ultrasound spectroscopy (RUS) is a powerful method to determine elastic constants, because RUS simultaneously measures all elastic constants in small, low symmetry samples with high precision and accuracy. Conventionally, elastic constants in RUS are obtained from resonant frequencies assuming the sample freely resonates. However, achieving free resonance is often incompatible with experimental situations, because such configurations are inherently unstable. This limitation has hindered utilizing RUS to study phases arising in extreme environments like strong magnetic fields. To overcome these obstacles, we introduce a variation of RUS in which small, finite-area contact is maintained between the sample and ultrasonic transducers using an adhesive. First, we establish the conditions under which this clamped point contact can be treated as a small perturbation to free resonance. After comparing predictions from this modelling with experiment, we then experimentally demonstrate the ability to extract elastic constants, and their temperature dependence, with comparable accuracy and precision to conventional RUS. Finally, we show we can reproducibly map phase boundaries in temperature and magnetic fields using our new approach.
In search of the missing resolved harmonics: Neural and behavioral studies of pitch discrimination
Authors: Delgutte Bertrand
Published: April 2023

The pitch of harmonic complex tones (HCT) plays important roles in speech and music perception and in the perceptual organization of sound. Human listeners rely primarily on the spectral pattern of harmonics individually resolved by the frequency analysis in the cochlea to derive a pitch percept. Yet, evidence for a robust neural representation of resolved harmonics in animal models has been elusive, and some species appear to rely on temporal envelope cues rather than on resolved harmonics to discriminate pitch. We performed both behavioral experiments on pitch discrimination by rabbits and single-unit recordings from the auditory nerve (AN) and inferior colliculus (IC) using HCTs with equal-amplitude harmonics in which the fundamental frequency (F0) was varied over a wide range. We found that rabbits can discriminate the pitch of HCT using the spectral pattern of resolved harmonics for F0s within the range of conspecific vocalizations. Correspondingly, many IC neurons contribute to a rate-place code for the frequencies of resolved harmonics for F0s >500 Hz, and this code is more robust to variations in stimulus level than that found in the AN. A remaining challenge is to identify the neural mechanisms underlying enhanced rate-place coding in IC. [Work supported by NIH-NIDCD DC002258.]
Laser Doppler vibrometry-based measurements on viscoelastic panels for flexural damping properties
Authors: Xiang Ning , Taylor Jack , Miller Max
Published: April 2023

Bending wave propagation is of central importance when enhancing sound transmission losses of sandwiched wall board systems incorporating viscoelastic panels as constrained damping layers. The damping properties of constrained damping layers made of viscoelastic materials can often be characterized by bending wave excitations. However, the multifactor, dispersive nature of the bending waves leads to challenges in reliable dynamic material characterization. To better understand the damping mechanism of the constrained damping layers, an experimental methodology employing complex bending wave theory has been developed to determine these flexural wave properties, including the loss factor and the bending stiffness of highly viscous panels. Relying on a transfer function from the experimentally measured bending velocities between two locations radially away from a flexural wave exciter on the viscoelastic panel under test, this methodology yields the broadband bending loss factor, the bending phase speed, and the bending stiffness. This paper discusses the experimental method for characterizing the above properties from laser Doppler vibrometry-based measurements of bending velocities. This paper also discusses the challenges with this method as well as an approach to mitigate the challenging effects and improve measurement accuracy.
The acoustics of shrieking perforated panels
Authors: Hord Samuel K. , Pearson Robert M. , Dickerson Michael L. , Shafer Benjamin M.
Published: April 2023

Under windy conditions, vortex shedding can cause perforated metal skins to emit undesirable noise. This phenomenon was observed, measured, and replicated. The acoustic spectrum was analyzed and compared to the modes of a vibrating plate. An extensional-damping layer was added to the plates for vibration isolation. The damping layer was applied as a high-loss painted coating to the surface of the plates. The acoustic spectrum was then analyzed again and compared to the spectrum without treatment. This study describes the process used to investigate and solve this noise control problem.
Modeling nonlinear acoustic damping due to flow separation over a baffle blade
Authors: Day Joseph , Quinlan J. M.
Published: April 2023

Nonlinear acoustic damping has been observed in many high-amplitude acoustic systems as a result of flow separation and shear layer vortical motion, eventually transforming some of the acoustical energy into heat. The amount of nonlinear acoustic damping helps determine the nonlinear limit cycle amplitude, e.g., damping caused by baffle blades in a liquid rocket engine to reduce combustion instabilities. The damping mechanism is dependent on both the location and phase of flow separation. Flow separation is a function of both the boundary layer growth and the acoustically imposed pressure gradient. When the acoustic pressure gradient is adverse, the boundary layer is more prone to separation. Using this as a basis, a model can be created, applicable to general geometry, which can approximate nonlinear acoustic damping in flow over baffle blades. The constructed model will be compared to established cases, such as an orifice in a duct, to validate the model. Once validated, this model can approximate the nonlinear acoustic damping caused by a baffle blade, for both standing and traveling waves, and will be compared to experimental results to test accuracy. This model could result in designing rocket engines based on engine specific damping requirements rather than past successful designs.
Compressed sensing using a trajectory-based model for ultrasonic tomography in a wooden medium with cylindrical symmetry
Authors: Lee Yishi
Published: April 2023

Stress wave propagation induced by embedded waveguides in circular cross-sections produces radial AW1a, reflected mode (AW1b), and Rayleigh propagations (AW2). Prior studies in this area have developed optimal filtering techniques to extract the characteristics of different arrival components from the time-series waveform. This study exploits the information uncovered in the time-series signal to reduce the sensing requirements for stress wave tomographic inversion. This work employs the algebraic reconstruction technique (ART) and the trajectory estimation from the transient finite element model (FEM) to perform the tomographic inversion. The proposed methodology consists of the following steps: (1) Estimate the arrival trajectories using the time-dependent energy flux propagation vector from the existing FEM-based propagation model. (2) Formulate the pixel contribution matrix based on the estimated trajectories from step 1. (3) Based on a known priori, perform tomographic inversion based on the optimal relaxation and additive iterative techniques. This presentation will discuss the technique and the associated algorithm and present the results of the proposed reconstruction technique with numerical validations. Its broader impact will drastically reduce the traditional through-transmission tomography from 28 measurements around the circular cross-sectional region to 6, providing rapid data collection with comparable efficacy.
Optimization of synthetic aperture delay-multiply-and-sum reconstruction
Authors: Holmes Philip M. , Lee Hyungkyi , Urban Matthew W.
Published: April 2023

Synthetic aperture (SA) acquisition allows for focusing at all points in ultrasound images during reconstruction. Both delay-and-sum (DAS) and delay-multiply-and-sum (DMAS) have been used to reconstruct SA images. An integral part of both algorithms is the aperture size used to define the beam shape with the f-number. Although f-number variation has been studied in DAS reconstruction, there has not been a systematic study on this topic for DMAS reconstruction in SA imaging. In this work, we evaluated the effects of f-number in DMAS reconstruction using an imaging phantom (CIRS 040GSE). We reconstructed DAS and DMAS images of hyperechoic, hypoechoic, and anechoic contrast targets, as well as point targets, while varying the transmit and receive f-numbers between 0 and 7 in 0.2 increments. Generalized contrast-to-noise ratio (gCNR) was measured for contrast targets. The full width at half maximum (FWHM) was evaluated using point targets. When imaging contrast targets, the DAS and DMAS algorithms responded very differently when varying the f-numbers. DMAS produced higher gCNR values with low transmit f-numbers and high receive f-numbers, while DAS produced higher gCNR values with high transmit and receive f-numbers. When evaluating FWHM, the optimal receive f-number was close to 1 for both algorithms.
Rapid beamforming of ultrasound chirp signals in frequency domain using the chirp scaling algorithm
Authors: Zhuang Louise L. , Dahl Jeremy , Zebker Howard , Jakovljevic Marko
Published: April 2023

Linear frequency-modulated (chirp) transmits have been used successfully in the past to increase penetration depth of ultrasound signals in tissue and to improve the signal-to-noise ratio (SNR) in the resulting ultrasound images. However, beamforming chirp signals using delay-and-sum (DAS) can be slow on systems without a GPU. We propose using the chirp scaling algorithm (CSA), originally developed for synthetic aperture radar, as a faster alternative to DAS on CPU that results in similar image quality, especially at larger depths. To perform preliminary comparisons of the beamforming methods, we simulated in FIELD II monostatic synthetic aperture data containing point targets up to 300 mm in depth. The simulation accounted for average signal attenuation in soft tissue of 0.5 dB per MHz per cm. We analyzed the point spread functions and the runtimes of the methods in MATLAB with a single CPU. Beamformed point targets above 80 mm depth had almost identical sidelobe levels and full-width-at-half-maximum between the two methods, while the median runtime for CSA was 9.3 times faster than for DAS. We further extend CSA to multistatic acquisitions with chirp transmits and with curvilinear arrays for more clinical applicability and improved image quality.
Spatiotemporal image reconstruction for photoacoustic computed tomography of tumor vascular perfusion in murine models
Authors: Cam Refik Mert , Park Seonyeong , Anastasio Mark , Villa Umberto
Published: April 2023

Monitoring critical physiological processes in murine models like tumor vascular perfusion and its response to prospective anti-cancer treatments is a significant potential use case of dynamic photoacoustic computed tomography (PACT). Previously reported studies of dynamic PACT are based on a frame-by-frame image reconstruction (FBFIR) procedure in which full-view measurement data are assumed to be rapidly acquired. However, many commercial three-dimensional PACT imagers acquire measurements at each tomographic view rotating the object in discrete steps. The time to collect the full-view data is limited by the rotation speed of the object holder and the laser repetition rate. Therefore, FBFIR techniques are not applicable, and there is a critical need for accurate and efficient spatiotemporal image reconstruction (STIR) techniques that can account for spatiotemporal redundancies in the object’s features. To address this, we propose a low-rank matrix estimation-based STIR technique in which the sought-after dynamic image is approximated using a semiseparable approximation in space and time. To validate the proposed method, we also develop a virtual imaging framework for PACT employing dynamic numerical mouse phantoms with a physiologically realistic respiratory motion and perfusion model. The studies demonstrated that the proposed method accurately recovers the tumor vascular perfusion and object motion.
Rapid refocusing of ultrasound images in frequency domain using range-Doppler algorithm
Authors: Jakovljevic Marko , Zhuang Louise L. , Samir Anthony E.
Published: April 2023

The ability to maintain image uniformity and high resolution over large depths is important for several clinical applications of ultrasound, including deep abdominal imaging in patients with high BMI. One way to improve image quality in such cases is to use retrospective transmit focusing, which involves combining received data from different focused transmits to improve image resolution and SNR outside of transmit focal zone. Retrospective transmit is typically accomplished using the delay-and-sum (DAS) beamforming, which can be slow on systems without a GPU. As a faster alternative, we treat beamsummed signals from focused transmits as monostatic synthetic aperture data from virtual sources, and apply a frequency-domain beamformer such as RDA to rapidly refocus an RF image. We demonstrate the concept using FIELD II simulated ultrasound signals from a point target phantom over 200 mm depth. The RDA-refocused image shows a uniform point spread function, and the reduction in full-width at half maximum by a factor of 2.5 compared to the original image from focused transmits at f-number 10. RDA-based refocusing also achieves a speedup by a factor of 14 relative to the DAS-based retrospective beamformer.
Learning source-receiver range in a laboratory tank with variable water temperature
Authors: Dobbs Corey E. , Hopps Alexandra M. , Neilsen Tracianne B.
Published: April 2023

Deep learning has great potential to be useful for ocean acoustics problems. However, uncertainty in an ocean environment must be taken into account, because it affects the ability of trained machine learning models to generalize. Because ocean measurements are costly, we are using a laboratory water tank to help develop our deep learning neural networks. In addition, using a water tank in a lab increases some level of control over the amount of uncertainty in data used to train neural networks. A residual convolutional neural network architecture is trained to identify source-receiver range in an underwater tank environment at room temperature. The model is then tested on data taken with variable water temperature. For comparison, two different source signals are used (sine waves and linear chirps) to analyze the usefulness of broadband sounds. These tests explore how environmental uncertainty impacts source localization and will lead to insights on how to develop robust machine learning for ocean acoustics problems. [Work supported by the Office of Naval Research.]
Hydrophone calibration between 1 kHz and 10 kHz using elastic waveguides
Authors: Drinnan Robert , Barclay David R.
Published: April 2023

Modern techniques for hydrophone calibration from IEC 60565:2020 typically require sensors to be placed in a free field or within a hydrostatically varying chamber. At mid-frequencies (defined as 1 kHz–10 kHz), the wavelength is too long for free-field conditions in tanks available to most manufacturers and academics. A novel technique to calibrate hydrophones is investigated to address the measurement gap between very-low-frequency (0.1 Hz–1 kHz) and high-frequency (10 kHz–200 kHz) techniques. The measurement environment consists of a 12-meter length of copper tubing that is coiled into a 1-meter diameter helix. Propagation in the elastic waveguide decreases the speed of sound within the apparatus and the wavelength relative to its free-space equivalent. This provides a longer reverb-free time within which to make the calibration measurements using a small (<1 m3) volume. To increase the gain of the system, the recorded files are matched filtered against normalized transmission replicas to determine the signal energy at the receiver. The propagation within the waveguide is studied, including investigating the modal dispersion and channel gain. Calibrations are performed on multiple Ocean Sonics icListen hydrophones, including independently calibrated reference units, using an uncalibrated source to determine the accuracy and precision of the system.
Using Bayesian optimization to refine laboratory tank sound propagation modeling
Authors: Hollingsworth Scott P. , Neilsen Tracianne B.
Published: April 2023

Because ocean measurements are costly, a laboratory water tank provides opportunities to take scaled measurements and develop approaches to machine learning that are transferable to ocean acoustic problems. These applications are better achieved if reflections off the side walls are significantly reduced. To reduce these reflections, the side walls of the tank are lined with Aptile SF5048 echo reducing tiles made by Precision Acoustics. This work studies the extent to which two ocean sound propagation models (namely ORCA and BELLHOP) can predict relative transmission loss as a function of source-receiver range and frequency. The modeling parameters of sound speed and density that determine the reflections at the bottom of the tank were refined through a Bayesian optimization algorithm. We found that the optimized parameters improve the model-data agreement and that the models fit the data at certain frequencies corresponding mainly to peaks in the echo reduction for the Aptile panels. This agreement implies that at certain frequencies, sound propagation in our tank acts as it would in a large body of water. Using our tank as a testbed for developing machine learning algorithms is a reasonable approach.
A vector classifier for sound similarity classification based on audio features
Authors: Yilmazer Cengiz , Yilmazer Semiha
Published: April 2023

This study introduces a vector classifier for Sound Similarity Classification. Sound classification using the known features can be accepted as the prime definition within a limited time. However, the sound is a function not only of spectral composition but also a change of this composition in time Then, it should be characterized with flexible classifier vectors as a function of time segment. The study considers (1) steady-state time segmentation of sound with respect to feature deviations and creating time-marked classifier vectors within the segment made of the know features and (2) using long-time combined segments and histogram base classifiers within the classifier vector. The main subject of the work is the reduction of memory and computation time effectiveness and similarity detection capability.
A retrospective on monitoring noise pollution with machine learning in the Sounds of New York City project
Authors: Cartwright Mark , Mydlarz Charles , Bello Juan P.
Published: April 2023

The Sounds of New York City (SONYC) project (2016–2022) was a project to monitor and mitigate urban noise pollution using a smart acoustic sensor network, citizen scientists, and collaboration with city agencies. During its lifetime, the project deployed 75 fixed-location sensors and collected over 150 × 106 10-s audio recordings. A key element of the project was the development of machine listening models to detect the sources of noise pollution rather than just the overall noise level. In this talk, we first discuss our initial approach to data collection and machine listening including sensor development and deployment, citizen-science data annotation, self-supervised audio representation learning, and downstream sound-event detection model training. We then discuss analysis results using the outputs of these models, followed by the challenges and limitations of our initial approach. Finally, we discuss our solutions to overcome those challenges, such as citizen-deployed sensors, source-specific loudness estimation, and few-shot sound-event detection.
Random forest regression to predict design performance of concert halls
Authors: Broyles Jonathan , Rusk Zane T.
Published: April 2023

Over the last couple decades, machine learning (ML) and advanced computational strategies have been successful when employed in building physics problems. ML models have known applications in the operations of buildings, including real-time energy monitoring and automated mechanical systems. They can also be used to inform design decisions for complex problems during conceptualization. For acousticians and building designers, trained ML models could provide better insight on expected performance without requiring extensive calculations or room acoustic simulations. This presentation describes a computational method for predicting the design performance (i.e., mid-frequency reverberation time) of various concert halls. More specifically, a random forest (RF) regression model is trained on architectural and measured acoustical data to predict the reverberation time. The RF models are tuned and act as a surrogate model for predicting the mid-frequency reverberation time of concert halls that were not used in model training. The estimated reverberation times are then compared to calculations from conventional equations (i.e., Sabine and Norris-Eyring equations) and room acoustic simulations using ray-tracing methods. This work shows how acousticians and architects can employ ML strategies in the conceptual design phase to improve estimated performance accuracy without expending significant computational resources.
Quantification of elastic anisotropy of human skin in vivo with dynamic optical coherence elastography and polarization-sensitive OCT
Authors: Pelivanov Ivan , Kirby Mitchell , Tang Peijun , Kuriakose Maju , Regnault Gabriel , O'Donnell Matthew , Wang Ruikang K. , Ettinger Russell , Pham Tam
Published: April 2023

The complex structure of skin ensures a broad range of biological functions. The loss of a large skin area due to trauma or disease usually requires reconstructive surgery that often involves grafting or flapping. The clinical need for non-contact objective measurements of skin elasticity is necessary to guide grafting procedures to minimize complications such as secondary contracture or hypertrophic scars. Here, we report a non-contact and non-invasive method combining acoustic micro-tapping optical coherence elastography (AμT-OCE) with polarization-sensitive (PS-) optical coherence tomography (OCT) to quantify anisotropic elastic properties of skin. We show that all three elastic constants that define skin’s anisotropic elastic deformation and the orientation of collagen fibers in the dermis can be determined from propagating elastic waves over the skin surface. Measurements were performed on healthy volunteers in vivo. A nearly incompressible transverse isotropic model of skin elasticity was used to reconstruct the moduli from experimental data after being validated in extensive numerical simulations. Finally, we demonstrate that combining several OCT modalities (structural OCT, OCT angiography, PS-OCT, and AμT-OCE) may provide rich information about skin and demonstrate the potential for complex characterization of scar.
Shear wave elastography based on noise correlation and time reversal: From 1d to 3d shear elasticity imaging
Authors: Brum Javier , Bernal Miguel , Rabin Carolina , Negreira Carlos , Benech Nicolas
Published: April 2023

Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to image soft tissue’s shear elasticity. However, coherent shear wave tracking is not always possible due to scattered or interfering waves that arise from inhomogeneities, muscular activity, heart beating, or external sources. To overcome this limitation, we developed an alternative approach using a complex elastic wave-field. Based on the analogy between time reversal and seismic noise correlation, this complex field is “transformed” into a coherent converging-diverging time-reversal field using spatial-temporal cross-correlations [1]. Using the computed time reversal field, there are different ways to image the shear elasticity: tracking the coherent shear wave as it focuses, measuring the focus size (Rayleigh criteria) or evaluating the vibration amplitude at the focus [2]. One advantage of this approach is its compatibility with low imaging rates, which led to innovative applications in SWE. Thus, the goal of this talk is to review the major developments in wave-physics for 1D and 2D elasticity imaging using noise correlation of shear waves and to present its latest applications involving passive elastography and 3D elasticity imaging using row-column arrays. [1] Catheline, Phys. Rev. Lett. (2008); Brum, JASA (2008); Benech, IEEE-TUFFC (2009). [2] Brum, Front. Phys. (2021).
A Scholte wave based ultrasound elastography method for imaging superficial tissue
Authors: Masud Abdullah A. , Liu Jingfei
Published: April 2023

Pathological changes in tissues are often related to changes in tissue mechanical properties, making elastography an important tool for medical applications. Among the existing elastography methods, ultrasound elastography is of great interest due to the inherent advantages of ultrasound imaging technology, such as low cost, portability, safety, and wide availability. However, the current ultrasound elastography methods, including shear wave elastography, can readily image deep tissue but cannot assess superficial tissue. To address this challenge, we proposed an ultrasonic Scholte-wave-based approach for imaging the elasticity of superficial tissue. The feasibility of the proposed technique was tested using a gelatin phantom with a cylindrical inclusion. In the tests, Scholte (surface) and shear (bulk) waves were simultaneously generated by the same excitation but propagated in the superficial and deeper regions of the phantom, respectively. In this study, we first demonstrated that the elasticity of superficial tissue could be evaluated by utilizing the generated Scholte wave alone and further showed that a comprehensive elasticity imaging of the tissue extending from the superficial to deep regions can be achieved by combining the proposed Scholte wave technique and the conventional shear wave technique.
Biaxial prestress and waveguide effects on estimates of the complex shear modulus using optical elastography in a transverse isotropic cornea phantom
Authors: Dore Marta , Luna Aime , Sun Michael , Royston Thomas
Published: April 2023

Tensile prestress is inherent to the functional role of some biological tissues currently being studied using elastography, such as skeletal and cardiac muscle, arterial walls, and the cornea. Therefore, the impact of prestress coupled with waveguide effects due to small dimensions in one or more directions needs to be better understood. An experimental configuration is designed, fabricated, and experimentally tested using optical elastography. Thin layered isotropic and transversely isotropic phantoms are statically stretched biaxially in plane while simultaneously conducting optical elastography measurements of out of plane motion. Guided by analytical models and numerical finite element simulations, experimental measurements are post-processed to obtain an estimate of the complex (viscoelastic) shear modulus as a function of prestress level and frequency of vibratory motion.
A simulation framework for pulse wave and vector flow imaging using fluid–structure interaction and FIELD-II simulations
Authors: Liang Pengcheng , Mobadersany Nima , Konofagou Elisa
Published: April 2023

Pulse Wave Imaging (PWI) utilizes ultrasound elasticity imaging and normalized cross-correlation (NCC) tracking pulse-induced arterial wall distension propagations to perform localized pulse wave velocity and assess arterial compliance mapping for the early detection of vulnerable carotid plaques. At the same time, Vector Flow Imaging (VFI) using a singular value decomposition filter and NCC with axially and laterally shifted axial kernels provides blood flow information. In this study, fluid–structure interaction (FSI) simulations (FEBio) were integrated with FIELD-II ultrasound imaging simulations to optimize both PWI and VFI for simultaneous estimation of compliance and flow in structures of variable vessel geometry and plaque stiffness at distinct ultrasound parameters. The spatiotemporal maps of wall distension rate between FSI ground truth and PWI method were in excellent agreement (r2 = 0.968–0.982) at plane wave angles compounding at (−1°, 0, 1°) and NCC window size of 7 wavelengths in both straight and 87% stenotic vessel geometries. Similar agreement was found in 2D blood flow velocity estimation between FSI ground truth and VFI with a maximum correlation of 0.9464 at the systolic upstroke and r2 of 0.7426 at the angles of (−2°, 0, 2°) and NCC window size of 60 wavelengths. Overall, the framework presented herein allowed PWI and VFI technique validation and optimization prior to in vivo application.
Investigating the change in point spread function and resolution of random apodization passive cavitation images
Authors: Gaskins Weston P. , Haworth Kevin J.
Published: April 2023

Passive cavitation imaging is an important technique in measuring cavitation dynamics, localizing concomitant bioeffects, and guiding various ultrasound therapies. The canonical algorithm for passive cavitation imaging operates via a delay, sum, and integrate method. With standard diagnostic arrays, this method yields poor axial resolution. We hypothesized that using a random apodization, minimum projection compounding technique could overcome this limitation. The random apodization approach randomly selected only half of the elements to be included in the delay, sum, and integrate algorithm to form a PCI. This process was repeated 30 times using the same data set but a different random subset of half the elements to create 30 images. The final image was obtained via a minimum intensity projection across the 30 images. The improvement of image quality can be tracked by comparing the point spread function (PSF), and the distance at which two cavitation sources can still be resolved, relative to when using the standard algorithm. The PSF reduced by 86% ± 9% when the random apodization was applied. Lateral and axial resolution exhibited qualitative changes associated with a lower PSF, but no quantitative change in resolution, based on the Rayleigh criteria, was observed.
Contrast-specific imaging of histotripsy: Chirp-coded subharmonic imaging combined with Volterra Filtering
Authors: Trivedi Vishwas , Wallach Emily , Bader Kenneth B. , Shekhar Himanshu
Published: April 2023

Histotripsy is a non-thermal focused ultrasound therapy under development to ablate tissue mechanically via bubble cloud activity. Real-time ultrasound imaging is used for treatment guidance. Bubble cloud hyperechogenicity is reduced in deep abdominal targets, making contrast-specific imaging an active area of research. Subharmonic imaging with chirp-coded excitation can improve bubble cloud detection, though the contrast-to-tissue ratio (CTR) was still limited to nearly 6 dB. Nonlinear components of a signal can be delineated with Volterra filtering, including those associated with bubble oscillations. In this study, we tested Volterra filtering as a means to enhance bubble cloud detection. Histotripsy bubble clouds were generated in scattering tissue-mimicking phantoms. Imaging of the bubble clouds was performed with a chirped pulse (1.9-μs duration, 7–12 MHz bandwidth). The scattered signals were processed with a subharmonic matched filter, followed by a tuned second-order Volterra filter. Volterra filtering improved the CTR for bubble cloud detection two-fold relative to matched filtering alone (12.5 dB vs 5.6 dB). Further improvement in bubble contrast was observed for third-order Volterra filtering (CTR of 20.3 dB) but at the cost of underestimating the bubble cloud area. Overall, these findings indicate the utility of Volterra filtering as a means to improve histotripsy image guidance.
PAM, not spam: Towards quantitative, reproducible, and energy-preserving cavitation imaging
Authors: Smith Cameron , Bau Luca , Gray Michael , Coussios Constantin
Published: April 2023

Since the development of the original passive acoustic mapping (PAM) algorithm for cavitation imaging in 2008, which employed a conventional beamformer adapted from seismology (time exposure acoustics), sequential algorithmic improvements have sought to enhance spatial resolution, reduce computation time and enable increasingly setup-independent reporting of cavitation activity. These enhancements have included the use of frequency-domain rather than time-domain implementations to improve computational efficiency, the introduction of the Robust Capon Beamformer to reduce artefacts, sub-aperture processing to further increase frame rate and the implementation of corrections for frequency-dependent attenuation and for array sensitivity and diffraction to account for probe- and depth-related variability. Once these corrections are taken into account, current PAM algorithms produce accurate estimates of cavitation source strength at a single location, but not in the surrounding region, leading to inaccurate estimates of the total cavitation energy over the treatment volume. We present an energy-preserving and computationally efficient PAM algorithm based on Lucy-Richardson deconvolution, that enables the calculation of a set-up independent Cavitational Radiated Energy Density (CRED) that ensures cavitation images accurately reflect the total energy of radiated acoustic emissions within the imaging domain.
High-performance computing in phononic materials with applications to nonlinearity and fluid–structure interaction
Authors: Matlack Kathryn
Published: April 2023

Phononic materials contain periodic and resonant substructures that enable novel acoustic and elastic wave behaviors, such as band gaps, topologically protected wave propagation, and negative refraction. Phononic materials preferentially take advantage of complex structures and intricate geometries, and even richer dynamics can occur in phononic materials that are nonlinear, multi-physics, or multi-phase. Certain phononic materials are often represented with reduced-order models such as lumped masses and springs, where the underlying physics can be revealed and systematically probed. However, high fidelity and/or performance simulations are critical to, e.g., interpret experimental validations, particularly with additively manufactured samples, analyze realistic structures and loadings, and for systematic optimizations. This talk presents two examples where high fidelity and high-performance computing enables the analysis of new behaviors of phononic materials and structures: (1) strongly nonlinear phononic materials that exploit history-dependent phenomena and effects of a continuum and (2) interactions between phononic materials and a surrounding fluid flow, where coupled nonlinear effects such as fluid–structure interaction are critical. Finally, opportunities for how high-performance computing that can advance phononic materials are discussed.
Sound generation in the flapping wing flight of insects
Authors: Allen John S. , O'Rourke Kevin
Published: April 2023

Flapping wing flight has been topic of recent interest with respect to the maneuverability and agility of insects. Computational fluid dynamics methods have been used to investigate the aerodynamics though typically for incompressible flow. The underlying sound generation mechanism, though of fundamental biological and physical interest, have much less attention. Experimental acoustical and high speed video studies of the Coconut Rhinoceros Beetle (Oryctes rhinoceros) and the Oriental Flower Beetle (Protaetia orientalis) have motivated large scale simulations accounting for three dimension flow, compressibility, and fluid structure interactions. Computational fluid dynamics simulations were performed using the unsteady compressible flow solver (CAESIM, Adaptive Research, Inc.) using a high resolution (TVD) methodology. Models of the wing flapping motion were accomplished using mesh deformation techniques with the flapping following from rotation with prescribed bending and coupled rotation and translation from the wing’s hinge position. Fluid structure interactions with respect to the wing’s flexibility are investigated in terms of the wing bending and the leading edge vortex formation.
Large-scale simulation of high-intensity focused ultrasound with Sierra/SD
Authors: Treweek Benjamin C. , Brody Jacob H. , Erturk Alper , Swift S. H. , Smith Chandler , McCormick Cameron A. , Walsh Timothy , Moore Nathan W.
Published: April 2023

High-frequency simulations of acoustic wave propagation are known to be computationally challenging, and the difficulty is compounded for large domains. For problems like high-intensity focused ultrasound (HIFU) with coupling between piezoelectric and acoustic media, both challenges are present. The larger domain sizes, higher-order elements, and greater levels of refinement necessary in such simulations result in millions of degrees of freedom, large system matrices, and substantial memory requirements, raising the need for parallel high-performance computing (HPC). Sierra/SD is a massively parallel HPC application developed for finite element method simulations in structural dynamics and acoustics. In this work, Sierra/SD is used to simulate an acoustic pulse from a piezoelectric transducer focused on an elastic scatterer in a fluid medium. Three-dimensional simulation results are presented for the acoustic field in the fluid and the stress field in the scatterer, and performance is compared between Sierra/SD and COMSOL Multiphysics for smaller geometries. Finally, to showcase the expanded analysis possibilities afforded by HPC for HIFU, an example is presented using a support vector machine to determine a decision boundary for maximum stress in the scatterer. [SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.]
Lessons learned from failures
Authors: Ludwigsen Daniel
Published: April 2023

In certain communities of engineering education, especially where intersections with entrepreneurship shape the discussion, “Learning from Failure” has become a catch phrase. Usually these refer to pedagogical approaches in which students recognize the benefits of trying, failing, reflecting, and trying again. This iterative process also describes a teacher’s journey over a decade, learning to implement and practice research-based educational techniques with patience and a focus on the students. However, the stakes can be much higher when teachers try and fail! Examples from an elective course designed for a wide engineering audience, Acoustics in the Human Environment, will trace its evolution. It began as an experiment in a studio classroom format and became an asynchronous online class intended to mirror an engineering work environment. Milestones marking the steps of this journey: parallels to iteration involved in the engineering design process; suggested elements that provide a safety net for teaching failure, and other lessons learned along the way.
A tale of two activities
Authors: Morrison Andrew C.
Published: April 2023

It was the best of intentions, it was the worst of receptions, it was the semester for scientific engagement, it was the semester of sitting silently in the classroom, we had meaningful conversations about the science of sound, we had hushed whispers of hiding information from the course instructor—in short, the semester was like many semesters before it. With apologies to Charles Dickens, I will share the experience of having two sections of the same class, in the same semester, with the same conditions, which ultimately yielded dramatically different levels of student engagement. As an example, the difference in how each section received an in-class activity will be discussed. I will share lessons I learned as a teacher and ways that I hope to grow as an instructor based on this experience.
Making group-work work: Navigating conflict and encouraging collaborative revision
Authors: Kloepper Laura
Published: April 2023

Group work, especially for comprehensive class projects, is ubiquitous in higher education, yet despised by many students. In college, many students simply do not learn how to interact when in groups and how to collaborate effectively. Furthermore, by limiting student assessment of group work solely to a final project grade, students do not have the opportunity to collaboratively reflect on feedback and revise. Inspired by the massive failure of group comprehensive projects in my bioacoustics course, I will share tips I learned to navigate intra-group conflict, provide students with critical feedback on work at 3 key periods throughout the course, encourage collaborative revision, and engage with other groups via peer feedback.
On the notional impact of background noise on the human response to UAVs
Authors: Christian Andrew
Published: April 2023

Proponents of UAV-based industries would like to think that their aircraft will be incapable of causing annoyance (among other negative responses) in the communities that they serve due to the noise of their vehicles simply not being heard over the existing soundscape. No measures of noise that are in wide use today for aviation take background sound into consideration and, thus, would not predict this outcome. This work is an attempt to bridge this gap by looking at past results from psychoacoustic research in which background sounds appear to play a significant role (not just for aviation sources). It includes information on the problem of human auditory detection in general—what is the transductive mechanism of the ear, how does one quantify detectability, etc., and it attempts to make the connection between detectability and annoyance. A notional schematic version of how measures/predictions of these two aspects may be incorporated into a single assessment of noise is given. Overall, detectability is shown to be very complex to predict relative to conventional noise metrics that are used to correlate with human response. Given this, the outlook for the use of measures of detectability in scientific, industrial, and regulatory applications is discussed.