bluuebunny/crossref_metadata_2025 huggingface dataset:
Directional dependence of nonlinear piezoelectric surface acoustic waves in lithium niobate
Authors: Cormack John M. , Hamilton Mark F.
Published: November 2021

A model for the propagation of finite-amplitude surface acoustic waves (SAWs) in a piezoelectric material [Hamilton et al., J. Acoust. Soc. Am. 100, 2567(A) (1996)] is used to investigate the dependence of SAW nonlinearity on crystal cut and propagation direction in lithium niobate (LiNbO3). The model is based on Hamiltonian formalism, in which the boundary conditions at the free surface need only be evaluated at linear order, thus simplifying computation of the nonlinear problem. In contrast with the scalar coefficient of nonlinearity that appears in evolution equations for bulk planewaves, nonlinearity of SAWs is described by a matrix for harmonic interaction due to the variation of depth dependence of the SAW field with frequency. Components of the nonlinearity matrix are generally complex-valued as a result of material anisotropy and piezoelectricity. Variation with propagation direction of the (1,1) component of the nonlinearity matrix, which governs second-harmonic generation, is presented for LiNbO3 crystals that are X-cut, Y-cut, and Z-cut. Relative contribution of each nonlinear mechanism (nonlinear elasticity, nonlinear piezoelectricity, electrostriction, and nonlinear dielectricity) to the nonlinearity matrix is examined. Distortion of an initially sinusoidal waveform during propagation is demonstrated by integrating coupled spectral evolution equations for the harmonic amplitudes.
Improving ultrasonic evaluation of osteochondritis dissecans using a cadaveric model
Authors: Holmes Philip M. , Chen Kun-Hui , Lee Hyungkyi , Leng Shuai , Fitzsimmons James , O'Driscoll Shawn , Urban Matthew W.
Published: November 2021

Osteochondritis dissecans (OCD) is a joint disease that is prevalent among youth athletes. Medical ultrasound is currently limited in its ability to detect and monitor OCD due to limitations of current Delay-and-Sum (DAS) reconstruction algorithms. In this work, we used a Delay-Multiply-and-Sum (DMAS) reconstruction algorithm to improve medical ultrasound’s ability to diagnose OCD. We artificially generated OCD lesions in unfixed cadaveric elbows and imaged them with a research ultrasound machine. We also imaged these cadaveric limbs with x-ray computed tomography (CT) with a high-resolution acquisition. These CT images were used as a gold standard for OCD geometry. We reconstructed the ultrasound images using both DAS and DMAS algorithms and compared them quantitatively by taking several profiles across the images of the artificial OCD lesions. The image metrics that we measured within these profiles were OCD lesion contrast, bone interface clarity, and lesion crack thickness accuracy. We found that the DMAS algorithm improved OCD lesion contrast by up to 26% when compared to DAS. We also found that the DMAS algorithm reduced the variability of bone interface clarity overall. Future work will involve an in vivo study, as well as optimization, of the DMAS algorithm for OCD lesion imaging.
Z-section and 3D rendering imaging using 130 and 50 MHz ultrasound and bacteria generated ultrasound contrast agents
Authors: Kim Sangnam , Hwang Gyoyeon , Yoon Sangpil
Published: November 2021

We present an ultrasound z-sectioning imaging approach to visualize small vasculature. The major difference between confocal and conventional microscopy is the sectioning capability to generate three-dimensional images by stacking multiple sections. To visualize small vessels, we used 130 and 50 MHz ultrasonic transducers and gas vesicles (GV) isolated from bacteria as contrast agents. We developed 130 and 50 MHz ultrasonic transducers using lithium niobate. The focus and aperture of 130 MHz transducer are 1.5 and 1 mm and 50 MHz transducer has 3 mm aperture and 4 mm focus. These transducers were attached to ultrasound biomicroscopy for scanning phantoms and mouse liver specimen ex vivo with 1 micrometer steps. Saved radiofrequency data was post-process to reconstruct B-mode images and mid-band fit (MBF) maps. Four types of GVs were isolated in house. GV sizes were ranging from 200 to 600 nm. Three GV species present unclustered morphology but GVs isolated from one bacteria species present clustered morphology. Distinct MBF maps were created from clustered and unclustered GVs which were suitable for multiplexed imaging. The results demonstrated that MBF and GV based ultrasound imaging approach can image thin slices of tissue specimen with multiplexed imaging capability.
Foam gratings as an alternative to customised acoustic lenses
Authors: Richards Luke A. , Stride Eleanor P. , Cleveland Robin O.
Published: November 2021

Tissue inhomogeneity can affect the accuracy with which ultrasound can be focused into the body. In existing clinical systems, phase corrections are typically made using ultrasound arrays, but with the advent of 3D printers there has been increased interest in producing patient-specific acoustic lenses. Acoustic lenses offer a more compact and affordable system than an equivalent array and may be suited for therapeutic applications where there is well defined target location. This study explored the properties of gratings made of foam machined with holes as an alternative to acoustic lenses. The approach was investigated with an analytical model, a full-wave numerical model, and experimental measurements. A grating is demonstrated that mimics a conventional ultrasound lens, modulating the phase of transmitted ultrasound while maintaining uniform amplitude. The performance of a foam grating is compared to lenses made of PDMS or 3D printed resin. Using two gratings, independent control of amplitude and phase is demonstrated, with increased insertion loss. The primary advantages of this technique over conventional lenses are rapid manufacture (<30 min) and the ability to control both the amplitude and phase of the transmitted ultrasound. Potential applications include generation of complex ultrasound fields for patient specific treatments in ultrasound therapy.
Detection of cellular mineralization using the Doppler ultrasound twinkling artifact
Authors: Ruge-Jones Lucas , Berntsen Lisa , Hayes Daniel , Simon Julianna
Published: November 2021

Heterotopic ossification (HO), or the growth of bone in soft tissue where bone does not usually exist, can occur after any musculoskeletal trauma. While the exact cause of HO is unknown, it can take 2i–3 months before HO can be detected on x-ray or computed tomography (CT). The color ultrasound Doppler twinkling artifact is a rapid color shift that was discovered when imaging kidney stones. Here, our objective is to determine whether twinkling can be used to detect the earliest signs of cellular mineralization in HO. A Vantage-128 research ultrasound system with Philips/ATL L7-4, L12-5, and Vermon L22-14 transducers was used to image human bone marrow-derived stem cells (hBMSCs) cultured in osteogenic media and supersaturated solutions of calcium phosphate. Preliminary results show a 50% increase in Doppler magnitude and a 250% increase in Doppler variance in the presence of cellular mineralization or calcium phosphate crystals compared to images of cells without minerals or in non-crystalline solutions. The L7-4 was found to be more sensitive to twinkling from mineralization than the higher frequency transducers. The increase in Doppler magnitude and variance with cellular mineralization suggests twinkling may be a sensitive early detector of HO. [Work supported by DoD CDMRP PR201164.]
On mitigating the opacity of digital twins
Authors: Banyay Gregory A.
Published: November 2021

Digital twins, or variants thereof, are becoming ubiquitous across many disciplines of computational science and engineering modeling and simulation. Despite the increased use of this concept, industrial practitioners and academic researchers alike lack consensus as to what exactly constitutes a digital twin, much less how one might quantify associated uncertainties to support the verification, validation, and ultimately credibility assessment thereof. Furthermore, the complexities involved in modeling structural vibration and acoustics can exacerbate the epistemic uncertainties of this opaque portrait. We therefore posit that use of goal structured notation (GSN) in the context of a credibility assessment framework (CAF) provides one viable means by which key stakeholders in both the development and deployment of digital twins can collectively work towards increased clarity. One can expect that achieving greater clarity for requirements of digital twins, particularly those of phenomenological relevance to structural dynamics and acoustics, computational, experimental, and operational disciplines can more optimally combine to achieve desired engineering outcomes.
Diffraction problems in an architectural acoustics benchmark
Authors: Vorlaender Michael , Aspoeck Lukas
Published: November 2021

In 2016/2017, the first round robin on auralization in room acoustics was performed. This project allowed participants to contribute results of their simulation model for typical scenarios of sound propagation and room acoustics. The outcome of the round robin and details of the related scene database were published in two papers [Brinkmann et al. J. Acoust. Soc. Am. 145 (4), 2746 (2019); Brinkmann et al., Appl. Acoust. 176, 107867 (2021)]. As concerns diffraction effects, however, just a few integrated room-acoustic simulation tools could contribute to the comparison. In this paper, the reference measurements for the diffraction cases are described, and results obtained with simulation models are discussed in three categories: a finite screen on rigid ground, a finite panel in free field and an array of panels in free field.
Validating a phase-inversion procedure to assess the signal-to-noise ratios at the output of hearing aids with wide-dynamic-range compression
Authors: Yun Donghyeon , Shen Yi , Lentz Jennifer
Published: November 2021

Even for the same signal-to-noise ratio (SNR) at the input of a hearing aid, the output SNR may vary due to nonlinear compression algorithms. To quantify the output SNR of hearing aids, a phase-inversion technique is commonly used. The current study was designed to determine whether the phase-inversion technique accurately estimates the SNR for a simulated hearing aid. A simulated hearing aid was used to allow the explicit control of the compression algorithm and the calculation of the actual SNR at its output. The actual output SNRs were then used as the ground truth to evaluate the estimated output SNRs using the phase-inversion technique. Connected speech added to background noise (two- or twenty-talker babble), presented at SNRs of –10 to +10 dB, was used as test stimuli at the input of the simulated hearing aid. Four representative audiograms were used to set the gain and compression ratio for the simulated hearing aid according to a standard prescription method. In separate conditions, the hearing-aid compression was either fast- or slow-acting. Results showed that the estimated and actual output SNRs were not significantly different and their differences were within ±0.12 dB across all test conditions, indicating satisfactory agreement.
Using the lattice Boltzman method and GPU computing to model flow in organ pipes
Authors: Kaplan Connor N. , Gabriel Jack D. , David-Sivelle Adrien , Coyle Whitney L.
Published: November 2021

The lattice Boltzman method (LBM) has been used to study oscillating air flow in musical instruments since the early 1990s. Most of the work has focused on flow into organ pipes and flow behavior around the instrument’s labium. The current work intends to use GPU computing to simulate oscillations in 3D modeled and printed organ pipes of different cross-sectional geometries. These pipes will be used in experimental validation measurements of flow at the pipe exit (see TCMU general session for this work). The domain space required to visualize each outlet of air (around the labium and the pipe’s open end) simultaneously with a sufficient resolution was larger than could fit in our GPU's memory. The resolution and space requirements of the simulations has required the use of high-memory GPUs (a physical machine as well as Google Cloud GPU have been tested). The physical and computational parameter optimization, GPU processes, and the simulation difficulties encountered will be discussed. Finally, preliminary comparisons between experiment and model will be shared.
Cryogenic testing of microphones and preamplifiers for MEMS quench detection in superconducting magnets
Authors: Baris Reid , Anilus Mischael , Zhao Zijia , Chau Steve , Liu Wayne , Desai Amish , Emerling Michael , Littrell Robert , Core Craig , Tang Stacey , Chiesa Luisa , Takayasu Makoto , White Robert D.
Published: November 2021

High Temperature Superconducting (HTS) tapes are needed for high field magnets in high-energy physics and nuclear fusion. However, quench events, in which the superconductor loses its superconductivity, can cause significant and costly damage to the device if allowed to propagate. Consequently, rapid quench detection methods are crucial. Existing methods such as voltage taps can be less effective in HTS applications, as the normal zone propagation velocities of HTS devices are slow, drastically increasing quench detection time (Iwasa, Cryogenics, 2003). We propose an alternative method that utilizes a linear array of MEMS microphones embedded in the cryogenic coolant channel (Takayasu, IEEE Transactions on Applied Superconductivity, 2019). The system requires amplifiers and acoustic sensors capable of operation at cryogenic temperatures as low as 4.2 K, although operation at 20 K may be sufficient. We report on cryogenic testing of the Vesper microphone preamplifier ASIC, as well as opamp based preamplifiers using the OPA838, LT1464, AD8591, and AD8057 ICs. The amplifiers are being used with the Vesper VM4 MEMS microphone to achieve acoustic measurements in gaseous helium at temperatures as low as 8 K. A charge amp scheme using the AD8591 achieved the best results to date. [Support from DOE STTR DE-SC0019905.]
Calculation of the trumpet impedance with various mouthpieces
Authors: Babione Sarah , Jaeger Herbert
Published: November 2021

This project explored computationally how mouthpieces of various dimensions affect the acoustic input impedance for the entire trumpet. Theimpedance was calculated using a cone approximation. The trumpet was divided into cones shorter than the wavelengths considered. The measurements for the trumpet were taken from the literature. Each cone was further divided into 1 mm-long slices in order to get an accurate value for the thermal and viscous wall losses. The load impedance at the open bell was taken as zero. The input impedance of the trumpet with mouthpiece was calculated iteratively such that the input impedance of one cone was used as the load impedance for the next cone. Calculations were done for frequencies up to 2000 Hz and for a variety of mouthpiece geometries but with the same trumpet sections. The effect of the mouthpiece geometry on the instrument’s impedance spectrum will be discussed.
Measurements of ship noise using an acoustic camera: A first survey
Authors: Bocanegra Johan A. , Borelli Davide , Schenone Corrado
Published: November 2021

While the acoustic impact of harbours is becoming an increasingly important issue, to the point of limiting their growth, the measurement of noise from ships and port operations is still rough. Two of the main problems that are commonly encountered are source overlapping and large distance from the emitting sources. Source overlapping prevents from identifying the specific contribution coming from each acoustic source. The large distance from the emitting sources, for instance the funnel of a ship or the engine of a transtainer crane, makes the measurement inaccurate. By using the acoustic camera it is possible to tackle these two problems at the same time. Noise measurements can be made with equipment far from noise source, while distinguishing the contribution from each single source emitting within the sound field. The paper demonstrates this enhanced measurement technique through a set of surveys performed inside French and Italian ports. The ship emissions are analyzed through the acoustic camera for ship on the way, maneuvering inside the harbour, and berthed at wharf. The effectiveness of beamforming technique is discussed, investigating the measurements accuracy, their qualitative and quantitative significance, and the possibility to introduce specific measurement standards for ships based on this methodology.
Duct, duct, goose chase? Revisiting algorithms for duct flow noise
Authors: Cudequest Brandon
Published: November 2021

The American Society for Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) has several practical resources for flow noise prediction. There are reference tables for maximum air velocities for a given background noise rating as well as tables for maximum “free area” speeds for supply diffusers or return registers. For other duct fittings, engineers may use a variety of algorithms to predict octave band sound power levels. Experiments have demonstrated a direct relationship between flow noise and duct size, aspect ratio, and pressure drop. Currently, few prediction methods accurately take these factors into account because the underpinning algorithms are based on a limited set of ductwork sizes. To better understand how these factors impact airflow generated noise, ASHRAE has conditionally approved Work Statement 1919: The effects of duct size and aspect ratio on flow noise in elbows. This paper will review past literature, highlight shortcomings of current prediction methods, and discuss the proposed methodology for upcoming research.
Correlation properties of wind noise pressure on the ground surface
Authors: Raspet Richard , Hickey Craig J. , Samad Md A.
Published: November 2021

Recent studies of the seismic displacement of the ground use the theory developed by Jiao Yu to predict the pressure spectrum of the wind noise on the ground. The prediction of the displacement due to this pressure employs the ground properties and the spatial correlation properties of the pressure on the ground. The theory is successful at predicting the amplitude of the seismic displacement at the surface but does not predict the correct behavior with depth. These calculations used the low frequency correlation functions measured by Shields [JASA 1(17), 3489–3496 (2005)]. The sensors in Shields’ study were on the ground surface and may have been subject to stagnation pressure contributions in addition to the surface pressure fluctuations. A new measurement of the surface pressure correlation using 12 microphones mounted in two perpendicular arms, flush to the ground surface, has been performed. Since the arms cannot be moved to align with the wind, new analysis methods have been employed to extract the correlation coefficients along and perpendicular to the wind direction. Initial analysis indicates that the correlation coefficients are significantly smaller than those of Shields and the convection velocity is slightly larger than the .7 *U(2.0 m) used by Yu.
Wind noise performance analysis of a prototype compact infrasound array
Authors: Frazier Garth , Harris David
Published: November 2021

Previously, presentations have been given at ASA meetings that demonstrated the potential for compact arrays of infrasound sensors achieving high gain against wind noise under appropriate environmental conditions without the use of large windscreens. These presentations focused on using specific models for the spatiotemporal correlation function of the wind noise as part of the processing methodology, and they did not directly address the features of the compact array design that influence performance. This presentation will study the effects of several compact array features on performance using a recently published cross-spectral density model for wall-bounded turbulent pressure fluctuations. Additionally, data from several experiments will be presented including data from a prototype compact infrasound array.
Large porous wind barriers as a mitigation technique for turbulence induced infrasonic noise
Authors: Abbott JohnPaul R.
Published: November 2021

An infrasonic wind barrier is a large porous device that effectively reduces wind noise by disrupting and minimizing the flow near the pressure sensor, and transferring the local and direct turbulence induced noise interactions from the pressure sensor to the surface of the barrier where the sum total of the poorly correlated noise induced turbulence interactions are reduced by area averaging. In addition to effective wind noise reduction these devices maintain acoustic waveform fidelity, work in adverse conditions, and can reduce noise frequencies with associated turbulence scales sizes that are several times the size of the barrier itself. This paper will review wind barrier research conducted at the National Center for Physical. This will include a discussion on the mechanical properties of the barrier that lead to effective noise reduction including its porosity, size, shape, and number of filtering layers. Barriers designed and studied at the National Center for Physical Acoustics and by others are compared and discussed. A simple empirical model predicting wind noise reduction based on the mechanical properties of the barrier and the turbulence flow interactions located inside, on the surface, and outside of the barrier is given
Comparison of wind filter designs for infrasound sensors
Authors: McComas Sarah , Hayward Chris , Arrowsmith Stephen , Stump Brian , McKenna Mihan
Published: November 2021

Sensors in infrasound arrays measure the total acoustic field that contains signals of interest as well as coherent and incoherent noise. Modern array designs utilize sensors that have a quantified response that extends across the acoustic spectrum from the infrasound passband (<20 Hz) into the low-end audible passband (<1000 Hz). Mechanical wind filters applied to individual sensors are an integral part of array designs that reduce incoherent noise and improve the signal-to-noise ratio of coherent signals. Common forms of these filters are porous hose rosettes and domes, which provide spatial averaging of coherent energy over the dimension of the mechanical filter. These filters also provide additional noise reduction by limiting the sensor’s sensitivity to the effects of the turbulent boundary layer. This presentation will focus on direct comparison of four wind filter designs: 4- and 10-hose porous hose rosettes, a 1-m fabric dome, and a high-frequency shroud. The analysis presented will quantify similarities and differences in the wind filter performance that led to recommendations for specific use cases dependent on expected environmental conditions. [Permission to publish was granted by the Director, Geotechnical and Structures Laboratory.]
On the role of head rotation in solving the HRTF inverse problem
Authors: Brimijoin W. Owen , Warnecke Michaela
Published: November 2021

The sound arriving at the eardrum is a complex composition of the sound source spectrum, the acoustic properties of the listener’s environment, and the directionally dependent filtering of the listener’s head-related transfer function (HRTF). Listeners only ever have access to this mixture, and it remains unknown how they are nonetheless capable of disentangling features intrinsic to the sound source from those created by the source’s position in the environment. We hypothesized that head movements, by changing only the HRTF-related components of an arriving sound, inform a listener’s judgement of source spectrum. We tested this with virtual acoustics, presenting listeners with a speech sound rendered at an elevated frontal location and asked them to judge which of two subsequent copies of the same sound rendered at the horizon had spectral noise added to them. The test sounds were either head-locked, world-locked, or moved inverted to the listener’s movements, and were rendered with either individual or non-individual HRTFs. Error patterns across HRTF and motion conditions appear to confirm the hypothesis that head rotation plays a role in the estimation of sound source spectrum, and further indicate that listeners have expectations about how the signal at the ear should change as the head moves.
How human listeners make sense of crowded acoustic scenes
Authors: Chait Maria
Published: November 2021

The notion that sensitivity to the statistical structure of the environment is pivotal to perception has recently garnered considerable attention. I will discuss a series of recent experiments in which we investigated this sensitivity in the context of crowded acoustic scenes. Stimuli are artificial ‘soundscapes’ populated by multiple (up to 14) simultaneous streams (“auditory objects”) comprised of tone-pip sequences, each with a distinct frequency and pattern of amplitude modulation. Sequences are either temporally regular or random. We show that listeners’ ability to detect abrupt appearance or disappearance of a stream is facilitated when scene streams were characterized by a temporally regular fluctuation pattern and that this ability is preserved during healthy aging. Remarkably, listeners benefit from regularity even when they are not consciously aware of it. These findings establish that perception of complex acoustic scenes relies on the availability of detailed representations of the regularities automatically extracted from multiple concurrent streams.
Asymmetric lateral beaming of sound in a bianisotropic phononic crystal
Authors: Su Xiaoshi , Banerjee Debasish
Published: November 2021

Willis materials or bianisotropic acoustic materials that couples pressure to particle velocity provide rich physics for sound manipulation. It has recently been shown that tailored Willis acoustic scatterers with resonance effects can display significant cross-coupling between the monopole and dipole responses. In this talk, we show that the multiple scattering in a bianisotropic phononic crystal composed of Willis acoustic scatterers also leads to interesting coupling behavior. The asymmetric structure in our design is non-resonant in the frequency range of interest. However, the nonlocal effect due to the multiple scattering among the scatterers leads to coupling between quadrupole and dipole responses. The phononic crystal is tuned to match the second-order Bragg scattering with two leaky guided modes. We show that a normally incident wave can be steered to propagate along the positive and negative directions perpendicular to the incident direction with different amounts of energy. Simulation and experimental results will be discussed.
Extreme effective material parameters enabled by non-local Willis coupling
Authors: Craig Steven R. , Welch Phoebe J. , Shi Chengzhi
Published: November 2021

While traditional acoustic metamaterial designs based on monopolar and dipolar resonance realize effective densities and bulk moduli that go beyond the those of natural materials, their reliance on local resonance ultimately limits their ability to access extreme effective parameter values. Here, we use an active metamaterial with non-local Willis coupling to drastically extend the accessible range of the effective density and bulk modulus by at least two orders of magnitude compared to a non-Willis metamaterial that relies on local resonance. Our design introduces Willis coupling with two sensor-transducer pairs on both sides of the metamaterial that detects incident waves and superimposes an asymmetric active acoustic signal on an otherwise passive unit cell. The asymmetry of the active signal results from feedback control circuits with unequal gains and/or phases. In our setup, an asymmetric feedback control circuit induces the non-local Willis coupling that potentially increases the effective length of wave propagation and extends the range of effective density and bulk modulus of the metamaterial. Active metamaterials with extreme effective material parameters via non-local Willis coupling will enable improved control over acoustic propagation and yield valuable advancements in biomedical imaging, noise control, and invisibility cloaking technology.
Improved sound diffuser performance using spatiotemporally modulated metasurfaces
Authors: Kang Janghoon , Haberman Michael R.
Published: November 2021

Conventional sound diffuser designs consist of a periodic arrangement of variable depth wells which result in a quasi-random spatial distribution of the reflected phase and minimal energy loss. Diffuser performance depends on geometric parameters such as well depth, number of elements per diffuser period, and in-plane dimensions. We previously showed that coiled-space acoustic metasurfaces (AMS) can significantly reduce diffuser depth while maintaining the performance when compared to classical quadratic residue diffusers (QRD) [Kang and Haberman, J. Acoust. Soc. Am., 149(4), A141 (2021)]. However, all conventional and AMS diffuser performance is limited by geometry due to the linear relationship between frequency and wavelength. Here we consider spatiotemporal modulation of an AMS to control and improve sound diffusion using a technique inspired by nonreciprocal vibrations in Euler beams [Goldsberry et al., Phys. Rev. B 102 (2020)]. A theoretical model is developed using the classical grating equation augmented with a surface impedance that is modulated as a travelling wave function. Properly selected modulation parameters lead to increased diffusion coefficients associated with scattering into harmonics of the temporal modulation frequency and nonreciprocal scattering patterns dependent on the spatiotemporal modulation. Diffuser performance is demonstrated and investigated through the angular dependence of the scattered field magnitude.
Study of three-dimensional elastic metamaterials based on a lattice system
Authors: Mumme Zachary , Fan Jiadi , Sang Sheng
Published: November 2021

In this paper, a three dimensional (3D) mass-in-mass lattice system is proposed to understand how elastic waves propagate through 3D metamaterials. In our model, we included spring elements that protrude in all three dimensions, along with spring elements protruding in only one or two dimensions to properly analyze the system’s elastic properties. Due to the dispersion equation containing four variables, it must be graphed in three different perspectives to produce plots in which the stop bands’ values can be interpreted with ease. In essence, the stop bands are produced by aligning the graphed structure along each orthogonal plane. By modifying the spring elements’ constants, each of the stop bands can be shifted into higher or lower frequency ranges independent of each other, theoretically providing complete control over how a wave propagates through the metamaterial. From this, real world applications can be developed such as absorbing elastic waves in undesired directions, focusing elastic waves to specific points, guiding waves along complicated paths, and creating elastic superlenses.
Symmetry-protected, zero-energy disclination modes and their observation in an acoustic lattice
Authors: Deng Yuanchen , Benalcazar Wladimir , Chen Zeguo , Oudich Mourad , Ma Guancong , Jing Yun
Published: November 2021

Building upon the bulk-boundary correspondence in topological phases, disclinations-crystalline topological defects that induce a curvature singularity in a lattice-have been harnessed for trapping modes within the bulk of synthetic lattices. These trapped modes are useful in photonic and sonic crystals because the bulk surrounding a defect generates a bandgap that isolates the mode from the gapless free space. However, in current realizations, these modes are not protected from delocalization because so far, experimentally realized mode-trapping disclinations have broken chiral symmetry. As such, their modes do not lie at mid-gap and can hybridize with bulk modes to form resonances, losing their confinement. Here, we devise a fundamentally new paradigm that allows the protection of modes bound to disclinations that preserve chiral symmetry. These disclination modes are consequently pinned at the mid-gap, which in turn result in their protected maximal confinement. By presenting a protection mechanism that rests on the interplay between the topology of the lattice and the point group symmetry of defects and by experimentally probing these modes in judiciously designed chiral-symmetric acoustic lattices, our work demonstrates the existence of protected modes within the bulk of synthetic lattices.
Elastic topological pumping for surface acoustic waves
Authors: Oudich Mourad , Jing Yun
Published: November 2021

This talk is concerned with Thouless pumping of topological states for surface acoustic waves (SAW). We first designed an elastic waveguide analog of high-index optical fiber, that supports highly confined surface acoustic modes with controllable acoustic index. The “elastic fiber” is made of a silica waveguide embedded in a silicon substrate at the surface, which enables the existence of elastic modes propagating on the surface of the substrate, while being confined along the silica waveguide. The evanescent field outside the silica waveguide can be controlled via the geometrical dimensions of the waveguide which directly affects the coupling between adjacent waveguides. We then constructed a topological structure made of a finite number of elastic waveguides that support topological elastic states, and modulated the coupling between the silica waveguides to demonstrate for the first time Thouless pumping for SAW.
Topology optimization design of metasurfaces to control Lamb wave propagation
Authors: Giraldo-Guzman Daniel , Lissenden Cliff , Frecker Mary , Shokouhi Parisa
Published: November 2021

Metasurfaces are engineered metamaterials with a structured surface used in electromagnetics, optics, elastodynamics, and acoustics. Elastodynamic metasurfaces can control plate or surface waves. Wave control using metasurfaces has applications across length scales from designing electronics to vibration control systems. Previous works have approached the design of metasurfaces through experimentation and parameter-tuned designs, but no systematic design methodology has been proposed yet. This work addresses the design of resonant metasurfaces to forbid the propagation of plate waves. This is achieved through designing the local resonators using a density-based topology optimization method. Specifically, we design resonators that at their base, fulfill a set of continuity conditions. These are equivalent to boundary conditions mathematically proven to provide reflection and mode conversion for Lamb or Rayleigh waves. Thus, the optimization problem is defined as the minimization of a weighted sum of the displacements and stresses that define such boundary conditions. A topology optimization algorithm is developed that includes material interpolation models, penalization schemes, filtering techniques, sensitivity analysis, and solution methods. A complex scheme integrating the density-based mathematical parametrization, finite element models, data processing modules, optimization solvers, and 3D structural visualization is implemented
Toward improving road traffic noise characterization: A reduced-order model for representing traffic flow dynamics
Authors: Cook Mylan R. , Gee Kent L. , Transtrum Mark K. , Lympany Shane V. , Calton Matt
Published: November 2021

The National Transportation Noise Map predicts time-averaged road traffic noise across the continental United States (CONUS) based on average annual daily traffic counts. However, traffic counts may vary significantly with time. Since traffic noise is correlated with traffic counts, a more detailed temporal representation of traffic noise requires knowledge of the time-varying traffic counts. Each year, the Federal Highway Administration tabulates the hourly traffic counts recorded at more than 5000 traffic monitoring sites across CONUS. Each site records up to 8760 traffic counts corresponding to each hour of the year. The hourly traffic counts can be treated as time-dependent signals upon which signal processing techniques can be applied. First, Fourier analysis is used to find the daily, weekly, and yearly temporal cycles present at each traffic monitoring site. Next, principal component analysis is applied to the peaks in the Fourier spectra. A reduced-order model using the first 11 principal components represents much of the temporal variability in traffic counts while requiring only 0.13% as many values as the original hourly traffic counts. This reduced-order model can be used in conjunction with sound mapping tools to predict traffic noise on hourly, rather than time-averaged, timescales. [Work supported by U.S. Army SBIR.]
Acoustic pressure oscillations in the decay envelope of the initial shock radiated by an underwater explosion
Authors: McNeese Andrew R. , Wilson Preston S. , Knobles David P. , Dahl Peter H. , Dall'Osto David , Chapman Ross
Published: November 2021

Cole described the initial shock of an underwater explosion as a monotonically decaying exponential, a model widely used [Underwater Explosions, Princeton University Press (1948)]. When viewed on a time scale that includes bubble pulses, virtually all of the published measurement data also appears to follow the shape of a decaying exponential. The authors have made recent recordings of underwater explosions produced by Sound, Underwater Signal (SUS) devices that reveal repeatable oscillations in the decay of the initial shock. At first, these oscillations were considered to be artifacts of the measurement system, but then two different systems designed specifically to avoid such artifacts were used and the same oscillations were found. Chapman’s data from the mid-1980s, which was not originally published on a time scale that could reveal these oscillations, was re-examined and found to exhibit similar oscillations. Cole describes a similar effect for explosions from multiple charges that are not detonated at the same time, but the authors have found no explanation for this effect from a single mass of explosive material. Examples are shown and a possible explanation is proposed. [Work supported by ONR.]
Vector acoustic properties of explosive underwater sound
Authors: Dahl Peter H. , Dall'Osto David R.
Published: November 2021

The relation between acoustic pressure and velocity associated with propagating sound from explosive sources is studied. Data originate from the 2017 Sediment Characterization Experiment where the sound source is 38 g SUS, measurement ranges are order 10 km in waters 75 m; and recent experimental studies on the effects of explosive underwater sound on fish off San Diego where the source is 4.7 kg net explosive weight, ranges are order 100 m in waters 20 m. Horizontal components of velocity are resolved into a single radial component and with the vertical component the intensity vector is derived and associated energy streamlines from simulations are presented. It is also shown how radial component of acoustic velocity is phase- locked with pressure, and nearly corresponds to it upon multiplication by the characteristic impedance; including vertical velocity for total velocity magnitude the correspondence with pressure magnitude is within calibration uncertainty. This self-evident finding concerning high-bandwidth signals is worth noting to inform the discussion on the importance of acoustic velocity to fishes. An exception for short ranges is a low-amplitude, narrow band, Scholte wave arrival that decays precipitously away from the water/sediment interface. [Research support by ONR and by the Navy LMR program.]
Two-stage algorithm for the simulation of thin shocks in multirelaxing fluids
Authors: Willis William A. , Cormack John M. , Hamilton Mark F.
Published: November 2021

An efficient two-stage algorithm is presented for simulating a weak shock in an arbitrary waveform propagating in a fluid with multiple relaxation mechanisms. The first stage of the algorithm is based on an evolution equation expressed in intrinsic coordinates for nonlinear propagation in a relaxing fluid [Hammerton and Crighton, JFM (1993)], and it includes effects of spherical spreading. Simulation using intrinsic coordinates allows the pressure waveform to become multivalued, avoiding the need to discretize thin shocks. At selected distances, a shock is inserted into the multivalued pressure waveform according to the equal-area rule, rendering the waveform single-valued. Waveforms calculated in this way agree with corresponding time-domain solutions of a Burgers equation augmented to include relaxation, while simulation with intrinsic coordinates requires orders of magnitude less computation time. An analytical solution for shock evolution [Crighton and Scott, Philos. Trans. R. Soc. A (1979)] is used to estimate shock thickness as a function of propagation distance for determining the appropriate distance at which the second stage, the time-domain solution of the augmented Burgers equation, can be used to continue propagation into the far field. [WAW is supported by the ARL:UT Chester M. McKinney Graduate Fellowship in Acoustics.]
Geoacoustic inversion using explosive air gun signals received by a single hydrophone in the East Siberian Sea, Arctic Ocean
Authors: Lee Dae Hyeok , Choi Jee Woong , Han Dong-Gyun , La Hyoung Sul , Yang Eun Jin
Published: November 2021

Goacoustic inversions using low-frequency impulsive sources in shallow water have been recently performed to estimate geoacoustic parameters of sediments. In this talk, we present the geoacoustic inversion results estimated using explosive air gun data received by a single hydrophone in the East Siberian Sea in September 2019. The single hydrophone was deployed by the Korean icebreaker R/V Araon operated by Korea Polar Research Institute. The geoacoustic inversion is carried out by extracting modal dispersion curves from air gun data received from tens of km. A signal processing method called warping is applied to separate normal mode components and then the extracted dispersion curves are compared to the replicas predicted by the KRAKEN normal mode program. Although it was not possible to compare to in situ measurements of sediment, our inversion results are valuable in that they provide indirect information about geoacoustic parameters of the Arctic Ocean. [This research was a part of the project titled ‘Korea-Arctic Ocean Warming and Response of Ecosystem (K-AWARE, KOPRI, 1525011760)’, funded by the Ministry of Oceans and Fisheries, Korea and supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2020R1A2C2007772).]
Adaptive thermal comfort factors in classroom acoustics
Authors: Ogoli David M.
Published: November 2021

Climate change is affecting the built environment with a growing need to balance adaptive comfort models by relating ambient room temperature and outdoor climatic factors, on the one hand, with adequate classroom acoustics, on the other hand. The adaptive approach allows occupants of a space to adjust their clothing, activity and posture in a space to minimize thermal discomfort while strategizing for adequate reverberant energy and speech clarity. A parametric digital classroom model was built and simulated to various thermal comfort conditions while simultaneously observing the reverberation times (RT) to determine how quickly sound decayed in the space. Building materials were tested parametrically with variable thermal transmittance (U-values) analyzed with corresponding changes in reverberation times. Observed outdoor environmental variables included mean monthly outdoor temperature and relative humidity. A classroom with thirty University students were observed. Measured and simulated data were analyzed for the parametric model applying scatter plot of utilizing the ASHRAE seven-point predicted mean vote (PMV), percentage people dissatisfied (PPD) and reverberation time measurements. Initial findings assessed using ANSI/ASHRAE Standard 55 indicate that occupants of a space tend to reach adaptive thermal comfort in a wider range of conditions than commonly noted but inadvertently negatively affect good classroom acoustics.
Passive acoustic monitoring of hydrothermal vents at the endeavour hydrothermal vent field
Authors: Smith Brendan , Barclay David R.
Published: November 2021

Passive acoustics may provide a method for detection and long-term monitoring of hydrothermal vents. Direct measurement of vent activity can be challenging as vent plumes are often high temperature (i>300°C) and acidic. The discovery of new vent sites can also be challenging as detection of vent plumes or high-resolution seafloor mapping is required. For these reasons, remote detection and monitoring with passive acoustics can be advantageous. In this presentation, long-term passive acoustic data recorded in 2019 from an Ocean Networks Canada (ONC) bottom-mounted hydrophone in the Endeavour Hydrothermal Vent field are presented. A 6-month time window from April through October 2019 was selected for analysis, when fin whale calls were less prevalent. Statistical noise level metrics (e.g., the median) were used to reduce the influence of transient, infrequent events such as fin whale calls and ship noise, as the vent signal was expected to be relatively constant compared to these sources. Spectral analysis of the resulting time series across multiple frequency bins shows evidence of tidal-period variations in power spectral density which may be related to hydrothermal vent dynamics. Comparison is made to other nearby ONC sensors such as vent temperature, bottom pressure, and acoustic doppler current profiler measurements.
Tagging ocean soundscapes with machine learning and topological approaches
Authors: Thilges Kayla , Plumley Meredith , McMillan Justin , Summers Jason E.
Published: November 2021

With a multitude of sources simultaneously contributing to the ambient ocean soundscape, it is important to disaggregate noise source contributions for better monitoring and assessing noise impacts. Our work adopts a modular set of neural networks and topological pipelines to analyze multiple representations of time-series samples of the ambient ocean noise. Specifically, a convolutional neural network (CNN) is used to broadly tag the presence of local shipping and marine mammal vocalizations from spectrogram representations. Multiple approaches are investigated using topological data analysis to predict a class label of the ship hull type or specific marine mammal species using the audio data as input. The datasets used in training, testing, and validation comprise hydrophone recordings across varying sensors and ocean environments to address the wide variation in ambient background noise and propagation paths. Algorithm performance is characterized by classification accuracy on labeled data. This approach demonstrates a generalized tagging cabilitility of the presence of marine mammals and local shipping activity.