bluuebunny/crossref_metadata_2025 huggingface dataset:
Field-effect transistor-based transduction and acoustic receiving transducers
Authors: Moon Wonkyu , Sung Min , Shin Kumjae , Kim Junsoo
Published: June 2017

Microphones and hydrophones are representative acoustic receiving transducers. To properly receive sound waves, a receiver must be smaller than the wavelength of the target sound. The target wave characteristics do not impose any lower limits on the size of microphones. When the performance of a smaller microphone or hydrophone will be satisfactory, users generally choose a smaller device since smaller receivers are easier to install and use. However, miniaturized microphones are less sensitive at low frequencies and conventional infrasound detectors are considerably larger than those for higher frequency sounds. These trends in receiver size can be explained by considering the transduction characteristics of microphones and hydrophones. We describe two transduction mechanisms based on field-effect transistors (FET) and use them to develop new microphones and hydrophones. We used theoretical analysis and experiments to show that the sensitivity and frequency response functions of FET-based microphones and hydrophones are size-independent. These results suggest that more sensitive micro-machined microphones and hydrophones, with better frequency response functions, may be available for use in the near future. [Work supported by the Institute of Civil Military Technology Cooperation Center (16-CM-SS-18).]
Characterization of a virtual array based on MEMS microphones for the analysis of acoustic sources
Authors: Izquierdo Alberto , Villacorta Juan J. , del-Val Lara , Suarez Luis
Published: June 2017

Using arrays with digital MEMS microphones and FPGA-based acquisition/processing systems allows to build systems with hundreds of sensors at a reduced cost. This work analyzes the performance of a virtual array with 6400 MEMS (80 × 80) microphones. The system is composed by a 2D positioning system that places a physical array of 64 microphones (8 × 8) in a grid with 8 x 8 positions, obtaining a spatial aperture of 2 x 2 meters. The measured beampattern is compared with the theoretical one for several frequencies and pointing angles. The beampattern of the physical array is also estimated for each one of the 64 positions used by the positioning system. Also, the measured beampattern and the focusing capacity are analyzed, since beamforming algorithms assume spherical wave due to the large dimensions of the array. Finally, frequency and spatial responses for a set of different acoustic sources are obtained showing angular resolutions of the order of tenths of degree.
A model for the observed decorrelation of partials in the overtone spectra of bowed stringed instruments
Authors: Smith Sarah R. , Bocko Mark F.
Published: June 2017

It has been shown that the overtone frequencies in the spectra of bowed stringed instruments played with vibrato exhibit less than perfect pairwise correlations. However, these results are inconsistent with the mechanism of performing vibrato by changing the length of the string. Since modulating the string length affects the frequencies of all string modes proportionately, it is curious that the overtones exhibit less than perfect correlations. The observed decorrelations, therefore, may be attributed to the filtering of the string’s vibrations by the mechanical-acoustic resonant modes of the instrument body. The exact frequency deviations depend upon the frequencies of instrument’s resonant modes in relation to the string’s overtone frequencies and the width and rate of the vibrato. By modelling the instrument body as a sum of resonant modes driven by a frequency modulated saw tooth wave, we develop an analytical model relating the observed frequency deviations to the modal properties of the instrument. The effect of a single resonant mode on the instantaneous frequency trajectories is found analytically and informs numerical simulations of instruments with multiple modes. The simulated results compare well with data from recorded violin tones.
Construction of a finite element model of the Japanese koto
Authors: Coaldrake Angela K.
Published: June 2017

This paper presents the steps in developing a finite element model of the Japanese koto (13-stringed zither) in Comsol Multiphysics® v5.2a and some of the issues encountered. As the instrument is 1.8 meters in length and hand crafted there are many internal irregular shapes. Early attempts at creating a geometry were unsatisfactory. To address this issue a CT scan with 2400 cross-sections was used to measure the internal details. A mesh was created from the scan using Simpleware® software. The result was a mesh with 430,000 elements for the instrument alone, placed in a sphere of air resulting in over 7 million degrees of freedom. This new model therefore has required the use of high performance computing to produce a second of acoustic output. The issue of the physical properties of paulownia, the less well-characterized highly anisotropic wood used to construct the koto, has proven more intractable. Scanning electron microscopy, frequency response and acoustic camera studies of the original instrument provided important insights into paulownia in particular and developing the model in general. A number of studies have been undertaken to validate the model including comparing it with the original instrument. Further studies of the acoustics of the koto are in progress.
Use of H1-H2 to quantify formant tuning for notes and portions of the vibrato cycle in the second passaggio of a professional female singer
Authors: Lissemore Richard C. , Shadle Christine H. , Roon Kevin , Whalen D. H.
Published: June 2017

Singing voice pedagogy emphasizes that an acoustic change occurs in standard, classical, techniqued soprano voice between the musical notes D5♮ (587 Hz) and F5♮ (698 Hz). For low vowels, this involves a transition from tuning of the second resonance to the second harmonic (F2/H2) to tuning of the first resonance to the fundamental (F1/F0). In this single-subject study, we quantified the acoustics of this transition as the amplitude difference between the first and second harmonics (H1-H2). Results showed a clear and substantial change from negative to positive H1-H2 values at a pivot point between E5♭ and E5♮, implying the resonance tuning. Non-techniqued singing, with the same singer, showed no such change. F0 fluctuation (vibrato) of ±90 cent at the pivot point resulted in positive H1-H2 values at vibrato maxima and negative ones at vibrato minima. Additionally, H1-H2 values were consistently higher at vibrato maxima than minima throughout the transition area. Potential explanations for the latter result are: (i) vocal tract resonances are located just above the sung F0, or (ii) the vibrato cycle is accompanied by an articulatory change, possibly laryngeal movement. This illustrates the intricacies of formant tuning and suggests future possibilities for numerical assessment of vocal technique.
Velocity analysis of the vacuum-driven clarinet reed
Authors: Richard Carter K. , Coyle Whitney L.
Published: June 2017

A vacuumed artificial mouth has been assembled and tested to measure reed velocity for a Bb clarinet along the width of the reed. Reed velocity measurements may be useful for better estimation of parameters in physical models, such as the relevant surface area of the vibrating reed. Use of a vacuum system instead of a pressurized mouth chamber allows straightforward observation and manipulation of the mouthpiece apparatus. Point measurements of reed velocity were obtained via a laser-Doppler vibrometer directed at the reed surface when artificially blown. Simultaneous high-speed exposures were recorded to visualize reed motion. Preliminary results indicate that the velocity amplitude of any torsional motion in the reed is negligible compared to an asymmetric reed velocity, likely caused by natural limitations of the clarinet ligature. Velocity measurements also indicate that the reed may sometimes rebound against the mouthpiece in its oscillatory period. High-speed exposures support this conclusion by visualizing the reed deformation as it collides with the mouthpiece. This “rebound” deformation may contribute flow into the clarinet system. Further work will expand this measurement technique for a full grid along the surface of the reed, with various ligature mounts, and will seek to verify experimental measurement with analytic models.
A study on assessing clarity in pronunciation of soprano singers
Authors: Song Uk-Jin , bae myungjin
Published: June 2017

The voice of soprano singers reaches at the highest notes among female vocalists. Soprano singers usually have low clarity with respect to pronunciation because their jaw joints and mouth shapes tend to stay rigid in order to maintain high notes for a long time. Five formants found in human voice are differently shaped depending on his or her different physical structures. Especially, high clarity in pronunciation has a distinct formant shape from F1 through F5, because the jaw joint and the mouth shape have a large influence on F4 and F5 appearing in the high frequency range. This paper comparatively analyzes the vocal voices of four different Korean soprano singers concerning clarity in pronunciation. The results of acoustic analysis of these four singers shows that the singer A and the singer D show from F1 ~ up to F3 above 2 kHz but F4 and F5 do not appear in this range, and the singer C had somewhat inconsistency with her formant characteristics as a whole. In the singer B, formants from F1 through F5 are distinctly shown even above 2 kHz. The study concludes that the singer B has the best clarity in pronunciation.
Real-time localization and tracking of musical instruments with spherical microphone arrays
Authors: Mathews Jonathan , Braasch Jonas
Published: June 2017

This research describes a method for dynamic beamforming with a particle filter to localize and track musical instruments in a real-time context. Using a spherical harmonic framework, spherical microphone arrays are able to decompose three-dimensional sound fields into their basic components, which enables detailed analysis and efficient spatial filtering algorithms. In recent years, methods for determining relative source positions around an array using steerable beams have been studied. By creating multiple weighting functions based on spherical harmonic components, many beams can be generated simultaneously and can be used to dynamically track instruments via an iterative process.
Intonation detection in a melodic context
Authors: Marrone Gabriella , Aaronson Neil L.
Published: June 2017

Listeners with a wide range of formal and informal musical experience were asked to listen to an eight-tone diatonic C Major scale, generated using a piano sample library, in which one of four notes (D4, F4, A4, or C5) would be mistuned in 13 different mounts between -32¢ and + 32¢. Listeners were told which note might be mistuned and were simply asked to indicate whether the scale was in-tune or not. Each listener was exposed to each degree of mistuning ten times. The frequency with which they said a scale was in-tune as a function of the degree of mistuning was plotted for each note and listener, to which a three-parameter pseudo-normal distribution (mean, standard deviation, height) was fitted. The standard deviation indicated the sensitivity of the listener to intonation in each case (large deviation implied low sensitivity to intonation). Listeners were then ranked based on their musical background, training, and experience. The effect of musical training on intonation sensitivity was a significant factor (p<0.001). There was also a significant effect of the particular note on the sensitivity of listeners, with the intonation of A4 being most difficult to detect across listeners (p<0.001).
Exploring some questions on occlusion effect in the human auditory system when a musician or singer's external ear canal is blocked
Authors: Biswas Amitava
Published: June 2017

Sometimes some musicians and singers prefer to use their palm or other objects to cover or occlude at least one ear during performance. This practice may be helpful to enhance their self monitoring of the sound production using the occlusion effect. The basic occlusion effect in the human auditory system has been explored and reported in the literature by several individuals. According to those reports, the musician or singer can hear his or her own voice or musical instrument significantly louder when the ear canal is blocked at the outer end. Many clinicians routinely utilize detectability of vibrations from a tuning fork when placed on the mastoid process and the ear canal is occluded. This is popularly known as the Bing effect. These empirical data suggest existence of an efficient acoustic connectivity from the vocal tract to the ear canal for healthy individuals. Therefore, this study will explore quantified effects of the classic Bing effect for normal healthy musicians and singers across the audio spectrum.
Applying community tolerance level to high-energy impulse sounds
Authors: Schomer Paul D.
Published: June 2017

Fidell, Schultz and Green [JASA 84, pp. 2109-2113 (1988)] and Green and Fidell [JASA 89, pp. 234-243 (1991)] suggested a systematic approach to distinguishing loudness-driven from community-specific contributions to the prevalence of transportation noise-induced annoyance. Schomer [JASA 86, pp. 835-836 (1989)] showed how the approach could be adapted to predicting community response to high amplitude impulsive noise, simply by changing the exponent of the dosage-response function. The current presentation demonstrates in a more accessible fashion that the basic approach identified in the 1989 paper can be applied to predicting community response to high amplitude impulsive noise. The approach builds on an application by Schomer et al. [JASA 131, pp. 2772-2786 (2012)] of the CTL approach to road and rail traffic noise. The latter paper explains the “Community Tolerance Level” method from the perspective of an observer watching a process, rather than as a participant in the process. These principles are used in this paper to reinforce the conclusions of the 1989 analysis by Schomer.
Statistics of supersonic signatures propagated through simulated atmospheric turbulence
Authors: Stout Trevor A. , Sparrow Victor
Published: June 2017

The issue of annoyance caused by acoustical signatures from supersonic aircraft may be quantitatively predicted through propagation simulations. In particular, a model of energy focusing or defocussing due to turbulence in the atmospheric boundary layer is necessary to predict the real variations found whenever measurements are taken at multiple locations or at multiple times. The present algorithm solves the Khoklov-Zobolotskaya-Kuznetzov (KZK) equation and attempts to account for all important atmospheric effects such as refraction, thermoviscous absorption, relaxation processes, and nonlinearity, as well as turbulence effects due to temperature and vector wind variations. The turbulence model uses von Karman spectra, with vertically-varying length scales to better model the full extent of the boundary layer. The presentation will discuss some early results and relevant statistics, as well as the feasibility of comparison to recent overflight tests in NASA's SonicBAT program. [Work supported by NASA via a subcontract from KBRwyle.]
Evaluation of finite difference approximations of absorption and dispersion implemented in sonic boom propagation model equations
Authors: Collmar Matthew T. , Salamone Joseph A.
Published: June 2017

Recently developed one-dimensional far-field sonic boom propagation model equations are variants of an augmented Burgers equation. The Gulfstream Aerospace Corporation far-field sonic boom propagation tool, GACBoom, employs a numerical approach that consists of operator splitting in the time-domain. The mechanisms in the equation include geometric spreading, atmospheric stratification, nonlinearity, absorption, and dispersion. For propagation of sonic booms in the atmosphere, the predominant dissipative mechanisms are thermoviscous attenuation and molecular relaxation due to diatomic oxygen and nitrogen, the latter of which also contribute to dispersion. One method for utilizing predictions with these mechanisms is to employ a finite difference approximation to the dissipative and dispersive terms in the sonic boom propagation model equation. This paper uses a discrete Fourier analysis to investigate both spatial and temporal discretization ramifications for the dissipative and dispersive components included in the model equations and compares the results against analytic formulations found in the literature. Concluding remarks include numerical considerations when accounting for the influence of absorption and dispersion in sonic boom propagation.
The use of optical methods for measuring irregular reflection of weak acoustic shock pulses from a solid surface in air
Authors: Karzova Maria M. , Yuldashev Petr V. , Dragna Didier , Ollivier Sébastien , Khokhlova Vera , Blanc-Benon Philippe
Published: June 2017

Irregular reflection ofacoustic weak shockwaves (acoustic Mach numbers less than 0.01) is known as the von Neumann paradox and could not be described by the three-shock theory. In this work, nonlinear reflection regimes were studied experimentally using spark-generated spherically divergent N-waves reflecting from a plane rigid surface. Two optical methods were used in the measurements: a Schlieren system to visualize reflection patterns and a Mach-Zehnder interferometer to reconstruct pressure waveforms. The reconstruction was performed by applying the inverse Abel transform to the phase of the signal measured by the interferometer. The Mach stem formation was observed close to the surface as a result of collision of the incident and reflected front shocks of the N-wave and further away from the surface where the reflected front shock interacted with the incident rear shock. It was shown that irregular reflection occurred in a dynamic way and the length of the Mach stem increased while the N-wave propagated along the surface. In addition, reflection patterns were analyzed for several rough plane surfaces with different roughness size. The height of the Mash stem was found shorter for surfaces with larger dimension of the roughness.
What is a safe noise exposure level for the public?
Authors: Fink Daniel
Published: June 2017

What is a safe noise exposure level for the public? This question should underlie basic and applied research on the effects of sound on humans, and regulatory efforts to control public noise exposure. The safe public noise exposure level cannot be an unadjusted occupational standard. Unlike other occupational exposures, noise exposure continues outside the workplace. Occupational limits must be adjusted for increased exposure time, from 8 to 24 hours daily, 240 workdays to 365 days annually, and from 40 work years to the entire lifespan. Recommended safe noise exposure levels depend on which adverse noise effect is being considered. To prevent hearing loss, the U.S. Environmental Protection Agency (EPA) adjusted the U.S. occupational recommended exposure level of 85 A-weighted decibels for additional exposure time to calculate a 70 decibel time weighted average (TWA) exposure level. EPA did not adjust for lifespan years so the correct safe exposure level is likely lower. The World Health Organization (WHO) also recommends 70 decibels to prevent hearing loss. EPA and WHO determined that non-auditory health impacts of noise occur at 55 decibels TWA, with annoyance starting at 45 decibels. These are the safe noise exposure levels for the public.
Noise exposure in berthing rooms of Naval ships
Authors: Davis Shakti K. , Smalt Christopher , Calamia Paul
Published: June 2017

Noise on aircraft carriers is known to exceed hazardous noise levels as jets launch and land on the flight deck and loud machinery operates below deck. Crew members often reach their daily noise allowance while performing work duties but the conditions for auditory recovery onboard are not well understood. To address this gap, we assisted the Navy in recording 24h persistent noise measurements in several berthing rooms on the USS Nimitz (CVN-68). During flight operations, the 8h time-weighted average (TWA) noise levels in these below-deck living spaces ranged between 75 and 81 dBA. While the levels fall below the Department of Defense TWA limit of 85 dBA, these conditions may not support auditory recovery from temporary threshold shifts that occurred during work hours. Another potential noise hazard in these rooms is impulse noise from flight deck catapults and arresting wires, with peak levels as high as 143 dB. In this presentation, we describe an analysis of the 24h noise exposure from aircraft-carrier berthing rooms including steady-state and impulse noise exposure metrics defined in MIL-STD-1474E. [Work supported by the ONR under Air Force Contract No. FA8721-05-C-0002.]
On-body and in-ear noise exposure monitoring
Authors: Smalt Christopher , Davis Shakti K. , Calamia Paul , Lacirignola Joe , Townsend Olha , Weston Christine , Collins Paula
Published: June 2017

Accurately estimating noise dosage can be challenging for personnel who move through multiple noise environments. Dose estimates can also be confounded by the requirement to wear hearing protection in some areas, but not others. One concept for improved dose estimates under these conditions is to capture noise in-the-ear and on-body simultaneously. An additional benefit of this setup is that hearing protection fit can be assessed in real time. To evaluate this dual-microphone approach, we prototyped a noise dosimetry device for military environments where loud impulse noise such as weapons fire drives the need for high dynamic range and a high sampling rate. In this presentation, we describe a system where the in-ear microphone is acoustically coupled to a disposable foam or flange hearing protection eartip. Initial laboratory tests with a shock tube and acoustic test fixture (ATF) show more than 30 dB noise reduction between the on-body and in-ear microphones. Furthermore, in-ear levels are consistent with eardrum measurements in the ATF. One concern with body-worn dosimeters is their susceptibility to shock artifacts from microphone motion or handling. To address this issue, we also investigate co-locating an accelerometer with the on-body microphone to help remove shock artifacts. [Work supported by the Office of Naval Research.]
An assessment of the permissible exposure limit for industrial complex noise exposure
Authors: Qiu Wei , Zhang Meibian , Jiang Jianmin
Published: June 2017

An 8-hr time-weighted average exposure of 85 dBA was adopted as the permissible exposure limit (PEL) by most current international standards for exposure to noise. Using the definition of material hearing impairment (MHI) as the average of hearing threshold levels for both ears exceeded 25 dB at 1, 2, 3, and 4 kHz, NIOSH estimated that the excess risk was 8% for workers exposed to an average noise level of 85 dBA over a 40-year working lifetime. However, this 85 dBA PEL was based on the data that was acquired from workers exposed to steady state (Gaussian) noises. In this study a database of 648 workers (age 36.9 yrs + /- 7.8, exposure duration 12.8 yrs + /- 8.0) exposed to non-Gaussian noises were used to assess the 85 dBA PEL. Among them 222 subjects exposed to noise at level of 80-84 dBA and 426 subjects at 85-89 dBA. Although the average duration of exposure from non-Gaussian database was much less than 40 years, the prevalence of MHI was 16.7% at level of 80-84 dBA and 31.5% at level of 84-89 dBA. The results show that 85 dBA PEL may not well protect hearing for workers exposed to non-Gaussian complex noise exposure.
Smart-phone application to collect ambient noise field-data for users, audiologists, and researchers
Authors: Logan Roger M.
Published: June 2017

Could / should a smart-phone application be developed to measure and analyze social ambient noise that would: provide results to the user, store analyses locally for use by audiologists, and upload data for scientific research?
Numerical prediction of the broadband sound attenuation of a commercial earmuff: Impact of the cushion modeling
Authors: Carillo Kévin , Sgard Franck C. , Doutres Olivier
Published: June 2017

Passive earmuffs are commonly used when the sound level cannot be reduced at the source. They are mainly characterized by their sound attenuation that can be either measured or simulated. In this work, the sound attenuation of a commercial earmuff is calculated using a finite element model from 100 Hz to 5 kHz. Emphasis is put on the foam-filled cushion which is the trickiest component to model because of its physical complexity. This multiphasic cushion is modeled in a simplified way as an equivalent solid, either isotropic or transverse isotropic in order to take into account the added transverse stiffness due to the bulging of the cushion polymeric sheath. The accuracy of these models is investigated by comparison with measurements. The insertion loss (IL) predicted with the isotropic cushion model is highly underestimated between 500 Hz and 2.5 kHz due to the presence of an unrealistic mode of transverse deformation. It is found that (1) neglecting the acoustic excitation on the cushion’s flanks of the isotropic model or (2) using the transverse isotropic cushion model significantly improves the simulated IL.
Nonlinear elastic waves in architected soft solids
Authors: Deng Bolei , Raney Jordan R. , Bertoldi Katia , Tournat Vincent
Published: June 2017

In this presentation, we analyze different regimes of elastic wave propagation in a family of architected soft solids, the rotating square structures, known to exhibit negative Poisson ratio. We show that it is possible, via a discrete model of finite size masses coupled by soft and highly deformable elastic ligaments, to describe the nonlinear wave propagation of displacement and rotation modes in a two-dimensional configuration. In turn, the geometrical characteristics and local elastic parameters of the architected structures can be put in correspondence with the dispersive and nonlinear wave properties, thus allowing for the dispersion and nonlinearity management. By exploring several designs and the influence of geometry, we show that the parameters of the governing nonlinear wave equations can be controlled, and even the type of governing equation and their dominant nonlinearity can be modified. In particular, we report that for several studied configurations, vector elastic solitons are predicted and experimentally observed. These results could be useful for the design of nonlinear elastic metamaterials, aiming at controlling high amplitude vibrations and elastic waves, or achieving amplitude dependent operations on waves.
Numerical investigation on the effect of structure parameter of acoustic field rotator on its operating bandwidth
Authors: Zhang Xiuhai , Qu Zhiguo , Tian Di , Liu Zhi
Published: June 2017

The theory about transformation acoustics is introduced to indicate that designing an acoustic field rotator, in reality, is feasible. Then, numerical research is conducted to investigate the effect of geometrical parameters on the high cut-off frequency, including the size of building block, the aspect ratio of building block, the size of acoustic field rotator, the external diameter of acoustic field rotator, and the internal diameter of acoustic field rotator. The results suggest that the sizes of building blocks of acoustic field rotators are inversely proportional to their high cut-off frequencies in the studied frequencies. The effect of the size of acoustic field rotator mainly lies in the size of building block instead of the number of the building block. There is a linear relationship between the aspect ratio of the building block and high cut-off frequency in the studied frequencies. In addition, the layer of building block has an effect on high cut-off frequency as well. The current numerical study is helpful to give a better guidance for designing the acoustic field rotator.
Time-resolved dynamics of micrometer-sized bubbles undergoing shape oscillations
Authors: Guédra Matthieu , Cleve Sarah , Mauger Cyril , Inserra Claude , Blanc-Benon Philippe
Published: June 2017

Bubbles in a cavitation cloud can exhibit shape oscillations when insonified at large acoustic pressure amplitudes, which are generally connected to collective effects of the bubbles population (subharmonic emission, erratic motions of bubbles, coalescence, or fragmentation). The onset conditions and the oscillating properties of such shape modes are analyzed experimentally through highly time-resolved dynamics of micrometric bubbles. Single bubbles of radius ranging from 30 to 80 micrometers are nucleated with a laser pulse, trapped in a 30kHz ultrasonic field and imaged using two triggered CCD cameras at an acquisition rate of 180 kfps. A large parametric analysis over the bubbles radius and driving amplitude allows to recover the stable / unstable areas of the parametrically excited shape modes. Experimental evidence of nonzonal harmonics are reported, together with nonlinear modal interactions for sufficiently high driving amplitudes and large shape deformations, which are highlighted through (1) the subsequent excitation of nonresonant shape modes, (2) the trigger of the translational motion of the bubble, and (3) an alteration of the spherical response of the bubble. [Work supported by the French National Research Agency, LabEx CeLyA (ANR-10-LABX-0060) and granted by the ANR-MOST project CARIBBBOU (ANR-15-CE19-0003).]
Triggering of surface modes by bubble coalescence at high pressure amplitudes
Authors: Cleve Sarah , Guédra Matthieu , Mauger Cyril , Inserra Claude , Blanc-Benon Philippe
Published: June 2017

In order to study surface instabilities of small bubbles, a single spherical bubble is usually trapped in an ultrasound field and submitted to increasing acoustic pressure until reaching the necessary threshold. In the current work, coalescence between two bubbles is used as a trigger for non-spherical oscillations. Experiments are conducted in water with air bubbles of radii ranking from of 10 to 80 μm, at a driving frequency of 30 kHz and captured at 67 kHz. While most literature deals with bubble coalescence at relatively low pressure amplitudes implying spherical bubbles, coalescence at high pressure amplitudes (in the present case up to 30 kPa) leads to surface instabilities during and after the coalescence. During the impact and the immediately following oscillations, transitory surface deformations appear. After this transitory period, the bubbles stabilize either being in a purely spherical oscillation mode or exhibiting a stable surface mode. We analyze under which conditions either of the two cases applies. Lastly, apart from conventional coalescence of two bubbles becoming one single bubble, observations of long-lasting bouncing of a pair of bubbles are reported. [Work supported by the LabEx Centre Lyonnais d’Acoustique of the Université de Lyon, operated by the French National Research Agency (ANR-10-LABX-0060/ANR-11-IDEX-0007).]
To predict a thermoacoustic engine's limit cycle from its impedance measurement
Authors: Zorgnotti Valentin , Penelet Guillaume , Poignand Gaëlle , Garrett Steven L.
Published: June 2017

Thermoacoustic engines are self-oscillating systems converting thermal energy into acoustic waves. Recent studies on such engines highlight much nonlinear effects responsible for the engine’s saturation, leading to a limit cycle, which can be stable or not. Those effects however, are not sufficiently known, even with today knowledges, to accurately predict a limit cycle oscillations amplitude. This work suggests a new approach, based on acoustic impedance measurement at large forcing amplitudes, to predict the limit amplitude in steady state for a given engine. This method allows one to predict an engine’s saturation amplitude without studying in detail its intern geometry. In the case of a quarter wave length engine, its input impedance can easily be obtained from an impedance sensor for example. Increasing the speaker’s forcing leads to a nonlinear impedance depending on the acoustic field amplitude. Once measured, this function contains information such as the limit cycle amplitude, its stability and the engine’s efficiency depending on parameters as the applied heating and stack’s position. In the case of a standing wave prime mover, this study shows first results obtained from this method. Later on, this work should lead to steady state predictions for any, unknown, given engine.
Effect of RC load on the performance of a three-stage looped thermoacoustic engine
Authors: Jin Tao , Wang Yi , Yang Rui , Tan Jingqi , Feng Ye
Published: June 2017

Thermoacoustic heat engine is a type of machine converting thermal energy into acoustic energy with the attracting characteristics of high reliability and environmental friendliness. This work proposed a three-stage looped thermoacoustic engine, where a compliance tube is utilized as the phase adjuster, to realize the high acoustic impedance and the near traveling-wave acoustic field in the regenerator, which is significant for effective thermoacoustic conversion. In order to investigate its performance with low-grade thermal energy, the output acoustic power of the engine is measured with the variable load method. It can be found that as the resistance decreases, the efficiency of the engine may rise, but the required heating temperature also rises. Thus, there exists a trade-off between the efficiency and the heating temperature, and the relative Carnot efficiency is adopted as a main index to evaluate the performance of the system. The maximum relative Carnot efficiency of 12.6% (the corresponding efficiency was 3.2%) was achieved in our experiments, when the heating temperatures of the three stages were 120 °C.
Metal scaffolds for acoustic trapping of polystyrene particles in water suspensions
Authors: Gonzalez Iciar , Bonilla del Rio Zuriñe
Published: June 2017

The concept of ultrasonic 3D caging is based in wells designed to host three orthogonal half-wave acoustic resonances defined by its three dimensions generating a single-pressure-node in the center where particles collect to aggregate. A replacement of the planar shapes in these cavities by curved walls introduce changes in the pressure patterns, generating different effects on the particles exposed to the acoustic field. Here we present an experimental study of the acoustic behavior of aqueous suspensions of micron-sized polystyrene particles (Cv~1%) exposed to ultrasounds at a frequency f~1MHz in a metal scaffold made up of stainless steel wires crossed-linked orthogonally to form a mesh with a light of 1mm (something larger than λ/2). Once applied the acoustic field, the particles are rapidly attracted by the rods of the mesh distances much larger than their diameter (Φp = 6µm), where are trapped and remain adhered to the scaffold during the acoustic actuation and even later, providing stable aggregates. Hydrodynamic mechanisms associated to viscous disturbances and mutual radiation pressure induced by the metal rods could be responsible of this massive trapping effect on the polymeric particles according to previous theoretical and experimental studies carried by the authors in aerosols.
Cavitation detection in a nozzle flow
Authors: Do Huy K. , Dele-Oni Purity , Tang Tony , Poe Daniel , Bird James , Grace Sheryl , Ryan Emily , Holt Ray
Published: June 2017

The presence of cavitation inside fuel injector nozzles has been linked not only to damage associated with cavity collapse near the walls, but also more intriguingly to improved spray atomization. Previous studies have shown that cavitation is associated with increased spray angle. Our goal is to investigate the underlying mechanics. In this talk we describe our initial efforts to employ both acoustic techniques (passive cavitation detection, or PCD) and optical techniques (optical cavitation detection, or OCD) to characterize nozzle cavitation. Experiments are conducted with acrylic nozzles of various geometry. Unfocused single element transducers are used for PCD, while digital imaging is used for OCD. Cavitation onset thresholds and development are studied as functions of flow rate, nozzle geometry, and upstream fluid preparation. Cavitation characterization results will be compared with an in-house computational code being developed to model cavitation in fuel injectors.
Rayleigh surface wave in a porothermoelastic solid half-space
Authors: Singh Baljeet
Published: June 2017

In the present paper, the Rayleigh wave at a stress free thermally insulated surface of a generalized porothermoelastic solid half-space is considered. The governing equations of generalized porothermoelasticity are solved for general surface wave solution. The particular solutions satisfying the required radiation conditions are obtained. These solutions are applied to boundary conditions at stress free thermally insulated surface. In order to satisfy the relevant boundary conditions, a secular equation for wave speed of Rayleigh wave is obtained. Numerical simulations are done using an experimental data given by Yew and Jogi (1976) [J. Acoust. Soc. Am. 60, 2-8]. The wave speed is computed to observe the effects of frequency, porosity, coefficients of thermal expansion, and thermoelastic coupling coefficients.
Generation of ultrasonic finite-amplitude waves through a multiple scattering medium by time reversal in a waveguide
Authors: Garay Gonzalo A. , Benech Nicolás , Negreira Carlos , Abraham Yamil
Published: June 2017

Time-reversal process has been studied and applied in several acoustical systems. Two particular systems have gain our attention: an acoustical waveguide and a multiple scattering medium. Applied in a waveguide, time-reversal process can be employed to generate finite-amplitude waves by using low-power electronics. We used seven low-power ultrasonic transducers attached to the waveguide. After a 1-bit time-reversal, the waveform clearly shows time-trace distortion typical of shock waves. We analyzed the spectrum of the focal spot. As expected in a non-linear regime, it showed higher order harmonics. We find that for low input amplitude levels, the second harmonic have a lower amplitude in the focal point than in the surrounding region. As the input amplitude increase, the second harmonic’s amplitude in the focal point reaches the maximum level. In a second stage, we interpose a multiple scattering medium between the guide and the receiver. Its width was larger than the mean free path. The nonlinear wave is still present but with lower amplitude. However, we observe a narrower focal spot with reduced side-lobes. Thus, the multiple scattering medium improves the quality of acoustic focalization while it still allows the formation of shock waves.
Computation of nonlinear acoustic waves using smoothed particle hydrodynamics
Authors: Zhang Yong Ou , Wang Sheng , Gong Zhixiong , Zhang Tao , Li Tianyun , Hou Qing Zhi
Published: June 2017

A Lagrangian approach for solving nonlinear acoustic wave problems is presented with direct computation from smoothed particle hydrodynamics. The traditional smoothed particle hydrodynamics method has been applied to solve linear acoustic wave propagations. However, nonlinear acoustic problems are common in medical ultrasonography, sonic boom research, and acoustic levitation. Smoothed particle hydrodynamics is a Lagrangian meshfree particle method that shows advantages in modeling nonlinear phenomena, such as the shock tube problem, and other nonlinear problems with material separation or deformable boundaries. The method is used to solve the governing equations of fluid dynamics for simulating nonlinear acoustics. The present work also tests the method in solving the nonlinear simple wave equation based on Burgers’ equation. Effects of initial particle spacing, kernel length, and time step are then discussed based on the wave propagation simulation. Different kernel functions are also evaluated. The results of numerical experiments are compared with the exact solution to confirm the accuracy, convergence, and efficiency of the Lagrangian smoothed particle hydrodynamics method.
State changes in lipid interfaces observed during cavitation
Authors: Shrivastava Shamit , Cleveland Robin
Published: June 2017

Here we investigate the cavitation phenomenon at a lipid interface of multilaminar vesicles (MLVs) subjected to acoustic shock waves. The lipid membranes contain a fluorescent dye, Laurdan, which produces a fluorescence emission sensitive to the thermodynamic state of the interface. Fluorescence emissions were measured at 438nm and 470nm using two photomultiplier tubes (with 8 MHz bandwidth) from which the temporal evolution of the interface’s thermodynamic state was determined with submicrosecond resolution. Acoustic emissions were recorded simultaneously in order to detect the presence of cavitation. Different lipids were used to prepare the MLVs in order to observe cavitation phenomenon as a function of the state of the interface. It was deduced that the interface behaves as an adiabatic system decoupled from the bulk, where the entropy increase due to vaporization during cavitation is compensated by the entropy decrease resulting from condensation and dehydration of the lipids. These results show that cavitation physics critically depends on the thermodynamics of the interface. While applied here on a simple system of pure lipid MLVs, the thermodynamic approach is applicable to native biological membranes and cavitation phenomenon in general. [Work supported by UK EPSRC EP/L024012/1.]
A novel acoustic cell processing platform for cell concentration and washing
Authors: Dionne Jason P. , Dutra Brian , Chitale Kedar C. , Ghoshal Goutam , Leidel Chris , Lipkens Bart
Published: June 2017

FloDesign Sonics has developed a technology to enable a single use (gamma irradiated) continuous cell concentration and wash application for manufacturing of cell-based therapies. The device has been designed to be able to process several liters of a suspended cell culture, e.g., T-cells, at concentrations of 1 to 10 M cells/ml. The cell suspension flows through the device and the acoustic radiation force field is used to trap and hold the cells in the acoustic field. After concentrating the cells, one or multiple washing steps are accomplished by flowing the washing fluid through the device, using the acoustic field to trap the cells while displacing the original cell culture fluid. The holdup volume of the device is about 30 ml. Results are shown for prototypes with a 1x0.75 inch flow chamber driven by 2 MHz PZT-8 transducers operating at flow rates of 1-2L/h, measured cell recoveries of 90% have been achieved with concentration factors of 20 to 50 for Jurkat T-cell suspensions, depending on cell concentration and initial volume of the cell suspension. Scaling strategies used previously for cell clarification will be used to scale up the current cell concentration device to accommodate larger volumes.
Effect of ultrasound pressure and bubble-bubble interaction on the nonlinear attenuation and sound speed in a bubbly medium
Authors: Jafari Sojahrood Amin , Li Qian , Haghi Hossein , Karshafian Raffi , Porter Tyrone M. , Kolios Michael C.
Published: June 2017

The presence of bubbles changes the attenuation and sound speed of a medium. These changes in medium properties depend on the nonlinear behavior of bubbles which are not well understood. Previous studies employed linear models for the calculation of the attenuation and sound speed of bubbly mediums. These predictions are not valid in the regime of nonlinear oscillations. In addition, bubble-bubble interactions are often neglected. In this work, we have numerically simulated the attenuation and sound speed of a bubbly medium by solving a recently developed nonlinear model and considering the bubble-bubble interactions. A cluster of 52 interacting bubbles was simulated, with sizes derived from experimental measurements. Broadband attenuation measurements of monodisperse solutions were performed with peak pressures ranging within 10-100 kPa. The bubble solutions had mean diameters of 4-6 micron and peak concentrations of 1000 to 15000 bubbles/ml. At lower concentrations (with minimal microbubble interactions) model predictions are in good agreement with experimental measurements. At higher concentrations, new secondary peaks in plots of attenuation and sound speed as a function of frequency appear. By simulating bubble-bubble interactions, the numerical results could predict the frequency shift of the peaks of attenuation and sound speed, and the generation of secondary peaks.
All I really need to know I learned from Lou and Nat: Nat Durlach
Authors: Picheny Michael
Published: June 2017

Nat Durlach was one of my two primary mentors in graduate school at MIT. In the context of my PhD thesis, Nat taught me the invaluable lesson of how to think. In this talk I will describe how I applied to Speech Recognition what I learned from him about the value of reviewing prior literature, how to write a strong research proposal, and the need to question basic assumptions. These are eternal gifts Nat bequeathed to me, and I will highlight them in a series of applications using examples over my career at IBM. Specifically, I will draw from work in making advances in core speech recognition, the creation of the interdisciplinary multi-site NSF MALACH project on providing access to large spoken archives of speech, and building one of the early Speech Recognition systems for Mandarin. In addition, I will also describe applications of our work in Clear speech to a set of speech recognition related problems, including the issue of “Sheep and Goats”—why speech recognition works well on some speakers but not others—and also work done some years ago on using Speech Recognition to improve perception and understandability of speech by non-native speakers of English.
Pressure enhancement in water-based passive acoustic metamaterials
Authors: Popa Bogdan Ioan
Published: June 2017

It has recently been shown that anisotropic passive acoustic metamaterials can enhance significantly the pressure of sound waves (Chen et al., Nature Commun. 2014). The effect was attributed to strong wave compression inside carefully designed anisotropic metamaterials and was shown to lead to directional acoustic sensors whose sensing threshold is greatly improved. The improved sensing strategy was demonstrated in air but cannot be trivially ported to a water environment where it could find many applications in sonar systems, ultrasound imagers, or underwater communication systems. In this presentation, we will demonstrate new strategies different from Chen et al. that lead to pressure amplification in passive metamaterials, and, more importantly, we show that these strategies are suitable to water-based applications. We will further show that the wave compression phenomenon proposed by Chen et al. is not a necessary requirement, and both isotropic and anisotropic metamaterial structures can be used to obtain strong pressure enhancements. We will present specific metamaterial structures for underwater operation designed using the new approach, and their significant pressure amplification ability and directivity will be quantified.
Negative refraction and superresolution by a steel-methanol phononic crystal
Authors: Koju Ukesh , Mobley Joel
Published: June 2017

Negative refraction and the associated lensing effect of a two-dimensional (2D) phononic crystal (PC) in the MHz regime were studied both experimentally and numerically. The PC consists of a hexagonal array of steel cylinders (r = 0.4 mm, a = 0.5 mm) in a methanol matrix for use in an aqueous medium. FEM simulations of the pressure field show negative refraction of plane waves through a prism shaped crystal and superresolution lensing through a rectangular crystal. These phenomena were observed with hydrophone scans of the transmitted pressure fields through the steel-methanol PC in a water tank.