Journal articles: 'Air bubbles; Acoustic impedance'

1

Lynnworth, Lawrence C. "Air transducers with high acoustic impedance." Journal of the Acoustical Society of America 103, no. 5 (May 1998): 2833. http://dx.doi.org/10.1121/1.421383.

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2

Hsiao, P. Y., M. Devaud, and J. C. Bacri. "Acoustic coupling between two air bubbles in water." European Physical Journal E 4, no. 1 (January 2001): 5–10. http://dx.doi.org/10.1007/s101890170136.

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Ye, Zhen. "Acoustic scattering by arrays of air bubbles in water." Journal of the Acoustical Society of America 108, no. 5 (November 2000): 2639. http://dx.doi.org/10.1121/1.4743829.

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4

Deane, Grant B., and M. Dale Stokes. "The acoustic excitation of air bubbles fragmenting in sheared flow." Journal of the Acoustical Society of America 124, no. 6 (December 2008): 3450–63. http://dx.doi.org/10.1121/1.3003076.

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5

Gubaidullin, Damir, and Anatolii Nikiforov. "Interaction acoustic waves with a layered structure containing layer of bubbly liquid." MATEC Web of Conferences 148 (2018): 15006. http://dx.doi.org/10.1051/matecconf/201814815006.

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The results of a theoretical study of the effect of a bubble layer on the propagation of acoustic waves through a thin three-layered barrier at various angles of incidence are presented. The barrier consists of a layer of gel with polydisperse air bubbles bounded by layers of polycarbonate. It is shown that the presence of polydisperse air bubbles in the gel layer significantly changes the transmission and reflection of the acoustic signal when it interacts with such an obstacle for frequencies close to the resonant frequency of natural oscillations of the bubbles. The frequency range is identified where the angle of incidence has little effect on the reflection and transmission coefficients of acoustic waves.

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6

Gomez Alvarez-Arenas, T. E. "Acoustic impedance matching of piezoelectric transducers to the air." IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 51, no. 5 (May 2004): 624–33. http://dx.doi.org/10.1109/tuffc.2004.1302770.

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Gomez Alvarez-Arenas, T. E. "Acoustic Impedance Matching of Piezoelectric Transducers to the Air." IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 51, no. 5 (May 2004): 624–33. http://dx.doi.org/10.1109/tuffc.2004.1308697.

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Alvarez-Arenas, T. E. G. "Acoustic impedance matching of piezoelectric transducers to the air." IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 51, no. 5 (May 2004): 624–33. http://dx.doi.org/10.1109/tuffc.2004.1320834.

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9

Ye, Zhen. "Resonant scattering of acoustic waves by ellipsoid air bubbles in liquids." Journal of the Acoustical Society of America 101, no. 2 (February 1997): 681–85. http://dx.doi.org/10.1121/1.418279.

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10

Bin, Liang, Zhu Zhe-Min, and Cheng Jian-Chun. "Acoustic Localization in Weakly Compressible Elastic Media Permeated with Air Bubbles." Chinese Physics Letters 23, no. 4 (March 30, 2006): 871–74. http://dx.doi.org/10.1088/0256-307x/23/4/031.

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Bin, Liang, and Cheng Jian-Chun. "Optimal Acoustic Attenuation of Weakly Compressible Media Permeated with Air Bubbles." Chinese Physics Letters 24, no. 6 (June 2007): 1607–10. http://dx.doi.org/10.1088/0256-307x/24/6/049.

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12

Liu, Jixiao, Bowen Li, Tong Zhu, Yidi Zhou, Shanshan Li, Shijie Guo, and Tiejun Li. "Tunable microfluidic standing air bubbles and its application in acoustic microstreaming." Biomicrofluidics 13, no. 3 (May 2019): 034114. http://dx.doi.org/10.1063/1.5086920.

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13

Bin, Liang, Zhu Zhe-Min, and Cheng Jian-Chun. "Propagation of acoustic wave in viscoelastic medium permeated with air bubbles." Chinese Physics 15, no. 2 (January 16, 2006): 412–21. http://dx.doi.org/10.1088/1009-1963/15/2/030.

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14

Postnov, G. A. "Acoustic field of a point source in water with air bubbles." Acoustical Physics 46, no. 4 (July 2000): 461–65. http://dx.doi.org/10.1134/1.29910.

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15

Longuet-Higgins, Michael S., Bryan R. Kerman, and Knud Lunde. "The release of air bubbles from an underwater nozzle." Journal of Fluid Mechanics 230 (September 1991): 365–90. http://dx.doi.org/10.1017/s0022112091000836.

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Air bubbles released from an underwater nozzle emit an acoustical pulse which is of interest both for the study of bubble detachment and for elucidating the mechanism of sound generation by a newly formed bubble. In this paper we calculate theoretically the sequence of bubble shapes from a given nozzle and show that there is for each nozzle a bubble of maximum volume vmax Assuming that the bubble becomes detached at its ‘neck’, and that the volume of the detached bubble equals the volume V* of the undetached bubble above its ’neck’, we determine for each nozzle diameter D an acoustic frequency f* corresponding to 'slow’ bubble release.Experiments show that the acoustic frequency, hence the bubble size, depends on the rate of air.flow to the bubble, but for slow rates of flow the frequency f is very close to the theoretical frequency f*.High-speed photographs suggest that when the bubble pinches off. the limiting form of the surface is almost a cone. This is accounted for by assuming a line sink along the axis of symmetry. Immediately following pinch-off there is evidence of the formation of an axial jet going upwards into the bubble. This may play a part in stimulating the emission of sound.

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Gavrilev, Stepan, and Mikhail Ivanov. "Passive Acoustic Method in Bubble Size Distribution Determination." MATEC Web of Conferences 320 (2020): 00031. http://dx.doi.org/10.1051/matecconf/202032000031.

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The paper is considering existing methods for determining the gas phase hydrodynamic properties in liquid medium. This paper presents a passive hydroacoustic method for determining the air bubbles size distribution in water. Advantage of this method contrasting to the active ones lies in its invasiveness. Mathematical model proposed for converting the spectrum of noise emitted by a cloud of bubbles into size distribution was tested in a number of experiments. Experiments were carried out in a glass cubic reservoir filled with water. Experiment results were verified by comparison with the photometric method.

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17

Ziolkowski, Anton. "Measurement of air‐gun bubble oscillations." GEOPHYSICS 63, no. 6 (November 1998): 2009–24. http://dx.doi.org/10.1190/1.1444494.

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In this paper, I provide a theoretical basis for a practical approach to measuring the pressure field of an air gun array and present an algorithm for computing its wavefield from pressure measurements made at known positions in the vicinity of the gun ports. The theory for the oscillations of a single bubble is essentially a straight‐forward extension of Lamb’s original paper and provides a continuous, smooth transition from the oscillating wall of the bubble to the far‐field, preserving both the fluid flow and the acoustic radiation, all to the same accuracy and valid for bubbles with initial pressures up to about 200 atm (3000 psi or 20 MPa). The simplifying assumption, based on an argument of Lamb, is that the particle velocity potential obeys the linear acoustic wave equation. This is used then in the basic dynamic and kinematic equations to lead, without further approximations, to the nonlinear equation of motion of the bubble wall and the wavefield in the water. Given the initial bubble radius, the initial bubble wall velocity, and the pressure variation at any point inside or outside the bubble, the algorithm can be used to calculate the bubble motion and the acoustic wavefield. The interaction among air‐gun bubbles and the resultant total wavefield is formulated using the notional source concept, in which each bubble is replaced by an equivalent notional bubble obeying the same equation of motion but oscillating in water of hydrostatic pressure, thus allowing the wavefields of the notional bubbles to be superposed. A separate calibration experiment using the same pressure transducers and firing the guns individually allows the initial values of the bubble radius and bubble wall velocity to be determined for each gun. An appendix to the paper provides a test of the algorithm on real data from a single gun.

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18

Ye, Zhen, and Haoran Hsu. "Phase transition and acoustic localization in arrays of air bubbles in water." Applied Physics Letters 79, no. 11 (September 10, 2001): 1724–26. http://dx.doi.org/10.1063/1.1403659.

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19

Kushwaha, M. S., B. Djafari‐Rouhani, and L. Dobrzynski. "Giant acoustic stop bands for cubic arrays of air bubbles in water." Journal of the Acoustical Society of America 110, no. 5 (November 2001): 2734. http://dx.doi.org/10.1121/1.4777482.

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20

Kafesaki, M., R. S. Penciu, and E. N. Economou. "Air Bubbles in Water: A Strongly Multiple Scattering Medium for Acoustic Waves." Physical Review Letters 84, no. 26 (June 26, 2000): 6050–53. http://dx.doi.org/10.1103/physrevlett.84.6050.

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21

Gavrilev, Stepan, Mikhail Ivanov, and Semen Totunov. "THE MONITORING OF THE LIQUID-GAS MIXTURE PARAMETERS BY THE PASSIVE ACOUSTIC METHOD." VOLUME 39, VOLUME 39 (2021): 148. http://dx.doi.org/10.36336/akustika202139148.

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The considers the actual problem of determining the dispersed composition of the gas phase in a liquid medium. The work uses a passive acoustic method based on the interaction between the vibration frequency of bubbles and their size. On the experimental setup, acoustic waves emitted by air bubbles in water were recorded using a hydrophone. The sizes of the bubbles were determined by the spectra of the recorded signal. In the course of the experiments, the bubble radius was varied from 1.7 to 2.4 mm. The spectrogram of the signal was used to estimate the intensity of the release of bubbles in the volume of the experimental apparatus. Using the technique of synchronous filming, a video recording of the process of bubbles allocation at the apparatus was made. The analysis of the recorded video showed the correspondence of the determination of the parameters of the liquid-gas mixture. There are proposed various application scenarios of the passive acoustic method in the oil and gas industry.

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22

Arnott, W. Pat, Henry E. Bass, and Richard Raspet. "Specific acoustic impedance measurements of an air‐filled thermoacoustic prime mover." Journal of the Acoustical Society of America 92, no. 6 (December 1992): 3432–34. http://dx.doi.org/10.1121/1.404167.

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23

He, Cunfu, Yaoyao Wang, Yan Lu, Yuepeng Liu, and Bin Wu. "Design and Fabrication of Air-Based 1-3 Piezoelectric Composite Transducer for Air-Coupled Ultrasonic Applications." Journal of Sensors 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/4982616.

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The air-based 1-3 piezoelectric composite transducers are designed and fabricated in order to solve the acoustic impedance matching problem. Firstly, a finite element model using honeycomb structure as the piezoelectric composite matrix is built to reduce the acoustic impedance of the sensitive element. Three important factors, volume fraction of piezoelectric materialsφ, the thicknessh, and the sizesof the square cross section of piezoelectric column, are examined and verified in simulation. Then, according to the result of simulation, the piezoelectric composites and the air-coupled transducers are fabricated. The honeycomb structures of resin are produced by the method of 3D printing technology, with the volume fraction of air being 30%. The impedance characteristics and the excitation/reception performance of the air-coupled transducers are measured and optimized. Meanwhile, a scanning experiment is carried out to demonstrate the crack detection process in monocrystalline silicon.A0mode of Lamb waves is excited and collected. The location and size of the defect will be determined by calculating the correlation coefficients of the received signals and reference signals. Finally, a 15 mm × 0.5 mm × 0.5 mm scratch is clearly distinguished.

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24

Culver, Richard Lee, and Mario F. Trujillo. "Effects of scattering by air bubbles on performance of an underwater acoustic array." Journal of the Acoustical Society of America 121, no. 5 (May 2007): 3033. http://dx.doi.org/10.1121/1.4781674.

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25

Bin, Liang, Zou Xin-Ye, and Cheng Jian-Chun. "Phase Transition in Acoustic Localization in a Soft Medium Permeated with Air Bubbles." Chinese Physics Letters 26, no. 2 (February 2009): 024301. http://dx.doi.org/10.1088/0256-307x/26/2/024301.

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26

Liu, Yu Cheng, Jin Huang Huang, Chen Hung Huang, Hong Ching Her, and Yu Chun Chuang. "Evaluation of Acoustic Characteristics for Various Composite Ventilation Material by Using Impedance Tube." Advanced Materials Research 910 (March 2014): 78–81. http://dx.doi.org/10.4028/www.scientific.net/amr.910.78.

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With the development of techniques, the acoustic performance of 3C electroacoustic products, such as earphone, headphone, microspeaker and etc., will be paid much attention. Ventilation material which is often used in the front and rear side of the product is also an important component to affect the acoustic performance. Depending on the diverse manufacture processes and materials, there are many kinds of ventilation materials, including paper, mesh, poron, nonwoven and etc.. This study aims to investigate acoustic characteristics of these ventilation materials, including air permeability, reflection coefficient, and acoustic impedance. The result indicates that mesh with different code number shows similar air permeability. Meanwhile, the reflection coefficients of each mesh material have no significant variation with the frequency. For the lower frequencies, the level of acoustic impedance is much related to the structure or material used. With the increment of frequency, the acoustic impedance of all the materials will converge to a certain value even for the higher density material.

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27

Sametov, S. P. "Experimental study of interaction of bubble media with acoustic field." Proceedings of the Mavlyutov Institute of Mechanics 12, no. 2 (2017): 180–86. http://dx.doi.org/10.21662/uim2017.2.027.

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In the paper, the procedure for performing experimental measurements and the results of studies on the dynamics of interaction of ultrasonic fields with a bubble liquid in a closed volume with reflecting walls and a free surface were detailed description. The influence of different concentrations of bubbles in the liquid on the nature of the purification of the medium from them is considered. In a bubble liquid, the velocity of acoustic waves decreases substantially, which leads to a redistribution of the conditions for the formation of standing waves. It was found that an increase in concentration leads to a more intensive displacement of air bubbles by an ultrasonic field with forming of a displacement front.

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28

Kanase, Mahesh M., Lamikant D. Mangate, and Mangesh B. Chaudhari. "Acoustic aspects of synthetic jet generated by acoustic actuator." Journal of Low Frequency Noise, Vibration and Active Control 37, no. 1 (February 19, 2018): 31–47. http://dx.doi.org/10.1177/1461348418757879.

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Thermal overstressing as a result of miniaturization is the foremost challenge for the next generation electronic devices. Shrinking size of electronic devices makes this problem even worse. Conventional cooling module which uses fan and a heat sink seems to be inadequate for cooling of electronic devices due to space constraints and higher circuit densities. Synthetic jet is a novel flow technique which synthesizes stagnant air to form a jet and is potentially useful for cooling applications. It results from periodic oscillations of a diaphragm in a cavity such that there is no net mass addition to the system. It is being recently researched as an effective alternative to fan but the existing rules on noise emissions constitute an impediment to the practical use of synthetic jet. Besides several nonauditory health effects, prolonged exposure to high levels of noise can cause noise-induced hearing loss. To adopt ameliorative solutions and for adherence to legislative regulations, it is essential to assess the noise exposure. Present study is embarked on to investigate the effect of excitation frequency and voltage on sound pressure level of synthetic jet for orifices of different diameter and thickness. This jet acoustic research is performed in an imperative and controlled acoustic environment, i.e. acoustic test chamber. Spectrum analysis clearly indicates impedance mismatch between audio amplifier and electric transducer used to generate the jet flow. Over the past few years extensive experimental and analytical results have led to good understanding of synthetic jet but study on impedance mismatch has always been elusive. The results on synthetic jet heat transfer, flow, and acoustic characteristics cannot be faithfully reproduced due to such hurdle. In order to vanquish or conquest over it, matching the impedance between source and the load is inevitable. The conclusion of this paper unveils the necessity of impedance matching for high fidelity measurements of synthetic jet.

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29

WHITTEMORE, KENNETH R., SAUMIL N. MERCHANT, and JOHN J. ROSOWSKI. "Acoustic Mechanisms." Otolaryngology–Head and Neck Surgery 118, no. 6 (June 1998): 751–61. http://dx.doi.org/10.1016/s0194-5998(98)70264-5.

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The contribution of the middle ear air spaces to sound transmission through the middle ear in canal wall-up and canal wall-down mastoidectomy was studied in human temporal bones by measurements of middle ear input impedance and sound pressure difference across the tympanic membrane for the frequency range 50 Hz to 5 kHz. These measurements indicate that, relative to canal wall-up procedures, canal wall-down mastoidectomy results in a 1 to 5 dB decrease in middle ear sound transmission below 1 kHz, a 0 to 10 dB increase between 1 and 3 kHz, and no change above 3 kHz. These results are consistent with those reported by Gyo et al. (Arch Otolaryngol Head Neck Surg 1986;112:1262-8), in which umbo displacement was used as a measure of sound transmission. A model analysis suggests that the reduction in sound transmission below 1 kHz can be explained by the smaller middle ear air space volume associated with the canal wall-down procedure. We conclude that as long as the middle ear air space is aerated and has a volume greater than 0.7 ml, canal wall-down mastoidectomy should generally cause less than 10 dB changes in middle ear sound transmission relative to the canal wall-up procedure. (Otolaryngol Head Neck Surg 1998;118:751-61.)

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30

Bin, Liang, Zou Xin-Ye, and Cheng Jian-Chun. "Localisation and phase transition of acoustic waves in a soft medium containing air bubbles." Chinese Physics B 19, no. 9 (September 2010): 094301. http://dx.doi.org/10.1088/1674-1056/19/9/094301.

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31

Zang, Duyang, Kejun Lin, Lin Li, Zhen Chen, Xiaoguang Li, and Xingguo Geng. "Acoustic levitation of soap bubbles in air: Beyond the half-wavelength limit of sound." Applied Physics Letters 110, no. 12 (March 20, 2017): 121602. http://dx.doi.org/10.1063/1.4979087.

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32

Prokhorov, V. E. "COLLISION OF THE DROPLET WITH THE FREE SURFACE: ACOUSTIC EMISSION IN THE WATER COLUMN." DEDICATED TO THE 90TH ANNIVERSARY OF PROF. K.N. FEDOROV OCEAN PHYSICS 47, no. 3 (November 6, 2019): 114–21. http://dx.doi.org/10.29006/1564-2291.jor-2019.47(3).10.

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An experimental study of the emission of sound by droplets falling into an unperturbed liquid was performed using wideband hydrophones and a high-speed video camera. Collision of a drop with a water surface is accompanied by air entrainment and the formation of underwater gas cavities, which leads to the appearance of surface forces and fast flows, generating extreme accelerations, which are sufficient for resonant acoustic excitation of cavities and emission of sound packets. The sequence of emitted signals contains a shock pulse, as well as one or more sound packets generated by resonant bubbles detached from underwater cavities. The number of resonating bubbles varies from experience to experience, depending on the collision scenario and further behavior, including, in particular, the process of fragmentation of the primary cavities. The dimensions of the bubbles, measured on video frames, correspond to the values calculated in accordance with the Minnaert resonance frequency.

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33

Wang, D. W., H. W. Wijesekera, E. Jarosz, W. J. Teague, and W. S. Pegau. "Turbulent Diffusivity under High Winds from Acoustic Measurements of Bubbles." Journal of Physical Oceanography 46, no. 5 (May 2016): 1593–613. http://dx.doi.org/10.1175/jpo-d-15-0164.1.

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AbstractBreaking surface waves generate layers of bubble clouds as air parcels entrain into the upper ocean through the action of turbulent motions. The turbulent diffusivity in the bubble cloud layer is investigated by combining measurements of surface winds, waves, bubble acoustic backscatter, currents, and hydrography. These measurements were made at water depths of 60–90 m on the shelf of the Gulf of Alaska near Kayak Island during late December 2012, a period when the ocean was experiencing winds and significant wave heights up to 22 m s−1 and 9 m, respectively. Vertical profiles of acoustic backscatter decayed exponentially from the wave surface with e-folding lengths of about 0.6 to 6 m, while the bubble penetration depths were about 3 to 30 m. Both e-folding lengths and bubble depths were highly correlated with surface wind and wave conditions. The turbulent diffusion coefficients, inferred from e-folding length and bubble depth, varied from about 0.01 to 0.4 m2 s−1. Analysis suggests that the turbulent diffusivity in the bubble layer can be parameterized as a function of the cube of the wind friction velocity with a proportionality coefficient that depends weakly on wave age. Furthermore, in the bubble layer, on average, the shear production of the turbulent kinetic energy estimated by the diffusion coefficients is a similar order of magnitude as the dissipation rate predicted by the wall boundary layer theory.

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34

Korobiichuk, Igor, Viktorij Mel’nick, and Volodimir Karachun. "Effect of Acoustic Shock on Submarine." Applied Sciences 10, no. 14 (July 20, 2020): 4993. http://dx.doi.org/10.3390/app10144993.

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The carried-out analysis of the dynamics of a submarine body’s translational motion affected by an acoustic shock in the ideal medium provides for the possibility to evaluate the physical properties of the medium and elastic properties of the external body of the submarine to the value of limited motion of a submersible vehicle. The results of analysis provide for the possibility to conduct a comparative analysis of the submersible vehicle’s translational motion affected by an acoustic shock, taking into account the peculiarities of the motion medium, or rather taking into account the viscosity of the real medium. In this work, evaluative measurements of the features of moving the layout of the submarine were carried out. The limiting values of the displacement of the layout of the submarine are established for the case of the presence of an external artificial diffuse disturbance. A fluid with air bubbles from a compressed air cylinder was used to create an artificial diffuse perturbation. Such conditions are possible with intensive local bombardment or the presence of other high-speed underwater vehicles involved in local underwater operations.

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35

Patuzzi, Robert, and Alison Cook. "Acoustic impedance rhinometry (AIR): a technique for monitoring dynamic changes in nasal congestion." Physiological Measurement 35, no. 4 (February 27, 2014): 501–15. http://dx.doi.org/10.1088/0967-3334/35/4/501.

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36

Peng, Yifeng, Qian Li, Raymond R. Seekell, John N. Kheir, Tyrone M. Porter, and Brian D. Polizzotti. "Tunable Nonlinear Acoustic Reporters Using Micro- and Nanosized Air Bubbles with Porous Polymeric Hard Shells." ACS Applied Materials & Interfaces 11, no. 1 (November 16, 2018): 7–12. http://dx.doi.org/10.1021/acsami.8b16737.

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37

Sitdikova, L. F., and I. K. Gimaltdinov. "The problem spreading acoustic waves in a porous environment with air bubbles on por walls." Journal of Physics: Conference Series 1614 (August 2020): 012088. http://dx.doi.org/10.1088/1742-6596/1614/1/012088.

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38

Li, Xin, Bilong Liu, and Chong Qin. "A Perforated Plate with Stepwise Apertures for Low Frequency Sound Absorption." Applied Sciences 11, no. 13 (July 2, 2021): 6180. http://dx.doi.org/10.3390/app11136180.

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A perforated plate with stepwise apertures (PPSA) is proposed to improve sound absorption for low frequencies. In contrast with an ordinary perforated plate with insufficient acoustic resistance and small acoustic mass, the perforated plate with stepped holes could match the acoustic resistance of air characteristic impedance and also moderately increase acoustic mass especially at low frequencies. Prototypes made by 3D printing technology are tested in an impedance tube. The measured results agree well with that of prediction through theoretical and numerical models. In addition, an absorber array of perforated plates with stepwise apertures is presented to extend the sound absorption bandwidth due to the introduced multiple local resonances.

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39

Ryapolov, Petr, Vyacheslav Polunin, Anatoly Ivanov, and Kirill Ryabcev. "Experimental study of gas inclusions dynamics in the magnetic fluid in the inhomogeneous magnetic field." EPJ Web of Conferences 196 (2019): 00060. http://dx.doi.org/10.1051/epjconf/201919600060.

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The results of an experimental study of the capture, transport, and subsequent destruction of the air cavity into bubbles by the magnetic fluid in the area of the ‘magnetic vacuum’ of the annular magnet are discussed. The study was performed using video recording and recording of electromagnetic and acoustic signals.

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40

Chanson, H., and R. Manasseh. "Air Entrainment Processes in a Circular Plunging Jet: Void-Fraction and Acoustic Measurements." Journal of Fluids Engineering 125, no. 5 (September 1, 2003): 910–21. http://dx.doi.org/10.1115/1.1595672.

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Circular plunging jets were studied by both void fraction and acoustic techniques. There were two aims: to measure the structure of the jet flow and its regimes as a function of jet speed and free-jet length; and to develop and validate the acoustic measurement technique in the developing flow. Void fractions and bubble count rates were measured in the developing shear layer of a large-size plunging jet d1=25 mm. The data compared well with a solution of an advective diffusion equation and showed an increased air entrainment rate with increasing free-jet length for x1/d1⩽12. The acoustic data were processed by a novel technique to extract both bubble count and bubble size data. Three plunging jet flow regimes were noted. Near inception, acoustic pulses are isolated and indicate individual bubble entrainment as observable visually. Above a characteristic jet velocity, the number of the bubble pulses increases sharply although bubbles are still produced intermittently. At higher velocities, bubble production becomes quasi-continuous. The study suggests that an acoustic technique calibrated through detailed laboratory measurements can provide useful, absolute data in high-void fraction flows. The robust acoustic sensor can then be used in hostile industrial or environmental flows where more delicate instruments are impractical.

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Jian-Fei, Ji, Liang Guo-Long, Pang Fu-Bin, and Zhang Guang-Pu. "Effect Comparative and Experimental Analysis of Diffraction Sound Field Caused by Impedance Sphere and Elastic Spherical Shell on Directivity of Vector Sensor." Noise & Vibration Worldwide 42, no. 11 (December 2011): 57–64. http://dx.doi.org/10.1260/0957-4565.42.11.57.

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The directivity of acoustic vector sensor (AVS) will be distorted by the sound diffraction of the AVS carrier. A common AVS carrier in accordance with its acoustic characteristics can be approximately classified into three types: absolute soft air cavity, absolute rigid solid metal body and elastic shell filled with air. The focus of this paper is placed on the pressure and vibration velocity component of diffraction acoustic field caused by impedance boundary and elastic spherical boundary. Their mathematical expressions are deduced, and their directivity is also analyzed at different frequencies for different impedances. The results show that: for impedance boundary, its influences on directivity of pressure and vibration velocity is decided by the diffraction background term, and for the elastic shell boundary filled with air, the diffraction acoustic field can be seen as the sum of the diffraction acoustic field of rigid boundary and the radiated sound field of elastic vibration spherical shell boundary. When the frequency of the incident plane wave deviates from the resonance frequency of the elastic vibration shell, the diffraction acoustic field of the rigid boundary plays a major role, but when the frequency of the incident plane wave is close to the resonance frequency, the radiated sound field of the elastic vibration shell will hold the dominance. The experimental data are treated and the errors between the experimental results and the theoretical results are analyzed.

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42

Gritsenko, Dmitry, and Roberto Paoli. "Theoretical Optimization of Trapped-Bubble-Based Acoustic Metamaterial Performance." Applied Sciences 10, no. 16 (August 18, 2020): 5720. http://dx.doi.org/10.3390/app10165720.

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Acoustic metamaterials have proven to be a versatile tool for the precise control and manipulation of sound waves. One of the promising designs of acoustic metamaterials employ the arrays of bubbles and find applications for soundproofing, blast mitigation, and many others. An obvious advantage of bubble-based metamaterials is their ability to be relatively thin while absorbing low-frequency sound waves. The vast majority of theories developed to predict resonant behavior of bubble-based metamaterials capitalize on Minnaert frequency. Here, we propose a novel theoretical approach to characterize bubble-based metamaterials that are based on our previous findings for a single bubble trapped in circular cavity modeled as a thin clamped plate. We obtain analytical expressions for resonant frequencies of bubble metascreens using self-consistent approximation. Two geometry factors, distance between bubble centers and distance between bubble center and interface of acoustic impedance change, are taken into account. We demonstrate the existence of multiple bandgaps and possibility of switching between them via adjustment of geometry parameters and reflector properties.

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Han, Jing, Shuai Lv, Zhongpeng Wu, Mingwei Zhang, and Jin Bai. "Study on measurement of sound attenuation coefficient in bubble wake by pool." E3S Web of Conferences 206 (2020): 03013. http://dx.doi.org/10.1051/e3sconf/202020603013.

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In this paper, bubbles are generated by controlling the air inlet volume of the ceramic tube array with a gas divider valve. Stimulation tests of sound attenuation characteristics of the wake of bubbles in a laboratory pool are performed. A measurement experiment of sound attenuation coefficient was carried out in the case of still water and bubbles with different particle sizes. The signal frequency is 20-200kHz. Through experimental research, it is found that the existence of bubbles makes the sound attenuation coefficient significantly larger. And the attenuation coefficient is related to the frequency of the sound waves and the size of the bubbles. At the same frequency, the larger the bubble size , the larger the attenuation coefficient will be. When the bubble size is constant, the attenuation of the acoustic signal in small bubbles will change greatly below 50kHz. Above 50kHz, the attenuation coefficient changes relatively smoothly and the fluctuation is small. In the case of medium and large bubbles, the fluctuation of the attenuation coefficient becomes larger than that in the small bubbles. Finally, the theoretically calculated sound attenuation coefficient is compared with the experimentally measured results. And the change trends of the two results are basically the same.

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Cain, T. "A correction to sonic boom theory." Aeronautical Journal 113, no. 1149 (November 2009): 739–45. http://dx.doi.org/10.1017/s0001924000003390.

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Abstract Current sonic boom theory is based on linear midfield solutions coupled with acoustic propagation models. Approximate corrections are made within the theory to account for non-linearities, in particular for the coalescence of compression waves and the formation of weak shocks. A very large adjustment is made to account for the increasing acoustic impedance that the waves encounter as they propagate from the low density air at cruise altitude to the high density air at sea level. Typically this correction reduces the calculated over pressure levels by a factor of three. Here the method of characteristics (MOC) is used to prove that the density gradient within a hydrostatic atmosphere has no direct effect on the propagation or intensity of the wave. However gravity and ambient temperature both affect the wave propagation and the combined pressure level attenuation is not dissimilar to that previously attributed to acoustic impedance. Although the flawed acoustic theory has given reasonable predictions of measured sonic booms, the omission of gravity from the equation of motion and the inclusion of a false impedance modification, makes the model unreliable for prediction of future designs, particularly those focused on boom minimisation. As an aid to quiet supersonic aircraft design, Whitham’s theory is extended to include gravity and ambient temperature variation and shown to be in good agreement with a MOC solution for the real atmosphere.

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Huang, Jie, Ke-Yu Pan, Xue-Lei Feng, and Yong Shen. "Analysis and Identification of Nonlinear Acoustic Damping in Miniature Loudspeakers." Applied Sciences 11, no. 16 (August 21, 2021): 7713. http://dx.doi.org/10.3390/app11167713.

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Nonlinear acoustic damping is a key nonlinearity in miniature loudspeakers when the air velocity is at a high amplitude. Measurement of nonlinear acoustic damping is beneficial for predicting and analyzing the performance of miniature loudspeakers. However, the general measuring methods for acoustic impedance, such as the standing-wave tube method or the impedance tube method, are not applicable in this scenario because the nonlinear acoustic damping in miniature loudspeakers is coupled with other system nonlinearities. In this study, a measurement method based on nonlinear system identification was constructed to address this issue. The nonlinear acoustic damping was first theoretically analyzed and then coupled in an equivalent circuit model (ECM) to describe the full dynamics of miniature loudspeakers. Based on the ECM model, the nonlinear acoustic damping was identified using measured electrical data and compared with theoretical calculations. The satisfactory agreement between the identification and theoretical calculations confirms the validity of the proposed identification method.

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Li, Jian, Chun An Ai, Xue Ren Wang, and Xiao Jun Zhang. "The Application and Development of Composite Material Detection Using Dry Coupled Acoustic Technology." Applied Mechanics and Materials 526 (February 2014): 75–79. http://dx.doi.org/10.4028/www.scientific.net/amm.526.75.

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This paper focus on the method of composite material detection, and five dry coupled acoustic technologies are introduced, which are dry pressure coupling method, acoustical impedance method, Local percussion method, air-coupled ultrasonic method and ultrasonic fixed spacing pitch-catch method. The principle, character and application of these five methods are discussed, and the development trend of dry coupled acoustic technology is previewed.

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Yuvaraj, L., and S. Jeyanthi. "Acoustic performance of countersunk micro-perforated panel in multilayer porous material." Building Acoustics 27, no. 1 (November 10, 2019): 3–20. http://dx.doi.org/10.1177/1351010x19886588.

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This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manufacturing is applied to create sub-millimeter perforation with different hole spacings on polymer micro-perforated panels. Experiments are conducted in an impedance tube, in which the effects of the perforation ratio, air gap, and varying porous layer configurations on the sound absorption capabilities are investigated. For validation, considering the converging hole profile in the micro-perforated panel, an integration method with end correction is used to calculate the tapered section impedance, and the traditional Maa theory is used for the uniform hole. The theoretical impedance of the multilayer absorber is calculated using the transfer matrix method and subsequently compared to the experimental results. The results demonstrate that the countersunk hole micro-perforated panel exhibits a significant improvement in sound absorption, and the introduction of porous materials extends the sound absorption bandwidth. Furthermore, the results indicate that the sound absorption capability depends on the porous material placement in the multilayer absorber configuration.

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Simon, Julianna C., Oleg A. Sapozhnikov, Vera A. Khokhlova, Lawrence A. Crum, and Michael R. Bailey. "Ultrasonic atomization of liquids in drop-chain acoustic fountains." Journal of Fluid Mechanics 766 (February 2, 2015): 129–46. http://dx.doi.org/10.1017/jfm.2015.11.

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AbstractWhen focused ultrasound waves of moderate intensity in liquid encounter an air interface, a chain of drops emerges from the liquid surface to form what is known as a drop-chain fountain. Atomization, or the emission of micro-droplets, occurs when the acoustic intensity exceeds a liquid-dependent threshold. While the cavitation-wave hypothesis, which states that atomization arises from a combination of capillary-wave instabilities and cavitation bubble oscillations, is currently the most accepted theory of atomization, more data on the roles of cavitation, capillary waves, and even heat deposition or boiling would be valuable. In this paper, we experimentally test whether bubbles are a significant mechanism of atomization in drop-chain fountains. High-speed photography was used to observe the formation and atomization of drop-chain fountains composed of water and other liquids. For a range of ultrasonic frequencies and liquid sound speeds, it was found that the drop diameters approximately equalled the ultrasonic wavelengths. When water was exchanged for other liquids, it was observed that the atomization threshold increased with shear viscosity. Upon heating water, it was found that the time to commence atomization decreased with increasing temperature. Finally, water was atomized in an overpressure chamber where it was found that atomization was significantly diminished when the static pressure was increased. These results indicate that bubbles, generated by either acoustic cavitation or boiling, contribute significantly to atomization in the drop-chain fountain.

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Martens, M. J. M., L. A. M. van der Heijden, H. H. J. Walthaus, and W. J. J. M. van Rens. "Classification of soils based on acoustic impedance, air flow resistivity, and other physical soil parameters." Journal of the Acoustical Society of America 78, no. 3 (September 1985): 970–80. http://dx.doi.org/10.1121/1.392930.

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Barmin, Roman A., Polina G. Rudakovskaya, Vasiliy S. Chernyshev, Olga I. Guslyakova, Pavel A. Belcov, Ekaterina N. Obukhova, Alexey V. Gayer, Evgeny A. Shirshin, and Dmitry A. Gorin. "Optoacoustic/Fluorescent/Acoustic Imaging Probe Based on Air-Filled Bubbles Functionalized with Gold Nanorods and Fluorescein Isothiocyanate." ACS Omega 6, no. 5 (January 25, 2021): 3809–21. http://dx.doi.org/10.1021/acsomega.0c05518.

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Journal articles on the topic 'Air bubbles; Acoustic impedance'

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