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Noncontact transportation and separation techniques using airborne ultrasound are attractive for use in industrial fields in which micrometer- to millimeter-sized objects can be levitated, rotated, and transported in the air using acoustic standing-wave and traveling-wave fields. This paper discusses a method to rotate a small object in the air without physical contact using ultrasound. The experimental system comprises a vibrating disk with four bolt-clamped Langevin-type ultrasound transducers and two semicircular reflectors. The flexural vibration of the disk generates an acoustic standing wave between them, and a small object can be levitated at the nodal position. An acoustic traveling wave was generated in the horizontal direction in an asymmetric acoustic field by inclining one of the two reflectors, which induced rotation of the object in the clockwise or counterclockwise direction. The acoustic intensity in the circumferential direction acting on the object was then calculated, and the directions of rotation predicted by the calculations corresponded with the experimental results. Higher input currents produced higher rotation speeds; the rotation speed reached a maximum value of 6.8 ± 0.9 rps at an input current of 1.1 App. [ABSTRACT FROM AUTHOR]

In the present paper, the paramount characteristics of the resonance of cylindrical bubbles in a compressible liquid are theoretically investigated with multi-scale analysis. Considering the liquid's compressibility, a dimensionless equation of the cylindrical bubble wall motion is established for the primary resonance under a single-frequency acoustic field. Comparing with the numerical results, the present analytical solution is verified in terms of accuracy. The key parameters on the characteristics of primary resonance are further explored including the equilibrium bubble radius, dimensionless amplitude of the acoustic field, and other detuning parameters. The main conclusions are given as follows: (1) During primary resonance, three typical nonlinear phenomena are observed: multivalued solutions, jumps, and hysteresis phenomena. (2) The liquid's compressibility affects the intensity of acoustic waves emitted by the bubbles during primary resonance. The maximum pressure at the bubble interface in the incompressible liquid is higher than that in the compressible liquid. (3) In the amplitude–frequency curve, the unstable region of the compressible liquid is smaller and the peak is lower than in the incompressible liquid. [ABSTRACT FROM AUTHOR]

The impedance matching is essential in producing high-intensity acoustic waves. This paper studies the impedance calculation methods of modulators and double-chamber Helmholtz resonators based on fluid mechanics, aeroacoustics, and electro-acoustic analogy principles. The results: ① The impedance expression of the resonators is derived. ② The impedance variation law of the chamber volume, the stator size, the air supply pressure, the air supply flow, and the working frequency is calculated. ③ The impedance-matching design scheme of the two-chamber Helmholtz low frequency and high acoustic intensity generator is given. Based on the experimental results of the high acoustic intensity generating device that the author has manufactured in the closed space, the correctness of the impedance calculation and matching design scheme in this paper is verified. This method has guiding significance for the design of high-intensity acoustic generating devices in confined space. [ABSTRACT FROM AUTHOR]

Spatiotemporal variability of the low-frequency sound field in a coastal wedge in the presence of an internal Kelvin wave (IKW) is studied both experimentally and theoretically. The experiments were carried out in Lake Kinneret, Israel (also known as the Sea of Galilee) in August 2021, with a wideband sound source deployed near the shore and receiving vertical line arrays located at the lake's center. Parameters of the IKW were obtained earlier from long-term thermistor string measurements combined with conductivity, temperature, and depth data. The IKW initiated range-dependent vertical displacements of the thermocline with a maximum amplitude near the shore and almost zero amplitude in the center of the lake. It corresponded to a thermocline inclination angle of ±0.08° with respect to the horizontal. Temporal variations in depth-averaged acoustic intensity, reaching almost 8 dB, and remarkable changes in the normal mode composition were registered. These effects are explained based on simulations using a parabolic equation and normal mode models. The role of mode coupling in acoustic intensity variations is assessed. [ABSTRACT FROM AUTHOR]

Acoustically‐driven bubbles at the micron scale can generate strong microstreaming flows in its surrounding fluidic medium. The tunable acoustic streaming strength of oscillating microbubbles and the diversity of the generated flow patterns enable the design of fast‐moving microrobots with multimodal locomotion suitable for biomedical applications. The acoustic microrobots holding two coupled microbubbles inside a rigid body are presented; trapped bubbles inside the L‐shaped structure with different orifices generate various streaming flows, thus allowing multiple degrees of freedom in locomotion. The streaming pattern and mean streaming speed depend on the intensity and frequency of the acoustic wave, which can trigger four dominant locomotion modes in the microrobot, denoted as translational and rotational, spinning, rotational, and translational modes. Next, the effect of various geometrical and actuation parameters on the control and navigation of the microrobot is investigated. Furthermore, the surface‐slipping multimodal locomotion, flow mixing, particle manipulation capabilities, the effective interaction of high flow rates with cells, and subsequent cancerous cell lysing abilities of the proposed microrobot are demonstrated. Overall, these results introduce a design toolbox for the next generation of acoustic microrobots with higher degrees of freedom with multimodal locomotion in biomedical applications. [ABSTRACT FROM AUTHOR]

Internal solitary waves evolving with time in shallow water are known to affect sound propagation significantly. Unlike prior work studying the acoustic effects of individual internal-wave properties separately, this paper elucidates and evaluates the influence of a complete evolution process of internal waves on acoustic fields both theoretically and by the coupled ocean-acoustic simulation. Two evolving wave properties considered here are shape deformations including the variations of wave amplitudes and widths and packet dispersion manifested as the increasing wavelength (i.e., the distance between successive solitons). The acoustic modal intensity expressed by the Dyson series solution is reformulated to explicitly reveal the modulation effects induced by the deformation and dispersion of internal waves. Dispersion leads to modal interference and causes the intensity envelope to oscillate with the varying wavelength. Deformation modulates intensity in a non-oscillatory manner that is less predictable due to the complexity of amplitude and width variations. In the environment reconstructed from the field observations of internal waves in the South China Sea, the modal intensity simulated by the parabolic-equation model exhibits pronounced modulation effects, where the modal interference due to dispersion dominates the intensity-envelope shape, and deformation affects the extremum positions of envelopes. [ABSTRACT FROM AUTHOR]

Tectonic coal seams are characterized by soft, low permeability and high gas outburst. The traditional gas control method is the intensive drilling and extraction in this seam, which is not only large in engineering quantity, high in cost, difficult to form holes and low in extraction efficiency, but also easy to induce coal and gas outburst, which is a difficult problem for global coal mine gas control. To solve this difficult problem, the controllable shockwave equipment developed by the author's team and successfully applied in the practice of permeability enhancement of coal seam, combined with the principles of shock vibration sound wave generation and shock wave attenuation and evolution in the rock stratum, a new idea of loading a controllable shock wave in the roof and floor of coal seam is proposed. The shock wave first attenuates and evolves into a high-strength sound wave in the roof and floor rock stratum, and then enters and loads into the coal seam to achieve the purpose of increasing permeability without damaging the physical properties of the tectonic coal seam and facilitating the opening of the original fractures. According to the new technical ideas, the implementation scheme and key parameters of the gas pre-extraction models in tectonic coal seam are designed, including the penetration drilling, roof and floor horizontal holes, shield tunneling and the high-strength acoustic wave of the working face, which provides a new technical approach to solve the problem of high efficiency and low cost gas extraction in the tectonic coal seam. [ABSTRACT FROM AUTHOR]

The safety of ultrasound exposure is very important for a patient's well-being. High-frequency (1–10 MHz) ultrasound waves are highly absorbed by biological tissue and have limited therapeutic effects on internal organs. This article presents the results of the development and application of a low-frequency (20–100 kHz) ultrasonic transducer for sonication of biological tissues. Using the methodology of digital twins, consisting of virtual and physical twins, an ultrasonic transducer has been developed that emits a focused ultrasound signal that penetrates into deeper biological tissues. For this purpose, the ring-shaped end surface of this transducer is excited not only by the main longitudinal vibrational mode, which is typical of the flat end surface transducers used to date, but also by higher mode radial vibrations. The virtual twin simulation shows that the acoustic signal emitted by the ring-shaped transducer, which is excited by a higher vibrational mode, is concentrated into a narrower and more precise acoustic wave that penetrates deeper into the biological tissue and affects only the part of the body to be treated, but not the whole body. [ABSTRACT FROM AUTHOR]

Proper mixing in microfluidic devices has been a concern since the early development stages. Acoustic micromixers (active micromixers) attract significant attention due to their high efficiency and ease of implementation. Finding the optimal geometries, structures, and characteristics of acoustic micromixers is still a challenging issue. In this study, we considered leaf-shaped obstacle(s) having a multi-lobed structure as the oscillatory part(s) of acoustic micromixers in a Y-junction microchannel. Four different types of leaf-shaped oscillatory obstacles, including 1, 2, 3, and 4-lobed structures, were defined, and their mixing performance for two fluid streams was evaluated numerically. The geometrical parameters of the leaf-shaped obstacle(s), including the number of lobes, lobes' length, lobes' inside angle, and lobes' pitch angle, were analyzed, and their optimum operational values were discovered. Additionally, the effects of the placement of oscillatory obstacles in three configurations, i.e., at the junction center, on the side walls, and both, on the mixing performance were evaluated. It was found that by increasing the number and length of lobes, the mixing efficiency improved. Furthermore, the effect of the operational parameters, such as inlet velocity, frequency, and intensity of acoustic waves, was examined on mixing efficiency. Meanwhile, the occurrence of a bimolecular reaction in the microchannel was analyzed at different reaction rates. It was proven that the reaction rate has a prominent effect at higher inlet velocities. [ABSTRACT FROM AUTHOR]

Fresnel zone plates (FZP) with quasi-planar structure and ultrathin thickness are capable of focusing light or acoustic waves efficiently. In this paper, we employ the FZP to manipulate the wave fields and suggest two acoustic functionalities. On one hand, by placing the moving coil-type microphone near the focal point of the FZP, enhanced acoustoelectric conversion is realized. The measured output voltage and power attained are 18.5 mV and 130 nW, respectively, which are 5.1 and 27.3 times that obtained without the FZP. On the other hand, by setting a tapered tube near the focal point of the FZP, deep-subwavelength and efficient localization of acoustic waves at the tube end (the mode size is around λ/20) are suggested theoretically. The cascaded focusing scheme leads to an enhancement of the acoustic intensity of the hotspot by more than 8700 times. The results are useful for realizing acoustic energy harvesting, strong mode localization, and acoustic-field enhancement. [ABSTRACT FROM AUTHOR]

• Our acoustic micromixer facilitated efficient mixing across a broad range of Re (0–323.46). • 3D vortices generated by the combination of acoustic and inertial effects were revealed. • Multi-variable controlled synthesis of nanomaterials was enabled in our acoustic micromixer. Acoustic micromixers have attracted considerable attention due to their rapid and efficient mixing capabilities, along with their flexibility, non-invasive operation, and strong compatibility, making them highly promising for applications in chemical analysis, drug development, and nanomaterial synthesis. However, the inherent limitation of low throughput and lack of stability restricts their broader application. In this study, we present an acoustic micromixer integrating both acoustic and inertial effects to generate multiple micro-vortices inducing three-dimensional convection for enhanced nanomaterial production. The device consisted of a serpentine channel with staggered sharp teethes on both sidewalls and a piezoelectric transducer (PZT) placed on top of the channels. The parameters such as PZT position, polydimethylsiloxane (PDMS)/glass thickness, sharp teeth density, and acoustic intensity influencing the mixing efficiency were firstly explored. Then the micromixer was validated to enable rapid and efficient mixing across a Reynolds number (Re) range of up to 323.46 (with flow rates reaching 3500 μL/min) at a steady low-frequency (0.4 kHz) acoustic wave, with a low power consumption of only 1.9 mW. The Re range is doubled compared to those reported in similar studies. Additionally, visualization of flowing beads and numerical simulations have revealed the flow patterns and clarified the mixing mechanism, further confirming its capability for rapid and effective mixing. Furthermore, the micromixer was successfully utilized to synthesize size-tunable, monodisperse zeolitic imidazolate framework-8 (ZIF-8) nanoparticles and Ti 3 C 2 T X /Pt-Pd nanocomposites loaded with ultrasmall Pt-Pd bimetallic nanoparticles, highlighting its practicality and versatility for various applications. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) detection through a liquid medium is a simple and effective method that can be widely applied to AE diagnosis for rotating machinery. As AE diagnosis is performed by correlating the signal intensity with the failure level and the frequency characteristics with the failure type, it is important to clarify the propagation characteristics of AE waves in liquid media to enable accurate AE diagnosis using a simpler system that utilizes AE propagation in a liquid medium. Therefore, in this study, systematic experiments were conducted focusing on the liquid medium type and the propagation distance as factors affecting the propagation characteristics of AE waves. As the area where AE waves propagate, we mainly focused on the near-field, where AE waves do not spread and are not attenuated with the propagation distance. First, we investigated the propagation and attenuation characteristics of AE waves in the near-field using an artificial AE source in liquid media such as purified water, cutting fluid solution, and lubricating oil. Differences in attenuation characteristics with the liquid medium were observed. Moreover, the propagation distance affected the attenuation characteristics, i.e., the signal intensity decreased with increasing propagation distance in a manner depending on the viscosity of the liquid medium, especially in the frequency bandwidth range from 1.5 to 3.0 MHz. Second, we theoretically verified some of the experimental results from the viewpoint of ultrasonic propagation in a liquid medium. As a result, the observed differences in attenuation characteristics with liquid medium were explained by the acoustic impedances of the liquid media, and the attenuation of the signal intensity of AE waves with increasing propagation distance was caused by the increasing absorption coefficient with increasing viscosity of the liquid medium. • Evaluation of propagation characteristics of acoustic emission waves propagating in liquid media. • Propagation distance and liquid medium type affect propagation characteristics. • Viscosity of the liquid medium affect the signal intensity of acoustic emission waves above 1.5 MHz. [ABSTRACT FROM AUTHOR]

The work described here considered the effectiveness with which di(2-ethylhexyl) phthalate might be removed from the solid matrix of bottom sediments using an ultrasonic field, hydrogen peroxide and the Fenton process. This was tested considering the influence of time, pH, amplitude of vibration, reagent dose and initial pollution content. The ultrasonic field applied had a vibration frequency of 20 kHz and a maximum acoustic wave intensity of 5.16 W/cm² . In the event, the highest efficiency obtained was 66.20%, where C0 = 10 mg/kg d.w., the pH value was 10 and the reaction was allowed to continue for 1 hour. Such a process proved more effective than hydrogen peroxide or the Fenton process, the removal efficiency after 1 h was at the level of 5.14% and 14.18%, respectively (pH = 3, C0 = 10 mg/kg d.w.). The ultrasonic field was ineffective in removing DEHP in the acid reaction medium. After 1 h of the process, the efficiency of DEHP removal was 2.54%. [ABSTRACT FROM AUTHOR]

Pulsed focused ultrasound (pFUS) utilizes short cycles of sound waves to mechanically shake cells within tissues which, in turn, causes transient local increases in cytokines, growth factors and cell adhesion molecules. Although the effect of pFUS has been investigated in several different organs including the kidney, muscle and heart, its effect on the pancreas has not been investigated. In the present work, we applied pFUS to the rodent pancreas with the following parameters: 1.1-MHz frequency, 5-Hz pulse repetition frequency, 5% duty cycle, 10-ms pulse length, 160-s duration. Low-intensity pFUS had a spatial average temporal average intensity of 11.5 W/cm2 and a negative peak pressure of 3 MPa; high-intensity pFUS had a spatial average temporal average intensity of 18.5 W/cm2 and negative peak pressure of 4 MPa. Here we found that pFUS changed the expression of several cytokines while having no effect on the underlying tissue histology or health of pancreatic cells (as reflected by no significant change in plasma levels of amylase and lipase). Furthermore, we found that this effect on cytokine expression in the pancreas was acoustic intensity dependent; while pFUS at low intensities turned off the expression of several cytokines, at high intensities it had the opposite effect and turned on the expression of these cytokines. The ability to non-invasively manipulate the microenvironment of the pancreas using sound waves could have profound implications for priming and modulating this organ for the application of cellular therapies in the context of both regenerative medicine (i.e., diabetes and pancreatitis) and oncology (i.e., pancreatic cancer). [ABSTRACT FROM AUTHOR]

Perfect sound absorption (PSA), producing an absorption coefficient of 1, can be achieved based upon the coherent interaction of acoustic waves, while it can merely be achieved within a narrow frequency-band due to critical impedance matching conditions. Here, we theoretically and experimentally study self-modulation and active-tunability in PSA created on account of a membrane-covered cavity. It is observed that due to the nonlinearity of the membrane, the frequency of PSA increases with the intensities of input acoustic waves, exhibiting a self-modulation property. Furthermore, we design an apparatus to control the elasticity of the membrane via four electromagnets, and thus, the PSA frequency can be freely and effectively adjusted by changing the direct-current driving voltage of the electromagnets. Despite the critical impedance matching conditions, the absorption coefficient achieved in our system holds at 1 when the PSA frequency is freely changed, which exhibits strong robustness in active-tunability. [ABSTRACT FROM AUTHOR]

The results of an experimental investigation of the discharge quenching by an acoustic wave are presented. Acoustic discharge quenching occurs as follows: an increase in the intensity of an acoustic wave causes a swirl, which mixes the gas in the radial direction, as a result of which the discharge in the tube shifts. An increase in the diameter of the positive column leads to an increase in the loss of charged particles on the walls of the tube, followed by an increase in the ionization frequency and the electric field. For a certain acoustic intensity, the voltage reaches a value that corresponds to the rated power of the supply unit, and at higher voltages the discharge is quenched. [ABSTRACT FROM AUTHOR]

A method is proposed for removing heat from the transducer of an acousto-optic deflector without substantial acoustic damping. The rear surface of the transducer and the heat–radiator surface are kept in contact through a thin sound-insulating fluid layer. The method is based on the considerable difference in the complex acoustic impedances for shear vibrations of fluids and a solid (the piezotransducer) by means of efficient heat transfer through the fluid. In the experiment, a continuous operation mode of the acousto-optic deflector is achieved with an acoustic wave intensity of more than 20 W/cm2. The acousto-optic deflector has been created that operates in the Bragg diffraction mode with a phase–modulation index of 3π with an input continuous controlling electric power of 3 W. The deflector characteristics for a light wavelength of 1.06 μm are as follows: diffraction efficiency no less than 90% in the 25 MHz frequency band at an absolute scanning angle of 40 mrad. [ABSTRACT FROM AUTHOR]

Distinguishing among different marine benthic habitat characteristics is of key importance in a wide set of seabed operations ranging from installations of oil rigs to laying networks of cables and monitoring the impact of humans on marine ecosystems. The Side-Scan Sonar (SSS) is a widely used imaging sensor in this regard. It produces high-resolution seafloor maps by logging the intensities of sound waves reflected back from the seafloor. In this work, we leverage these acoustic intensity maps to produce pixel-wise categorization of different seafloor types. We propose a novel architecture adapted from the Vision Transformer (ViT) in an encoder–decoder framework. Further, in doing so, the applicability of ViTs is evaluated on smaller datasets. To overcome the lack of CNN-like inductive biases, thereby making ViTs more conducive to applications in low data regimes, we propose a novel feature extraction module to replace the Multi-layer Perceptron (MLP) block within transformer layers and a novel module to extract multiscale patch embeddings. A lightweight decoder is also proposed to complement this design in order to further enhance multiscale feature extraction. With the modified architecture, we achieve state-of-the-art results and also meet real-time computational requirements. We make our code available at https://github.com/hayatrajani/s3seg-vit. • Design of a convolutional vision transformer for multiscale feature extraction. • Real-time semantic segmentation of the seafloor in side-scan sonar waterfalls. • Good generalizability even in the presence of noisy ground truth. [ABSTRACT FROM AUTHOR]

It has been known that the application of diffuse field theory to the sound field with a non-single-exponential sound decay did not comply well with listeners’ experience. Recent researches have concentrated on quantifying and controlling the non-single-exponential decay processes in rooms. However, the effect of non-single-exponential sound decay on listeners’ reverberance has not been clearly known in spite of its importance. The present work tried to explore the relationship between the non-single-exponential decay of sound in rooms and the listener’s reverberance, and further to develop a simple way of predicting subjective reverberance caused by non-single-exponential decay processes. A series of listening experiments were carried out with various computer generated non-single-exponential sound decay patterns using a two alternative forced choice (2AFC) paired comparison method. A simple way of predicting listeners’ reverberance for non-single-exponential sound decays was proposed by combining the results of subjective tests and the analysis of Schroeder decay curves using decay rates at multiple fixed intervals and their effects on listeners’ reverberance. The correlation analyses suggested that the proposed method could predict listeners’ reverberance caused by non-single-exponential sound decays better than conventional parameters within the range of non-single-exponential decay patterns examined in the present work. [ABSTRACT FROM AUTHOR]

For safe and efficient sonothrombolysis therapies, accurate estimation of ultrasound transmittance through the human skull is essential. The present study clarifies uncertainty surrounding this transmittance and experimentally verifies the equalization of transmittance through the modulation of ultrasound frequency. By changing three factors (ultrasound frequency, the thickness of a bone-phantom plate, and the distance between a transducer and a bone-phantom plate), we measured the intensity of ultrasound passing through the plate. Two activating methods, sinusoidal waves at 500 kHz and modulated waves, were compared. When we changed (1) the distance between a transducer and a bone-phantom plate and (2) the thickness of the bone-phantom plate, ultrasound transmittance through the plates substantially fluctuated. The substantial fluctuation in transmittance was observed also for a cut piece of human temporal skull bone. This fluctuation significantly declined for the modulated wave. In conclusion, modulation of ultrasound frequency can equalize the transmittance with an approximately 30–65% fluctuation drop and an approximately 40% fluctuation drop for a bone-phantom plate and for a cut piece of skull bone, respectively. By using modulated waves, we can develop safer and more effective sonothrombolysis therapies. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasound (US) incident obliquely on a cylindrical vessel is redistributed in space when the propagation path includes walls with acoustic impedance different from that of the surrounding media. We investigated this using low-density polyethylene (PE) as the vessel wall material. Both simulations and experiments were carried out. Direct hydrophone measurements of the acoustic field were made within a half section of the PE tube, and the distribution of backscattered Doppler power along a scan line was obtained using a range-Doppler instrument. Both simulation and hydrophone results demonstrate lateral shadow regions within the lumen. In every one of various Doppler flow experiments conducted, the backscattered Doppler power, compensated for on-axis transducer behaviour, increased with depth. Simulation results for an incident continuous-wave (CW) plane wave show that it tends to be focused by the curvature of the PE tube walls. The wall interactions are, however, angle-dependent and so the behaviour of a focused US beam depends on the beam as well as the walls. This study demonstrates alterations in the spatial distribution of US within a cylindrical vessel as a result of known vessel wall properties. It also provides evidence that local intensity variations within the lumen affect the relative Doppler power backscattered from small sample volumes. (E-mail: roset@maths.usyd.edu.au) [Copyright &y& Elsevier]

The work detailed here examined the impact of selected unit methods and ultrasonic removal of the widespread plastic additive di(2-ethylhexyl) phthalate (DEHP) from the bottom sediments of a body of water. To this end, hydrogen peroxide and a classic or modified Fenton process were used, supplemented by an ultrasonic field. The latter had a vibration frequency of 20 kHz and an acoustic wave intensity of 3.97 W/cm2. The impact of process parameters such as reaction environment, reaction time, initial impurity content, aging of the impurity, influence of processes on the content of organic matter and dissolved organic carbon, and elution of selected components from the matrix were all analysed. It emerged that the most effective process by which to remove DEHP from a solid matrix involved a modified Fenton process assisted by an ultrasonic field. The highest average degradation efficiency achieved in this way was 70.74%, for C0 = 10 mg/kg d.w. and t = 60 min. [ABSTRACT FROM AUTHOR]

Background: Transcranial focused ultrasound (tFUS) attracts wide attention in neuroscience as an effective noninvasive approach to modulate brain circuits. In spite of this, the effects of tFUS on the brain is still unclear, and further investigation is needed. The present study proposes to use near-infrared spectroscopy (NIRS) to observe cerebral hemodynamic change caused by tFUS in a noninvasive manner.Results: The results show a transient increase of oxyhemoglobin and decrease of deoxyhemoglobin concentration in the mouse model induced by ultrasound stimulation of the somatosensory cortex with a frequency of 8 MHz but not in sham. In addition, the amplitude of hemodynamics change can be related to the peak intensity of the acoustic wave.Conclusion: High frequency 8 MHz ultrasound was shown to induce hemodynamic changes measured using NIRS through the intact mouse head. The implementation of NIRS offers the possibility of investigating brain response noninvasively for different tFUS parameters through cerebral hemodynamic change. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate self-excited oscillation and shedding of millimeter-sized water drops, acoustically levitated in a single-node standing waves cavity, by decreasing the steady acoustic wave intensity below a threshold. The perturbation of the acoustic field by drop motion is a possible source for providing an effective negative damping for sustaining the growing amplitude of the self-excited motion. Its further interplay with surface tension, drop inertia, gravity and acoustic intensities, select various self-excited modes for different size of drops and acoustic intensity. The large drop exhibits quasiperiodic motion from a vertical mode and a zonal mode with growing coupling, as oscillation amplitudes grow, until falling on the floor. For small drops, chaotic oscillations constituted by several broadened sectorial modes and corresponding zonal modes are self-excited. The growing oscillation amplitude leads to droplet shedding from the edges of highly stretched lobes, where surface tension no longer holds the rapid expanding flow. [ABSTRACT FROM AUTHOR]