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Microfluidics offers a versatile and promising platform for various applications in biomedical and other fields, boasting cost-effectiveness, rapid analysis time, and a compact equipment footprint. However, achieving controlled and versatile microfluidic motion within implantable devices presents a significant challenge. In this study, we propose a novel bidirectional micro-pump design that leverages two sharp-edge microcantilever arrays, driven by ultrasound, to enable selective flow direction by manipulating the ultrasound frequency. Through systematic numerical simulation, we demonstrate the feasibility of this design and further optimize its performance through comprehensive parametric analysis. This work provides valuable guidance for the practical development of sharp-edge-based acoustic micro-pumps, particularly for potential implantable applications such as controlled drug release and in vivo sampling for advanced diagnostics., (© 2023 Wiley‐VCH GmbH.)

Current microflow cytometers suffer from complicated fluidic integration and low fluorescence collection efficiency, resulting in reduced portability and sensitivity. Herein, we demonstrated a new flow cell design based on an on-chip monolithically integrated microreflector with a bulk acoustic wave resonator (MBAW). It enables simultaneous 3D particle focusing and fluorescence enhancement without using shear flow. Benefited by the on-chip microreflector, the captured fluorescence intensity was 1.8-fold greater than that of the Si substrate and 8.3-fold greater than that of the SiO 2 substrate, greatly improving the detection sensitivity. Combined with the contactless acoustic streaming-based focusing, particle sensing with a coefficient of variation as low as 6.1% was achieved. We also demonstrated the difference between live and dead cells and performed a cell cycle assay using the as-developed microflow cytometry. This monolithic integrated MBAW provides a new type of opto-acoustofluidic system and has the potential to be a highly integrated, highly sensitive flow cytometer for applications such as in vitro diagnostics and point of care.

Diffusion limitations and nonspecific surface absorption are great challenges for developing micro-/nanoscale affinity biosensors. There are very limited approaches that can solve these issues at the same time. Here, an acoustic streaming approach enabled by a gigahertz (GHz) resonator is presented to promote mass transfer of analytes through the jet mode and biofouling removal through the shear mode, which can be switched by tuning the deviation angle, α, between the resonator and the sensor. Simulations show that the jet mode (α ≤ 0) drives the analytes in the fluid toward the sensing surface, overcomes the diffusion limitation, and enhances the binding; while the shear mode (0 < α < π/4) provides a scouring action to remove the biofouling from the sensor. Experimental studies were performed by integrating this GHz resonator with optoelectronic sensing systems, where a 34-fold enhancement for the initial binding rate was obtained. Featuring high efficiency, controllability, and versatility, we believe that this GHz acoustic streaming approach holds promise for many kinds of biosensing systems as well as lab-on-chip systems.

The strength of cell adhesion is important in understanding the cell's health and in culturing them. Quantitative measurement of cell adhesion strength is a significant challenge in bioengineering research. For this, the present study describes a system that can measure cell adhesion strength using acoustic streaming induced by Lamb waves. Cells are cultured on an ultrasound transducer using a range of preculture and incubation times with phosphate-buffered saline (PBS) just before the measurement. Acoustic streaming is then induced using several Lamb wave intensities, exposing the cells to shear flows and eventually detaching them. By relying upon a median detachment rate of 50 %, the corresponding detachment force, or force of cell adhesion, was determined to be on the order of several nN, consistent with previous reports. The stronger the induced shear flow, the more cells were detached. Further, we employed a preculture time of 8 to 24 h and a PBS incubation time of 0 to 60 min, producing cell adhesion forces that varied from 1.2 to 13 nN. Hence, the developed system can quantify cell adhesion strength over a wide range, possibly offering a fundamental tool for cell-based bioengineering., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Chikahiro Imashiro reports financial support was provided by Japan Society for the Promotion of Science. Kenjiro Takemura reports financial support was provided by Japan Society for the Promotion of Science. James Friend reports financial support was provided by the W.M. Keck Foundation., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Combined with thrombolytic drugs and/or microbubbles, ultrasound (US) has been regarded as a useful tool for thrombolysis treatment by taking its advantages of noninvasive, non-ionization, low cost, and accurate targeting of tissues deep in body. Recently, low-intensity pulsed US, which can cause fewer complications by stable cavitation and acoustic streaming other than more violent effects, has attracted broad attention., Purpose: However, the thrombolysis effect in practice might not achieve expectation because there is not an ideal parallel multilayered structure between the skin and the targeted vessel. Therefore, the current work aims to better elucidate the influence of US incident angle on the generation of acoustic streaming and thrombolysis effect., Methods: Systemic numerical and experimental studies, namely, finite element modeling (FEM), particle image velocimetry (PIV), and in vitro thrombolysis measurements, were performed to estimate the acoustical/streaming field pattern, maximum flow velocity, and shear stress on the surface of thrombus, as well as the lysis rate generated at different conditions. These methods aim at verifying the hypothesis that streaming-induced vortices can further accelerate the dissolution of the thrombus and optimized thrombolysis effected can be achieved by adjusting US incident angles., Results: The pool data results showed that the variation trends of the flow velocity and shear stress obtained from FEM simulation and PIV experiments are qualitatively consistent with each other. There exists an optimal incident angle that can maximize the flow velocity and shear stress on the surface of thrombus, so that superior stirring and mixing effect can be generated. Furthermore, as the flow velocity and shear stress on thrombus surface are both highly correlated with the thrombolysis effect (the correlation coefficient R1 = 0.988, R2 = 0.958, respectively), the peak value of lysis rate (increase by at least 5.02%) also occurred at 10°., Conclusions: The current results demonstrated that, with appropriately determined incident angle, higher thrombolysis rate could be achieved without increasing the driving pressure. It may shed the light on future US thrombolysis planning strategy that, if combined with other advanced technologies (e.g., machine-learning-based image analysis and image-guided adaptive US emission modulation), more efficient thrombolytic effect could be realized while minimizing undesired side-effects caused by excessively high pressure., (© 2022 American Association of Physicists in Medicine.)

Acoustofluidics inside the microchannel has already found its wide applications recently. Acoustic streaming and radiation force are two underlying mechanisms that determine the trajectory of microparticles and cells in the manipulation. Critical particle size of viscous effects is found to be about 1.6 µm in the conventional rectangular microchannel (W × H = 380 m × 160 m) at the frequency of 2 MHz, below which the acoustic streaming dominants, and is independent of the driving voltage. In order to effectively adjust such a critical size, a approach is proposed and evaluated numerically to enhance the acoustic streaming by adding some protrusions (i.e., in the shape of a wedge, rod, half-ellipse) to the middle of the top or bottom wall. It is found that the resonant frequency and acoustic pressure will decrease and the acoustic streaming velocity will increase significantly, respectively, with the increase of protrusion height (up to 30 µm while keeping the width the same as 8 µm). Subsequently, trajectory motion patterns of microparticles have apparent changes in comparison to those inside the rectangular microchannel, and acoustic streaming can even dominate the motion of large microparticles (i.e., 10 µm). As a result, the critical particle size could be increased up to 72.5 µm. Furthermore, different protrusion shapes (i.e., wedge, rod, half-ellipse) on the top wall were compared. The sharpness of protrusion at its tip seems to determine the acoustic streaming velocity. The wedge attached to the bottom wall had higher resonant frequency and lower acoustic streaming velocity compared with the top wedge in the same dimension. The patterns of acoustic streaming and microparticle trajectory motion in the microchannel with dual wedges on the top and bottom walls are not the superposition of those of the top and bottom wedge individually. In summary, the geometry of the microchannel has a significant effect on the induced acoustofluidics by the bulk acoustic waves. A much larger acoustic streaming velocity is produced at the tip of the protrusion to change the critical size of microparticles between acoustic streaming and radiation force. It suggests that more applications of acoustofluidics (i.e., mixing and sonoporation) to microparticles and cells in various sizes are feasible by designing an appropriate geometry of the microchannel., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Bead-based ELISA in microfluidics is a promising platform for reducing the reagent consumption and improving assay throughput due to its fast binding kinetics and low reagent consumption. Current microfluidic bead-based immunoassay mainly relies on magnetic and centrifugal forces to manipulate microparticles to complete an assay protocol. Here we report an acoustic streaming-based microfluidic method that can perform all the fluid and particle operations of bead-based ELISA. A series of sharp-edge structures are used to generate a long-range coupled acoustic streaming that enables simultaneous particle trapping and active molecular exchange in a dead-end microchannel. The device achieved >99% of molecular exchange in 4 min, while maintaining a particle trapping efficiency of 85%. This acoustofluidic-based method demonstrates all three key operations in a bead-based immunoassay: (1) Beads "immobilization"; (2) Active mixing of fluid for bead/target binding; (3) Active molecular exchange for reagent loading and washing. Finally, on-chip quantitative detection of biomarker IL-6 with a limit of detection ∼50 pg/mL is achieved using this platform including an enzymatic signal amplification step. The small footprint, simple setup, and continuous flow operation of the acoustic streaming-based method makes it an attractive platform for continuous flow bead-based immunoassay., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Micro/nanorobotic systems capable of targeted transporting and releasing hold considerable promise for drug delivery, cellular surgery, biosensing, nano assembling, etc . However, on-demand precise control of the micro/nanorobot movement remains a major challenge. In particular, a practical interface to realize instant and customized interactions between human and micro/nanorobots, which is quite essential for developing next generation intelligent micro/nanorobots, has seldom been explored. Here, we present a human-microrobot user interface to perform direct and agile recognition of user commands and signal conversion for driving the microrobot. The microrobot platform is built based on locally enhanced acoustic streaming which could precisely transport microparticles and cells along a given pathway, while the interface is enabled by tuning the actuation frequency and time with different instructions and inputs. Our numerical simulations and experimental demonstrations illustrate that microparticles can be readily transported along the path by the acoustic robotic system, due to the vibration-induced locally enhanced acoustic streaming and resultant propulsion force. The acoustic robotic platform allows large-scale parallel transportation for microparticles and cells along given paths. The human microrobot interface enables the micromanipulator to response promptly to the users' commands input by typing or music playing for accurate transport. For example, the music tone of a playing melody is used for manipulating a cancer cell to a targeted position. The interface offers several attractive capabilities, including tunable speed and orientation, quick response, considerable delivery capacities, high precision and favorable controllability. We expect that such interface will work as a compelling and versatile platform for myriad potential scenarios in transportation units of microrobots, single cell analysis instruments, lab-on-chip systems, microfactories, etc .

We demonstrated that sound can push fluid through a tissue-mimicking material. Although acoustic streaming in tissue has been proposed as a mechanism for biomedical ultrasound applications, such as neuromodulation and enhanced drug penetration, streaming in tissue or acoustic phantoms has not been directly observed. We developed a material that mimics the porous structure of tissue and used a dye and a video camera to track fluid movement. When applied above an acoustic intensity threshold, a continuous focused ultrasound beam (spatial peak time average intensity: 238 W/cm 2 , centre frequency: 5 MHz) was found to push the dye axially, that is, in the direction of wave propagation and in the radial direction. Dye clearance increased with ultrasound intensity and was modelled using an adapted version of Eckart's acoustic streaming velocity equation. No microstructural changes were observed in the sonicated region when assessed using scanning electron microscopy. Our study indicates that acoustic streaming can occur in soft porous materials and provides a mechanistic basis for future use of streaming for therapeutic or diagnostic purposes., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

We demonstrate an acoustic platform for micro-vortexing in disposable polymer microfluidic chips with small-volume (20 μl) reaction chambers. The described method is demonstrated for a variety of standard vortexing functions, including mixing of fluids, re-suspension of a pellet of magnetic beads collected by a magnet placed on the chip, and lysis of cells for DNA extraction. The device is based on a modified Langevin-type ultrasonic transducer with an exponential horn for efficient coupling into the microfluidic chip, which is actuated by a low-cost fixed-frequency electronic driver board. The transducer is optimized by numerical modelling, and different demonstrated vortexing functions are realized by actuating the transducer for varying times; from fractions of a second for fluid mixing, to half a minute for cell lysis and DNA extraction. The platform can be operated during 1 min below physiological temperatures with the help of a PC fan, a Peltier element and an aluminum heat sink acting as the chip holder. As a proof of principle for sample preparation applications, we demonstrate on-chip cell lysis and DNA extraction within 25 s. The method is of interest for automating and chip-integrating sample preparation procedures in various biological assays.

An acoustically actuated, bubble-based technique is developed to investigate the deformability of cells suspended in microfluidic devices. A microsized bubble is generated by an optothermal effect near the targeted cells, which are suspended in a microfluidic chamber. Subsequently, acoustic actuation is employed to create localized acoustic streaming. In turn, the streaming flow results in hydrodynamic forces that deform the cells in situ. The deformability of the cells is indicative of their mechanical properties. The method in this study measures mechanical biomarkers from multiple cells in a single experiment, and it can be conveniently integrated with other bioanalysis and drug-screening platforms. Using this technique, the mean deformability of tens of HeLa, HEK, and HUVEC cells is measured to distinguish their mechanical properties. HeLa cells are deformed upon treatment with Cytochalasin. The technique also reveals the deformability of each subpopulation in a mixed, heterogeneous cell sample by the use of both fluorescent markers and mechanical biomarkers. The technique in this study, apart from being relevant to cell biology, will also enable biophysical cellular diagnosis., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Manipulating objects with acoustics has been developed for hundreds of years since Chladni patterns in gaseous environments were exhibited. In recent decades, acoustic manipulation in microfluidics, known as acoustofluidics, has rapidly thrived and many sophisticated technologies were born. However, the basic background motion of particles under acoustic excitation is usually neglected and the classical Chladni patterns haven't been reproduced in an aqueous environment. In this study, we investigated the basic mechanism and the motion of suspended particles and sinking particles in a plain microchamber under low-frequency excitation (3-5 kHz). The mechanisms were clearly distinguished by comparing the differences among colored fluids, suspended particles, and sinking particles. The suspended particles rotated around the antinode with a speed up to 55.1 µm s-1 at 100 Vpp by the acoustic streaming and they approached each other by the secondary acoustic radiation force. The sinking particles concentrated at the node with a speed up to 22.3 µm s-1 at 100 Vpp by bouncing on the vibrating surface and the primary acoustic radiation force. We have reproduced the classical standard/inverse Chladni patterns in an aqueous environment for the first time, and they were leveraged to separate SiO2 particles with different sizes. The big particles with an average diameter of 9.68 µm were concentrated at the node while the small particles with an average diameter of 2.72 µm were collected at the antinode within 2 min. These results not only provide insightful perspectives of basic mechanisms, but also open up new possibilities for advanced acoustic tweezers. [ABSTRACT FROM AUTHOR]

The strength of cell adhesion is important in understanding the cell's health and in culturing them. Quantitative measurement of cell adhesion strength is a significant challenge in bioengineering research. For this, the present study describes a system that can measure cell adhesion strength using acoustic streaming induced by Lamb waves. Cells are cultured on an ultrasound transducer using a range of preculture and incubation times with phosphate-buffered saline (PBS) just before the measurement. Acoustic streaming is then induced using several Lamb wave intensities, exposing the cells to shear flows and eventually detaching them. By relying upon a median detachment rate of 50 %, the corresponding detachment force, or force of cell adhesion, was determined to be on the order of several nN, consistent with previous reports. The stronger the induced shear flow, the more cells were detached. Further, we employed a preculture time of 8 to 24 h and a PBS incubation time of 0 to 60 min, producing cell adhesion forces that varied from 1.2 to 13 nN. Hence, the developed system can quantify cell adhesion strength over a wide range, possibly offering a fundamental tool for cell-based bioengineering.

This study presents a numerical investigation of acoustic streaming motion (of the Rayleigh type) in a compressible gas inside two-dimensional rectangular enclosures. To numerically study the effects of the sound field intensity on the formation process of streaming structures, we propose to discretize the fully compressible form of the two-dimensional Navier-Stokes equations using a high-order (formally greater or equal to fourth-order) accurate numerical scheme in both space and time. The proposed numerical solver utilizes high-order compact schemes along each spatial dimension combined with a filtering procedure when it is necessary. Acoustic standing waves are excited inside the enclosures and the resulting acoustic streaming patterns are investigated for low and high-intensity waves, in both linear and nonlinear regimes following closely the work of Daru et al. (2013). An extended investigation indicates that without the incorporation of an appropriate filter, the application of the high-order compact schemes in case of fast streaming results in spurious oscillations which inhibit their applicability. Following the recent relevant literature, the numerical simulations performed demonstrate the ability of the proposed numerical approach to reproduce efficiently and robustly the transitions from regular acoustic streaming to irregular streaming and the relevant phenomena confirming results that have been previously presented. [ABSTRACT FROM AUTHOR]

The study explores twin bi-component drop evaporation at various acoustic frequencies and amplitudes. The drops have a fixed central spacing. The acoustic streaming around the drops varies with frequency and amplitude. The streaming rises with the amplitude at a given frequency. The acoustics push the outer flow away from the drop. Furthermore, the flow transforms from horizontal to vertical at higher amplitudes, indicating a rise in the outer flow. Correspondingly, the drops' internal circulation and evaporation rise. The maximum evaporation is observed at higher amplitudes and lower frequencies due to intense streaming. The intense streaming accelerates the circulation, forcing the oscillatory circulation to be steadier. In contrast, the circulation is unsteady for lower amplitudes and higher frequencies. The steady circulation escalates the convective current inside the drops and boosts the evaporation rate. An empirical expression is developed to predict the outer flow velocity and evaporation rate at various amplitudes for any twin bi-component drops under diverse acoustic conditions. The study's novelty lies in demonstrating how the amplitude plays a crucial role in modifying the outer flow and internal circulation to elevate the evaporation rate despite frequency. [ABSTRACT FROM AUTHOR]

A model coupling Reynolds-averaged Navier-Stokes (RANS) method and linearized Navier-Stokes equations (LNSEs) was established in order to investigate the acoustic excitation and attenuation effect from a coupling perspective of time–space–frequency under various flow velocities and mass fractions of methane. Results show that the energy distribution of acoustic modes under high-frequency acoustic excitation is more uniform. The amplitude of the acoustic oscillation at a multiple coupling physical field is 10,000 times higher than that at simple flow field. The case when w C H 4 = 0.8 owns the largest percentage of energy conversion from fundamental to high-frequency signals, the largest percentage of transmitted waves from the combustion chamber system to outside and the strongest non-linear effect. When w C H 4 rises, the amplitude of oscillations at points and the attenuation effect of high-frequency signals along the axial are enhanced. At the case of Uin = 15 m/s, the amplitude of harmonics is reduced by 18% compared with other cases, while the proportion of the high-frequency harmonic increases, proving the non-linearity cannot be neglected in this case. As velocity rises, the energy conversion from fundamental to high-frequency signals enhances; while closer to the outlet position, the more complex the oscillation signal is. Model-shapes analysis shows that a case of w C H 4 = 0.8 owns the largest amplitude of the second harmonic at downstream of the burner, while the amplitude of the harmonics rapidly increases at Uin = 15 m/s at the end of the burner, which further indicates that the energy conversion of low-frequency signals to high-frequency signals occurs mainly in the middle and downstream regions. [ABSTRACT FROM AUTHOR]

Stream acoustics has been proposed as a means of monitoring discharge and wave hazards from outside the stream channel. To better understand the dependence of sound on discharge and wave characteristics, this study analyzes discharge and infrasound data from an artificial wave feature which is adjusted to accommodate daily changes in recreational use and seasonal changes in irrigation demand. Monitorable sound is only observed when discharge exceeds ∼35 m3/s, and even above that threshold the sound‐discharge relationship is non‐linear and inconsistent. When sound is observed, it shows consistent dependence on wave type within a given year, but the direction of this dependence varies among the 3 years studied (2016, 2021, and 2022). These findings support previous research that establishes discharge and stream morphology as relevant controls on stream acoustics and highlights the complex, combined effects of these variables. Plain Language Summary: Previous research has explored the potential of using sound to measure stream discharge and evaluate stream hazards. Discharge and wave types were examined at an artificial wave feature that changes formation to adapt to daily changes in recreation and seasonal changes in irrigation. Through this study, we found that monitorable sound is only observed over a certain threshold and that the formation of the wave affects sound consistently during the year but changes between years, potentially due to outside effects on the overall stream. Future work should aim to better understand wave formation and specific wave traits that contribute to certain patterns of sound. Overall, this study supports the findings of previous research and applies them further by investigating the combined, complex effects of stream traits on sound. Key Points: For the first time, we examine combined effects of discharge and wave morphology on infrasoundMonitorable infrasound is only produced above discharge rates exceeding ∼35 m3/sWave morphology has potential to create powerful or insignificant infrasound, but interannual geomorphic changes may also be significant [ABSTRACT FROM AUTHOR]

Surround suppression (SS) is a fundamental property of sensory processing throughout the brain. In the auditory system, the early processing stream encodes sounds using a one dimensional physical space—frequency. Previous studies in the auditory system have shown SS to manifest as bandwidth tuning around the preferred frequency. We asked whether bandwidth tuning can be found around frequencies away from the preferred frequency. We exploited the simplicity of spectral representation of sounds to study SS by manipulating both sound frequency and bandwidth. We recorded single unit spiking activity from the auditory cortex (ACx) of awake mice in response to an array of broadband stimuli with varying central frequencies and bandwidths. Our recordings revealed that a significant portion of neuronal response profiles had a preferred bandwidth that varied in a regular way with the sound's central frequency. To gain insight into the possible mechanism underlying these responses, we modelled neuronal activity using a variation of the "Mexican hat" function often used to model SS. The model accounted for response properties of single neurons with high accuracy. Our data and model show that these responses in ACx obey simple rules resulting from the presence of lateral inhibitory sidebands, mostly above the excitatory band of the neuron, that result in sensitivity to the location of top frequency edges, invariant to other spectral attributes. Our work offers a simple explanation for auditory edge detection and possibly other computations of spectral content in sounds. Author summary: A central computation performed by the auditory system in the mammalian brain is frequency decomposition. As a result, single neurons throughout the auditory system are often characterized by their preference to basic sound frequencies such as pure tones. Here we tested how single neurons in the mouse auditory cortex respond to sound stimuli with a range of bandwidths around specific central frequencies. We found that single neurons respond strongly to specific bandwidths, and that these responses varied in a regular way based on the sound's central frequency. We could explain the nature of these responses using a simple mathematical model that considers the excitatory central response to frequency and the structure of its inhibitory side bands. We found that some neurons in the auditory cortex are best described by their responses to the location of sharp boundaries, or edges, in the frequency composition of sounds. Taken together, our work highlights aspects of neuronal responses in the mouse auditory cortex that go beyond responses to pure tones. [ABSTRACT FROM AUTHOR]

In this paper, the acoustic streaming effects of Sonic Black Hole (SBH) are deeply studied by using the numerical and simulation method. By solving Navier–Stokes equations of compressible fluid, we analyze the flow characteristics of acoustic medium in SBH excited by sound wave, and further discuss the acoustic streaming effects and sound wave capture mechanism of SBH. The phenomenon of simultaneous reduction of medium and high-frequency sound reflection and transmission is analyzed. Under the excitation of medium- and high-frequency sound waves, the interaction between fluid medium flow and SBH structure leads to the uneven internal velocity distribution in the sound propagation direction, which can lead to the phenomenon of sound wave capture and deceleration. For low-frequency sound waves, the velocity distribution of sound medium is uniform, and there is almost no change in velocity gradient, resulting in the uniform distribution of sound pressure without sound absorption. These theoretical and numerical results are in good agreement with the experimental results in the literature, and also verify our results. Finally, by improving the structure, increasing the complexity of sound medium flow and the gradient change in the direction of sound propagation, the sound absorption and insulation ability of the SBH can be further improved. This study reveals the sound transmission mechanism of SBH, which can provide a new idea for the suppression of low-frequency sound waves in SBH. [ABSTRACT FROM AUTHOR]

• The effect of oscillating flow induced by acoustic waves is greatly influenced by the natural convection effect. • The relative Nusselt numbers decrease exponentially with the increase of Strouhal number. • Acoustic waves can not only enhance the convective heat exchange process but also hinder the heat transfer process. • Low-frequency acoustic streaming and high-frequency oscillatory flow are the main mechanisms affecting heat transfer. This study has experimentally investigated the heat transfer characteristics of a heated steel pipe (diameter = 20 mm) placed horizontally in a vertical experimental cylindrical pipe under longitudinal sound waves. The ranges of sound parameters used in this study are as follows: sound frequency f = 210–1000 Hz, and sound pressure level SPL = 125–135 dB. The heat transfer coefficient and Nusselt number of the cross- section of the heated pipe are used to describe the influence of different sound parameters on the heat transfer behavior of the heated pipe. The results show that under the action of low-frequency strong sound wave (f < 230 Hz), the distribution of local Nusselt number of heated pipe decreases (0-90°) at first and then increases (90-180°), while under the action of high-frequency strong sound wave (f > 500 Hz), the distribution of local Nusselt number first increases and then decreases. The relative Nusselt number decreases exponentially with the increase of the Strouhal number. In addition, the oscillating flow induced by sound waves is greatly influenced by the natural convection. The local enhancing or weakening effects of strong sound waves with different parameters on the heat transfer in a hot steel pipe are related to the characteristics of local flow. [ABSTRACT FROM AUTHOR]

Recently, the phenomena of streaming suppression and relocation of inhomogeneous miscible fluids under acoustic fields were explained using the hypothesis on mean Eulerian pressure. In this work, we derive the expression for the acoustic body force without relying on any prior assumptions regarding the second-order Eulerian pressure.We present a theory of nonlinear acoustics for inhomogeneous fluids from first principles, which explains streaming suppression and acoustic relocation in both miscible and immiscible inhomogeneous fluids inside a microchannel. This theory predicts the relocation of higher impedance fluids to pressure nodes of the standing wave, which agrees with recent experiments. [ABSTRACT FROM AUTHOR]

The holding force acting on a levitated object during near-field acoustic levitation has not been statically and directly measured so far. In this study, it was considered to realize such a measurement when a levitated object has a large displacement from the vibration source. In previous studies, under restricted conditions, the holding force has been calculated indirectly by image processing or measured from the balance with gravity by tilting the apparatus. In this article, the force was measured based on the magnetic force (MF) compensation principle. This is the first attempt to measure the force directly and statically under arbitrary conditions. One side of a rectangular rotor, which was placed above the acoustic radiation surface, received the holding force. The other side of the rotor received the MF generated by a solenoid. The holding force was estimated from the electric current flowing in the solenoid when the holding force and the MF were balanced. The holding force acting on the rotor surfaces was affected by the deviation between the rotor and the radiation surface. The holding force increased with increasing vibration amplitude or decreasing air gap between the rotor and the radiation surface. When the vibration sources were opposed, the holding force was affected by their vibration phase difference. The holding force was maximum at the opposite vibration phase and decreased with decreasing vibration phase difference. When the vibration sources were arranged in the transportation direction, the transportation force occurred and increased with increasing vibration amplitude of the destination vibration source. These measurement results agree well with the analysis results. [ABSTRACT FROM AUTHOR]

In order to calculate the noise field distribution in the main transformer room of an indoor substation accurately, a thermal-acoustic coupling idea was introduced, and a noise field solving the algorithm based on thermal-acoustic coupling was proposed in view of the noise quality loss caused by the effect of ambient temperature changes. Firstly, the fluid-structure coupling model of the main transformer room is established, and the computational fluid dynamics method is used to calculate the flow field distribution and temperature boundary conditions under the action of the heat source; Then, extracting the rheological equation of the environmental boundary conditions in the flow field calculation, and use the difference function to couple the rheological equation to the sound grid to obtain the sound field coupling model under the condition of variable temperature; Finally, the modified parameter acoustic integral equation under the sound field coupling model is calculated based on the conventional Gauss numerical integration method, and the sound field of the main transformer room considering the effect of variable temperature is obtained. The algorithm has been successfully applied in the analysis of the noise field of Xi'an 110 kV Zhenxing Substation, and the error with the measured value is 2.083%. • Thermoacoustic coupling should be considered in the noise field of main transformer room. • Thermoacoustic coupling is calculated by bidirectional hysteresis coupling method. • The introduction of temperature rise parameters can improve the accuracy of acoustic FEM. • Thermoacoustic coupling should be considered in noise reduction of main transformer room. [ABSTRACT FROM AUTHOR]

We present an effective thermoviscous theory of acoustofluidics including pressure acoustics, thermoviscous boundary layers, and streaming for fluids embedded in elastic cavities. By including thermal fields, we thus extend the effective viscous theory by Bach and Bruus [J. Acoust. Soc. Am. 144, 766 (2018)]. The acoustic temperature field and the thermoviscous boundary layers are incorporated analytically as effective boundary conditions and time-averaged body forces on the thermoacoustic bulk fields. Because it avoids resolving the thin boundary layers, the effective model allows for numerical simulation of both thermoviscous acoustic and time-averaged fields in three-dimensional models of acoustofluidic systems. We show how the acoustic streaming depends strongly on steady and oscillating thermal fields through the temperature dependency of the material parameters, in particular the viscosity and the compressibility, affecting both the boundary conditions and spawning additional body forces in the bulk. We also show how even small steady temperature gradients (∼ 1 K / mm) induce gradients in compressibility and density that may result in very high streaming velocities (∼ 1 mm / s) for moderate acoustic energy densities (∼ 100 J / m 3 ). [ABSTRACT FROM AUTHOR]

The paper presents results of an experimental study of acoustic streaming excited by a focused ultrasound field. The streaming velocity reaches its maximum in the focal spot of the transducer. The dependence of the flow velocity on the electric voltage applied to the transducer is quadratic at low voltages and linear at high voltages. A theoretical assessment of this dependence is given. The article was prepared based on materials in a report at the Third All-Russian Acoustics Conference (September 21–25, 2020, St. Petersburg). [ABSTRACT FROM AUTHOR]

Modern advanced minimally invasive surgery has been implemented for most of the significant gastrointestinal diseases. However, patients with coagulopathy or unresectable tumors cannot be cured by current treatment methods. Moreover, other existing medical devices for targeted drug release are too large to be applied in gastric endoscope because the diameter of the biopsy channel is smaller than 3 mm. To address it, in this work, we developed a piezoelectric single crystal ultrasonic transducer (the diameter was only 2.2 mm and the mass was 0.076 g) to produce acoustic waves, which could promote the drug release in the designed position of the digestive tract through an endoscope. It exhibited the electromechanical coupling coefficient of 0.36 and the center frequency of 6.9 MHz with the −6-dB bandwidth of 23%. In in vitro sonophoresis experiment, the gastric mucosa permeability to Bovine Serum Albumin increased about 5.6 times when the ultrasonic transducer was activated at 40 Vpp and 60% duty ratio, proving that employment of this transducer could facilitate drug penetration in the gastric mucosa. Meanwhile, the permeability could be adjusted by tuning the duty ratio of the ultrasonic transducer. The corresponding sonophoresis mechanism was related to the acoustic streaming and the thermal effect produced by the transducer. In addition, the measured maximum power density was 128 mW/cm2 and the mechanical index of the ultrasonic transducer was 0.02. The results held a great implication for applications of the transducer for targeted drug release in the gastrointestinal tract. [ABSTRACT FROM AUTHOR]

The present study focuses on acoustically induced thermal effects on Rayleigh streaming inside a resonator. Firstly, we consider the effect of the transverse (or wall-normal) mean temperature gradient on the acoustic streaming flow generated by a standing wave between two parallel plates. Analytical expressions for acoustic quantities are developed and used to express the sources of linear streaming. The influence of a transverse temperature variation on the streaming velocity is clearly identified through a term proportional to the temperature difference and to the square of the half-width of the guide. This term modifies the Rayleigh streaming pattern and may generate an additional vortex. On the other hand, the longitudinal (or wall-parallel) temperature difference is calculated as a cumulated effect of thermoacoustic heat transport in the fluid, heat conduction in the wall and heat convection of the air outside the resonator. At high acoustic levels, heat is significantly convected by the streaming flow and the resulting transverse temperature difference is proportional to the longitudinal temperature difference. Combining these expressions brings out a new criterion parameter for the nonlinear Reynolds number ($Re_{NL}$) characterizing the transition in streaming patterns at high acoustic levels. This result explains previous experimental and numerical observations of the streaming flow dynamics at high acoustic amplitudes, under different temperature boundary conditions, and can provide a powerful prediction tool for streaming pattern transitions. [ABSTRACT FROM AUTHOR]

Penetration of nanoscale therapeutic agents into the extracellular matrix (ECM) of a tumor is a limiting factor for the sufficient delivery of drugs in tumors. Ultrasound (US) in combination with microbubbles causing cavitation is reported to improve delivery of nanoparticles (NPs) and drugs to tumors. Acoustic radiation force (ARF) could also enhance the penetration of NPs in tumor ECM. In this work, a collagen gel was used as a model for tumor ECM to study the effects of ARF on the penetration of NPs as well as the deformation of collagen gels applying different US parameters (varying pressure and duty cycle). The collagen gel was characterized, and the diffusion of water and NPs was measured. The penetration of NPs into the gel was measured by confocal laser scanning microscopy and numerical simulations were performed to determine the ARF and to estimate the penetration distance and extent of deformation. ARF had no effect on the penetration of NPs into the collagen gels for the US parameters and gel used, whereas a substantial deformation was observed. The width of the deformation on the collagen gel surface corresponded to the US beam. Comparing ARF caused by attenuation within the gel and Langevin pressure caused by reflection at the gel-water surface, ARF was the prevalent mechanism for the gel deformation. The experimental and theoretical results were consistent both with respect to the NP penetration and the gel deformation. [ABSTRACT FROM AUTHOR]

Patients with unresectable or nonablatable tumors are difficult to cure, but nanotherapy combining targeted nanoparticles has many severe side effects due to the toxicities of anticancer drugs. We found that acoustic energy can produce a local region with high concentration from a low concentration suspended liquid of nano-SiO2 particles at 2.5 MHz. Our calculated results show that the main reason for aggregation is the synthesized effect of the potential well of acoustic energy and streaming to trap them. In addition, the aggregated region can be manipulated to a targeted position in the vessel phantom by moving the ultrasound transducer external to the body. This noninvasive manipulation of suspended nanoparticles can rapidly increase the local drug concentration, but reduce the total dosage of anticancer drugs, which has the potential to be used for patients with advanced tumors by improving the physiological effects and reducing the side effects. [ABSTRACT FROM AUTHOR]

We develop a model for solid objects surrounded by a fluid that accounts for the possibility of acoustic pressures giving rise to damage on the surface of the solid. The propagation of an acoustic pressure in the fluid domain is modeled by the acoustic wave equation. On the other hand, the response of the solid is described by linear elastodynamics coupled with a gradient damage model, one that is based on a cohesive-type phase-field description of fracture. The interaction between the acoustic pressure and the deformation and damage of the solid are represented by transmission conditions at the fluid–solid interface. The resulting governing equations are discretized using a finite-element/finite-difference method that pays particular attention to the spatial and temporal scales that need to be resolved. Results from model-based simulations are provided for a benchmark problem as well as for recent experiments in nano-pulse lithotripsy. A parametric study is performed to illustrate how damage develops in response to the driving force (magnitude and location of the acoustic source) as a function of the fracture resistance of the solid. The results are shown to be qualitatively consistent with experimental observations for the location and size of the damage fields on the solid surface. A study of limiting cases also suggests that both the threshold for damage and the critical fracture energy are important to consider in order to capture the transition from damage initiation to complete localization. A low-cycle fatigue model is proposed that degrades the fracture resistance of the solid as a function of accumulated tensile strain energy, and it is shown to be capable of capturing damage localization in simulations of multi-pulse nano-pulse lithotripsy. • Formulation for modeling coupled acoustics, elastodynamics, and damage. • Validation of simulation results against experimental observations. • A new model for low-cycle fatigue. [ABSTRACT FROM AUTHOR]

Acoustofluidics is a burgeoning field that applies ultrasound to micro-scale to nano-scale fluidic systems. The discovery of the ability to effectively manipulate fluids and particles at small scales has yielded results that are superior to other approaches and has been built into a diverse range of research. Recasting the fundamentals of acoustics from the past to include new phenomena observed in recent years has allowed acoustical systems to impact new areas, such as drug delivery, diagnostics, and enhanced chemical processes. The contributions in this special issue address a diverse range of research topics in acoustofluidics. Topics include acoustic streaming, flows induced by bubbles, manipulation of particles using acoustic radiation forces, fluid and structural interactions, and contributions suggesting a natural limit to the particle velocity, the ability to deliver molecules to human immune T cells, and microdroplet generation via nozzle-based acoustic atomization. [ABSTRACT FROM AUTHOR]

Acoustic streaming generated by a plane standing wave between two infinite plates or inside a cylindrical tube is considered, under the isentropic flow assumption. A two-dimensional analysis is performed in the linear case of slow streaming motion, based on analytical formal solutions of separate problems, each associated with a specific source term (Reynolds stress term). In order to obtain these analytical solutions, a necessary geometrical hypothesis is that (R/L)2 ≪ 1, where R and L are the guide half-width (or radius) and length. The effect of the two source terms classically taken into account is quantified in order to derive the dependence of the maximum axial streaming velocity on the axis as a function of the ratio R/δν, where δν is the acoustic boundary layer thickness. The effect of two other source terms that are usually neglected, is then analysed. It is found that one of these terms can generate a counter-rotating streaming flow. While negligible for very narrow guides, this term can become important for some values of the aspect ratio L/R. [ABSTRACT FROM AUTHOR]

We consider acoustic propagation in a particle-laden fluid, specifically, a perfect gas, under a model system based on the theories of Marble (1970) and Thompson (1972). Our primary aim is to understand, via analytical methods, the impact of the particle phase on the acoustic velocity field. Working under the finite-amplitude approximation, we investigate singular surface and traveling wave phenomena, as admitted by both phases of the flow. We show, among other things, that the particle velocity field admits a singular surface one order higher than that of the gas phase, that the particle-to-gas density ratio plays a number of critical roles, and that traveling wave solutions are only possible for sufficiently small values of the Mach number. [ABSTRACT FROM AUTHOR]

The interaction of an acoustic wave with a stratified fluid can drive strong streaming flows owing to the baroclinic production of fluctuating vorticity, as recently demonstrated by Chini et al. (J. Fluid Mech., 744, 2014, pp. 329–351). In the present investigation, a set of wave/mean-flow interaction equations is derived that governs the coupled dynamics of a standing acoustic-wave mode of characteristic (small) amplitude ε and the streaming flow it drives in a thin channel with walls maintained at differing temperatures. Unlike classical Rayleigh streaming, the resulting mean flow arises at O (ε) rather than at O(ε²). Consequently, fully two-way coupling between the waves and the mean flow is possible: the streaming is sufficiently strong to induce O(1) rearrangements of the imposed background temperature and density fields, which modifies the spatial structure and frequency of the acoustic mode on the streaming time scale. A novel Wentzel–Kramers–Brillouin–Jeffreys analysis is developed to average over the fast wave dynamics, enabling the coupled system to be integrated strictly on the slow time scale of the streaming flow. Analytical solutions of the reduced system are derived for weak wave forcing and are shown to reproduce results from prior direct numerical simulations (DNS) of the compressible Navier–Stokes and heat equations with remarkable accuracy. Moreover, numerical simulations of the reduced system are performed in the regime of strong wave/mean-flow coupling for a fraction of the computational cost of the corresponding DNS. These simulations shed light on the potential for baroclinic acoustic streaming to be used as an effective means to enhance heat transfer. [ABSTRACT FROM AUTHOR]

• Wearable acoustic MNs enable intelligent transdermal drug delivery. • This MNs can actively release drugs via acoustic streaming effect. • Wearable circuits are designed for smart dosage administration. • This strategy holds promise for disease management and personalized therapy. Both acute and chronic diseases require on-demand and convenient drug delivery, particularly for life-threatening acute conditions. Although emerging microneedle arrays (MNs) offer a promising therapeutic platform for painlessly administering drug payloads to patients, current dissolving or diffusion-based MNs encounter significant challenges in achieving programmable and on-demand liquid drug delivery. In this study, we develop active programmable MNs based on a wearable acoustic platform, which enables the smart management of diseases. The vortex effect near the tips excited by acoustics is utilized to actively extract drugs from MNs, that are manufactured through high precision 3D printing. By digitally controlling acoustic signals, we demonstrate user-requirement-based drug releasing, in tissue-mimicking agar gel phantoms and mouse models. The system achieves precise dosage control through three different modes: rapid single delivery mode, batch delivery mode, and long-term slow-release mode. This versatility makes the system suitable for various disease conditions. The in situ acoustic drug delivery strategy implemented on this platform offers advantages in terms of miniaturization, ease of operation and intelligence. This platform is anticipated to provide a novel personalized therapeutic approach for clinics and biomedicine. [ABSTRACT FROM AUTHOR]

A combined top-down/bottom-up microfluidic assembly system is demonstrated in which microspheres undergo directed assembly within microchannels. The approach is adapted from macroscale templated assembly by selective removal (TASR), in which high-frequency acoustic excitations drive selective assembly into shape- and size-matched wells patterned in a planar surface. A PDMS layer patterned with microchannels is bonded to a PDMS layer molded to define assembly wells. A suspension of 10 $\mu \text{m}$ diameter polystyrene microspheres is flowed into the microchannels, and an external, high-frequency ultrasonic transducer circulates the microspheres within the channels and removes them from everywhere except the size-matched wells. Microspheres are successfully assembled in wells inside the microchannels with yields of up to 90%. Smaller channel dimensions reduce assembly yield in part because smaller internal channel volumes reduce the availability of microspheres relative to assembly wells. In addition, reducing channel width below about $500~\mu \text{m}$ is shown to be an independent predictor of low assembly yields; this is attributed to the physics of acoustic streaming flow under the acoustic excitation. Assembly yield is largely independent of the location of the assembly wells within the microchannels, and selectivity is confirmed by low assembly yield of $6~\mu \text{m}$ diameter microspheres into the larger wells. [2020-0072] [ABSTRACT FROM AUTHOR]

The brain decomposes mixtures of sounds, such as competing talkers, into perceptual streams that can be attended to individually. Attention can enhance the cortical representation of streams, but it is unknown what acoustic features the enhancement reflects, or where in the auditory pathways attentional enhancement is first observed. Here, behavioral measures of streaming were combined with simultaneous low- and high-frequency envelope-following responses (EFR) that are thought to originate primarily from cortical and subcortical regions, respectively. Repeating triplets of harmonic complex tones were presented with alternating fundamental frequencies. The tones were filtered to contain either low-numbered spectrally resolved harmonics, or only high-numbered unresolved harmonics. The behavioral results confirmed that segregation can be based on either tonotopic or pitch cues. The EFR results revealed no effects of streaming or attention on subcortical responses. Cortical responses revealed attentional enhancement under conditions of streaming, but only when tonotopic cues were available, not when streaming was based only on pitch cues. The results suggest that the attentional modulation of phase-locked responses is dominated by tonotopically tuned cortical neurons that are insensitive to pitch or periodicity cues. [ABSTRACT FROM AUTHOR]

We propose a system that controls the spatial distribution of odors in an environment by generating electronically steerable ultrasound-driven narrow air flows. The proposed system is designed not only to remotely present a preset fragrance to a user, but also to provide applications that would be conventionally inconceivable, such as: 1) fetching the odor of a generic object placed at a location remote from the user and guiding it to his or her nostrils, or 2) nullifying the odor of an object near a user by carrying it away before it reaches his or her nostrils (Fig. 1). These are all accomplished with an ultrasound-driven air stream serving as an airborne carrier of fragrant substances. The flow originates from a point in midair located away from the ultrasound source and travels while accelerating and maintaining its narrow cross-sectional area. These properties differentiate the flow from conventional jet- or fan-driven flows and contribute to achieving a midair flow. In our system, we employed a phased array of ultrasound transducers so that the traveling direction of the flow could be electronically and instantaneously controlled. In this paper, we describe the physical principle of odor control, the system construction, and experiments conducted to evaluate remote fragrance presentation and fragrance tracking. [ABSTRACT FROM PUBLISHER]

• We have designed a test example similar to a sonic black hole, a microperforated shell structure and a complicated resonator structure. Three in one. A high acoustic absorption coefficient was obtained for a wide range of frequencies, with a peak at the low frequency of 190 Hz. • Through theoretical calculation and simulation, the sound absorption mechanism of this structure is described using acoustic streaming effects. • By discussion on acoustic streaming effect of different frequencies, the resonator cavity and micro-perforated panels contributes more to the sound absorption performance at low frequencies, and the SBH maintains the high sound absorption coefficient at high frequencies. In order to improve and broaden the absorption performance of Sonic Black Hole (SBH), we propose a modified SBH structure with micro-perforated panels which is embedded the multiple resonator cavities, and investigate the sound absorption effect of the structure. Characteristics of acoustic streaming effects are embodied in sound pressure and flow velocity distribution. Further, proposed SBH structure can achieve high sound absorption under 6.0 kHz. Based on the symmetry of the structure, the Two-dimensional axisymmetric Finite Element Method (FEM) model is proposed to study the sound absorption mechanism, which shows that the change of flow velocity gradient of acoustic medium leads to the loss of acoustic energy inside the structure. By discussion on acoustic streaming effects of different frequencies, the resonator cavity and micro-perforated panels contributes more to the sound absorption performance at low frequencies, and SBH produces a sound absorption advantage at high frequencies. The theoretical calculation and simulation result match and prove the correctness of the sound streaming effect. Sound absorption tests by acoustic impedance tube confirm that the proposed structure can maintain a sound absorption coefficient of over 0.5 in the range of 0.05–6.0 kHz. The combination of micro-perforated panels and SBH structure is widely applicable to muffler design and has good application prospects. [ABSTRACT FROM AUTHOR]