Acoustic Particle Research Articles

Acoustic particle trapping driven by axial primary radiation force in shaped traps.

We study particle trapping driven by the axial primary radiation force (A-PRF) in shaped traps exposed to standing bulk acoustic waves (S-BAW) using numerical simulations and experiments. The utilization of the stronger A-PRF as the main retention force is a consequence of standing-wave formation along the flow direction, instead of the orthogonal direction as in the case of traditionally used lateral-PRF S-BAW trapping setups. The study of particle dynamics reveals that the competition between A-PRF and viscous drag force governs particle trajectory. The ratio of the acoustic energy to the viscous work (β) provides a general criterion for particle trapping at a distinctive off-node site that is spatially controllable. Particles get trapped for β≥β_{cr} at some distance away from the nodal plane and the distance varies as β^{-c}(c=0.6-1.0). The use of A-PRF as the retention force could potentially allow traditional S-BAW trapping systems to envisage high-throughput advancements surpassing the current standards in cell-handling unit operations.

An Acoustic Sea Glider for Deep-Sea Noise Profiling Using an Acoustic Vector Sensor

Abstract An acoustic sea glider has been developed for ambient sea noise measurement and target detection through the deployment of an acoustic vector sensor (AVS). The glider was designed with three cabins connected in sequence and it can dive to depths exceeding 1200m. The AVS fixed on the glider measure acoustic pressure and particle velocities related to undersea noise, and the inner attitude sensors can effectively eliminate the estimation deviation of the direction of arrival. The inherent self-noises of the acoustic sea glider and AVS are presented respectively in respect to the Knudsen spectra of sea noise. Sea trial results indicate that the AVS could work well for undersea noise measurement when the glider is smooth sliding, and the target azimuth estimated by AVS after correction is remarkably consistent with the values measured by the GPS, and direction-finding errors are less than 10 degrees. The research in this paper shows that the acoustic sea glider is able to undertake tasks such as a wide range of underwater acoustic measurement and detection.

Wake flow patterns and turbulence around naturally deposited and installed trees in a gravel bed river

AbstractLarge wood structures, such as wood fragments, debris jams, or entire trees, create flow and habitat diversity in rivers. A key flow feature associated with such structures is the wake, characterised by a core zone of reduced velocity and shear layers at its margins. Wakes are largely controlled by geometric and structural properties of the wood. In the present study, the flow patterns and turbulence created by different wood structures were compared at two study sites: naturally eroded and fragmented oaks (Site A) and artificial poplar installations (Site B). Flow and turbulence were quantified using pointwise velocity measurements with acoustic Doppler velocimeters (ADVs) and surface particle tracking velocimetry (SPTV). The measured flow patterns exhibited similarities with shallow porous wakes that feature fluid advection through the structure into the wake core downstream. Two additional features of wood structures were identified in the present study: (i) the growth of the shear layers was hindered by bed friction like for shallow mixing layers and (ii) the presence of a tree stem and sediment deposit in the wake centre delayed or even suppressed the interaction of the shear layers and vortex street formation similar to a wake‐splitter plate. Methodologically, the combined ADV/SPTV measurement approach and the use of analytical models for shallow mixing layers proved to be highly valuable to decipher the complex flow patterns around wood structures in the field.

Theoretical Investigation of Particles Manipulation in Fluids Using Acoustic Technique in a Microfluidic Channel

The present work is focused on discussing standing acoustic wave-based particles separation in PMMA microfluidic channel at tilted angle. A theoretical model is developed to describe the interaction of the particles at different sizes under an acoustic pressure with tilted angles. Tilted angle, acoustic pressure, acoustic wavelength, flow velocity and buffer solution viscosity are as key parameters to be investigated. It is demonstrated that these parameters can affect the particle motion in microfluidic channel, which play the important roles in particle separation. It’s shown the vital criteria of the microfluidic chip design for specific applications.

Synergistic Reconstruction of Temperature Field and Vortex Distribution Based On Nonlinear Acoustic Tomography and Particle Swarm Optimization

Synergistic Reconstruction of Temperature Field and Vortex Distribution Based On Nonlinear Acoustic Tomography and Particle Swarm Optimization

Numerical analysis of acoustic resistance affected by the corner shape of a resonator orifice

At the orifice of a Helmholtz resonator attached on a duct, acoustic resistance increases with the grazing flow speed. When the orifice corners are rounded, the increase in acoustic resistance due to the grazing flow is suppressed compared to when the orifices are right-angled. In this study, CFD analyses on the flow field including pressure fluctuation were performed for a resonator with right-angled orifice corners (NN model) and for a resonator with rounded orifice corners (RR model). The increase in acoustic resistance obtained from the CFD analysis qualitatively agrees with the previous experimental results; Acoustic resistances of both models are almost same when the grazing flow is slow. In contrast, when the grazing flow is fast, the acoustic resistance of the RR model is about half compared to that of the NN model. Moreover, Acoustic powers at cross sections normal to longitudinal direction of the duct were calculated by integrating acoustic intensity considering the effect of time averaged flow. The acoustic powers upstream and downstream of the resonator are both almost uniform, respectively, except the region in which the acoustic intensity is highly disordered. The difference in the acoustic powers at two sections upstream and downstream of the resonator coincides with the acoustic energy consumption rate calculated by using the acoustic resistance and particle velocity through the orifice. This shows that the acoustic resistance value estimated from the transfer function of sound pressures measured at two microphone positions is plausible.

Three-dimensional heating and patterning dynamics of particles in microscale acoustic tweezers.

Acoustic tweezers facilitate a noninvasive, contactless, and label-free method for the precise manipulation of micro objects, including biological cells. Although cells are exposed to mechanical and thermal stress, acoustic tweezers are usually considered as biocompatible. Here, we present a holistic experimental approach to reveal the correlation between acoustic fields, acoustophoretic motion and heating effects of particles induced by an acoustic tweezer setup. The system is based on surface acoustic waves and was characterized by applying laser Doppler vibrometry, astigmatism particle tracking velocimetry and luminescence lifetime imaging. In situ measurements with high spatial and temporal resolution reveal a three-dimensional particle patterning coinciding with the experimentally assisted numerical result of the acoustic radiation force distribution. In addition, a considerable and rapid heating up to 55 °C depending on specific parameters was observed. Although these temperatures may be harmful to living cells, counter-measures can be found as the time scales of patterning and heating are shown to be different.

Multi-target 2D tracking method for singing humpback whales using vector sensors

Acoustic vector sensors allow estimating the direction of travel of an acoustic wave at a single point by measuring both acoustic pressure and particle motion on orthogonal axes. In a two-dimensional plane, the location of an acoustic source can thus be determined by triangulation using the estimated azimuths from at least two vector sensors. However, when tracking multiple acoustic sources simultaneously, it becomes challenging to identify and link sequences of azimuthal measurements between sensors to their respective sources. This work illustrates how two-dimensional vector sensors, deployed off the coast of western Maui, can be used to generate azimuthal tracks from individual humpback whales singing simultaneously. Incorporating acoustic transport velocity estimates into the processing generates high-quality azimuthal tracks that can be linked between sensors by cross-correlating features of their respective azigrams, a particular time-frequency representation of sound directionality. Once the correct azimuthal track associations have been made between instruments, subsequent localization and tracking in latitude and longitude of simultaneous whales can be achieved using a minimum of two vector sensors. Two-dimensional tracks and positional uncertainties of six singing whales are presented, along with swimming speed estimates derived from a high-quality track.

Outer Acoustic Streaming Flow Driven by Asymmetric Acoustic Resonances.

While boundary-driven acoustic streaming resulting from the interaction of sound, fluids and walls in symmetric acoustic resonances have been intensively studied in the literature, the acoustic streaming fields driven by asymmetric acoustic resonances remain largely unexplored. Here, we present a theoretical and numerical analysis of outer acoustic streaming flows generated over a fluid–solid interface above which a symmetric or asymmetric acoustic standing wave is established. The asymmetric standing wave is defined by a shift of acoustic pressure in its magnitude, i.e., , and the resulting outer acoustic streaming is analyzed using the limiting velocity method. We show that, in symmetric acoustic resonances (), on a slip-velocity boundary, the limiting velocities always drive fluids from the acoustic pressure node towards adjacent antinodes. In confined geometry where a slip-velocity condition is applied to two parallel walls, the characteristics of the obtained outer acoustic streaming replicates that of Rayleigh streaming. In an asymmetric standing wave where , however, it is found that the resulting limiting velocity node (i.e., the dividing point of limiting velocities) on the slip-velocity boundary locates at a different position to acoustic pressure node and, more importantly, is shown to be independent of , enabling spatial separation of acoustic radiation force and acoustic streaming flows. The results show the richness of boundary-driven acoustic streaming pattern variations that arise in standing wave fields and have potentials in many microfluidics applications such as acoustic streaming flow control and particle manipulation.

Effect of acoustic perturbation on particle dispersion in a swirl-stabilized pulverized fuel burner: Cold-flow conditions

Inter-particle distance and particle dispersion during gasification of biomass have been found to significantly affect soot emission. Consequently, enhanced particle dispersion decreases energy losses and the risk for blockages of downstream equipment, increasing the efficiency and reliability of entrained flow reactors (EFRs). In this work, we investigated the interactions between imposed acoustic oscillations and particle dispersion under non-reacting conditions in a co-axial burner for a lab-scale EFR. A flow of air, laden with pulverized stem wood particles (Norwegian Spruce) of three different sizes (63–112 μm, 200–250 μm, and 500–600 μm), was forced axially through the burner center tube at Reynolds numbers ranged from 800 to 1700, and loading ratio of 0.7–4.2. The influences on particle dispersion from variations of the Strouhal number (0.12–0.6), the pressure amplitude at synthetic jet cavity (0.5–4.0 kPap-p), the swirl number (0–2.3), and the center jet velocity (1.9–3.9 m s−1) were investigated. Post-processed shadowgraph images revealed the influence of acoustic perturbations, which generate large structures with high particle concentration for both swirling and non-swirling conditions. Time-averaged contour maps showed a significantly higher particle dispersion, quantified as dispersion angle, for higher values of forcing amplitude and swirl numbers, with a stronger influence from the forcing amplitude, especially at lower Stokes number.

Two-Step Acoustophoresis Separation of Live Tumor Cells from Whole Blood.

There is an unmet clinical need to extract living circulating tumor cells (CTCs) for functional studies and in vitro expansion to enable drug testing and predict responses to therapy in metastatic cancer. Here, we present a novel two-step acoustophoresis (A2) method for isolation of unfixed, viable cancer cells from red blood cell (RBC) lysed whole blood. The A2 method uses an initial acoustofluidic preseparation step to separate cells based on their acoustic mobility. This acoustofluidic step enriches viable cancer cells in a central outlet, but a significant number of white blood cells (WBCs) remain in the central outlet fraction due to overlapping acoustophysical properties of these viable cells. A subsequent purging step was employed to remove contaminating WBCs through negative selection acoustophoresis with anti-CD45-functionalized negative acoustic contrast particles. We processed 1 mL samples of 1:1 diluted RBC lysed whole blood mixed with 10 000 DU145 cells through the A2 method. Additional experiments were performed using 1000 DU145 cells spiked into 1.5 × 106 WBCs in 1 mL of buffer to further elucidate the dynamic range of the method. Using samples with 10 000 DU145 cells, we obtained 459 ± 188-fold depletion of WBC and 42% recovery of viable cancer cells. Based on spiked samples with 1000 DU145 cells, our cancer cell recovery was 28% with 247 ± 156-fold WBC depletion corresponding to a depletion efficacy of ≥99.5%. The novel A2 method provides extensive elimination of WBCs combined with the gentle recovery of viable cancer cells suitable for downstream functional analyses and in vitro culture.

3-D Acoustic Tweezers Using a 2-D Matrix Array With Time-Multiplexed Traps.

The use of acoustic tweezers for precise manipulation of microparticles in the aqueous environment is essential and challenging for biomechanical applications in vivo. A 3-D acoustic tweezer is developed in this study for 3-D manipulation by using a two-dimensional (2-D) phased array consisting of 256 elements operating at 1.04 MHz. The emission phases of each element are iteratively determined by a backpropagation algorithm to generate multiple acoustic traps. Different traps are multiplexed in time, thus forming synthesized acoustic fields. We demonstrate the 3-D levitation and translation of positive acoustic contrast particles, a major class of bioparticles, in water by different acoustic traps, and compare the positional deviation along the intended path via experimentally measured trajectories. Improved manipulating stability was achieved by multiplexed acoustic traps. The 3-D acoustic tweezers proposed in this study provide a versatile approach of contactless bioparticle trapping and translation, paving the way toward future application of nanodroplet and microbubble manipulations.

Acoustic particle migration and focusing in a tilted acoustic field

Surface acoustic wave-based particle/bioparticle manipulation has emerged as a promising tool for disease diagnosis. The effects of the titled angle of the acoustic field θ and the microchannel aspect ratios β on the particle migration mode, the force of particle, and the three-dimensional focusing behavior are studied by using simulation and high-speed microscopic visualizations experiments. The acoustic field tilt range is from 0° to 15°, and the wavelength is 160 μm. Particle migration trajectory is observed from high-speed photographic images. Compared with most parallel acoustic fields, the particle migration efficiency of the tilted acoustic field is higher because the acoustic radiation force (Fr) continues to act on the particles in the lateral direction. The tilted angle of the acoustic field is not a fixed value (usually 15°), and there is an optimal angle to match the maximum lateral migration of the target particles. A model is put forward to predict the optimal acoustic field tilt-angle for acoustofluidic devices, which can achieve 96% separation of 15 μm target particles. The change in the direction of the Fr drives the particles to create two typical migration states during the lateral migration process, named continuous migration and intermittent migration. The phenomenon of multi-layer particle focus in the vertical Z-direction of the microchannel is experimentally observed for the first time, which mainly depends on whether the microchannel has enough height to make multiple acoustic pressure nodes in the vertical direction. Two or even three layers of particle focus lines can be observed in the vertical direction at the microchannel aspect ratios β > 0.5. The research results provide new insight into the high-throughput development of microfluidic devices.

A Vector Wavenumber Integration Model of Underwater Acoustic Propagation Based on the Matched Interface and Boundary Method

Acoustic particle velocities can provide additional energy flow information of the sound field; thus, the vector acoustic model is attracting increasing attention. In the current study, a vector wavenumber integration (VWI) model was established to provide benchmark solutions of ocean acoustic propagation. The depth-separated wave equation was solved using finite difference (FD) methods with second- and fourth-order accuracy, and the sound source singularity in this equation was treated using the matched interface and boundary method. Moreover, the particle velocity was calculated using the wavenumber integration method, consistent with the calculation of the sound pressure. Furthermore, the VWI model was verified using acoustic test cases of the free acoustic field, the ideal fluid waveguide, the Bucker waveguide, and the Munk waveguide by comparing the solutions of the VWI model, the analytical formula, and the image method. In the free acoustic field case, the errors of the second- and fourth-order FD schemes for solving the depth-separated equation were calculated, and the actual orders of accuracy of the FD schemes were tested. Moreover, the time-averaged sound intensity (TASI) was calculated using the pressure and particle velocity, and the TASI streamlines were traced to visualize the time-independent energy flow in the acoustic field and better understand the distribution of the acoustic transmission loss.

Acoustic radiation force on a rigid cylinder near rigid corner boundaries exerted by a Gaussian beam field

Acoustic manipulation is one of the well-known technologies of particle control and a top research in acoustic field. Calculation of acoustic radiation force on a particle nearby boundaries is one of the critical tasks, as it approximates realistic applications. Nevertheless, it is quite difficult to solve the problem by theoretical method when the boundary conditions are intricate. In this study, we present a finite element method numerical model for the acoustic radiation force exerting on a rigid cylindrical particle immersed in fluid near a rigid corner. The effects of the boundaries on acoustic radiation force of a rigid cylinder are analyzed with particular emphasis on the non-dimensional frequency and the distance from the center of cylinder to each boundary. The results reveal that these parameters play important roles in acoustic manipulation for particle-nearby complicated rigid boundaries. This study verifies the feasibility of numerical analysis on the issue of acoustic radiation force calculation close to complex boundaries, which may provide a new idea on analyzing the acoustic particle manipulation in confined space.

Estimation of seabed attenuation in the New England Mud Patch

Measurements of acoustic pressure and particle velocity were made during the Seabed Characterization Experiment (SBCEX-2017) in the New England Mud Patch south of Cape Cod in about 70 m of water. This experimental location is characterized by a “soft” layer of surficial sediment consisting of mud. University of Rhode Island and Woods Hole Oceanographic Institution deployed the “geosled” with a four-element geophone array, a tetrahedral array of four hydrophones, and several hydrophone receive units (SHRUs) as data acquisition packages. In addition, a new low frequency source, interface Wave Sediment Profiler (iWaSP) was deployed to excite interface waves (Scholte waves). The geophone array was localized using the known locations of the acoustic sources and noise from the research vessel. Modal arrivals from broadband sources on geophones and hydrophones were used to invert for compressional and shear wave speeds and attenuation in the mud layer and the underlying sand layer. Effect of shear conversion effects on the modal attenuation estimates and it’s frequency dependence will be explored. The role of shear conversion along the mud-sand interface will be discussed. [Work supported by the Office of Naval research, code 322 OA.]

On underwater acoustic particle velocity channels: Some experimental results

Studies have shown that acoustic particle velocity channels, in addition to the acoustic pressure channel, can be beneficial for underwater acoustic communication [A. Abdi and H. Guo, “A new compact multichannel receiver for underwater wireless communication networks,” IEEE Trans. Wireless Commun. 8, 3326–3329 (2009); A. Abdi, et al., “An overview of underwater acoustic communication via particle velocity channels: Channel modeling and transceiver design,” Proc. Meetings Acoust. 9, 070002 (2010)]. In this paper, we use experimentally measured acoustic particle velocity and acoustic pressure channels, using transmitted linearly frequency modulated (LFM) signals, to investigate and compare various signal and noise characteristics of these channels. Examples include signal and noise powers and ratios, delay spreads of the channels, temporal and spatial auto and cross covariance functions for the particle velocity and acoustic pressure noise components, and frequency responses of the acoustic particle velocity and acoustic pressure channels. Understanding these signal and noise characteristics allows a system designer to design and implement reliable and efficient underwater acoustic communication systems that employ multiple acoustic particle velocity channels, together with the acoustic pressure channel. [The work is supported in part by the National Science Foundation (NSF), Grant IIP-1500123.]

Signal detection in time spreading underwater environments using vector and scalar sensors

In this paper, we aim to examine the effects of the time-spreading signal distortion caused by multipath propagation in underwater environments, using experimental data. We use the Replica Correlation Integration detector [B. Friedlander and A. Zeira, “Detection of broadband signals in frequency and time dispersive channels,” IEEE Trans. Signal Process. 44(7), 1613–1622 (1996)], which is designed to take the multiple echoes of the transmitted signal into consideration. We apply this detector to measured data collected by underwater acoustic sensors. We use two types of sensors. The first sensor is a hydrophone that measures only the scalar component of the acoustic field, i.e., the acoustic pressure. The second sensor is a vector sensor that simultaneously measures the scalar and the three vector components of the acoustic field, i.e., the three acoustic particle velocity x, y, and z components. This sensor can perform as a multi-channel detector. Analysis of the measured data provides insights into the signal detection capabilities of the vector field components in time-spreading underwater environments. [The work is supported in part by NSF, Grant IIP-1500123, and ONR.]

Periodic acoustic pulse generation by mode locked thermoacoustic oscillator.

This study documents periodic acoustic pulse generation by heat in a thermoacoustic oscillator system constructed from a gas-filled acoustic resonance tube having a porous medium called a stack. When the system's dissonancy was enhanced by a local cross-sectional area change in the resonance tube, the periodic pulsed state was turned to a quasiperiodic state. This observation suggests that the acoustic pulse was created through the mode-locking of internal oscillation modes. Propagation of pulsed acoustic intensity in the resonance tube was evidenced by simultaneous measurements of acoustic pressure and axial acoustic particle velocity of the gas.

Calibration methods and facilities for vector receivers using a laser Doppler vibrometer in the frequency range 20 Hz to 10 kHz.

Calibration methods and facilities have been employed to directly obtain sensitivities of an underwater acoustic vector receiver using two methods based on laser Doppler vibrometry. The vector receiver was first calibrated in a standing wave tube over the frequency range 20 Hz to 2 kHz, where the oscillatory velocity of the water-air interface was measured to determine the sound particle velocity at the position of vector receiver based on waveguide theory. In the frequency range 2.5-10 kHz, the vector receiver was calibrated in an anechoic vessel with dimensions of 1.2 m diameter × 1.8 m length using wideband signals, with a laser Doppler vibrometer used to detect the oscillatory motion of a plastic pellicle, which was sufficiently thin to follow the acoustic particle motion. The uncertainties of the calibration using the optical method were estimated to be 0.7-0.8 dB at 95% confidence interval. The calibration results were compared with those obtained using a reciprocity method in a 50 m × 15 m × 10 m water tank and using a comparison method in a standing wave tube, and the largest deviation did not exceed 1.0 dB over the frequency range 20 Hz to 10 kHz.