Ultrasonic Standing Wave Field Research Articles

The visualization of an ultrasonic standing wave field using scanning-focused laser differential interferometry

In this study, a 20 kHz ultrasonic standing wave field in a water tank is studied using scanning-focused laser differential interferometry (SFLDI). The emitting and receiving ends of the focused laser differential interferometry system are mounted on two high-precision three-dimensional coordinate frames that can move synchronously. A high-speed schlieren measurement and numerical simulations are conducted to validate the SFLDI results. The SFLDI system exhibits good synchronicity between the emitting and receiving ends as it scans the water tank with the acoustic field off, as well as a good frequency response to 20 kHz waves with the acoustic field on. Consistent with both the schlieren measurement and simulations, the SFLDI results clearly show a typical multi-column standing wave pattern with a mean square error of about 6.8% compared to the simulations. This study provides a new approach for quantitatively visualizing acoustic fields with high frequencies.

Numerical study of micro–sized bubble deformation and shape oscillation in ultrasonic standing wave fields

To promote the development of science and technology such as underwater explosions, water cleaning, and medical treatment, it is necessary to understand the mechanism of the influence of ultrasonic fields on bubble dynamics. The authors investigated in depth the effects of the dimensionless sound pressure amplitude pa*, the dimensionless wave number k* and the liquid–gas viscosity ratio μl/μg on the micro–sized bubble deformation and shape oscillation using the volume of fluid (VOF) method. It was found that the bubble deformation and oscillation types can be classified into four categories: volume oscillation, shape oscillation, splitting oscillation and other types of oscillation. Both the dimensionless sound pressure amplitude pa* and the dimensionless wave number k* determine the bubble oscillation types. The regime map of predicting the micro–sized bubble deformation and shape oscillation was drawn based on pa* and k*. If the shape oscillation occurs in a micro–sized bubble, the dimensionless time τ*, when the micro–sized bubble experiences the shape oscillation, decreases with an increase in pa*, but increases with an increase in k* and μl/μg. The mode number n of shape oscillation increases with an increase in k* but decreases with an increase in μl/μg, and it is irrelevant to pa*. If the splitting oscillation happens to a micro–sized bubble, τ*, when a micro–sized bubble experiences splitting, decreases with an increase in pa* and increases with an increase in k*, while the liquid–gas viscosity ratio μl/μg has a negligible effect on this phenomenon.

Study on demulsification characteristics of crude oil based on orthogonal dual frequency ultrasonic standing wave field

In this paper, we conducted an experimental study on the demulsification and dewatering characteristics of water-in-oil emulsions under orthogonal dual-frequency ultrasonic standing wave fields. Firstly, the absolute and relative dehydration rates are defined as the evaluation criteria to measure the effect of demulsification and dehydration; then, the influence laws of absolute and relative dehydration rates of water-in-oil emulsions under the action of single frequency standing wave field and orthogonal dual-frequency standing wave field by ultrasonic frequency, power, irradiation time, initial water content and concentration of emulsifier are analyzed in detail, and through data comparison and analysis, it was found that By comparing and analyzing the data, it was found that the relative water content remained between 1.0 and 2.0 in most cases under the action of orthogonal dual-frequency standing wave field, and the ratio of 1.2–1.8 is large, which highlighted the advantages of orthogonal dual frequency ultrasonic standing wave field.

Acoustic Enrichment of Heterogeneous Circulating Tumor Cells and Clusters from Metastatic Prostate Cancer Patients.

There are important unmet clinical needs to develop cell enrichment technologies to enable unbiased label-free isolation of both single cell and clusters of circulating tumor cells (CTCs) manifesting heterogeneous lineage specificity. Here, we report a pilot study based on the microfluidic acoustophoresis enrichment of CTCs using the CellSearch CTC assay as a reference modality. Acoustophoresis uses an ultrasonic standing wave field to separate cells based on biomechanical properties (size, density, and compressibility), resulting in inherently label-free and epitope-independent cell enrichment. Following red blood cell lysis and paraformaldehyde fixation, 6 mL of whole blood from 12 patients with metastatic prostate cancer and 20 healthy controls were processed with acoustophoresis and subsequent image cytometry. Acoustophoresis enabled enrichment and characterization of phenotypic CTCs (EpCAM+, Cytokeratin+, DAPI+, CD45-/CD66b-) in all patients with metastatic prostate cancer and detected CTC-clusters composed of only CTCs or heterogeneous aggregates of CTCs clustered with various types of white blood cells in 9 out of 12 patients. By contrast, CellSearch did not detect any CTC clusters, but detected comparable numbers of phenotypic CTCs as acoustophoresis, with trends of finding a higher number of CTCs using acoustophoresis. Our preliminary data indicate that acoustophoresis provides excellent possibilities to detect and characterize CTC clusters as a putative marker of metastatic disease and outcomes. Moreover, acoustophoresis enables the sensitive label-free enrichment of cells with epithelial phenotypes in blood and offers opportunities to detect and characterize CTCs undergoing epithelial-to-mesenchymal transitioning and lineage plasticity.

Dynamics of droplets entering ultrasonic standing wave field at different angles

We, herein, present dynamic behaviors of droplets entering an ultrasonic standing wave field (19 800 Hz) at different angles. In experiments, droplets’ motion is recorded by using a high-speed camera, and an in-house Python program is used to obtain droplet positions and morphological characteristics as functions of time. The experimental results indicate that when the sound intensity is lower than the instability intensity and higher than the levitation intensity, the vertically falling droplet will oscillate up and down based on the equilibrium position. Although the oscillation amplitude decays from 0.52Tl to 0.01Tl (Tl = λ/2, λ is the wavelength) under the action of viscous resistance, the oscillation frequency of the droplet remains unchanged. Meanwhile, as the droplet’s position oscillates, the acoustic radiation force on the droplet also periodically fluctuates, resulting in the acoustically forced oscillation of the droplet shape. In addition, when the droplet enters the sound field with a horizontal tilt angle θ of 15°, it undergoes a V-shaped translational motion, first descending and then ascending. As the sound pressure amplitude increases, the rebound position of the droplet advances. When the sound pressure amplitude reaches the instability value (7900 Pa), the droplet undergoes right-hand and left-hand disintegration during its descent and ascent, respectively. This instability is due to the acoustic radiation pressure distribution and the droplet’s V-shaped trajectory. This work comprehensively discussed the complex motion of moving droplets in the acoustic standing wave field, which may inspire revealing the spray motion in the liquid engine with high-intensity resonance.

Research on excitation technology of high-throughput ultrasonic micro-separator based on micro-nano fabrication

The excitation technology of ultrasonic standing wave field is the core key to realize ultrasonic separation. This paper analyzes the excitation technology of (1, 1) mode ultrasonic separation of high-throughput ultrasonic micro-separator. There are two main problems: the coexistence of multiple modes in the separation cavity and the insufficient acoustic radiation force. In order to solve these two problems, this paper uses integrated circuit micromachining technology to process the ultrasonic micro-separator. The depth dimension of the cavity reaches 200 ± 0.5 µm, and the verticality of the side wall of the cavity reaches 83.36°. The degree of SFPD (Site Focal Plane Deviation) is less than or equal to 0.25 µm. Besides, this paper proposes an excitation method of saw-tooth frequency sweep of two anti-phase acoustic drivers. Finally, the experiments of the separator processed by the processing method proposed in this paper shows that, the excitation method proposed in this paper can effectively excite the (1, 1) mode, and shortens the time for the pattern formation of particle convergence, which greatly improves the separation efficiency. The separation throughput (flow rate) in one single cavity in this work can reach to 100 µl/min. It provides an effective basis for ultrasonic micro-separation technology.

Mathematical modeling and experimental study on solid–liquid suspension separation in ultrasonic standing wave field

A new method of removing waste chips is proposed by focusing on the key factors affecting the processing quality and efficiency of high energy beams. Firstly, a mathematical model has been established to provide the theoretical basis for the separation of solid–liquid suspension under ultrasonic standing wave. Secondly, the distribution of sound field with and without droplet has been simulated. Thirdly, the deformation and movement of droplets are simulated and tested. It is found that the sound pressure around the droplet is greater than the sound pressure in the droplet, which can promote the separation of droplets and provide theoretical support for the ultrasonic suspension separation of droplet; under the interaction of acoustic radiation force, surface tension, adhesion, and static pressure, the droplet is deformed so that the gas fluid around the droplet is concentrated in the center to achieve droplet separation, and the droplet just as a flat ball with a central sag is stably suspended in the acoustic wave node.

Gravity-Aided Ultrasonic Separation of Nanoparticles from Liquid Using Macro-Scale Separator

Acoustophoresis is the technology to separate the microparticles and cells from suspending fluid. This research focuses on the separation of nanoparticles from water by using macro-scale fluidic separator which works based on gravity-aided ultrasonic standing wave technology. Titanium dioxide particles of 40 nm diameter were concentrated by the combination of ultrasonic standing wave field at 2.2 MHz and gravity-aided sedimentation. The purpose of this study is to investigate the performance of gravity-aided ultrasonic particle to concentrate nanoparticles. It was found that the separation efficiency is 83% at a flow rate of 0.1 mL/min. FEM simulations were also conducted to evaluate characteristics of variation of acoustic energy inside the fluidic channel. Results indicate that nanoparticles can be concentrated using gravity-aided ultrasonic standing wave field, however optimization of the design of the fluidic channel is required for increasing throughput of the separator.

A novel strategy to identify gases by a single catalytic combustible sensor working in its linear range

Gas identification by a single sensing element is a challenging and promising technology. In this work, a novel strategy to identify gases by a single catalytic combustible sensor working in its linear range is proposed and investigated. In the strategy, a half-wavelength standing wave ultrasonic field is used to catalyze the combustion reaction on the sensing surface, and quantified ultrasonic enhancement effect on the sensing response, which is independent of the gas concentration and varies with the species of analyte gases, is employed to identify the gases. The experimental results show that the success rate of gas identification can reach 100 % when the ultrasonic vibration is strong enough, and the gas identification method has anti-interference capability when there is impurity gas in the target gas. The cause of the anti-interference capability is analyzed. The strategy proposed in this work provides a new design way which can make the structure, data processing and calibration of gas identification systems simpler.

Microstructural Evolution and Wear Behavior of SiCp/7085 Composites Manufactured by Ultrasonic Stirring Casting

In this work, SiCp/7085 composites with a volume fraction of 10% were fabricated by ultrasonic stirring casting. The evolution of the microstructure and wear properties of SiCp/7085 composites, as well as the mechanism of ultrasonic action in the process of preparation, when the ultrasonic treatments last for 0 min, 5 min, 10 min, and 15 min, respectively, were studied using the optical effects (OM), scanning electron microscope (SEM), and X-ray diffraction (XRD). The experimental results show that the high temperature and high pressure formed by the cavitation of ultrasound can effectively eliminate the cluster of particles, improve the distribution of SiC particles, increase the interfacial wettability of the composites, and form MgAl2O4 and MgO on the particle surface, thereby ultimately improving the wear resistance of the composites. Because the particles in the melt are affected by the segregation effect of ultrasonic standing wave field, there exists an optimal value for the ultrasonic treatment time. When the melt is treated with the ultrasonic wave with an amplitude of 12 μm and a treatment duration of 10 min in the test conditions given in this paper, the composites have the most uniform distribution of particles, the best wear resistance, a large and stable friction coefficient, and the minimum weight loss of sample wear: 12 mg. The change of wear resistance is consistent with the variation of solidification structure and interface properties.

Effect of Bulk Viscosity and Emulsion Droplet Size on the Separation Efficiency of Model Mineral Oil-in-Water (O/W) Emulsions under Ultrasonic Standing Wave Fields: A Theoretical and Experimental Investigation

Ultrasound standing waves can be used to separate emulsions. So far, they have been applied to oil-in-water emulsions with low continuous phase viscosity. This technique has the potential to be used for novel applications such as separating lipids from algal biomass; however, this requires the methodology to be optimized to process viscous emulsions. We have addressed this issue by studying the effects of bulk phase viscosity (1–23 mPa·s), emulsion droplet size (4.5–20 μm), power (10–54 W/L), and frequency (1 and 2 MHz) of ultrasound on the separation efficiency of model mineral oil-in-water–glycerol-mixture emulsions. For the small droplet size (4.5 μm) emulsion in water, the maximum separation achieved increased from 36 to 79% when ultrasound power increased from 10 to 54 W/L. However, for the large droplet size (11 μm) emulsion, the maximum separation was greater than 95% and was independent of ultrasound power. The maximum separation efficiency for small droplet size (4.5–6 μm) emulsions decreased from 80 to 14% when the viscosity increased from 1 to 23 mPa·s. However, for the large droplet size (11–20 μm) emulsion, the maximum separation efficiency decreased from 98 to 62% when the viscosity of the bulk phase was increased from 1 to 23 mPa·s. The experimental results were then interpreted using analytical and numerical simulations by calculating the time required for the emulsion droplets to migrate to the nearest pressure antinodal plane under the influence of ultrasound standing waves. Further experiments showed that increasing the ultrasound frequency from 1 to 2 MHz increased the maximum separation from 36 to 86% for fine emulsions and water as the continuous phase.

A Quantitative Study of the Secondary Acoustic Radiation Force on Biological Cells during Acoustophoresis

We investigate cell-particle secondary acoustic radiation forces in a plain ultrasonic standing wave field inside a microfluidic channel. The effect of secondary acoustic radiation forces on biological cells is measured in a location between a pressure node and a pressure anti-node and the result is compared with theory by considering both compressibility and density dependent effects. The secondary acoustic force between motile red blood cells (RBCs) and MCF-7 cells and fixed 20 µm silica beads is investigated in a half-wavelength wide microchannel actuated at 2 MHz ultrasonic frequency. Our study shows that the secondary acoustic force between cells in acoustofluidic devices could play an important role for cell separation, sorting, and trapping purposes. Our results also demonstrate the possibility to isolate individual cells at trapping positions provided by silica beads immobilized and adhered to the microchannel bottom. We conclude that during certain experimental conditions, the secondary acoustic force acting on biological cells can dominate over the primary acoustic radiation force, which could open up for new microscale acoustofluidic methods.

Interfacial microstructure and mechanical properties of ultrasonic-assisted brazing joints between Ti–6Al–4V and ZrO2

Ultrasonic-assisted brazing (28.8 kHz, 180 W) was introduced to achieve high-quality joints between Ti–6Al–4V alloy and ZrO2 ceramic with Al-5wt.%Si brazing filler in air. The interfacial microstructure of intermetallic compounds (IMCs) and the phase constitution of joints ultrasonic-assisted brazed at 700 °C for different ultrasonic time were investigated in detail using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer and X-ray diffractometer. When the ultrasonic time was 20s, the average shear strength of the joint reached a maximum value of 90.68MPa and two important types of IMCs Ti(Al,Si)3 and Ti7Al5Si12 formed at the interface between the Ti–6Al–4V and the filler. Ultrasonic played a vital role in the formation of Si segregation regions at the interface near the Ti–6Al–4V and in the centre of the joint. A change in the Ti molar fraction, resulting from the cavitation effect of ultrasonic on the surface of Ti–6Al–4V, increased the chemical potential gradient of Si across the joint. Meanwhile, driven by the ultrasonic standing wave field in the liquid Al-5wt.%Si filler, Si atoms moved to the ultrasonic antinode-plane spontaneously. Ultrasonic-assisted brazing proved to be an effective method of joining Ti–6Al–4V and ZrO2 with Al-5wt.%Si filler.

Design, modeling, and experimental validation of an acoustofluidic platform for nanoscale molecular synthesis and detection.

Microfluidic technologies are increasingly implemented to replace manual methods in biological and biochemical sample processing. We explore the feasibility of an acoustofluidic trap for confinement of microparticle reaction substrates against continuously flowing reagents in chemical synthesis and detection applications. Computational models are used to predict the flow and ultrasonic standing wave fields within two longitudinal standing bulk acoustic wave (LSBAW) microchannels operated in the 0.5-2.0 MHz range. Glass (gLSBAW) and silicon (siLSBAW) pillar arrays comprise trapping structures that augment the local acoustic field, while openings between pillars evenly distribute the flow for uniform exposure of substrates to reagents. Frequency spectra (acoustic energy density E ac vs frequency) and model-predicted pressure fields are used to identify longitudinal resonances with pressure minima in bands oriented perpendicular to the inflow direction. Polymeric and glass particles (10- and 20-µm diameter polystyrene beads, 6 µm hollow glass spheres, and 5 µm porous silica microparticles) are confined within acoustic traps operated at longitudinal first and second half-wavelength resonant frequencies (f 1,E = 575 kHz, gLSBAW; f 1,E = 666 kHz; and f 2,E = 1.278 MHz, siLSBAW) as reagents are introduced at 5-10 µl min-1. Anisotropic silicon etched traps are found to improve augmentation of the acoustic pressure field without reducing the volumetric throughput. Finally, in-channel synthesis of a double-labeled antibody conjugate on ultrasound-confined porous silica microparticles demonstrates the feasibility of the LSBAW platform for synthesis and detection. The results provide a computational and experimental framework for continued advancement of the LSBAW platform for other synthetic processes and molecular detection applications.

Finite element simulation of ultrasonic standing wave fields inside cylindrical piezoelectric transducers

At the present work, we have studied high-intensity ultrasound fields of standing cylindrical waves, generated by cylindrical piezoelectric transducer with radial polarization in its internal volume filled by liquid. The paper is focused on the study of length-extensional and thickness vibrational modes of cylindrical piezoelectric transducer. We have performed the finite-element simulations of standing cylindrical waves formation inside the cylindrical transducer filled with a liquid by those oscillation modes of piezoelectric cylinder using ANSYS software package and compared effectiveness of different regimes of standing waves generation.

Acoustic waves improves retroviral transduction in human retinal stem cells

BackgroundsThe plasticity of retinal stem cells (RSCs), a type of cells that can differentiate into neuron cells and photoreceptor cells, endows them with potential therapeutic properties that can be applied to regenerative medicine. Gene modification of these stem cells before trans-differentiation and transplantation enhances their survival and increases their therapeutic function. The different ways to effectively deliver gene into RSCs are still discussed. This study aimed to use the acoustic waves to improve the efficacy of gene delivery for RSCs. MethodsRSCs were obtained from non-fetal human ocular pigmented ciliary margin tissues. The enhanced green fluorescent protein-encoded murine stem cell retroviruses (MSCV) were prepared and used to infect RSCs. Glass chambers containing RSCs, retroviruses, and various concentrations of polybrene (0, 0.8, 2, 4 and 8 μg/mL) were exposed under 20 or 25 Vp-p ultrasonic standing wave fields (USWF) for 5 min. The percentage of green fluorescent protein positive cells in each sample was calculated and compared to test the efficacy of gene transduction. ResultsOur results showed that the efficiency of gene transduction by MSCV infection was enhanced following the concentration of polybrene and the energy of USWF. The percentage of green fluorescent protein positive cells was significantly higher in chambers that contained 8 μg/mL of polybrene and was exposed to 20Vp-p of USWF for 5 min. In addition, the percentage increased in chambers contained 2, 4 and 8 μg/mL of polybrene when they were exposed to 25Vp-p of USWF. Comparing to those did not treated with ultrasound, the efficiency of retroviral transduction to RSCs increased 4-fold after exposed to USWF for 5 min. ConclusionWe demonstrated the ability of ultrasound standing waves to improve retroviral transduction into RSCs. We believe that this may be applied to the experimental designs of future studies and may have possible therapeutic uses.

Continuous micro-feeding of fine cohesive powders actuated by pulse inertia force and acoustic radiation force in ultrasonic standing wave field

Stable continuous micro-feeding of fine cohesive powders has recently gained importance in many fields. However, it remains a great challenge in practice because of the powder aggregate caused by interparticle cohesive forces in small capillaries. This paper describes a novel method of feeding fine cohesive powder actuated by a pulse inertia force and acoustic radiation force simultaneously in an ultrasonic standing wave field using a tapered glass nozzle. Nozzles with different outlet diameters are fabricated using glass via a heating process. A pulse inertia force is excited to drive powder movement to the outlet section of the nozzle in a consolidated columnar rod mode. An acoustic radiation force is generated to suspend the particles and make the rod break into large quantities of small agglomerates which impact each other randomly. So the aggregation phenomenon in the fluidization of cohesive powders can be eliminated. The suspended powder is discharged continuously from the nozzle orifice owing to the self-gravities and collisions between the inner particles. The micro-feeding rates can be controlled accurately and the minimum values for RespitoseSV003 and Granulac230 are 0.4 mg/s and 0.5 mg/s respectively. The relative standard deviations of all data points are below 0.12, which is considerably smaller than those of existing vibration feeders with small capillaries.

Study on separation characteristics of water in oil (W/O) emulsion under ultrasonic standing wave field

The separation characteristics of W/O emulsion were investigated under ultrasonic standing wave field in this paper. The effects of the irradiation time, acoustic intensity, frequency, oil viscosity, and oil-water interfacial tension on the separation characteristics of emulsion were studied in details. It was proved that there existed an optimal irradiation time, acoustic intensity and oil-water interfacial tension to achieve the maximum separation efficiency in ultrasonic treatment process. Excessive long irradiation time had little effect on improving the dehydration rate of emulsion but rather increased unnecessary processing time. Excessive high acoustic intensity caused the occurrence of acoustic cavitation phenomenon. The acoustic cavitation would cause the aggregated droplets to be dispersed by oscillating bubbles or even emulsified again by high speed micro jets. The acoustic cavitation threshold is effectively and accurately obtained by a spectral analysis method. The micro acoustic streaming which resulted from the attenuation of acoustic energy occurred with the increase of frequency. It sheared the aggregated droplets, destroyed the stable droplets banding and reduced the separation efficiency of emulsion. The excess surfactant adsorbed on the oil-water interface resulted in the increase of the interfacial film strength, which hindered the coalescence process of droplets and reduced the separation efficiency.

Quantitative calibration of sound pressure in ultrasonic standing waves using the Schlieren method.

We investigated the use of the Schlieren method to calibrate the sound pressure in an ultrasonic standing-wave field. Specifically, we derived an equation to calculate the light intensity of the diffraction fringe induced by the standing-wave field. The results indicated that the sound pressure in the standing-wave field relates to the light intensity of the diffraction fringe. Simulations and experiments were conducted to verify the theoretical calculation. We demonstrated that the ratio of the light intensity of different diffraction orders relates to the sound pressure amplitude, allowing the pressure amplitude to be calibrated with the Schlieren method. Therefore, this work presents a non-intrusive calibration method that is particularly suitable for calibrating high-frequency ultrasonic standing-wave fields.

Ultrasound assisted low-concentration VOC sensing

This paper reports a new method to ultrasonically enhance the metal oxide gas sensor’s sensitivity to low-concentration volatile organic compound (VOC) gases. The system uses an ultrasonic transducer to produce an ultrasonic standing wave field above the sensing layer. Ultrasonic field near the sensing layer drives the VOC molecules to the sensing layer, and promotes the oxidation-reduction reaction between the VOC molecules and reactive oxygen species on the surface of the sensing layer, which increases the resistance change of the sensing resistor. The experiments show that this method can greatly enhance the gas sensor’s sensitivity to low-concentration VOC gases. With the assistance of ultrasound, the sensitivity can be increased up to 30 times.