• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.46-50
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• 2020

On-demand droplet generation with tunable droplet volume is fundamental in many droplet microfluidic applications. In this work, we propose an acoustofluidic method to produce water-in-oil droplets with prescribed volume in an on-demand manner. Surface acoustic waves produced from a slanted interdigital transducer are coupled with parallel laminar streams of dispersed and continuous phase fluids. Acoustic radiation force acting on the fluid interface enable generation of droplets in a microfluidic chip. We expect that the proposed acoustofluidic droplet generation method will serve as a promising tool for on-demand droplet generation with on-chip droplet volume control.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.96-103
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• 2024

As micro-electronic devices are getting miniaturized, technology that can manage the temperature of confined area is required. On these demands, microchannel heat exchanger is suggested as promising solution. However, due to laminar flow created inside the microchannel with high Reynolds number suppresses diffusion based natural convection, leads to low heat transfer performance of microchannel. This paper shows how acoustic streaming flow enhances the heat transfer performance inside the microchannel without using additional structure or nanoparticle inside the straight microchannel and fluid numerically. Various parameters, such as Reynolds number (Re), initial displacement (ξ) was adopted to evaluate the influence of acoustic streaming flow. The results showed that acoustic streaming flow can disturb the thermal boundary, by creating the micro-vortex inside the straight-microchannel and enhance the heat transfer performance.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.35-43
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• 2024

Microparticle separation has demonstrated significant potential for biological, chemical, and medical applications. We introduce a surface acoustic wave (SAW)-based microfluidic device for separation of elastic and rigid microspheres based on their property and size. By tuning the SAWs to match the resonant frequencies of certain microspheres, those particles could be selectively separated from the other microspheres. When microspheres are exposed to an acoustic field, they experience the SAW-induced acoustic radiation force (ARF), whose magnitude is dependent on the microparticle size and properties. We modeled the SAW-induced ARF based on elastic sphere theory and conducted a series of experiments to separate elastic and rigid microspheres. We further utilized the acoustofluidic method for the separation of Thalassiosira Eccentrica microalgae based on the differences in their sizes with purity exceeding 90%. We anticipate that our technique will open up new possibilities for sample preparation, detection, and diagnosis in various emerging biological and medical analyses.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.19-26
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• 2022

In droplet microfluidics, precise droplet manipulation is required in numerous applications. This study presents ultrasonic surface acoustic wave (USAW)-based microfluidic device for label-free droplet separation based on size. The proposed device is composed of a slanted-finger interdigital transducer on a piezoelectric substrate and a polydimethylsiloxane microchannel placed on the substrate. The microchannel is aligned in the cross-type configuration where the USAWs propagate in a perpendicular direction to the flow in the microchannel. When droplets are exposed to an acoustic field, they experience the USAW-induced acoustic radiation force (ARF), whose magnitude varies depending on the droplet size. We modeled the USAW-induced ARF based on ray acoustics and conducted a series of experiments to separate different-sized droplets. We found that the experimental results were in good agreement with the theoretical estimation. We believe that the proposed method will serve as a promising tool for size-based droplet separation in a label-free manner.

• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.93-100
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• 2023

The yeast Saccharomyces cerevisiae (S. cerevisiae) is considered an ideal eukaryotic model and has long been recognized for its pivotal role in numerous industrial production processes. Depending on the cell cycle phases, microenvironment, and species, S. cerevisiae varies in shape and has different sizes of each shape such as singlets, doublets, and clusters. Obtaining high-purity populations of uniformly shaped S. cerevisiae cells is crucial in fundamental biological research and industrial operations. In this study, we propose an acoustofluidic method for separating S. cerevisiae cells based on their size using surface acoustic wave (SAW)-induced acoustic radiation force (ARF). The SAW-induced ARF increased with cell diameter, which enabled a successful size-based separation of S. cerevisiae cells using an acoustofluidics device. We anticipate that the proposed acoustofluidics approach for yeast cell separation will provide new opportunities in industrial applications.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.47-52
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• 2017

In droplet-based microfluidic systems, in-droplet preconcentration of a sample is one of the important prerequisites for biochemical or medical analysis. There have been a few studies on preconcentration in a moving droplet, but they are limited to practical applications since 1) their method are time-consuming or 2) they require specific properties such as electric and magnetic properties. In this study, we demonstrated the position control of polystyrene particles of 5 and $10{\mu}m$ in diameter inside a moving water-in-oil droplet using traveling surface acoustic waves. Since the frequencies for effective control of each diameter were found, microparticles with no labels could be utilized. In addition, the proposed method enabled on-demand preconcentration inside a polydimethylsiloxane microchannel. In-droplet preconcentration of microparticles was realized by splitting a mother droplet with manipulated particles at a downstream bifurcation zone. Given these advantages, the proposed system is a promising acoustofluidic lab-on-a-chip platform for preconcentration inside a droplet.