Keita Ando - Profile on Academia.edu (original) (raw)

Papers by Keita Ando

2013 IEEE 26th International Conference on Micro Electro Mechanical Systems (MEMS), 2013

This paper demonstrates the dynamic stressing of viscous liquids in microfluidic channels. An inf... more This paper demonstrates the dynamic stressing of viscous liquids in microfluidic channels. An infrared laser pulse is focused within the testing liquid in a microfluidic channel and a spherical shock wave near an air-liquid interface is created. The shock is reflected as a tension wave by the free surface due to the acoustic impedance mismatch. The displacement of the free surface within hundred nanoseconds is captured by a developed double-exposure optical system. The tensile strength can be estimated by extrapolating a series of shock pressure approximation at several different distances between the bubble and the free surface to the measurement accuracy. This study has a great potential in the optical breakdown of biomaterials.

Abstract: The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion re... more Abstract: The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion relation is modified by including the effect of liquid compressibility on the natural frequency of the bubbles. The modified theory is shown to more accurately predict the trend in measured attenuation of ultrasonic waves. The model limitations associated with such high-frequency waves are discussed.

Experimental Study of Free-Surface Deformation and Cavitation Bubble Dynamics in a Megasonic Cleaning Bath

Volume 5: Multiphase Flow, 2019

Underwater ultrasound causes various physical phenomena in megasonic cleaning baths, e.g. cavitat... more Underwater ultrasound causes various physical phenomena in megasonic cleaning baths, e.g. cavitation inception, bubble translation and free-surface deformation (FSD) due to acoustic radiation pressure. Because FSD is especially noticeable in the case of high frequency ultrasound due to its high directivity, it is essential to investigate the interaction between FSD and bubble translation in megasonic cleaning bath. In our present experiments, we construct a typical setup for megasonic cleaning and irradiate water with 1 MHz ultrasound vertically upwards. We visualize FSD and bubbles and analyze the height of FSD and the translational velocity in frequency space. The bubbles translate in both short and long time scales caused by bubble-bubble interaction and periodic FSD, respectively, and the latter has periodicity. The most dominant frequency component in FSD shows good agreement with that in the translational velocity of the bubbles and does not depend on whether cavitation occurs...

Quantitative Analysis of Acoustic Pressure for Sonophoresis and Its Effect on Transdermal Penetration

Ultrasound in Medicine & Biology, 2022

Bubble cloud nucleation induced by the interaction between multiple laser-induced shocks and bubbles

Bulletin of the American Physical Society, 2013

Chemically controlled megasonic cleaning of patterned structures using solutions with dissolved gas and surfactant

Ultrasonics Sonochemistry, 2021

Graphical abstract

International Journal of Multiphase Flow, 2011

The effect of distributed bubble nuclei sizes on shock propagation in a bubbly liquid is numerica... more The effect of distributed bubble nuclei sizes on shock propagation in a bubbly liquid is numerically investigated. An ensemble-averaged technique is employed to derive the statistically averaged conservation laws for polydisperse bubbly flows. A finite-volume method is developed to solve the continuum bubbly flow equations coupled to a single-bubble-dynamic equation that incorporates the effects of heat transfer, liquid viscosity and compressibility. The one-dimensional shock computations reveal that the distribution of equilibrium bubble sizes leads to an apparent damping of the averaged shock dynamics due to phase cancellations in oscillations of the different-sized bubbles. If the distribution is sufficiently broad, the phase cancellation effect can dominate over the single-bubble-dynamic dissipation and the averaged shock profile is smoothed out.

Bubble Dynamics and Shock Waves, 2013

We investigate the shock dynamics of liquid flows containing small gas bubbles with numerical sim... more We investigate the shock dynamics of liquid flows containing small gas bubbles with numerical simulations based on a continuum bubbly flow model. Particular attention is devoted to the effects of distributed bubble sizes and gas-phase nonlinearity on shock dynamics. Ensemble-averaged conservation laws for polydisperse bubbly flows are closed with a Rayleigh-Plesset-type model for single bubble dynamics. Numerical simulations of one-dimensional shock propagation reveal that phase cancellations in the oscillations of different-sized bubbles can lead to an apparent damping of the averaged shock dynamics. Experimentally, we study the propagation of waves in a deformable tube filled with a bubbly liquid. The model is extended to quasi-one-dimensional cases. This leads to steady shock relations that account for the compressibilities associated with tube deformation, bubbles and host liquid. A comparison between the theory and the water-hammer experiments suggests that the gas-phase nonlinearity plays an essential role in the propagation of shocks.

Physics of Fluids, 2008

The problem of predicting the moments of the distribution of bubble radius in bubbly flows is con... more The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid ͑impulsive or step change͒ change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one. For sufficiently broad distributions of bubble equilibrium ͑or initial͒ radius, it is demonstrated that bubble statistics reach equilibrium on a time scale that is fast compared to physical damping of bubble oscillations due to viscosity, heat transfer, and liquid compressibility. The period-averaged bubble radius may then be used to predict the slow changes in the moments caused by the damping. A benefit is that period averaging gives a much smoother integrand, and accurate statistics can be obtained by tracking as few as five bubbles from the broad distribution. The period-averaged formula may therefore prove useful in reducing computational effort in models of dilute bubbly flow wherein bubbles are forced by shock waves or other rapid pressure changes, for which, at present, the strong effects caused by a distribution in bubble size can only be accurately predicted by tracking thousands of bubbles. Some challenges associated with extending the results to more general ͑nonimpulsive͒ forcing and strong two-way coupled bubbly flows are briefly discussed.

Lab on a Chip, 2011

A method for on-demand droplet fusion in a microfluidic channel is presented using the flow creat... more A method for on-demand droplet fusion in a microfluidic channel is presented using the flow created from a single explosively expanding cavitation bubble. We test the technique for water-in-oil droplets, which are produced using a T-junction design in a microfluidic chip. The cavitation bubble is created with a pulsed laser beam focused into one droplet. High-speed photography of the dynamics reveals that the droplet fusion can be induced within a few tens of microseconds and is caused by the rapid thinning of the continuous phase film separating the droplets. The cavitation bubble collapses and recondenses into the droplet. Droplet fusion is demonstrated for static and moving droplets, and for droplets of equal and unequal sizes. Furthermore, we reveal the diffusion dominated mixing flow and the transport of a single encapsulated cell into a fused droplet. This laser-based droplet fusion technique may find applications in micro-droplet based chemical synthesis and bioassays.

Journal of Fluid Mechanics, 2011

Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one... more Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one-dimensional mixture-averaged flow equations that include fluid–structure interaction are formulated. The steady shock relations are derived and the nonlinear effect due to the gas-phase compressibility is examined. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material and pressure on the tube wall are measured. The experimental data indicate that the linear theory is incapable of properly predicting the propagation speeds of finite-amplitude waves in a mixture-filled tube; the shock theory is found to more accurately estimate the measured wave speeds.

The Journal of the Acoustical Society of America, 2009

The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion relation is ... more The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion relation is modified by including the effect of liquid compressibility on the natural frequency of the bubbles. The modified theory is shown to more accurately predict the trend in measured attenuation of ultrasonic waves. The model limitations associated with such high-frequency waves are discussed.

Video: Drop fragmentation on impact

70th Annual Meeting of the APS Division of Fluid Dynamics - Gallery of Fluid Motion

The Journal of the Acoustical Society of America

Large-scale cell suspension culture technology opens up opportunities for numerous medical and bi... more Large-scale cell suspension culture technology opens up opportunities for numerous medical and bioengineering applications. For these purposes, scale-up of the culture system is paramount. For initial small-scale culture, a simple static suspension culture (SSC) is generally employed. However, cell sedimentation due to the lack of agitation limits the culture volume feasible for SSC. Thus, when scaling up, cell suspensions must be manually transferred from the culture flask to another vessel suitable for agitation, which increases the risk of contamination and human error. Ideally, the number of culture transfer steps should be kept to a minimum. The present study describes the fabrication of an ultrasonic suspension culture system that stirs cell suspensions with the use of acoustic streaming generated by ultrasound irradiation at a MHz frequency. This system was applied to 100-mL suspension cultures of Chinese hamster ovary cells-a volume tenfold larger than that generally used. The cell proliferation rate in this system was 1.88/day when applying an input voltage of 40 V to the ultrasonic transducer, while that of the SSC was 1.14/day. Hence, the proposed method can extend the volume limit of static cell suspension cultures, thereby reducing the number of cell culture transfer steps.

When a droplet impacts a solid surface at high speed, the contact periphery expands very quickly ... more When a droplet impacts a solid surface at high speed, the contact periphery expands very quickly and liquid compressibility plays an important role in the initial dynamics and the formation of lateral jets. The high speed impact results in high pressures that can account for the surface erosion. In this study, we numerically investigated a high speed droplet impacts on a solid wall. The multicomponent Euler equations with the stiffened equation of state are computed using a FV-WENO scheme with an HLLC Riemann solver (Johnsen & Colonius 2006) that accurately captures shocks and interfaces. In order to compare the available theories and experiments, 1D, 2D and axisymmetric solutions are obtained. The generated pressures, shock speeds, and the lateral jetting generation are investigated. In addition, the effect of target compliance is evaluated.

Effects of bubble size distributions on acoustics of dilute bubbly liquids

ABSTRACT

Solid State Phenomena

Visualization experiments are performed to examine the role of acoustic cavitation bubbles that a... more Visualization experiments are performed to examine the role of acoustic cavitation bubbles that appear in 0.43-MHz ultrasonic water flow spreading over glass surfaces in the context of physical cleaning. The cleaning performance is evaluated using glass samples on which small silica particles are spin-coated. The visualization suggests that acoustic cavitation bubbles play a major role in particle removal as in the case of conventional cleaning with ultrasonic cleaning baths.

Shock propagation through a bubbly liquid filled in a deformable cylindrical tube is considered. ... more Shock propagation through a bubbly liquid filled in a deformable cylindrical tube is considered. Quasi-one-dimensional bubbly flow equations that include fluid-structure interaction are formulated, and the steady shock relations are derived. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material are measured. The experimental data indicate that the linear theory cannot properly predict the propagation speeds of shock waves in mixture-filled tubes; the shock theory is found to more accurately estimate the measured wave speeds.

Shock Propagation in Polydisperse Bubbly Flows

The effect of distributed bubble size on shock propagation in homogeneous bubbly liquids is compu... more The effect of distributed bubble size on shock propagation in homogeneous bubbly liquids is computed using a continuum two-phase model. An ensemble-averaging technique is employed to derive the statistically averaged equations and a finite-volume method is used to solve the model equations. The bubble dynamics are incorporated using a Rayleigh-Plesset-type equation which includes the effects of heat transfer, liquid viscosity and compressibility. For the case of monodisperse bubbles, it is known that relaxation oscillations occur behind the shock due to the bubble dynamics. The present computations for the case of polydisperse bubbles show that bubble size distributions lead to additional damping of the shock dynamics. If the distribution is sufficiently broad, the statistical effect dominates over the physical damping associated with the single bubble dynamics. This smooths out the oscillatory shock structure.