91 research outputs found
Dynamic radiation force of acoustic waves on solid elastic spheres
The present study concerns the dynamic radiation force on solid elastic
spheres exerted by a plane wave with two frequencies (bichromatic wave)
considering the nonlinearity of the fluid. Our approach is based on solving the
wave scattering for the sphere in the quasilinear approximation within the
preshock wave range. The dynamic radiation force is then obtained by
integrating the component of the momentum flux tensor at the difference of the
primary frequencies over the boundary of the sphere. Results reveal that
effects of the nonlinearity of the fluid plays a major role in dynamic
radiation force leading it to a parametric amplification regime. The developed
theory is used to calculate the dynamic radiation force on three different
solid spheres (aluminium, silver, and tungsten). Resonances are observed in the
spectrum of the force on the spheres. They have larger amplitude and better
shape than resonances present in static radiation force.Comment: 9 pages, 4 figures, to appear in Physical Review
Theory of pressure acoustics with boundary layers and streaming in curved elastic cavities
The acoustic fields and streaming in a confined fluid depend strongly on the
acoustic boundary layer forming near the wall. The width of this layer is
typically much smaller than the bulk length scale set by the geometry or the
acoustic wavelength, which makes direct numerical simulations challenging.
Based on this separation in length scales, we extend the classical theory of
pressure acoustics by deriving a boundary condition for the acoustic pressure
that takes boundary-layer effects fully into account. Using the same
length-scale separation for the steady second-order streaming, and combining it
with time-averaged short-range products of first-order fields, we replace the
usual limiting-velocity theory with an analytical slip-velocity condition on
the long-range streaming field at the wall. The derived boundary conditions are
valid for oscillating cavities of arbitrary shape and wall motion as long as
the wall curvature and displacement amplitude are both sufficiently small.
Finally, we validate our theory by comparison with direct numerical simulation
in two examples of two-dimensional water-filled cavities: The well-studied
rectangular cavity with prescribed wall actuation, and the more generic
elliptical cavity embedded in an externally actuated rectangular elastic glass
block.Comment: 18 pages, 5 figures, pdfLatex, RevTe
Acoustic radiation- and streaming-induced microparticle velocities determined by micro-PIV in an ultrasound symmetry plane
We present micro-PIV measurements of suspended microparticles of diameters
from 0.6 um to 10 um undergoing acoustophoresis in an ultrasound symmetry plane
in a microchannel. The motion of the smallest particles are dominated by the
Stokes drag from the induced acoustic streaming flow, while the motion of the
largest particles are dominated by the acoustic radiation force. For all
particle sizes we predict theoretically how much of the particle velocity is
due to radiation and streaming, respectively. These predictions include
corrections for particle-wall interactions and ultrasonic thermoviscous
effects, and they match our measurements within the experimental uncertainty.
Finally, we predict theoretically and confirm experimentally that the ratio
between the acoustic radiation- and streaming-induced particle velocities is
proportional to the square of the particle size, the actuation frequency and
the acoustic contrast factor, while it is inversely proportional to the
kinematic viscosity.Comment: 11 pages, 9 figures, RevTex 4-
Integrated acoustic and magnetic separation in microfluidic channels
With a growing number of cell-based biotechnological applications, there is a need for particle separation systems capable of multiparameter separations at high purity and throughput, beyond what is presently offered by traditional methods including fluorescence activated cell sorting and column-based magnetic separation. Toward this aim, we report on the integration of microfluidic acoustic and magnetic separation in a monolithic device for multiparameter particle separation. Using our device, we demonstrate high-purity separation of a multicomponent particle mixture at a throughput of up to 10(8) particles/hr. (C) 2009 American Institute of Physics. [doi:10.1063/1.3275577
Particle separation by phase modulated surface acoustic waves
High efficiency isolation of cells or particles from a heterogeneous mixture is a critical processing step in lab-on-a-chip devices. Acoustic techniques offer contactless and label-free manipulation, preserve viability of biological cells, and provide versatility as the applied electrical signal can be adapted to various scenarios. Conventional acoustic separation methods use time-of-flight and achieve separation up to distances of quarter wavelength with limited separation power due to slow gradients in the force. The method proposed here allows separation by half of the wavelength and can be extended by repeating the modulation pattern and can ensure maximum force acting on the particles. In this work, we propose an optimised phase modulation scheme for particle separation in a surface acoustic wave microfluidic device. An expression for the acoustic radiation force arising from the interaction between acoustic waves in the fluid was derived. We demonstrated, for the first time, that the expression of the acoustic radiation force differs in surface acoustic wave and bulk devices, due to the presence of a geometric scaling factor. Two phase modulation schemes are investigated theoretically and experimentally. Theoretical findings were experimentally validated for different mixtures of polystyrene particles confirming that the method offers high selectivity. A Monte-Carlo simulation enabled us to assess performance in real situations, including the effects of particle size variation and non-uniform acoustic field on sorting efficiency and purity, validating the ability to separate particles with high purity and high resolution
Deformation of red blood cells using acoustic radiation forces
Acoustic radiation forces have been used to manipulate cells and bacteria in a number of recent microfluidic applications. The net force on a cell has been subject to careful investigation over a number of decades. We demonstrate that the radiation forces also act to deform cells. An ultrasonic standing wave field is created in a 0.1 mm glass capillary at a frequency of 7.9 MHz. Using osmotically swollen red-blood cells we show observable deformations up to an aspect ratio of 1.35, comparable to deformations created by optical tweezing. In contrast to optical technologies, ultrasonic devices are potentially capable of deforming thousands of cells simultaneously. We create a finite element model that includes both the acoustic environment of the cell, and a model of the cell membrane subject to forces resulting from the non-linear aspects of the acoustic field. The model is found to give reasonable agreement with the experimental results, and shows that the deformation is the result of variation in an acoustic force that is directed outwards at all points on the cell membrane. We foresee applications in diagnostic devices, and in the possibility of mechanically stimulating cells to promote differentiation and physiological effects
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