Acoustic radiation force

The axial component of the primary acoustic radiation forces, which is parallel to the z-direction of the ooordinates and accelerates the particles towards the pressure nodal planes of the standing wave field. 

An original method involves quadrupole oscillations of drops K The drop (a) in a host liquid (P) is acoustically levitated. This can be achieved by creating a standing acoustic wave the time-averaged second order effect of this wave gives rise to an acoustic radiation force. This drives the drop up or down in p, depending on the compressibilities of the two fluids, till gravity and acoustic forces balance. From then onwards the free droplet is, also acoustically, driven into quadrupole shape oscillations that are opposed by the capillary pressure. From the resonance frequency the interfacial tension can be computed. The authors describe the instrumentation and present some results for a number of oil-water interfaces. 

The existence of this acoustic radiation force was established a long time ago by Dvorak in 1876, and Raleigh in 1878 gave the basis of a theoretical study. Since that time many papers have been published in this field [77,78], and it has been the subject of some controversy due to the complexity of the problem. For this reason only some of the elements relating to this topic will be discussed here. 

When reducing the dimensions, that is, going into the microscale domain with channel dimensions smaller than 500 p,m, inherent benefits in terms of an increased primary acoustic radiation force is obtained due to the higher resonance frequency of the resonator. 

FIGURE 44.1 Fluorescently labeled polystyrene particles gathered in the pressure nodal plane (in plane with the image focus) of an acoustic standing wave by the primary acoustic radiation force in a 70 xm deep microchannel. The microbeads are also clustered in a dense hexagonal pattern by Bjerknes forces. 

An optional mode of performing a binary particle separation utilizes the mobility of the particle species to be separated. The motion of each particle is defined by its individual primary acoustic radiation force and the opposing hydrodynamic drag force. Equation 44.4, where v is the fluid velocity, p, is the fluid viscosity, and Dp is the particle diameter ... 

Fig. 25 Schematic illustration of the acoustic radiation force (ARF)-based FIRMS (force-induced remnant magnetisation spectroscopy) approach for the selective cleavage of non-covalent bonds. Reproduced with permission from [132]. Copyright 2014 The Royal Society of Chemistry...

De Silva L, Yao L, Xu S (2014) Mechanically resolving noncovalent bonds using acoustic radiation force. Chem Commun 50 10786-10789... 

In this part, mathematical modeling of the acoustic radiation force acting on particles in a... 

This error is large in the case of bubbles within a resonant field. In the light of this, Yosioka and Kawasima extended King s theory to allow for compressible spheres in 1955. They demonstrated that the time-averaged acoustic radiation force on a spherical particle of radius a, at position X within a one-dimensional standing wave of acoustic energy density e is... 

Bruus H (2012) Acoustofluidics 7 the acoustic radiation force on small particles. Lab Chip 12 1014-1021... 

Yasuda, K. Kamakura, T. Acoustic radiation force on micrometer-size particles. Appl. Phys. Lett. 1997, 71 (13), 1771. 

It has been known for many years that acoustic standing waves can influence the behaviour of particles in either a liquid or gaseous medium. This effect relies on acoustic radiation forces that act on particles and other acoustic discontinuities (such as second phase fluids) within an ultrasonic field [1]. These forces are generally larger... 

For a more detailed description of the background, including key references, see Grosehl s 1998 paper [ 1 ]. King provided the first comprehensive calculation of acoustic radiation forces on a small particle within a standing wave in 1934. This theory was developed for rigid spheres in an inviscid fluid and predicts that particles will move toward either the node or antinode of the field depending on the ratio of the fluid and particle densities. When the ratio of the incompressible particle density to the fluid density is... 

The acoustic radiation force Facrx in thn x-direction experienced by particles of densities pp suspended in a medium of density pf has already been expressed by equation (3.1.48) ... 

Nightingale K, Soo M, Nightingale R, Trahey G (2002) Acoustic radiation force impulse imaging in vivo demonstration of clinical feasibility. Ultrasound Med Biol 28 227-235. 

The assessment of RBCs deformability can also be performed by active methods, through the application of external force fields, such as acoustic, optical, electrical, and magnetic ones. Acoustic radiation force has been reported for fast and direct measurement of the mechanical properties of cells in a microfluidic chip. This method is based on the formation of an acoustic standing wave within a straight microchannel that moves the cells to the acoustic pressure nodes, with a movement speed dependent on the compressibility (Hartono et al., 2011). 

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