Alexander A. Doinikov

Acoustic radiation force on a spherical particle in a viscous heat-conducting fluid. I. General formula

The acoustic radiation force exerted by an axisymmetric sound field on a spherical particle is calculated assuming that the surrounding fluid is viscous and heat conducting. The incident sound field pressure amplitude is supposed to be small enough such that nonlinear effects like generation of subharmonics do not occur. No restrictions are imposed on the particle size, which means that the particle can be of an arbitrary radius with respect to the sound, viscous, and thermal wavelengths in the surrounding fluid. The obtained formula for the radiation force is general in that it is applicable to first, any axisymmetric sound field, such as a plane, traveling or standing wave and a spherical wave, and, second, any of the following types of dispersed particles: a gas bubble, a liquid drop, a rigid or elastic sphere, a spherical shell, etc. The force is expressed in terms of the linear scattering coefficients to be determined by the particle type. Thus, to obtain the force on a specific particle the problem ...

Review of shell models for contrast agent microbubbles

Micrometer-scale encapsulated gas bubbles, known as ultrasound contrast agents, are used in ultrasound medical diagnostics for enhancing blood-tissue contrast during an ultrasonic examination. They are also employed in therapy as an activator of drug incorporation or extravasation. Adequate modeling of the effect of encapsulation is of primary importance because it is the encapsulating shell that determines many of the functional properties of contrast agents. In this review, existing approaches to the modeling of the radial motion of an encapsulated bubble are discussed and comparative analysis of available shell models is conducted. The capabilities of the shell models are evaluated in the context of recent experimental observations, such as compression-only behavior and the dependence of shell material properties on initial bubble radius. It is shown that for early shell models, the main problem is that the behavior of encapsulation is described by linear elastic and viscous laws, whereas recent experimental data attest to complicated rheological properties inherent in shell materials. Currently, a trend toward models involving nonlinear laws for shell elasticity and viscosity is observed. In particular, nonlinear models have been proposed that allow one to reproduce compression-only behavior. However, the problem of the radius dependence of shell material parameters remains unsolved.

Acoustic radiation pressure on a compressible sphere in a viscous fluid

The acoustic radiation pressure exerted by a plane — progressive or standing — sound wave on a compressible sphere suspended freely in a viscous fluid is calculated. In deriving the general expression for the radiation pressure, it is supposed that the radius of the sphere is arbitrary. Two limiting cases of interest are then considered. In the first of these, it is assumed that the sound wavelength is much larger than the radius of the sphere which is, in turn, much larger than the viscous wavelength, it being supposed that this condition is satisfied both outside and inside the sphere. In the second case, the situation is investigated when the radius of the sphere is small compared with the viscous wavelength which is, in turn, much smaller than the sound wavelength, it being supposed that this condition is satisfied, as before, both outside and inside the sphere. It is shown that in both cases the expressions for the radiation pressure are drastically different from the well-known expressions for the radiation pressure in a perfect fluid: the calculation of the radiation pressure from the formulae obtained for a perfect fluid in the cases when the effect of viscosity is not negligible gives both quantitatively and qualitatively wrong results.

Secondary Bjerknes forces between two bubbles and the phenomenon of acoustic streamers

The translational velocities of two spherical gas bubbles oscillating in water, which is irradiated by a high-intensity acoustic wave field, are calculated. The two bubbles are assumed to be located far enough apart so that shape oscillations can be neglected. Viscous effects are included owing to the small size of the bubbles. An asymptotic solution is obtained that accounts for the viscous drag on each bubble, for large

Acoustic radiation force on a spherical particle in a viscous heat-conducting fluid. III. Force on a liquid drop

{\it Re}

Theoretical investigation of shear stress generated by a contrast microbubble on the cell membrane as a mechanism for sonoporation

based on the radial part of the motion, in a form similar to the leading-order prediction by Levich (1962),

Mathematical model for collective bubble dynamics in strong ultrasound fields

C_{D} = 48/{\it Re}_{T}

Acoustic scattering from a contrast agent microbubble near an elastic wall of finite thickness

;

Acoustic microstreaming around a gas bubble.

{\it Re}_{T} \to \infty

Time delays in coupled multibubble systems (L)

based on the translational velocity. In this context the translational velocity of each bubble, which is a direct measure of the secondary Bjerknes force between the two bubbles, is evaluated asymptotically and calculated numerically for sound intensities as large as the Blake threshold. Two cases are examined. First, two bubbles of unequal size with radii on the order of