Acoustic dissipation

This definition is special to acoustics and is different from the usage in radiation, where the absorption factor corresponds to the acoustic dissipation factor. 

Fast motions of a bubble surface produce sound waves. Small (but non-zero) compressibility of the liquid is responsible for a finite velocity of acoustic signals propagation and leads to appearance of additional kind of the energy losses, called acoustic dissipation. When the bubble oscillates in a sound field, the acoustic losses entail an additional phase shift between the pressure in the incident wave and the interface motion. Since the bubbles are much more compressible than the surrounding liquid, the monopole sound scattering makes a major contribution to acoustic dissipation. The action of an incident wave on a bubble may be considered as spherically-symmetric for sound wavelengths in the liquid lr >Ro-When the spherical bubble with radius is at rest in the liquid at ambient pressure, pg), the internal pressure, p, differs from p by the value of capillary pressure, that is... 

Willemsen, A. 2012. An experimental characterization of the acoustically dissipative properties of light-weight nanocomposite polyurethane foams augmented with carbon nanotubes. J.Acoust. Soc.Am. 131 3271. 

Thus far we have discussed the direct mechanism of dissipation, when the reaction coordinate is coupled directly to the continuous spectrum of the bath degrees of freedom. For chemical reactions this situation is rather rare, since low-frequency acoustic phonon modes have much larger wavelengths than the size of the reaction complex, and so they cannot cause a considerable relative displacement of the reactants. The direct mechanism may play an essential role in long-distance electron transfer in dielectric media, when the reorganization energy is created by displacement of equilibrium positions of low-frequency polarization phonons. Another cause of friction may be anharmonicity of solids which leads to multiphonon processes. In particular, the Raman processes may provide small energy losses. 

Damping The loss of energy, as dissipated heat, that results when a material or material system is subjected to an oscillatory load or displacement. Perfectly elastic materials have no mechanical damping. Damping reduces vibrations (mechanical and acoustical) and... 

Slip is not always a purely dissipative process, and some energy can be stored at the solid-liquid interface. In the case that storage and dissipation at the interface are independent processes, a two-parameter slip model can be used. This can occur for a surface oscillating in the shear direction. Such a situation involves bulk-mode acoustic wave devices operating in liquid, which is where our interest in hydrodynamic couphng effects stems from. This type of sensor, an example of which is the transverse-shear mode acoustic wave device, the oft-quoted quartz crystal microbalance (QCM), measures changes in acoustic properties, such as resonant frequency and dissipation, in response to perturbations at the surface-liquid interface of the device. 

The shear-mode acoustic wave sensor, when operated in liquids, measures mass accumulation in the form of a resonant frequency shift, and it measures viscous perturbations as shifts in both frequency and dissipation. The limits of device operation are purely rigid (elastic) or purely viscous interfaces. The addition of a purely rigid layer at the solid-liquid interface will result a frequency shift with no dissipation. The addition of a purely viscous layer will result in frequency and dissipation shifts, in opposite directions, where both of these shifts will be proportional to the square root of the liquid density-viscosity product v Pifti-... 

Shanahan and Carre [31-36, 55, 56] have done extensive theoretical work on the coating of viscoelastic surfaces and the effect of soft surfaces on hydrodynamic forces. Again, we have considered this area in a recent review [44]. This area is important in how energy is transferred or lost at the interface. Coupling changes at an inner interface can result in either an increase or decease in the energy dissipated. This has been discussed and observed for a number of acoustic systems [40, 41, 54, 57, 58]. 

Figure 4. Theoretical trends for —(storage) and dissipation as the inner slip is varied between no slip (0) and strong slip (1) for a coated transverse shear acoustic wave device in water. The thickness of the film is 5 nm. The solid line displays the decrease in storage, and the dashed line shows the change in dissipation.

Gel with energy dissipation in the acoustic frequency range. 

Abstract In this paper the effect of ultrasound on flow through porous media has been investigated both experimentally and theoretically. Ultrasounds (20 and 40 kHz) have been proved to increase the flow rate through porous media. Two effects have been found of relevance. Decrease in viscosity due to dissipation of acoustic waves and acoustic streaming. The two effects have been modeled and those models compared with experimental data. 

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