Sound attenuation by small spheroidal particles due to visco-inertial coupling

Abstract

The sound attenuation at ultrasonic frequencies caused by small spheroidal particles in a fluid is examined with regard to the size parameters that determine the shape of the attenuation spectrum. Our investigations are based on a coupled phase model for spheroids with arbitrary orientation, thus facilitating the calculation of average attenuation for a given orientation distribution. Since the model just considers the visco-inertial coupling, its applicability is restricted to small solid particles with high density contrast. The calculated attenuation spectra of mono-sized, randomly aligned spheroidal particles are compared with the attenuation spectra of mono-sized spheres. When the latter approximate the former to a reasonable degree the size of the spheres is called attenuation equivalent diameter. It is shown that the concept of attenuation equivalent diameter can be applied only to slightly elongated prolates. Oblates and very stretched prolates yield considerably broader attenuation spectra than mono-sized spheres. While for oblates and for slightly elongated prolates the characteristic frequency of the attenuation spectrum is determined by the volume specific surface, no such attenuation determining size parameter could be identified for very stretched prolates.

Use of Ultrasound Attenuation Spectroscopy to Determine the Size Distribution of Clay Tactoids in Aqueous Suspensions

“…As a clay platelet is anisotropic, the viscous loss is dependent on its orientation relative to the sound propagation direction. A disc moving edgewise causes greater viscous loss than a disc moving broadside [26,27]. The theory discussed above considers the dispersed particles as spheres.…”

Measurement and density normalisation of acoustic attenuation and backscattering constants of arbitrary suspensions within the Rayleigh scattering regime

“…11b) suggests a weaker density-normalised correlation, with noticeably more scatter in the data at the low-ka region, which may have a number of causes. The roles of particle properties such as shape, orientation, aggregation state, surface roughness and cavities, for example, can cause deviation in the attenuation behaviour of non-spherical particles relative to that estimated using expressions for spherical particles with the same equivalent diameter [13,52,53]. These are further complexities that this density normalisation is unable to fully capture, especially in the case of titania and barytes.…”

Enzyme Reaction in the Pores of CaCO3 Particles upon Ultrasound Disruption of Attached Substrate‐Filled Liposomes

“…In contrast, the lipid shells of liposomes freely suspended in solution do not provide a pronounced density gradient and liposomes are not disrupted. Absorption of ultrasound by particles is minimal (for silica particles, <0.1 dB cm −1 MHz −1 )20b at the operating low‐frequency range, but the higher particle density in the vicinity of the liposomes suffices for disrupting the lipid membrane. The mechanism of transport through the lipid membrane has been proposed to involve the formation of transient hydrophilic or hydrophobic pores 20c.…”