Theory of Sound Propagation in Superfluid Solutions Filled Porous Media

TL;DR

This paper develops a comprehensive theoretical framework for sound wave propagation in porous media filled with superfluid solutions, expressing elastic coefficients through measurable quantities and analyzing volume modes, including specific cases like superfluid in aerogel.

Contribution

It introduces a new theoretical model that describes all volume modes in superfluid-filled porous media, including the case where the normal fluid component is immobilized.

Findings

Velocities of two longitudinal sound modes calculated for superfluid in aerogel.

Elastic coefficients expressed in terms of measurable physical quantities.

Theoretical equations describe all propagating volume modes in the system.

Abstract

A theory of the propagation of acoustic waves in a porous medium filled with superfluid solution is developed. The elastic coefficients in the system of equations are expressed in terms of physically measurable quantities. The equations obtained describe all volume modes that can propagate in a porous medium saturated with superfluid solution. Finally, derived equations are applied to the most important particular case when the normal fluid component is locked inside a highly porous media (aerogel) by viscous forces and the velocities of two longitudinal sound modes are calculated.