[1] When a longitudinal sound wave travels through a solvent, the associated pressure gradients push the fluid particles back and forth, and it is easy in practice to create such accelerations that measure thousands or millions of g's.
This relative motion is essentially the same phenomenon that occurs in a centrifuge, or more simply, it is essentially the same phenomenon that occurs when low-density objects float to the top of a glass of water, and high-density particles sink to the bottom (see the equivalence principle, which states that gravity is just like any other acceleration).
IVI concerns the case where the particles in question are anions and cations.
In general, they will have different amounts of motion relative to the fluid during the sound wave oscillations, and that discrepancy creates an alternating electric potential between various points in a sound wave.
These works are mostly associated with the names of Zana and Yaeger, who published a review of their studies in 1982.