Ultrasonic study of a smectic-Bliquid crystal

Anisotropy in the velocity and attenuation of longitudinal ultrasound was studied for the first time in a stable smectic-$B$ liquid crystal ($\beta$-methyl-butyl-methoxybenzylidene amino cinnamate). Anisotropy in the velocity was found to be consistent with the predictions of the Martin-Parodi-Pershan hydrodynamic theory in both smectic-$A$ and -$B$ phases, but was significantly smaller than when measured in the same material by Brillouin scattering. Furthermore, strong dispersion was observed near the smectic-$A$—smectic-$B$ phase transition for sound propagating perpendicular to the symmetry direction.