Ultrasonic study of a smectic-B liquid crystal

Anisotropy in the velocity and attenuation of longitudinal ultrasound was studied for the first time in a stable smectic-B liquid crystal (β-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.