Abstract
The effects of electric fields on ultrasonic attenuation in nematic and cholesteric liquid crystals was investigated. It is found that the ultrasonic attenuation of the nematic liquid crystal MBBA, when the propagation direction of the sound waves is parallel to the direction of applied electric field, decreases as the field increases for small fields, while above a certain field intensity it begins to increase reaching a saturation value. When the propagation direction of the sound waves is perpendicular to the electric field, the change occurs in the opposite way, since MBBA has a negative electric characteristic. On the other hand, for positive N. Mix. , the change in attenuation varies monotonically. These phenomena can be explained by molecular alignment together with the ultrasound scattering due to the fluctuation of the liquid density. The magnitude of the ultrasonic attenuation in cholesteric liquid crystals is a few-tenths of that in nematic liquid crystals.
