Abstract
Detection and visualization techniques for ultrasonic fields and vibrations by means of cholesteric and nematic liquid crystals are first examined. Ultrasonic fields of a circular vibrator in a sectional plane perpendicular or parallel to the vibrator are visualized on the detective cholesteric liquid crystal plate inserted (Fig. 4, 6 and 8). The patterns (change of the color) corresponding to the sound pressure or temperature distributions are measured by a hydrophone or a thermocouple with a small sound absorbing ball (Fig. 5 and 7). Simple ultrasonic camera is demonstrated by making use of this cholesteric liquid crystal plate(Fig. 9). A visualization technique for the vibrational modes of a viblator is developed. A cholesteric liquid crystal sheet is attached to the surface of the vibrator by means of electron grease as a loose coupling means. the pattern appeared corresponds to its verocity distribution. On the other hand, when α-cyano acrylate (alone alpha) is used for tight attachment, the pattern corresponds to the temperature distribution. That is, the color is just in reverse to the former (Fig. 10). Similar experiments are carried out for nematic liquid crystal as a detector. Ultrasonic field patterns of a circular vibrator in a sectional plane parallel to the vibrator are visualized on the nematic liquid crystal layer sandwiched by glass plates (Fig. 11). Two treatments were tested for orientating the crystal molecular axis perpendicular to glass substrates. One is to paint lecithin on the substrates and the other to dope a small amount of Cetyltrimethylammonium bromide into the liquid crystal. Detection sensitivity is found to be far better for the latter than for the former (Fig. 12). It is also found that the sensitivity is increased by several times with reasonable electric field superposed (Fig. 13). It is shown that the nematic liquid crystal can be used for visualizing the vibrational modes of a vibrator. On the vibrator surface, a nematic liquid crystal layer is formed, which is then covered by a thin glass plate. Similar treatments are necessary for molecular orientation. THe modal pattern can be observed by bare eyes, which is due to the dynamic scattering mode (Fig. 14). The cholesteric liquid crystal detector provides better resolution than the nematic, while the sensitivity is rather same.
