Observation of ultrasonic wavefronts by synchronous Schlieren imaging

A synchronous Schlieren system for observation of ultrasound wavefronts was developed. Since high-intensity and short-response-time GaN/InGaN green light-emitting diodes (LEDs) are suitable light sources of a Schlieren system, we constructed such a system by pulsed illumination synchronized to ultrasound. We used it to observed progressive plane waves and their transmission through a thin plate. Morever, we used it to observe Lamb waves in the plate by ultrasonic field in the fluid in its vicinity. The results obtained showed the effectiveness of this system. It has also been proven to be useful for overviewing the spatial distribution of the phase factor of an ultrasonic field, which may be similar to that of ultrasonic power.