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A Simultaneous Observation System for Microbubble Vibration in an Acoustic Field by using a High-speed Camera and an LDV

Optical simultaneous observations for the vibration of microbubble are performed using a high-speed video camera and an LDV. As a method to observe the microbubble vibration, high speed camera is ordinary used, because it enables to capture a whole movement of the microbubble behavior in time variation. However, the frame rate of the camera is generally slower than bubble motion driven by ultrasound. Additionally, due to the low spatial resolution of the observed pictures taken by high-speed camera, it is difficult to measure the precise behavior of the microbubble. To solve these problems, a laser Doppler vibrometer was introduced with the ordinary high-speed camera observation system. Both of the observed results were compared to each other. As a result, the spherical bubble vibration at 27 kHz with the vibrational displacement amplitude of 2 P m could be observed and the experimental results by two methods showed a good agreement. A nonspherical vibration was also observed. The radius versus time curve was similar to each other, but the vibration amplitude measured by LDV was about two times smaller than that measured by high speed camera. For the complicated behaviors such as nonspherical vibrations, we found that the bubble vibration can be measured precisely by adjusting the focal point of LDV to the center of the bubble. By using the presented observation system, it is expected that more precise observation of bubble vibration behavior can be realized.