Observation of the Growth of Cavitation Bubble Clouds by the Backscattering of Focused Ultrasound from a Laser-Induced Bubble
Observation of the Growth of Cavitation Bubble Clouds by the Backscattering of Focused Ultrasound from a Laser-Induced Bubble
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通过激光诱导气泡的聚焦超声波反向散射观察空化气泡云的生长
DOI：
10.1117/12.2270465
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
H. Takahira
中科院分区：
文献类型：
--
作者：
T. Horiba;T. Sano;T. Ogasawara;H. Takahira
本研究涉及激光诱导气泡的聚焦超声波反向散射导致空化的开始和空化气泡云的生长。通过帧速率高达 1.25 Mfps 的高速摄像机观察到靠近激光诱导气泡界面的空化起始，并在各种超声条件下讨论了其位置和连续空化云的生长。结果表明，超声波长对空化起始位置与气泡界面之间的归一化距离是 η = t0/ ts 的增函数，其中时间 t0 是空化气泡破裂的特征时间，时间 ts 是超声周期。无量纲距离的大小约为超声波长的0.05-0.3倍，空化起始的超声正压阈值约为35MPa。还表明，由入射超声波反向散射产生的空化气泡云沿着聚焦超声波的传播轴呈圆锥形生长。随着焦点处的入射聚焦超声压力变强或聚焦超声持续时间变长，空化气泡云变得更大。然而，即使超声持续时间变得更长，当空化气泡云生长到聚焦超声的焦点区域之外时，这种生长也会结束并达到有限值。
The present study is concerned with the cavitation inception and the growth of a cavitation bubble cloud by the backscattering of focused ultrasound from a laser-induced bubble. The cavitation inception close to the interface of a laser-induced bubble has been observed by a high-speed video camera with the frame rate of up to 1.25 Mfps, and its location and the successive cavitation cloud growth are discussed for various ultrasound conditions. It is shown that the normalized distance between the cavitation inception location and the bubble interface by the wavelength of ultrasound is an increasing function of η = t0/ tswhere the time t0is the characteristic time for cavitation bubble collapse and the time tsthe period of ultrasound. Also the magnitude of the dimensionless distance is about 0.05-0.3 times of the wavelength of ultrasound, and the positive pressure threshold of ultrasound for a cavitation inception is about 35 MPa. It is also shown that the cavitation bubble cloud by the backscattering of the incident ultrasound grows conically along the propagation axis of the focused ultrasound. As the incident focused ultrasound pressure at the focus becomes stronger or the duration of the focused ultrasound becomes longer, the cavitation bubble cloud grows larger. However, even though the ultrasound duration becomes longer, this growth ends up and reaches a limited value when the cavitation bubble cloud grows out of the focal region of the focused ultrasound.