Laboratory for Laser Techniques, Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva Cesta 6, 1000 Ljubljana, Slovenia.
Sensors (Basel). 2023 Jan 10;23(2):771. doi: 10.3390/s23020771.
Cavitation bubbles are used in medicine as a mechanism to generate shock waves. The study of cavitation bubble dynamics plays a crucial role in understanding and utilizing such phenomena for practical applications and purposes. Since the lifetime of cavitation bubbles is in the range of hundreds of microseconds and the radii are in the millimeter range, the observation of bubble dynamics requires complicated and expensive equipment. High-speed cameras or other optical techniques require transparent containers or at least a transparent optical window to access the region. Fiber optic probe tips are commonly used to monitor water pressure, density, and temperature, but no study has used a fiber tip sensor in an interferometric setup to measure cavitation bubble dynamics. We present how a fiber tip sensor system, originally intended as a hydrophone, can be used to track the expansion and contraction of cavitation bubbles. The measurement is based on interference between light reflected from the fiber tip surface and light reflected from the cavitation bubble itself. We used a continuous-wave laser to generate cavitation bubbles and a high-speed camera to validate our measurements. The shock wave resulting from the collapse of a bubble can also be measured with a delay in the order of 1 µs since the probe tip can be placed less than 1 mm away from the origin of the cavitation bubble. By combining the information on the bubble expansion velocity and the time of bubble collapse, the lifetime of a bubble can be estimated. The bubble expansion velocity is measured with a spatial resolution of 488 nm, half the wavelength of the measuring laser. Our results demonstrate an alternative method for monitoring bubble dynamics without the need for expensive equipment. The method is flexible and can be adapted to different environmental conditions, opening up new perspectives in many application areas.
空化气泡在医学中被用作产生冲击波的机制。空化气泡动力学的研究对于理解和利用这些现象实现实际应用和目的起着至关重要的作用。由于空化气泡的寿命在数百微秒范围内，而其半径在毫米范围内，因此需要复杂和昂贵的设备来观察气泡动力学。高速摄像机或其他光学技术需要透明容器或至少透明光学窗口才能进入该区域。光纤探头通常用于监测水的压力、密度和温度，但没有研究使用光纤尖端传感器在干涉测量设置中测量空化气泡动力学。我们展示了如何使用光纤尖端传感器系统（最初用作水听器）来跟踪空化气泡的膨胀和收缩。该测量基于光纤尖端表面反射的光与空化气泡本身反射的光之间的干涉。我们使用连续波激光产生空化气泡，并使用高速摄像机验证我们的测量结果。由于探头尖端可以放置在距离空化气泡原点不到 1 毫米的位置，因此可以在 1 µs 左右的延迟时间内测量气泡坍塌产生的冲击波。通过结合气泡膨胀速度和气泡坍塌时间的信息，可以估计气泡的寿命。气泡膨胀速度的测量空间分辨率为 488nm，为测量激光波长的一半。我们的结果展示了一种无需昂贵设备即可监测气泡动力学的替代方法。该方法灵活，可以适应不同的环境条件，为许多应用领域开辟了新的视角。
