Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48105, USA.
J Acoust Soc Am. 2020 Mar;147(3):1339. doi: 10.1121/10.0000802.
This paper describes a method for acquiring high temporal and spatial resolution images of cavitation events using a multiple-flash-per-camera-exposure imaging technique. A primary challenge associated with imaging cavitation is that the velocity of the bubble wall reaches its maximum (∼1.5×10 m/s) as the bubble size approaches its minimum (≲1 μm). In order to adequately resolve dynamics on these scales, specialized-often prohibitively expensive-cameras with ultra-high frame-rates and resolutions are generally required. This paper describes low-cost, high-speed light emitting diode (LED) flash sources with minimum pulse widths of 20 ns that can be pulsed at rates of up to 17 MHz. The flashes are used to illuminate images of bubbles captured using high-resolution "still-frame" cameras wherein multiple flashes are issued from the LED(s) at known time intervals within a single camera exposure, resulting in overlapping snapshots of the same bubble at multiple unique time-points in a single image. The overlapping snapshots can be uniquely associated with the known time-points of the flashes based on their relative levels brightness. This paper demonstrate effective frame-rates up to 4 Mfps using this technique and the acquisition of snapshots at up to 13 unique time-points per exposure. Hardware descriptions of the flash sources and the programmable device used to control them are provided.
本文描述了一种使用多次闪光/单次曝光成像技术获取空化事件的高时空分辨率图像的方法。与空化成像相关的一个主要挑战是，当气泡尺寸接近最小值（≲1μm）时，气泡壁的速度达到最大值（∼1.5×10 m/s）。为了在这些尺度上充分解析动力学，通常需要专门的——通常非常昂贵的——具有超高帧率和分辨率的相机。本文描述了低成本、高速发光二极管（LED）闪光源，其最小脉冲宽度为 20ns，可以以高达 17MHz 的频率脉冲。这些闪光用于照亮使用高分辨率“静帧”相机捕获的气泡图像，其中在单个相机曝光内的已知时间间隔内从 LED 发出多个闪光，从而在单个图像中以多个独特的时间点对同一气泡的重叠快照进行曝光。可以根据相对亮度将重叠的快照唯一地关联到闪光的已知时间点。本文证明了使用该技术可实现高达 4Mfps 的有效帧率，并可在每个曝光中获取多达 13 个独特时间点的快照。提供了闪光源的硬件描述以及用于控制它们的可编程设备。
