Volumetric Visualization of Acoustic Streaming by Digital Inline Holographic Microscopic Particle Tracking Velocimetry
Wei-Hsin Tien
Mechanical Engineering, National Taiwan University of Science and Technology
whtien@mail.ntust.edu.tw
Abstract
Rapid advances in microfluidics have led to the requirement for more complicated flow phenomena, and the use of advanced manufacturing techniques such as 3-D printing helps to design and build more sophisticated flow channels. Traditional 2-D ![]()
technique has limitations in measuring the 3-D flow patterns in these flow, and volumetric methods for visualizing the 3-D flow patterns in microscale becomes critical in the development of these new designs of microfluidics. In this study, a volumetric imaging technique using Digital Inline Holographic Microscopy (DIHM) is developed and applied to visualizing the 3-D flow patterns of an acoustic streaming in a microchannel. Illuminated by a 450nm continuous laser, the magnified holography of the motion of tracer particles was recorded by a low-cost industrial microscope with a machine vision camera. The first solution of Reyleigh-Sommerfield in Huygens-Fresnel theorem was adopted to reconstruct the 3-D locations of the tracer particles, and 3-D particle tracking is then performed to obtain the volumetric flow field. The measurement range was evaluated as ![]()
, and the 3-D reconstruction algorithm was calibrated and the measurement accuracy in the depth location was verified with a calibration target. Using the proposed reconstruction algorithm with holographic images, 3-D locations of the out-of-focus particle images can be resolved and the diffraction information can be preserved, which was discarded as noise in the traditional 2-D PIV method. Compared to some 3-D techniques using diffraction ring patterns for 3-D reconstruction, the proposed method is more robust in dealing with the overlapped diffraction ring patterns from different particles, and higher particle image density can be achieved. As a proof of concept, this method was applied to measuring the 3-D flow patterns of acoustic streaming induced by a triangular obstruction that was unable to be visualized before with the 2-D ![]()
technique before.
Short Bio
Wei-Hsin Tien received his PhD degree at University of Washington in 2013 and joined National Taiwan University of Science and Technology since 2014. He is currently an assistant professor in the department of mechanical engineering. His main research interest is to develop advanced flow visualization techniques to resolve complex flow phenomena in microscale. He is currently working on the development of Temperature Sensitive Tracer Particles, 3-D volumetric imaging methods using Digital Inline Holographic Microscopy (DIHM) and post-processing techniques for Particle-Tracking Velocimetry (PTV) and Particle Streak Velocimetry (PSV). He is also interested in acoustofluidics, especially the complicated flow patterns induced by acoustic streaming and ultrasonic standing wave (USW).
