Development of a novel micro echo particle image velocimetry system.

摘要

The microfluidics industry is currently valued at several billion dollars, and it is still growing, pushed by the development of such devices as the Flu Chip, the Microscale Integrated Sperm Sorter and other micro-total analysis systems (also called lab-on-a-chip). A practical method is required to non-invasively resolve velocity vectors in the flow field for microfluidic flows that are optically opaque.;A new system for microfluidic flow measurement was developed: Micro Echo Particle Image Velocimetry (muEcho PIV). This system used a swept scan of a single element ultrasound transducer to produce sequential images of a flow seeded with microbubbles. The images were cross-correlated, and the resulting PIV vectors were input into a particule tracking velocimetry (PTV) algorithm where they were further refined.;The Micro Echo PIV system used a broad bandwidth mechanically scanned single element transducer to create B-mode images at a transmit frequency of 15.3MHz. This gave the system an axial resolution of 100 mum and a lateral resolution of 200mum at the focal point 25.6 mm from the transducer. The measured dynamic velocity range was 0-4 mm/s. This was acceptable, as microfluidic devices typically have flow rates of 64 muL/min and maximum velocities of less than 10 mm/s.;An advantage of the Micro Echo PIV system is that it can resolve two orthogonal velocity components in a 2-D opaque flow field. A disadvantage of the system is a very low frame rate (mechanically scanned transducer elements are slower than an electronically fired phased array transducer in creating the same image frame).;It is expected that future iterations of this system will use a higher transducer center frequency, for better spatial resolution, and, will optimize the motorized stage path for a higher frame rate and a greater velocity dynamic range.;Potential non-invasive applications include evaluation of hemodynamics in the superficial vasculature of small animal models, and fluid dynamics in polymer microfluidic 2-D and 3-D arrays (with implications for applied and basic research in the agricultural, computer and pharmaceutical industries).