Instrumentation, techniques, and evaluation of ePTV for particle manipulation studies using micro-scale oscillators
1 online resource (303 pages) : PDF
University of North Carolina at Charlotte
A need for dynamic micro-particle manipulation is the ability to position fragile particles without damaging them, for instance biological particles like blood cells, stem cells, neurons, pancreatic β cells, DNA, chromosomes, for repeated measurement without altering their behavior. An oscillating fiber will induce vortices in a slurry of particles, subsequently the vortex force created by this oscillation attracts and traps the particles located at steady streaming micro-eddies. If multiple oscillatory fibers are placed inside the slurry, depending on frequency and timing of oscillation this method can be used for contact-free particle shepherding and sorting and for transporting particles from one location to another. Due to the complicated dynamics of particles traveling in the fluid and the presence of noise, and significant number of particles, attempts to use commercial PIV softwares to track individual particle paths could not discriminate real particles from noise interference. To enhance identification and tracking of individual particles a novel encoded-particle tracking velocimetry (ePTV) technique is developed in this dissertation work and used in the experiments to track the particle trajectories. An analytic model is developed to determine the number of lost particles due to the finite image size based on a calculation of the probability that imaged particles of a specific mean velocity or having a uniform velocity distribution and encoding pattern will exit the field of view. The encoded pulse technique has been implemented in experiments for which images containing 100-200 objects including encoded trajectories have been measured. Using the developed ePTV algorithm approximately 30 % of the identified objects were classified as an encoded particle trajectory. Two types of oscillation mechanism are used in the experimental component of this study, a PZT flexure-based macro-probe driven at frequencies around 250 Hz and higher frequency dynamic-absorber, quartz-based, micro-probes driven at frequencies around 32 kHz. Two models for predicting the frequency response of micro-scale oscillatory probes are developed in this dissertation. In these studies, the attached fibers were either 75 µm diameter tungsten or 7 µm diameter carbon with lengths ranging from around 1 to 15 mm. The oscillators used in these experiments were commercial 32.768 kHz quartz tuning forks. Theoretical predictions of the values of the natural frequencies for different vibration modes show an asymptotic relationship with the length and a linear relationship with the diameter of the attached fiber. Similar results are observed from experiment, one with a tungsten probe having an initial fiber length of 14.11 mm incrementally etched down to 0.83 mm, and another tungsten probe of length 8.16 mm incrementally etched in diameter, in both cases using chronocoulometry to determine incremental volumetric material removal. Of particular relevance is that, when a ‘zero’ is observed in the response of the tine, one mode of the fiber is matched to the tine frequency and is acting as an absorber. This represents an optimal condition for contact sensing and for transferring energy to the fiber for fluid mixing, touch sensing and surface modification applications. Consequently the parametric models developed in this dissertation can be utilized for designing probes of arbitrary sizes thereby eliminating the empirical trial and error previously used.
ENCODED-PARTICLE TRACKING VELOCIMETRYINSTRUMENTATIONMECHATRONICSMICRO-SENSORSPARTICLE MANIPULATIONPRECISION MEASUREMENT
Kelly, ScottSchmitz, TonyConrad, JamesSell, Susan
Thesis (Ph.D.)--University of North Carolina at Charlotte, 2017.
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