| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 106 === Microfluidic devices are applied extensively and conveniently, and are often used for the purpose of droplet mix, cells separation, and particles concentration. The major control mechanisms for microdroplets include electrowetting and surface acoustic waves, where the electrowetting control requires the applications of the electric field and complicated circuit, and additionally creating suitable electric property carried by the particles. On the other hand, the surface acoustic wave control may overcome the drawbacks of electrowetting. In respect of droplet driven by surface acoustic waves, most existing searches presented the control its movement and mix. It is much more difficult to effectively control the particles separation by surface acoustic waves due to the fact that the acoustic pressure and acoustic streaming is uneasy to build by the incoming surface acoustic waves required by the particles separation inside a droplet. Accordingly, the relevant researches are few. Nevertheless, desired acoustic pressure and streaming fields still may be built by tailoring the incident acoustic wave field to the droplet. Therefore, we change the incident field distribution of surface acoustic waves with the so-called acoustic band gap of phononic crystal structures to locally block the transmission of surface acoustic waves, allowing the creation of acoustic pressure field and acoustic streaming field as required for particles separation within the droplets and further control the movement of particles in different sizes inside the droplets.
This thesis studies the control of the microfluidic droplets using high-frequency surface acoustic waves incorporated with 2D phononic crystal to tailor the surface acoustic wave field and build different acoustic field environment within the droplets. The particles of different sizes could be separated via the rational flow in the droplets generated by acoustic streaming and internal acoustic radiation force. The working mechanisms of the particle separation devices proposed in this study were simulated by periodic structure piezoelectric wave theory and viscous sound pressure theory with finite-element method (FEM). Analysis and discussions were conducted based on the FEM calculation results. Furthermore, devices were fabricated on a 128°Y–X LiNbO3 piezoelectric wafer using MEMS process to observe the movements of particles of different sizes within the droplets affected by the surface acoustic waves with and without the phononic crystal structures. According to the experimental results, the proposed devices have successfully controlled the droplets for the purpose of particle size separation.
In brief, this study proposes the surface acoustic wave microfluidic devices with 2D phnonic crystals. Effective droplets control for microparticle size separation via surface acoustic waves and phononic crystals is achieved. In addition, it can be further applied for the mix of biomedical droplets, cell or particle separation to achieve non-invasive, non-destructive manipulation of particles in a droplet.
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