Utilization of phononic crystals in nanoparticle sorting via surface acoustic waves

In this thesis, size-based separation and classification of spherical particles with dimension on the order of 100 nm by means of two-dimensional phononic crystals, which are composed of annular grooves on a piezoelectric substance with square or triangular lattice geometry, are numerically investigated. Through calculations employing the Finite Element Method (FEM), it is determined that the phononic crystal with a period around 10 µm exhibits a band gap with 5% width around 100 MHz. It is also demonstrated through FEM simulations that Rayleigh surface acoustic waves (SAWs) with 10 MHz band width around 100 MHz can be generated via an interdigital transducer (IDT) having 11 finger pairs whose widths linearly vary between 5 m and 15 m. As a result of calculations where the IDT-phononic crystal spacing is set to an integer multiple of the wavelength (approximately 40 m), standing SAW formation in the IDT-phononic crystal gap is exhibited. When a polydimethylsiloxane (PDMS) mold containing a microchannel whose width and height are 35 m is placed on piezoelectric surface, symmetric nodes are observed around the center, while the acoustic field in the cross-section of the fluid in the microchannel has maximum pressure at the channel center. By simultaneously calculating the acoustic radiation and drag forces acting on spherical nanoparticles with different sizes released to the microchannel, time-dependent trajectories of the particles are obtained. Radius distribution of particles that are pushed towards the nodes along the length of the channel and of the ones remaining in the central region are analyzed, where the separation efficiency of the microfluidic system and the threshold radius for separation are calculated. Thesis results can be used to detect and analyze nanovesicles such as exosomes released from cells, as well as other nanoscale biomaterials.