EAGER: Monolithic Phononic Crystals and Programmable Surface Acoustic Wave Microfluidics

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The last few decades, a number of major technological breakthroughs are mainly enabled by our ability to control two elementary particles: electrons and photons. Phonon is another important elementary particle that is responsible from heat and sound transfer. However, there are only limited studies focused on exploiting phonons for our needs. Harvesting phonons, specifically surface acoustic waves, could lead to new practical microfluidic devices with novel properties. Acoustic phonons can exert strong radiation forces to bioparticles (viruses, bacteria and cell) and manipulate them with high precision and efficiency. This proposal offers using phononic crystals to achieve this. Incorporation of such phononic crystals with microfluidics provides an unprecedented level of control on surface acoustic waves in microfluidic system. This capability can potentially lead to monolithic, ultra-compact, versatile and programmable microfluidic devices. Fusing of phononics and microfluidics could open door to a new world of lab-on-chip biomedical technologies and impact everyday life in previously unthinkable ways, in a similar fashion to how electrons and photons did so far. The educational component of this program is expected to provide UCSC undergraduate and graduate students with interdisciplinary training in physics, electrical engineering and biological sciences. Outcomes of the research will be integrated in a graduate student curriculum and results will be disseminated to broader audience by presentations to middle school Girls through 'Girls in Engineering Program' and to underrepresented minorities through 'Multicultural Engineering Program' The objective of this research proposal is to explore the feasibility of developing microfluidic devices with new functionalities using phononic crystals on silicon substrates. Phononic crystals offer potentially unlimited ways of tailoring acoustic waves. However, to date, they have not been used in acousto-microfluidic applications, other than few simple applications related to mixing and guiding of microdroplets resting on a solid substrate in open air. Full integration of continuous flow microfluidics and phononic crystals has yet to be demonstrated. This project aims to demonstrate practical, facile utilization of phononic crystals in acoustofluidics by making use of the concepts such as band gap formation and evanescent modes of defect states. In this one-year proposal, two basic design concepts will be explored: (i) phononic crystal reflectors, and (ii) phononic crystal waveguide structures. These two structures offer a complete set of basic building blocks to achieve more complex phononic crystal microfluidics with enhanced capabilities (see motivation section below). This one-year project has four specific goals: (1)To design phononic crystal devices with theoretical modeling and finite element simulations. (2)To fabricate of phononic crystal devices and integrate them with interdigital transducers on a silicon substrate. (3)To characterize surface acoustic wave behavior of the integrated structures. (4)To integrate microfluidics with phononic crystals and interdigital transducers to achieve size based micro-particle separation and micro-particle guiding. The proposed research program involves numerical design of monolithic acoustofluidic systems in which particle manipulation is taken care of by phononic crystals through techniques, such as finite-element method. The devices are fabricated using well-established microfabrication techniques such as photolithography, metal deposition, soft lithography and deep reactive ion etching. In this proposal, microfuidic testing will be limited to fluorescent silica particles for rapid device development purposes.