Modeling and characterization of elastic wave propagation in micro-scale photonic crystals

Micro-scale phononic crystals are micro-electro-mechanical-systems (MEMS) made of one material periodically embedded in another material, leading to periodic changes in elastic properties of the composite structure. Such devices exhibit elastic bandgaps, which are very useful in many commercial applications. Filtering, guiding and mirroring of elastic waves are a few applications in which phononic crystals can be used. In this manuscript, the physical origins of phononic bandgaps were successfully determined using a one-dimensional model to isolate resonances contributing to the creation of phononic bandgaps. Photonic crystals were further modeled using a two-dimensional technique called the Plane Wave Expansion Method. A solution for the convergence problem of the plane wave expansion method, previously believed to be a result of the large elastic impedance difference between the constituent materials, was successfully demonstrated. This new formulation of the plane wave expansion method reduced the computation time from 18 hours, using Fortran running on a Unix environment with eight parallelized processors, to 1 minute using Matlab running on a simple windows machine. The computation time was more than 1000 times faster than that using the conventional plane wave expansion method formulation. Finally, phononic crystal devices operating in the MHz as well as devices operating at the GHz frequency range were modeled, designed, fabricated, and tested. Good agreement between theoretical and experimental results was observed. In the future, phononic crystal high-Q cavities should be considered, including their fabrication procedure as well as developing a method by which elastic coupling into such cavities is readily achieved.Sandia National LaboratoriesElectrical EngineeringMastersUniversity of New Mexico. Dept. of Electrical and Computer EngineeringLeseman, ZaydLeseman, ZaydOlsson, RoyEl-kady, IhabFleddermann, CharlesSu, Mehme