Realization of optimal bandgaps in solid-solid, solid-air, and hybrid solid-air-solid phononic crystal slabs

We investigate the optimal conditions for bandgap formation in square-lattice phononic crystal (PnC) slabs composed of a solid matrix with solid or air inclusions. To ensure sufficient impedance mismatch (key for bandgap formation) and fabrication amenability, silicon and silica were chosen as candidate matrix materials with either air or tungsten inclusions. Solid-solid PnCs were found to exhibit larger bandgaps while relaxing the topological constraints as compared to solid-air PnCs for all but the largest filling fractions. We also demonstrate a hybridized lattice incorporating both air and solid inclusions in the matrix that further relaxes the constraints for realizing wide bandgaps. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3543848]