Omnidirectional Band Gap Mirror for Surface Acoustic Wave

We report on the theoretical and experimental evidence for the occurrence of an omnidirectional elastic band gaps in one-dimensional phononic crystal structures. The structure is constituted by a periodically layered mirror deposited on a specific substrate that exhibits total reflection of waves for all incident angles and polarizations in a given frequency range. We study in this paper the influence of the nature and the filling fraction of the layered structures as well as of the substrate nature on the omnidirectional band gap. By introducing a defect piezoelectric layer in the finite size layered structure, selective resonance modes can occur within the omnidirectional bang gap under certain conditions. In this case, the elastic energy is confined to the defect layer. The frequencies of the defect modes are sensitive to the nature of the material and to the layer thicknesses. We excite the localized mode in the defect layer via interdigital transducers deposited on the substrate surface. We show a high frequency one port resonator at 4.3 GHz with high phase velocity of 43 km/s. The omnidirectional character of the band gap is crucial to confine the elastic energy in the defect layer.