The OmniSaw device concept (OmniSAW: Omnidirectional band gap for surface acoustic wave)

We report the theoretical evidence for the occurrence of omnidirectional elastic band gap in one-dimensional phononic crystal structures. The structure is constituted by a periodic layered deposited on a specific substrate that exhibit total reflection of waves for all incident angles and polarizations in a given frequency range the omnidirectional band gap. We present the influence of the nature and filling fraction of the layered structures as well as the substrate nature on the omnidirectional band gap. By introducing a defect piezoelectric layer, for instance AlN or ZnO, in the finite size layered structure, under certain condition a selective resonance modes occur within the omnidirectional bang gap. In this case, the elastic energy is localized in the defect layer. The frequencies of the defect modes are sensitive to the nature of the material and to the layer thicknesses. In order to excite the localized mode in the defect layer. We introduce interdigital transducers on the top of the surface. This implies the introduction of a new spatial periodicity and the reduction of the parallel wave vector in the first Brillouin zone. The omnidirectional character of the bad gap in this case is crucial to confine the elastic energy in the defect layer.