Hybrid surface-bulk mode in periodic gratings

We report on a SAW/BAW hybrid mode (SBH), which arises from surface skimming bulk wave due to the trapping of its energy by a counter-propagating surface wave (SAW) or leaky surface wave (LSAW), in periodic grating structures. The SBH is the result of an interaction between surface and bulk waves and exists within limited frequency region, outside which it is decomposed into counterpropagating SAW and BAW. Different examples of SBH mode illustrate interactions of BAW with pure SAW, leaky and high-velocity leaky waves. The behavior of the SBH mode was numerically investigated using the harmonic admittance function. Calculation of velocity dispersion revealed the existence of an additional branch of the dispersion curve, which refers to the SBH mode. A stopband occurs due to SAW/BAW interaction and manifests itself by a resonance of harmonic admittance at its lower edge, which can be considered as the cut-off frequency of bulk wave radiation.