Analysis of bulk wave effect on harmonic admittance of periodic grating

We suggest an approximation of the effect of the surface skimming bulk wave (SSBW) on harmonic admittance of periodic grating. The approximation is valid on both sides of cut-off frequency and predicts the existence of surface-bulk hybrid mode (SBH), if such mode occurs in the grating due to SAW/SSBW interaction. As an example, parameters of approximating function were calculated for 36°X, Y+90° cut of quartz with Al grating and plotted versus metalization ratio a/p. They revealed the existence of SBH mode for a/p >0.685. The resonance frequency of additional resonance of harmonic admittance, which corresponds to this mode, was predicted with high accuracy from approximation of harmonic admittance around the cut-off frequency.