Dispersion characteristics versus strip thickness and material of SAW propagating under a periodic metal grating on GaAs substrate

Dispersion characteristics of SAW under a periodic metal grating on a GaAs substrate is studied based on the full impedance approach we presented at the 2002 IEEE Ultrasonics Symposium. Grating mode dispersion curves are calculated for the GaAs substrate coated with either a continuous uniform thin film or a discrete periodic array, taking into account both electrical and mechanical effects of the metallic strips system. Our numerical results show that stop band width increases in nearly direct proportion with the strip thickness (h/p) increase and, for h/p value higher than a certain limit, the stop band becomes independent of whether the grating is electrically open or shorted. Far from the stop band, SAW velocity can be either increased or decreased, depending essentially on the material of the grating which behaves like a uniform layer with a certain mean thickness. The decisive factor affecting the numerical accuracy is the number of space harmonics included in computations. The minimum number that is necessary varies from 6 to 12 depending on the strip material and as a function of h/p.