Dispersion of Lamb Waves Propagating Under a Periodic Metal Grating in AlN Plates

Dispersion of Lamb waves propagating in AlN plates with a periodic Al grating on the top surface and an Al electrode on the bottom surface is investigated using the numerical technique SDA-FEM-SDA. The structures of typical Lamb waves are examined via visualization of the instantaneous displacement fields in the AlN plate. The mechanism of building hybrid modes, which arise from intermode coupling between the counter-propagating Lamb waves of different symmetry and order, is illustrated by the mode propagating with wavelength lambda = 3p, where p is the pitch of the grating.