Interface wave-modes in comb transducers

An elastic body with periodic teeth of finite height (a comb), insonified by incident ultrasonic wave and applied, with sliding contact, to the surface of another elastic body (a substrate), constitutes a typical arrangement of ultrasonic nondestructive testing system exploiting comb transducers. The arising scattering problem of incident wave on periodic voids between the teeth and the sliding teeth-substrate contact is considered in the full-wave formulation. In physical interpretation, the vibrating teeth generate surface Rayleigh wave in the substrate by the incident wave pressure exerted on the substrate. In fact, the interface waves are generated which differ from the Rayleigh wave in both the propagation velocity and the wave-mode shape. These interface waves, their velocity and modal shape are the main subject of this paper; an approximated formula is presented for the relation between the most important Bloch components of interface modes in the considered periodic system.