G. Martin et al., PROPERTIES OF INTERDIGITAL TRANSDUCERS IN RELATION TO THE SUBSTRATE CRYSTAL SYMMETRY, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 43(4), 1996, pp. 646-653
Exclusively from the crystal symmetry, we obtain results concerning pr
operties of interdigital transducers radiating Rayleigh waves along hi
gh-symmetrical crystal directions. Three cases of high-symmetrical dir
ections are considered: the propagation direction is parallel to a rot
ation axis, perpendicular to a mirror plane, or parallel to a rotoinve
rsion axis of the substrate crystal. In respect to the symmetry proper
ties of the piezoelectric tensor related to a mirror operation on a pl
ane perpendicular to the propagation direction, the three original cas
es can be concentrated in three symmetry cases. The crystal symmetry d
etermines the properties of the piezoelectric tensor, and consequently
the wave excitation by transducers. These considerations enable one t
o ascertain the positions of the transduction centers and the influenc
e of internal reflections to the amplitude characteristics. Furthermor
e, we are able to discuss natural single-phase unidirectional transduc
er (NSPUDT) effects in layer structures, the old question ''crossed-fi
eld or in-line model,'' and the existence of cross-coupling of waves,
similar to multistrip couplers, in interdigital transducers (IDT's). T
he theoretical predictions are compared with our own and other authors
' experimental results.