A network model for arbitrarily oriented IDT structures

The network model approach given by E. L. Adler et al. (IEEE Trans. Ultrason. Ferroelec. Freq. Contr., vol.38, no.3, pp.220-230, May 1991) for analyzing arbitrarily oriented short-circuited surface acoustic wave (SAW) grating structures is extended to include interdigital transducers (IDTs) which are also arbitrarily oriented. The IDT structure is divided into cells, each modeled by a sequence of mismatched transmission lines consisting of metallized and unmetallized regions. The model includes: (1) the impedance difference between metallized and free regions, the reflection coefficient at the metallization upstep, the reflection coefficient in the reverse direction at the downstep (all deduced from the Datta-Hunsinger perturbation formula); (2) the velocity difference between the free and metallized regions obtained using the SAW propagation calculation software of Adler et al. for arbitrarily oriented multilayers; and (3) the energy storage susceptance at each finger discontinuity. This model permits good physical insight into the structure´s characteristics and allows simple procedures for finding high directivity (so-called NSPUDT) orientations. This unit-cell-based arbitrarily oriented IDT model applies to any desired IDT geometry