  A lattice model is developed to describe the mechanical displacement of and
current through each electrode of a surface acoustic wave (SAW) interdigitated
tranducer (IDT). Each electrode of an IDT is treated as a mass connected
mechanically to its neighbors with a spring and electrically with a capacitor.
Simulations for the electrical admittance of a typical SAW IDT are performed
and compared with the results of an accurate finite element method simulation.
The utility of this lattice model is demonstrated by simulating the admittance
of an IDT structure known as a hiccup resonator, which has a mode in the center
of the band gap. It is shown here that this mode is a topologically protected
edge state described by the 1D Su-Schrieffer-Heeger (SSH) model. Hiccup
resonators have been used in commercial products for decades, and as such it
may considered the first mass-produced topological mechanical metamaterial.
