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SAW interdigitated transducers as topological mechanical metamaterial

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.