Asymmetry of Acoustic Wave Propagation in Layered Structures

Layered structures widely used today as substrates for surface acoustic wave (SAW) devices are characterized by asymmetry of wave propagation, which manifests itself as variation of SAW or leaky SAW characteristics and admittance function of SAW resonators built on these substrates with inversion of propagation direction or interchange of top/bottom surfaces in one of combined materials. In this paper, matrix formalism known as an effective tool for theoretical and numerical investigation of acoustic wave propagation in multilayered structures is used to explain the existence of asymmetry in the behavior of acoustic waves. This phenomenon is illustrated by two examples of layered structures using different types of acoustic waves and previously reported as promising substrates for SAW devices with improved performance.