A Phononic Crystal Waveguide Using Surface Waves Below the Sound Cone

TL;DR

This paper presents a novel phononic crystal waveguide design that uses specially shaped surface inclusions to confine surface acoustic waves below the sound cone, reducing energy loss and enhancing wave confinement.

Contribution

It introduces alternative inclusion shapes with reduced symmetry to lower Rayleigh wave speed below shear horizontal modes, enabling surface confinement with minimal bulk coupling.

Findings

Wave mode confined below the sound line

Reduced energy loss due to limited bulk coupling

Strong surface and waveguide confinement demonstrated

Abstract

Surface acoustic waves are commonly used in a variety of radio-frequency electrical devices as a result of their operation at high frequencies and robust nature. For devices based on Rayleigh-like plane waves, functionality is based on the fact that the Rayleigh wave mode is confined at the solid-air interface. However, to create advanced functionality through the use of phononic crystal structures, standard cylindrical inclusions have been shown to couple Rayleigh modes to the shear horizontal bulk modes and provide a significant pathway to energy loss. We introduce alternative inclusion shapes with a reduced 2-fold symmetry that lowers the speed of the Rayleigh-like surface acoustic wave to below that of the shear horizontal mode. With an eigenfrequency below the sound line, the new mode is confined to the surface with limited coupling and loss to the bulk. Based on these inclusions, an acoustic waveguide design is proposed that demonstrates a strong confinement of wave energy both at the surface and within the waveguide.