Guidance of surface elastic waves along a linear chain of pillars

Mohammed Al Lethawe,Abdelkrim Khelif,Sarah Benchabane,Mahmoud Addouche,Vincent Laude

doi:10.1063/1.4972552

Abstract

The propagation of surface elastic waves, or surface phonons, is considered along a linear and periodic chain of cylindrical pillars sitting on a semi-infinite solid substrate. A variety of guided modes, some of them exhibiting a very low group velocity, are shown to exist at frequencies close to the resonance frequencies of the pillars. Although the pillar diameter is typically smaller than half the relevant wavelength, lateral radiation on the surface is found to be canceled. Surface guidance is explained by the hybridization of the resonating pillars with the continuum of elastic waves of the substrate.

Highlights

The problem of guiding elastic waves or acoustic phonons along a surface is of great fundamental and practical interest
Surface acoustic wave (SAW) devices are for instance widely used for analog radiofrequency signal processing in modern telecommunication systems
Waveguides relying on a local resonance of a 2D lattice of pillars on a surface have been demonstrated.[5,6,7,8,9,10]. In both types of phononic crystal waveguides, though guidance is obtained inside a defect the width of which is smaller than the wavelength, the full structure still has to cover a larger part of the surface as a minimal number of phononic crystal layers have to be present on both sides of the waveguide to ensure wave confinement

Summary

INTRODUCTION

The problem of guiding elastic waves or acoustic phonons along a surface is of great fundamental and practical interest. Surface acoustic wave (SAW) devices are for instance widely used for analog radiofrequency signal processing in modern telecommunication systems These devices usually rely on the use of Rayleigh waves or other types of surface guided waves traveling on a homogeneous surface that only provide guidance for straight-crested waves propagating in very large beams. We especially discuss this structure as a waveguide for surface phonons. Simulations performed on a chain of finite size show that the elastic energy can be strongly trapped in the pillars, resulting in an enhancement of the total displacement compared to the one obtained at the homogeneous substrate surface

DISPERSION OF GUIDED SURFACE PHONONS

LEAKAGE IN THE RADIATIVE REGION

GUIDANCE ALONG A FINITE CHAIN OF PILLARS

CONCLUSION