Evidences of evanescent Bloch waves in Phononic Crystals

TL;DR

This paper demonstrates both experimentally and theoretically the evanescent behavior of modes within the band gap of finite phononic crystals, highlighting their importance for designing wave filters and guides.

Contribution

It provides the first combined experimental and numerical analysis of evanescent modes in phononic crystal band gaps, validating the complex band structure approach.

Findings

Good agreement between experimental and numerical imaginary wave vectors

Evanescent behavior observed in localized defect modes

Implications for designing phononic crystal-based filters and waveguides

Abstract

We show both experimentally and theoretically the evanescent behaviour of modes in the Band Gap (BG) of finite Phononic Crystal (PC). Based on experimental and numerical data we obtain the imaginary part of the wave vector in good agreement with the complex band structures obtained by the Extended Plane Wave Expansion (EPWE). The calculated and measured acoustic field of a localized mode out of the point defect inside the PC presents also evanescent behaviour. The correct understanding of evanescent modes is fundamental for designing narrow filters and wave guides based on Phononic Crystals with defects.