Spectral flow of a localized mode in elastic media
Résumé
The introduction of structural defects in otherwise periodic media is well known to grant space control and localization of waves in several fields of physics, from electromagnetism to acoustics and elasticity. Despite the variety of designs proposed so far to achieve mode localization, most of the approaches derive from contextual modifications that do not translate into a design paradigm due to the lack of a general theory. Few exceptions include designs endowed with topological dispersion bands, which, however, require changes over substantial portions of the structure. To overcome these limitations, here we introduce a rationale inspired by fractional electronic charges, to achieve topologically protected localized modes in continuous elastic media. We theoretically predict and experimentally observe the spectral flow of a localized mode across a bulk frequency gap by modulating a single structural parameter at any chosen location of architectured elastic media. The simplicity and generality of this approach may open avenues in designing elastic-wave-based devices for energy localization and harvesting.