Dear Colleagues,

Phononic crystals are periodic structures for phonons or acoustic/elastic waves, resembling macroscopic analogs of the crystalline structures for electrons. Due to the artificial periodicity and the freedom of design, dispersion can be manipulated on demand, offering many possibilities for sound wave propagation management. Phenomena not found in conventional matter, such as the formation of band gaps, negative refraction, beam self-collimation, subwavelength imaging, localization, waveguiding, and many others, have been exhaustively studied.

Recent trends in this field are oriented towards the discovery of new physical phenomena, and concepts such as nonlinearity, causality and non-hermiticity, reciprocity, and others, find a unique physical frame in phononic systems, and pave the way for new interesting potential applications, such as topological insulation, energy harvesting, or perfect absorption.

On the other hand, the inclusion of local resonances in periodic systems has opened new approaches to wave manipulation. Phononic materials behave then as metamaterials, with the ability to manipulate waves also in the deep subwavelength regime.

This Special Issue provides a unique forum for the discussion and presentation of recent advances in the fields of research related to phononic crystals and metamaterials. Scientists working in this broad field are invited to present their work in this Issue, related to (but not limited to) the following topics:

• Linear and nonlinear wave propagation in periodic structures;
• Acoustic/elastic metamaterials and phononic crystals;
• Acoustic/elastic metasurfaces;
• Acoustic/elastic meta-devices based on transformation acoustics, parity-time symmetric acoustics, topological acoustics;
• Novel physical concepts for harnessing acoustic/elastic waves;
• New applications of metamaterial-based functional devices for acoustic sensing, cloaking, imaging, absorption, and energy harvesting;
• Non-reciprocal manipulation of acoustic/elastic waves.

Dr. Victor J. Sanchez-Morcillo
Dr. Noe Jiménez
Dr. Alejandro Cebrecos
Guest Editors

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• phononic crystals
• metamaterials
• metasurfaces