The discussion article [1] written by Professor Brian Mace provides complementary analysis of several aspects of the dynamics of phononic materials and structures and an insightful perspective on some of the intriguing concepts. We hope that between the two articles, the original review [2] and the discussion, the reader will not only find a broad and in-depth overview of the field but also be stimulated by the rich underlying dynamics inherent in these systems and the vast possibilities they present for future research. In this brief note, we provide further commentary on a few topics mentioned in Ref. [1], especially those that often emerge in discussions of the peculiar dynamics of phononic crystals and metamaterials.
The notions of “negative group velocity” and “negative mass” (and, similarly, “negative stiffness”) are commonly referred to among the unusual properties of locally resonant metamaterials. In Ref. [1...
