Introduction to the special issue on active and tunable acoustic metamaterialsa)

Acoustic metamaterials are a class of architected materials with dynamic properties that are designed at the sub-wavelength scale to achieve exotic or unique macroscopic response. Although early concepts of acoustic metamaterials relied on static configurations, recent research has further expanded the limits of acoustic customization by incorporating active or tunable responses. This article provides an introduction to the special issues of The Journal of the Acoustical Society of America and JASA Express Letters on active and tunable acoustic metamaterials and begins with a brief description of the general categories of active control and tunable response included in the contributions to the special issue and, then, provides a brief description of the articles in this special issue, grouped by general category, and how the research presented in these works contribute to the advancement of acoustic metamaterial research.