Acoustic metamaterials are artificially fabricated materials designed to control, direct, and manipulate sound waves as these might occur in gases, liquids, and solids. Dr. Steven Cummer's group develops metmaterials that cover a large range of effective mass densities, bulk moduli, positive and negative refractive indexes [Xie, Y. et al, "Measurement of broadband negative index with space-coiling acoustic metamaterials", Phys. Rev. Lett. 110, 175501 (2013)], high anisotropy factors, as well as media having highly non-linear responses [LINK: Popa, B.-I. and S. A. Cummer, "Non-reciprocal and highly nonlinear active acoustic metamaterials", Nature Communications 5, 3398 (2014)]. This wealth of available material parameters is employed in a wide range of applications hard to implement using other methods. In this regard, Dr. Steven Cummer's team has demonstrated scattering reducing shells known as "acoustic cloaks" working in air over a very broad band of frequencies in the audio spectrum [L. Zigoneanu, B.-I. Popa, S.A. Cummer, "Three-dimensional broadband omnidirectional acoustic ground cloak", Nature Materials 13, 352-355 (2014)]. In addition, Dr. Cummer's group is actively pursuing metamaterial based solutions for hard acoustic imaging problems. Thus, the group is involved in the development of various types of metamaterial-based sound manipulating devices capable of not only sound focusing and extraordinary acoustic beam steering, but also having unique functionalities such as conversion from propagating to surface waves and negative refraction. These devices provide unprecedented possibilities to a variety of applicable areas ranging from underwater communication systems to medical imaging.
