The acoustic "sisters" of electromagnetic invisibility cloaks are long-sought devices that could defeat sonars. Unlike optical cloaks, such devices are not constrained by special relativity and could operate in a very wide frequency range. The existence of two types of acoustic waves in elastic media, however, makes acoustic cloaks difficult to build from solid materials. The paper by Yaroslav Urzhumov and co-workers, published recently in the New Journal of Physics (July 12, 2010), is the first report on the feasibility of an elastic cloak made of common materials. A new paradigm for designing acoustical and optical cloaking transformations with a given composite material is introduced, and exemplified with a layered composite material. On November 16, the article has been selected for inclusion in IOP Select, a special collection of articles recognized as significant or influential breakthroughs; it is free to read through November 2011.
Acoustic cloaking transformations from attainable material properties, Urzhumov, Yaroslav A., Ghezzo F., Hunt J., and Smith D. R. , New Journal of Physics, 07/2010, Volume 12, Number 7, p.073014, (2010).