Acoustic Cloaking
Design for meta­materials that deflect sound waves

Source: “Acoustic cloaking in two dimensions: a feasible approach”
Daniel Torrent and José Sánchez-Dehesa
New Journal of Physics 10: 63015-63025

Results: Designs have been drawn up for a material that could lead to the first acoustic cloaking device. Computer models suggest that alternating layers of two types of patterned, elastic rods, called sonic crystals, would direct sound waves around an object so that they re-formed on the other side with no distortion, as if the sound waves had never encountered the object.

Why it matters: The cloak could make ships invisible to sonar and improve the acoustics of concert halls by allowing sound to pass around load-bearing columns. Buildings covered in the material would be shielded from street noise. Other researchers have designed and built materials that can cloak objects from microwaves, but they divert only particular wavelengths. The new research predicts that an acoustic cloak would shield objects from a broad spectrum of sounds, from high pitches to low.

Methods: The researchers developed computer models based on previous theoretical work and used them to simulate the movement of sound waves around acoustic cloaks with varying numbers of layers. The models showed that sound waves flow best around materials made of 200 layers of composite sonic crystals.

Next steps: The designed material would work only in two dimensions–with sound waves traveling in a plane. The researchers will extend their theoretical work, developing new designs for materials that work in three dimensions, and then build and test them.