A One-Way Wall of Silence

In a previous entry I highlighted this work. Here is another citation of it [http://www.sciencemag.org/content/331/6022/twil.full?sa_campaign=Email/toc/3316022twil]:

The recent development of metamaterials and photonic crystals has provided a route to control the propagation of electromagnetic waves through the engineered structure of a material. Combined with transformation optics, such control is rewriting the expected rules of behavior governing the propagation of electromagnetic waves, and offers myriad possibilities ranging from imaging to communications and stealth applications. Sound is also a wave, and so the manipulation of acoustic waves may be expected to carry over by analogy to their electromagnetic counterparts. Li et al. present a sonic crystal composed of a periodic array of steel rods, the geometry of which was selected to give rise to a band gap, whereby the transmission of sound waves in a specific frequency range is prohibited in one direction but allowed in the opposite direction. The authors also show that by mechanically changing the spacing of the array (by rotating the square steel rods), the diode-like behavior can be switched on and off. A range of applications might be expected to follow, from acoustic isolation and filtering to ultrasound imaging.

Phys. Rev. Lett. 106, 84301 (2011).