Extraordinary Sound Transmission through Density-Near-Zero Ultranarrow   Channels
  We introduce the acoustic equivalent of 'supercoupling' by studying the anomalous sound transmission and uniform energy squeezing through ultranarrow acoustic channels filled with zero-density metamaterials. We propose their realization by inserting transverse membranes with a subwavelength period along the channel, and we prove a novel form of acoustic tunneling based on impedance matching and infinite phase velocity at the zero-density operation. We envision applications in sensing, noise control, cloaking and energy harvesting. 
Romain Fleury, Andrea Alu
cond-mat.mtrl-sci physics.class-ph