Acoustic imaging and collimating by slabs of sonic crystals made from   arrays of rigid cylinders in air
  We show some new properties of the acoustic propagation in two-dimensional sonic crystals, formed by parallel rigid cylinders placed in air. The transmission through slabs of sonic crystals and the associated band structures are considered. It is shown that within partial bandgaps, the waves tend to be collimated or guided into the direction in which the propagation is allowed. Such a feature also prevails in the situations in which deaf bands appear. We show that within the partial bandgaps, a stable imaging effect can be obtained for flat sonic crystal slabs, in analogy to the cases with photonic crystals. 
Liang-Shan Chen, Chao-Hsien Kuo, Zhen Ye