Phononic crystals and acoustic metamaterials are periodic structures whose effective properties can be tailored at will to achieve extreme control on wave propagation. Their refractive index is obtained from the homogenization of the infinite periodic system, but it is possible to locally change the ...
Huang, Acoustic beamwidth compressor using gradient-index phononic crystals, Journal of Physics D: Applied Physics, 42 (2009) 185502.Z. C. S. Lin, B. R. Tittmann, J. H. Sun, T. T. Wu and T. J. Huang, “Acoustic beamwidth compressor using gradient-index phononic crystals”, J. ...