Sketch of an acoustic lens based on a two-dimensional sonic crystal
and a map of the resulting sound level (in dB). The sketch is drawn
to scale. The lens-like sample measure 1.2 m of width. In this experiment,
the researchers use a sonic crystal consisting of a triangular lattice
of 4-cm-diameter cylinders, the pitch being 6.35 cm. The sound pressure
has been taken at a frequency of 1700 Hz, which is well below the first
acoustic gap that starts at 2300 Hz.
Schematic drawing of an acoustic lens using a two-dimensional sonic
crystal. The circular dots represent cylinders cross sections. The sound
velocity is independent of direction inside the crystal and one should
expect a single focal length f. Nevertheless, the actual lens shows
strong aberration effects owing to surface roughness.
Reported by: Cervera
et al., Physical Review Letters, 14 January 2002.
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