Acoustic waveguiding by pliable conduits with axial cross sections as linear waveguides in two-dimensional sonic crystals

Abstract

Pliable conduits composed of periodically arranged concentric aluminum tori in air, with their axial cross sections acting as linear waveguides in two-dimensional sonic crystals, are numerically shown to guide acoustic waves in three dimensions in a flexible manner. Waveguide band structures are obtained by exploiting axial symmetry in a super-cell approach through two-dimensional finite-element simulations under the periodic boundary conditions. One isolated band having a bandwidth of 19.66% or 10.10% is observed for each guide, whose cross section is either in square or triangular geometry, respectively. Corresponding mode profiles indicate efficient guiding, as the acoustic energy is mainly concentrated in the hollow-core region of the guides. Transmittance spectra calculated through finite-element simulations are in agreement with the computed guiding bands. Transmittance along the waveguides with square and triangular axial cross sections around mid-band frequencies of their guiding bands varies slightly from -6.05 and -6.65 dB to -5.98 and -8.86 dB, respectively, as the guide length is increased from 10 to 200 periods. Efficient guiding across the smooth bends over circular arcs up to 90 deg is also demonstrated through three-dimensional finite-element method simulations.

Sharp bends of phononic crystal surface modes

“…Moreover, gradient-index PnCs, in which the effective index over the PnC is a function of position, can also be used to steer acoustic waves by 90 degrees through a smooth bend by gradually rotating anisotropic scatterers [19] or gradually varying the scatterer sizes across the bend [20]. A more recent approach facilitates wave transmission between two arbitrary points through smooth bends of radially symmetric PnCs where low-loss transmission up to a 180 degree bend is demonstrated [21].…”

Acoustical routing based on diffraction inhibition in two-dimensional sonic crystal

“…5) Cicek et al extended this effect to 3D scenarios to guide acoustic waves in a flexible manner. 6) The sub-diffraction (or self-collimation) effect, namely suppressing the diffraction of light, has been carried out in 2D photonic crystals, 7) which also exist in 2D SCs. Víctor et al first demonstrated the self-collimation propagation of sound beams in a 2D SC.…”