Abstract
The Dirac point and associated linear dispersion exhibited in the band structure of bound (non-radiative) acoustic surface modes supported on a honeycomb array of holes is explored. An aluminium plate with a honeycomb lattice of periodic sub-wavelength perforations is characterised by local pressure field measurements above the sample surface to obtain the full band-structure of bound modes. The local pressure fields of the bound modes at the K and M symmetry points are imaged, and the losses at frequencies near the Dirac frequency are shown to increase monotonically as the mode travels through the K point at the Dirac frequency on the honeycomb lattice. Results are contrasted with those from a simple hexagonal array of similar holes, and both experimentally obtained dispersion relations are shown to agree well with the predictions of a numerical model.
Highlights
The Dirac point and associated linear dispersion exhibited in the band structure of bound acoustic surface modes supported on a honeycomb array of holes is explored
Observed Dirac cone acoustic surface waves at the Brillouin zone corners were first reported by Torrent et al.[23], who studied the dispersion relation of an acoustically rigid surface with cylindrical cavities drilled in a honeycomb lattice using a phase-delay measurement
The presence of Dirac points in the dispersion relation of the acoustic surface waves supported by this surface was demonstrated, with comparisons made between experiment and theory
Summary
The Dirac point and associated linear dispersion exhibited in the band structure of bound (non-radiative) acoustic surface modes supported on a honeycomb array of holes is explored. Bound acoustic surface waves on sculpted surfaces arise from the interference between localised (evanescent) and propagating fields, and have been used to demonstrate applications such as super-resolution[20] and deep-subwavelength focusing[21]. On these structures, the pressure field profile decays exponentially in the direction normal to the surface, and the magnitude of momentum supported in the direction parallel to the surface significantly exceeds the momentum of sound in air. The presence of Dirac points in the dispersion relation of the acoustic surface waves supported by this surface was demonstrated, with comparisons made between experiment and theory
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