Abstract
Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre.
Highlights
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not
We report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre
This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source
Summary
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. We report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Metamaterials with negative effective mass density and bulk modulus were experimentally developed using locally resonant sonic crystal[1] and Helmholtz resonators[2], respectively These materials are called single negative materials as only one of their parameters is negative. While single zero materials have been explored both in electromagnetic (epsilon near zero)[22,23,24,25] and acoustic metamaterials (density near zero)[26,27,28,29], these media suffer from low-transmission the impedance of due to an a material impedance is given by
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