A sound wave travelling in water is scattered by a periodic assembly of air bubbles. The local structure matters even in the low frequency regime. If the bubbles are arranged in a face-centered cubic (fcc) lattice, a total bandgap opens near the Minnaert resonance frequency. If they are arranged in the diamond structure, which one obtains by simply adding a second bubble to the unit cell, one finds an additional branch with a negative slope (optical branch). For a single specific frequency, the medium behaves as if its refractive index (relative to water) is exactly . We show that a slab of this material can be used to design a three-dimensional flat lens. We also report super-resolution focusing in the near field of the slab and illustrate its potential for imaging in three dimensions.
Three-dimensional acoustic lensing with a bubbly diamond metamaterial
Maxime Lanoy, Fabrice Lemoult, Geoffroy Lerosey, Arnaud Tourin, Valentin Leroy, John H. Page; Three-dimensional acoustic lensing with a bubbly diamond metamaterial. J. Appl. Phys. 28 June 2021; 129 (24): 245107. https://doi.org/10.1063/5.0046090
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