Abstract
A sound source (3 cm in diameter) image in air, formed in the far wave zone behind a two-dimensional periodic lattice, was experimentally obtained. The lattice consisted of plane parallel rows of steel cylinders with a diameter of 1.58 cm, forming an acoustic crystal with hexagonal structure, The crystal lattice constant (a = 2.14 cm) is smaller than the emission wavelength in air (∼ 3.4 cm). The relations between the emission wavelength and lattice parameters were selected according to model calculation in the second transmission band of the crystal at its negative refractive index n = −0.7. The lateral size of the focused (over the sound pressure distribution) image of the sound source is close to the emission wavelength. A distinctive feature of the experiment is the formation of such a sharply focused image under conditions of an extremely small output aperture (the beam diameter at the acoustic crystal output did not exceed 2.5 acoustic wavelengths in air). It can be considered that the flat acoustic lens is realized. Possible explanations of the observed effect are discussed.
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Vinogradov, E.A., Babintsev, V.A., Veselago, V.G. et al. Acoustic wave focusing by two-dimensional lattice of cylinders in air. Phys. Wave Phen. 15, 126–129 (2007). https://doi.org/10.3103/S1541308X07020070
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DOI: https://doi.org/10.3103/S1541308X07020070