An extremely anisotropic phononic crystal with open elliptical dispersion for energy convergence and beam squeezing

An extremely anisotropic phononic crystal with open elliptical dispersion is proposed for energy convergence and beam squeezing. The proposed crystal consists of multiple arrays of Helmholtz resonator pairs, where the Bragg scattering contributes to the negative slope and the resonance of Helmholtz resonators contributes to the extreme anisotropy with open elliptical dispersion from 4.8 kHz to 5.15 kHz. The crystal shows the negative refraction with a reduced range of refraction angles for the incident beams, giving rise to efficient energy convergence in the far-fields of the outgoing interface for acoustic waves emitted from a point source and the beam squeezing effect for divergent sound waves irradiating from a line source. The experimental results agree well with the theoretical analysis and numerical simulations. Our design may provide a potential possibility for sound manipulation, which may find usage in angular filtering and acoustic imaging.