Negative birefraction of acoustic waves in a sonic crystal

Abstract

Optical birefringence and dichroism are classical and important effects originating from two independent polarizations of optical waves in anisotropic crystals. Furthermore, the distinct dispersion relations of transverse electric and transverse magnetic polarized electromagnetic waves in photonic crystals can lead to birefringence more easily. However, it is impossible for acoustic waves in the fluid to show such a birefringence because only the longitudinal mode exists. The emergence of an artificial sonic crystal (SC) has significantly broadened the range of acoustic materials in nature that can give rise to acoustic bandgaps and be used to control the propagation of acoustic waves. Recently, negative refraction has attracted a lot of attention and has been demonstrated in both left-handed materials and photonic crystals. Similar to left-handed materials and photonic crystals, negative refractions have also been found in SCs. Here we report, for the first time, the acoustic negative-birefraction phenomenon in a two-dimensional SC, even with the same frequency and the same 'polarization' state. By means of this feature, double focusing images of a point source have been realized. This birefraction concept may be extended to other periodic systems corresponding to other forms of waves, showing great impacts on both fundamental physics and device applications.

Reducing the losses of optical metamaterials

“…They also include artificial dielectrics, artificial magnetic materials, and bi-isotropic and bi-anisotropic composites (such as chiral metamaterials), etc. In a more general case, metamaterials are beyond the field of electromagnetics and the idea has been introduced in the research of acoustics and seismology [31][32][33][34]. This is an example where the identification of new material parameters can prompt the development of similar concepts in similar research areas.…”

Beam paths of flexural Lamb waves at high frequency in the first band within phononic crystal-based acoustic lenses

“…Analogously to heterostructures designed to achieve negative refraction of electromagnetic waves, 1,2 PCs have been conceived in order to focus acoustic waves in a frequency range where the negative refraction is possible. [3][4][5][6][7][8] It has been proved both theoretically and experimentally that such PCs can realize the subwavelength focusing or imaging. [3][4][5][6][7][8] To a certain extent, the resolution of the focusing was beyond the diffraction limit with the evanescent waves being gathered at the focusing through the bound modes.…”

Enhanced acoustic sensing through wave compression and pressure amplification in anisotropic metamaterials

“…Over the past decade, acoustic metamaterials have been extended far beyond the scope of original negative refraction materials, and metamaterials with large values of positive or negative mass densities, bulk moduli and refractive indices have been demonstrated [15][16][17][18][19][20] . On the other hand, there have been evergrowing activities in the development of acoustic metamaterial devices, such as metamaterial imaging and lenses systems [21][22][23][24][25] , waveguide 26 , invisible cloaking [27][28][29][30][31] , sound isolators [32][33][34] and acoustic absorbers 35 , which have superior performance over their conventional counterparts.…”