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 c… Show more
“…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.…”
“…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.…”
“…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.…”
International audienceThis work deals with an analytical and numerical study of the focusing of the lowest order anti-symmetric Lamb wave in gradient index phononic crystals. Computing the ray trajectories of the elastic beam allowed us to analyze the lateral dimensions and shape of the focus, either in the inner or behind the phononic crystal-based acoustic lenses, for frequencies within a broad range in the first band. We analyzed and discussed the focus-ing behaviors inside the acoustic lenses where the focalization at sub-wavelength scale was achieved. The focalization behind the gradient index phononic crystal is shown to be efficient as well: we report on FMHM = 0.63λ at 11MHz
“…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.…”
Acoustic sensors play an important role in many areas, such as homeland security, navigation, communication, health care and industry. However, the fundamental pressure detection limit hinders the performance of current acoustic sensing technologies. Here, through analytical, numerical and experimental studies, we show that anisotropic acoustic metamaterials can be designed to have strong wave compression effect that renders direct amplification of pressure fields in metamaterials. This enables a sensing mechanism that can help overcome the detection limit of conventional acoustic sensing systems. We further demonstrate a metamaterial-enhanced acoustic sensing system that achieves more than 20 dB signal-to-noise enhancement (over an order of magnitude enhancement in detection limit). With this system, weak acoustic pulse signals overwhelmed by the noise are successfully recovered. This work opens up new vistas for the development of metamaterialbased acoustic sensors with improved performance and functionalities that are highly desirable for many applications.
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