Sound focusing by gradient index sonic lenses

Climente, Alfonso; Torrent, Daniel; Sánchez‐Dehesa, José

doi:10.1063/1.3488349

Cited by 191 publications

(149 citation statements)

References 16 publications

(28 reference statements)

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“…The phase through the electronic circuit is tunable as well, and it is an additional degree of freedom usable in some applications. For example, it can be used to implement unidirectional acoustic lenses by varying the phase delay through each cell in the same way reciprocal passive metamaterial lenses are designed [1][2][3][4][5][6] .…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the extended range of material parameters provided by metamaterials has lead to the implementation of devices such as acoustic lenses [1][2][3][4][5][6] , or even exotic structures designed using coordinate transformation methods 7,8 . Recently, significant attention has been given to unidirectional devices that pass acoustic energy in only one direction [9][10][11][12][13][14][15] and therefore mimic the general behaviour of diodes in the microwave regime, and Faraday rotator media in the optical domain.…”

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confidence: 99%

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Non-reciprocal and highly nonlinear active acoustic metamaterials

2014

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Unidirectional devices that pass acoustic energy in only one direction have numerous applications and, consequently, have recently received significant attention. However, for most practical applications that require unidirectionality at audio and low frequencies, subwavelength implementations capable of the necessary time-reversal symmetry breaking remain elusive. Here we describe a design approach based on metamaterial techniques that provides highly subwavelength and strongly non-reciprocal devices. We demonstrate this approach by designing and experimentally characterizing a non-reciprocal active acoustic metamaterial unit cell composed of a single piezoelectric membrane augmented by a nonlinear electronic circuit, and sandwiched between Helmholtz cavities tuned to different frequencies. The design is thinner than a tenth of a wavelength, yet it has an isolation factor of 410 dB. The design method generates relatively broadband unidirectional devices and is a good candidate for numerous acoustic applications.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Non-reciprocal and highly nonlinear active acoustic metamaterials

2014

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“…GRIN geometries are utilized for a broad range of metamaterial applications including scattering reduction [6,7], wave focusing [8][9][10][11][12][13][14][15][16], and bending [1][2][3]17,18]. In contrast to previous lens designs, we present a lens composed of impedance-matched, hollow-shell elements with sound speeds higher than water.…”

Section: Introductionmentioning

confidence: 94%

Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

et al. 2015

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Spatial gradients in a refractive index are used extensively in acoustic metamaterial applications to control wave propagation through phase delay. This study reports the design and experimental realization of an acoustic gradient-index lens using a sonic crystal lattice that is impedance matched to water over a broad bandwidth. In contrast to previous designs, the underlying lattice features refractive indices that are lower than the water background, which facilitates propagation control based on a phase advance as opposed to a delay. The index gradient is achieved by varying the filling fraction of hollow, air-filled aluminum tubes that individually exhibit a higher sound speed than water and matched impedance. Acoustic focusing is observed over a broad bandwidth of frequencies in the homogenization limit of the lattice, with intensity magnifications in excess of 7 dB. An anisotropic lattice design facilitates a flatfaceted geometry with low backscattering at 18 dB below the incident sound-pressure level. A threedimensional Rayleigh-Sommerfeld integration that accounts for the anisotropic refraction is used to accurately predict the experimentally measured focal patterns.

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“…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. It is expected that acoustic metamaterials will continue to offer unprecedented opportunities to advance acoustic technologies.…”

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confidence: 99%

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

et al. 2014

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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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Sound focusing by gradient index sonic lenses

Cited by 191 publications

References 16 publications

Non-reciprocal and highly nonlinear active acoustic metamaterials

Non-reciprocal and highly nonlinear active acoustic metamaterials

Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

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

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