Flat lens for pulse focusing of elastic waves in thin plates

Dubois, Marc; Farhat, Mohamed; Bossy, Emmanuel; Enoch, Stefan; Guenneau, Sébastien; Sebbah, Patrick

doi:10.1063/1.4818716

Cited by 89 publications

(59 citation statements)

References 38 publications

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“…Lee et al 24 conducted NR experiments with guided shear-horizontal waves in a thin PC plate with unit cell size E0.63 l at 210-260 kHz. Dubois et al 25 investigated elastic wave propagation in a thin PC plate with circular perforated air holes. The lattice constant is 0.34 l at 10 kHz and the dispersion band is used to generate NR and achieve focusing.…”

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confidence: 99%

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial

et al. 2014

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Negative refraction of elastic waves has been studied and experimentally demonstrated in three-and two-dimensional phononic crystals, but Bragg scattering is impractical for low-frequency wave control because of the need to scale the structures to manageable sizes. Here we present an elastic metamaterial with chiral microstructure made of a single-phase solid material that aims to achieve subwavelength negative refraction of elastic waves. Both negative effective mass density and modulus are observed owing to simultaneous translational and rotational resonances. We experimentally demonstrate negative refraction of the longitudinal elastic wave at the deep-subwavelength scale in the metamaterial fabricated in a stainless steel plate. The experimental measurements are in good agreement with numerical simulations. Moreover, wave mode conversion related with negative refraction is revealed and discussed. The proposed elastic metamaterial may thus be used as a flat lens for elastic wave focusing.

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confidence: 99%

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial

et al. 2014

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“…In this vein, a flat lens was experimentally demonstrated around 10 kHz using anomalous dispersion in a duraluminium plate with a square array of circular air holes [5]. This work is reminiscent of negative refraction observed for Lamb waves in a silicon plate with air inclusions [6].…”

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confidence: 74%

Experiments on Maxwell's fish-eye dynamics in elastic plates

Lefebvre

Dubois

Beauvais

et al. 2015

Applied Physics Letters

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We experimentally demonstrate that a Duraluminium thin plate with a thickness profile varying radially in a piecewise constant fashion as h(r) = h(0)(1 + (r/Rmax)2 ) 2 , with h(0) = 0.5 mm, h(Rmax) = 2 mm and Rmax = 10 cm behaves in many ways as Maxwell's fish-eye lens in optics, since its imaging properties for a Gaussian pulse with central frequencies 30 kHz and 60 kHz are very similar to those predicted by ray trajectories (great circles) on a virtual sphere (rays emanating from the North pole meet at the South pole). However, refocusing time depends on the carrier frequency as a direct consequence of the dispersive nature of flexural waves in thin plates. Importantly, experimental results are in good agreement with FiniteDifference-Time-Domain simulations.

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“…For example, negative-index complementary metamaterials are proposed to significantly enhance the transparency through aberrating materials [30]. Superfocusing from a flat lens geometry was recently explored in elastic plates where pulsed excitation is demonstrated to significantly improve the focal resolution below the diffraction limit [31,32]. Given that this technique relies on the interference of resonant lattice modes in the time domain, it should be readily applicable to flatfaceted acoustic lenses similar to our design.…”

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confidence: 99%

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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Flat lens for pulse focusing of elastic waves in thin plates

Cited by 89 publications

References 38 publications

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial

Experiments on Maxwell's fish-eye dynamics in elastic plates

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

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