Broad-angle negative reflection and focusing of elastic waves from a plate edge

Veres, István A.; Grünsteidl, Clemens; Stobbe, David M.; Murray, Todd W.

doi:10.1103/physrevb.93.174304

Cited by 16 publications

(6 citation statements)

References 35 publications

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“…In a pionneering experiment, few years ago, Germano et al showed that this conversion from forward to backward Lamb waves also occurs at a simple free edge of an elastic plate, giving rise to negative reflection [18]. More recently, in a concurrent study by Veres et al , the negative reflection of Lamb waves has been investigated above the ZGV resonance through numerical simulations and laser-ultrasound experiments [19].…”

Section: Introductionmentioning

confidence: 99%

Negative reflection of Lamb waves at a free edge: Tunable focusing and mimicking phase conjugation

Gérardin

Laurent

Prada

et al. 2016

The Journal of the Acoustical Society of America

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The paper studies the interaction of Lamb waves with the free edge of a plate. The reflection coefficients of a Lamb mode at a plate free edge are calculated using a semi-analytical method, as a function of frequency and angle of incidence. The conversion between forward and backward Lamb modes is thoroughly investigated. It is shown that, at the zero-group velocity (ZGV) frequency, the forward S1 Lamb mode fully converts into the backward S 2b Lamb mode at normal incidence. Besides, this conversion is very efficient over most of the angular spectrum and remains dominant at frequencies just above the ZGV-point. This effect is observed experimentally on a Duralumin plate. Firstly, the S1 Lamb mode is selectively generated using a transducer array, secondly the S 2b mode is excited using a single circular transducer. The normal displacement field is probed with an interferometer. The free edge is shown to retro-focus the incident wave at different depths depending on the wave number mismatch between the forward and backward propagating modes. In the vicinity of the ZGV-point, wave numbers coincide and the wave is retro-reflected on the source. In this frequency range, the free edge acts as a perfect phase conjugating mirror.

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Section: Introductionmentioning

confidence: 99%

Negative reflection of Lamb waves at a free edge: Tunable focusing and mimicking phase conjugation

Gérardin

Laurent

Prada

et al. 2016

The Journal of the Acoustical Society of America

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“…The randomly disordered slab can therefore act as a band gap material. The observation of such super-focusing phenomena would require an experiment with an extremely fine frequency tuning 42 . Moreover, it should also involve a non-invasive point-like source capable of a selective excitation of the forward or backward mode.…”

Section: Discussionmentioning

confidence: 99%

“…NR is therefore a very general phenomenon and this work can be, in principle, transposed to all the aforementioned systems. In this article, we have chosen to consider the NR of elastic waves in plates because they provide an excellent platform to investigate negative refraction [38][39][40] and reflection [41][42][43] . Indeed, laser interferometry allows to probe the wave-field over the whole plate surface with an excellent spatial, temporal and spectral resolution.…”

Section: Introductionmentioning

confidence: 99%

Negative reflection of elastic guided waves in chaotic and random scattering media

Gérardin

Laurent

Legrand

et al. 2019

Sci Rep

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The propagation of waves in complex media can be harnessed either by taming the incident wave-field impinging on the medium or by forcing waves along desired paths through its careful design. These two alternative strategies have given rise to fascinating concepts such as time reversal or negative refraction. Here, we show how these two processes are intimately linked through the negative reflection phenomenon. A negative reflecting mirror converts a wave of positive phase velocity into its negative counterpart and vice versa. In this article, we experimentally demonstrate this phenomenon with elastic waves in a 2D billiard and in a disordered plate by means of laser interferometry. Despite the complexity of such configurations, the negatively reflected wave field focuses back towards the initial source location, thereby mimicking a phase conjugation operation while being a fully passive process. The super-focusing capability of negative reflection is also highlighted in a monochromatic regime. The negative reflection phenomenon is not restricted to guided elastic waves since it can occur in zero-gap systems such as photonic crystals, chiral metamaterials or graphene. Negative reflection can thus become a tool of choice for the control of waves in all fields of wave physics.

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“…Such zero group velocity (ZGV) points exhibit a strong resonance that can be efficiently generated with a laser excitation source, and they have been used for a variety of applications in the nondestructive evaluation of materials [5][6][7][8][9]. In addition, it has been demonstrated that the mode conversion between backward and forward propagating Lamb waves at a thickness step in a plate or at a plate edge gives rise to non-intuitive effects such as negative refraction and negative reflection [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Conical dispersion of Lamb waves in elastic plates

Stobbe

Murray

2017

Phys. Rev. B

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Guided elastic waves in homogeneous isotropic plates exhibit conical dispersion at zero wavenumber for discrete values of Poisson's ratio where accidental degeneracy between longitudinal and transverse thickness resonances occur. Waves excited at the coincidence frequency have the infinite phase velocity associated with thickness mode resonances, but the group velocity remains finite. This leads to propagating waves that oscillate in time but are spatially uniform over the plate surface. Here, accidental degeneracy is induced in an aluminum plate by cooling the plate to tune the Poisson's ratio through the degenerate point. We measure linear dispersion in the transition from forward to backward propagating waves near zero wavenumber. In addition, we demonstrate that waves generated near the coincidence frequency exhibit spatially uniform phase over the plate surface, and show angle independent mode conversion upon encountering the free edge of the plate. We propose that elastic plates offer a simple system to explore the physics of conical dispersion at zero wavenumber, and that this phenomena may find application in acoustic devices and nondestructive testing.

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Broad-angle negative reflection and focusing of elastic waves from a plate edge

Cited by 16 publications

References 35 publications

Negative reflection of Lamb waves at a free edge: Tunable focusing and mimicking phase conjugation

Negative reflection of Lamb waves at a free edge: Tunable focusing and mimicking phase conjugation

Negative reflection of elastic guided waves in chaotic and random scattering media

Conical dispersion of Lamb waves in elastic plates

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