239 results found
Farhat M, Chen PY, Guenneau S, et al., 2021, Self-dual singularity through lasing and antilasing in thin elastic plates, Physical Review B, Vol: 103, ISSN: 2469-9950
We show here that a coherent perfect absorber and laser (CPAL) enabled by parity-time (PT)-symmetry breaking may be exploited to build monochromatic amplifying devices for flexural waves. The fourth-order partial differential equation governing the propagation of flexural waves in thin-elastic piezoelectric plates leads to 4×4 transfer matrices, and captures the interplay between propagating and evanescent waves that is translated into PT-symmetry properties specific to elastic plate systems. We thus demonstrate the possibility of using CPAL for such systems and we argue the possibility of using this concept to detect extremely small-scale vibration perturbation with important outcomes in surface science (imaging of nanometer vibration) and geophysics (improving seismic sensors like velocimeters). The device can also generate finite signals using very low exciting intensities and/or alternatively can be used as a perfect absorber for flexural energy, by tailoring the left and right incident wave amplitude and phase, with evident energy harvesting applications.
Ji Q, Chen X, Liang J, et al., 2021, Designing thermal energy harvesting devices with natural materials through optimized microstructures, International Journal of Heat and Mass Transfer, Vol: 169, ISSN: 0017-9310
Metamaterial thermal energy devices obtained from transformation optics have recently attracted wide attention due to their vast potential in energy storage, thermal harvesting or heat manipulation. However, these devices usually require inhomogeneous and extreme material parameters which are difficult to realize in large-scale applications. Here, we demonstrate a general process to design thermal harvesting devices with available natural materials through optimized composite microstructures. We first design a cross-shaped microstructure and apply two-scale homogenization theory to obtain its effective properties. Optimal Latin hypercube technique, combined with a genetic algorithm, is then implemented on the microstructure to achieve optimized geometrical parameters. The optimized microstructure can accurately approximate the behavior of transformed materials. We design such devices and numerically characterize good thermal energy harvesting performances. To validate the wide application range of our approach, we illustrate other types of microstructures like split rings and rectangles, and show that they mimic well the required constitutive parameters. The approach we propose can be used to design novel thermal harvesting devices available with existing technology, and can also act as a beneficial vehicle to explore other transformation opticcs enabled designs.
Tang K, Xu C, Guenneau S, et al., 2021, Pulse Dynamics of Flexural Waves in Transformed Plates, ADVANCED FUNCTIONAL MATERIALS, Vol: 31, ISSN: 1616-301X
Brûlé S, Guenneau S, 2021, Past, present and future of seismic metamaterials: Experiments on soil dynamics, cloaking, large scale analogue computer and space–time modulations, Comptes Rendus Physique, Vol: 21, Pages: 767-785, ISSN: 1631-0705
Some properties of electromagnetic metamaterials have been translated, using some wave analogies, to surface seismic wave control in sedimentary soils structured at the meter scale. Two large scale experiments performed in 2012 near the French cities of Grenoble  and Lyon  have confirmed the usefulness of this methodology and its potential influence on soil-structure interaction. We present here a new perspective on the in-situ experiment near Lyon, which unveils energy corridors in the seismic lens. We further introduce a concept of time-modulated seismic metamaterial underpined by an effective model based on Willis’s equations. As a first application, we propose that ambient seismic noise time-modulates structured soils that can be viewed as moving media. In the same spirit, a design of an analogous seismic computer is proposed making use of ambient seismic noise. We recall that ancient Roman theaters and forests of trees are two examples of large scale structures that behave in a way similar to electromagnetic metamaterials: invisibility cloaks and rainbows, respectively. Seismic metamaterials can thus not only be implemented for shielding, lensing and cloaking of potentially deleterious Rayleigh waves, but they also have potential applications in energy harvesting and analogous computations using ambient seismic noise, and this opens new vistas in seismic energy harvesting and conversion through the use of natural or artificial soil structuring.
Gralak B, Guenneau S, 2021, Foreword, Comptes Rendus Physique, Vol: 21, Pages: 311-341, ISSN: 1631-0705
Farhat M, Guenneau S, Chen P-Y, et al., 2020, Parity-Time Symmetry and Exceptional Points for Flexural-Gravity Waves in Buoyant Thin-Plates, CRYSTALS, Vol: 10, ISSN: 2073-4352
Marigo JJ, Pham K, Maurel A, et al., 2020, Effective model for elastic waves propagating in a substrate supporting a dense array of plates/beams with flexural resonances, Journal of the Mechanics and Physics of Solids, Vol: 143, ISSN: 0022-5096
We consider the effect of an array of plates or beams over a semi-infinite elastic ground on the propagation of elastic waves hitting the interface. The plates/beams are slender bodies with flexural resonances at low frequencies able to perturb significantly the propagation of waves in the ground. An effective model is obtained using asymptotic analysis and homogenization techniques, which can be expressed in terms of the ground alone with effective dynamic (frequency-dependent) boundary conditions of the Robin's type. For an incident plane wave at oblique incidence, the displacement fields and the reflection coefficients are obtained in closed forms and their validity is inspected by comparison with direct numerics in a two-dimensional setting.
Makwana M, Wiltshaw R, Guenneau S, et al., 2020, Hybrid topological guiding mechanisms for photonic crystal fibers, Optics Express, Vol: 28, Pages: 30871-30888, ISSN: 1094-4087
We create hybrid topological-photonic localisation of light by introducing concepts from the field of topological matter to that of photonic crystal fiber arrays. S-polarized obliquely propagating electromagnetic waves are guided by hexagonal, and square, lattice topological systems along an array of infinitely conducting fibers. The theory utilises perfectly periodic arrays that, in frequency space, have gapped Dirac cones producing band gaps demarcated by pronounced valleys locally imbued with a nonzero local topological quantity. These broken symmetry-induced stop-bands allow for localised guidance of electromagnetic edge-waves along the crystal fiber axis. Finite element simulations, complemented by asymptotic techniques, demonstrate the effectiveness of the proposed designs for localising energy in finite arrays in a robust manner.
Guenneau S, Zolla F, Cherkaev E, et al., 2020, Multiple scale method applied to homogenization of irrational metamaterials, Pages: 162-164
We adapt the multiple scale method introduced over 40 years ago for the homogenization of periodic structures , to the quasiperiodic (cut-and-projection) setting. We make use of partial differential operators (gradient, divergence and curl) acting on periodic functions of m variables in a higher-dimensional space that are projected onto operators acting on quasiperiodic functions in the n-dimensional physical space (mn). We replace heterogeneous quasiperiodic structures, coined irrational metamaterials in , by homogeneous media with anisotropic permittivity and permeability tensors, obtained from the solution of annex problems of electrostatic type in a periodic cell in higher dimensional space. This approach is valid when the wavelength is much larger than the period of the higher dimensional elementary cell.
Chen Y, Kadic M, Guenneau S, et al., 2020, Isotropic Chiral Acoustic Phonons in 3D Quasicrystalline Metamaterials, PHYSICAL REVIEW LETTERS, Vol: 124, ISSN: 0031-9007
Farhat M, Guenneau S, Alu A, et al., 2020, Scattering cancellation technique for acoustic spinning objects, PHYSICAL REVIEW B, Vol: 101, ISSN: 2469-9950
Pham K, Maurel A, Félix S, et al., 2020, Hybridized love waves in a guiding layer supporting an array of plates with decorative endings, Materials, Vol: 13, Pages: 1-27
This study follows from Maurel et al., Phys. Rev. B 98, 134311 (2018), where we reported on direct numerical observations of out-of-plane shear surface waves propagating along an array of plates atop a guiding layer, as a model for a forest of trees. We derived closed form dispersion relations using the homogenization procedure and investigated the effect of heterogeneities at the top of the plates (the foliage of trees). Here, we extend the study to the derivation of a homogenized model accounting for heterogeneities at both endings of the plates. The derivation is presented in the time domain, which allows for an energetic analysis of the effective problem. The effect of these heterogeneous endings on the properties of the surface waves is inspected for hard heterogeneities. It is shown that top heterogeneities affect the resonances of the plates, hence modifying the cut-off frequencies of a wave mathematically similar to the so-called Spoof Plasmon Polariton (SPP) wave, while the bottom heterogeneities affect the behavior of the layer, hence modifying the dispersion relation of the Love waves. The complete system simply mixes these two ingredients, resulting in hybrid surface waves accurately described by our model.
Makwana M, Laforge N, Craster R, et al., 2020, Experimental observations of topologically guided water waves within non-hexagonal structures, Applied Physics Letters, Vol: 116, Pages: 131603-1-131603-5, ISSN: 0003-6951
We investigate symmetry-protected topological water waves within a strategically engineered square lattice system. Thus far, symmetry-protected topological modes in hexagonal systems have primarily been studied in electromagnetism and acoustics, i.e. dispersionless media. Herein, we show experimentally how crucial geometrical properties of square structures allow for topological transport that is ordinarily forbidden within conventional hexagonal structures. We perform numerical simulations that take into account the inherent dispersion within water waves and devise a topological insulator that supports symmetry-protected transport along the domain walls. Our measurements, viewed with a high-speed camera under stroboscopic illumination, unambiguously demonstrate the valley-locked transport of water waves within a non-hexagonal structure. Due to the tunability of the energy's directionality by geometry, our results could be used for developing highly-efficient energy harvesters, filters and beam-splitters within dispersive media.
Chen Y, Frenzel T, Guenneau S, et al., 2020, Mapping acoustical activity in 3D chiral mechanical metamaterials onto micropolar continuum elasticity, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 137, ISSN: 0022-5096
Ungureanu B, Makwana M, Craster R, et al., 2020, Localising symmetry protected edge waves via the topological rainbow effect, Publisher: arXiv
We combine two different fields, topological physics and metamaterials to design a topological metasurface tocontrol and redirect elastic waves. We strategically design a two-dimensional crystalline perforated elastic platethat hosts symmetry-induced topological edge states. By concurrently allowing the elastic substrate to spatiallyvary in depth, we are able to convert the incident slow wave into a series of robust modes, with differing envelopemodulations. This adiabatic transition localises the incoming energy into a concentrated region where it can thenbe damped or extracted. For larger transitions, different behaviour is observed; the incoming energy propagatesalong the interface before being partitioned into two disparate chiral beams. This “topological rainbow” effectleverages two main concepts, namely the quantum valley-Hall effect and the rainbow effect usually associatedwith electromagnetic metamaterials. The topological rainbow effect transcends specific physical systems, hence,the phenomena we describe can be transposed to other wave physics. Due to the directional tunability of theelastic energy by geometry our results have far-reaching implications for applications such as switches, filtersand energy-harvesters.
Farhat M, Chen PY, Bagci H, et al., 2020, Scattering theory and cancellation of gravity-flexural waves of floating plates, Physical Review B, Vol: 101, ISSN: 2469-9950
We combine theories of scattering for linearized water waves and flexural waves in thin elastic plates to characterize and achieve control of water wave scattering using floating plates. This requires manipulating a sixth-order partial differential equation with appropriate boundary conditions of the velocity potential. Making use of multipole expansions, we reduce the scattering problem to a linear algebraic system. The response of a floating plate in the quasistatic limit simplifies, considering a distinct behavior for water and flexural waves. Unlike for similar studies in electromagnetics and acoustics, scattering of gravity-flexural waves results in a nonvanishing scattering cross-section in the zero-frequency limit, dominated by its zeroth-order multipole. Potential applications lie in floating structures manipulating ocean water waves.
Brule S, Enoch S, Guenneau S, 2020, Emergence of seismic metamaterials: Current state and future perspectives, PHYSICS LETTERS A, Vol: 384, ISSN: 0375-9601
Kadic M, Wegener M, Nicolet A, et al., 2020, Elastodynamic behavior of mechanical cloaks designed by direct lattice transformations, Wave Motion, Vol: 92, ISSN: 0165-2125
Steering waves in elastic solids is more demanding than steering waves in electromagnetism or acoustics. As a result, designing material distributions which are the counterpart of optical invisibility cloaks in elasticity poses a major challenge. Waves of all polarizations should be guided around an obstacle to emerge on the downstream side as though no obstacle were there. Recently, we have introduced the direct-lattice-transformation approach. This simple and explicit construction procedure led to extremely good cloaking results in the static case. Here, we transfer this approach to the dynamic case, i.e., to elastic waves or phonons. We demonstrate broadband reduction of scattering, with best suppressions exceeding a factor of five when using cubic coordinate transformations instead of linear ones. To reliably and quantitatively test these cloaks efficiency, we use an effective-medium approach.
Pomot L, Payan C, Remillieux M, et al., 2020, Acoustic cloaking: Geometric transform, homogenization and a genetic algorithm, Wave Motion, Vol: 92, ISSN: 0165-2125
A general process is proposed to experimentally design anisotropic inhomogeneous metamaterials obtained through a change of coordinates in the Helmholtz equation. The method is applied to the case of a cylindrical transformation that allows cloaking to be performed. To approximate such complex metamaterials we apply results of the theory of homogenization and combine them with a genetic algorithm. To illustrate the power of our approach, we design three types of cloaks composed of isotropic concentric layers structured with three types of perforations: curved rectangles, split rings and crosses. These cloaks have parameters compatible with existing technology and they mimic the behavior of the transformed material. Numerical simulations have been performed to qualitatively and quantitatively study the cloaking efficiency of these metamaterials.
We propose a design of cylindrical cloak for coupled in-plane shear waves consisting of concentric layers of sub-wavelength resonant stress-free inclusions shaped as Swiss rolls. The scaling factor between inclusions' sizes is according to Pendry's transform. Unlike the hitherto known situations, the present geometric transform starts from a Willis medium and further assumes that displacement fields u in original medium and u' in transformed medium remain unaffected (u' = u). This breaks the minor symmetries of the rank-4 and rank-3 tensors in theWillis equation that describe the transformed effective medium. We achieve some cloaking for a shear polarized source at specific, resonant sub-wavelength, frequencies, when it is located in close proximity to a clamped obstacle surrounded by the structured cloak. The structured medium approximating the effective medium allows for strong Willis coupling, notwithstanding potential chiral elastic effects, and thus mitigates roles ofWillis and Cosserat media in the achieved elastodynamic cloaking.
Brule S, Enoch S, Guenneau S, 2019, Role of nanophotonics in the birth of seismic megastructures, NANOPHOTONICS, Vol: 8, Pages: 1591-1605, ISSN: 2192-8606
Brûlé S, Enoch S, Guenneau S, 2019, Role of nanophotonics in the birth of seismic megastructures, Nanophotonics, Vol: 8, Pages: 1591-1605
The discovery of photonic crystals 30 years ago in conjunction with research advances in plasmonics and metamaterials, has inspired the concept of decameter scale metasurfaces, coined seismic metamaterials for an enhanced control of surface (Love and Rayleigh) and bulk (shear and pressure) elastodynamic waves. These powerful mathematical tools of coordinate transforms, effective medium and Floquet-Bloch theories which have revolutionized nanophotonics, can be translated in the language of civil engineering and geophysics. Experiments on seismic metamaterials made of buried elements in the soil demonstrate that the fore mentioned tools make a possible novel description of complex phenomena of soil-structure interaction during a seismic disturbance. But the concepts are already moving to more futuristic concepts and the same notions developed for structured soils are now used to examine the effects of buildings viewed as above surface resonators in megastructures such as metacities. But this perspective of future should not make us forget the heritage of the ancient peoples. Indeed, we finally point out the striking similarity between an invisible cloak design and the architecture of some ancient megastructures as the antique Gallo-Roman theaters and amphitheatres.
Cherkaev E, Guenneau S, Hutridurga H, et al., 2019, Quasiperiodic composites: Multiscale reiterated homogenization, Pages: X086-X088
With recent technological advances, quasiperiodic and aperiodic materials present a novel class of metamaterials that possess very unusual, extraordinary properties such as superconductivity, unusual mechanical properties and diffraction patterns, extremely low thermal conductivity, etc. As all these properties critically depend on the microgeometry of the media, the methods that allow characterizing the effective properties of such materials are of paramount importance. In this paper, we analyze the effective properties of a class of multiscale composites consisting of periodic and quasiperiodic phases appearing at different scales. We derive homogenized equations for the effective behavior of the composite and discover a variety of new effects which could have interesting applications in the control of wave and diffusion phenomena.
Huidobro PA, Galiffi E, Guenneau S, et al., 2019, Fresnel drag in space-time-modulated metamaterials, Publisher: arXiv
A moving medium drags light along with it as measured by Fizeau and explained by Einstein's theory of special relativity. Here we show that the same effect can be obtained in a situation where there is no physical motion of the medium. Modulations of both the permittivity and permeability, phased in space and time in the form of travelling waves, are the basis of our model. Space-time metamaterials are represented by effective bianisotropic parameters, which can in turn be mapped to a moving homogeneous medium. Hence these metamaterials mimic a relativistic effect without the need for any actual material motion. We discuss how both the permittivity and permeability need to be modulated in order to achieve these effects, and we present an equivalent transmission line model.
Kadic M, Diatta A, Frenzel T, et al., 2019, Static chiral Willis continuum mechanics for three-dimensional chiral mechanical metamaterials, Physical Review B, Vol: 99, ISSN: 2469-9950
Recent static experiments on twist effects in chiral three-dimensional mechanical metamaterials have been discussed in the context of micropolar Eringen continuum mechanics, which is a generalization of linear Cauchy elasticity. For cubic symmetry, Eringen elasticity comprises nine additional parameters with respect to linear Cauchy elasticity, of which three directly influence chiral effects. Here, we discuss the behavior of the static case of an alternative generalization of linear Cauchy elasticity, the Willis equations. We show that in the homogeneous static cubic case, only one additional parameter with respect to linear Cauchy elasticity results, which directly influences chiral effects. We show that the static Willis equations qualitatively describe the experimentally observed chiral twist effects, too. We connect the behavior to a characteristic length scale.
Makwana M, Craster R, Guenneau S, 2019, Topological beam-splitting in photonic crystals, Optics Express, Vol: 27, Pages: 16088-16102, ISSN: 1094-4087
We create a passive wave splitter, created purely by geometry, to engineer three-way beam splitting in electromagnetism in transverse electric and magnetic polarisation. We do so by considering arrangements of Indium Phosphide dielectric pillars in air, in particular we place several inclusions within a cell that is then extended periodically upon a square lattice. Hexagonal lattice structures are more commonly used in topological valleytronics but, as we discuss, three-way splitting is only possible using a square, or rectangular, lattice. To achieve splitting and transport around a sharp bend we use accidental, and not symmetry-induced, Dirac cones. Within each cell pillars are either arranged around a triangle or square; we demonstrate the mechanism of splitting and why it does not occur for one of the cases. The theory is developed and full scattering simulations demonstrate the effectiveness of the proposed designs.
Cherkaev E, Guenneau S, Wellander N, 2019, Forward and inverse homogenization of the electromagnetic properties of a quasiperiodic composite
The paper deals with forward and inverse homogenization of Maxwell's equations with a geometry on a microscopic scale given by a quasiperiodic distribution of piece-wise constant components defined by the use of a mapping R: reals → reals , m > n, and a periodic unit cell in R . Inverse homogenization makes use of a Stieltjes analytic representation for the effective complex permittivity, which depends upon R, unlike for the periodic case. n m m
Farhat M, Guenneau S, Chen PY, et al., 2019, Scattering Cancellation-Based Cloaking for the Maxwell-Cattaneo Heat Waves, Physical Review Applied, Vol: 11
We theoretically propose scattering cancellation-based cloaks for heat waves that obey the Maxwell-Cattaneo equation. The proposed cloaks possess carefully tailored diffusivity to cancel the dipole scattering from the object that they surround, and thus can render a small object invisible in the near and far fields, as demonstrated by full-wave finite-element simulations. Mantle heat cloaking is further analyzed and proposed to simplify the design and bring this cloaking technology one step closer to its practical implementation, with promising applications in nanoelectronics and defense-related applications.
Klotz G, Malléjac N, Guenneau S, et al., 2019, Controlling frequency dispersion in electromagnetic invisibility cloaks., Sci Rep, Vol: 9
Electromagnetic cloaking, as challenging as it may be to the physicist and the engineer has become a topical subject over the past decade. Thanks to the transformations optics (TO) invisibility devices are in sight even though quite drastic limitations remain yet to be lifted. The extreme material properties which are deduced from TO can be achieved in practice using dispersive metamaterials. However, the bandwidth over which a metamaterial cloak is efficient is drastically limited. We design and simulate a spherical cloak which takes into account the dispersive nature of relative permittivity and permeability tensors realized by plasma-like metamaterials. This spherical cloak works over a broad frequency-band even though these materials are of a highly dispersive nature. We establish two equations of state that link the eigenvalues of the permittivity and permeability tensors in every spherical cloak regardless of the geometrical transformation. Frequency dispersive properties do not disrupt cloaking as long as the equations of states are satisfied in the metamaterial cloak.
Acoustic flat lensing is achieved here by tuning a phononic array to have indefinite medium behavior in a narrow frequency spectral region along the acoustic branch in the irreducible Brillouin zone (IBZ). This is confirmed by the occurrence of a flat band along an unusual path in the IBZ and by interpreting the intersection point of isofrequency contours on the corresponding isofrequency surface; coherent directive collimated beams are formed whose reflection from the array surfaces create lensing. Theoretical predictions using a mass-spring lattice approximation of the phononic crystal (PC) are corroborated by time-domain experiments, airborne acoustic waves generated by a source with a frequency centered about 10.6 kHz, placed at three different distances from one side of a finite PC slab, constructed from polymeric spheres, yielding distinctive focal spots on the other side. These experiments evaluate the pressure field using optical feedback interferometry and demonstrate precise control of the three-dimensional wave trajectory through a sonic crystal.
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