arXiv subjects

Vincent Laude

Publications and source records attributed to Vincent Laude.

At least 19 recordsLinked to original sources

arXiv2025

Identifying bound states in the continuum by their boundary sensitivity

We introduce a method for effectively identifying bound states in the continuum (BICs) - notably without computing the imaginary part of the eigenvalues - thereby simplifying the modeling and potentially reducing computation time. In real, open, physical systems, wave decay must be taken into account. This phenomenon is captured by complex-valued solutions of the harmonic wave equation, the so-called quasi-normal modes (QNMs). BICs, however, constitute a limiting class of solutions that do not radiate energy to infinity and are therefore, by their very nature, insensitive to the region surrounding the physical structure. Building on this observation, we identify BICs by varying the external boundary conditions that close the computational domain; the resulting behavior is displayed in the form of spectral histograms. We demonstrate the effectiveness of this procedure by comparing it with conventional QNM analysis employing perfectly matched layers. Two representative examples are considered: a periodic system of permeable inclusions supporting guided Rayleigh-Bloch waves, and a whispering-gallery resonator constructed from this configuration. Finally, we provide a mathematical explanation for the method's validity by deriving integral reciprocity statements.

physics.class-ph↗

arXiv2025

Metamaterials and Fluid Flows

Understanding and controlling the dynamic interactions between fluid flows and solid materials and structures-a field known as fluid-structure interaction -is central not only to established disciplines such as aerospace and naval engineering but also to emerging technologies such as energy harvesting, soft robotics, and biomedical devices. In recent years, the advent of metamaterials-rationally designed composites with properties beyond their constituents, often not found in conventional materials-has provided exciting opportunities for rethinking and redesigning fluid-structure interaction. The premise of engineering the internal structure of materials interfacing with fluid flows is opening a new horizon for precise and effective manipulation and control of coupled fluidic, acoustic, and elastodynamics responses. This review focuses on this relatively unexplored interdisciplinary theme with broad real-world technological significance. Key performance metrics, such as fuel consumption of transport systems, efficiency of renewable energy extraction, mitigation of noise emissions, and resilience to structural fatigue, depend on the control of interactions between flow, acoustic, and vibration mechanisms. Flow control, for example, which spans a wealth of regimes such as laminar, transitional, turbulent, and unsteady separated flows, is highly influenced by the ability to tailor fluid-structure interaction behavior. We survey and discuss theoretical frameworks that describe the interplay between fluids and elastic solids, with a focus on contemporary work and emerging concepts. The paper is organised into three main sections-flow-structure interactions, acoustic-structure interactions, and exotic metamaterial concepts with potential impact on fluid-structure interaction-and concludes with perspectives on current challenges and future directions in this rapidly expanding area of research.

cond-mat.soft↗

arXiv2025

Complex dispersion relation of Rayleigh-Bloch waves trapped by slow inclusions

Rayleigh-Bloch waves are guided acoustic waves propagating along a periodic line of inclusions placed inside an open, infinite medium. Below the sound cone, they are transversely evanescent on both sides of the line of inclusions. Guidance is then achieved without any cladding surrounding the segmented core. Inclusions usually impose definite boundary conditions, resulting in a single guided band. We consider instead the case of permeable, slow inclusions inside a fast medium. Introducing the concept of guided quasi-normal modes, we obtain the complex dispersion relation taking into account radiation at infinity. We thus show that multiple bands of leaky Rayleigh-Bloch waves appear and that guided bound states in the continuum arise as a result of the combination of symmetry and periodicity.

physics.gen-ph↗

arXiv2025

Strong shape-dependent intensity of inelastic light scattering by gold nanocrystals

We present a numerical approach to calculate inelastic light scattering spectra from gold nanocrystals, based on the finite element method. This approach is validated by comparison with previous analytic calculations for spherically symmetric scatterers. Superellipsoid nanocrystals are considered in order to smoothly vary the shape from octahedra to cubes via spheres, while preserving cubic symmetry. Spectra are calculated and discussed taking into account the irreducible representation of the involved vibration modes. A strong increase in the inelastically scattered light intensity is observed for small variations of the shape around the sphere. This increase is related to variations of the electric field inside the nanocrystals, which are very small for small nanospheres but increase quickly for non-spherical nanocrystals. This strong dependence with shape must be taken into account when interpreting experimental spectra acquired from inhomogeneous ensembles of nanocrystals whose shape dispersion are usually neglected. The overall changes in the spectra when varying the shape of the nanocrystals provide additional insight into previously published results. Preliminary calculations for chiral shapes further show a significant difference between spectra obtained with right or left circularly polarized light.

cond-mat.mes-hall↗

arXiv2024

Pumping with Symmetry

Re-configurable materials and meta-materials can jump between space symmetry classes during their deformations. Here, we introduce the concept of singular symmetry enhancement, which refers to an abrupt jump to a higher symmetry class accompanied by an un-avoidable reduction in the number of dispersion bands of the excitations of the material. Such phenomenon prompts closings of some of the spectral resonant gaps along singular manifolds in a parameter space. In this work, we demonstrate that these singular manifolds can carry topological charges. As a concrete example, we show that a deformation of an acoustic crystal that encircles a p11g-symmetric configuration of an array of cavity resonators results in an adiabatic cycle that carries a Chern number in the bulk and displays Thouless pumping at the edges. This points to a very general guiding principle for recognizing cyclic adiabatic processes with high potential for topological pumping in complex materials and meta-materials, which rests entirely on symmetry arguments.

cond-mat.mtrl-sci↗

arXiv2022

Quasinormal mode representation of radiating resonators in open phononic systems

Open phononic systems including resonators radiating inside an unbounded medium support localized phonons characterized by a complex frequency. In this context, the concept of elastic quasinormal mode (QNM) arises naturally, as in the cases of nanophotonic and plasmonic open systems. Based on a complex, unconjugated form of reciprocity theorem for elastodynamics, the eigenfunction expansion theorem expressed on the elastic QNM basis yields an accurate approximation to the response function, for an arbitrary excitation. The description of the elastic Purcell effect then requires defining a complex-valued modal volume for each QNM. For validation, we first consider the case a vibrating nylon rod radiating in water. As a second test example, we consider a slender nickel ridge on the surface of a fused silica substrate, before extending our attention to a nanoscale tuning fork composed of two such ridges. In all cases, the response estimated from only a few elastic QNMs agrees with the solution to the elastodynamic equation.

physics.class-ph↗

arXiv2022

Topological waves guided by a glide-reflection symmetric crystal interface

A domain wall separating two different topological phases of the same crystal can support the propagation of backscattering-immune guided waves. In valley-Hall and quantum-Hall crystal waveguides, this property stems from symmetry protection and results from a topological transition at a Dirac point. Since an initially closed band gap has to open, the guidance bandwidth remains limited compared to that of wide band gap crystals. When a glide-symmetric dislocation is introduced in a 2D crystal, we show that a pair of wide-bandwidth, single-mode, and symmetry-protected guided waves appear in the bulk band gap. The 2D Zak phase changes by $π$ on either side of the interface, providing a topological invariant protected by glide-reflection symmetry at the X point of the Brillouin zone. A demonstration experiment is performed with acoustic waves in water, at ultrasonic frequencies, and shows the continuous tuning of transmission as a function of the glide parameter. The concept further extends to other types of waves, including the case of elastic waves in solids, but also of optical and electromagnetic waves.

physics.class-ph↗

arXiv2021

Coherent interplay between surface acoustic waves and coupled mechanical resonators: transition from plasmon-like to surface mediated coupling

Manipulation of mechanical motion at the micro-scale has been attracting continuous attention, leading to the successful implementation of various strategies with potential impact on classical and quantum information processing. We here propose an approach based on the interplay between a pair of localized mechanical resonators and travelling surface acoustic waves (SAW). We demonstrate the existence of a two-sided interaction, allowing to use SAW to trigger and control the resonator oscillation, and to manipulate the elastic energy distribution on the substrate through resonator coupling. Observation of the vectorial structure of the resonator motion reveals the existence of two coupling regimes, a dipole-dipole-like interaction at small separation distance versus a surface-mediated mechanical coupling at larger separation. These results illustrate the potential of this platform for coherent control of mechanical vibration at a resonator level, and reciprocally for manipulating SAW propagation using sub-wavelength elements.

cond-mat.mes-hall↗

arXiv2021

Effective anisotropy of periodic acoustic and elastic composites

The propagation of acoustic or elastic waves in artificial crystals, including the case of phononic and sonic crystals, is inherently anisotropic. As is known from the theory of periodic composites, anisotropy is directly dictated by the space group of the unit cell of the crystal and the rank of the elastic tensor. Here, we examine effective velocities in the long wavelength limit of periodic acoustic and elastic composites as a function of the direction of propagation. We derive explicit and efficient formulas for estimating the effective velocity surfaces, based on second-order perturbation theory, generalizing the Christofell equation for elastic waves in solids. We identify strongly anisotropic sonic crystals for scalar acoustic waves and strongly anisotropic phononic crystals for vector elastic waves. Furthermore, we observe that under specific conditions, quasi-longitudinal waves can be made much slower than shear waves propagating in the same direction.

physics.class-ph↗

arXiv2020

Acoustic topological circuitry in square and rectangular phononic crystals

We systematically engineer a series of square and rectangular phononic crystals to create experimental realisations of complex topological phononic circuits. The exotic topological transport observed is wholly reliant upon the underlying structure which must belong to either a square or rectangular lattice system and not to any hexagonal-based structure. The phononic system chosen consists of a periodic array of square steel bars which partitions acoustic waves in water over a broadband range of frequencies (~0.5 MHz). An ultrasonic transducer launches an acoustic pulse which propagates along a domain wall, before encountering a nodal point, from which the acoustic signal partitions towards three exit ports. Numerical simulations are performed to clearly illustrate the highly resolved edge states as well as corroborate our experimental findings. To achieve complete control over the flow of energy, power division and redirection devices are required. The tunability afforded by our designs, in conjunction with the topological robustness of the modes, will result in their assimilation into acoustical devices.

cond-mat.mes-hall↗

arXiv2020

Designing thermal energy harvesting devices with natural materials through optimized microstructures

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 apply two-scale homogenization theory to obtain effective properties of the microstructures. Optimal Latin hypercube technique, combined with a genetic algorithm, is then implemented on the microstructures to achieve optimized design parameters. The optimized microstructures can accurately approximate the behavior of transformed materials. We design such devices and numerically characterize good thermal-energy harvesting performances. To validate the wide-range application of our approach, we illustrate other types of microstructures that mimic well the 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 optics enabled designs.

physics.app-ph↗

arXiv2020

Experimental observations of topologically guided water waves within non-hexagonal structures

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.

physics.flu-dyn↗

arXiv2020

Optimal isotropic, reusable truss lattice material with near-zero Poisson's ratio

Cork is a natural amorphous material with near-zero Poisson's ratio that is ubiquitously used for sealing glass bottles. It is an anisotropic, transversally isotropic, composite that can hardly be scaled down. Here, we propose a new class of isotropic and reusable cork-like metamaterial that is designed from an hybrid truss-lattice material to show an isotropic Poisson's ratio close to zero. Optimization is conducted using a multi-objective genetic algorithm, assisted by an elliptical basis function neural network, and coupled with finite element simulations. The optimal micro-structured metamaterial, fabricated by two-photon lithography with a lattice constant of 300 \micro\meter, has an almost isotropic Poisson's ratio smaller than 0.08 in all directions. It can recover $96.6\%$ of its original shape after a compressional test exceeding $20\%$ strain.

physics.app-ph↗

arXiv2019

Observation of topological gravity-capillary waves in a water wave crystal

The discovery of topological phases of matter, initially driven by theoretical advances in quantum condensed matter physics, has been recently extended to classical wave systems, reaching out to a wealth of novel potential applications in signal manipulation and energy concentration. Despite the fact that many realistic wave media (metals at optical frequencies, polymers at ultrasonic frequencies) are inherently dispersive, topological wave transport in photonic and phononic crystals has so far been limited to ideal situations and proof-of-concept experiments involving dispersionless media. Here, we report the first experimental demonstration of topological edge states in a classical water wave system supporting highly dispersive wave propagation, in the intermediate regime of gravity-capillary waves. We use a stochastic method to rigorously take into account the inherent dispersion and devise a water wave crystal insulator supporting valley-selective transport at topological domain walls. Our measurements, performed with a high-speed camera under stroboscopic illumination, unambiguously demonstrate the possibility of valley-locked transport of water waves.

cond-mat.mes-hall↗

arXiv2018

Stochastic band structure for waves propagating in periodic media or along waveguides

We introduce the stochastic band structure, a method giving the dispersion relation for waves propagating in periodic media or along waveguides, and subject to material loss or radiation damping. Instead of considering an explicit or implicit functional relation between frequency $ω$ and wavenumber $k$, as is usually done, we consider a mapping of the resolvent set in the dispersion space $(ω, k)$. Bands appear as as the trace of Lorentzian responses containing local information on propagation loss both in time and space domains. For illustration purposes, the method is applied to a lossy sonic crystal, a radiating surface phononic crystal, and a radiating optical waveguide. The stochastic band structure can be obtained for any system described by a time-harmonic wave equation.

physics.comp-ph↗

arXiv2017

Longitudinal near-field coupling between acoustic resonators grafted onto a waveguide

We investigate longitudinal near-field coupling between acoustic resonators grafted onto a waveguide. Experiments are performed in the audible range with a simple acoustic system composed of a finite aperiodic sequence of air resonators. Transmission typically shows a zero around a resonance frequency of a single resonator, as is well known. When two identical resonators are brought in close proximity, however, we observe that longitudinal near-field coupling strongly influences the acoustic transmission. When the separation between resonators is increased so that they can be considered in the far field of one another, we further observe the appearance of Fano-like transmission profiles. We explain this observation by the formation of locally resonant Fabry-Perot interferometers from every pair of resonators. All experimental results are compared to three-dimensional finite element analysis of the acoustic system.

physics.class-ph↗

arXiv2014

Stimulated Brillouin scattering from surface acoustic waves in sub-wavelength photonic microwires

Brillouin scattering in optical fibres is a fundamental interaction between light and sound with important implications ranging from optical sensors to slow and fast light. In usual optical fibres, light both excites and feels shear and longitudinal bulk elastic waves, giving rise to forward guided acoustic wave Brillouin scattering and backward stimulated Brillouin scattering. In a subwavelength-diameter optical fibre, the situation changes dramatically, as we here report with the first experimental observation of stimulated Brillouin scattering from surface acoustic waves. These Rayleigh-type hypersound waves travel the wire surface at a specific velocity of 3400 m.s$^{\mathrm{-1}}$ and backscatter the light with a Doppler shift of about 6 GHz. As these acoustic resonances are highly sensitive to surface defects or features, surface acoustic wave Brillouin scattering opens new opportunities for various sensing applications, but also in other domains such as microwave photonics and nonlinear plasmonics.

physics.optics↗

arXiv2013

Effect of loss on the dispersion relation of photonic and phononic crystals

A theoretical analysis is made of the transformation of the dispersion relation of waves in artificial crystals under the influence of loss, including the case of photonic and phononic crystals. Considering a general dispersion relation in implicit form, an analytic procedure is derived to obtain the transformed dispersion relation. It is shown that the dispersion relation is generally shifted in the complex $(k,ω)$ plane, with $k$ the wavenumber and $ω$ the angular frequency. The value of the shift is obtained explicitly as a function of the perturbation of material constants accounting for loss. The method is shown to predict correctly the transformation of the complex band structure $k(ω)$. Several models of the dispersion relation near a symmetry point of the Brillouin zone are analyzed. A lower bound for the group velocity, related to the local shape of the band around symmetry points, is derived for each case.

physics.optics↗