arXiv subjects

Vincent Pagneux

Publications and source records attributed to Vincent Pagneux.

At least 19 recordsLinked to original sources

arXiv2025

Characterisation of temporal aiming for water waves with an anisotropic metabathymetry

The deflection of waves by combining the effects of time modulation with anisotropy has been recently proposed in the context of electromagnetism. In this work, we characterise this phenomenon, called temporal aiming, for water waves using a time-varying metabathymetry. This metabathymetry is composed of thin vertical plates that are periodically arranged at the fluid bottom and which act as an effective anisotropic medium for the surface wave in the long-wavelength approximation. When this plate array is vertically lifted at the fluid bottom at a given time, the medium switches from isotropic to anisotropic, causing a wavepacket to scatter in time and deflect from its initial trajectory. Following a simple modelling, we obtain the scattering coefficients of the two waves generated due to the sudden medium change as well as the angle of deviation with respect to the incident angle. We then numerically evaluate this scattering problem with simulations of the full 2D effective anisotropic wave equation, with a time-dependent anisotropy tensor. Finally, we provide experimental evidence of the temporal aiming, using space time resolved measurement techniques, demonstrating the trajectory shift of a wavepacket and measuring its angle of deviation.

physics.flu-dyn↗

arXiv2025

Experimental study of Su-Schrieffer-Heeger edge modes for water waves in linear and nonlinear regime

This paper experimentally investigates topologically protected edge modes in a water wave channel through a direct geometric mapping to the one-dimensional Su-Schrieffer-Heeger (SSH) model. By designing a periodic channel with alternating widths, we replicate the key features of the SSH model, leading to the emergence of robust zero-energy sloshing edge modes localized at the boundaries. Experimental data show excellent agreement with theoretical predictions, supported by two-dimensional numerical simulations. In the nonlinear regime, two distinct bifurcations are observed, indicating the appearance of secondary resonances. This study highlights the relevance of the SSH model for water wave systems and provides an accessible method to explore topological edge states in classical wave systems.

physics.flu-dyn↗

arXiv2025

Inverse design of mirror-symmetric disordered systems for broadband perfect transmission

We present a framework for achieving broadband perfect wave transmission in complex systems by optimizing symmetric disordered media via inverse design. We show that leveraging symmetry of complex media reduces the optimization's complexity enabling the incorporation of additional constraints in the parameter space. Starting from a single perfectly transmitting state with predefined input and output wavefronts at a specific frequency, we progressively broaden the bandwidth - from a reflectionless exceptional point with a flattened lineshape to narrowband filters and ultimately to broadband quasi-perfect transmission exhibiting a rainbow effect. Numerical simulations based on the coupled dipole approximation are validated experimentally in a multichannel microwave waveguide with dielectric and metallic scatterers. Finally, we demonstrate broadband enhanced wave transmission through barriers highlighting the potential for advanced wave control applications.

physics.optics↗

arXiv2025

Direct experimental observation of total absorption and loss compensation using sound waves with complex frequencies

In this study, we experimentally investigate the application of a transient signal with complex frequencies to the absorption and transmission of sound waves. Indeed, the emission of a wave with an exponentially varying amplitude in time is analogous, in the frequency domain, to a monochromatic wave with spatial gain or loss. Our results show that by exciting a non-critically coupled Helmholtz resonator with a wave having a growing amplitude, total absorption can still be achieved. Furthermore, the lossy propagation of a traveling wave in a duct is also studied, and it is shown that the losses embedded in the complex wavenumber can be compensated by using a transient signal with decreasing amplitude. These results confirm the potential of complex frequency excitation for exploring new means of manipulating sound waves to mimic gain and loss.

physics.app-ph↗

arXiv2025

Robustness of perfect transmission resonances to asymmetric perturbation

We investigate the impact of asymmetric perturbations on the perfect transmission resonances (PTRs) of one-dimensional finite periodic systems. With no perturbations, the scattering region consists of $N$ identical cells, and the transmission spectrum exhibits at least $N-1$ PTRs in each pass band of the Bloch dispersion of the unit cell. By introducing a perturbation, the periodic structure is broken, which \textit{a priori} results in the elimination of all PTRs. However, we demonstrate that PTRs can still arise under asymmetric perturbations when the unperturbed system possesses mirror symmetry, utilizing the $\mathcal{PT}$ symmetry of the unperturbed reflectionless eigenvalue problem. We also reveal an intriguing connection between two seemingly independent PTRs that lies in the symmetry of the unperturbed unit cell: If one PTR is preserved, then a dual one is necessarily also preserved. Our findings offer insights for the design of, for example, a robust antireflection setup at multiple wavelengths or all-optical diode devices.

quant-ph↗

arXiv2024

A nonreciprocal and tunable active acoustic scatterer

A passive loudspeaker mounted in a duct acts as a reciprocal scatterer for plane waves impinging on either of its sides. However, the reciprocity can be broken by means of an asymmetric electroacoustic feedback which supplies to the loudspeaker a signal picked-up from a microphone facing only one of its sides. This simple modification offers new opportunities for the control and manipulation of sound waves. In this paper, we investigate the scattering features of a pair of such actively controlled loudspeakers connected by means of a short and narrow duct. The theoretical and experimental results demonstrate that by tuning the feedback loops, the system exhibits several exotic effects, which include an asymmetric reflectionless configuration with one-way transmission or absorption, a directional amplifier with an isolation of 42 dB, and a quasi CPA-lasing configuration. All of these effects were achieved using a single setup in the subwavelength regime, highlighting the versatility of such an asymmetrically active scatterer.

physics.app-ph↗

arXiv2024

Floquet scattering of shallow water waves by a vertically oscillating plate

We report on the scattering of a plane wave from a vertically oscillating plate in the low frequency approximation by means of Floquet theory. In the case of a static plate, the scattering coefficients are evaluated via mode matching method for the full two-dimensional linearised water wave problem and are compared with the coefficients obtained from a reduced one-dimensional model in the shallow water approximation. The main part of the analysis is the extension of this 1D shallow water approximation to the case of a vertically oscillating plate, where time modulation is only encapsulated in the blockage coefficient. We show that the incident wave is scattered into Floquet sidebands and extract the scattering coefficients for each harmonic using a Floquet scattering formalism. Finally, considering a slowly oscillating plate, we propose a quasistatic approximation which appears to be particularly accurate.

physics.class-ph↗

arXiv2024

Topologically invisible defects in chiral mirror lattices

One of the hallmark of topological insulators is having conductivity properties that are unaffected by the possible presence of defects. In this work, we go beyond backscattering immunity and obtain topological invisibility across defects or disorder. Using a combination of chiral and mirror symmetry, the transmission coefficient is guaranteed to be unity. Importantly, but no phase shift is induced making the defect completely invisible. Many lattices possess the chiral-mirror symmetry, and we choose to demonstrate the principle on an hexagonal lattice model with Kekule distortion displaying topological edge waves, and we show analytically and numerically that the transmission across symmetry preserving defects is unity. We then realize this lattice in an acoustic system, and confirm the invisibility with numerical experiments. We foresee that the versatility of our model will trigger new experiments to observe topological invisibility in various wave systems, such as photonics, cold atoms or elastic waves.

cond-mat.mes-hall↗

arXiv2024

Regular sloshing modes in irregular cavities using metabathymetry

We present a comprehensive investigation, combining numerical simulations and experimental measurements, into the manipulation of water waves and resonance characteristics within closed cavities utilizing anisotropic metamaterials. We engineer the anisotropic media with subwavelength-scale layered bathymetry through the application of coordinate transformation theory and the homogenization technique to a fully three-dimensional linear water wave problem. Experimental and numerical analyses of deformed cavities employing anisotropic metamaterial bathymetry demonstrate regular sloshing mode patterns and eigenfrequencies akin to those observed in rectangular reference cavities with flat bathymetry. Our study underscores the potential of water wave metamaterials in establishing robust anisotropic metabathymetry for the precise control of sloshing modes.

physics.flu-dyn↗

arXiv2024

Transient amplification in stable Floquet media

The Mathieu equation occurs naturally in the description of vibrations or in the propagation of waves in media with time-periodic refractive index. It is known to lead to exponential parametric instability in some regions of the parameter space. However, even in the stable region the matrix that propagates the initial conditions forward in time is non-normal and therefore it can result in transient amplification. By optimizing over initial conditions as well as initial time we show that significant transient amplifications can be obtained, going beyond the one simply stemming from adiabatic invariance. Moreover, we explore the monodromy matrix in more depth, by studying its $ε$-pseudospectra and Petermann factors, demonstrating that is the degree of non-normality of this matrix that determines the global amplifying features. In the context of wave propagation in time-varying media, this transient behavior allows us to display arbitrary amplification of the wave amplitude that is not due to exponential parametric instability.

cond-mat.other↗

arXiv2023

Backscattering reduction in a sharply bent water wave channel

We study theoretically and experimentally how to reduce the backscattering of water waves in a channel with multiple turns. We show that it is not only possible to cancel backscattering but also to achieve a remarkable transmission in such geometries. In order to avoid the reflection that naturally arises at each turn of the waveguide, an anisotropic metamaterial made of closely-spaced thin vertical plates is used. The efficiency of the metamaterial arrangement depends only slightly on the frequency of the incident wave, as long as its wavelength is much larger than the periodicity of the array. This phenomenon is not restricted only to water wave channels but also applies to any type of waves with Neumann boundary conditions.

physics.class-ph↗

arXiv2023

Emergent non-Hermitian models

The Hatano-Nelson and the non-Hermitian Su-Schrieffer-Heeger model are paradigmatic examples of non-Hermitian systems that host non-trivial boundary phenomena. In this work, we use recently developed graph-theoretical tools to design systems whose isospectral reduction -- akin to an effective Hamiltonian -- has the form of either of these two models. In the reduced version, the couplings and on-site potentials become energy-dependent. We show that this leads to interesting phenomena such as an energy-dependent non-Hermitian skin effect, where eigenstates can simultaneously localize on either ends of the systems, with different localization lengths. Moreover, we predict the existence of various topological edge states, pinned at non-zero energies, with different exponential envelopes, depending on their energy. Overall, our work sheds new light on the nature of topological phases and the non-Hermitian skin effect in one-dimensional systems.

quant-ph↗

arXiv2023

Latent Su-Schrieffer-Heeger models

The Su-Schrieffer-Heeger (SSH) chain is the reference model of a one-dimensional topological insulator. Its topological nature can be explained by the quantization of the Zak phase, due to reflection symmetry of the unit cell, or of the winding number, due to chiral symmetry. Here, we harness recent graph-theoretical results to construct families of setups whose unit cell features neither of these symmetries, but instead a so-called latent or hidden reflection symmetry. This causes the isospectral reduction -- akin to an effective Hamiltonian -- of the resulting lattice to have the form of an SSH model. As we show, these latent SSH models exhibit features such as multiple topological transitions and edge states, as well as a quantized Zak phase. Relying on a generally applicable discrete framework, we experimentally validate our findings using electric circuits.

cond-mat.mes-hall↗

arXiv2023

Higher-order mode filtering by a resistive layer

A method of higher-order modes filtering in an air-filled waveguide using a resistive layer is proposed. An analogue of Cremer's criterion is discussed and used to obtain the optimal modal attenuation of the non-planar waves while the plane wave is preserved. Numerical validation of the concept is performed for a straight waveguide and an abrupt expansion in a waveguide.

physics.app-ph↗

arXiv2023

Exact analogue of the Hatano-Nelson model in 1D continuous nonreciprocal systems

We propose a general framework that enables the exact mapping of continuous nonreciprocal 1D periodic systems to the Hatano-Nelson (HN) model. Our approach, based on the two-port transfer matrix, is broadband and is applicable across various physical systems and, as an illustration, we consider the implementation of our model in acoustic waveguides. Through theoretical analysis and experimental demonstrations, we successfully achieve the mapping to the HN model by utilizing active acoustic elements, thereby observing the renowned skin effect. Moreover, our experimental setup enables the exploration of the transition from periodic to open boundary conditions by employing diaphragms of varying radii. Our experimental results, unveil the exponential sensitivity of the system to changes in boundary conditions. By establishing a profound connection between continuous systems and the fundamental discrete HN model, our results significantly broaden the potential application of nonreciprocal wave systems and the underlying phenomena.

physics.app-ph↗

arXiv2023

Hidden symmetries in acoustic wave systems

Mirror symmetry of a wave system imposes corresponding even or odd parity on its eigenmodes. For a discrete system, eigenmode parity on a specific subset of sites may also originate from so-called latent symmetry. This symmetry is hidden, but can be revealed in an effective model upon reduction of the original system onto the latently symmetric sites. Here we show how latent symmetries can be leveraged for continuous wave setups in the form of acoustic networks. These are systematically designed to have point-wise amplitude parity between selected waveguide junctions for all low frequency eigenmodes. We further develop a modular principle: latently symmetric networks can be interconnected to feature multiple latently symmetric junction pairs, allowing the design of arbitrarily large latently symmetric networks. By connecting such networks to a mirror symmetric subsystem, we design asymmetric setups featuring eigenmodes with domain-wise parity. Bridging the gap between discrete and continuous models, our work takes a pivotal step towards exploiting hidden geometrical symmetries in realistic wave setups.

physics.class-ph↗

arXiv2022

Formation and dynamics of a semi vortex ring connected to a free surface

Playing a role in the locomotion of some animals such as the water strider, the formation and dynamics of a semi vortex ring connected to a free surface are experimentally investigated. This semi vortex ring is generated by the circular motion of a flat circular disk in water. Digital Particle Image Velocimetry provides velocity fields and vortex properties. We show how in a broad range of Reynolds numbers, the properties of the semi vortex rings are related to the disk characteristics. In particular, our results highlight a formation process more complex than for a complete vortex ring produced by a piston stroke. In addition to the classical rolling up at the rear of the disk, a shedding phenomenon occurs on the leading edge, producing secondary vortices. The Strouhal number related to this shedding process reveals that it comes from the free-shear instability of the boundary layer identified in the near wake of a cylinder by Bloor. Finally we show that the disk thickness affects the final properties of the semi vortex rings through emission frequency of secondary vortices.

physics.flu-dyn↗

arXiv2022

Space-time resolved measurements of the effect of pinned contact line on the dispersion relation of water waves

We report on an experimental investigation of the propagation of gravity-capillary waves in a narrow channel with a pinned contact line. By using Fourier Transform Profilometry (FTP) we measure the static curved meniscus as well as the surface perturbation. By varying the channel width, between 7 and 15 times the capillary length, we show how edge constraints modify the surface curvature and therefore the dispersion relation. From the space-time resolved field, we obtain a decomposition of the linear mode onto transverse modes satisfying the condition of pinned contact line. This approach, in which we complement the theoretical model with experimental analysis, allows computations of wavenumbers and natural frequencies with a robust statistics. We verify experimentally the convergence of the model and the pertinence of the linear approximation. In addition, we analyze the relative contribution of the experimentally measured static meniscus. An excellent agreement between the computed natural frequencies and the forcing frequency confirms the contribution of the actual space-time resolved measured surface. These experimental results are an accurate estimation of the influence of the additional restoring force exerted by the pinned contact line on the deformed surface which increases the wave celerity. The local character of this effect is evidenced by the decrease of the shift of the dispersion relation as a function of the channel width.

physics.flu-dyn↗