arXiv subjects

Brahim Lemkalli

Publications and source records attributed to Brahim Lemkalli.

10 recordsLinked to original sources

arXiv2026

Nonreciprocal topological kink-wave propagation in mechanical metamaterials

Nonlinear mechanical metamaterials can exhibit emergent transport phenomena that mimic topological protection without relying on linear band topology. Here, we realize a bifurcation-induced nonreciprocal lattice that supports robust propagation of elastic kink waves. Each unit is a prestrained, hinged-beam circulator that develops angular momentum bias during snap-through transitions between buckling states, producing an effective breaking of time reversal symmetry. Coupling such units into a hexagonal array yields a mechanically chiral network where localized soliton-like excitations propagate unidirectionally along interfaces and edges, immune to sharp bends. We demonstrate non-dispersive kink transport governed by a SineGordon type field whose effective bias encodes mechanical chirality. This framework bridges bifurcation dynamics and nonreciprocal transport, establishing a nonlinear route toward topological like mechanical functionality without magnetic or gyroscopic bias.

cond-mat.mtrl-sci↗

arXiv2025

On the Practicability of Ceramic-Tiled Walls for Sound Absorption by Tuning Cavities

We present the practicality of structuring ceramic tiles for enhancing sound absorption on rigid walls. The cornerstone of our methodology is to structure walls with cavities so that walls effectively behave as heterogeneous absorbing surfaces over a large frequency bandwidth. Using this approach, ceramic tiled walls are developed by integrating tuned cavity structures based on Helmholtz resonators. Such a design leverages the empty joints between tiles to form resonator necks, while the space between the ceramic tiles and the wall acts as the resonator chambers. By arranging these resonators in a spatially graded array, we achieve broadband sound absorption which targets low-frequency noise generated by impacts, footsteps and ambient sources. This makes the system highly suitable for practical architectural applications. The study encompasses the entire process, from numerical modeling and analytical formulation to the fabrication and mounting of resonant tiles, followed by experimental validation, clearly demonstrating the effectiveness of the proposed solution in real-world conditions. The findings highlight the strong potential of this approach for practical tiled room acoustic treatment and noise mitigation.

physics.app-ph↗

arXiv2025

Space-Time Elastic Metamaterials for Zero-Frequency and Zero-Wavenumber Bandgaps

We create wave-matter space-time metamaterials using optical trapping forces to manipulate mass-spring chains and create zero-frequency and zero-wavenumber band gaps: the bosonic nature of phonons, and hence this elastodynamic setting, traditionally prohibits either zero-frequency or zero-wavenumber band gaps. Here, we generate zero-frequency gaps using optomechanical interactions within a 3D mass-spring chain by applying an optical trapping force to hold or manipulate a mass in a contactless manner independent of its elastodynamic excitations. Through careful modification of the geometrical parameters in the trapped monoatomic mass-spring chain, we demonstrate the existence of a zero-frequency gap generated by the optical forces on the masses. The precise control we have over the system allows us to drive another set of masses and springs out of phase with its traveling wave thereby creating a zero-wavenumber band gap.

physics.optics↗

arXiv2025

Controlling the Propagation of Flexural Elastic Waves With Ceramic Metatiles

In this work, we examine the application of phononic metamaterials for elastic impact noise insulation in tiled flooring, through the development of an innovative ceramic metatile that incorporates phononic crystals with optimized joint configurations. First, we optimize the geometrical and material parameters of the proposed metatile, which is composed of small ceramic subtiles connected by silicon joints, in order to reduce longitudinal and flexural wave propagation on tiled floors, which are responsible for noise vibrations in tiled environments. A bandgap is achieved that effectively suppresses the transmission of impact noise through the periodic structural configuration. For flexural waves, the ceramic metatile exhibits a pronounced attenuation of wave transmission in the range of $500$-$1900$ Hz along the $[100]$ direction, and $500$-$1400$ Hz along the $[110]$ direction. For longitudinal waves, a broad bandgap is observed, spanning from $400$ Hz to $1950$ Hz in both the $[100]$ and $[110]$ directions. Additionally, the bandgaps shift toward lower frequencies with increasing width of the subtiles and silicon joints, or with a decrease in the Young's modulus of the silicon. In both experimental and numerical tests, it is demonstrated that the integration of silicon joints inside the ceramic metatile improves the acoustic insulation performance, as measured by the reduction of impact noise levels across a wide range of low frequencies. The findings highlight the potential of metamaterials in architectural acoustics, offering innovative solutions for elastic wave control in tiled environments.

physics.app-ph↗

arXiv2024

Optical chiral microrobot for out-of-plane rotation

Optical microrobots (OPTOBOTs) have garnered significant interest, particularly in the medical field, due to their potential for precise cell manipulation in various biological studies and microsurgical applications. Previously described OPTOBOTs demonstrate multiple degrees of freedom, yet improvements are needed, especially in achieving reliable out-of-plane rotation. Here, we propose an OPTOBOT design based on chirality that enables full-cycle out-of-plane rotations using optical tweezers. The OPTOBOT has an arrow-like structure with two handles aligned on the same axis, maintaining its horizontal orientation and facilitating controlled movement. Additionally, the OPTOBOT's tail is a chiral helix, which induces repetitive out-of-plane rotations around its longer axis when targeted by a laser beam that is due to broken axial parity. Finite element analysis is employed to design the OPTOBOT and assess its capacity to generate mono-directional high optical torque. Experimental results confirm various actuation modes, supporting future integration of OPTOBOTs in complex micromanipulation tasks.

physics.optics↗

arXiv2023

Bi-functional metamaterial based on Helmholtz resonators for sound and heat insulation

Over the last few decades, both heat and broadband sound reduction have become increasingly significant as a result of concerns about the environment and noise pollution. In order to address this challenge, we provide a finite element analysis study of an acoustic metamaterial panel consisting of a unit cell made of two Helmholtz Resonators with a guide in between. These panels can attenuate and control both sound propagation and heat flux. For noise pollution in a building, we first determine the geometric dimension that corresponds to the operative frequency range. Furthermore, we investigate the sound transmission loss of the proposed panel as a function of the periodicity of an array of unit cells. Additionally, we investigate the thermal flux induced by the panel, especially within a 24-hour period. The simulation results show that the proposed panel provides a level of sound attenuation within the frequency range of 400 Hz to 2.5 kHz, as well as interesting heat protection. The structure is compared to panels made up of a homogeneous medium and without Helmholtz resonators.

cond-mat.mtrl-sci↗

arXiv2023

Clay metaBrick-based motif to enhance thermal and acoustic insulation

Acoustic metamaterials have gained popularity as promising materials for enhancing noise reduction. Here, we explore the use of metamaterials, based on Helmholtz resonators (HRs), to enhance the performance of standard clay hollow brick. By incorporating HRs in the upper and lower hollows, we transform the standard brick into metaBrick, which is essentially designed based on metamaterial principles. We evaluate the acoustic and thermal performance of walls constructed with clay metaBricks, focusing on sound transmission loss and heat resistance. Both the finite element method and experimental analysis were employed to highlight the performance of metaBricks compared to standard clay bricks. Results show that metaBricks significantly enhance acoustic and thermal insulation, achieving an attenuation of $20$ \si{dB} across a broad frequency range from $500$ to $2500$ \si{Hz} and an $8$\% increase in thermal resistance. However, compressive strength is reduced by $33$\%, though it remains above the standard requirements for building materials. These findings indicate that metaBrick is a promising building material, offering improved sound and thermal insulation.

cond-mat.mtrl-sci↗

arXiv2023

The emergence of low-frequency dual Fano resonances in chiral twisting metamaterials

In the current work, through a finite element analysis, we demonstrate that a configuration of chiral cells having syndiotactic symmetry provides dual Fano resonances at low frequency. From the phononic dispersion and transmission response, we compare the signature provided by a composite made of chiral cells to the ones of homogeneous medium, isotactic nonchiral, and isotactic chiral beams. The study results in an innovative design of a mechanical metamaterial that induces the Fano resonance at low frequency with a relatively high quality factor. This might be a significant step forward for mechanical wave filtering and detection. Performances have been evaluated using a sensor that will be implemented as a thermometer.

physics.app-ph↗

arXiv2022

Mapping of Elastic Properties of Twisting Metamaterials onto Micropolar Continuum using Static Calculations

Recent developments in the engineering of metamaterials have brought forth a myriad of mesmerizing mechanical properties that do not exist in ordinary solids. Among these, twisting metamaterials, acoustical chirality, or Willis coupling are sample-size dependent. The purpose of this work is, first, to examine the mechanical performance of a new twisting cubic metamaterial. Then, we perform a comparative investigation of its twisting behavior using the finite element method on microstructure elements computation, an analytical model, and we compare them to Eringen micropolar continuum. Notably, the results of the three models are in good qualitative and quantitative agreements. Finally, a systematic comparison of dispersion relations was made for the continuum and for the microstructures with different sizes in unit cells as final proof of perfect mapping.

physics.app-ph↗

arXiv2022

Longitudinal-Twist Wave Converter based on Chiral Metamaterials

Advances in material architectures have enabled endowing materials with exotic attributes not commonly available in the conventional realm of mechanical engineering. Twisting, a mechanism whereby metamaterials are used to transform static axial load into twist motion, is of particular interest to this study. Herein, computations based on the finite element method, corroborated by an analytical approach derived from applying Lagrange's equations to a monoatomic spring-mass system, are employed to explore the longitudinal-twist (L-T) conversion exhibited by a chiral tetragonal-beam metamaterial. Firstly, we perform an eigenvalue analysis taking into account the polarization states to highlight the potential contribution of the longitudinal mode in the L-T conversion. We contrast the twisting behavior of the chiral cell with that of other homogeneous medium, octagonal-tube, and non-chiral cells. Moreover, we demonstrate the influence of the cell's chirality on the L-T conversion using both time-domain and frequency-domain studies. The findings indicate that at least a portion of the longitudinally propagating wave is transformed into twist throughout a broad frequency range and even quasi-totally converted at distinct frequencies.

physics.app-ph↗