arXiv subjects

Osama R. Bilal

Publications and source records attributed to Osama R. Bilal.

At least 19 recordsLinked to original sources

arXiv2026

Topological mode conservation and conversion in phononic crystals with temporal interfaces

A sudden change in material properties creates a temporal interface and forces a propagating wave to change its frequency while preserving its wavenumber. In contrast to monoatomic lattices with a single frequency-wavenumber pair, polyatomic lattices support multiple frequencies for each wavenumber. To date, experimental observations are limited to topologically trivial monoatomic phononic systems. Here, we utilize analytical, numerical, and experimental methods to examine topologically non-trivial phononic lattices subject to temporal interfaces. In particular, we realize phononic lattices demonstrating single-frequency shift (i.e., mode conservation) and multi-frequency splitting (i.e., mode conversion) following a temporal interface. Accordingly, we generalize temporal analogues of Snell's law and Fresnel equations. Moreover, we utilize Bloch mode overlaps to obtain a phononic time lens and a classical analogue of dynamic quantum phase transitions for phonons. Such overlap determines the probability of mode conversion or conservation after a temporal interface and, more importantly, can carry hidden topological characteristics. Our methodology paves the way for the use of temporal interfaces in probing phonon band topology and the realization of advanced acoustic devices.

physics.class-ph↗

arXiv2026

Hierarchical metamaterials with tunable flat bands, zero-frequency, and wavenumber gaps

Metamaterials are arrangement of basic building blocks that repeat in space, time, or both. These material systems serve as an excellent platform for controlling waves, such as engineering wavenumber band gaps, flat bands, and zero-frequency band gaps. However, combining one or more of these exotic features within the same unit cell design remains a challenge. Moreover, once a metamaterial is realized, its dispersive properties are usually fixed. In this work, we present a tunable passive hierarchical metamaterial capable of exhibiting wavenumber band gaps, flat bands, and zero-frequency band gaps within the same dispersion curve. Our metamaterial is composed of magnetic elements confined within a fixed magnetic boundary. The metamaterial can be tuned by adjusting the magnetic boundary, which in turn can alter the lattice periodicity. We open wavenumber band gaps by incorporating magnetic coupling within the unit cell elements, resulting in negative physical stiffness. The tunability of the magnetic coupling also enables complete flattening of the dispersion bands. Moreover, the ground stiffness within our unit-cell design causes the opening of zero-frequency band gaps. We present our approach through a combination of analytical, numerical, and experimental methods. The analytical framework provides a blueprint for obtaining each of these exotic dispersion characteristics. The numerical analysis, using both linear and nonlinear models, validates our analytical predictions, which we further confirm through experimental demonstrations. Our work opens the door to exploring magnetic tunability and hierarchy in engineering metamaterial systems with exotic properties that can be harnessed in advanced acoustic and mechanical devices.

physics.app-ph↗

arXiv2025

Ultra-lightweight multi-functional gyroid-based metamaterial for simultaneous sound insulation, vibration suppression, and impact mitigation in all directions

Multi-functional materials are increasingly essential in many applications due to their ability to serve multiple purposes, simultaneously. Metamaterials can offer tailored functionality based on carefully designed tessellating basic building blocks, or unit cells, in space. These unit cells are most commonly designed for a single objective, for example, to mitigate an impact, insulate sound, or dampen vibrations. However, a metamaterial that can mitigate impact, attenuate elastic vibrations, insulate airborne sound, while being ultra-light and ultra-stiff remains elusive. Here, we present three gyroid-based metamaterial designs, which are numerically and experimentally examined, that can simultaneously serve all these functions in all directions. Our designs have band gaps reaching 60% with as low as 367 Hz starting band gap frequency, while being up to 77% lighter than a homogeneous block of the same material. Our findings highlight the potential of metamaterials for applications that require wave manipulation, mechanical resilience, and impact mitigation with limited mass and volume, simultaneously.

physics.app-ph↗

arXiv2025

Harnessing curvature for helical wave generation in spiral-based metamaterial structures

Linearly polarized elastic waves propagating in a linear path have been extensively explored in numerous applications from biomedical imaging to structural health monitoring. However, elastic waves propagating in a circularly polarized helical path are less explored because of the challenges in their generation and control. In this paper, we harness conventional actuation methods combined with sheets decorated by Archimedean spirals to generate elastic helical waves. We show that our metamaterials can support the propagation of such waves along a curved path without backscattering in a topologically protected manner. Moreover, we also show the creation and propagation of helical waves in our metamaterials without the need to wave guiding or domain interfaces, all with a single mode excitation source. We establish our methodology for flat plates and show the wave evolution as the metamaterials transition from slightly curved plates to fully curved cylinders. We observe the preservation of topologically protected edge states and helical wave beaming at different frequencies without the need to domain interferences. Furthermore, we leverage the mode to tune the helicity of the propagating waves. Our methodology can open new avenues for the generation and control of elastic helical waves using single source actuation that can be used in numerous applications.

physics.app-ph↗

arXiv2025

Observation of dispersion anomalies by design

Band structures encode electronic, optical, and acoustic properties of matter and can serve as an essential tool in material discovery and design. Dispersion anomalies -- sharp, non-standard features in the frequency-wavenumber relation -- have been historically correlated with phonon-electron coupling or long-range interaction. Through a combination of experimental, numerical, and analytical methods, we show how magnetic couplings can induce negative stiffness and sculpt dispersion relations to support zero-frequency phonon anomalies at arbitrary, non-zero wavenumbers. Our approach enables the realization of complete wavenumber band gaps without time-modulation, electron-phonon coupling, or long-range interactions. We identify the conditions under which non-differentiable zero-frequency phonons exist away from the high-symmetry points. Our framework generalizes across monoatomic and diatomic lattices, locally resonant metamaterials, non-local systems, as well as higher dimensional crystals. In addition, we report the first passive- or active- experimental observation of wavenumber band gaps in higher dimensions. Our work establishes a new paradigm in dispersion engineering and provides means for understanding wave-matter interaction in both the frequency and wavenumber domains.

physics.app-ph↗

arXiv2025

Experimental observation of flow instability control by metamaterial subsurfaces

Flow instabilities within a fluid flow can cause laminar-to-turbulent transition over surfaces. These instabilities can result from upstream, wake-generating disturbances, leading to increased drag and turbulence-induced energy losses. Flow control strategies can address these issues through active methods, requiring energy input, or passive systems, which operate without added input. Here, we present a passive approach to flow control using embedded phononic metamaterials to alter vortex instability development, without changing the outer-surface's texture, roughness or compliance. Experiments confirm that our subsurface can suppress vortex growth at target frequencies, demonstrating the potential for energy-efficient flow management with phononic subsurfaces.

physics.app-ph↗

arXiv2025

Static and dynamic analysis of auxetic three-dimensional curved metamaterials in both axial and circumferential directions

Metamaterials can enable unique mechanical properties based on their geometry rather than their chemical composition. Such properties can go beyond what is possible using conventional materials. Most of the existing literature consider metamaterials in Cartesian coordinates with zero curvature. However, realistic utilization of meta-structures is highly likely to involve a degree of curvature. In this paper, we study both the effective static and dynamic properties of metamaterials in the presence of curvature. To capture the effect of curvature on the static behavior of our metamaterial, we calculate the effective Poisson's ratio of the metamaterial in the presence of curvature. We conduct our analysis on three-dimensional metamaterials with varying effective Poisson's ratio. We observe a significant change in the values of the effective Poisson's ratio of the metamaterial duo to curvature. To capture the effect of curvature on the dynamics of our metamaterials, we calculate dispersion curves of curved metamaterial at different circumferential directions. We show both numerically and experimentally the change of the dynamic behavior of auxetic metamaterial from attenuation to transmission and vice-versa due to curvature. Our findings underscore the importance of curvature in both static and dynamic analysis of metamaterial design and could provide the means to guide practical implementations of metamaterials for functional use.

physics.app-ph↗

arXiv2024

Re-programmable self-assembly of magnetic lattices

Simple local interactions can cause primitive building blocks to self-assemble into complex and functional patterns. However, even for a small number of blocks, there exist a vast number of possible configurations that are plausible, stable, and with varying degree of order. The ability to dynamically shift between multi-stable patterns (i.e., reprogram the self-assembly) entails navigating an intractable search space, which remains a challenge. In this paper, we engineer the self-assembly of macroscopic magnetic particles to create metamaterials with dynamically reversible emergent phases. We utilize a boundary composed of magnetic hinges to confine free-floating magnetic disks into different stable assemblies. We exploit the non-destructive nature of the magnetic boundaries to create re-programmable two-dimensional metamaterials that morphs from crystalline to quasi-crystalline to disordered assembly using the same number of disks and boundary. Furthermore, we explore their utility to control the propagation of sound waves in an effectively undamped media with rich nonlinearities. Our findings can expand the metamaterials horizon into functional and tunable devices.

cond-mat.soft↗

arXiv2023

Harnessing asymmetry to reprogram nonlinear metamaterials on-the-fly with no moving parts

Various two-dimensional fabrication methods, such as deposition, etching, milling, laser cutting, and water jetting, suffer from asymmetry between the top and the bottom surface of fabricated parts. Such asymmetry is usually undesirable and can compromise functionality, or at least add uncertainty to fabricated components. The common practice is to assume symmetry between the top and the bottom surfaces by using average dimensions. In this study, we harness such asymmetry to realize metamaterials with dynamically tunable (i. e., re-programmable) properties. Our metamaterial is composed of identical unit cells with two concentric Archimedean spiral cuts and a permanent magnet embedded in the unit cell's center. By utilizing external electromagnets, we further amplify the fabrication asymmetry, through the inherent asymmetry between a repulsive vs attractive state between the permanent magnets and the electromagnets. We demonstrate the utility of our metamaterials by programming its spatiotemporal response in both time and frequency even in the presence of high amplitude harmonic excitation. Our findings can be utilized for broad range of applications, from seismic sensing at low frequency to ultrasonic imaging at higher frequencies.

physics.app-ph↗

arXiv2021

Harnessing re-programmable phase transitions to control the propagation of sound waves

Metamaterials can enable peculiar static and dynamic behavior (such as negative effective mass density, dynamical stiffness, and Poisson's ratio) due to their geometry rather than their chemical composition. The geometry of these metamaterials can be thought of as the phase of the material, which is usually fixed once the material is fabricated. While there exist many theoretical and numerical studies of metamaterials that can change phase, or re-program, experimental realizations remain limited due to challenges in manufacturability, the destructive nature of the re-programming and inherent non-linearities. Through a combination of analytical, numerical and experimental analyses, we utilize tunable, self-assembled, nonlinear magnetic lattices to realize metamaterials with reversible phase transitions. Our metamaterials are composed of free-floating disks, with embedded permanent magnets, confined within magnetic boundaries. We exploit the non-destructive nature of the adjustable magnetic boundaries to create a set of re-programmable metamaterials to control the propagation of sound waves. Furthermore, we demonstrate a robust, real-time tunable wave filter at ultra-low frequencies. Our findings can expand the metamaterials horizon into functional and tunable devices.

cond-mat.soft↗

arXiv2021

Exploiting Localized Transition Waves to Tune Sound Propagation in Soft Materials

Programmable materials hold great potential for many applications such as deployable structures, soft robotics, and wave control, however, the presence of instability and disorder might hinder their utilization. Through a combination of analytical, numerical, and experimental analyses, we harness the interplay between instabilities, geometric frustration, and mechanical deformations to control the propagation of sound waves within self-assembled soft materials. We consider levitated magnetic disks confined by a magnetic boundary in-plane. The assemblies can be either ordered or disordered depending on the intrinsic disk symmetry. By applying an external load to the assembly, we observe the nucleation and propagation of different topological defects within the lattices. In the presence of instabilities, the defect propagation gives rise to time-independent localized transition waves. Surprisingly, in the presence of frustration, the applied load briefly introduces deformation-induced order to the material. By further deforming the lattices, new patterns emerge across all disk symmetries. We utilize these patterns to tune sound propagation through the material. Our findings could open new possibilities for designing exotic materials with potential applications ranging from sound control to soft robotics.

cond-mat.soft↗

arXiv2020

Demultiplexing infrasound phonons with tunable magnetic lattices

Controlling infrasound signals is crucial to many processes ranging from predicting atmospheric events and seismic activities to sensing nuclear detonations. These waves can be manipulated through phononic crystals and acoustic metamaterials. However, at such ultra-low frequencies, the size (usually on the order of meters) and the mass (usually on the order of many kilograms) of these materials can hinder its potential applications in the infrasonic domain. Here, we utilize tunable lattices of repelling magnets to guide and sort infrasound waves into different channels based on their frequencies. We construct our lattices by confining meta-atoms (free-floating macroscopic disks with embedded magnets) within a magnetic boundary. By changing the confining boundary, we control the meta-atoms' spacing and therefore the intensity of their coupling potentials and wave propagation characteristics. As a demonstration of principle, we present the first experimental realization of an infrasound phonon demultiplexer (i.e., guiding ultra-low frequency waves into different channels based on their frequencies). The realized platform can be utilized to manipulate ultra-low frequency waves, within a relatively small volume, while utilizing negligible mass. In addition, the self-assembly nature of the meta-atoms can be key in creating re-programmable materials with exceptional nonlinear properties.

physics.app-ph↗

arXiv2020

Experimental realization of phonon demultiplexing in three-dimensions

Phononic metamaterials enabled the realization of many acoustic components analogous to their electronic counterparts, such as transistors, logic gates and calculators. A key component among these is the demultiplexer, a device that receives multiple signals and sorts them based on their frequencies into separate channels. Previous experimental realizations of acoustic and elastic multiplexers have employed plates with pillars or holes to demultiplex frequencies. However, existing realizations are confined to two-dimensions, which can limit potential acoustic or elastic circuit design. Here we show the first experimental realization of a three-dimensional, four channel phononic demultiplexer. Our design methodology is based on bundles of pass-bands within a large band gap that can easily be tuned for multi-channel frequency demultiplexing. The proposed design can be utilized in acoustic and elastic information processing, nondestructive evaluation and communication applications among others.

physics.app-ph↗

arXiv2020

Observation of a phononic quadrupole topological insulator

The modern theory of charge polarization in solids is based on a generalization of Berry's phase. Its possible quantization lies at the heart of our understanding of all systems with topological band structures that were discovered over the last decades. While based on the concept of the "charge" polarization, the same theory can be used as an elegant tool to characterize the Bloch bands of neutral bosonic systems such as photonic or phononic crystals. Recently, the theory of this quantized polarization was extended from the dipole- to higher multipole-moments. In particular, a two-dimensional quantized quadrupole insulator is predicted to have gapped yet topological one-dimensional edge-modes, which in turn stabilize zero-dimensional in-gap corner states. However, such a state of matter has not been observed experimentally. Here, we provide the first measurements of a phononic quadrupole insulator. We experimentally characterize the bulk, edge, and corner physics of a mechanical metamaterial and find the predicted gapped edge and in-gap corner states. We further corroborate our findings by comparing the mechanical properties of a topologically non-trivial system to samples in other phases predicted by the quadrupole theory. From an application point of view, these topological corner states are an important stepping stone on the way to topologically protected wave-guides in higher dimensions and thereby open a new design path for metamaterials.

cond-mat.mtrl-sci↗

arXiv2020

A flexible spiraling-metasurface as a versatile haptic interface

Haptic feedback is the most significant sensory interface following visual cues. Developing thin, flexible surfaces that function as haptic interfaces is important for augmenting virtual reality, wearable devices, robotics and prostheses. For example, adding a haptic feedback interface to prosthesis could improve their acceptance among amputees. State of the art programmable interfaces targeting the skin feel-of-touch through mechano-receptors are limited by inadequate sensory feedback, cumbersome mechanisms or narrow frequency of operation. Here, we present a flexible metasurface as a generic haptic interface capable of producing complex tactile patterns on the human skin at wide range of frequencies. The metasurface is composed of multiple "pixels" that can locally amplify both input displacements and forces. Each of these pixels encodes various deformation patterns capable of producing different sensations on contact. The metasurface can transform a harmonic signal containing multiple frequencies into a complex preprogrammed tactile pattern. Our findings, corroborated by user studies conducted on human candidates, can open new avenues for wearable and robotic interfaces.

physics.app-ph↗

arXiv2020

Enhancement of deep-subwavelength band gaps in flat spiral-based phononic metasurfaces using the trampoline phenomena

Elastic and acoustic metamaterials can sculpt dispersion of waves through resonances. In turn, resonances can give rise to negative effective properties, usually localized around the resonance frequencies, which support band gaps at subwavelength frequencies (i.e., below the Bragg-scattering limit). However, the band gaps width correlates strongly with the resonators' mass and volume, which limits their functionality in applications. Trampoline phenomena have been numerically and experimentally shown to broaden the operational frequency ranges of two-dimensional, pillar-based metamaterials through perforation. In this work, we demonstrate trampoline phenomena in lightweight and planar lattices consisting of arrays of Archimedean spirals in unit cells. Spiral-based metamaterials have been shown to support different band gap opening mechanisms, namely, Bragg-scattering, local resonances and inertia amplification. Here, we numerically analyze and experimentally realize trampoline phenomena in planar metasurfaces for different lattice tessellations. Finally, we carry out a comparative study between trampoline pillars and spirals and show that trampoline spirals outperform the pillars in lightweight, compactness and operational bandwidth.

physics.app-ph↗

arXiv2018

Autonomous Deployment of a Solar Panel Using an Elastic Origami and Distributed Shape Memory Polymer Actuators

Deployable mechanical systems such as space solar panels rely on the intricate stowage of passive modules, and sophisticated deployment using a network of motorized actuators. As a result, a significant portion of the stowed mass and volume are occupied by these support systems. An autonomous solar panel array deployed using the inherent material behavior remains elusive. In this work, we develop an autonomous self-deploying solar panel array that is programmed to activate in response to changes in the surrounding temperature. We study an elastic "flasher" origami sheet embedded in a circle of scissor mechanisms, both printed with shape memory polymers. The scissor mechanisms are optimized to provide the maximum expansion ratio while delivering the necessary force for deployment. The origami sheet is also optimized to carry the maximum number of solar panels given space constraints. We show how the folding of the "flasher" origami exhibits a bifurcation behavior resulting in either a cone or disk shape both numerically and in experiments. A folding strategy is devised to avoid the undesired cone shape. The resulting design is entirely 3D printed, achieves an expansion ratio of 1000% in under 40 seconds, and shows excellent agreement with simulation prediction both in the stowed and deployed configurations.

physics.app-ph↗

arXiv2018

Architected lattices for simultaneous broadband attenuation of airborne sound and mechanical vibrations in all directions

Phononic crystals and acoustic metamaterials are architected lattices designed to control the propagation of acoustic or elastic waves. In these materials, the dispersion properties and the energy transfer are controlled by selecting the lattices' geometry and their constitutive material properties. Most designs, however, only affect one mode of energy propagation, transmitted either as acoustic, airborne sound or as elastic, structural vibrations. Here, we present a design methodology to attenuate both acoustic and elastic waves simultaneously in all polarizations. We experimentally realize the first three-dimensional, load bearing, architected lattice, composed of a single-material, that responds in a broadband frequency range in all directions.

physics.app-ph↗