Architected metamaterials derive their exceptional mechanical performance from their precisely-tailored underlying topologies, enabling access to regions of materials selection charts unattainable by conventional materials. While substantial advances have been achieved at micro-, meso-, and macroscales, further improvements are increasingly constrained, motivating exploration of nanoscale architected materials where surface and size effects dominate the overall multiphysics performance. Here, we resort to molecular dynamics simulations to systematically explore the mechanical response of nickel-based nano-architected metamaterials. By varying topology, relative density, crystallinity, and grain size, we demonstrate the broad tunability of elastic moduli, strength, and Poisson's ratio enabled by the rational design of underlying nano-architecture. Notably, the proposed nano-architected metamaterials outperform most previously reported architected materials at comparable densities, highlighting the effectiveness of nanoscale topology-driven designs. Atomistic analyses reveal that nanoscale free surfaces promote dislocation nucleation while inhibiting dislocation propagation, leading to flow stresses exceeding those of bulk counterparts. To bridge length scales and draw inspiration from crystallography, we design and 3D print hierarchical polymeric metamaterials and experimentally characterize their mechanical behavior. Despite being fabricated from an intrinsically brittle polymer, these structures exhibit topology-dependent stiffness and strength, alongside ductile plastic deformation and enhanced toughness, attributable to their hierarchical architectures. Together, this work introduces a crystallography-inspired architectural design paradigm for mechanical metamaterials and imparts scalable guidelines for achieving lightweight, mechanically efficient structures across multiple length scales.
The limited and scattered fatigue performances and their difficult predictability remain critical barriers for the widespread adoption of Laser-based Powder Bed Fusion (L-PBF) metamaterials in engineering applications, as fatigue damage initiation is highly sensitive to manufacturing-induced geometric imperfections. While X-ray computed tomography (CT) provides high-fidelity as-built reconstructions fundamental for metamaterials' structural health monitoring, its cost and complexity hinder routine integration into fatigue assessment workflows at the design stage. In this work, we propose a computationally efficient framework for the development of synthetic as-built CAD models, serving as digital twins for fatigue life and failure location prediction. The proposed model is herein reported for L-PBF Ti-6Al-4V struts, the elemental building blocks of metamaterial architectures, manufactured at different building orientations. Leveraging stereomicroscopy input images, a modular reconstruction pipeline capturing orientation-dependent surface morphology and partially fused particles allows the generation of as-built CAD models that retain the geometric variability governing fatigue behaviour, without reliance on volumetric imaging. Synthetic models are coupled with finite element analyses and a statistical strain energy density criterion to identify failure-critical locations. Validation against CT-derived counterparts demonstrates close morphological agreement and, since the design stage, the ability to estimate fatigue life and predict experimental failure locations within established scatter bands.
Periodic beam-based metamaterials have been extensively explored for their tunable stiffness, strength, and wave dispersion. Recent efforts extend this concept by maintaining the lattice topology but replacing beams by more complex structural members-such as straws or intertwined fibers. These mechanical metamaterials leverage underexplored mechanisms from the small-scale design such as contact, friction, and sliding, or multistability and reversible reconfigurability. This provides opportunities for untapped design spaces and performance exploration.
The inherent directionality of piezoelectric materials is constrained by the symmetry of their crystal structure, which limits the property space in natural piezoelectric materials. To alleviate this limitation, one could leverage geometry or architecture at the mesoscale. Here, we present a framework for designing and 3D-printing piezoelectric truss metamaterials with customizable anisotropic responses. We employ generative machine learning to design truss metamaterials and achieve unconventional behaviors, including auxetic, unidirectional, and omnidirectional piezoelectricity. Then, we develop an in-gel-3D printing method to fabricate these structures using a composite slurry of photo-curable resin and lead-free piezoelectric particles. We achieve an improvement of over 48% in the specific hydrostatic piezoelectric coefficient in optimized metamaterials over bulk lead zirconate titanate (PZT), and the rare phenomenon of higher transverse piezoelectric coefficients than the longitudinal coefficient. Our approach enables customizable piezoelectric responses and paves the way towards the development of a new generation of electro-active animate materials.
The untapped potential of thermal metamaterials requires the simultaneous observation of both diffusive and wave-like heat propagation across multiple length scales that can only be realised through theories beyond Fourier. Here, we demonstrate that tailored material patterning significantly modifies heat transport dynamics with enhanced non-Fourier behaviour, effectively trapping heat (temporarily). By bridging phonon scattering mechanisms with macroscopic heat flux via a novel perturbation-theory approach, we derive the hyperbolic Cattaneo model directly from particle dynamics, establishing a direct link between relaxation time and phonon lifetimes. Our micro-scale patterned systems exhibit extended non-Fourier characteristics, where internal interfaces mediate wave-like energy propagation, diverging sharply from diffusive Fourier predictions. These results provide a unified framework connecting micro-scale interactions to macroscopic transport, resolving long-standing limitations of the Cattaneo model. This work underscores the transformative potential of thermal metamaterials for ultra-fast thermal management and nanoscale energy applications, laying a theoretical foundation for next-generation thermal technologies.
The inverse design of curved truss structures in mechanical metamaterials remains underexplored due to the vast, discrete design space, lack of structural representation, high dimensionality, and inversion ambiguity. This work introduces a geometric AI framework to address these challenges and enable the design of curved cellular structures with targeted effective properties. A graph-based representation is developed and used to generate a dataset of over 200,000 unique structures, combining stiff straight beams with compliant curved elements, guided by tetragonal symmetry. A joint-attributed network embedding variational autoencoder constructs a continuous latent space encoding both topology and geometry, enabling prediction of linear and nonlinear properties. The inverse problem is solved in latent space using gradient-based optimization and a diffusion model conditioned on linear properties. The diffusion model achieves higher accuracy and efficiency, offering a scalable, flexible approach for discovering structures with both compliant and ultra-stiff behaviors and tunable nonlinear responses.
Composite structures with conformal coatings on porous backbones are widely employed in energy storage, flexible electronics, and biomedical devices. However, expansion-induced stresses can lead to mechanical degradation of the coatings, thereby limiting their performance. In this study, we use finite element simulations to evaluate how substrate morphology - including curvature, shape, and coating configuration - governs the mechanical response of expanding thin-film coatings, using lithiation of silicon anodes as a model case of extreme expansion. The peak stress and strain energy density of the expanding film are used as indicators of failure, and empirical relationships are introduced to predict their scaling with curvature. We find that films on shell-backbones consistently exhibit higher tensile stress but lower strain energy density than those on solid-backbones, reflecting a trade-off between cracking and delamination risks. In all studied configurations, substrates with positive Gaussian curvature amplify the in-plane stresses of the film and increase the propensity for mechanical degradation, whereas substrates with negative Gaussian curvature effectively redistribute stresses and enhance the mechanical resilience. This work highlights the advantages of shell-backbone saddle substrates for expanding thin-film systems and provides general guidelines for the design of mechanically robust architected composites and shell-based metamaterials.
Anthropogenic underwater noise poses a significant threat to marine ecosystems, disrupting key biological functions. Common mitigation strategies include enclosing noise sources within acoustic barriers. Current designs include locally resonant absorbers, which offer narrow-band performance, and reflective systems with limited effectiveness at low frequencies. In this work, we propose an approach to design thin anisotropic metamaterial-based acoustic barriers for broadband underwater noise attenuation at deep sub-wavelength scales using topology optimization to maximize the coupling between normal stresses and shear strains. Unlike conventional methods, the proposed optimization is formulated in the static regime, relying solely on the homogenized elastic properties of the structured material and not on the characteristics of the surrounding fluid. The resulting metabarriers achieve a high sound transmission loss (STL, 100 dB peak) above 2 kHz, while maintaining a thickness-to-wavelength ratio as low as 1/70 below 1 kHz and STL of approximately 20-30 dB. The influence of hydrostatic pressure on performance is also evaluated, and structural modifications for practical deployment are proposed. The results demonstrate the potential of anisotropy-driven metamaterials as compact and efficient solutions for the control of underwater noise, offering a promising avenue for future acoustic insulation technologies.
Manipulating intensity, phase and polarisation of the electromagnetic fields on ultrafast timescales is essential for all-optical switching, optical information processing and development of novel time-variant media. Noble metal based plasmonics has provided numerous platforms for optical switching and control, enabled by strong local field enhancement, artificially engineered dispersion and strong Kerr-type free-electron nonlinearities. However, achieving precise control over switching times and spectral response remains challenging, often limited by hot-electron gas relaxation on picosecond timescales and by the intrinsic band structure of the materials. Here, we experimentally demonstrate a strong and tunable nonlinearity in a metamaterial-on-a-mirror geometry, controlled by the wavelength of excitation, which imprints a specific, non-uniform hot-electron population distribution, driving targeted electron and lattice dynamics. The synergistic exchange of electromagnetic, electronic and mechanical energies enables reflection changes on sub-300 fs timescales in selected spectral ranges, surpassing the limitations imposed by the inherent material response of metamaterial constituents. The observed effect-present in reflection due to leaky guided modes of the metamaterial, but absent in transmission-is highly spectrally selective and sensitive to polarisation of light, opening a pathway to tailoring switching rates through the choice of operating wavelength and nanostructure design. The ability to manipulate temporal, spectral, and mechanical aspects of light-matter interactions underscores new opportunities for nonlinear optical applications where polarisation diversity, spectral selectivity, and ultrafast modulation are important.
Second-order nonlinear optical processes are fundamental to photonics, spectroscopy, and information technologies, with material platforms playing a pivotal role in advancing these applications. Here, we demonstrate the exceptional nonlinear optical properties of the van der Waals crystal 3R-MoS2, a rhombohedral polymorph exhibiting high second-order optical susceptibility (χ (2)) and remarkable second-harmonic generation (SHG) capabilities. By designing high quality factor resonances in 3R-MoS2 metasurfaces supporting quasi-bound states in the continuum (qBIC), we first demonstrate SHG efficiency enhancement exceeding 102. Additionally, by using degenerate pump-probe spectroscopy, we harness the C 3v system's symmetry to realize ultrafast SHG polarization switching with near-unity modulation depth. The operation speeds are limited only by the excitation pulse duration, allowing its characterization via the nonlinear autocorrelation function. These findings establish 3R-MoS2 as a transformative platform for nanoscale nonlinear optics, offering large conversion efficiencies and ultrafast response times for advanced pulse measurement devices, integrated photonics, and quantum technologies.
This study presents a computational framework for optimising a hip implant through a functionally graded biomimetic lattice structure, designed to reduce stress shielding. The optimisation technique, inspired by an inverse bone remodelling algorithm, promotes even stress distribution by reducing density and stiffness in regions with high strain energy compared to a reference level. The resulting non-uniform density distribution showed lower density levels along the implant stem's sides and higher density around its medial axis. This optimised material distribution was captured using mapping of a triply periodic minimal surface lattice structure on the implant, creating porous lattice surfaces within the solid structure. The porous implant's performance was evaluated using a finite element bone remodelling algorithm, comparing its bone response to a femur with a fully solid implant model, in terms of stress distribution and mass change. Results demonstrated improved bone formation at the bone-implant interface and enhanced stress transmission to the surrounding bone.
Over the last two decades, breakthrough works in the field of non-linear phononics have revealed that high-frequency lattice vibrations, when driven to high amplitude by mid- to far-infrared optical pulses, can bolster the light-matter interaction and thereby lend control over a variety of spontaneous orderings. This approach fundamentally relies on the resonant excitation of infrared-active transverse optical phonon modes, which are characterized by a maximum in the imaginary part of the medium's permittivity. Here, in this Perspective article, we discuss an alternative strategy where the light pulses are instead tailored to match the frequency at which the real part of the medium's permittivity goes to zero. This so-called epsilon-near-zero regime, popularly studied in the context of metamaterials, naturally emerges to some extent in all dielectric crystals in the infrared spectral range. We find that the light-matter interaction in the phononic epsilon-near-zero regime becomes strongly enhanced, yielding even the possibility of permanently switching both spin and polarization order parameters. We provide our perspective on how this hitherto-neglected yet fertile research area can be explored in future, with the aim to outline and highlight the exciting challenges and opportunities ahead.
NASA’s futuristic X-59 jet is about to face its biggest challenge yet: breaking the sound barrier for the first time。 After a successful series of test flights that pushed the aircraft to near-supersonic speeds, engineers are preparing to fly it faster than Mach 1 and eventually up to Mach 1。6 at 60,000 feet
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SpaceX won’t get easy access to billions of dollars from passive investors
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