Anastasiia Krushynska

Large scale mechanical metamaterials as seismic shields

Earthquakes represent one of the most catastrophic natural events affecting mankind. At present, a universally accepted risk mitigation strategy for seismic events remains to be proposed. Most approaches are based on vibration isolation of structures rather than on the remote shielding of incoming waves. In this work, we propose a novel approach to the problem and discuss the feasibility of a passive isolation strategy for seismic waves based on large-scale mechanical metamaterials, including for the first time numerical analysis of both surface and guided waves, soil dissipation effects, and adopting a full 3D simulations. The study focuses on realistic structures that can be effective in frequency ranges of interest for seismic waves, and optimal design criteria are provided, exploring different metamaterial configurations, combining phononic crystals and locally resonant structures and different ranges of mechanical properties. Dispersion analysis and full-scale 3D transient wave transmission simulations are carried out on finite size systems to assess the seismic wave amplitude attenuation in realistic conditions. Results reveal that both surface and bulk seismic waves can be considerably attenuated, making this strategy viable for the protection of civil structures against seismic risk. The proposed remote shielding approach could open up new perspectives in the field of seismology and in related areas of low-frequency vibration damping or blast protection.

Proof of Concept for an Ultrasensitive Technique to Detect and Localize Sources of Elastic Nonlinearity Using Phononic Crystals

M. Miniaci, A. S. Gliozzi, ∗ B. Morvan, A. Krushynska, F. Bosia, M. Scalerandi, and N. M. Pugno † University of Le Havre, Laboratoire Ondes et Milieux Complexes, UMR CNRS 6294, 75 Rue Bellot, 76600 Le Havre, France Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy Department of Physics, University of Torino, Via Pietro Giuria 1, 10125 Torino, Italy Laboratory of Bio-Inspired and Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano 77, 38123 Trento, Italy (Dated: September 3, 2018)The appearance of nonlinear effects in elastic wave propagation is one of the most reliable and sensitive indicators of the onset of material damage. However, these effects are usually very small and can be detected only using cumbersome digital signal processing techniques. Here, we propose and experimentally validate an alternative approach, using the filtering and focusing properties of phononic crystals to naturally select and reflect the higher harmonics generated by nonlinear effects, enabling the realization of time-reversal procedures for nonlinear elastic source detection. The proposed device demonstrates its potential as an efficient, compact, portable, passive apparatus for nonlinear elastic wave sensing and damage detection.

Spider web-structured labyrinthine acoustic metamaterials for low-frequency sound control

Attenuating low-frequency sound remains a challenge, despite many advances in this field. Recently-developed acoustic metamaterials are characterized by unusual wave manipulation abilities that make them ideal candidates for efficient subwavelength sound control. In particular, labyrinthine acoustic metamaterials exhibit extremely high wave reflectivity, conical dispersion, and multiple artificial resonant modes originating from the specifically-designed topological architectures. These features enable broadband sound attenuation, negative refraction, acoustic cloaking and other peculiar effects. However, hybrid and/or tunable metamaterial performance implying enhanced wave reflection and simultaneous presence of conical dispersion at desired frequencies has not been reported so far. In this paper, we propose a new type of labyrinthine acoustic metamaterials (LAMMs) with hybrid dispersion characteristics by exploiting spider web-structured configurations. The developed design approach consists in adding a square surrounding frame to sectorial circular-shaped labyrinthine channels described in previous publications (e.g. (11)). Despite its simplicity, this approach provides tunability in the metamaterial functionality, such as the activation/elimination of subwavelength band gaps and negative group-velocity modes by increasing/decreasing the edge cavity dimensions. Since these cavities can be treated as extensions of variable-width internal channels, it becomes possible to exploit geometrical features, such as channel width, to shift the band gap position and size to desired frequencies. Time transient simulations demonstrate the effectiveness of the proposed metastructures for wave manipulation in terms of transmission or reflection coefficients, amplitude attenuation and time delay at subwavelength frequencies. The obtained results can be important for practical applications of LAMMs such as lightweight acoustic barriers with enhanced broadband wave-reflecting performances.

Spider web-inspired acoustic metamaterials

Spider silk is a remarkable example of bio-material with superior mechanical characteristics. Its multilevel structural organization of dragline and viscid silk leads to unusual and tunable properties, extensively studied from a quasi-static point of view. In this study, inspired by the Nephila spider orb web architecture, we propose a design for mechanical metamaterials based on its periodic repetition. We demonstrate that spider-web metamaterial structure plays an important role in the dynamic response and wave attenuation mechanisms. The capability of the resulting structure to inhibit elastic wave propagation in sub-wavelength frequency ranges is assessed, and parametric studies are performed to derive optimal configurations and constituent mechanical properties. The results show promise for the design of innovative lightweight structures for tunable vibration damping and impact protection, or the protection of large scale infrastructure such as suspended bridges.

Multi-layered inclusions in locally resonant metamaterials: two-dimensional vs. three-dimensional modeling

Locally resonant metamaterials (LRMs) controlling low-frequency waves due to resonant scattering are usually characterized by narrow band gaps (BGs) and a poor wave filtering performance. To remedy this shortcoming, multiresonant metamaterial structures with closely located BGs have been proposed and widely studied. However, the analysis is generally limited to two-dimensional (2D) structures neglecting the finite height of any real resonator. The aim of this paper is the comparison of the wave dispersion for two- and three-dimensional (3D) metamaterial models and evaluation of the applicability ranges of 2D results. Numerical study reveals that dual-resonant structures with cylindrical inclusions possess only a single (compared to two in the 2D case) BG for certain height-to-width ratios. In contrast, the wave dispersion in metamaterials with multiple spherical resonators can be accurately evaluated using a 2D approximation, enabling a significant simplification of resource-consuming 3D models.

Nonlinear damage detection and localization via an innovative metamaterial-based sensor

In recent years, acoustic metamaterials have attracted increasing scientific interest for very diverse technological applications ranging from sound abatement to ultrasonic imaging, mainly due to their ability to act as band-stop filters. At the same time, the concept of chaotic cavities has been recently proposed as an efficient tool to enhance the quality of nonlinear signal analysis, particularly in the ultrasonic/acoustic case. The goal of the present work is to merge the two concepts to propose a metamaterial-based device that can be used as a natural and selective linear filter for the detection of signals resulting from the propagation of elastic waves in nonlinear solids, e.g., in the presence of damage, and as a detector for the damage itself in time reversal experiments. Numerical simulations and experimental measurements based on scanning laser Doppler vibrometer demonstrate the feasibility of the approach and the potential of the device in providing improved signal to noise ratios and enhanced focusing on scatterer locations.

Fractal and bio-inspired labyrinthine acoustic metamaterials

Control of low-frequency sound is a challenge, despite numerous advances in the field. Recently emerged acoustic metamaterials have already proven their efficiency for the development of innovative systems for sound control and demonstration of such fascinating phenomena as super-resolution imaging, transformation acoustics, acoustic cloaking, etc. For sound attenuation, a common attenuation mechanism relies on dispersion induced by local resonances that results in the generation of slow sound inside a metastructure at resonant frequencies. However, the selective bandwidth of metamaterials with identical resonators restricts their practical applications. To overcome this limitation, one can introduce rainbow-type resonators that leads to the increase of structural sizes and raises manufacturing costs. We present fractal and bio-inspired labyrinthine acoustic metamaterials with non-resonant elements for low-frequency sound control. Designed configurations contain sets of narrow channels extending wave propagation paths that leads to reduction of effective sound speed within a structure. We show that by folding these channels into fractal space-filling curves or bio-inspired geometries, one can induce strong artificial Mie-type resonances that allow the achievement of total broadband sound reflection at deep subwavelength scales. This unique phenomenon can be used to develop small-size metastructures with total reflectance of low-frequency sound for versatile applications.Control of low-frequency sound is a challenge, despite numerous advances in the field. Recently emerged acoustic metamaterials have already proven their efficiency for the development of innovative systems for sound control and demonstration of such fascinating phenomena as super-resolution imaging, transformation acoustics, acoustic cloaking, etc. For sound attenuation, a common attenuation mechanism relies on dispersion induced by local resonances that results in the generation of slow sound inside a metastructure at resonant frequencies. However, the selective bandwidth of metamaterials with identical resonators restricts their practical applications. To overcome this limitation, one can introduce rainbow-type resonators that leads to the increase of structural sizes and raises manufacturing costs. We present fractal and bio-inspired labyrinthine acoustic metamaterials with non-resonant elements for low-frequency sound control. Designed configurations contain sets of narrow channels extending wave prop...

Editorial: Advances in Mechanical Metamaterials

Bio-Inspired & Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy, 3 School of Aerospace Engineering and School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States, 4 Laboratoire Ondes et Milieux Complexes, UMR CNRS 6294, University of Le Havre, Le Havre, France, 5 School of Engineering & Materials Science, Queen Mary University of London, London, United Kingdom, 6 KET Labs, Edoardo Amaldi Foundation, Italian Space Agency, Rome, Italy