arXiv subjects

Marco Miniaci

Publications and source records attributed to Marco Miniaci.

14 recordsLinked to original sources

arXiv2026

Diatom frustules as naturally occurring resonant microarchitectures: revealing vibrational eigenmodes across pennate and centric species

Diatom frustules, the hierarchically structured, species-specific silica exoskeletons of diatom microalgae, are among Nature's most sophisticated examples of bottom-up self-assembly, exhibiting nanoscale porosity, multifunctional mechanical and optical properties, and a morphological diversity that spans nearly three orders of magnitude in size. Despite growing interest in their optical and static mechanical properties, the elastodynamic behaviour of frustules has remained largely unexplored. Here we report the first experimental detection and spatially resolved reconstruction of vibrational eigenmodes in diatom frustules, combining laser Doppler vibrometry with morphology-faithful finite-element models informed by scanning electron microscopy (SEM) and focused-ion-beam scanning electron microscopy (FIB-SEM). Two morphologically contrasting taxa were investigated as model systems: the pennate diatom Rhaphoneis amphiceros and the centric diatom Stictodiscus californicus var. nitida, spanning the two principal branches of diatom diversity. Four eigenmodes were identified for R. amphiceros in the 5.90-14.17 MHz range and three for S. californicus in the 9.96-17.62 MHz range; the simulations yield a complete modal landscape for each species, including modally split and nearly degenerate eigenmodes arising from deviations from ideal symmetry, and show quantitative agreement with the experimentally measured mode shapes and resonant frequencies. These results establish diatom frustules as a class of naturally occurring resonant microarchitectures, and open new avenues for their integration as bio-derived functional elements in nanomechanical and MEMS/NEMS applications.

physics.app-ph↗

arXiv2026

Hyperuniformity as a unifying organizational principle across diatom architectures

Diatom frustules have long fascinated scientists for the extraordinary beauty, diversity, and functionality of their intricate silica architectures. Yet, the spatial organization of these structures has so far been primarily described in terms of morphology, symmetry, and crystallographic order, leaving common statistical properties across distinct diatom architectures largely unexplored. By analyzing diatom frustules through the lens of hyperuniformity for the first time, we reveal a striking commonality across their remarkable diversity: all analyzed genera exhibit signatures of suppressed long-wavelength density fluctuations. Specifically, we find that these architectures range from strongly ordered Class I to disordered Class III hyperuniform systems. We show that local order, spatial correlations, and long-range fluctuation suppression can vary partially independently, giving rise to a continuous spectrum of multiscale architectures. Our multiscale approach reveals that hyperuniformity can be reliably characterized in finite biological structures, beyond what conventional asymptotic diagnostics can resolve. Together, these results prove that hyperuniformity provides a unifying statistical framework for describing diatom diversity beyond conventional classifications of structural order.

physics.app-ph↗

arXiv2025

Longitudinal-flexural wave mode conversion via periodically undulated waveguides with constant and graded profiles

Wave mode conversion allows to transform energy from one propagating wave type to another at a boundary where a change in material properties or geometry occurs. Converting longitudinal waves to flexural ones is of particular interest in elasticity due to their significant displacement amplitudes, facilitating detection at the surface for practical applications. Typically, the design of wave conversion devices requires (i) the use of locally resonant structures with a spacing much shorter than the associated wavelengths, or (ii) architected media whose effective properties yield efficient mode conversion at selected frequencies. In both cases, the realization of these devices may incur in fabrication difficulties, thus requiring alternative solutions based on simpler designs that can retain the wave manipulation capabilities of interest. In this paper, we propose the use of single-phase periodically undulated beams to design phononic crystals that achieve wave mode conversion between longitudinal and flexural waves. We derive the corresponding dispersion relations using the plane wave expansion method and demonstrate that the coupling between longitudinal and flexural wave modes can be manipulated using an undulated profile, generating mode veering with inverted group velocities. The wave conversion mechanism is verified both computationally and experimentally, showing good agreement. Our findings indicate a versatile design strategy for phononic crystals with efficient wave conversion property, enabling applications in structural health monitoring, sensing, and non-destructive testing.

physics.app-ph↗

arXiv2024

An ultrasensitive device with embedded phononic crystals for the detection and localisation of nonlinear guided waves

In this work, a novel approach for the detection and localisation of nonlinear guided waves often associated with the presence of damage in structural components is proposed. The method is active and consists of a piezoelectric transducer bonded to the inspected structure exciting a narrow frequency band wave packet and sensors placed at the proposed ultrasonic devices with embedded phononic crystals. Unit cells of phononic crystals are optimized to open a band gap at the excitation frequency so that the excited waves are attenuated, while the sensitivity detection of higher harmonics is increased. The proposed approach is tested numerically and validated experimentally by considering various manufacturing methods, materials, and unit cell geometries. A parametric study of the angle of attachment of the ultrasonic devices with the embedded phononic crystals to the inspected structure is performed. Band gaps and filtering capabilities of several prototypes are tested. Numerical simulations of guided wave propagation that include the effect of delamination clapping proved that the proposed designs are sensitive enough to detect higher harmonics by simple signal thresholding. The most promising prototype is tested experimentally showing its capability of detection and localisation of a simulated damage.

physics.app-ph↗

arXiv2022

Band gap enhancement in periodic frames using hierarchical structures

The quest for novel designs for lightweight phononic crystals and elastic metamaterials with wide lowfrequency band gaps has proven to be a significant challenge in recent years. In this context, lattice-type materials represent a promising solution, providing both lightweight properties and significant possibilities of tailoring mechanical and dynamic properties. Additionally, lattice structures also enable the generation of hierarchical architectures, in which basic constitutive elements with different characteristic length scales can be combined. In this work, we propose 1D- and 2D-periodic phononic crystals made of spatial frames inspired by a spider web-based architecture. Specifically, hierarchical plane structures based on a combination of frames with a variable cross-section are proposed and exploited to open and enhance band gaps with respect to their non-hierarchical counterparts. Our results show that hierarchy is effective in broadening existing band gaps as well as opening new full band gaps in non-hierarchical periodic structures.

physics.app-ph↗

arXiv2021

Spectral flow of a localized mode in elastic media

The introduction of structural defects in otherwise periodic media is well known to grant exceptional space control and localization of waves in various physical fields, including elasticity. Despite the variety of designs proposed so far, most of the approaches derive from contextual modifications that do not translate into a design paradigm due to the lack of a general theory. Few exceptions include designs endowed with topological dispersion bands, which, however, require changes over substantial portions of the structure. To overcome these limitations, here we introduce a new rationale based on real-space topology to achieve localized modes in continuous elastic media. We theoretically predict and experimentally demonstrate the spectral flow of a localized mode across a bulk frequency gap by modulating a single structural parameter at any chosen location in the structure. The simplicity and generality of this approach opens new avenues in designing wave-based devices for energy localization and control.

physics.app-ph↗

arXiv2019

Shapely Atoms

The study of vibrational properties in engineered periodic structures relies on the early intuitions of Ha\"uy and Boscovich, who regarded crystals as ensembles of periodically arranged mass points interacting via attractive and repulsive forces. Contrary to electromagnetism, where mechanical properties do not couple to the wave propagation mechanism, in elasticity this paradigm inevitably led to low stiffness and high-density materials. Here, we transcend the Ha\"uy-Boscovich perception, proposing the concept of shaped atoms, which relaxes the link between the mass and inertia of atoms, to achieve unusual dynamic behavior at lower frequencies, leaving the stiffness unaltered. Exploiting tacticity, we successfully demonstrate its feasibility in continuous elastic chiral systems, opening the way to the conception of new mechanisms for wave control, selective wave filtering and vibration isolation.

cond-mat.mes-hall↗

arXiv2018

Valley based splitting of topologically protected helical waves in elastic plates

Topological protection offers unprecedented opportunities for wave manipulation and energy transport in various fields of physics, including elasticity, acoustics, quantum mechanics and electromagnetism. Distinct classes of topological waves have been investigated by establishing analogues with the quantum, spin and valley Hall effects. We here propose and experimentally demonstrate the possibility of supporting multiple classes of topological modes within a single platform. Starting from a patterned elastic plate featuring a double Dirac cone, we create distinct topological interfaces by lifting such degeneracy through selective breaking of symmetries across the thickness and in the plane of the plate. We observe the propagation of a new class of heterogeneous helical-valley edge waves capable of isolating modes on the basis of their distinct polarization. Our results show the onset of wave splitting resulting from the interaction of multiple topological equal-frequency wave modes, which may have significance in applications involving elastic beam-splitters, switches, and filters.

physics.app-ph↗

arXiv2018

A frequency-preserving and time-invariant metamaterial-based nonlinear acoustic diode

We present the realization of an acoustic diode or rectifier, exploiting symmetry-breaking nonlinear effects like harmonic generation and wave mixing and the filtering capabilities of metamaterials. The essential difference and advantage compared with previous acoustic diode realizations is that the present is simultaneously a time invariant, frequency preserving and switchable device. This allows its application also as an on-off or amplitude-tuning switch. We evaluate its properties by means of a numerical study and demonstrate its feasibility in a preliminary experimental realization. This work may provide new opportunities for the practical realization of structural components with one-way wave propagation properties.

physics.app-ph↗

arXiv2017

Relaxed micromorphic modeling of the interface between a homogeneous solid and a band-gap metamaterial: new perspectives towards meta-structural design

In the present paper, the material parameters of the isotropic relaxed micromorphic model derived for a specific metamaterial in a previous contribution are used to model its transmission properties. Specifically, the reflection and transmission coefficients at an interface between a homogeneous solid and the chosen metamaterial are analyzed by using both the relaxed micromorphic model and a direct FEM implementation of the detailed microstructure. The obtained results show an excellent agreement between the transmission spectra derived via our enriched continuum model and those issued by the direct FEM simulation. Such excellent agreement validates the indirect measure of the material parameters and opens the way towards an efficient meta-structural design.

cond-mat.mtrl-sci↗

arXiv2016

Proof of concept for an ultrasensitive meta-device to detect and localize nonlinear elastic sources

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 elastic metamaterials to naturally select the higher harmonics generated by nonlinear effects and to increase their signal-to noise ratios, 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.

physics.ins-det↗

arXiv2016

Modeling real phononic crystals via the weighted relaxed micromorphic model with free and gradient micro-inertia

In this paper the relaxed micromorphic continuum model with weighted free and gradient micro-inertia is used to describe the dynamical behavior of a real two-dimensional phononic crystal for a wide range of wavelengths. In particular, a periodic structure with specific micro-structural topology and mechanical properties, capable of opening a phononic band-gap, is chosen with the criterion of showing a low degree of anisotropy (the band-gap is almost independent of the direction of propagation of the traveling wave). A Bloch wave analysis is performed to obtain the dispersion curves and the corresponding vibrational modes of the periodic structure. A linear-elastic, isotropic, relaxed micromorphic model including both a free micro-inertia (related to free vibrations of the microstructures) and a gradient micro-inertia (related to the motions of the microstructure which are coupled to the macro-deformation of the unit cell) is introduced and particularized to the case of plane wave propagation. The parameters of the relaxed model, which are independent of frequency, are then calibrated on the dispersion curves of the phononic crystal showing an excellent agreement in terms of both dispersion curves and vibrational modes. Almost all the homogenized elastic parameters of the relaxed micromorphic model result to be determined. This opens the way to the design of morphologically complex meta-structures which make use of the chosen phononic structure as the basic building block and which preserve its ability of "stopping" elastic wave propagation at the scale of the structure.

physics.class-ph↗

arXiv2016

Spider-Web Inspired Mechanical 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 novel 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.

cond-mat.mtrl-sci↗

arXiv2016

Bio-inspired hierarchical dissipative metamaterials

Hierarchical structures with constituents over multiple length scales are found in various natural materials like bones, shells, spider silk and others, all of which display enhanced quasi-static mechanical properties, such as high specific strength, stiffness and toughness. At the same time, the role of hierarchy on the dynamic behaviour of metamaterials remains largely unexplored. This study assesses the effect of bio-inspired hierarchical organization as well as of viscoelasticity on the wave attenuation properties of continuous mechanical metamaterials. We consider single-phase metamaterials formed by self-similar unit cells with different hierarchical levels and types of hierarchy. Results highlight a number of advantages through the introduction of structural hierarchy. Band gaps relative to the corresponding non-hierarchical structures are mostly preserved, while additional "hierarchically-induced" band gaps appear. Additionally, the hierarchical configuration allows the tuning of the band gap frequencies of regular metamaterial to lower frequencies, with a simultaneous significant reduction of the global structural weight. We show that even small viscoelastic effects, not treated in the current literature, are essential in determining this behaviour. The approach we propose allows the addition of hierarchical elements to existing metamaterial configurations, with the corresponding improvement of the wave damping properties, thus providing indications for the design of structures for practical applications.

cond-mat.mtrl-sci↗