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Acoustic and Mechanical Metamaterials: Recent Advances
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Acoustic and Mechanical Metamaterials: Recent Advances

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Mechanics of Materials".

Deadline for manuscript submissions: 20 February 2025 | Viewed by 8163

Special Issue Editor

Dr. Reza Hedayati

E-Mail Website
Guest Editor
Aerospace Structures and Materials (ASM), Delft University of Technology, Postbus 5, 2600 AA Delft, The Netherland
Interests: mechanical properties; mechanical behavior of materials; mechanical testing; mechanics of materials; finite element analysis; acoustics; solid mechanics; finite element modeling; biomechanics; biomaterials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Metamaterials, artificially architectured materials with abnormal physical and mechanical properties, have recently been gaining momentum in research and industrial applications. This is because recent advances in advanced manufacturing technologies, such as additive manufacturing, have made fabricating these intricate materials feasible. It is well known that acoustic metamaterials are usually designed to effectively manipulate acoustic waves. On the other hand, mechanical metamaterials are used not only for their mechanical aspects such as auxeticity, shape morphing, and energy absorption, but in many cases, they are used for their excellent capability to manipulate acoustic wavs. This is why there is a relatively broad overlap of research in the fields of acoustic and mechanical metamaterials.

In this Special Issue, we aim to explore the latest advances in the design and manufacture of acoustic and mechanical metamaterials.

This Special Issue welcomes original research papers and review articles covering all relevant topics, including but not limited to:

  • Pentamodes;
  • Double-negative acoustic metamaterial;
  • Auxetic metamaterials;
  • Cosserat metamaterials;
  • Split-ring resonators;
  • Phononic crystals;
  • Superlenses;
  • Metamaterials with negative compressibility;
  • Willis materials.

Dr. Reza Hedayati
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • acoustic metamaterial
  • mechanical metamaterials
  • auxetics
  • resonators
  • pentamodes

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Published Papers (6 papers)

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Research

22 pages, 26955 KiB  
Article
Bandgap Calculation and Experimental Analysis of Piezoelectric Phononic Crystals Based on Partial Differential Equations
by Chunsheng Song, Yurun Han, Youliang Jiang, Muyan Xie, Yang Jiang and Kangchao Tang
Materials 2024, 17(15), 3780; https://doi.org/10.3390/ma17153780 - 1 Aug 2024
Viewed by 510
Abstract
Focusing on the bending wave characteristic of plate–shell structures, this paper derives the complex band curve of piezoelectric phononic crystal based on the equilibrium differential equation in the plane stress state using COMSOL PDE 6.2. To ascertain the computational model’s accuracy, the computed [...] Read more.
Focusing on the bending wave characteristic of plate–shell structures, this paper derives the complex band curve of piezoelectric phononic crystal based on the equilibrium differential equation in the plane stress state using COMSOL PDE 6.2. To ascertain the computational model’s accuracy, the computed complex band curve is then cross-validated against real band curves obtained through coupling simulations. Utilizing this model, this paper investigates the impact of structural and electrical parameters on the bandgap range and the attenuation coefficient in the bandgap. Results indicate that the larger surface areas of the piezoelectric sheet correspond to lower center bands in the bandgap, while increased thickness widens the attenuation coefficient range with increased peak values. Furthermore, the influence of inductance on the bandgap conforms to the variation law of the electrical LC resonance frequency, and increased resistance widens the attenuation coefficient range albeit with decreased peak values. The incorporation of negative capacitance significantly expands the low-frequency bandgap range. Visualized through vibration transfer simulations, the vibration-damping ability of the piezoelectric phononic crystal is demonstrated. Experimentally, this paper finds that two propagation modes of bending waves (symmetric and anti-symmetric) result in variable voltage amplitudes, and the average vibration of the system decreases by 4–5 dB within the range of 1710–1990 Hz. The comparison between experimental and model-generated data confirms the accuracy of the attenuation coefficient calculation model. This convergence between experimental and computational results emphasizes the validity and usefulness of the proposed model, and this paper provides theoretical support for the application of piezoelectric phononic crystals in the field of plate–shell vibration reduction. Full article
(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)
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27 pages, 14006 KiB  
Article
Effect of Degradation of Polylactic Acid (PLA) on Dynamic Mechanical Response of 3D Printed Lattice Structures
by Reza Hedayati, Melikasadat Alavi and Mojtaba Sadighi
Materials 2024, 17(15), 3674; https://doi.org/10.3390/ma17153674 - 25 Jul 2024
Viewed by 725
Abstract
Material-extrusion-based 3D printing with polylactic acid (PLA) has transformed the production of lightweight lattice structures with a high strength-to-weight ratio for various industries. While PLA offers advantages such as eco-friendliness, affordability, and printability, its mechanical properties degrade due to environmental factors. This study [...] Read more.
Material-extrusion-based 3D printing with polylactic acid (PLA) has transformed the production of lightweight lattice structures with a high strength-to-weight ratio for various industries. While PLA offers advantages such as eco-friendliness, affordability, and printability, its mechanical properties degrade due to environmental factors. This study investigated the impact resistance of PLA lattice structures subjected to material degradation under room temperature, humidity, and natural light exposure. Four lattice core types (auxetic, negative-to-positive (NTP) gradient in terms of Poisson’s ratio, positive-to-negative (PTN) gradient in terms of Poisson’s ratio, and honeycomb) were analyzed for variations in mechanical properties due to declines in yield stress and failure strain. Mechanical testing and numerical simulations at various yield stress and failure strain levels evaluated the degradation effect, using undegraded material as a reference. The results showed that structures with a negative Poisson’s ratio exhibited superior resistance to local crushing despite material weakening. Reducing the material’s brittleness (failure strain) had a greater impact on impact response compared to reducing its yield stress. This study also revealed the potential of gradient cores, which exhibited a balance between strength (maintaining similar peak force to auxetic cores around 800 N) and energy absorption (up to 40% higher than auxetic cores) under moderate degradation (yield strength and failure strain at 60% and 80% of reference values). These findings suggest that gradient structures with varying Poisson’s ratios employing auxetic designs are valuable choices for AM parts requiring both strength and resilience in variable environmental conditions. Full article
(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)
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23 pages, 8131 KiB  
Article
Active Acoustic Metamaterial Based on Helmholtz Resonators to Absorb Broadband Low-Frequency Noise
by Reza Hedayati and Sandhya P. Lakshmanan
Materials 2024, 17(4), 962; https://doi.org/10.3390/ma17040962 - 19 Feb 2024
Cited by 1 | Viewed by 1545
Abstract
The aim of the present work is to design active acoustic metamaterial consisting of an array of Helmholtz resonators and fabricating them using an additive manufacturing technique in order to assist in a reduction in noise levels in aerospace applications. To this aim, [...] Read more.
The aim of the present work is to design active acoustic metamaterial consisting of an array of Helmholtz resonators and fabricating them using an additive manufacturing technique in order to assist in a reduction in noise levels in aerospace applications. To this aim, initially, a passive metamaterial consisting of an array of 64 Helmholtz resonator unit cells is designed and tested to establish the effectiveness and region of performance. The selected design variable for change is identified as the resonator cavity depth through the frequency response for each parameter of the Helmholtz resonance equation and randomized to achieve a broadband frequency range of the passive metamaterial. An active model of this design (actuated by a stepper motor) is fabricated and tested. The metamaterials are tested under two acoustic set-ups: a closed system aimed at recreating the environment of a soundproof room and an open-system aimed to recreate the condition of an active liner. For the case of passive system, the metamaterial gave sound attenuation of 18 dB (for f = 150 Hz) in open system configuration and 33 dB (f = 350 Hz) in closed system configuration. The attenuation obtained for the active model was 10–15 dB over the mean line performance for the case of closed system and 15–20 dB for the case of open system. The closed system was also tested for performance at multiple cavity depths by setting two wall depths at 10 mm and three walls at 50 mm. This test yielded an attenuation of 15 dB at 180 Hz, the frequency corresponding to 50 mm cavity depth, and 10 dB at 515 Hz, corresponding to 10 mm cavity depth. Full article
(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)
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17 pages, 7263 KiB  
Article
Investigation and Tailoring of Rotating Squares’ and Rectangles’ Auxetic Structure Behavior through Computational Simulations of 6082T6 Aluminum Alloy Structures
by Mahmoud Elsamanty, Hassan Elshokrofy, Abdelkader Ibrahim, Antti Järvenpää and Mahmoud Khedr
Materials 2023, 16(24), 7597; https://doi.org/10.3390/ma16247597 - 11 Dec 2023
Cited by 3 | Viewed by 1437
Abstract
Auxetic structures, renowned for their unique lateral expansion under longitudinal strain, have attracted significant research interest due to their extraordinary mechanical characteristics, such as enhanced toughness and shear resistance. This study provides a systematic exploration of these structures, constructed from rigid rotating square [...] Read more.
Auxetic structures, renowned for their unique lateral expansion under longitudinal strain, have attracted significant research interest due to their extraordinary mechanical characteristics, such as enhanced toughness and shear resistance. This study provides a systematic exploration of these structures, constructed from rigid rotating square or rectangular unit cells. Incremental alterations were applied to key geometrical parameters, including the angle (θ) between connected units, the side length (a), the side width (b) of the rotating rigid unit, and the overlap distance (t). This resulted in a broad tunable range of negative Poisson’s ratio values from −0.43 to −1.78. Through comprehensive three-dimensional finite-element analyses, the intricate relationships between the geometric variables and the resulting bulk Poisson’s ratio of the modeled auxetic structure were elucidated. This analysis affirmed the auxetic behavior of all investigated samples, characterized by lateral expansion under tensile force. The study also revealed potential stress concentration points at interconnections between rotating units, which could impact the material’s performance under high load conditions. A detailed investigation of various geometrical parameters yielded fifty unique samples, enabling in-depth observation of the impacts of geometric modifications on the overall behavior of the structures. Notably, an increase in the side width significantly enhanced the Poisson’s ratio, while an increase in the overlap distance notably reduced it. The greatest observable change in the Poisson’s ratio was a remarkable 202.8%, emphasizing the profound influence of geometric parameter manipulation. A cascaded forward propagation–backpropagation neural network model was deployed to determine the Poisson’s ratio for auxetic structures, based on the geometric parameters and material properties of the structure. The model’s architecture consisted of five layers with varying numbers of neurons. The model’s validity was affirmed by comparing its predictions with FEA simulations, with the maximum error observed in the predicted Poisson’s ratio being 8.62%. Full article
(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)
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14 pages, 3835 KiB  
Article
Martensitic Phase-Transforming Metamaterial: Concept and Model
by Sosuke Kanegae, Masayuki Okugawa and Yuichiro Koizumi
Materials 2023, 16(21), 6854; https://doi.org/10.3390/ma16216854 - 25 Oct 2023
Viewed by 1080
Abstract
We successfully developed a mechanical metamaterial that displays martensitic transformation for the first time. This metamaterial has a bistable structure capable of transitioning between two stable configurations through shear deformation. The outer shape of the unit cell of this structure is a parallelogram, [...] Read more.
We successfully developed a mechanical metamaterial that displays martensitic transformation for the first time. This metamaterial has a bistable structure capable of transitioning between two stable configurations through shear deformation. The outer shape of the unit cell of this structure is a parallelogram, with its upper and lower sides forming the bases of two solid triangles. The vertices from these triangles within the parallelogram are linked by short beams, while the remaining vertices are linked by long beams. The elastic energy of the essential model of the metamaterial was formulated analytically. The energy barrier between these two stable configurations consists of the elastic strain energy due to the tensile deformation of the short beams, the compressive deformation of the long beams, and the bending deformation of the connecting hinges. One example of a novel metamaterial was additively manufactured via the materials extrusion (MEX) process of thermoplastic polyurethane. The metamaterial exhibited deformation behaviors characteristic of martensitic transformations. This mechanical metamaterial has the potential to obtain properties caused by martensitic transformation in actual materials, such as the shape memory effect and superelasticity. Full article
(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)
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33 pages, 44626 KiB  
Article
Study on Sound-Insulation Performance of an Acoustic Metamaterial of Air-Permeable Multiple-Parallel-Connection Folding Chambers by Acoustic Finite Element Simulation
by Wenqiang Peng, Shaohua Bi, Xinmin Shen, Xiaocui Yang, Fei Yang and Enshuai Wang
Materials 2023, 16(12), 4298; https://doi.org/10.3390/ma16124298 - 9 Jun 2023
Cited by 3 | Viewed by 1697
Abstract
In order to achieve a balance between sound insulation and ventilation, a novel acoustic metamaterial of air-permeable multiple-parallel-connection folding chambers was proposed in this study that was based on Fano-like interference, and its sound-insulation performance was investigated through acoustic finite element simulation. Each [...] Read more.
In order to achieve a balance between sound insulation and ventilation, a novel acoustic metamaterial of air-permeable multiple-parallel-connection folding chambers was proposed in this study that was based on Fano-like interference, and its sound-insulation performance was investigated through acoustic finite element simulation. Each layer of the multiple-parallel-connection folding chambers consisted of a square front panel with many apertures and a corresponding chamber with many cavities, which were able to extend both in the thickness direction and in the plane direction. Parametric analysis was conducted for the number of layers nl and turns nt, the thickness of each layer L2, the inner side lengths of the helical chamber a1, and the interval s among the various cavities. With the parameters of nl = 10, nt = 1, L2 = 10 mm, a1 = 28 mm, and s = 1 mm, there were 21 sound-transmission-loss peaks in the frequency range 200–1600 Hz, and the sound-transmission loss reached 26.05 dB, 26.85 dB, 27.03 dB, and 33.6 dB at the low frequencies 468 Hz, 525 Hz, 560 Hz, and 580 Hz, respectively. Meanwhile, the corresponding open area for air passage reached 55.18%, which yielded a capacity for both efficient ventilation and high selective-sound-insulation performance. Full article
(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)
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