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Acoustic Metamaterials and Acoustic Foams: Recent Advances

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: closed (10 December 2021) | Viewed by 11734

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Special Issue Editors

Dr. Reza Hedayati

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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; materials testing; solid mechanics; finite element modeling; biomechanics; biomaterials
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Dr. Mahdi Bodaghi

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Department of Engineering, School of Science and Technology, Nottingham Trent University, Nottingham NG11 8NS, UK
Interests: mechanics of biomaterials; smart materials and structures; meta-materials; soft matters; regenerative medicine; 3D and 4D printing technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleague，

Acoustic metamaterials are synthetic materials made of repeating unit cells which are designed to address an acoustic problem by the rational design of their micro-features. The characteristics of acoustic metamaterials are dominated by their rationally designed microarchitecture rather than the base material. Particularly, acoustic metamaterials can manipulate sound and elastic waves both spatially and spectrally in unpreceded ways. Such properties include super-focusing, super-lensing, cloaking, active membrane structures, phononic plates, fluid cavities separated by piezoelectric boundaries, and tunable noise attenuation based on Helmholtz resonators.

This class of materials did not exist until recently, as manufacturing their complex features was either impossible or prohibitively expensive. Recent advances in additive manufacturing (3D printing) have made it possible to manufacture such constructions with complex internal geometries and at much lower cost. Even though acoustic metamaterials are becoming more and more prevalent in academic and industrial sectors, acoustic foams have still kept their importance in addressing noise issues, due to their relatively low cost and high noise mitigation performance.

This Special Issue explores the latest advances in the development of acoustic metamaterials as well as recent advances in acoustic foams.

Dr. Reza Hedayati
Dr. Mahdi Bodaghi
Guest Editors

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Keywords

noise control
acoustic metamaterials
broadband noise attenuation
additive manufacturing
acoustic foams
3D printing

Published Papers (4 papers)

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Editorial

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2 pages, 170 KiB

Open AccessEditorial

Acoustic Metamaterials and Acoustic Foams: Recent Advances

by Reza Hedayati and Mahdi Bodaghi

Appl. Sci. 2022, 12(6), 3096; https://0-doi-org.brum.beds.ac.uk/10.3390/app12063096 - 18 Mar 2022

Cited by 5 | Viewed by 2570

Abstract

Acoustic metamaterials are synthetic materials, made of repeating unit cells that are designed to address an acoustic problem, through the rational design of their micro-features [...] Full article

(This article belongs to the Special Issue Acoustic Metamaterials and Acoustic Foams: Recent Advances)

Research

Jump to: Editorial

15 pages, 6506 KiB

Open AccessArticle

Combined Attenuation Zones of Combined Layered Periodic Foundations

by Xinnan Liu, Yiqiang Ren and Xiaoruan Song

Appl. Sci. 2021, 11(15), 7114; https://0-doi-org.brum.beds.ac.uk/10.3390/app11157114 - 31 Jul 2021

Cited by 6 | Viewed by 1366

Abstract

Layered periodic foundations (LPFs) with identical unit cells have been proposed as a type of seismic metamaterials due to the unique dynamic characteristic of attenuation zones. However, it is difficult to design attenuation zones with both comparatively low starting frequencies and large bandwidths for traditional LPFs with identical unit cells. In this paper, combined layered periodic foundations (CLPFs) are proposed by combining two traditional LPFs with different unit cells in tandem. Combined attenuation zones of the CLPFs are identified by investigating the frequency response functions of the CLPFs. The generation mechanism of the combined attenuation zones was studied by varying the configuration of CLPFs. The results show that the combined attenuation zones are the union of attenuation zones of the two traditional LPFs. To verify the efficiency of CLPFs, the seismic responses of a four-story frame structure with CLPF are simulated. The present work is very helpful for the design of CLPFs with attenuation zones with a low starting frequency and large bandwidth. Full article

(This article belongs to the Special Issue Acoustic Metamaterials and Acoustic Foams: Recent Advances)

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13 pages, 2058 KiB

Open AccessArticle

A Metawindow with Optimised Acoustic and Ventilation Performance

by Gioia Fusaro, Xiang Yu, Zhenbo Lu, Fangsen Cui and Jian Kang

Appl. Sci. 2021, 11(7), 3168; https://0-doi-org.brum.beds.ac.uk/10.3390/app11073168 - 02 Apr 2021

Cited by 19 | Viewed by 2844

Abstract

Crucial factors in window performance, such as natural ventilation and noise control, are generally conceived separately, forcing users to choose one over the other. To solve this dualism, this study aimed to develop an acoustic metamaterial (AMM) ergonomic window design to allow noise control without dependence on the natural ventilation duration and vice versa. First, the finite element method (FEM) was used to investigate the noise control performance of the acoustic metawindow (AMW) unit, followed by anechoic chamber testing, which also served as the validation of the FEM models. Furthermore, FEM analysis was used to optimise the acoustic performance and assess the ventilation potential. The numerical and experimental results exhibited an overall mean sound reduction of 15 dB within a bandwidth of 380 to 5000 Hz. A good agreement between the measured and numerical results was obtained, with a mean variation of 30%. Therefore, the AMW unit optimised acoustic performance, resulting in a higher noise reduction, especially from 50 to 500 Hz. Finally, most of the AMW unit configurations are suitable for natural ventilation, and a dynamic tuned ventilation capacity can be achieved for particular ranges by adjusting the window’s ventilation opening. The proposed designs have potential applications in building acoustics and engineering where natural ventilation and noise mitigation are required to meet regulations simultaneously. Full article

(This article belongs to the Special Issue Acoustic Metamaterials and Acoustic Foams: Recent Advances)

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36 pages, 9413 KiB

Open AccessArticle

Improving the Accuracy of Analytical Relationships for Mechanical Properties of Permeable Metamaterials

by Reza Hedayati, Naeim Ghavidelnia, Mojtaba Sadighi and Mahdi Bodaghi

Appl. Sci. 2021, 11(3), 1332; https://0-doi-org.brum.beds.ac.uk/10.3390/app11031332 - 02 Feb 2021

Cited by 19 | Viewed by 3302

Abstract

Permeable porous implants must satisfy several physical and biological requirements in order to be promising materials for orthopaedic application: they should have the proper levels of stiffness, permeability, and fatigue resistance approximately matching the corresponding levels in bone tissues. This can be achieved using designer materials, which exhibit exotic properties, commonly known as metamaterials. In recent years, several experimental, numerical, and analytical studies have been carried out on the influence of unit cell micro-architecture on the mechanical and physical properties of metamaterials. Even though experimental and numerical approaches can study and predict the behaviour of different micro-structures effectively, they lack the ease and quickness provided by analytical relationships in predicting the answer. Although it is well known that Timoshenko beam theory is much more accurate in predicting the deformation of a beam (and as a result lattice structures), many of the already-existing relationships in the literature have been derived based on Euler–Bernoulli beam theory. The question that arises here is whether or not there exists a convenient way to convert the already-existing analytical relationships based on Euler–Bernoulli theory to relationships based on Timoshenko beam theory without the need to rewrite all the derivations from the start point. In this paper, this question is addressed and answered, and a handy and easy-to-use approach is presented. This technique is applied to six unit cell types (body-centred cubic (BCC), hexagonal packing, rhombicuboctahedron, diamond, truncated cube, and truncated octahedron) for which Euler–Bernoulli analytical relationships already exist in the literature while Timoshenko theory-based relationships could not be found. The results of this study demonstrated that converting analytical relationships based on Euler–Bernoulli to equivalent Timoshenko ones can decrease the difference between the analytical and numerical values for one order of magnitude, which is a significant improvement in accuracy of the analytical formulas. The methodology presented in this study is not only beneficial for improving the already-existing analytical relationships, but it also facilitates derivation of accurate analytical relationships for other, yet unexplored, unit cell types. Full article

(This article belongs to the Special Issue Acoustic Metamaterials and Acoustic Foams: Recent Advances)

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