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Elastic and Thermal Metamaterials: Novel Properties and Applications

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

Deadline for manuscript submissions: closed (10 July 2023) | Viewed by 8433

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Prof. Dr. Tungyang Chen

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Guest Editor

Department of Civil Engineering, National Cheng Kung University, Tainan 70101, Taiwan
Interests: seismic metamaterials; thermal metamaterials; composites; micromechanics

Prof. Dr. Kuo-Chun Chang

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Guest Editor

Department of Civil Engineering, National Taiwan University, Taipei 10617, Taiwan
Interests: dynamic structural tests; structural mechanics; earthquake resistance design; passive structural control
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Special Issue Information

Dear Colleagues,

Metamaterials are synthetic composite materials with artificial structures that are specifically designed to have intriguing properties in controlling physical fields, and have enabled a wide range of new applications. In the last few years, there has been tremendous progress made in realizing artificial metamaterials and metastructures both in theoretical and experimental aspects, for example in electromagnetic and acoustic waves. The studies on elastic metamaterials, particularly for seismic waves, and also thermal metamaterials are relatively recent. The cloaking of seismic waves, encompassing different types of surface waves produced by earthquakes, is much more challenging. These waves have long wavelengths and low frequencies, and in particular travel through an anisotropic and irregular propagation medium, soil. A viable strategy may offer a potential solution that complements current civil engineering solutions to ensure the safety of buildings and infrastructures. On the other hand, heat transfer and thermodynamics are transport phenomena and are equally important. The cloaking of heat can have potential applications in advanced energy control and management.

This Special Issue aims to further focus on elastic and thermal metamaterials, presenting new discoveries in relevant subjects through new theoretical concepts and design approaches, new numerical simulations, experimental implementations, and various novel applications. This Special Issue will serve as a platform for researchers from different disciplines to bring together recent scientific advances to demonstrate what can be done and what can be envisaged in the future.

Prof. Dr. Tungyang Chen
Prof. Dr. Kuo-Chun Chang
Guest Editors

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Keywords

elastic metamaterials
thermal metamaterials
theoretical modelling and numerical simulations
material and physical properties
technological applications
experimental verifications

Published Papers (5 papers)

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Research

16 pages, 6359 KiB

Open AccessArticle

Metamaterials of Auxetic Geometry for Seismic Energy Absorption

by Ahmed Abdalfatah Saddek, Tzu-Kang Lin, Wen-Kuei Chang, Chia-Han Chen and Kuo-Chun Chang

Materials 2023, 16(15), 5499; https://doi.org/10.3390/ma16155499 - 07 Aug 2023

Cited by 1 | Viewed by 1406

Abstract

The propagation of earthquake energy occurs primarily through elastic waves. If the seismic force input to a structure can be directly reduced from the source, then the structure can be protected from seismic wave energy. Seismic metamaterials, regarded as periodic structures with properties different from conventional materials, use wave propagation characteristics and bandgaps to dissipate seismic wave energy. When the seismic wave is located in the bandgap, the transmission of seismic wave energy is effectively reduced, which protects the structure from the damage caused by seismic disturbance. In practical application, locating seismic frequencies below ten Hz is a challenge for seismic metamaterials. In the commonly used method, high-mass materials are employed to induce the effect of local resonance, which is not economically feasible. In this study, a lightweight design using auxetic geometry is proposed to facilitate the practical feasibility of seismic metamaterials. The benefits of this design are proven by comparing conventional seismic metamaterials with metamaterials of auxetic geometry. Different geometric parameters are defined using auxetic geometry to determine the structure with the best bandgap performance. Finite element simulations are conducted to evaluate the vibration reduction benefits of auxetic seismic metamaterials in time and frequency domains. Additionally, the relationship between the mass and stiffness of the unit structure is derived from the analytical solution of one-dimensional periodic structures, and modal analysis results of auxetic metamaterials are verified. This study provides seismic metamaterials that are lightweight, small in volume, and possess low-frequency bandgaps for practical applications. Full article

(This article belongs to the Special Issue Elastic and Thermal Metamaterials: Novel Properties and Applications)

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13 pages, 2829 KiB

Open AccessArticle

Gradient V-Shaped and N-Shaped Seismic Metamaterials

by Yu-Chi Su and Sheng-Shiang Wang

Materials 2023, 16(8), 3074; https://doi.org/10.3390/ma16083074 - 13 Apr 2023

Cited by 1 | Viewed by 1225

Abstract

Seismic metamaterials provide an innovative alternative in earthquake engineering by reducing the hazards from seismic waves without modifying the existing structures. Although many seismic metamaterials have been proposed, a design for a broad bandgap at low frequencies is still in demand. In this study, two novel seismic metamaterials, V- and N-shaped designs, are proposed. We found that by adding a line to the letter V, turning the V-shaped design into an N-shaped design, the bandgap can be broadened. Both the V- and N-shaped designs are arranged in a gradient pattern to combine the bandgaps from metamaterials with different heights. Using only concrete as the base material for the design makes the proposed seismic metamaterial cost effective. Finite element transient analysis and band structures are in good agreement, validating the accuracy of the numerical simulations. Surface waves are effectively attenuated over a broad range of low frequencies using the gradient V- and N-shaped seismic metamaterials. Full article

(This article belongs to the Special Issue Elastic and Thermal Metamaterials: Novel Properties and Applications)

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20 pages, 7630 KiB

Open AccessArticle

Design of Two-Dimensional Transient Circular Thermal Cloaks with Imperfect Interfaces

by Jun-Hong Lin and Tungyang Chen

Materials 2023, 16(6), 2297; https://doi.org/10.3390/ma16062297 - 13 Mar 2023

Cited by 2 | Viewed by 1092

Abstract

In this paper, analytic modeling for the design of a transient thermal invisibility cloak with imperfect interfaces is presented together with numerical simulations. In contrast to steady-state conditions, it is shown that an object can only be made partially invisible under a transient-state condition with either ideal or imperfect interfaces. The thermal visibility of an object to the external region can be optimally suppressed under certain conditions referred to as the “weak invisibility conditions” for the transient response, which are different from the “strong invisibility conditions” that can completely conceal an object in a steady state. In the formulation, a homogeneous metamaterial with constant volumetric heat capacity and constant anisotropic conductivity tensor is employed. It can be demonstrated that the interface’s bonding conditions will have a significant effect on the design of metamaterials. Two typical types of imperfect interfaces, referred to as low-conductivity- and high-conductivity-type interfaces, are considered. Conditions, that render an object mostly undetectable, are analytically found and expressed in simple forms under quasi-static approximations. Within the quasi-static limit, the thermal localization in the target region can be tuned with the anisotropy of the conductivity tensor. Thermal shielding or concentrating effects in the target region are exemplified based on finite element simulations to demonstrate the manipulation of heat flux in the target region. The present findings make new advances in theoretical fundamentals and numerical simulations on the effect of the imperfect interface in the transient regime and can serve as guidelines in the design of thermal metamaterials through the entire conduction process. Full article

(This article belongs to the Special Issue Elastic and Thermal Metamaterials: Novel Properties and Applications)

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23 pages, 6859 KiB

Open AccessArticle

Deep-Learning-Based Acoustic Metamaterial Design for Attenuating Structure-Borne Noise in Auditory Frequency Bands

by Ting-Wei Liu, Chun-Tat Chan and Rih-Teng Wu

Materials 2023, 16(5), 1879; https://doi.org/10.3390/ma16051879 - 24 Feb 2023

Cited by 8 | Viewed by 2422

Abstract

In engineering acoustics, the propagation of elastic flexural waves in plate and shell structures is a common transmission path of vibrations and structure-borne noises. Phononic metamaterials with a frequency band gap can effectively block elastic waves in certain frequency ranges, but often require a tedious trial-and-error design process. In recent years, deep neural networks (DNNs) have shown competence in solving various inverse problems. This study proposes a deep-learning-based workflow for phononic plate metamaterial design. The Mindlin plate formulation was used to expedite the forward calculations, and the neural network was trained for inverse design. We showed that, with only 360 sets of data for training and testing, the neural network attained a 2% error in achieving the target band gap, by optimizing five design parameters. The designed metamaterial plate showed a −1 dB/mm omnidirectional attenuation for flexural waves around 3 kHz. Full article

(This article belongs to the Special Issue Elastic and Thermal Metamaterials: Novel Properties and Applications)

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21 pages, 6992 KiB

Open AccessArticle

Evaluation of a Hybrid Underwater Sound-Absorbing Metastructure by Using the Transfer Matrix Method

by Han-Chun Lin, Shu-Cheng Lu and Hsin-Haou Huang

Materials 2023, 16(4), 1718; https://doi.org/10.3390/ma16041718 - 18 Feb 2023

Cited by 1 | Viewed by 1668

Abstract

In this study, we designed a novel hybrid underwater sound-absorbing material of the metastructure that contains a viscoelastic substrate with a microperforated panel. Two types of sound-absorbing metastructures were combined to achieve satisfactory sound absorption performance in the low-frequency range. A homogenized equivalent layer and the integrated transfer matrix method were used to theoretically evaluate the sound absorption performance of the designed nonhomogeneous hybrid metastructure. The theoretical results were then compared with the results obtained using the finite-element method. The designed hybrid sound-absorbing metastructure exhibited two absorption peaks because of its different sound-absorbing mechanisms. The acoustic performance of the developed metastructure is considerably better than that of a traditional sound absorber, and the sound absorption coefficient of the developed metastructure is 0.8 in the frequency range of 3–10 kHz. In addition, an adjustment method for the practical underwater application of the designed metastructure is described in this research. Further studies show that the sound absorption coefficient of the adjusted metastructure still has 0.75 in the frequency range of 3–10 kHz, which indicates that this metastructure has the potential to be used as an underwater sound-absorbing structure. The results of this study can be used as a reference in the design of other novel hybrid underwater sound-absorbing structures. Full article

(This article belongs to the Special Issue Elastic and Thermal Metamaterials: Novel Properties and Applications)

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