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13 pages, 7175 KiB

Open AccessArticle

Analysis of Antichiral Thermomechanical Metamaterials with Continuous Negative Thermal Expansion Properties

by Debajyoti Saha, Paul Glanville and Eduard G. Karpov

Materials 2020, 13(9), 2139; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13092139 - 06 May 2020

Cited by 10 | Viewed by 3193

Abstract

Negative thermal expansion is an interesting and appealing phenomenon for various scientific and engineering applications, while rarely occurring in natural materials. Here, using a universal antichiral metamaterial model with bimetal beams or strips, a generic theory has been developed to predict magnitude of [...] Read more.

Negative thermal expansion is an interesting and appealing phenomenon for various scientific and engineering applications, while rarely occurring in natural materials. Here, using a universal antichiral metamaterial model with bimetal beams or strips, a generic theory has been developed to predict magnitude of the negative thermal expansion effect from model parameters. Thermal expansivity of the metamaterial is written as an explicit function of temperature and only three design parameters: relative node size, chirality angle, and a bimetal constant. Experimental measurements follow theoretical predictions well, where thermal expansivity in the range of negative 0.0006–0.0041 °C⁻¹ has been seen. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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11 pages, 1858 KiB

Open AccessArticle

On the Broadening of Single-Layer Metasurface Bandwidth by Coupling Resonances

by Humberto Fernández Álvarez, María Elena de Cos Gómez and Fernando Las-Heras Andrés

Materials 2020, 13(9), 2063; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13092063 - 29 Apr 2020

Cited by 5 | Viewed by 2217

Abstract

In this contribution a new technique to increase the bandwidth of metasurfaces without increasing their profile is presented. This work takes advantage of the potential multiresonant behavior of a metamaterial whose unit cells comprise nested metallization geometries in the same layer. The novelty [...] Read more.

In this contribution a new technique to increase the bandwidth of metasurfaces without increasing their profile is presented. This work takes advantage of the potential multiresonant behavior of a metamaterial whose unit cells comprise nested metallization geometries in the same layer. The novelty stems from the possibility of overlapping these resonances for increasing the bandwidth (instead of obtaining a multiresonant metasurface). Several guidelines to achieve the aforementioned bandwidth broadening, which are applicable to all metasurface designs, will be provided. An equivalent circuit model will be used to better explain the presented technique; then, it will be applied to several metasurface absorbers (MTAs), showing not only a bandwidth broadening but also an absorption reinforcement. Measurements will be also presented to corroborate the simulation results. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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6 pages, 1717 KiB

Open AccessArticle

Negative Effective Mass in Plasmonic Systems

by Edward Bormashenko and Irina Legchenkova

Materials 2020, 13(8), 1890; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13081890 - 17 Apr 2020

Cited by 9 | Viewed by 4236

Abstract

We report the negative effective mass (density) metamaterials based on the electro-mechanical coupling exploiting plasma oscillations of a free electron gas. The negative mass appears as a result of the vibration of a metallic particle with a frequency of ω, which is [...] Read more.

We report the negative effective mass (density) metamaterials based on the electro-mechanical coupling exploiting plasma oscillations of a free electron gas. The negative mass appears as a result of the vibration of a metallic particle with a frequency of ω, which is close the frequency of the plasma oscillations of the electron gas

m_{2}

relative to the ionic lattice

m_{1}

. The plasma oscillations are represented with the elastic spring

k_{2} = ω_{p}^{2} m_{2}

, where

ω_{p}

is the plasma frequency. Thus, the metallic particle vibrated with the external frequency ω is described by the effective mass

m_{e f f} = m_{1} + \frac{m_{2} ω_{p}^{2}}{ω_{p}^{2} - ω^{2}}

, which is negative when the frequency

ω

approaches

ω_{p}

from above. The idea is exemplified with two conducting metals, namely Au and Li. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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12 pages, 5023 KiB

Open AccessArticle

A Low-Profile Wideband Linear-to-Circular Polarization Conversion Slot Antenna Using Metasurface

by Jian Dong, Chang Ding and Jinjun Mo

Materials 2020, 13(5), 1164; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13051164 - 05 Mar 2020

Cited by 44 | Viewed by 4281

Abstract

A new low-profile wideband linear-to-circular polarization conversion microstrip slot antenna based on a metasurface for C-band satellite communication applications is proposed in this paper. The metasurface basically consists of four unit cells with parasitic square cross gaps arranged in a 2 × 2 [...] Read more.

A new low-profile wideband linear-to-circular polarization conversion microstrip slot antenna based on a metasurface for C-band satellite communication applications is proposed in this paper. The metasurface basically consists of four unit cells with parasitic square cross gaps arranged in a 2 × 2 layout. By loading the metasurface on the microstrip slot antenna, linearly polarized (LP) waves from the source antenna are converted into circularly polarized (CP) waves. Then, by etching three more parasitic square cross gaps in the middle of the metasurface, enhanced impedance bandwidth and axial ratio bandwidth (ARBW) are achieved. Furthermore, an equivalent circuit and a phase analysis are presented to explain how a wide ARBW is realized by the metasurface. A final model with an overall size of 36 × 36 × 3.5 mm³ (approximately 0.65λ₀ × 0.65λ₀ × 0.06λ₀ at 5.5 GHz) was designed and fabricated. The measured S₁₁ bandwidth and 3 dB ARBW were 39.25% from 4.28 GHz to 6.37 GHz and 17.77% from 5.18 GHz to 6.19 GHz, respectively. As a result, the proposed antenna shows great potential for satellite communication applications due to its low profile and compact structure, wide impedance bandwidth, and wide axial ratio bandwidth. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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12 pages, 3098 KiB

Open AccessArticle

Simulated and Experimental Research of Multi-Band Acoustic Metamaterial with a Single Resonant Structure

by Huaijun Chen and Changlin Ding

Materials 2019, 12(21), 3469; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12213469 - 23 Oct 2019

Cited by 12 | Viewed by 2463

Abstract

We present a multi-band acoustic metamaterial (AMM) with a single structural unit of a nested split hollow sphere (NSHS). The transmissions of the NSHS-AMM from the simulation and experiment revealed two dips which were attributed to local coupling resonance. Using the retrieval method [...] Read more.

We present a multi-band acoustic metamaterial (AMM) with a single structural unit of a nested split hollow sphere (NSHS). The transmissions of the NSHS-AMM from the simulation and experiment revealed two dips which were attributed to local coupling resonance. Using the retrieval method from the experimental data, we calculated the effective modulus of the NSHS-AMM and found it to be negative near the bands of the two dips. The AMM with a negative modulus can be easily tuned due to the coupling effect in the NSHS. The two dips can be simultaneously tuned by changing the diameter and the direction angle of the split holes of the interior and exterior split hollow sphere (SHS) in the NSHS. We designed a three-nested SHS-AMM with a negative modulus in three bands. Given the obvious local coupling resonance in the NSHS, such NSHS-AMMs may provide a viable path for the design of broadband AMMs or acoustic metasurfaces. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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13 pages, 12558 KiB

Open AccessArticle

Optically Transparent Metamaterial Absorber Using Inkjet Printing Technology

by Heijun Jeong, Manos M. Tentzeris and Sungjoon Lim

Materials 2019, 12(20), 3406; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12203406 - 17 Oct 2019

Cited by 5 | Viewed by 3165

Abstract

An optically transparent metamaterial absorber that can be obtained using inkjet printing technology is proposed. In order to make the metamaterial absorber optically transparent, an inkjet printer was used to fabricate a thin conductive loop pattern. The loop pattern had a width of [...] Read more.

An optically transparent metamaterial absorber that can be obtained using inkjet printing technology is proposed. In order to make the metamaterial absorber optically transparent, an inkjet printer was used to fabricate a thin conductive loop pattern. The loop pattern had a width of 0.2 mm and was located on the top surface of the metamaterial absorber, and polyethylene terephthalate films were used for fabricating the substrate. An optically transparent conductive indium tin oxide film was introduced in the bottom ground plane. Therefore, the proposed metamaterial absorber was optically transparent. The metamaterial absorber was demonstrated by performing a full-wave electromagnetic simulation and measured in free space. In the simulation, the 90% absorption bandwidth ranged from 26.6 to 28.8 GHz, while the measured 90% absorption bandwidth was 26.8–28.2 GHz. Therefore, it is successfully demonstrated by electromagnetic simulation and measurement results. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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12 pages, 33453 KiB

Open AccessArticle

Frequency-Diverse Bunching Metamaterial Antenna for Coincidence Imaging

by Mengran Zhao, Shitao Zhu, Jianxing Li, Hongyu Shi, Juan Chen, Yuchen He and Anxue Zhang

Materials 2019, 12(11), 1817; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12111817 - 04 Jun 2019

Cited by 24 | Viewed by 3089

Abstract

A frequency-diverse bunching metamaterial antenna for coincidence imaging in the Ka band is proposed in this paper. The bunching metamaterial antenna includes a broadband circular array and a frequency-diverse bunching metalens. Firstly, in order to enhance the bunching characteristic, the broadband circular array [...] Read more.

A frequency-diverse bunching metamaterial antenna for coincidence imaging in the Ka band is proposed in this paper. The bunching metamaterial antenna includes a broadband circular array and a frequency-diverse bunching metalens. Firstly, in order to enhance the bunching characteristic, the broadband circular array is designed based on the 60-degree beamwidth design to generate radiation patterns from 32 GHz to 36 GHz. Then, types of metamaterial elements with different transmission phases are selected to form the frequency-diverse bunching metalens based on a random distribution design and gradient zoom coefficient design. Moreover, the bunching metamaterial antenna is constituted by loading the frequency-diverse bunching metalens to the broadband circular array, which can generate frequency-diverse bunching random radiation patterns with beamwidth less than 100 degrees from 32 GHz to 36 GHz. Furthermore, the performances of the bunching metamaterial antenna, including the reflection coefficient, the radiation efficiency, and the correlation coefficients of radiation patterns at different frequencies are evaluated. Finally, the coincidence imaging experiment is implemented using the bunching metamaterial antenna and the image of the target is reconstructed successfully. The design is verified by simulations and measurements. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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20 pages, 18422 KiB

Open AccessArticle

Reprogramming Static Deformation Patterns in Mechanical Metamaterials

by Larry A. Danso and Eduard G. Karpov

Materials 2018, 11(10), 2050; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11102050 - 20 Oct 2018

Cited by 6 | Viewed by 4010

Abstract

This paper discusses an x-braced metamaterial lattice with the unusual property of exhibiting bandgaps in their deformation decay spectrum, and, hence, the capacity for reprogramming deformation patterns. The design of polarizing non-local lattice arising from the scenario of repeated zero eigenvalues of a [...] Read more.

This paper discusses an x-braced metamaterial lattice with the unusual property of exhibiting bandgaps in their deformation decay spectrum, and, hence, the capacity for reprogramming deformation patterns. The design of polarizing non-local lattice arising from the scenario of repeated zero eigenvalues of a system transfer matrix is also introduced. We develop a single mode fundamental solution for lattices with multiple degrees of freedom per node in the form of static Raleigh waves. These waves can be blocked at the material boundary when the solution is constructed with the polarization vectors of the bandgap. This single mode solution is used as a basis to build analytical displacement solutions for any applied essential and natural boundary condition. Subsequently, we address the bandgap design, leading to a comprehensive approach for predicting deformation pattern behavior within the interior of an x-braced plane lattice. Overall, we show that the stiffness parameter and unit-cell aspect ratio of the x-braced lattice can be tuned to completely block or filter static boundary deformations, and to reverse the dependence of deformation or strain energy decay parameter on the Raleigh wavenumber, a behavior known as the reverse Saint Venant’s edge effect (RSV). These findings could guide future research in engineering smart materials and structures with interesting functionalities, such as load pattern recognition, strain energy redistribution, and stress alleviation. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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9 pages, 2006 KiB

Open AccessArticle

Tunable Acoustic Metasurface with High-Q Spectrum Splitting

by Shilong Zhai, Kun Song, Changlin Ding, Yuanbo Wang, Yibao Dong and Xiaopeng Zhao

Materials 2018, 11(10), 1976; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11101976 - 14 Oct 2018

Cited by 17 | Viewed by 3783

Abstract

We propose a tunable acoustic metasurface using a nested structure as the microunit, which is constituted by two distinct resonators. Thanks to the coupling resonance for the microunit and by simply adjusting the rotation angle of the inner split cavity, this nested structure [...] Read more.

We propose a tunable acoustic metasurface using a nested structure as the microunit, which is constituted by two distinct resonators. Thanks to the coupling resonance for the microunit and by simply adjusting the rotation angle of the inner split cavity, this nested structure provides nearly 2π phase shift. The full-wave simulations demonstrate that the constructed metasurface can be tuned to reflect incident sound waves to different directions in the operation frequency region with a very narrow bandwidth, which is a key functionality for many applications such as filtering and imaging. Meanwhile, the reflected sound waves out of the operation frequency region always remain unchanged. As a result, a high Q-factor spectrum splitting can be realised. The presented metasurface is of importance to develop many metamaterial-based devices, such as tunable acoustic cloaks and acoustic switching devices. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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Review

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16 pages, 3986 KiB

Open AccessReview

Mechanical Metamaterials on the Way from Laboratory Scale to Industrial Applications: Challenges for Characterization and Scalability

by Sarah C. L. Fischer, Leonie Hillen and Chris Eberl

Materials 2020, 13(16), 3605; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13163605 - 14 Aug 2020

Cited by 39 | Viewed by 6064

Abstract

Mechanical metamaterials promise a paradigm shift in materials design, as the classical processing-microstructure-property relationship is no longer exhaustively describing the material properties. The present review article provides an application-centered view on the research field and aims to highlight challenges and pitfalls for the [...] Read more.

Mechanical metamaterials promise a paradigm shift in materials design, as the classical processing-microstructure-property relationship is no longer exhaustively describing the material properties. The present review article provides an application-centered view on the research field and aims to highlight challenges and pitfalls for the introduction of mechanical metamaterials into technical applications. The main difference compared to classical materials is the addition of the mesoscopic scale into the materials design space. Geometrically designed unit cells, small enough that the metamaterial acts like a mechanical continuum, enabling the integration of a variety of properties and functionalities. This presents new challenges for the design of functional components, their manufacturing and characterization. This article provides an overview of the design space for metamaterials, with focus on critical factors for scaling of manufacturing in order to fulfill industrial standards. The role of experimental and simulation tools for characterization and scaling of metamaterial concepts are summarized and herewith limitations highlighted. Finally, the authors discuss key aspects in order to enable metamaterials for industrial applications and how the design approach has to change to include reliability and resilience. Full article

(This article belongs to the Special Issue Metamaterials and Devices)

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