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Crystals
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Metamaterials and Their Devices, Second Edition
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Metamaterials and Their Devices, Second Edition

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Hybrid and Composite Crystalline Materials".

Deadline for manuscript submissions: 30 June 2025 | Viewed by 3155

Special Issue Editor

Prof. Dr. Youngpak Lee

E-Mail Website
Guest Editor
1. Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China
2. Quantum Photonic Science Research Center and RINS, Department of Physics, Hanyang University, Seoul 04763, Republic of Korea
Interests: metamaterials; spin-photonic crystals; magneto-optical properties
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Over the past two decades, metamaterials (MMs) have led a revolution in new material science through the artificial arrangement of electric- and magnetic-resonance structures (meta-atoms) at the subwavelength scale. In particular, they have enriched the fundamental rules of matter–light interactions, such as slow light, super-resolution, super-lensing, and electromagnetic (EM) cloaking. The main reason for the attention paid to MMs is that they are very close in appearance to real life, such as perfect absorbers. EM MMs reveal remarkable responses to the incident EM wave, such as negative-refraction index, extraordinary optical transmission, electromagnetically induced transparency-like effects, and ultra-thin and broadband absorbers. The designed structures, the structural parameters, and the properties of used materials yield the effective electric permittivity (εeff(ω)) and the effective magnetic permeability (μeff(ω)) of overall MMs, based on the effective-medium theory. Studies on the control of EM response and its spatial distribution and dispersion are ripe and lead to potential and almost-realized applications. There are emerging fields in MM research, such as nonlinear, switchable, gain-assisted, sensor, quantum, and coding MMs, all representing a variety of MM applications.

Prof. Dr. Youngpak Lee
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. Crystals is an international peer-reviewed open access monthly 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 2100 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

  • metamaterials
  • lattice metamaterials
  • crystal materials and structures
  • plasmonic and dielectric metamaterials
  • photonic crystals
  • phononic crystals
  • metasurfaces
  • fundamental issues
  • emerging fields for MMs
  • electromagnetic response
  • magnetic-resonance
  • electric-resonance
  • numerical methods
  • applications

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Related Special Issue

Published Papers (5 papers)

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Research

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12 pages, 3635 KiB  
Article
Design of Multifunctional Polarization Waveplates Based on Thermal Phase-Change Metasurfaces
by Bo Cheng, Yuxiao Zou, Zihui Ge, Longfeng Lv, Taohua Liang, Kunpeng Zhai and Guofeng Song
Crystals 2025, 15(5), 462; https://doi.org/10.3390/cryst15050462 - 14 May 2025
Viewed by 126
Abstract
The switching function of traditional waveplates necessitates mechanical replacement or the superimposition of multiple waveplates, which gives rise to a complex system and a large volume. We have devised a multifunctional micro-waveplate based on the COMSOL simulation platform (v5.6), which concurrently integrates the [...] Read more.
The switching function of traditional waveplates necessitates mechanical replacement or the superimposition of multiple waveplates, which gives rise to a complex system and a large volume. We have devised a multifunctional micro-waveplate based on the COMSOL simulation platform (v5.6), which concurrently integrates the compact nature of metasurfaces and the dynamic regulatory features of phase-change materials. When the phase-change material is in the crystalline phase, the metasurface possesses the functionality of a half-waveplate (HWP) and is capable of performing chirality inversion of circularly polarized light within the wavelength range of 1.45 μm to 1.52 μm and 1.56 μm to 1.61 μm. When the phase-change material is in the amorphous phase, the metasurface serves as a quarter-waveplate (QWP) and can achieve the conversion between linear and circular polarization through a 90° phase delay. The phase-change metasurface breaks through the constraint of fixed functions of traditional optical waveplates, facilitating the development of optical systems towards miniaturization, intelligence, and low power consumption and providing a crucial technical route for the next generation of photonic integration and dynamic optical applications. Full article
(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)
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15 pages, 4412 KiB  
Article
Evolution of Phonon Spectral Energy Density in Superlattice Structures
by Milad Nasiri and Yan Wang
Crystals 2025, 15(5), 446; https://doi.org/10.3390/cryst15050446 - 9 May 2025
Viewed by 230
Abstract
Superlattices are a distinctive class of artificial nanostructures formed by the periodic stacking of two or more materials. The high density of interfaces in these structures often gives rise to exotic physical properties. In the context of thermal transport, it is well established [...] Read more.
Superlattices are a distinctive class of artificial nanostructures formed by the periodic stacking of two or more materials. The high density of interfaces in these structures often gives rise to exotic physical properties. In the context of thermal transport, it is well established that such interfaces can significantly scatter particle-like phonons while also inducing constructive or destructive interference in wave-like phonons, depending on the relationship between the phonons’ coherence lengths and the superlattice’s period thickness. In this work, we systematically investigate the effect of temperature on the spectral energy density of phonon modes in superlattices. Additionally, we examine how variations in superlattice period thickness influence phonon lifetimes and energy density. Our findings provide critical insights into the spectral phonon properties of superlattices, particularly in terms of their coherence and lifetimes. Full article
(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)
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11 pages, 3003 KiB  
Article
A Compact and Fast Resonant Cavity-Based Encoder in Photonic Crystal Platform
by Mohammad Soroosh, Faris K. AL-Shammri, Mohammad Javad Maleki, Venkatachalam Rajarajan Balaji and Ehsan Adibnia
Crystals 2025, 15(1), 24; https://doi.org/10.3390/cryst15010024 - 28 Dec 2024
Cited by 4 | Viewed by 976
Abstract
A novel 4-to-2 photonic crystal encoder is proposed by modulating the intensity of four input optical signals, and four distinct output states are achieved. Nonlinear rods are employed to couple input waves into resonant cavities, directing the light to the desired output waveguides. [...] Read more.
A novel 4-to-2 photonic crystal encoder is proposed by modulating the intensity of four input optical signals, and four distinct output states are achieved. Nonlinear rods are employed to couple input waves into resonant cavities, directing the light to the desired output waveguides. The proposed design, with a footprint of 114 µm2, demonstrates efficient encoding operation at a wavelength of 1550 nm and is highly suitable for integrated photonics applications. A comprehensive comparative analysis revealed that the proposed 4-to-2 encoder exhibits a time response 176 fs faster than previously presented encoders. Furthermore, the contrast ratio of the designed structure is as high as 13.78 dB to distinguish between logic 0 and 1. These advancements hold significant potential for enhancing the performance of compact, high-speed digital circuits. Full article
(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)
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14 pages, 4971 KiB  
Article
Embedded Rough-Neck Helmholtz Resonator Low-Frequency Acoustic Attenuator
by Xianming Sun, Tao Yu, Lipeng Wang, Yunshu Lu and Changzheng Chen
Crystals 2025, 15(1), 12; https://doi.org/10.3390/cryst15010012 - 26 Dec 2024
Viewed by 900
Abstract
In various practical noise control scenarios, such as duct noise mitigation, industrial machinery, architectural acoustics, and underwater applications, it is essential to develop noise absorbers that deliver effective low-frequency attenuation while maintaining compact dimensions. To achieve low-frequency absorption within a limited spatial volume, [...] Read more.
In various practical noise control scenarios, such as duct noise mitigation, industrial machinery, architectural acoustics, and underwater applications, it is essential to develop noise absorbers that deliver effective low-frequency attenuation while maintaining compact dimensions. To achieve low-frequency absorption within a limited spatial volume, this study proposes an embedded Helmholtz resonator featuring a roughened neck and establishes a numerical computational model that incorporates thermos viscous effects. A quantitative investigation is conducted on three types of embedded rough-neck geometries (rectangular-grooved, triangular-grooved, and undulated) to elucidate their acoustic performance, with particular attention to differences in acoustic transmission loss and acoustic impedance characteristics. In response to the practical demand for even lower-frequency attenuation, this work further focuses on optimizing the structural parameters of an embedded rectangular-grooved Helmholtz resonator (ERHR). A back-propagation (BP) neural network models and predicts how structural parameters impact the acoustic transmission coefficient, elucidating the effects of geometric variations. Moreover, by coupling the BP network with the Golden Jackal Optimization (GJO) algorithm, a BP-GJO optimization model is developed to refine the structural parameters. The findings reveal that the proposed method significantly improves resonator spatial utilization at a specific noise frequency while preserving acoustic transmission loss performance. This work thereby provides a promising strategy for designing low-frequency, compact Helmholtz resonators suitable for a wide range of noise control applications. Full article
(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)
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Review

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39 pages, 2266 KiB  
Review
Design and Processing of Metamaterials
by Andrei Teodor Matei, Anita Ioana Vișan and Gianina Florentina Popescu-Pelin
Crystals 2025, 15(4), 374; https://doi.org/10.3390/cryst15040374 - 18 Apr 2025
Viewed by 656
Abstract
Metamaterials represent artificially structured materials that exhibit unusual properties, such as a negative refractive index, negative permeability and permittivity, negative cloaking by Poisson ratios and optical effects, etc., which are inaccessible in natural materials. According to recent developments, novel devices and tools based [...] Read more.
Metamaterials represent artificially structured materials that exhibit unusual properties, such as a negative refractive index, negative permeability and permittivity, negative cloaking by Poisson ratios and optical effects, etc., which are inaccessible in natural materials. According to recent developments, novel devices and tools based on metamaterials are attracting great interest as they offer improved performance, functionality, sensitivity, biocompatibility, complex structures, and design freedom. Leveraging numerical design approaches, such as finite element analysis and finite difference time domain methods, researchers have tailored metamaterials to meet specific requirements in various areas through a range of manufacturing techniques. These materials can be broadly classified into optical, mechanical, thermal, electromagnetic, and acoustic categories based on their properties and intended use. The choice of fabrication method depends heavily on the specific application, the desired scale, and the complexity of the metamaterial design. These manufacturing methods can be broadly divided into top-down and bottom-up approaches, while each of them has advantages and limitations and offers valuable pathways for the development of the final product. This review offers a basic overview of metamaterials, covering their fundamental principles, fabrication and characterization techniques, and current design methodologies. It also explores their diverse applications, including specific case studies in medicine, while addressing existing limitations and challenges. Finally, this review highlights future perspectives, emphasizing the need for continued innovation in fabrication and characterization to unlock the full potential of metamaterials. Full article
(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)
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