Electromagnetic Metamaterials Research Articles

Smart reconfigurable electromagnetic metamaterials based on thermadapt shape memory Poly(ethylene–vinyl acetate)

Smart reconfigurable metamaterials can better adapt to changing electromagnetic environments and broaden the range of applications. However, constructing electromagnetic reconfigurable metamaterials, especially those with large areas or applied to complex surfaces via a universal approach, is still a challenge. Here, we introduce a smart reconfigurable metamaterial consisting of a thermadapt shape memory polymer ethylene vinyl acetate copolymer (EVA) matrix and a flowable liquid–metal resonant unit. Based on the excellent self-healing properties of EVA, large-area metamaterials can be constructed by thermal assembly of metamaterial units. In addition, the original shape of the metamaterial can be reprogrammed to apply to complex three-dimensional surfaces with the reprocessing properties of EVA. Moreover, by utilizing the shape memory performance of the EVA, the temporary resonant frequency of the metamaterial can be set by programming and the resonant frequency tuning of the metamaterial can be controlled under external temperature stimulation, achieving noncontact tuning. In the future, this concept can be broadly applied in fields such as complex structure stealth layers and multifunction filters.

Lignin-Derived Lightweight Carbon Aerogels for Tunable Epsilon-Negative Response.

Electromagnetic (EM) metamaterials have garnered considerable attention due to their capacity to achieve negative parameters, significantly influencing the integration of natural materials with artificially structural media. The emergence of carbon aerogels (CAs) offers an opportunity to create lightweight EM metamaterials, notable for their promising EM shielding or absorption effects. This paper introduces an efficient, low-cost method for fabricating CAs without requiring stringent drying conditions. By finely tuning the ZnCl2/lignin ratio, the porosity is controlled in CAs. This control leads to an epsilon-negative response in the radio-frequency region, driven by the intrinsic plasmonic state of the 3D carbon network, as opposed to traditional periodic building blocks. This approach yields a tunable and weakly epsilon-negative response, reaching an order of magnitude of -103 under MHz frequencies. Equivalent circuit analysis highlights the inductive characteristics of CAs, correlating their significant dielectric loss at low frequencies. Additionally, EM simulations are performed to evaluate the distribution of the electric field vector in epsilon-negative CAs, showcasing their potential for effective EM shielding. The lignin-derived, lightweight CAs with their tunable epsilon-negative response hold promise for pioneering new directions in EM metamaterials and broadening their application in diverse extreme conditions.

Loss Analysis of the Electromagnetic Metamaterial Applied to Antenna Size Reductions

The research of transformation electromagnetics uses spatial coordinate transformation method to transform Maxwell’s equations for the propagations of electromagnetic waves in space, thereby achieving the goal of designing the path of electromagnetic waves, which eventually leads to a more complex tensor design of its constitutive parameters of metamaterials. This demand for artificial design of material parameters has been combined with the rapid development of micro-scale, molecular-scale, and atomic-scale experimental engineering techniques in recent years, enabling metamaterials to be developed, fabricated, and applied in various frontier fields. In this paper, the metamaterial electromagnetic wave concentrator used to reduce the antenna size is mainly discussed and detailed simulations and researches on the electromagnetic lossy conditions of the metamaterial parameters are given, which can better verify the electromagnetic scattering performance under actual engineering conditions. Solutions and quantitative simulations for the attenuation characteristics are also provided, which can deepen the research on the engineering performance of the metamaterial electromagnetic transformation devices.

Poles and residues of lossy and dispersive electromagnetic metamaterials

This paper proposes a system-based pole-residue approach to describe loss and dispersion in double-positive (DPS), epsilon-negative (ENG), and epsilon-near-zero (ENZ) isotropic metamaterials. The matrix pencil (MP) method extracts the poles and residues from the damped sinusoids of the singular expansion (SEM) of the impulse responses of the transmitted and reflected waves. The complex values of poles and residues serve as a basis for a computational tool to discriminate between lossless, lossy, and dispersive materials. The extracted poles and residues can also be used to classify the material under test as a DPS, an ENG, or an ENZ metamaterial. The proposed method delivers reliable results even with noisy transmission and reflection data.

Application of Metamaterial in Renewable Energy: A Review

Metamaterial advancements hold promise for compact renewable energy harvesting, capturing acoustic, electromagnetic, mechanical, and solar energy on a modest scale across global industries. Engineered structures surpass natural material limitations, offering capabilities unattainable in traditional counterparts. This investigation explores metamaterials' manipulation of acoustic, electromagnetic, mechanical, and solar energy. Mechanical metamaterials convert strain into electrical energy, applicable from interstellar travel to terrestrial infrastructure. Precision-configured acoustic metamaterials efficiently harness dispersed acoustic energy, improving renewable energy methodologies. Integration into photovoltaic cells showcases metamaterials' solar potential, with innovative designs enhancing solar energy conversion efficiency. Electromagnetic metamaterials efficiently absorb and convert frequencies into usable energy from communications and monitoring systems, in the agricultural and environmental sectors. Comparative analyses highlight noteworthy efficiency advancements, underscoring metamaterials' transformative influence on renewable energy. As they redefine the sector, implications extend to both small-scale devices and large-scale applications, positioning them as pivotal contributors. The paper critically evaluates metamaterial effectiveness in harnessing diverse energy sources, guiding future research. Metamaterial adaptability to different sizes and integration into technology reveals possibilities for compact energy sources. Ongoing research addresses scientific and economic challenges, paving the way for scaling metamaterial applications to commercial operations and emphasizing their importance in incorporating renewable energy into our technological milieu.

Metamaterial Absorbers with Archimedean Tiling Structures: Toward Response and Absorption of Multiband Electromagnetic Waves.

With the continuous development of electromagnetic wave-absorbing materials, the design of artificial structures for electromagnetic absorbers based on the concept of metamaterials is becoming more abundant. However, in the design process, it is difficult to further broaden the effective absorption band due to the limitation that the traditional single-size structure responds to electromagnetic waves only in specific frequency bands. Therefore, in this paper, based on the moth-eye bionic hexagonal structure absorber with antireflection performance, an Archimedean tiling structure is designed to optimize it, and through the introduction of a variety of primitives with large differences in dimensions, a multifrequency band-response mechanism is achieved to enhance the multireflection mechanism, which can effectively broaden the absorption band and improve the wave absorption performance. Ultimately, the moth-eye bionic structure absorber optimized by (3.4.6.4) can achieve an effective absorption of 10.26 GHz at a thickness of 2 mm. This work presents a new idea for the design work of electromagnetic wave-absorbing metamaterials, which has a broad application prospect in the aerospace, electronic information countermeasures, communication, and detection industries.

Experimental Demonstration of Controllable PT and Anti-PT Coupling in a Non-Hermitian Metamaterial.

Non-Hermiticity has recently emerged as a rapidly developing field due to its exotic characteristics related to open systems, where the dissipation plays a critical role. In the presence of balanced energy gain and loss with environment, the system exhibits parity-time (PT) symmetry, meanwhile as the conjugate counterpart, anti-PT symmetry can be achieved with dissipative coupling within the system. Here, we demonstrate the coherence of complex dissipative coupling can control the transition between PT and anti-PT symmetry in an electromagnetic metamaterial. Notably, the achievement of the anti-PT symmetric phase is independent of variations in dissipation. Furthermore, we observe phase transitions as the system crosses exceptional points in both anti-PT and PT symmetric metamaterial configurations, achieved by manipulating the frequency and dissipation of resonators. This work provides a promising metamaterial design for broader exploration of non-Hermitian physics and practical application with a controllable Hamiltonian.

A non-conformal domain decomposition method utilizing rotating subdomains and non-matching grids for periodic metamaterial simulation

Electromagnetic metamaterials possess characteristics such as having large-scale, periodic, multi-media, and complex geometric structures, making them highly suitable for simulation using the finite element domain decomposition method (DDM). This work proposes a non-conformal DDM for simulating finite-period metamaterials, achieving simulation with a minimal number of domains while significantly reducing computational resource consumption. First, the computational domain of the periodic metamaterial is partitioned into several non-conformal hexahedral subdomains. Subsequently, a limited number of non-repetitive subdomain models with non-matching grids are constructed, leveraging the three-dimensional rotational and translational properties of these subdomains to facilitate simulation. By eliminating the necessity to construct models for every subdomain, a substantial reduction in memory consumption is achieved. Second, an iteration method for solving the matrix equations of subdomains is enhanced by introducing a multifrontal block incomplete Cholesky decomposition preconditioner, thereby enhancing the computational efficiency of matrix equations with a large number of unknowns. Meanwhile, parallel computing techniques are employed to accelerate the proposed method. Finally, we integrate the aforementioned method into a solver and leverage it to develop an electromagnetic simulation tool tailored for metamaterials. The tool is employed to simulate metamaterial structures of varying scales, resulting in notable reductions in both memory and time consumption while maintaining accuracy comparable to commercial software.

Transfer learning for metamaterial design and simulation

Abstract We demonstrate transfer learning as a tool to improve the efficacy of training deep learning models based on residual neural networks (ResNets). Specifically, we examine its use for study of multi-scale electrically large metasurface arrays under open boundary conditions in electromagnetic metamaterials. Our aim is to assess the efficiency of transfer learning across a range of problem domains that vary in their resemblance to the original base problem for which the ResNet model was initially trained. We use a quasi-analytical discrete dipole approximation (DDA) method to simulate electrically large metasurface arrays to obtain ground truth data for training and testing of our deep neural network. Our approach can save significant time for examining novel metasurface designs by harnessing the power of transfer learning, as it effectively mitigates the pervasive data bottleneck issue commonly encountered in deep learning. We demonstrate that for the best case when the transfer task is sufficiently similar to the target task, a new task can be effectively trained using only a few data points yet still achieve a test mean absolute relative error of 3 % with a pre-trained neural network, realizing data reduction by a factor of 1000.

Fundamental absorption bandwidth to thickness limit for transparent homogeneous layers

Abstract Past work has considered the analytic properties of the reflection coefficient for a metal-backed slab. The primary result established a fundamental relationship for the minimal layer thickness to bandwidth ratio achievable for an absorber. There has yet to be establishment of a similar relationship for non-metal-backed layers, and here we present the universal result based on the Kramers–Kronig relations. Our theory is validated with transfer matrix calculations of homogeneous materials, and full-wave numerical simulations of electromagnetic metamaterials. Our results place more general fundamental limits on absorbers and thus will be important for both fundamental and applied studies.

Multiscale Supercrystal Meta-atoms.

Meta-atoms are the building blocks of metamaterials, which are employed to control both generation and propagation of light as well as provide novel functionalities of localization and directivity of electromagnetic radiation. In many cases, simple dielectric or metallic resonators are employed as meta-atoms to create different types of electromagnetic metamaterials. Here, we fabricate and study supercrystal meta-atoms composed of coupled perovskite quantum dots. We reveal that these multiscale structures exhibit specific emission properties, such as spectrum splitting and polaritonic effects. We believe that such multiscale supercrystal meta-atoms will provide novel functionalities in the design of many novel types of active metamaterials and metasurfaces.

Passive trapping of biomolecules in hotspots with all-dielectric terahertz metamaterials

Electromagnetic metamaterials feature the capability of squeezing photons into hotspot regions of high intensity near-field enhancement for strong light-matter interaction, underpinning the next generation of emerging biosensors. However, randomly dispersed biomolecules around the hotspots lead to weak interactions. Here, we demonstrate an all-silicon dielectric terahertz metamaterial sensor design capable of passively trapping biomoleculars into the resonant cavities confined with powerful electric field. Specifically, multiple controllable high-quality factor resonances driven by bound states in the continuum (BIC) are realized by employing longitudinal symmetry breaking. The dielectric metamaterial sensor with nearly 15.2 experimental figure-of-merit enabling qualitative and quantitative identification of different amino acids by delivering biomolecules to the hotspots for strong light-matter interactions. It is envisioned that the presented strategy will enlighten high-performance meta-sensors design from microwaves to visible frequencies, and serve as a potential platform for microfluidic sensing, biomolecular capture, and sorting devices.

Composite metamaterial antenna with super mechanical and electromagnetic performances integrated by three-dimensional weaving technique

The integration of structure and function was crucial for the application of microstrip antennas. Layered microstrip antennas were prone to delamination, which severely limits their performance stability. The textile conformal microstrip antenna with integrated structure design prevented the layered failure and greatly improved the damage resistance of the antenna. However, textiles had an inherent deficiency in suppressing surface waves due to their discontinuous mesh structure, critically deteriorating the radiation performance of microstrip antennas. Electromagnetic metamaterial with a specific pattern resonated in the excitation of electromagnetic waves to form a forbidden bandgap, which was expected to suppress surface wave radiation of microstrip antennas. In this study, a textile-based microstrip antenna integrated with electromagnetic metamaterials (MA-EBG) was proposed by embedding conductive copper wires in three-dimensional (3D) spacer fabric to form an integrated structure. Due to the function of the forbidden bandgap in metamaterial structure, the surface wave radiation was suppressed and the gain of antenna was increased from 5.1 dB to 9.6 dB. Owing to the tight physical binding, MA-EBG retained its structural integrity with proper electromagnetic performance under the impact of 24 J. The application of electromagnetic metamaterials elevated the gain of textile-based microstrip antennas, which provided a new method for the design of high-gain textile-based microstrip antennas with excellent mechanical properties.

Electromagnetic metamaterials for biomedical applications: short review and trends

This mini-review examines the most prominent features and usages of metamaterials, such as metamaterial-based and metamaterial-inspired RF components used for biomedical applications. Emphasis is given to applications on sensing and imaging systems, wearable and implantable antennas for telemetry, and metamaterials used as flexible absorbers for protection against extreme electromagnetic (EM) radiation. A short discussion and trends on the metamaterial composition, implementation, and phantom preparation are presented. This review seeks to compile the state-of-the-art biomedical systems that utilize metamaterial concepts for enhancing their performance in some form or another. The goal is to highlight the diverse applications of metamaterials and demonstrate how different metamaterial techniques impact EM biomedical applications from RF to THz frequency range. Insights and open problems are discussed, illuminating the prototyping process.

Controllable Wrinkling Inspired Multifunctional Metamaterial for Near‐Field and Holographic Displays

AbstractTunable electromagnetic (EM) metamaterials have received significant attention due to their compelling advantages of integration and minimization compared with conventional bulky devices. Meanwhile, mechanically reconfigurable metamaterials have witnessed a striving period over recent years due to their simplified structural composition and confined modulation capabilities. Here, a controllable‐wrinkling‐based reconfiguration method is proposed to design split‐ring resonant units with dynamic transmittance spectra by switching between planar and wrinkling morphologies. For the linear polarized incidence, the geometries of planar and wrinkled units are optimized to achieve on‐demanded manipulation of the phases and amplitudes, respectively. By simultaneously implementing the amplitude design and the phase gradient, the mechanically inspired metamaterial is engineered to display a near‐field and a holographic image. For circularly polarized incidences, the spin‐decoupled phases and chiral effects demonstrated in the planar and wrinkled state assist in designing a metamaterial to possess spin‐multiplexed and strain‐modulated fourfold displays. These results demonstrate the practical feasibility of the wrinkling method in engineering tunable metamaterials, and the design flexibility, as well as the mechanical strategy, can extend the potential toward the application scenarios such as information processing, sensing, imaging, flexible meta‐devices, etc.

Digital light processing and electromagnetic wave absorption performance tuning of SiOC/SiO2 ceramics

SiOC ceramics have been applied to the fabrication of electromagnetic wave (EMW) absorbing metastructures by stereolithography and demonstrate excellent absorptivity due to the designability of the macrostructure. However, the pyrolysis of photosensitive polysiloxane preceramics may result in macroscopic cracking due to high mass loss and shrinkage. These factors can restrict the structural design flexibility. Combining high residual preceramics with appropriate solid phase fillers is one potential solution. In this study, two preceramics with high residual rates were physically blended with photosensitizing resins in various proportions. This was carried out with the objective of preparing photosensitized preceramics that have high ceramic yields and tunable dielectric properties in the final SiOC ceramics. Then, SiO2 fillers were incorporated into the photosensitive preceramics for the first time to reduce pyrolytic shrinkage and used to match the impedance matching properties of SiOC ceramics in order to enhance EMW absorption performance. The SiOC/SiO2 ceramics achieved a minimum reflection loss of −28.10 dB with a thickness of 1.90 mm. Additionally, the sample demonstrated an effective absorption bandwidth of 6.38 GHz at a thickness of 2.30 mm. The SiOC/SiO2 ceramics have potential applications in the rapid preparation of all-dielectric electromagnetic metamaterials, which exhibit the simplicity of the raw material preparation process and the wide effective absorption bandwidth with a high ceramics yield.

Broadband and precise reconfiguration of megahertz electromagnetic metamaterials for wireless power transfer

It is a significant challenge to construct reconfigurable electromagnetic metamaterials that can precisely manipulate broadband megahertz electromagnetic waves. Herein, we report a reconfigurable electromagnetic metamaterial (REMM) composed of a two-dimensional periodic array of spiral copper-clad unit cells, each paralleled with a micro-tunable capacitor, which has nearly linear voltage-controlled properties. Moreover, the on-board integrated sample-and-hold modules, linked to all the REMM unit cells, are activated sequentially to perform precise voltage regulation of micro-tunable capacitors for controlling the electromagnetic properties of each unit cell. The experiment results demonstrate that the REMM sample has a maximum frequency adjustment range of 2.1 MHz, ranging from 8.7 MHz to 10.9 MHz with less than 0.1 MHz adjustment step. Furthermore, in a wireless power transfer system, the proposed REMM can achieve the desirable magnetic-field manipulation by precisely adjusting the permeability distribution compared with the traditional metamaterial slab merely capable of full-negative permeability. As a result, the power transfer efficiency (PTE) can be increased from 9.53% to 11.51% (1.69% for the case without the metamaterial slab), and approximately 3.5-fold improvement (from 0.28% to 0.98%) can be achieved when coils are misaligned. This work lays the foundation for the control of electromagnetic waves through using broadband and precise reconfiguration of megahertz electromagnetic metamaterials.

Wireless microwave energy harvester uses electromagnetic metamaterials to power electrical devices

By converting electromagnetic radiation into thermal energy first, this harvester circumvents the inefficiencies of other wireless energy converters.

Dielectric‐Based Electromagnetically Induced Transparency Metamaterial in the Microwave Band

AbstractAn electromagnetically induced transparency metamaterial (EITM) based on dielectric resonators is presented in this paper, which consists of a cut wire (CW) and ten dielectric columns. Destructive interference between the CW, which is a branch of the microstrip line, and the dielectric resonators causes the EIT phenomenon. The simulation results show that the dielectric‐based EITM designed can obtain a transmission peak of 0.938 at 2.17 GHz, and the two‐oscillator model is utilized to verify the effectiveness of the structure. In addition, samples of the dielectric‐based EITM are also fabricated and the effectiveness of the metamaterial is experimentally verified. The proposed metamaterial has several advantages, including high efficiency, low loss, a simple structure, and ease of manufacture, which has good prospects for application in the fields of electromagnetic switches, sensors, and nonlinear metamaterials.

Simulation of the expanding universe in hyperbolic metamaterials.

The particle horizon represents the boundary between observable and unobservable regions of the universe, which changes as the universe expands. Based on transformation optics, hyperbolic electromagnetic metamaterials can be utilized to simulate metrics with different signs due to their unique anisotropic properties. In this paper, we use hyperbolic metamaterials to visually depict the variation of the particle horizon under three models of an expanding universe (open, flat, and closed) by substituting one-dimensional time with one-dimensional space. The good agreement between theory and simulation confirms that hyperbolic metamaterials are excellent for simulating space-times, suggesting their potential as a new platform for cosmological analogies.