Metamaterial Slab Research Articles

Dispersion Relation and Power Flux of Chiral Metamaterial Slab Waveguide with Graphene Interface

Dispersion Relation and Power Flux of Chiral Metamaterial Slab Waveguide with Graphene Interface

Dyakonov surface waves in dielectric crystals with negative anisotropy

Abstract Since the initial discovery of Dyakonov surface waves at a flat infinite interface of two dielectrics, at least one of which is positively anisotropic, extensive research has been conducted towards their theoretical and experimental studies in materials with positive anisotropy. The potential applications of these waves were initially limited due to the stringent conditions for their existence and the requirement for position anisotropy. In our study, we present the theoretical prediction and experimental observation of a novel type of Dyakonov surface waves that propagate along the flat strip of the interface between two dielectrics with negative anisotropy. We demonstrate that the conditions for surface waves are satisfied for negatively anisotropic dielectrics owing to the specific boundaries of the strip waveguide confined between two metallic plates. We study such modes theoretically by using the perturbation theory in the approximation of weak anisotropy and demonstrate that the electromagnetic field distribution in these modes is chiral. Experimental verification of theoretical predictions is made in the microwave range using 3D-printed negatively anisotropic water-dielectric metamaterial slabs. The existence of Dyakonov surface waves in negative crystals prompts a reassessment of the list of materials suitable for practical realization of these waves in the visible and infrared ranges. Due to the ability of the considered modes to transmit chiral light, they have potential in the sensing of chiral organic molecules.

De-embedding method for a sensing area characterization of planar microstrip sensors without evaluating error networks

A de-embedding method for determining all scattering (S-) parameters (e.g., characterization) of a sensing area of planar microstrip sensors (two-port network or line) is proposed using measurements of S-parameters with no calibration. The method requires only (partially known) non-reflecting line and reflecting line standards to accomplish such a characterization. It utilizes uncalibrated S-parameter measurements of a reflecting line, direct and reversed configurations of a non-reflecting line, and direct and reversed configurations of the sensing area. As different from previous similar studies, it performs such a characterization without any sign ambiguity. The method is first validated by extracting the S-parameters of a bianisotropic metamaterial slab, as for a two-port network (line), constructed by split-ring-resonators (SRRs) from waveguide measurements. Then, it is applied for determining the S-parameters of a sensing area of a microstrip sensor involving double SRRs next to a microstrip line. The root-mean-square-error (RMSE) analysis was utilized to analyze the accuracy of our method in comparison with other techniques in the literature. It has been observed from such an analysis that our proposed de-embedding technique has the lowest RMSE values for the extracted S-parameters of the sensing area of the designed sensor in comparison with those of the compared other de-embedding techniques in the literature, and have similar RMSE values in reference to those of the thru-reflect-line calibration technique. For example, while RMSE values of real and imaginary parts of the forward reflection S-parameter of this sensing area are, respectively, around 0.0271 and 0.0279 for our de-embedding method, those of one of the compared de-embedding techniques approach as high as 0.0318 and 0.0324.

Magnetostatic waves in metallic rectangular waveguides filled with uniaxial negative permeability media

The propagation characteristics of magneto-quasistatic waves, more commonly, known as magnetostatic waves in a long, metallic rectangular waveguide filled with a metamaterial slab are comprehensively investigated. The metamaterial slab consists of split-ring resonators as an anisotropic uniaxial medium with transversal negative effective permeability. Some analytical relations and numerical validations on the characteristics of these waves are presented. The results include the dispersion relations, mode patterns (field distributions) that can be supported by such media, and their corresponding cutoff frequencies, group velocities, power flows, and storage energies of magnetostatic waves. The findings from the present research study can be advantageous to advance the synthesis and development of negative permeability materials with peculiar features in guiding structures.

Complete mode conversion of elastic waves by utilizing hexapole resonances in a double-scatterers structure

In recent years, the emergence of elastic metamaterial has provided new methods to manipulate the polarization of elastic waves, achieving elastic mode conversions. This paper theoretically investigates a complete mode conversion effect, where longitudinal waves are completely converted into transverse waves after being reflected by one layer of metamaterial slab. The slab structure contains a pair of cylinders, and the conversion is attributed to the out-of-phase coupled hexapole resonances of the two cylinders. Unlike the monopole, dipole, and quadrupole resonances, the hexapole resonances induce trivially, nearly constantly, effective parameters. The proposed design does not follow the recent popular “reversely designing parameters” method. The conversion based on the hexapole resonances is relatively broadband and wide-angle, which is beneficial for practical applications such as sound absorption.

Guided-wave Suppression in Uniaxial Anisotropic Metamaterial Slab for Radiation Pattern Control of Covered Dipoles

Guided-wave Suppression in Uniaxial Anisotropic Metamaterial Slab for Radiation Pattern Control of Covered Dipoles

Metamaterial Slabs for Electric Vehicle Wireless Charging Application

Metamaterial Slabs for Electric Vehicle Wireless Charging Application

SLOW ELECTROMAGNETIC WAVES IN PLANAR THREE-COMPONENT WAVEGUIDE STRUCTURE WITH MU-NEGATIVE METAMATERIAL

This work is devoted to study of the dispersive properties of the slow electromagnetic waves that propagate along the planar waveguide structure that consists of semi-bounded plasma region, metamaterial slab and semibounded region of ordinary dielectric. It is studied the case when all media are homogeneous and isotropic. The dispersion properties, the phase and group velocities, as well as the electromagnetic field spatial structure of the eigen TE modes are studied in the frequency range where the metamaterial possess negative permeability.

Theory on coherent perfect absorber and laser via a metamaterial slab with complex parameters

Abstract We explicitly derive the general conditions of a metamaterial slab to achieve coherent perfect absorber (CPA) and laser under the excitation of two counter-propagating incident waves. Our results provide a unified theory that could be applied in designing homogenous metamaterial with complex parameters for realizing CPAs and lasers. Especially, the theory discusses two special cases, i.e., case 1) a metamaterial slab with complex permittivity and real permeability, or complex permeability and real permittivity, and case 2) a metamaterial slab with both complex permittivity and permeability, which encompass the entire range of metamaterials with complex parameters. For both cases, our theory accurately derives the required parameters of the metamaterial for CPA, laser and their coexistence, as validated by numerical simulations. Our work serves as a guide for designing CPAs and lasers via general metamaterial slabs of complex parameters.

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.

Slow Electromagnetic Surface TM-Waves in Planar Waveguide Structure with Mu-Negative Metamaterial Slab

In this work, we study the properties of slow electromagnetic surface TM-waves propagating along the planar waveguide structure involving the mu-negative metamaterial slab. The planar mu-negative metamaterial layer separates two semi-infinite regions: the plasma and the conventional dielectric. All media are assumed to be linear, homogeneous, and isotropic. The dispersion properties, the phase and group velocities, the spatial distribution of the electromagnetic fields of the TM mode in frequency range where the metamaterial has a negative permeability are under the consideration. The properties of this TM-eigenwave of the structure and two other TE modes are compared. It is studied the TM-eigenwave properties variation with metamaterail and plasma-like media properties changing. It is shown that for the considered structure, the properties of the TM mode depend significantly on the parameters of the plasma-like medium.

Improved voice acquisition using acoustic metamaterials

Voice acquisition and recognition are important, because sound is the most convenient and efficient media to realize seamless and hands-free human–machine interaction. Many applications, such as smart phones, humanoid robots, smart home, autonomous vehicles, and Internet of Things, demand for high-quality voice acquisition, especially in a noisy environment. In this report, we show that the evanescent portion of human voice can be amplified by setting an acoustic metamaterial in front of a microphone; thus, the signal to noise ratio can be enhanced remarkably. Such an effect is demonstrated through a double negative acoustic metamaterial slab with simultaneous negative density and bulk modulus induced by coexisting and coupled Helmholtz and Fabry–Pérot resonances. This work provides a passive and physical means, rather than the traditional active and algorithmic method, to improve the quality of voice sound acquisition.

Propagation behavior in rectangular metallic waveguide periodically loaded with single negative metamaterial slabs

This paper focused on propagation characteristics of a single mode supporting waveguide enclosed by metallic sidewalls periodically loaded with lossless single negative (SNG) metamaterial slabs along axial direction. The gap between two successive SNG slabs is filled with a double positive (DPS) material. For the analysis, the periodic structure is assumed having symmetric unit cell (UC) and simplified as a two-port network which is one-half of the symmetric UC. Scattering parameters (S-parameters) are defined by even/odd mode analysis of the symmetric UC, and then the total S-parameters are calculated by solving the cascade connection of N unit cells. Eigenvalue equations are also obtained to explicit the solutions of band edge and pass/stopband diagrams in the microwave regime. Since a SNG can be either epsilon-negative (ENG) or mu-negative (MNG), S-parameters and dispersion behavior are illustrated with numerical examples and discussed for each periodic structure constructed with ENG or MNG slabs.

Complete mode conversion between longitudinal and transverse waves by an elastic metamaterial slab with a double-scatterer structure

In this work, we propose a design of a double-scatterer structure to achieve complete conversion for elastic bulk waves. Every unit of the elastic metamaterial slab contains a pair of scatterers with a relatively oblique direction. When the slab attaches on a semi-infinite solid background, it can completely convert the normal incident longitudinal wave into the reflected shear wave, or vice versa. The conversion can be attributed to the in-phase coupling of the double scatterers’ quadrupolar resonances. The coupled two quadrupoles could interact with the background and bring oblique displacements. Consequently, the oblique displacements generate horizontal displacements for reflected waves.

Design of new metamaterial with negative permeability for efficient wireless power transfer

SummaryTo solve the problem that the efficiency of a wireless power transfer system decreases with increasing transmission distance, metamaterial (MTM) has offered an effective solution. In this paper, a novel compact MTM with negative permeability is designed to improve the transfer efficiency of wireless power transfer at the operating frequency of 13.56 MHz. By placing the MTM slab at different positions between coils, the transmission coefficient of the wireless power transfer system with one MTM slab is calculated. Also, the impact of transmission distance is studied. Based on the two‐port network method, the transfer efficiency of wireless power transfer is respectively calculated for the system with one MTM slab and with two MTM slabs. The results demonstrate that transfer efficiency at the transmission distance of 150, 200, and 250 mm are, respectively, 82.4%, 67.8%, and 47.3% when one MTM slab is introduced. For the system with two MTM slabs, the corresponding transfer efficiency is 84.9%, 77.3%, and 66.1% separately. Compared with the system without MTM, it is found that there is a large improvement in transfer efficiency especially when two MTM slabs are positioned between coils at the transmission distance of 250 mm. The magnetic field distribution of the system with one or two MTM slabs introduced is investigated. The results show that magnetic coupling between coils is strengthened, which is favorable for transfer efficiency enhancement.

Multi-point scattering measurements for effective property extraction from metamaterials with skin effects

Scattering experiments can be leveraged to extract the effective properties of a heterogeneous metamaterial slab based on multi-point measurements in surrounding media. In this technique, two measurements are made in the ambient media on each side of a finite thickness micro-structured slab to decompose incoming and outgoing waves. The method is applied to an example with locally resonant micro-structured inclusions while paying close attention to parameters that influence the extracted material parameters. It is observed that the extracted overall parameters converge to limiting values when the number of unit cells across the slab thickness or ambient media modulus are increased. Dependence of extracted material parameters on the number of cells through thickness or ambient media properties are attributed to the different response of boundary (skin) and interior cells. A method is presented which represents a finite array with different effective properties for the skin regions vs. the interior regions with great success in reproducing the scattering for different slab thicknesses, and through which the interior regions properties become independent of ambient media properties. In stop bands with lower material loss, challenges arise that are associated with extremely small transmission. The assumption of continuity in transmission phase is enforceable to remove phase ambiguity, although in certain cases (associated with nearly lossless specimens) this assumption appears to fail. In such cases, interference from coupled shear modes may lead to apparent higher longitudinal transmission within the stop band. This work provides a proof of concept for the development of an experimental methodology capable of extracting the effective properties and dispersion behavior of heterogeneous mechanical metamaterials without any knowledge of the internal fields.

Analysis of transmission performance on wireless power transfer system with metamaterial

Abstract In order to solve the problems of low power transfer efficiency (PTE) and limited distance in magnetic coupling resonant wireless power transfer (MCR-WPT) technology. In this paper, based on the magnetic field control ability of metamaterials (MMs), the way to improve the performance of MCR-WPT systems is studied. First, the influence of MMs on the coupling of MCR-WPT system is theoretically analyzed by establishing an equivalent circuit model. Through a series of simulations and experiments, the relationships between the PTE and the array and placement of the MM slab are investigated. The results demonstrate that when one MM slab is placed in the middle, near the Tx coil or the Rx coil, the optimal PTE can be obtained by inserting one slab with $6 \times 6$ , $1 \times 1$ , and $6 \times 6$ arrays, respectively. Moreover, the systems with multilayer MM slabs are also studied. The measured PTEs on one, two, and three layers of MM slabs can increase by 20.6%, 29.3%, and 22.6%, respectively. The efficiency improvement capability of one MM slab is better than three slabs but worse than two slabs. This paper discusses the application of MMs in MCR-WPT systems, which has a certain reference significance.

Phonon transmission through a nonlocal metamaterial slab

Previous theory and experiment has shown that introducing strong (nonlocal) beyond-nearest-neighbor interactions in addition to (local) nearest-neighbor interactions into rationally designed periodic lattices called metamaterials can lead to unusual wave dispersion relations of the lowest band. For roton-like dispersions, this especially includes the possibility of multiple solutions for the wavenumber at a given frequency. Here, we study the one-dimensional frequency-dependent acoustical phonon transmission of a slab of such nonlocal metamaterial in a local surrounding. In addition to the usual Fabry-Perot resonances, we find a series of bound states in the continuum. In their vicinity, sharp Fano-type transmission resonances occur, with sharp zero-transmission minima next to sharp transmission maxima. Our theoretical discussion starts with a discrete mass-and-spring model. We compare these results with solutions of a generalized wave equation for heterogeneous nonlocal effective media. We validate our findings by numerical calculations on three-dimensional metamaterial microstructures for one-dimensional acoustical wave propagation.

Euler–Lagrange analysis of metamaterial slabs in near field systems

The Euler–Lagrange method is proposed for the rigorous modeling of low-frequency metamaterial (MTM) slabs in near field systems. The mechanisms of the extraordinary performance-enhancing capabilities of MTM slabs in near field systems are analyzed in numerical studies. The proposed method is verified by experimental studies of a prototype MTM-coil system. This work focuses on low-frequency MTM slabs and enables rigorous, flexible, and feasible analysis of MTM-based near field systems in electrical engineering.

Nonlocality-mediated spatiotemporal optical vortex generation in nanorod-based epsilon-near-zero metamaterials.

Optical vortices have myriad applications in photonics. Very recently, promising concepts of spatiotemporal optical vortex (STOV) pulses based on the phase helicity in the space-time coordinates have attracted much attention owing to their donut shape. We elaborate on the molding of STOV under the transmission of femtosecond pulses through a thin epsilon-near-zero (ENZ) metamaterial slab based on a silver nanorod array in a dielectric host. At the heart of the proposed approach is the interference of the so-called main and additional optical waves enabled by strong optical nonlocality of these ENZ metamaterials, which leads to the appearance of phase singularities in transmission spectra. The cascaded metamaterial structure is proposed for high-order STOV generation.