Metamaterial Cylinder Research Articles

Wave scattering and radiation by a surface-piercing vertical truncated metamaterial cylinder

In this paper, we study wave scattering and radiation by a surface-piercing vertical truncated metamaterial cylinder composed of a closely spaced array of thin vertical barriers, between which fluid can flow. A theoretical model is developed under full depth-dependent linearised water wave theory, where an effective medium equation and effective boundary conditions are employed, respectively, to describe the fluid motion inside the cylinder and match the flow between the fluid regions in and outside the metamaterial cylinder. A damping mechanism is introduced at the surface of the fluid occupied by the metamaterial cylinder to consider the wave power dissipation in narrow gaps between the thin vertical plates. The wave excitation forces acting on the cylinder and the hydrodynamic coefficients can be calculated straightforwardly in terms of the velocity potential inside the cylinder. An alternative way is by using the velocity potential outside the cylinder, the expression of which has the reduction of the integral and an infinite accumulation that are included in the straightforward expression. The results highlight the patterns of the radiated waves induced by the oscillation of the cylinder and the characteristics of the hydrodynamic coefficients. The metamaterial cylinder when fixed in place and with a damping mechanism included is found to capture more wave power than that of a traditional axisymmetric heaving wave energy converter over a wide range of wave frequencies.

A tunable electromagnetic metagrating

We explore electromagnetic (EM) wave incidence upon gratings of reconfigurable metamaterial cylinders, which collectively act as a metagrating, to identify their potential as reconfigurable subwavelength surfaces. The metacylinders are created by a closely spaced, microstructured array of thin plates that, in the limit of small inter-plate spacing, are described by a semi-analytical continuum model. We build upon metacylinder analysis in water waves, translating this to EM for TE polarization (longitudinal magnetic field) for which the metacylinders exhibit anisotropic scattering; this is exploited for the multiple scattering of light by an infinite metagrating of uniform cylinder radius and angle, for which we retrieve the far-field reflection and transmission spectra for plane-wave incidence. These spectra reveal unusual effects including perfect reflection and a negative Goos–Hänchen shift in the transmitted field, as well as perfect symmetry in the far-field scattering coefficients. The metagrating also hosts Rayleigh–Bloch surface waves, whose dispersion is contingent on the uniform cylinder angle, shifting under rotation towards the light-line as the cylinder angle approaches the horizontal. For both plane-wave scattering and the calculation of the array-guided modes, the cylinder angle is the principal variable in determining the wave interaction, and the metagrating is tunable simply through rotation of the constituent metacylinders.

Wave power absorption by a metamaterial cylinder with internal paddle power take-off system

In this paper, a novel type of wave energy converter is considered. Thin vertical parallel plates extending through the depth are confined to a vertical cylinder and the fluid in the narrow channels is excited at the cylindrical boundary by plane incident waves. Each narrow channel is divided into two unconnected fluid domains along its centreplane by a pair of opposing paddles, hinged below the surface and attached to springs and dampers through which useful energy is harvested. The problem is simplified by introducing a continuum approximation which replaces the effect of the narrow channels by an effective medium equation and considers the displacement of the two opposing rows of discrete paddles as two continuous functions of the position. This allows the development of a solution by separation of variables which is simple to implement and efficient to compute. The results provide some surprising results, including the capacity to generate power well in excess of an equivalent cylindrical device operating in rigid body motion and without introducing large unphysical amplitudes in the paddle displacement or the wave field. We also show that the power generated by this wave energy converter is relatively insensitive to the incident wave heading. Some optimisation is performed to show the maximum power harvesting potential of the proposed device.

Efficient Modelling of Acoustic Metamaterials for the Performance Enhancement of an Automotive Silencer

Significant potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date, acoustic metamaterials have not been demonstrated in a commercial automotive silencer for performance enhancement. A significant obstacle to the practical use of acoustic metamaterials is the need for low cost and efficient modelling strategies in the design phase. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. The acoustic metamaterial design is achieved using a combination of analytical and finite element models, validated by experiment. The acoustic metamaterial is then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of a labyrinthine metamaterial cylinder proved to be a significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. The research has successfully shown that acoustic metamaterials can be used in practical settings, such as an automotive silencer, to improve the overall sound attenuating performance. The described analytical model demonstrates the potential for industrially relevant low cost design tools.

General Analysis of a Loop Antenna Located on a Uniaxial Metamaterial Cylinder

The general problem of determining the electrodynamic characteristics of a circular loop antenna located coaxially on the surface of a metamaterial cylinder is studied using the integral equation method. The antenna has the form of a perfectly conducting, infinitesimally thin, narrow strip coiled into a ring and is excited by a given time-harmonic voltage. The cylinder is assumed to be filled with a uniaxial metamaterial and surrounded by an isotropic magnetodielectric. Integral equations for azimuthal harmonics of the antenna current are derived and solved in the cases where the normal waves of the metamaterial inside the cylinder have either hyperbolic or nonhyperbolic dispersion. Based on the solutions of these equations, the current distribution and input impedance of the antenna are found in closed form. The behavior of the antenna characteristics as functions of the metamaterial parameters is discussed.

A Surface-Piercing Truncated Metamaterial Cylinder Operating as a Wave Energy Converter

A Surface-Piercing Truncated Metamaterial Cylinder Operating as a Wave Energy Converter

Controlled snapping sequence and energy absorption in multistable mechanical metamaterial cylinders

Mechancial metamaterials comprising bistable unit cells utilize a sinusoidal beam to enable significant deformation between stable states, which is associated with energy absorption. A stack of similar bistable unit cells, i.e., multistable metamaterials, will snap to a second stable state in a seemingly random sequence that is influenced by minute variations in manufacturing. However, it is desirable to tailor the energy absorbed and the snapping sequence to obtain predictable geometric reconfiguration in multistable cylindrical metamaterials. Additive Manufacturing (AM) processes, such as Fused Deposition Modeling (FDM), are able to produce these structures with flexible filaments, such as Thermoplastic Polyurethane (TPU), to enable flexible, multistable cylindrical structures. In this study, we investigated experimentally and computationally the mechanical behavior and controlled snapping sequence of bistable lattices incorporated into cylindrical shells. Individual layers are printed using FDM and assembled into a cylinder. Experimental and computational results for uniaxial tension and compression tests, applied along the length of the cylinder, are used to evaluate the non-linear mechanical behavior and quantify energy absorption of the system during both loading (tension) and unloading (compression). It was shown that energy absorption during loading was always greater than unloading and increased with an increasing number of layers. The energy absorbed by individual layer was approximately 1.25 J in loading and 0.52 J in unloading for a layer with sinusoidal beam thickness of 1.5 mm. The direction dependence of the energy absorption is attributed to the printed configuration of the lattices. Individual layers can be stacked to tailor the amount of energy absorption. In addition, the energy absorbed and the snapping sequence of the multistable cylinder could be controlled by changing the thickness of the sinusoidal beams in each layer. The variation of energy absorbed is strongly influenced by the thickness of the sinusoidal beam. By increasing the beam thickness from 1 mm to 2 mm, energy absorption increased by approximately a factor of three. Beam thickness accurately controlled the snap-through behavior in experimental samples, but the computational model experienced re-distribution of strain and snap-close forces that cause less predictable snap-through behavior in unloading (compression). The design, analysis and control of snapping sequence of cylindrical shells with multistable states provides new opportunities in practical application of control of elastic waves, energy absorption and reconfigurable structures.

Wave scattering by an array of metamaterial cylinders

Abstract

Scattering and absorption characteristics of graphene coated metamaterial cylinder

Terahertz (THz) wave interaction from graphene coated metamaterial cylinder has been investigated analytically and numerically. The analytical formulation of electromagnetic fields is being modeled in the frame work of Mie theory while the modeling of the graphene is done by random phase approximation method. The causality principle based Kramer-Kroing relations are used to simulate the DNG metamaterial, while the DPS metamaterial is modeled by the Drude relations of SiO2. The analytical formulation is developed for both parallel and perpendicular polarized waves. The impedance boundary conditions (IBC) approach is used to model the infinitely thin graphene coating on metamaterial cylinder. Further the IBC at the interface of graphene layer and metamaterial cylinder are applied to compute the unknown scattering coefficients. The efficiency factors i.e., scattering efficiency (Qsca), extinction efficiency (Qexc) & absorption efficiency (Qabs) and bistatic radar cross section (RCS) have been computed analytically as well as numerically for both micro and nano cores. The influence of graphene parameters i.e., chemical potential (μc) & scattering rate (τ1) and size of metamaterial cylinder (R) on the scattering efficiency (Qsca) and extinction efficiency (Qexc) has been analyzed for DPS and DNG cores. It is observed that the in the nano regime, for perpendicularly polarized wave, graphene coated metamaterial cylinder supports the localized surface plasmon resonance (LSPR) modes and LSPR is found sensitive to the change in the graphene parameters and core size. However, it is reported that the parallel polarized wave has same response towards the DPS and DNG cores in the nano regime. It is concluded that under suitable parameters the graphene coating may provide extraordinary degree of freedom to actively control the THz interactions i.e., scattering efficiency, extinction efficiency and bistatic RCS. The present work may have potential applications in designing and manufacturing of Electromagnetic invisibility, cloaking and target protection devices for THz region.

Microwave Analysis of Scattered and Absorbed Powers of Semiconductor and Metamaterial Cylinder Structures.

Here is presented our numerical investigations based on the rigorous solution of the Maxwell’s equations for analyses of absorbed and scattered powers of a semiconductor-metamaterial array with a window defect. The array structure consists of a finite set of infinite parallel, circular cylinders that can be made of the different lossy and/or lossless isotropic materials. We used our developed computer code, which allowed us to consider an array consisting of an arbitrary number of cylinders. According to our code, cylinders can be located at different distances and have differing diameters. There is a limitation: Cylinders should not cross each other. We numerically examined two cylindrical arrays with electromagnetic (EM) band-gap (EBG) defects. The absorbed and scattered powers were analyzed there for parallel and perpendicular polarizations of the incident microwave. We investigated dependencies on the operating frequency and the radius (R) of an arc of the arranged thirteen n-Si cylinders with the low semiconductor specific resistivity of 0.5, 2, and 10 Ω∙m. We have discovered that the arrays may have features of a waveguide or a microwave reflector.

A numerically stable algorithm for scattering from several circular cylinders including metamaterials with different boundary conditions

The analytically obtained algebraic equation systems for the TM/TE-z polarized monochromatic waves scattering from eccentrically layered circular cylinders are ill-conditioned for numerical calculations. Therefore, such ill conditioned systems must be regularized for reliable numerical results. Here, the steps of the regularization of the ill conditioned system obtained for the scattered field from a circular metamaterial cylinder includes three parallel circular cylinders: a dielectric, an impedance and a perfect electric conductor is explained. In the regularization procedure used here each circular boundary brings block(s) correspond to its electromagnetic property and the regularization procedure is done according to this block(s). For this end a system that consists of perfect electric conductor (PEC), impedance, dielectric, and metamaterial cylinders is discussed and thus the steps of a regularization procedure for a general system that has all the type of boundaries in terms of electromagnetics will be explained here. As a result, if a new boundary is included to the system then it is sufficient to locate the blocks related to this boundary suitably.

Resonance absorption at scattering by a metamaterial cylinder

The problem of scattering of the field induced by a filament of magnetic current by a metamaterial cylinder is solved using the method of continued boundary conditions. The effect of the frequency dispersion of permittivity and permeability of the cylinder material on the phenomenon of resonance absorption is investigated.

STUDY OF THE EFFECTS OF ECCENTRIC PLASMA COATING OVER METAMATERIAL CYLINDER

A plasma sheath can significantly alter the electromagnetic properties of an object, which leads to many practical applications. In this article, the electromagnetic scattering properties of a DB metamaterial cylinder coated with unmagnetized plasma are presented. The effects of layer thickness, non-uniform cladding (eccentric coating), electron number density, electron-neutral collision frequency and the frequency of incident wave on radar cross-section (RCS) of the object are discussed. It is found that the RCS of the DB metamaterial objects can be reduced or enhanced by appropriate values of plasma parameters, thickness or eccentricity. The anomalous behavior of backscattering cross-section of plasma coated DB cylinder has been observed at frequencies near plasma frequency. The results may serve as a noteworthy reference for experimentalists working in plasma stealth technology for metamaterials.

High-Q resonanaces of surface waves in thin metamaterial cylinders

The 2D problem of excitation of a circular metamaterial cylinder by a filament source is numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances occur in cylinders of an electrically small diameter. Near- and far-field patterns are calculated. It is discovered that, under resonance conditions, a multilobe scattering pattern typical of superdirective antennas is formed. The influence of loss on the resonance characteristics is investigated.

Scattering characteristics of structures of lossy metamaterial–semiconductor cylinders

Here, we present for the first time the rigorous boundary problem solution of the Maxwell’s equations for the determination of scattering characteristics of a structure. The structure consists of a finite set of infinite parallel circular cylinders that can be made of different lossy isotropic materials. We numerically analyzed two structures that differ only in the symmetrical arrangement of semiconductor cylinders in relation to a central metamaterial cylinder. The electrical radii of cylinders can be arbitrary. Both polarizations of the incident microwave are considered in this work. The Poynting vector of the plane microwave that reflected from and transmitted through the structures analyzed here. We investigated dependency on the radius of an arc where are placed the semiconductor cylinders, the semiconductor-specific resistivity, the operating frequency at two radii of the metamaterial cylinder. We discovered that the structure can have features of a band gap photonic crystal dependent on the topology and the polarization of the incident microwave. We have found that the structure can operate as a microwave reflector at the certain radius of the arc on which are located thirteen n-Si cylinders. The Poynting vector is very sensitive to the change of semiconductor-specific resistivity when the incident microwave has the parallel polarization.

Resonance transformation of the field of a linear source into multipole radiation with the help of a cylindrical metamaterial layer

A hollow circular metamaterial cylinder with a negative permittivity and a negative permeability is considered. The 2D problem of excitation of the cylinder by a filament source is numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances exist in hollow cylinders of an electrically small diameter. It is shown that, when the cylindrical wave source is situated inside the cavity, omnidirectional radiation is transformed at the resonance frequency into multipole radiation with a large number of identical lobes in the pattern. Near- and far-field patterns are calculated. The influence of loss on the resonance characteristics is investigated.

Optical properties of two-dimensional metamaterial photonic crystals

In the present work, we theoretically study a 2D photonic crystal (PC) comprised by double negative (DNG) metamaterial cylinders, showing that such a system presents a superior light-matter interaction when compared with their single negative (SNG) plasmonic PC counterparts, suggesting a route to enhance the performance of sensors and photovoltaic cells. On the other hand, we have observed that depending on the frequency, the mode symmetry resembles either the case of SNG electric (SNG-E) or SNG magnetic (SNG-M) PC, suggesting that either the electric or magnetic character of the DNG metamaterial dominates in each case.

Low-frequency resonances in hollow metamaterial cylinders

The 2D problem of excitation of a hollow circular metamaterial cylinder by a filament source is analytically and numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances exist in hollow cylinders of an electrically small radius. Near- and far-field patterns are calculated. It is found that, under resonance conditions, a multilobe scattering pattern typical of superdirective antennas is formed. The influence of loss on the resonance characteristics is investigated.

The effect of subwavelength localization of the electromagnetic field on the surface of a circular metamaterial cylinder

The 2D problem of excitation of a circular metamaterial cylinder by a filamentary source is numerically investigated. It is found that, for the minus one values of the relative permittivity and permeability, the field on the surface of the cylinder concentrates in a region that is located on the illuminated surface of the cylinder and that is small compared to the wavelength.

Propagation properties of an elliptical anisotropic metamaterial cylinder

The propagation characteristics were investigated of an open elliptical cylinder comprising a uniaxial anisotropic metamaterial. The dispersion relation for hybrid modes in this cylinder was examined theoretically. It is shown that forward and backward waves can be supported by such a metamaterial cylinder. Even and odd modes have different losses in a realistic anisotropic elliptical cylinder. The forward wave can propagate longer distances than the backward wave because of its lower loss. The light can propagate backward on the cylinder without the limit of structure size. The odd modes have higher operating wavelengths than the even modes. The extraordinary properties in this structure are identified as multilayer plasmons. The validity of the effective medium approximation of this structure is examined.