Metamaterials最新文献

A slab with permittivity $-1$, relative to the environment, can be used as a near-field superlens (NFSL) for one polarization. To design a NFSL for any chosen visible wavelength, we investigate periodic silver–dielectric composites with effective permittivity close to $-1$. The initial design choices are based on the Maxwell Garnett mixing formula, and these are further refined using a combination of the Rayleigh formula and the Drude model for the complex permittivity of silver. The most promising composite turns out to be a silver slab with cylindrical air-holes occupying a volume fraction between 35 and 73%, which covers the whole visible range from 400 to 700 nm. The quasistatic accuracy of the predicted effective permittivity is verified using an accurate analytical solution, and the superlensing effect is demonstrated for one composite NFSL setup for violet light using numerical simulations. Finally, the correction required by nanoscale size effects on the permittivity function of silver is taken into consideration and its effect on the performance of the composite lens is estimated.

Monocrystals of Cu(Ge,Si)O₃ with self-organized SiO₂–GeO₂ vitreous fibers running along the growth axis of the crystal, is a promising class of composites. This new material is achieved by floating zone technique using a ceramics with a composition located in a two-phase domain of the stability diagram of Cu(Ge,Si)O₃. We report our results on the relation between the various crystal growth parameters and the periodicity and the size of the fibers. We reached 1.2 and 0.6 μm respectively, and the refractive index contrast is around 0.35. These figures open the door towards telecom applications. These ones are important information for the realization of this composite from these oxides. After observation of the transverse section of this material, we report long fibers (≈750 μm) not published so far as second phase structure. After chemical analyses, we showed that physico-chemical conditions are met for the appearance of Turing like structures, explaining in such a way that the composite self-organizes during the solidification and turns into an ordered structure that can be useful as metamaterials or photonic crystal. This can help for suggesting other oxide systems and to define a general method for self-organization starting in the neighbourhood of an eutectic mixture.

A full-vector semi-analytical method is presented for the analysis of a frequency selective surface consisting of patches printed on substrates having periodic inhomogeneity and both electric and magnetic anisotropy. Based on a multiconductor transmission line model for the substrate, a matrix is obtained which can be considered as the Green’s function matrix. The resulting integral equation becomes a series equation for a periodic structure. The equation can be solved by the method of moments with sub-domain rooftop basis functions and Galerkin testing functions. Several examples are analyzed using this technique. Numerical results demonstrate the effect of periodic substrates and anisotropy on the performance of the frequency selective surfaces. It is shown that using periodic substrates brings some degrees of freedom for better controlling the electromagnetic characteristics of the device. For some special cases, comparisons with measurement results and Maxwell solvers are performed.

This paper shows, numerically and experimentally, that imaging is realizable with a strongly curved wire medium. In a first part, simulation results obtained for various curvatures are presented and sub-wavelength imaging on a wide bandwidth is demonstrated. It is also shown that the collimation phenomenon remains very effective for structures having a cross-section corresponding to about a hundredth of the wavelength. In a second part, experimental results are shown for transmission of a medical image through a $63°$ curved wire medium in which the receiving antenna has been inserted.

A metafilm (also referred to as a metasurface) is the surface equivalent of a metamaterial. More precisely, a metafilm is a surface distribution of suitably chosen electrically small scatterers. Metafilms are becoming popular as an alternative to full three-dimensional metamaterials. Unfortunately, many papers in the literature present incorrect interpretations and mischaracterizations of these metafilms. In fact, some of the characterizations presented in the literature result in non-unique parameters for a uniquely defined metafilm. In this paper we discuss an appropriate interpretation and characterization of metafilms and present a correct manner to characterize a metafilm. Additionally, we illustrate the error that results from an incorrect characterization of metafilms. We present various examples to emphasize these points. Finally we present a retrieval approach for determining the uniquely defined quantities (the electric and magnetic susceptibilities of its constituent scatterers) that characterize a metafilm.

The article proposes an LC-circuit model for single split ring resonators (SRRs) operating at far infrared and optical frequencies. Taking the effects of magnetic and kinetic inductances as well as gap and surface capacitances into account, we obtain analytical expressions for the resonant frequency of the singly, doubly, and quadruply split SRRs. Comparing the analytical results with numerical simulations, we show that the numerical simulations agree better with the present model than with the models reported previously. We also discuss a size dependent correction to the electron collision frequency which takes into account electron collisions with SRR walls.

In this paper, we present a study of the waveguiding properties of metamaterial layers. We pay particular attention to peculiar features that have not yet been given sufficient consideration in previous publications, with an emphasis on the physical interpretation of these results. We attempt to follow the transition of waves guided by a solitary “metamaterial–vacuum” boundary (the so-called true surface wave—TSW) to modes guided by the metamaterial layer. We considered the way TSW of different types (forward, backward and degenerated) transform to the layer modes and examined the features arising in the dispersion curves. For example, “pulling” of the dispersion curve into the frequency region where TSWs do not exist separately, presence of the bend for all modes produced by backward TSWs, existence of the waves with complex conjugate propagation constants, etc.

The frequency dependence of the coefficient of spin wave reflection from a semi-infinite magnonic crystal with a periodically modulated value of the uniaxial anisotropy and a finite thickness of interfaces has been investigated, assuming a linear distribution of the anisotropy value in the interfaces. The analysis shows that the performance of magnonic devices employing magnonic crystals as a filtering element can degrade as the thickness of interfaces increases, e.g. due to the process of diffusion between constituent layers of the magnonic crystals.

We discuss a relationship between the traditional framework of the frequency-dependent dielectric permittivity $\varepsilon \left(\omega \right)$ and magnetic permeability $\mu \left(\omega \right)$ in the electrodynamics of continuous media and the spatial dispersion framework utilizing the dielectric tensor ${\varepsilon }_{ij}\left(\omega \text{,}\text{k}\right)$ depending both on the frequency $\omega$ and wavevector $\text{k}$. For electromagnetic waves, the latter approach includes the former as a specific limiting case for small k within the $k^2$ accuracy. While the dispersion of the transverse electromagnetic waves in this approximation is captured by the $\varepsilon \left(\omega \right)–\mu \left(\omega \right)$ phenomenology, the dispersion of the longitudinal electric waves would be missed. The general ${\varepsilon }_{ij}\left(\omega \text{,}\text{k}\right)$ framework also accommodates more complex situations such as excitonic resonances and additional electromagnetic waves. We also review the well-known Landau–Lifshitz arguments on the physical meaning of $\mu \left(\omega \right)$ at sufficiently high frequencies. In that context, the need is discussed for the effective medium response to include contributions from the spatial dispersion of the electric-dipole polarization and from the electric-quadrupole polarization on an equal footing with contributions from the magnetic-dipole resonances.

Monofilar, bifilar, trifilar and quadrifilar Archimedean spiral metamaterial particles are analyzed by using point group symmetry and the methods of crystallography. From the symmetry properties electromagnetic response is determined. Magnetic, electric and magnetoelectric modes of the particles are identified along with their isotropy characteristics. Theoretical methods show that all the particles, except monofilar spiral, are non-bianisotropic. Numerical simulation results are presented to verify the analysis. Finally, effective medium theory is applied to extract the effective permeability of the spiral medium. The results indicate negative values for permeability in certain frequency ranges.