Electromagnetic field energy density in artificial microwave materials with negative parameters

General relations for the stored reactive field energy density in passive linear artificial microwave materials are established. These relations account for dispersion and absorption effects in these materials, and they are valid also in the regions where the real parts of the material parameters are negative. These relations always give physically sound positive values for the energy density in passive metamaterials. The energy density and field solutions in active metamaterials with non-dispersive negative parameters are also considered. Basic physical limitations on the frequency dispersion of material parameters of artificial passive materials with negative real parts of the effective parameters are discussed. It is shown that field solutions in hypothetical materials with negative and non-dispersive parameters are unstable

Coherently Time-Varying Metasurfaces

[EN] Known coherent metasurfaces control the interference of waves of a given frequency with other coherent waves at the same frequency, either illuminating from a different direction or created as intermodulation products. In this paper, we introduce a class of metasurfaces that are modulated in time coherently with the illuminating radiation. Such modulation opens a possibility to control reflection, absorption, and transmission at multiple frequencies, including illuminations by two or more incoherent waves. In particular, we study dynamic resistive layers and show how to use them to design thin multifrequency perfect absorbers that overcome the bandwidth limit for static linear absorbers. Furthermore, we demonstrate possibilities of remote tuning of the absorption level. We hope that this work opens up alternative avenues in wave engineering using coherent modulation of metasurface parameters.This work is supported by the Academy of Finland under Grants No. 330957 and No. 330260. This work is partially supported by the Spanish Ministerio de Educacion y Formacion Profesional under the Grant Beatriz Galindo BG20/00024. This work is based on the master's thesis of the first author Mohamed Mostafa. The authors wish to thank Dr. Xuchen Wang for helping to draw Fig. 1 of this paper. The authors also wish to thank Dr. Prasad Jayathurathnage and Dr. Grigorii Ptitcyn for useful discussions.Mostafa, M.; Diaz Rubio, A.; Mirmoosa, M.; Tretyakov, S. (2022). Coherently Time-Varying Metasurfaces. Physical Review Applied. 17(6):064048-1-064048-16. https://doi.org/10.1103/PhysRevApplied.17.064048064048-1064048-1617

On effective electromagnetic parameters of artificial nanostructured magnetic materials

In this paper we discuss effective material parameter description of new nanostructures designed to perform as artificial magnetic materials for vis- ible light. Among these structures there are various split-ring resonators, dual-bar structures, fishnet layers and other geometries. Artificial magnetic response in these structures appears due to weak spatial dispersion effects, and it is important to study the conditions under which the magnetic re- sponse can be adequately measured with effective permeability tensor. On the examples of dual bars and split rings we show that this is possible only under some quite restrictive conditions. In the general case, more compli- cated constitutive relations with more effective material parameters need to be developed.Comment: 20 pages, 2 figure

Transmission characteristics of bianisotropic metamaterials based on omega shaped metallic inclusions

The authors report the transmission properties of omega shaped metallic inclusions on a dielectric medium that exhibits bianisotropic properties. The resonance frequencies of single omega resonators are investigated experimentally and numerically. The resonance frequency of an ω structure depends on its orientation with respect to the incident electric field. Increasing the tail length of the ω resonator causes a decrease in resonance frequency. Band gaps due to the magnetoelectric resonances are observed for various types of periodic omega arrays. A transmission band is observed when a periodic ω media is combined with a negative permittivity media of periodic thin wires. The transmission band appears below the band gap of periodic omega media, in turn indicating right-handed behavior. A dual transmission band is obtained by composing two different types of metamaterials that are arranged periodically. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

The principle of symmetry of kinetic coefficients for media with ferrite inclusions and its application to nonreciprocal BI-ANISOTROPIC composites

The principle of the symmetry of kinetic coefficients (the Onsager-Casimir principle) is formulated for bi-anisotropic media containing dissipative ferrite inclusions and metal strip elements. Electrodynamic description of bi-anisotropic particles on the base of strip-line-coupled magnetostatic wave resonators is developed and analytical closed-form expressions for the tensor polarizabilities are obtained for an arbitrary direction of the bias magnetic field and an arbitrary resonator shape. The results open a pos-sibility to theoretically predict properties of novel nonreciprocal electrically controllable bi-anisotropic composites with exotic electromagnetic properties

Modelling of Dispersive Chiral Media: Limitations on Material Parameters

Single-resonance models of the constitutive parameters of artificial isotropic chiral composites are analysed. Limitations on the medium parameters which follow from non-negativeness of the field energy density are established and discussed. The analysis is restricted to the frequency regions where the losses can be neglected. As a results, it is shown that the single-resonance model cannot be used at frequencies far from the resonance or the low-frequency region

Effect of optical processing on the surface structure of paratellurite single crystals

The effect of optical treatment of the surfaces of a paratellurite single crystal corresponding to the (100), (110), and (001) crystallographic planes was studied. Using a NanoMap WLI1000 optical profilometer, the relief layer of the sample surface (paratellurite single crystal) was controlled. To study the influence of the polishing method, the process was carried out using three techniques – neutral polishing, acid polishing and alkaline polishing. The characteristics of paratellurite surfaces after grinding and polishing are determined. Conclusions are drawn about the predominant use of polishing with chemical reagents. The anisotropy of surfaces differing in crystallographic directions on the speed of grinding and polishing and on the characteristics of the surfaces is shown. Studies of the structure of ground and polished surfaces corresponding to crystallographic planes have shown that the maximum roughness height is observed for the (001) plane. The smoothest surface is achieved for surfaces coinciding with the crystallographic plane (110)