O. Zhuromskyy

Phonon-like dispersion curves of magnetoinductive waves

The dispersion characteristics of magnetoinductive (MI) waves for a one-dimensional array of metamaterial elements are investigated for the case where the element properties vary in a bi-periodic manner. It is shown that, by this means (analogously to acoustic waves in a solid), a variety of dispersion curves can be obtained including those displaying an “optical” branch. The flexibility of the metamaterial design makes it possible to apply this approach for obtaining specified dispersion properties. A design permitting parametric amplification is proposed.

Rotational resonance of magnetoinductive waves : Basic concept and application to nuclear magnetic resonance

Magnetoinductive waves propagating along a set of resonant metamaterial elements are studied under the condition when the wave travels round a closed circular path and the total phase shift is an integral multiple of 2π. The resonant frequency of the circulating wave is shown to be related to the resonant frequency of the element via the known dispersion relationship. The currents in the elements are determined with the aid of the impedance matrix when the excitation is by a rotating magnetic dipole located at the center of the structure. It is shown that the power taken out from one element in the loop may approach N times that from a single element, where N is the number of elements, provided the quality factor of the individual elements is sufficiently high and suitable modifications are made to nearby elements. Potential applications to magnetic resonance spectroscopy are discussed.

Painting by Numbers: Nanoparticle‐Based Colorants in the Post‐Empirical Age

The visual appearance of the artificial world is largely governed by films or composites containing particles with at least one dimension smaller than a micron. Over the past century and a half, the optical properties of such materials have been scrutinized and a broad range of colorant products, based mostly on empirical microstructural improvements, developed. With the advent of advanced synthetic approaches capable of tailoring particle shape, size and composition on the nanoscale, the question of what is the optimum particle for a certain optical property can no longer be answered solely by experimentation. Instead, new and improved computational approaches are required to invert the structure-function relationship. This progress report reviews the development in our understanding of this relationship and indicates recent examples of how theoretical design is taking an ever increasingly important role in the search for enhanced or multifunctional colorants.

Slow waves on magnetic metamaterials and on chains of plasmonic nanoparticles: Driven solutions in the presence of retardation

Slow waves on chains or lattices of resonant elements offer a unique tool for guiding and manipulating the electromagnetic radiation on a subwavelength scale. Applications range from radio waves to optics with two major classes of structures being used: (i) metamaterials made of coupled ring resonators supporting magnetoinductive waves and (ii) plasmonic crystals made of nanoparticles supporting waves of near-field coupling. We derive dispersion equations of both types of slow waves for the case when the interelement coupling is governed by retardation effects, and show how closely they are related. The current distribution is found from Kirchhoff’s equation by inverting the impedance matrix. In contrast to previous treatments power conservation is demonstrated in a form relevant to a finite structure: the input power is shown to be equal to the radiated power plus the powers absorbed in the Ohmic resistance of the elements and the terminal impedance. The relations between frequency and wave number are de...

Interacting waves on chains of split-ring resonators in the presence of retardation

Wave propagation is studied experimentally in a one-dimensional periodic chain of magnetically coupled split-ring resonators with a spacing of about one tenth of the resonant wavelength. Retardation leads to a strong interaction between magnetoinductive and free-space waves. Two kinds of guided modes are observed: a slow backward wave which propagates far outside the light cone, and a fast forward wave close to the light cone. The two merge in a region of zero group velocity. The results are relevant for all one- and two-dimensional periodic systems interacting with waves of the surrounding space.

Circuit model optimization of a nano split ring resonator dimer antenna operating in infrared spectral range

Metamaterials are comprised of metallic structures with a strong response to incident electromagnetic radiation, like, for example, split ring resonators. The interaction of resonator ensembles with electromagnetic waves can be simulated with finite difference or finite elements algorithms, however, above a certain ensemble size simulations become inadmissibly time or memory consuming. Alternatively a circuit description of metamaterials, a well developed modelling tool at radio and microwave frequencies, allows to significantly increase the simulated ensemble size. This approach can be extended to the IR spectral range with an appropriate set of circuit element parameters accounting for physical effects such as electron inertia and finite conductivity. The model is verified by comparing the coupling coefficients with the ones obtained from the full wave numerical simulations, and used to optimize the nano-antenna design with improved radiation characteristics.

MAGNETIC RESPONSE FROM A COMPOSITE OF METAL-DIELECTRIC PARTICLES IN THE VISIBLE RANGE: T-MATRIX SIMULATION

Normal 0 false false false MicrosoftInternetExplorer4 The optical response of a particle composed of a dielectric core surrounded by a densely packed shell of small metal spheres is simulated with the superposition T-matrix method for realistic material parameters. In order to compute the electric and magnetic particle polarizabilities a single expansion T-matrix is derived from a particle centered T-matrix. Finally the permeability of a medium comprising such particles is found to deviate considerable from unity resulting in a noticeable optical response.

Coupling mechanisms of resonators in the THz regime

Circuit model analysis extensively used to describe metamaterials response at radio and microwave frequencies needs significant revision for application to metallic resonators in the infrared frequency range. A self consistent filament current based approach is elaborated providing parameter values accurately describing resonators internal properties as well as inter-resonator couplings. The model is verified by comparing the excitations in a five element array obtained from the numerical simulation using CST MWS solver with the predictions provided by the model. Although the results presented here concern with loop like magnetic resonators, the model can also be extended to other resonator shapes, for example metallic rods.

Interplay of Mie and Bragg resonances in partly ordered monolayers of colloidal spheres

The transformation of 2-dimensional slab photonic crystal into 2-dimensional photonic glass was achieved by gradually increasing the sphere spacing and by randomising the lattice. The materials were prepared by assembling colloidal particles at the air/water interface using a Langmuir-Blodgett trough and the subsequent deposition on glass substrates. Highly ordered monolayers were obtained by using colloids of one size, while use particles of two different sizes and different partial concentrations allows to increase the spacing of the larger spheres and to randomize the lattice. Changes in the spheres arrangements result in a change of in-plane light propagation from band-like to hopping photon transport.

Coupling mechanisms in nano-U dimers

Properties of split-ring metamaterials are governed by inter-element interactions. These interactions lead to slow eigenmodes of coupling, which, due to their short wavelengths, are ideal candidates for the design of near-field manipulating devices. In this paper we explore the electric and magnetic coupling mechanisms in nano-U and nano-SRR dimers comprising of two identical nano-resonators arranged axially and twisted relative to each other by an arbitrary angle. We study theoretically the couplings in a periodic chain of nano-dimers for the frequencies from 100 to 300 THz. In our analytical model, the electric and magnetic couplings can be expressed through the self and mutual terms for the magnetic and electric field energy. In addition, we incorporate the effect of kinetic inductance due to the inertia of the electrons (noticeable as element dimensions approach 100nm or smaller). The resulting dependence of the electric, magnetic and the total coupling constants on the twist angle within the dimer obtained analytically is shown to agree with numerical simulations (CST Microwave Studio). Our approach should enable an effective design of metamaterial structures with desired properties and would be a useful tool in developing THz range manipulating devices based on propagation of slow waves by virtue of coupling.