George Semouchkin

FDTD study of resonance Processes in metamaterials

The finite-difference time-domain simulations in the frequency domain are used to study resonance phenomena in left-handed metamaterials consisting of the arrays of split-ring resonators (SRRs) and metal rods. It is demonstrated that, at frequencies corresponding to the band of enhanced transmission of the metamaterial, the half-wavelength resonances occur in both the SRRs and rods. The observed resonances in rods make questionable the applicability of the plasma concept to the analysis of the metamaterial performance. We also show that overlapping of electric or magnetic fields at resonance causes coupling between resonators and assembling them in three-dimensional groups, which rearrange in dependence on frequency inside the transmission band. As the result, the resonance phenomena in the metamaterial proceed essentially nonuniform, although the size of the metamaterial units is less than the wavelength. We suggest that coupling between resonators is capable of providing the electromagnetic response, similar to that observed at the backward-wave propagation in double-negative media. The latter is demonstrated on the example of the all-dielectric metamaterial composed from an array of dielectric resonators.

An infrared invisibility cloak composed of glass

We propose to implement a nonmetallic low-loss cloak for the infrared range from identical chalcogenide glass resonators. Based on transformation optics for cylindrical objects, our approach does not require metamaterial response to be homogeneous and accounts for the discrete nature of elementary responses governed by resonator shape, illumination angle, and inter-resonator coupling. Air fractions are employed to obtain the desired distribution of the cloak effective parameters. The effect of cloaking is verified by full-wave simulations of the true multiresonator structure. The feasibility of cloak fabrication is demonstrated by prototyping glass grating structures with the dimensions characteristic for the cloak resonators.

Design optimization and implementation of bandpass filters with normally fed microstrip resonators loaded by high-permittivity dielectric

Different approaches for designing bandpass filters with transmission zeroes are investigated by using the transmission-line theory and the finite-difference time-domain method. The filters are composed of capacitively coupled uniform impedance microstrip resonators, stepped-impedance microstrip resonators, and tapped feed lines. Different design modifications are discussed and, as a result, a design with double-coupled resonators is proposed. Based on this structure, a miniaturized filter capacitively loaded by high-permittivity dielectric inclusions and fabricated by using low-temperature co-fired ceramic (LTCC) technology is presented. The measured and simulated S-parameter spectra of the LTCC-filter are in good agreement.

Mie scattering as a cascade of Fano resonances

We reveal that the resonant Mie scattering by high-index dielectric nanoparticles can be presented through cascades of Fano resonances. We employ the exact solution of Maxwells equations and demonstrate that the Lorenz-Mie coefficients of the Mie problem can be expressed generically as infinite series of Fano functions as they describe interference between the background radiation originated from an incident wave and narrow-spectrum Mie scattering modes that lead to Fano resonances.

New approaches for designing microstrip filters utilizing mixed dielectrics

A strategy is developed for designing capacitively loaded microstrip filters on low-temperature co-fired ceramic (LTCC) substrates with inclusions or superstrate layers of higher permittivity dielectrics. Finite-difference time-domain simulations of the field distribution at resonant frequencies are used to determine the optimal locations and size of capacitive loads. It is demonstrated that strategic capacitive load placement enables altering the center and attenuation pole frequencies, the shape and width of the passband, and input impedance of the filter by modification of selected resonant modes. Capacitive loading with higher permittivity dielectrics is shown to be very efficient in decreasing dimensions of microstrip filters with low-permittivity substrates. The designs of novel compact resonators and filters have been developed and the prototypes fabricated by using LTCC technology. The results of prototype measurements agree with the simulation results, which validates the proposed approach

Sensing based on Fano-type resonance response of all-dielectric metamaterials.

A new sensing approach utilizing Mie resonances in metamaterial arrays composed of dielectric resonators is proposed. These arrays were found to exhibit specific, extremely high-Q factor (up to 15,000) resonances at frequencies corresponding to the lower edge of the array second transmission band. The observed resonances possessed with features typical for Fano resonances (FRs), which were initially revealed in atomic processes and recently detected in macro-structures, where they resulted from interference between local resonances and a continuum of background waves. Our studies demonstrate that frequencies and strength of Fano-type resonances in all-dielectric arrays are defined by interaction between local Mie resonances and Fabry-Perot oscillations of Bloch eigenmodes that makes possible controlling the resonance responses by changing array arrangements. The opportunity for obtaining high-Q responses in compact arrays is investigated and promising designs for sensing the dielectric properties of analytes in the ambient are proposed.

Design optimization of microstrip square-ring band-pass filter with quasi-elliptic function

Resonant processes in dual-mode microstrip square-ring band-pass filter fed through L-shaped coupling arms have been studied using the Finite Difference Time Domain (FDTD) simulations. The performed field analysis has revealed that coupling arms act as additional half-wavelength resonators coupled with the ring through both electric and magnetic fields. New filter designs with horseshoe resonators instead of coupling arms have been developed, which provide either pure magnetic or electric coupling at the resonant frequency. The obtained results demonstrate the possibility to essentially improve filter characteristics. Simulations results have been verified by the measurements of fabricated prototypes.

Electromagnetic response of the split-ring resonator placed inside a waveguide

The EM response of split ring resonators, conventionally employed to design the left-handed metamaterials, was studied by modeling the behavior of one ring located in a standard waveguide. It was shown that, besides the expected half and full-wavelength resonances, an additional resonance is excited in the SRR at an intermediate frequency due to coupling between the SRR and the waveguide. This resonance supports longitudinal mode in the waveguide and magnetic dipole-type fields near the SRR. While the response of the SRR at the first resonance can be described by negative permeability, the full-wavelength resonance features negative permittivity and the intermediate resonance exhibits more complex behaviors of the constitutive parameters. The properties of this resonance could be used to design novel metamaterials.

Field-simulation-based strategy for designing microstrip filters

The insertion loss spectrum of a microstrip open-loop square ring band-pass filter is analyzed by using the Finite Difference Time Domain (FDTD) field simulations. Visualization of standing waves at resonant frequencies guides the placement of stepped impedance sections or capacitive loads at electric field maxima. Strategic load placement enables us to modify selected resonant modes, to monitor efficiently center and attenuation pole frequencies, to affect the shape and width of the pass-band, and to alter the input impedance. The presented approach is useful for miniaturizing various types of microstrip filters and antennas and optimizing their performance.

Analysis of Electromagnetic Response of 3-D Dielectric Fractals of Menger Sponge Type

Experimental studies and finite-difference time-domain simulations of electromagnetic (EM) response of the second-stage Menger sponge dielectric structures have been performed with different types of excitation in order to gain deeper insight into the phenomenon of EM wave localization in these fractals. Analysis of simulated amplitude distributionExperimental studies and finite-difference time-domain simulations of electromagnetic (EM) response of the second-stage Menger sponge dielectric structures have been performed with different types of excitation in order to gain deeper insight into the phenomenon of EM wave localization in these fractals. Analysis of simulated amplitude distributions of electric field oscillations in the Menger sponges has revealed bandgap-like effects caused by resonances in the front part of the structures, as well as formation of the full-wave resonance mode in the central cavity at the localization frequency. It is demonstrated that penetration of the waves inside the structure at the localization frequency leads to equalizing of the EM response from different parts of the 3D fractal, however, no high-Q eigenmode is formed in the second-stage Menger sponge. Simulations of the modified fractal structures have been used to show the potential of formation of a bandgap with defect-related localized photon states by 3D fractals.s of electric field oscillations in the Menger sponges has revealed bandgap-like effects caused by resonances in the front part of the structures, as well as formation of the full-wave resonance mode in the central cavity at the localization frequency. It is demonstrated that penetration of the waves inside the structure at the localization frequency leads to equalizing of the EM response from different parts of the 3D fractal, however, no high-Q eigenmode is formed in the second-stage Menger sponge. Simulations of the modified fractal structures have been used to show the potential of formation of a bandgap with defect-related localized photon states by 3D fractals.