EMPLOYING DIELECTRIC-BASED MEDIA FOR CONTROLLING FIELD PATTERNS AND WAVE PROPAGATION IN ADVANCED ELECTROMAGNETIC DEVICES

Rapid progress in developing electromagnetic devices and in governing the wave propagation during last years caused renewed interest to dielectric materials. First, engineered dielectric structures with spatial dispersion of their parameters came to replace uniform substrates in antennas and other resonance devices. Then additional boom of dielectric applications was caused by the possibility to employ dielectrics as materials of artificial media. Later, attention of researchers was attracted to properties of the media composed of dielectric resonators (DRs). Currently DRs are used to create metamaterials – the media with unprecedented properties, which cannot be found in nature. Dielectric photonic crystals and metamaterials are considered as the most perspective materials for photonics, since they can be integrated in devices without loss problems, which characterize, for example, plasmonic techniques. Recently, a booming interest emerged to employing in photonics directional light scattering from dielectric particles, since the wavelengths of this light could be controlled by dimensions of particles and their dielectric permittivity. Our work followed basic innovations, which defined contemporary employment of dielectrics in electromagnetics and photonics. In particular, we started from working out new engineering approaches to developing dielectric substrates in patch structures inspired by microstrip patch antennas, which are proposed to serve as MRI RF probes (Chapter 2). Then we redirected our attention to the problems, which restricted employment of dielectrics in left-handed media. In particular, we have shown that negative refraction in all-dielectric metamaterials is irrelevant to Mie resonances in dielectric elements (Chapter 3). Next, we turned to analysis of problems defining directional scattering from dielectric metasurfaces and have demonstrated that the nature of observed phenomena cannot be correctly understood without accounting for strong interaction between “atoms” of metasurafces (Chapter 4). Finally we discussed selected problems met at implementation of photonic crystals in the media of transformation optics based devices and have shown that some of the problems can be solved at employing the phenomenon of self-collimation, characteristic for periodic photonic structures (Chapter 5)

All-dielectric metamaterials: irrelevance of negative refraction to overlapped Mie resonances

All-dielectric metamaterials comprised of identical resonators draw a lot of attention as low-loss media providing for negative refraction, which is commonly attributed to the double negativity of effective material parameters caused by overlapping of Mie resonances. We study dispersion diagrams of such metamaterials composed of dielectric rod arrays and show that bandwidths of positive and negative refraction and its type are irrelevant to the negativity of effective parameters; instead, they are unambiguously defined by the shape and the location of the second transmission branch in dispersion diagrams and thus can be controlled by the lattice constants

Spatial dispersion of index components required for building invisibility cloak medium from photonic crystals

The opportunities to use dielectric photonic crystals (PhCs) as the media of cylindrical invisibility cloaks, designed using transformation optics (TO) concepts, are investigated. It is shown that TO-based prescriptions for radial index dispersion, responsible for turning waves around hidden objects, can be dropped if the PhC media support self-collimation of waves in bent crystals. Otherwise, to provide prescribed anisotropy of index dispersion, it is possible to employ PhCs with rectangular lattices. It is found, however, that at acceptable cloak thicknesses, modifications of crystal parameters do not allow for achieving the prescribed level of index anisotropy. This problem is solved by finding the reduced spatial dispersion law for the radial index component, which is characterized by decreased against TO-prescriptions values near the target and increased values in outer layers of the cloak. The cloak utilizing reduced prescriptions for indices is shown to perform almost as efficiently as a TO-based cloak, in terms of both wave front restoration behind the target and reducing the total scattering cross-width of the target

Employing self-collimation phenomena in photonic crystals for the invisibility cloak development

© 2016 IEEE. We demonstrate that self-collimation effects in the invisibility cloak medium formed from 2D dielectric Photonic Crystal (PhC) can support wave propagation along curvilinear paths around an object to be hidden, with superluminal phase velocities controlled by deformation of PhC lattice cells. These effects can be used for the development of uni-directional cloaks with wave phase preservation, which can be scaled from microwave to optical frequencies. The obtained results show that employment of self-collimation effects can make PhCs advantageous with respect to metamaterials at the formation of the media requested by coordinate transformation techniques for the development of new electromagnetic devices

Unconventional RF Probes Comprised of Microstrip Patch Antennas for High-Field MRI Scanners

© 2016 IEEE. We have developed a system of microstrip patch antennas for replacing conventional RF coils in high-field Magnetic Resonance Imaging (MRI) scanners. The substrates of antennas were engineered by using high permittivity inserts to provide required resonance responses of miniaturized antennas at 600 MHz for 14T MRI scanners and to produce highly uniform magnetic field distribution in the sampling volume. A tuning circuit for the antenna system has been worked out

Electromagnetic responses from planar arrays of dielectric nano-disks at overlapping dipolar resonances

Periodic arrays of dielectric nano-disk resonators are investigated to clarify the nature of their electromagnetic responses, in particular, the relation of light transmission to Kerker\u27s conditions at overlapping dipolar resonances. It is concluded that periodicity and inter-resonator coupling define the observed responses

Frequency selective transmission through waveguides with ENZ sections

© 2015 IEEE. Multi-sectional waveguide structures providing frequency selective transmission controlled by transverse insertion of metal rods in the ENZ sections, are proposed and investigated by using full-wave simulations. It is demonstrated, that when the diameter of the inserted rod is adequately chosen, the position of the full transmission peak in the waveguide spectrum can be furnished at any frequency within the range of 0.75 GHz above the cut-off frequency of the ENZ section

Specifics of scattering and radiation from sparse and dense dielectric meta-surfaces

Metasurfaces composed of nanosized silicon particles are considered prospective low-loss media for future planar devices with subwavelength thickness, capable of realizing many optical functionalities, including beam steering, focusing, and holography. Previous studies revealed an opportunity to provide directional scattering from silicon metasurfaces at Kerker’s conditions and projected obtaining significantly enhanced intensity of scattering at overlapping of dipolar magnetic and electric resonances in particles at their specific geometries. Although silicon metasurfaces are usually represented by dense arrays, interactions between resonators are often neglected in their analysis, which typically uses metamaterial concepts, assuming that responses of arrays can be represented by responses of single “meta-atoms.” In this work, we investigate cooperative resonance phenomena in dielectric metasurfaces, including interactions between electric and magnetic resonances within single particles and inter-resonator interactions in arrays. First, we analyze the transformation of the responses of single resonators, when their shape changes from a sphere to a cylinder, and then to a disk, and, in particular, describe the specifics of the formation of electric and magnetic dipole modes at a coincidence of resonances. Then, phenomena in arrays are considered, including the effects of arraying on resonator responses and the effects of packing density on metasurface responses. We demonstrate that dense packing causes strong changes of resonances, transverse coupling, and integration of resonance fields, affecting scattering and radiation from metasurfaces. The obtained results are important for understanding the complexity of responses of dielectric metasurfaces and provide guidance for their design and for scattering and radiation control

Scattering from dielectric metasurfaces in optical and microwave ranges

Metasurfaces composed of cylindrical dielectric resonators, responding either in optical or microwave ranges, are investigated with the goal of clarifying common features of their electromagnetic responses and their transformations at variations of array lattice constants and resonator heights. It is found that occurrence of dipolar electric resonances in dense metasurfaces is accompanied by full transmission without relation to overlapping of two dipolar resonances. Since electric resonances in dense metasurfaces experience strong coupling, these structures could not be considered as homogenized media of identical meta-atoms. We demonstrate the possibility of scaling metasurfaces, in order to substitute challenging optical experiments by experiments at microwaves

Electromagnetically induced transparency and lattice resonances in metasurfaces composed of silicon nanocylinders

Densely packed metasurfaces composed of cylindrical silicon nano-resonators were found to demonstrate the phenomenon of electromagnetically induced transparency at electric dipolar resonances. It was shown that this phenomenon is not related to overlapping of dipolar resonances or to the Kerker’s effects. The observed transparency appeared to be related to interference between waves scattered by nano-resonators and by additional scattering centers including the electric branch of lattice resonances. Coupled resonance fields were also found to contribute to observed phenomena