arXiv subjects

C. R. Simovski

Publications and source records attributed to C. R. Simovski.

At least 19 recordsLinked to original sources

arXiv2023

Electromagnetic Effects in Anti-Hermitian Media with Gain and Loss

Incorporating both gain and loss into electromagnetic systems provides possibilities to engineer effects in unprecedented ways. Concerning electromagnetic effects in isotropic media that have concurrently electric and magnetic responses, there is in fact a degree of freedom to distribute the gain and loss in different effective material parameters. In this paper, we analytically scrutinize wave interactions with those media, and, most importantly, we contemplate the extreme scenario where such media are anti-Hermitian. Considering various conditions for excitation, polarization, and geometry, we uncover important effects and functionalities such as lasing into both surface waves and propagating waves, conversion of evanescent source fields to transmitted propagating waves, full absorption, and enhancing backward to forward scattering ratio. We hope that these findings explicitly show the potential of anti-Hermiticity to be used in optical physics as well as microwave engineering for creating and using unconventional wave phenomena.

physics.app-ph↗

arXiv2023

Effective Mid-Range Wireless Power Transfer with Compensated Radiation Loss

In conventional inductive wireless power devices, the energy is transferred via only reactive near fields, which is equivalent to non-radiative Förster energy transfer in optics. Radiation from transmitting and receiving coils is usually considered as a parasitic effect that reduces the power transfer efficiency. As long as the distance between the two antennas is small as compared to the antenna size, conventional WPT devices offer rather high power transfer efficiency, of the order of 80-90\%. However, for larger distances, the transfer efficiency dramatically drops, making such devices not practical. In this paper, we develop a dynamic theory of wireless power transfer between two small loop antennas, clarify the role of far-field radiation, and find a possibility to realize efficient wireless power transfer at large distances utilizing the regime of radiation suppression due to optimized mutual dynamic interactions between the transmitting and receiving antennas. The analytical results have been validated by simulations and measurements, and they open a possibility to greatly expand the range of distances of compact wireless power transfer devices. The developed theory can be applied also to coupling between antennas of different types and to energy transfer between nano-objects.

physics.app-ph↗

arXiv2020

Role of the normal polarization in the far-field subwavelength imaging by a dielectric microsphere or microcylinder

Role of the normal polarization in the far-field subwavelength imaging granted by a dielectric microsphere or microcylinder is discussed and the hypotheses explaining this experimental fact are suggested. One of these hypotheses is confirmed by exact numerical simulations. This mechanism of the magnifying superlens operation is based on the excitation of creeping waves at a curved dielectric interface by a normally polarized dipole. The set of creeping waves after their ejection from the surface creates an imaging beam which may mimic either a Bessel beam or a Mathieu beam depending on the microparticle radius. This mechanism corresponds to the asymmetric coherent illumination.

physics.optics↗

arXiv2018

On-Site Wireless Power Generation

Conventional wireless power transfer systems consist of a microwave power generator and a microwave power receiver separated by some distance. To realize efficient power transfer, the system is typically brought to resonance, and the coupled-antenna mode is optimized to reduce radiation into the surrounding space. In this scheme, any modification of the receiver position or of its electromagnetic properties results in the necessity of dynamically tuning the whole system to restore the resonant matching condition. It implies poor robustness to the receiver location and load impedance, as well as additional energy consumption in the control network. In this study, we introduce a new paradigm for wireless power delivery based on which the whole system, including transmitter and receiver and the space in between, forms a unified microwave power generator. In our proposed scenario the load itself becomes part of the generator. Microwave oscillations are created directly at the receiver location, eliminating the need for dynamical tuning of the system within the range of the self-oscillation regime. The proposed concept has relevant connections with the recent interest in parity-time symmetric systems, in which balanced loss and gain distributions enable unusual electromagnetic responses.

physics.app-ph↗

arXiv2017

Shadow-free multimers as extreme-performance meta-atoms

We generalize the concept of parity-time symmetric structures with the goal to create meta-atoms exhibiting extraordinary abilities to overcome the presumed limitations in the scattering of overall lossless particles, such as non-zero forward scattering and the equality of scattering and extinction powers for all lossless particles. Although the forward scattering amplitude and the extinction cross section of our proposed meta-atoms vanish, they scatter incident energy into other directions, with controllable directionality. These meta-atoms possess extreme electromagnetic properties not achievable for passive scatterers. As an example, we study meta-atoms consisting of two or three small dipole scatters. We consider possible microwave realizations in the form of short dipole antennas loaded by lumped elements. The proposed meta-atom empowers extraordinary response of a shadow-free scatterer and theoretically enables most unusual material properties when used as a building block of an artificial medium.

physics.optics↗

arXiv2016

Magnetic hyperbolic metamaterial of polaritonic nanowires

We show that the axial component of the magnetic permeability tensor is resonant for a wire medium consisting of high-index epsilon-positive nanowires, and its real part changes the sign at a certain frequency. At this frequency the medium experiences the topological transition from the hyperbolic to the elliptic type of dispersion. We show that the transition regime is characterized by extremely strong dependence of the permeability on the wave vector. This implies very high density of electromagnetic states that results in the filamentary pattern and noticeable Purcell factor for a transversely oriented magnetic dipole.

cond-mat.mes-hall↗

arXiv2015

Microgap thermophotovoltaic systems with low emission temperature and high electric output

We theoretically show that a thermophotovoltaic (TPV) system enhanced by a wire metamaterial opens the door to a prospective microgap thermophotovoltaics which will combine high electric output with relatively low temperatures of the emitter. The suggested system comprises an array of parallel metal nanowires grown on top of a photovoltaic semiconductor and standing free in the vacuum gap between the host dielectric layer and the emitter, so that their ends are sufficiently close to the emitting surface. Due to the resonant near-field coupling between this wire medium and the emitter and due to the optimized layered structure of the whole system, the strongly super-Planckian radiative heat flux of resonant nature is engineered.

cond-mat.mes-hall↗

arXiv2015

Double resonant wideband Purcell effect in a polaritonic wire medium

In this paper, we theoretically show that a broadband resonant enhancement of emission may occur for infrared sources located in a polaritonic wire medium. The reason of this enhancement is overlapping of two topological transitions of the wave dispersion in the medium. The first topological transition has been recently revealed as an effect inherent to polaritonic wire media. The second one was theoretically uncovered in another material. In this work we reveal it for wire media and prove the possibility to combine both these transitions with the purpose to obtain the broadband resonant Purcell factor. We compare the results obtained for two orientations of a subwavelength electric dipole embedded into wire medium -- that along the optical axis and that perpendicular to it -- and report on the resonant isotropic radiation enhancement. Also, we reveal the enhancement of radiation to free space from a finite sample of the wire medium.

cond-mat.mes-hall↗

arXiv2015

Topological phase transition in wire medium enables high Purcell factor at infrared frequencies

In this paper, we study topological phase transition in a wire medium operating at infrared frequencies. This transition occurs in the reciprocal space between the indefinite (open-surface) regime of the metamaterial to its dielectric (closed-surface) regime. Due to the spatial dispersion inherent to wire medium, a hybrid regime turns out to be possible at the transition frequency. Both such surfaces exist at the same frequency and touch one another. At this frequency, all values of the axial wavevector correspond to propagating spatial harmonics. The implication of this regime is the overwhelming radiation enhancement. We numerically investigated the gain in radiated power for a sub-wavelength dipole source submerged into such the medium. In contrast to all previous works, this gain (called the Purcell factor) turns out to be higher for an axial dipole than for a transversal one.

cond-mat.mes-hall↗

arXiv2015

Full light absorption in single arrays of spherical nanoparticles

In this paper we show that arrays of core-shell nanoparticles function as effective thin absorbers of light. In contrast to known metamaterial absorbers, the introduced absorbers are formed by single planar arrays of spherical inclusions and enable full absorption of light incident on either or both sides of the array. We demonstrate possibilities for realizing different kinds of symmetric absorbers, including resonant, ultra-broadband, angularly selective, and all-angle absorbers. The physical principle behind these designs is explained considering balanced electric and magnetic responses of unit cells. Photovoltaic devices and thermal emitters are the two most important potential applications of the proposed designs.

physics.optics↗

arXiv2015

Topological transition in a nanowire medium and its radiative implication

We reveal and study the topological transition in a metamaterial formed by parallel nanowires of polaritonic material. When the dispersion transits from the elliptic (epsilon-positive) to hyperbolic (epsilon-indefinite) regime, a very specific isofrequency surface arises which implies an extraordinary Purcell factor in spite of noticeable optical losses.

cond-mat.mes-hall↗

arXiv2014

Polarizabilities of nonreciprocal bianisotropic particles

For two electrically small nonreciprocal scatterers an analytical electromagnetic model of polarizabilities is developed. Both particles are bianisotropic: the so-called Tellegen-omega particle and moving-chiral particle. Analytical results are compared to the full-wave numerical simulations. Both models satisfy to main physical restrictions and leave no doubts in the possibility to realize these particles experimentally. This paper is a necessary step towards applications of nonreciprocal bianisotropic particles such as perfect electromagnetic isolators, twist polarizers, thin-sheet phase shifters, and other devices.

physics.optics↗

arXiv2012

Huge local field enhancement in perfect plasmonic absorbers

In this Letter we theoretically study the possibility of total power absorption of light in a planar grid modelled as an effective sheet with zero optical thickness. The key prerequisite of this effect is the simultaneous presence of both resonant electric and magnetic modes in the structure. We show that the needed level of the magnetic mode is achievable using the effect of substrate-induced bianisotropy which also allows the huge local field enhancement at the same wavelength where the maximal absorption holds.

cond-mat.mtrl-sci↗

arXiv2008

Metamaterial nanotips

Nanostructured metamaterials, especially arrays of metallic nanoparticles which sustain the excitation of localized plasmon polaritons, provide excellent opportunities to mold the flow of light in the linear regime. We suggest a metamaterial structure whose properties are determined not only by its inner geometry but also by its entire shape. We call this structure a \emph{metamaterial nanotip}. We evaluate the potential of this nanotip to control the size and the location of the field enhancement. Two-dimensional implementations of this metamaterial nanotip were comprehensively numerically simulated and confirm the expected, physically distinct regimes of operation.

physics.optics↗

arXiv2008

Towards isotropic negative magnetics in the visible range

The idea of isotropic resonant magnetism in the visible range of frequencies known from precedent publications is developed having in mind achievements of the modern chemistry. Plasmonic colloidal nanoparticles covering a silica core form a cluster with resonant and isotropic magnetic response. Two approximate models giving the qualitative mutual agreement are used to evaluate the magnetic polarizability of the cluster. It is shown that the electrostatic interaction of nanocolloids decreases the resonant frequency of an individual complex magnetic scatterer (nanocluster) compared to the previously studied variant of a planar circular nanocluster with same size. This means the reduction of the optical size of nanoclusters that presumably allows one to avoid strong spatial dispersion within the frequency range of the negative permeability.

physics.optics↗

arXiv2005

Patch antennas with new artificial magnetic layers

A new type of high-impedance surfaces (HIS) has been introduced by C.R. Simovski et al. recently. In this paper, we propose to use such layers as artificial magnetic materials in the design of patch antennas. The new HIS is simulated and patch antennas partially filled by these composite layers are measured in order to test how much the antenna dimensions can be reduced. In order to experimentally investigate the frequency behavior of the material, different sizes of the patches are designed and tested with the same material layer. Also the height of the patch is changed in order to find the best possible position for minimizing the antenna size. This composite layer of an artificial magnetic material has made the antenna smaller while keeping the bandwidth characteristics of the antenna about the same. About 40% of size reduction has been achieved.

physics.class-ph↗

arXiv2004

On the low-frequency spatial dispersion in wire media

The work is dedicated to the theoretic analysis of wire media, i.e. lattices of perfectly conducting wires comprised of two or three doubly periodic arrays of parallel wires which are orthogonal to one another. An analytical method based on local field approach is used. The explicit dispersion equations are presented and studied. A possibility to introduce a dielectric permittivity is discussed. The theory is validated by comparison with the numerical data available in the literature.

cond-mat.mtrl-sci↗

arXiv2004

Toward creating wide-band uniaxial left-handed materials with small losses

In this work a possible realizations of a uniaxial variant of left-handed material (LHM) at microwaves is considered. The meta-material has some features of the known structure studied by the group of D. Smith in 2001, however in the present structure a lattice of parallel wires and a lattice of artificial magnetic resonators (MRs) are unified and the MRs are not split-ring resonators. The optimizing of MRs allows significantly decrease the magnetic losses and broaden the band within which the meta-material becomes a LHM.

cond-mat.mtrl-sci↗