arXiv subjects

Constantin Simovski

Publications and source records attributed to Constantin Simovski.

At least 19 recordsLinked to original sources

arXiv2025

Roadmap on Nonlocality in Photonic Materials and Metamaterials

Photonic technologies continue to drive the quest for new optical materials with unprecedented responses. A major frontier in this field is the exploration of nonlocal (spatially dispersive) materials, going beyond the local, wavevector-independent assumption traditionally made in optical material modeling. On one end, the growing interest in plasmonic, polaritonic and quantum materials has revealed naturally occurring nonlocalities, emphasizing the need for more accurate models to predict and design their optical responses. This has major implications also for topological, nonreciprocal, and time-varying systems based on these material platforms. Beyond natural materials, artificially structured materials--metamaterials and metasurfaces--can provide even stronger and engineered nonlocal effects, emerging from long-range interactions or multipolar effects. This is a rapidly expanding area in the field of photonic metamaterials, with open frontiers yet to be explored. In the case of metasurfaces, in particular, nonlocality engineering has become a powerful tool for designing strongly wavevector-dependent responses, enabling enhanced wavefront control, spatial compression, multifunctional devices, and wave-based computing. Furthermore, nonlocality and related concepts play a critical role in defining the ultimate limits of what is possible in optics, photonics, and wave physics. This Roadmap aims to survey the most exciting developments in nonlocal photonic materials, highlight new opportunities and open challenges, and chart new pathways that will drive this emerging field forward--toward new scientific discoveries and technological advancements.

cond-mat.mes-hall↗

arXiv2024

Uniform Field in Microwave Cavities Through the Use of Effective Magnetic Walls

Wire media (WM) resonators have emerged as promising realization for plasma haloscopes -- devices designed to detect axions, a potential component of dark matter. Key factors influencing the detection probability include cavity volume, resonance quality factor, and form factor. While the form factor has been explored for resonant frequency tuning, its optimization for axion detection remains unexplored. In this work, we present a novel approach to significantly enhance the form factor of WM plasma haloscopes. By shifting the metal walls of the resonator by a quarter wavelength, we effectively convert an electric wall boundary condition into a magnetic wall one, allowing for an almost uniform mode. Theoretical analysis and numerical simulations confirm that this modification improves the electric field profile and boosts the form factor. We validate these findings through experimental results from two prototype resonators: one with a standard geometry and another with a quarter-wave air gap between the WM and the walls. Additionally, our method provides a simple way to control the field profile within WM cavities, which can be explored for further applications.

physics.ins-det↗

arXiv2024

Time Interfaces in Nanoplasma-Switched Wire Media

In this work, we consider instantaneous transitions of an infinitely extended uniaxial dielectric into a wire medium (WM) of continuous infinitely long conducting wires. Due to the strong spatial dispersion in the WM the known (Morgenthaler's) theory of temporal discontinuities is not applicable. We solve this problem analytically in time domain. We show that a transverse electromagnetic (TM) plane wave transforms into four waves: a pair of TM waves and a pair of transverse electromagnetic waves. This way, the power flow splits into two different directions, with one of them along the wires. Such a transition can possibly be achieved by nanoplasma discharges in the gaps of the split wires, initiated by an external voltage source applied to the wire and transforming the split wires forming the uniaxial dielectric into continuous ones.

physics.optics↗

arXiv2024

Electromagnetic Time Interfaces in Wire Media: Innovations for Subwavelength Imaging

In this work, we theoretically study temporal interfaces between media with strong spatial dispersion and dielectrics. In particular, we consider a temporal discontinuity that transforms a wire medium sample, a metamaterial with resonant spatial dispersion, into a uniaxial dielectric. We show that this transition results in a transformation of the deeply subwavelength spatial spectrum of TEM waves propagating in the wire medium at a certain frequency into a spectrum of plane waves at new frequencies that are all higher than the initial one. The waves at different frequencies propagate in different directions. Their complex amplitudes and propagation directions are uniquely related to the amplitudes of the spatial harmonics of the fields which existed before the transition. We explain how to implement this transition. The revealed effect may result in a promising method of subwavelength imaging.

physics.optics↗

arXiv2024

Physically Consistent RIS: From Reradiation Mode Optimization to Practical Realization

We propose a practical framework for designing a physically consistent reconfigurable intelligent surface (RIS) to overcome the inefficiency of the conventional phase gradient approach. For a section of Cape Town and across three different coverage enhancement scenarios, we optimize the amplitude of the RIS reradiation modes using Sionna ray tracing and a gradient-based learning technique. We then determine the required RIS surface/sheet impedance given the desired amplitudes for the reradiation modes, design the corresponding unitcells, and validate the performance through full-wave numerical simulations using CST Microwave Studio. We further validate our approach by fabricating a RIS using the parallel plate waveguide technique and conducting experimental measurements that align with our theoretical predictions.

physics.app-ph↗

arXiv2023

Engineering of intelligent reflecting surfaces: Reflection locality and angular stability

Reconfigurable intelligent surfaces (RISs) are electromagnetically passive controllable structures, deflecting the incident wave beam in directions predefined by the control signal. A usual way to design RIS based on metasurfaces (MSs) is based on the application of the approximation in which the reflective properties of a uniform MS are attributed to a unit cell of the non-uniform one. We call this approximation the reflection locality. In the present paper, we show that this approximation may result in heavy errors. We also find a condition under which this approximation is applicable for a wide range of incidence and deflection angles. This condition is the angular stability of the reflection phase of a uniform MS based on which the non-uniform one is generated. We present an approximate analytical proof of the equivalence of the reflection locality and angular stability. As an example, we report theoretical and experimental results we obtained for a binary RIS whose generic uniform analogue has the angular stability. Meanwhile, for its counterpart without angular stability (the so-called mushroom MS) the same model fails.

physics.optics↗

arXiv2022

Wire metamaterial filled metallic resonators

In this work we study electromagnetic properties of a resonator recently suggested for the search of axions - a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of wire medium works for this resonator without mesoscopic corrections, and that the resonator quality $Q$ at the frequency of our interest drops versus the growth of the resonator volume $V$ until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands, an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve WM loaded resonators.

hep-ph↗

arXiv2021

Up-And-Coming Physical Concepts of Wireless Power Transfer

The rapid development of chargeable devices has caused a great deal of interest in efficient and stable wireless power transfer (WPT) solutions. Most conventional WPT technologies exploit outdated electromagnetic field control methods proposed in the 20th century, wherein some essential parameters are sacrificed in favour of the other ones (efficiency vs. stability), making available WPT systems far from the optimal ones. Over the last few years, the development of novel approaches to electromagnetic field manipulation has enabled many up-and-coming technologies holding great promises for advanced WPT. Examples include coherent perfect absorption, exceptional points in non-Hermitian systems, non-radiating states and anapoles, advanced artificial materials and metastructures. This work overviews the recent achievements in novel physical effects and materials for advanced WPT. We provide a consistent analysis of existing technologies, their pros and cons, and attempt to envision possible perspectives.

physics.app-ph↗

arXiv2020

A dielectric microcylinder makes a nanocylindrical trap for atoms and ions

In the diffraction of visible light by a dielectric microcylinder packages of evanescent waves always arise. However, a single-wave incidence corresponds to rather small impact of evanescent waves outside the cylinder. In this paper, we theoretically show that a symmetric pair of plane waves impinging a glass microcylinder corresponds to much higher impact of the evanescent waves. Namely, the interference of the evanescent waves with the propagating ones results in the suppression of the electromagnetic field in an area with very small cross section. This area is located in free space at a substantial distance from the {rear side of the microcylinder and along its axis}. It may serve a linear optical trap for cold atoms and ions.

physics.optics↗

arXiv2020

Double-resonant decoupling method in very dense dipole arrays

In this paper an approach for broadening of operational band in a dense array of dipole antennas by implementing passive split-loop resonators (SLRs) as decouplers is presented. Compared to the previous method, where three closely located active dipoles were decoupled by two passive dipole, the operational band is significantly improved from $0.5 \%$ to $1.6 \%$ at the same level of decoupling -8dB for the cross-talk and inter-channel transmittance. To delineate, the presence of two SLRs results in birefringence of the resonant interaction of SLRs which creates two different eigenmodes for decoupling. As a result, a dual-resonant decoupled band is obtained. Alongside with analytical investigation, numerical and experimental investigations verify the veracity of our approach. Moreover, the possibility of decoupling by SLRs for arrays with more active dipoles is investigated numerically.

physics.app-ph↗

arXiv2020

Analysis of High Impedance Coils both in Transmission and Reception Regimes

Theory of a high impedance coil (HIC) - a cable loop antenna with a modified shield - is discussed comprehensively for both in transmitting and receiving regimes. Understanding a weakness of the previously reported HIC in transmitting regime, we suggest another HIC which is advantageous in both transmitting and receiving regimes compared to a conventional loop antenna. In contrast with a claim of previous works, only this HIC is a practical transceiver HIC. Using the perturbation approach and adding gaps to both shield and inner wire of the cable, we tune the resonance frequency to be suitable for ultra-high field (UHF) magnetic resonance imaging (MRI). Our theoretical model is verified by simulations. Designing the HIC theoretically, we have fabricated an array of three HICs operating at 298 MHz. The operation of the array has been experimentally studied in presence of different phantoms used in UHF MRI and the results compared with those obtained for a conventional array.

physics.med-ph↗

arXiv2019

Dual-metasurface superlens: a comprehensive study

We present a theoretical and numerical study of a dual metasurface superlens dedicated to the near field optical imaging of submicron objects. Compared to the previous studies of dual metasurface plasmonic superlenses, we suggest a more adequate theoretical model of their operation. The new model allows us to obtain twice better operational characteristics of the redisigned superlens. For the first time, we describe the operation of such the superlens using full wave numerical simulations, taking into account the interfaces of the host medium slab and proving the nanoimaging for scattering objects instead of a radiating source. We discuss and address both application and fabrication issue for this superlens.

physics.optics↗

arXiv2019

Omnidirectional Wireless Power Transfer with Automatic Power Flow Control

We present an omnidirectional wireless power transfer (WPT) system capable of automatic power flow control using three orthogonal transmitter (Tx)-repeater (Rp) pairs. The power drawn from each transmitter is automatically adjusted depending on the mutual inductance between the receiver and the Tx-Rp pair. The proposed approach enables the receiver to harvest almost uniform power with high efficiency (90\%) regardless of its position.

eess.SY↗

arXiv2019

Automatic Receiver Tracking and Power Channeling for Multi-Transmitter Wireless Power Transfer

Free positioning of receivers is one of the key requirements for many wireless power transfer (WPT) applications, required from the end-user point of view. However, realization of stable and effective wireless power transfer for freely positioned receivers is technically challenging task because of the requirement of complex control and tuning. In this paper, we propose a concept of automatic receiver tracking and power channeling for multi-transmitter WPT systems using uncoupled transmitter and uncoupled repeaters. Each transmitter-repeater pair forms an independent power transfer channel providing an effective link for the power flow from the transmitter to the receiver. The proposed WPT system is capable of maintaining stable output power with constant high efficiency regardless of the receiver position and without having any active control or tuning. The proposed concept is numerically and experimentally verified by using a four-transmitter WPT system in form of a linear array. The experimental results show that the efficiency of the proposed WPT system can reach 94.5\% with a variation less than 2\% against the receiver position.

eess.SP↗

arXiv2019

Decoupling of Two Closely Located Dipoles by a Single Passive Scatterer for Ultra-High Field MRI

We report decoupling of two closely located resonant dipole antennas dedicated for ultra-high field magnetic resonance imaging (MRI). We show that a scatterer slightly raised over the plane of antennas grants a sufficient decoupling even for antennas separated by very small gap (below 1/30 of the wavelength). We compare the operation of two decoupling scatterers. One of them is a shortcut resonant dipole and another is a split-loop resonator (SLR). Previously, we have shown that the SLR offers a wider operational band than the dipole and the same level of decoupling. However, it was so for an array in free space. The presence of the body phantom drastically changes the decoupling conditions. Moreover, the requirement to minimize the parasitic scattering from the decoupling element into the body makes the decoupling dipole much more advantageous compared to the SLR.

physics.med-ph↗

arXiv2018

Smart Table Based on Metasurface for Wireless Power Transfer

Metasurfaces have been investigated and its numerous exotic functionalities and the potentials to arbitrarily control of the electromagnetic fields have been extensively explored. However, only limited types of metasurface have finally entered into real products. Here, we introduce a concept of a metasurface-based smart table for wirelessly charging portable devices and report its first prototype. The proposed metasurface can efficiently transform evanescent fields into propagating waves which significantly improves the near field coupling to charge a receiving device arbitrarily placed on its surface wirelessly through magnetic resonance coupling. In this way, power transfer efficiency of 80$\%$ is experimentally obtained when the receiver is placed at any distances from the transmitter. The proposed concept enables a variety of important applications in the fields of consumer electronics, electric automobiles, implanted medical devices, etc. The further developed metasurface-based smart table may serve as an ultimate 2-dimensional platform and support charging multiple receivers.

physics.app-ph↗

arXiv2018

Ultrahigh field MR-imaging: new frontiers and possibilities

Increasing the static magnetic field strength into the realm of ultrahigh fields (7 T and higher) is the central trend in modern magnetic resonance (MR) imaging. The use of ultrahigh fields in MR-imaging leads to numerous effects some of them raising the image quality, some degrading, some previously undetected in lower fields. This review aims to outline the main consequences of introducing ultrahigh fields in MR-imaging, including new challenges and the proposed solutions, as well as new scanning possibilities unattainable at lower field strengths (below 7 T).

physics.med-ph↗

arXiv2018

Decoupling of Two Closely Located Dipole Antennas by a Split-Loop Resonator

In this letter, we theoretically and experimentally prove the possibility of the complete passive decoupling for two parallel resonant dipoles by a split-loop resonator. Unlike previously achieved decoupling by a similar resonant dipole, this decoupling technique allows us to avoid the shrink of the operation band. Compare to previous work, simulation and measurement show 100\% enhancemnet of relative operation band from 0.2% to 0.4%

physics.app-ph↗