arXiv subjects

Grigorii Ptitcyn

Publications and source records attributed to Grigorii Ptitcyn.

13 recordsLinked to original sources

arXiv2026

Photonic Temporal Illusion

Materials with unusual optical properties are central to advanced control of light. Yet, in nature, such materials may be exceedingly rare and often difficult to obtain. To overcome this limitation, here we introduce the concept of temporal illusion: A temporally dynamic framework in which carefully programmed temporal variations in effective parameters generate responses akin to those of, in principle, any arbitrary time-invariant structure. We theoretically demonstrate that proper modulation of the permittivity of a conventional dielectric in space and time replicates the optical behavior associated with exotic materials. Besides, we reveal that, beyond steady-state effects, temporal illusion also enables control over transient responses, for instance, by effectively lowering the time constant of high-quality-factor resonators, therefore, allowing faster energy accumulation. Moreover, by incorporating detuning between modulation and excitation, we show that the framework unlocks additional functionalities. The temporal illusion paradigm thus broadens the capabilities of space-time varying systems, offering a powerful route to synthesize material responses on demand and paving the way for new theoretical and experimental directions in optics and wave physics.

physics.optics↗

arXiv2025

Kapitza-Inspired Stabilization of Non-Foster Circuits via Time Modulations

With his formal analysis in 1951, the physicist Pyotr Kapitza demonstrated that an inverted pendulum with an externally vibrating base can be stable in its upper position, thus overcoming the force of gravity. Kapitza's work is an example that an originally unstable system can become stable after a minor perturbation of its properties or initial conditions is applied. Inspired by his ideas, we show how non-Foster circuits can be stabilized with the application of external \textit{electrical vibration}, i.e., time modulations. Non-Foster circuits are highly appreciated in the engineering community since their bandwidth characteristics are not limited by passive-circuits bounds. Unfortunately, non-Foster circuits are usually unstable and they must be stabilized prior to operation. Here, we focus on the study of non-Foster $L(t)C$ circuits with time-varying inductors and time-invariant negative capacitors. We find an intrinsic connection between Kapitza's inverted pendulum and non-Foster $L(t)C$ resonators. Moreover, we show how positive time-varying modulations of $L(t)>0$ can overcome and stabilize non-Foster negative capacitances $C<0$. These findings open up an alternative manner of stabilizing electric circuits with the use of time modulations, and lay the groundwork for application of, what we coin \textit{Vibrational Electromagnetics}, in more complex media.

physics.app-ph↗

arXiv2025

Temporal Interface in Dispersive Hyperbolic Media

Spatial inhomogeneity, temporal modulation, and engineered anisotropy of parameters of electromagnetic media offer numerous opportunities for manipulating light-matter interaction over the past decades. Here, we investigate a scenario in which we deal with the temporal interface, hyperbolic anisotropy in the form of layered structures, and frequency dispersion. We theoretically investigate how a monochromatic uniform plane wave - propagating in an unbounded, homogeneous, isotropic dielectric medium - undergoes changes due to the rapid temporal variation of such medium into a hyperbolic dispersive medium formed by the stack of thin metal-dielectric bilayers, in which the metal follows the lossless Drude dispersion and the dielectric is assumed to be dispersionless. We corroborate our analytical results by numerical simulations. We observe several interesting phenomena, such as the conversion of the original frequency into three pairs of frequencies, resulting in three sets of forward (FW) and backward (BW) waves. We present the amplitudes and the time-average Poynting vectors for such FW and BW waves and discuss some of the salient features of such temporal interface.

physics.optics↗

arXiv2025

Simultaneous Angle-of-Arrival Sensing and Anomalous Deflection with Aperiodically Loaded Patch Arrays

We propose and numerically demonstrate a reconfigurable patch antenna array that enables simultaneous incident wave sensing and anomalous reflection without prior knowledge of the propagation environment. We acquire anomalous reflection by suppressing parasitic scattering through accurate and efficient optimization of induced load currents and by varying impedances of reactive loads. By mitigating parasitic scattering lobes, we demonstrate the feasibility of accurately detecting the incoming illumination angle via the spatial Fourier transform of the optimized load current distribution, facilitated by tunable reactive loads. This approach eliminates the need for additional RF chains, pre-computed data, or calibration measurements. The developed strategy, which integrates arithmetic load optimization with angle-of-arrival sensing, is applicable to general finite-size arrays.

physics.app-ph↗

arXiv2024

Temporal Twistronics

The concept of twistronics and moiré physics, which is present in twisted two-dimensional bilayer materials, has recently attracted growing attention in various fields of science and engineering such as condensed matter physics, nanophotonics, polaritonics and excitonics. The twist angle between the two layers has offered an additional degree of control over electron and photon interaction with such structures. Inspired by the photonic version of twistronics, here we introduce and investigate theoretically the temporal analogue of twistronics in anisotropic optical media. We study how a monochromatic electromagnetic plane wave propagating in a spatially unbounded, anisotropic medium undergoes major changes when the relative permittivity tensor of the medium is rapidly changed in time to create a new anisotropic medium that is the rotated version of the original medium. We consider both the elliptic and hyperbolic anisotropic scenarios. The propagation-angle-dependent forward (FW) and backward (BW) waves with their converted frequencies and relative amplitudes are obtained. To concentrate on the main features of this concept without getting into details of dispersion, in our work here we assume dispersionless and lossless material parameters. Our results reveal how frequency conversion is highly dependent on the direction of propagation of the original wave, rotation angle, and initial values of the material parameters, proposing another class of "magic angles" for such temporal twistronics.

physics.optics↗

arXiv2024

Simultaneous High-Efficiency Anomalous Reflection and Angle of Arrival Sensing in Reconfigurable Intelligent Surfaces

In this work, we introduce reconfigurable intelligent surfaces designed to simultaneously perform reflection of single or multiple incident waves toward the receiver or receivers and sensing the angles of arrival. We achieve anomalous reflection with strongly suppressed parasitic scattering through an in-situ optimization of either the currents flowing on array elements or the far field in the receiver direction. The suppression of parasitic scattering allows us to accurately and without additional measurements or computations detect the angles of arrival of the illuminations through the spatial Fourier transform of the optimized current distribution through the controllable reactive loads. Therefore, unlike other recently proposed methods, our scheme of integrated sensing and communication does not require any pre-computed data sets and works for an arbitrary number of simultaneous illuminations. As a proof of principle, we design and analyze with full-wave simulations several reconfigurable intelligent surfaces consisting of an array of loaded wires above a ground plane.

physics.app-ph↗

arXiv2023

Tunable Perfect Anomalous Reflection Using Passive Aperiodic Gratings

Realizing continuous sweeping of perfect anomalous reflection in a wide angular range has become a technical challenge. This challenge cannot be overcome by the conventional aperiodic reflectarrays and periodic metasurfaces or metagratings. In this paper, we investigate means to create scanning reflectarrays for the reflection of plane waves coming from any direction into any other direction without any parasitic scattering. The reflection angle can be continuously adjusted by proper tuning of reactive loads of each array element, while the geometrical period is kept constant. We conceptually study simple canonical two-dimensional arrays formed by impedance strips above a perfectly reflecting plane. This setup allows fully analytical solutions, which we exploit for understanding the physical nature of parasitic scattering and finding means to overcome fundamental limitations of conventional reflectarray antennas. We propose to use subwavelength-spaced arrays and optimize current distribution in $λ/2$-sized supercells. As a result, we demonstrate perfect tunable reflection to any angle. Our work provides an effective approach to design reconfigurable intelligent surfaces with electrically tunable reflection angles.

physics.app-ph↗

arXiv2023

Time-modulated circuits and metasurfaces for emulating arbitrary transfer functions

Temporal modulation unlocks possibilities to dynamically control and modify the response of electromagnetic systems. Employing explicit dependencies of circuit or surface parameters on time enables the engineering of systems with conventionally unachievable functionalities. Here, we propose a novel approach that enables the emulation of electromagnetic systems that can have arbitrary frequency dispersion and nonlinear properties, including the non-Foster response. In particular, we show that a proper modulation of a time-varying capacitor allows one to mimic a static inductance, capacitance, or resistance having arbitrary values, both positive and negative. We discuss necessary modifications of determined ideal modulation functions that ensure the stability of the system. To demonstrate the applicability of the proposed method, we introduce and simulate an invisible sensor, i.e., a device that does not produce any scattering and is capable of sensing. Three different geometries are proposed and validated using full-wave simulations. In addition to that, we discuss the stability of the systems that are modulated externally. We believe that this study introduces a new paradigm of using time modulations to engineer system responses that can be applied not only to electromagnetic systems (in electronics, microwaves, and optics) but also to other branches of physics.

eess.SY↗

arXiv2023

Comparison Between Different Designs and Realizations of Anomalous Reflectors

Metasurfaces enable efficient manipulation of electromagnetic radiation. In particular, control over plane-wave reflection is one of the most useful features in many applications. Extensive research has been done in the field of anomalous reflectors over the past years, resulting in numerous introduced geometries and several distinct design approaches. Anomalously reflecting metasurfaces designed using different methods show different performances in terms of reflection efficiency, angular response, frequency bandwidth, etc. Without a comprehensive comparison between known design approaches, it is difficult to properly select the most appropriate design method and the most suitable metasurface geometry. Here, we consider four main approaches that can be used to design anomalous reflectors within the same basic topology of the structure and study the designed metasurfaces first on the level of the input impedance and then consider and compare the performance of the realized structures. We cover a wide range of performance aspects, such as the power efficiency and losses, angular response, and the scattering pattern of finite-size structures. We anticipate that this study will prove useful for developing new engineering methods and designing more sophisticated structures that include reconfigurable elements. Furthermore, we believe that this study can be considered referential since it provides comparative physical insight into anomalous reflectors in general.

physics.app-ph↗

arXiv2020

Nonreciprocity in Bianisotropic Systems with Uniform Time Modulation

Physical systems with material properties modulated in time provide versatile routes for designing magnetless nonreciprocal devices. Traditionally, nonreciprocity in such systems is achieved exploiting both temporal and spatial modulations, which inevitably requires a series of time-modulated elements distributed in space. In this paper, we introduce a concept of bianisotropic time-modulated systems capable of nonreciprocal wave propagation at the fundamental frequency and based on uniform, solely temporal material modulations. In the absence of temporal modulations, the considered bianisotropic systems are reciprocal. We theoretically explain the nonreciprocal effect by analyzing wave propagation in an unbounded bianisotropic time-modulated medium. The effect stems from temporal modulation of spatial dispersion effects which to date were not taken into account in previous studies based on the local-permittivity description. We propose a circuit design of a bianisotropic metasurface that can provide phase-insensitive isolation and unidirectional amplification.

physics.app-ph↗

arXiv2019

Dynamic meta-atoms

Interaction of electromagnetic radiation with time-variant objects is a fundamental problem whose study involves foundational principles of classical electrodynamics. Such study is a necessary preliminary step for delineating the novel research field of linear time-varying metamaterials and metasurfaces. A closer look to the literature, however, reveals that this crucial step has not been addressed and important simplifying assumptions have been made. Before proceeding to studies of linear time-varying metamaterials and metasurfaces with their effective parameters, we need to rigorously describe the electric and magnetic responses of a temporally-modulated meta-atom. Here, we introduce a theoretical model which describes a time-variant meta-atom and its interaction with incident electromagnetic waves in time domain. The developed general approach is specialized for a dipole emitter/scatterer loaded with a time-varying reactive element. We confirm the validity of the theoretical model with full-wave simulations. Our study is of major significance also in the area of nanophotonics and nano-optics because the optical properties of all-dielectric and plasmonic nanoparticles can be varied in time in order to achieve intriguing scattering phenomena.

physics.app-ph↗

arXiv2018

Extreme Asymmetry in Metasurfaces via Evanescent Fields Engineering: Angular-Asymmetric Absorption

On the quest towards full control over wave propagation, the development of compact devices that allow asymmetric response is a challenge. In this Letter, we introduce a new paradigm for the engineering of asymmetry in planar structures, revealing and exploiting unilateral excitation of evanescent waves. We test the idea with the design and experimental characterization of a metasurface for angular-asymmetric absorption. The results show that the contrast ratio of absorption (the asymmetry level) can be arbitrarily engineered from zero to infinity for waves coming from two oppositely tilted angles. We demonstrate that the revealed asymmetry effects cannot be realized using conventional diffraction gratings, reflectarrays, and phase-gradient metasurfaces. This Letter opens up promising possibilities for wave manipulation via evanescent waves engineering with applications in one-side detection and sensing, angle-encoded steganography, flat nonlinear devices and shaping the scattering patterns of various objects.

physics.app-ph↗

arXiv2018

Transmission magnitude and phase control for polarization-preserving reflectionless metasurfaces

For transmissive applications of electromagnetic metasurfaces, an array of subwavelength Huygens' metaatoms are typically used to eliminate reflection and achieve a high transmission power efficiency together with a wide transmission phase coverage. We show that the underlying principle of low reflection and full control over transmission is asymmetric scattering into the specular reflection and transmission directions that results from a superposition of symmetric and anti-symmetric scattering components, with Huygens' meta-atoms being one example configuration. Available for oblique illumination in TM polarization, a meta-atom configuration comprising normal and tangential electric polarizations is presented, which is capable of reflectionless, fullpower transmission and a $2π$ transmission phase coverage as well as full absorption. For lossy metasurfaces, we show that a complete phase coverage is still available for reflectionless designs for any value of absorptance. Numerical examples in the microwave and optical regimes are provided.

physics.optics↗