arXiv subjects

Stanislav Maslovski

Publications and source records attributed to Stanislav Maslovski.

15 recordsLinked to original sources

arXiv2026

Amplified up-conversion of electromagnetic waves using time-varying metasurfaces

Time-varying metamaterials and photonic time crystals offer a powerful route to wave amplification through temporal modulation of material parameters. Here, we experimentally demonstrate amplified up-conversion of free-space electromagnetic waves in the microwave regime using a time-varying metasurface composed of varactor-loaded coupled split-ring resonators. The metasurface supports a cascaded parametric process in which temporal modulation enhances the resonant response near the signal frequency and subsequently enables efficient radiation at higher sum-frequency components. Direct measurements in degenerate and non-degenerate regimes show amplified up-conversion exceeding the single-step conversion estimate based on the Manley-Rowe frequency ratio. These results establish time-varying metasurfaces as an efficient platform for amplification, generation, and frequency conversion of electromagnetic waves in the microwave and terahertz bands, with potential extension to higher frequencies using ultrafast modulation mechanisms.

physics.optics↗

arXiv2024

Radiative-Conductive Heat Transfer Dynamics in Dissipative Dispersive Anisotropic Media

We develop a self-consistent theoretical formalism to model the dynamics of heat transfer in dissipative, dispersive, anisotropic nanoscale media, such as metamaterials. We employ our envelope dyadic Green's function method to solve Maxwell's macroscopic equations for the propagation of fluctuating electromagnetic fields in these media. We assume that the photonic radiative heat transfer mechanism in these media is complemented by dynamic phononic mechanisms of heat storage and conduction, accounting for effects of local heat generation. By employing the Poynting theorem and the fluctuation-dissipation theorem, we derive novel closed-form expressions for the radiative heat flux and the coupling term of photonic and phononic subsystems, which contains the heating rate and the radiative heat power contributions. We apply our formalism to the paraxial heat transfer in uniaxial media and present relevant closed-form expressions. By considering a Gaussian transverse temperature profile, we also obtain and solve a system of integro-differential heat diffusion equations to model the paraxial heat transfer in uniaxial reciprocal media. By applying the developed analytical model to radiative-conductive heat tranfer in nanolayered media constructed by layers of silica and germanium, we compute the temperature profiles for the three first orders of expansion and the total temperature profile as well. The results of this research can be of interest in areas of science and technology related to thermophotovoltaics, energy harvesting, radiative cooling, and thermal management at micro- and nanoscale.

physics.class-ph↗

arXiv2022

Active control of thermal emission by graphene-nanowire coupled plasmonic metasurfaces

Metasurfaces, together with graphene plasmonics, have become prominent for the emissivity control in thermal engineering, both passively through changing the geometric parameters and packing density of the metasurfaces, and actively through graphene gating or doping. We demonstrate a graphene-nanowire coupled plasmonic metasurface utilizing the hybrid localized surface plasmon modes of the nanowire array and graphene. The nanowire array makes the hybrid surface plasmon mode localized, allowing a free-space excitation. The single layer graphene, via the gating between the underneath mirror and a top electrode, can actively tune the spectral emissivity by almost 90%. In addition, the hybrid plasmon mode provides an extra degree of freedom to modulate the p-polarized emissivity with a five-fold enhancement, especially for large emission angles.

physics.app-ph↗

arXiv2022

Analytical and numerical modeling of reconfigurable reflecting metasurfaces with capacitive memory

In this article, we develop analytical-numerical models for reconfigurable reflecting metasurfaces formed by chessboard-patterned arrays of metallic patches. These patch arrays are loaded with varactor diodes in order to enable surface impedance and reflection phase control. Two types of analytical models are considered. The first model based on the effective medium approach is used to predict the metasurface reflectivity. The second model is the Bloch wave dispersion model for the same structure understood as a two-dimensional transmission line metamaterial. The latter model is used to study ways to suppress parasitic resonances in finite-size beamforming metasurfaces. We validate the developed analytical models with full-wave numerical simulations. Finally, we outline a design of the metasurface control network with capacitive memory that may allow for independent programming of individual unit cells of the beamforming metasurface.

physics.app-ph↗

arXiv2021

Impact of die carrier on reliability of power LEDs

High power light emitting diodes (LEDs) suffer from heating effects that have a detrimental impact on the devices characteristics. The use LED carriers with high thermal conductivity promotes the extraction of heat away from the LED junction. Different materials can be used for this purpose, such as alumina, aluminium nitride, and silicon. Diamond has also been gaining momentum for demanding heat management applications. In order to evaluate the impact of the different carriers on the reliability of the devices, the junction temperature of Cree white Xamp XB-D LEDs was obtained with Ansys for various carrier at different LED current levels. The impact of the junction temperature on the LEDs lifetime, emission intensity, footprint and wavelength stability was then evaluated for each carrier based on the datasheet of the devices. The results provide additional knowledge regarding the impact of the carrier on the performance of the LED.

physics.app-ph↗

arXiv2011

Perfect lensing with phase conjugating surfaces: Towards practical realization

It is theoretically known that a pair of phase conjugating surfaces can function as a perfect lens, focusing propagating waves and enhancing evanescent waves. However, the known experimental approaches based on thin sheets of nonlinear materials cannot fully realize the required phase conjugation boundary condition. In this paper we show that the ideal phase conjugating surface is in principle physically realizable and investigate the necessary properties of nonlinear and nonreciprocal particles which can be used to build a perfect lens system. The physical principle of the lens operation is discussed in detail and directions of possible experimental realizations are outlined.

physics.optics↗

arXiv2008

Subwavelength microscope that uses frequency scanning for image reconstruction

A new principle of subwavelength imaging based on frequency scanning is considered. It is shown that it is possible to reconstruct the spatial profile of an external field exciting an array (or coupled arrays) of subwavelength-sized resonant particles with a frequency scan over the whole band of resonating array modes. During the scan it is enough to measure and store the values of the near field at one or at most two points. After the scan the distribution of the near field can be reconstructed with simple post-processing. The proposed near-field microscope has no moving parts.

physics.optics↗

arXiv2006

Experimental verification of the key properties of a three-dimensional isotropic transmission line based superlens

Design and experimental realization of a three-dimensional superlens based on LC-loaded transmission lines are presented. Commercially available components and materials are used in the design. Transmission properties of the designed structure are studied experimentally and the observed lens properties are compared with analytical predictions. Backward-wave propagation and amplification of evanescent waves in the prototype structure are verified both analytically and experimentally.

physics.optics↗

arXiv2005

Near-field enhancement and imaging in double cylindrical polariton-resonant structures: Enlarging perfect lens

We experimentally demonstrate a prototype of a cylindrical enlarging lens capable of enhancing and restoring evanescent fields. The enabling phenomenon is the resonant excitation of coupled surface modes in a system of two cylindrical arrays of small resonant particles. As was shown in [J. Appl. Phys. 96, 1293 (2004)], this phenomenon in planar arrays can be used in electromagnetic near-field imaging. Here, we use a similar structure in a cylindrically symmetric configuration, which gives us a possibility to obtain an enlarged near-field image.

physics.optics↗

arXiv2005

Experimental demonstration of sub-wavelength image channeling using capacitively loaded wire medium

In this letter we experimentally demonstrate a possibility to achieve significant sub-wavelength resolution of a near-field image channeled through a layer of an electromagnetic crystal. An image having radius of $λ/10$ has been realized using an electrically dense lattice of capacitively loaded wires. The loading allows to reduce the lattice period dramatically so that it is only a small fraction of the free-space wavelength. It is shown that losses in the structure only decrease the total amplitude of the image, but do not influence the resolution.

cond-mat.mtrl-sci↗

arXiv2005

On Artificial Magneto-Dielectric Loading for Improving the Impedance Bandwidth Properties of Microstrip Antennas

In the present paper we discuss the effect of artificial magneto-dielectric substrates on the impedance bandwidth properties of microstrip antennas. The results found in the literature for antenna miniaturization using magnetic or magneto-dielectric substrates are revised, and discussion is addressed to the practically realizable artificial magnetic media operating in the microwave regime. Using a transmission-line model we, first, reproduce the known results for antenna miniaturization with non-dispersive material fillings. Next, a realistic dispersive behavior of a practically realizable artificial substrate is embedded into the model, and we show that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of reduced size patch antennas loaded with dispersive magneto-dielectric substrates and high-permittivity substrates are compared. It is shown that unlike substrates with dispersion-free permeability, practically realizable artificial substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This conclusion is experimentally validated.

physics.class-ph↗

arXiv2005

Improving antenna near-field pattern by use of artificial impedance screens

An antenna prototype utilizing artificial impedance surfaces to control the near field distribution is described. The antenna is a folded dipole placed above a finite-size artificial impedance surface. We have found that the field screening is most effective if the surface is a metal conductor. However, to achieve a reasonable value of the radiation resistance the dipole should be located far off the screen. If the surface is a magnetic wall, the antenna design is more compact, but the field behind the screen is large. Here we realize a compromise solution using an inductive surface of a moderate surface impedance, which allows realization of an effective near-field screen with still a reasonably low-profile design.

physics.class-ph↗

arXiv2003

Near-field enhancement and imaging in double planar polariton-resonant structures

It is shown that a system of two coupled planar material sheets possessing surface mode (polariton) resonances can be used for the purpose of evanescent field restoration and, thus, for the sub-wavelength near-field imaging. The sheets are placed in free space so that they are parallel and separated by a certain distance. Due to interaction of the resonating surface modes (polaritons) of the sheets an exponential growth in the amplitude of an evanescent plane wave coming through the system can be achieved. This effect was predicted earlier for backward-wave (double-negative or Veselago) slab lenses. The alternative system considered here is proved to be realizable at microwaves by grids or arrays of resonant particles. The necessary electromagnetic properties of the resonating grids and the particles are investigated and established. Theoretical results are supported by microwave experiments that demonstrate amplification of evanescent modes.

physics.optics↗

arXiv2003

The planar perfect lens: physical requirements and possible alternative realizations

Several alternative possibilities of how to create an electromagnetic device being able to reconstruct near-field distribution of a source with sub-wavelength resolution (so-called perfect lens) are considered. It is shown that there is a variety of such means not involving double-negative (left-handed, or Veselago) materials or periodical backward-wave structures. It is demonstrated that devices working in a similar manner can be constructed using planar grids or material sheets imposing necessary boundary conditions at two parallel planes in air.

cond-mat.mtrl-sci↗

arXiv2002

Waves and energy in chiral nihility

A model for a chiral material in which both the permittivity and permeability are equal to zero is discussed. Such a material is referred by us as a ``chiral nihility". It is shown that this exotic material can be realized as a mixture of small helical inclusions. Wave solutions and energy in such a medium are analyzed. It is shown that an extraordinary wave in chiral nihility is a backward wave. Wave reflection and refraction on a chiral nihility interface is also considered. It is shown that a linearly polarized wave normally incident onto this interface produces the wave of "standing phase" and the same wave in the case of oblique incidence causes two refracted waves, one of them with an anomalous refraction.

cond-mat↗