Electromagnetic States Research Articles

A mechanical analogue of electromagnetic induction for waves in a chiral elastic structure

Classical Faraday’s law on electromagnetic induction states that a change of magnetic field through a coil wire induces a current in the wire. A mechanical analogue of the Lorentz force, induced by a magnetic field on an electric charge, is the gyroscopic force. Here, we demonstrate a mechanical analogy with a chiral elastic waveguide subjected to gyroscopic forcing. We study waves in an infinite mass-spring ‘gyrocore helix’, which consists of a helix and a central line (gyroscopic elastic core). The helicoidal geometric chirality is considered in conjunction with a physical chirality, induced by gyroscopic forces. It is shown that the interplay between these two chiral inputs leads to the breaking of symmetry of the associated dispersion diagram, resulting in a unidirectional waveform with the direction of propagation being tunable through the gyricity.

Polymer-integrated acoustic graphene plasmon resonator for sensitive detection of CO2 gas

Acoustic graphene plasmons (GPs) exhibit an exceptional density of electromagnetic states within the mid-infrared (MIR) and terahertz frequency ranges, leading to a pronounced near-field amplification and localization at the nanometer scale. This characteristic renders them highly promising for the development of ultra-sensitive plasmon-enhanced MIR sensing and spectroscopic applications. However, the tight spatial confinement inherent to acoustic GPs results in a significant momentum mismatch, which in turn leads to poor coupling efficiency with light in free space. To overcome this limitation, we leverage numerical simulations to show that GPs can act as an intermediary to facilitate efficient excitation of acoustic GPs by incident MIR radiation, achieving an extinction spectrum peak value of approximately 0.9. The proposed gas sensor based on the acoustic GP resonator is composed of pristine, large-area graphene, an array of periodic metal nanocubes, and a slender polyethylenimine (PEI) layer that adsorbs CO2, situated between the nanocubes and the graphene sheet. The sensing performance of the proposed sensor is numerically investigated. It is demonstrated that by incorporating a CO2-absorbing material into the acoustic GPs, we can perform highly sensitive assessments of the absorption bands within the PEI layer upon CO2 adsorption. The observed behavior of the acoustic GPs indicates a weakening and broadening with increasing CO2 concentrations, a phenomenon attributed to the alteration in the permittivity of the PEI in the interstitial layer due to CO2 adsorption. Numerical simulation results indicate that the sensitivity of the proposed hybrid gas sensor can reach up to 0.0183% ppm−1, which offers a remarkable 95-fold enhancement over the gas sensor based on graphene nanoribbons. Our findings underscore the potential of acoustic GP nanoresonators as a transformative platform for ultrasensitive plasmon-enhanced sensing applications, particularly when integrated with various gas adsorption layers or molecular agents.

Coupled circularly polarized electromagnetic soliton states in magnetized plasmas

The interaction between two co-propagating electromagnetic pulses in a magnetized plasma is considered, from first principles, relying on a fluid-Maxwell model. Two circularly polarized wavepackets by same group velocities are considered, characterized by opposite circular polarization, to be identified as left-hand- or right hand circularly polarized (i.e. LCP or RCP, respectively). A multiscale perturbative technique is adopted, leading to a pair of coupled nonlinear Schrödinger-type (NLS) equations for the modulated amplitudes of the respective vector potentials associated with the two pulses. Systematic analysis reveals the existence, in certain frequency bands, of three different types of vector soliton modes: an LCP-bright/RCP-bright coupled soliton pair state, an LCP-bright/RCP-dark soliton pair, and an LCP-dark/RCP-bright soliton pair. The value of the magnetic field plays a critical role since it determines the type of vector solitons that may occur in certain frequency bands and, on the other hand, it affects the width of those frequency bands that are characterized by a specific type of vector soliton (type). The magnetic field (strength) thus arises as an order parameter, affecting the existence conditions of each type of solution (in the form of an envelope soliton pair). An exhaustive parametric investigation is presented in terms of frequency bands and in a wide range of magnetic field (strength) values, leading to results that may be applicable in beam-plasma interaction scenarios as well as in space plasmas and in the ionosphere.

Parity-time imbalance induced by balanced gain and loss medium in non-Hermitian photonic crystals

Photonic crystals, including gain and loss materials, show numerous intriguing features than the ordinary photonic crystals. In this work, using the full wave simulation, we numerically investigate the photonic crystals with gain and loss which are satisfying the parity-time (PT) symmetry condition to reveal the effect of PT symmetry on the optical properties of photonic crystals, including the exceptional point, distribution of electromagnetic fields and edge states. This work reveals a novel mechanism of coexistence and competition between topological states and non-Hermiticity in all-dielectric photonic crystals and provides an innovative understanding of non-Hermiticity in topological photonic systems.

Эффекты отрицательного преломления волн в металлических фотонных кристаллах

The paper considers the interaction of optical radiation with the boundaries of media formed by two-dimensionally periodic systems of well-conducting cylindrical elements of small cross-section – metal photonic crystals. It is shown that at band gap frequencies in the spectrum of the crystal's own electromagnetic states when waves propagate obliquely relative to the elements, such structures can be characterized by hyperbolic isofrequency diagrams in the space of wave vectors. A consequence of this is the possibility of negative refraction effects occurring when waves are incident on the boundary of such an anisotropic hyperbolic medium formed by a two-dimensional crystal with elements of limited length. The problem of incidence of a plane-wave Gaussian optical beam on the surface of a metal photonic crystal is solved using the finite-difference method in the time domain. It has been proven that negative refraction of waves occurs under certain conditions at the boundary of the medium formed by such a crystal.

Rotation manipulation of high-order PT-symmetry for robust wireless power transfer

Magnetic resonance coupling plays an important role in the non-radiative wireless power transfer without cables. However, the basic near-field coupling also has some key limitations on the resonance wireless power transfer (WPT). On the one hand, when the transfer distance is short, the eigenfrequencies of the WPT system will split because of the strong near-field coupling between the resonance transmitter and receiver. On the other hand, although the working frequency is fixed for the long-distance case, the transfer efficiency will be significantly dropped for the weak coupling strength. Therefore, a long-captivated problem of the resonance WPT systems is that it is difficult to balance the fixed working frequency and high efficiency of the devices. In this work, we put forward the composite transmitter with a pair of resonance coils of different size. By assisting the rotational degrees of freedom in the composite transmitter, a high-order parity-time-symmetric non-Hermitian system can be established. Especially, in contrast to the conventional resonance WPT scheme, the robust WPT can maintain fixed working frequency and efficiency over a varying transfer distance in the optimized WPT system with composite transmitter, since this eigenfrequency is insensitive to the operational conditions. Our findings demonstrate that the composite transmitter possesses better performance for WPT than its single counterpart, offering the opportunities for engineering novel designer electromagnetic transfer states with unique robustness.

Experimental characterization of Spherical Bragg Resonators for electromagnetic emission engineering at microwave frequencies

This work reports experimental investigation and numerical validation of millimeter-sized Spherical Bragg Resonators (SBRs) fabricated using 3D printing technology. The frequency dependencies of the reflection and transmission coefficients were analyzed, and eigenfrequency values were calculated to examine the density of photonic states in air/PLA-polylactide SBRs, showing the appearance of an eigenmode and an increase in the local density of states in the core of a defect cavity. A decay rate enhancement of {sim 10}^{2} was obtained for a dipole placed in the core of the defect SBR. The study also investigated the influence of the source position on the resonator's electromagnetic wave energy. Scattering efficiencies up to order twelve of the multipole electric and magnetic contribution in a 10-layer SBR were calculated to validate the presence of the resonant modes observed in the scattering measurements performed for parallel and perpendicular polarizations. The results demonstrate that SBRs can act as omnidirectional cavities to enhance or inhibit spontaneous emission processes by modifying the density of electromagnetic states compared to free space. This finding highlights the potential of SBRs engineering spontaneous electromagnetic emission processes in various applications, including dielectric nanoantennas, optoelectronics devices, and quantum information across the entire electromagnetic spectrum.

Frequency Effect on Electromagnetic States Emitted from High Voltage Overhead Power Lines and Busbar Substation

Electrical power systems represent an immense source of electromagnetic radiation spanning a wide frequency range, encompassing low-frequency, transient states, and high-frequency emissions. The radiation poses a significant self-pollution challenge for electric and electronic devices situated in close proximity to these systems. The present article aims to address this research, and provides a comprehensive review of the electromagnetic effects and pollution at differences frequency’s ranges encompassing power systems network. In the context of the low-frequency range, the computation of electric and magnetic fields is conducted using quasi-static principles. To validate the behavior at high frequencies due to power line currents, Schelkunoff’s approach is employed. Additionally, transient electromagnetic fields are analyzed using an exact analytical method. The results of computer simulations are compared with previously published and measured data for low-frequency regime and transient overvoltage conditions, verifying their consistency. Additionally, high-frequency results are presented and corroborated through the utilization of a numerical electromagnetic code (NEC-4). These analyses underscore the valuable role of computer-based calculations in examining the electromagnetic environment of power system networks.

Analytical solutions for electromagnetic surface states at the interface between metal and gyromagnetic media

We systematically study the surface states at the interface between semi-infinite metal and gyromagnetic media, considering three orthogonal magnetization directions. By solving a full vectorial polarization-complete evanescent wave equation derived from Maxwell’s equations and all four boundary conditions, we obtain rigorous analytical solutions for the surface states. All analytical dispersion equations and field equations under the three configurations are solved. Simultaneously, the solutions also reveal the intriguing features of surface plasmon polaritons (SPPs) under the gyromagnetic effect. In the polar configuration (where the magnetization is perpendicular to the interface), the gyromagnetic effect uniquely results in candlelight-like field patterns in SPP. In the transversal configuration (where the magnetization is parallel to the interface and perpendicular to propagation), the unidirectional magnetic surface state is found. In the longitudinal configuration (where the magnetization is parallel to propagation), the SPP also exhibits candlelight-like field patterns but manifests a different polarization from the polar configuration. Our results reveal peculiar behaviors of SPPs under the gyromagnetic effect and would deepen the understanding of the magneto-optical effect on interfaces.

Chiral photonic topological states in Penrose quasicrystals.

Electromagnetic topological edge states typically are created in photonic systems with crystalline symmetry and these states emerge because of the topological feature of bulk Bloch bands in momentum space according to the bulk-edge correspondence principle. In this work, we demonstrate the existence of chiral topological electromagnetic edge states in Penrose-tiled photonic quasicrystals made of magneto-optical materials, without relying on the concept of bulk Bloch bands in momentum space. Despite the absence of bulk Bloch bands, which naturally defiles the conventional definition of topological invariants in momentum space characterizing these states, such as the Chern number, we show that some bandgaps in these photonic quasicrystals still could host unidirectional topological electromagnetic edge states immune to backscattering in both cylinders-in-air and holes-in-slab configurations. Employing a real-space topological invariant based on the Bott index, our calculations reveal that the bandgaps hosting these chiral topological edge states possess a nontrivial Bott index of ±1, depending on the direction of the external magnetic field. Our work opens the door to the study of topological states in photonic quasicrystals.

Permittivity-Asymmetric Quasi-Bound States in the Continuum.

Breaking the in-plane geometric symmetry of dielectric metasurfaces allows us to access a set of electromagnetic states termed symmetry-protected quasi-bound states in the continuum (qBICs). Here we demonstrate that qBICs can also be accessed by a symmetry breaking in the permittivity of the comprising materials. While the physical size of atoms imposes a limit on the lowest achievable geometrical asymmetry, weak permittivity modulations due to carrier doping, and electro-optical Pockels and Kerr effects, usually considered insignificant, open the possibility of infinitesimal permittivity asymmetries for on-demand, dynamically tunable resonances of extremely high quality factors. As a proof-of-principle, we probe the excitation of permittivity-asymmetric qBICs (ε-qBICs) using a prototype Si/TiO2 metasurface, in which the asymmetry in the unit cell is provided by the permittivity contrast of the materials. ε-qBICs are also numerically demonstrated in 1D gratings, where quality-factor enhancement and tailored interference phenomena of qBICs are shown via the interplay of geometrical and permittivity asymmetries.

MXenes as Alternative Plasmonic Coatings on 1D Photonic Crystals Platforms for Tamm Plasmon Polaritons

New materials are of essential importance for the advancement of nanophotonics and nanoplasmonics. Numerous electromagnetic modes, especially various evanescent surface waves, prove themselves useful in multitudinous practical applications. Here we investigate the use of MXenes as alternative plasmonic materials in freestanding (substrateless) planar nanocomposites that support the existence of Tamm plasmon polaritons (TPP). We use finite element simulations to consider the influence of using MXenes on the propagation and distribution of TPP and the difference in their electromagnetic behavior compared to that of commonly used noble metals. While MXenes allow for somewhat weaker coupling between incident light and TPP, even the thinnest MXene layers practically completely screen the structure behind them. Our diffraction grating-enhanced stacks achieved incident light direction-dependent improvement of the coupling strength and polarization-dependent hybridization of electromagnetic states. MXene ensures improvements in functionality, especially spectral, directional, and polarization selectivity, by imparting rich modal behavior. Importantly, we observed high optical asymmetry of reflectance when illuminating the structures from opposite directions and obtained large high-to-low reflection ratios with a very small number of dielectric layers in the capping 1D photonic crystal. We conclude that MXenes represent a viable alternative for TPP-supporting structures, offering many advantages.

Dispersion equation for electromagnetic waves in a Dicke system

The self-organization process in a Dicke model is studied with taking into account electromagnetic field states. The interaction between two-level emitters provided by the field results in generating field waves of increasing amplitudes. The picture of superradiance development in a prolonged system can be described in terms of electromagnetic field in continuous medium formed by emitters. The generalized induction in the Dicke system is introduced on the basis of the material equation for charge current obtained using the Bogolyubov reduced description method. The dispersion equation for waves and its solutions are derived and analyzed. Non-singular expressions for material coefficients are proposed and used for calculating the wave characteristics.

Molecular Plasmonics with Metamaterials.

Molecular plasmonics, the area which deals with the interactions between surface plasmons and molecules, has received enormous interest in fundamental research and found numerous technological applications. Plasmonic metamaterials, which offer rich opportunities to control the light intensity, field polarization, and local density of electromagnetic states on subwavelength scales, provide a versatile platform to enhance and tune light-molecule interactions. A variety of applications, including spontaneous emission enhancement, optical modulation, optical sensing, and photoactuated nanochemistry, have been reported by exploiting molecular interactions with plasmonic metamaterials. In this paper, we provide a comprehensive overview of the developments of molecular plasmonics with metamaterials. After a brief introduction to the optical properties of plasmonic metamaterials and relevant fabrication approaches, we discuss light-molecule interactions in plasmonic metamaterials in both weak and strong coupling regimes. We then highlight the exploitation of molecules in metamaterials for applications ranging from emission control and optical modulation to optical sensing. The role of hot carriers generated in metamaterials for nanochemistry is also discussed. Perspectives on the future development of molecular plasmonics with metamaterials conclude the review. The use of molecules in combination with designer metamaterials provides a rich playground both to actively control metamaterials using molecular interactions and, in turn, to use metamaterials to control molecular processes.

Electromagnetic multipolar quasi-bound states in the continuum for optical sensing

Optical sensing is of vital importance in many applications, which has received extensive attention in recent years. The pursuit of optical sensing mechanism with higher figure of merit (FOM) is very important for various sensing applications. Bound states in the continuum (BIC) with theoretical infinite Q factor is an ideal candidate to effectively improve the FOM of optical sensor. Herein, we propose and numerically demonstrate an optical refractive index sensor based on the electromagnetic multipolar quasi-BICs of all-dielectric metasurfaces. Based on the eigen-solution and excitation simulation, we find that magnetic dipole (MD) quasi-BIC is the best candidate for optical refractive index sensing among the electromagnetic multipolar quasi-BICs in the proposed all dielectric metasurface. The sensitivity (S) and the value of FOM for the optical refractive index sensor are 225.27 nm/RIU and 441762.93, respectively. It is anticipated that our results might shed new light on the optical refractive index sensing of high sensitivity and ultra-high FOM.

A Note on Representation of Electromagnetic Plane Wave Polarization State

Representations are studied for both natural and intuitive grasp of electromagnetic plane wave polarization states. The representations have been established, but unfortunately, the detailed definitions have variations depending on the references. These circumstances could cause unnecessary confusion. In order to resolve the confusion, representations are presented taking correspondence into consideration with both natural and intuitive grasp of polarization states. The presented representations are confirmed to be consistent with those in the references.

Reconfigurable Topological States in Arrays of Bianisotropic Particles

Topological photonics promotes a novel approach to resilient light manipulation by exploiting spatio-temporal symmetries of the system and dual symmetry of electromagnetic field. Various prospective device applications pose the need to flexibly control robust field localization associated with topological modes. Here we design a topological array of resonant dielectric meta-atoms with bianisotropic response induced by a spatial symmetry reduction. Mutual orientation of the designed meta-atoms encodes a staggered bianisotropy pattern capable of trapping topological states in a one-dimensional array containing a small number of particles. We show that the topological interface state can be tailored by the rotation of coaxial bianisotropic particles arranged in an equidistant lattice. Our experimental implementation based on ceramic horseshoe-shaped disks demonstrates remarkable reconfigurability of electromagnetic topological states.

TECHNICAL ASPECTS OF PSYCHOPHYSICAL STATE SIMULATING OF MILITARY PERSONNEL IN EXTREME AND COMBAT SITUATIONS

The subject matter of the article is the psychophysical state of a person in an extreme situation. The goal of the study is providing recommendations for the behavior of people in the conditions of instantaneous action of the excitation function and the subsequent transient process. The tasks to be solved are: to consider the mental and physical state of man, in terms of the basic principles of the theory of transients in electrical circuits and determine the analogy between the state of processes in storage in wildlife and technology and draw conclusions about the possibility of concretizing them mentally and physically; to apply the theoretical provisions of the theory of transients with two energy storage to model the psychophysical components of the human condition in extreme situations and combat situations; based on studies of the relationship between the human psychotype and the degree of inertia for behavior in transition and the assessment of possible time to its completion, to provide recommendations for human behavior, including military, in emergencies and combat situations. General scientific and special methods of scientific knowledge are used. The following results were obtained: an analogy has been made between the electromagnetic and psychophysical states of a person with the allocation of two-unit processes makes it possible to apply the theoretical provisions of the description of one kind (electromagnetic) to substantiate the behavior of other psychophysical constituents. The implementation of the results of this study allows for the general public with different theoretical background to find out the rules of behavior in difficult life situations. Conclusions. The psychophysical state of man includes a number of individual characteristics that are decisive and can be specified by mental and physical characteristics. Unconditional circumstances are the function of arousal and the subsequent transient process, the results of which have objective consequences, because they are due to the action of physical laws and do not depend on subjective desires. Understanding the analogy between the state of processes in wildlife storage and technology is necessary to take into account in everyday activities and, especially, in emergencies and hostilities. Active mental activity should be carried out during the responsible, anxious moments, the time of expectation, etc.: analysis of the situation, search for the best options for completing the task, poems, songs (religions usually recommend prayers). This will eliminate the possibility of losing control of the environment, eliminate the formation of panic, fear and negative mental phenomena. In any case, it is essential not to remain in a state of unconsciousness and apprehension, as the induced function will in this case lead to stupor and the impossibility of responding gracefully to the threat and taking a positive decision. The time of the transition process depends on the psychotype of the person and can be shortened by special training, experience and a conscious attitude towards autotraining.

Effect of the atomic dipole-dipole interaction on the phase diagrams of field-matter interactions: Variational procedure

We establish, within the second quantization method, the general dipole-dipole Hamiltonian interaction of a system of $n$-level atoms. The variational energy surface of the $n$-level atoms interacting with $\ell$-mode fields and under the Van Der Waals forces is calculated with respect the tensorial product of matter and electromagnetic field coherent states. This is used to determine the quantum phase diagram associated to the ground state of the system and quantify the effect of the dipole-dipole Hamiltonian interaction. By considering real induced electric dipole moments, we find the quantum phase transitions for $2$- and $3$-level atomic systems interacting with $1$- and $2$- modes of the electromagnetic field, respectively. The corresponding order of the transitions is established by means of Ehrenfest classification; for some undetermined cases, we propose two procedures: the difference of the expectation value of the Casimir operators of the $2$-level subsystems, and by maximizing the Bures distance between neighbor variational solutions.

Hybrid photonic-plasmonic mode-coupling induced enhancement of the spontaneous emission rate of CdS/CdSe quantum emitters

In this paper, a hybrid photonic-plasmonic resonator, which comprises an electrospun polymer fiber with a micrometer diameter and a core/shell nanostructure with a gold nanoparticle core, is constructed to investigate the dynamics of the coupled spontaneous emission of CdS/CdSe quantum dots (QDs). The gold nanoparticle core; covered with a silica shell, anchored with individual CdS/CdSe QDs, is placed inside a hollow cylindrical nanocavity formed on the surface of the microfiber to enable integration of the optical mode with the plasmonic effect, which is induced by the localized surface plasmons of the metal nanoparticle being present in the vicinity of the dipoles. The spontaneous emission rate of the QDs, coupled into the hybrid photonic-plasmonic mode, is measured to enhance by a factor of 23 via a time-resolved experimental technique. This result suggests that the regeneration of the optical mode-field inside the photonic-plasmonic resonator through the interaction of the dipoles with the localized surface plasmons of a metal nanoparticle strongly enhances the density of the electromagnetic states of the quantum emitters to facilitate an enhanced spontaneous emission within the host medium of the proposed polymer based-photonic structure.