Electromagnetic Wave Propagation Research Articles

Simulation and measurement of electromagnetic wave propagations along a wearable e-textile metasurface transmission line

This study introduces a compact wearable metasurface transmission line operating at 2.45 GHz, utilizing spoof surface plasmon polariton (SSPP). The design incorporates a periodic arrangement of hook unit cells and a tapering structure to enhance coupling efficiency between the microstrip feed line and the metasurface transmission line. For its implementation, a dielectric substrate composed entirely of cotton denim jeans is employed, along with e-textile conductive traces and a ground plane. Electromagnetic wave propagation along the transmission line is simulated, and the primary wave mode and associated propagation characteristics are analyzed. Both simulation and measurement results confirm the successful performance of the metasurface transmission line for on-body signal transmissions.

Electronic analogue of Fourier optics with massless Dirac fermions scattered by quantum dot lattice

Abstract The field of electron optics exploits the analogy between the movement of electrons or charged quasiparticles, primarily in two-dimensional materials subjected to electric and magnetic (EM) fields and the propagation of electromagnetic waves in a dielectric medium with varied refractive index. We significantly extend this analogy by introducing an electronic analogue of Fourier optics dubbed as Fourier electron optics (FEO) with massless Dirac fermions (MDF), namely the charge carriers of single-layer graphene under ambient conditions, by considering their scattering from a two-dimensional quantum dot lattice (TDQDL) treated within Lippmann–Schwinger formalism. By considering the scattering of MDF from TDQDL with a defect region, as well as the moiré pattern of twisted TDQDLs, we establish an electronic analogue of Babinet’s principle in optics. Exploiting the similarity of the resulting differential scattering cross-section with the Fraunhofer diffraction pattern, we construct a dictionary for such FEO. Subsequently, we evaluate the resistivity of such scattered MDF using the Boltzmann approach as a function of the angle made between the direction of propagation of these charge-carriers and the symmetry axis of the dot-lattice, and Fourier analyze them to show that the spatial frequency associated with the angle-resolved resistivity gets filtered according to the structural changes in the dot lattice, indicating wider applicability of FEO of MDF.

Square-root topological insulator for a dual-band photonic waveguide

We show that square-root topological insulators can be utilized as a platform for dual-band topological waveguides in 2-dimensional photonic crystals. Valley states for each of two frequency band gaps in differently perturbed decorated honeycomb lattices have opposite directions of the phase rotations, revealing opportunities for dual-band unidirectional topological valley transport. The topological valley edge states exist at the boundary between differently perturbed photonic crystals in the two frequency bands. In addition, unidirectional, and robust propagation of electromagnetic waves along the boundary in the two frequency bands are numerically performed. Our work provides extensions of square-root topological insulators to robust, unidirectional, and dual-band photonic waveguides.

Nodal discontinuous Galerkin methods for Maxwell's equations in Lorentz-Kerr-Raman medium without nonlinear algebraic solver

The propagation of electromagnetic waves is modeled by time-dependent Maxwell's equations coupled with constitutive laws that describe the responses of the media. In this work, we consider a nonlinear model that describes the electromagnetic wave in an optical medium with the linear Lorentz effect and the cubic nonlinear instantaneous Kerr and delayed Raman effects. Mathematically this model obeys an energy conservative/dissipative law. Though there have been active efforts in designing numerical methods (e.g. of finite difference / finite element /discontinuous Galerkin type) to simulate this model, the methods proposed here are distinctive in that they are free of any nonlinear algebraic solvers. Moreover, in the absence of the Raman effect, our methods also enjoy a provable discrete energy law, and optimal a priori error estimates are further established when the exact solutions are sufficiently smooth. The key ingredients of the new methods include some novel treatment in time discretizations and nodal discontinuous Galerkin spatial discretization for the specific nonlinearities, and they also render a local nature of the methods and hence their suitability for parallel implementation with great efficiency. Numerical experiments are performed to illustrate the accuracy, stability, computational efficiency and parallel scalability of the proposed methods. We further apply the methods to simulate some physically relevant problems in one, two, and three dimensions.

Ultrabroadband valley transmission and corner states in valley photonic crystals with dendritic structure

In photonic crystal systems, topologically protected edge states and corner states can be achieved by breaking spatial inversion symmetry, which is expected to be applied to topologically protected lasers, optical communication and integrated photonics. However, designing ultrabroadband topological photonic crystals is still a challenge. In this work, we propose a valley photonic crystal composed of dendritic structures, which can realize valley transmission with a relative bandwidth up to 59.65%. Compared with the previously reported two-dimensional broadband photonic crystals with 32.02% bandwidth, the relative bandwidth of the proposed valley transmission is increased by almost 100%. Theoretical analysis, numerical simulation and experimental measurement all confirm flexible manipulation of electromagnetic wave propagation paths. Ultrabroadband topological waveguides with the zigzag and armchair interface are demonstrated, which can achieve experimentally 58.71% and 36.78% relative bandwidth, respectively. In addition, several topological channel intersections are designed. Finally, two types of corner states with valley switchability and selectivity are demonstrated.

The development of cloaking techniques based on phase-modulated metasurfaces

Abstract More and more attention has been paid to explore the application background of cloaking techniques based on phase-modulated metasurfaces, which play an important role in modern engineering and military applications. Phase-modulated metasurfaces are an emerging field of research that explores how the propagation of electromagnetic waves can be manipulated by precisely controlling the phase on tiny elements. These tiny elements, usually nanoscale structures, are arranged on the metasurface to precisely control the propagation and scattering of electromagnetic waves in a specific frequency range. The thesis first reviews the development of metamaterial cloaking technology, introduces the realization of several mainstream metamaterial cloaking technologies, and points out the benefits of cloaking techniques based on phase-modulated metasurfaces compared with other cloaking technologies. Then the development history of cloaking techniques based on phase-modulated metasurfaces is introduced through four key time nodes. We can find that phase-modulated metasurfaces are not only getting thinner and thinner, but in addition to the stealth effect, i.e., the reduction of the RCS (Radar Cross Section), phase-modulated metasurfaces can also simulate different virtual shapes. Finally, the development and research progress of cloaking techniques based on phase-modulated metasurfaces are summarized, and personal opinions on its future development are put forward. This paper summarizes the advances in the field of phase-modulated metasurfaces over the last decade and presents some representative approaches to phase-modulated metasurfaces at various points in time, which can help readers better understand the field of metasurfaces and metamaterials.

A diagnostic method of radial electron density distribution based on microwave transmission of cylindrical plasma along multipath

Based on the multipath propagation phase shift of electromagnetic wave in cylindrical plasma, a method to obtain the radial electron density distribution of non-uniform cylindrical plasma is proposed in this paper. Focused lens antennas are used in multipath transmission distribution diagnosis (MTDD), where the propagation area in the plasma is approximately the size of the focal spot. The equivalent propagation thickness at each layer can be calculated for each path based on the propagation region and layer thickness. Combining with Fermat's shortest wavelength principle, electromagnetic waves propagate in a straight line between different layers. The phase shift caused by the propagation of electromagnetic waves in each layer, starting from the outermost layer, can obtain layer by layer electron density. To validate the MTDD method, multipath transmission propagation phase shift was simulated in CST, and the electron density distribution was obtained, which has a good agreement with the preset electron density. In addition, the MTDD method was applied to inductively coupled plasma, and the diagnostic results showed high agreement with the Langmuir probe results. The proposed MTDD method has higher spatial resolution than the transmission diagnosis method and can provide more precise plasma parameter information.

Artificial intelligence-powered intelligent reflecting surface systems countering adversarial attacks in machine learning

With the increase in the computation power of devices wireless communication has started adopting machine learning (ML) techniques. Intelligent reflecting surface (IRS) is a programmable device that can be used to control electromagnetic wave propagation by changing the electric and magnetic values of its surface. State-of-the-art ML especially on deep learning (DL)-based IRS-enhanced communication is an emerging topic. Yet while integrating IRS with other emerging technologies possibilities of adversarial data creaping is high. Threats to security, their mitigation, and complexes for AI-powered applications in next generation networks are continuously emerging. In this work the ability of an IRS enhanced wireless network in future-generation networks to prevent adversarial machinelearning attacks is studied. The artificial intelligence (AI) model is used to minimize the susceptibility of attacks using defense distillation mitigation technique. The outcome shows that the defensive distillation technique (DDT) increases the strength and performance by around 22% of the AI method under an adversarial attack.

An MPMD approach coupling electromagnetic continuum mechanics approximations in ALEGRA

Two complementary approximations for describing aspects of continuum electromagnetics in moving media are discussed: electroquasistatic and magnetoquasistatic. Each has been implemented in the finite element shock code ALEGRA for modeling dynamic electromechanical phenomena on typical engineering time scales, with fully integrated circuit coupling (Niederhaus et al. 2023). The approximations can be obtained by consistent asymptotic balancing of Maxwell’s equations relative to timescales associated with magnetic diffusion, charge relaxation, and electromagnetic wave propagation. In ALEGRA, the electroquasistatic approximation is used for ferroelectric (FE) modeling, while the magnetoquasistatic approximation is used for magnetohydrodynamic (MHD) modeling. In this paper we introduce for the first time a detailed derivation of a useful quasi-steady “low-Rm” variant of the MHD approximation applicable for cases, such as with detonators, where the thermodynamic pressure arising from Joule heating dominates over magnetic forces. An additional purpose of this paper is to present a coupling mode using Multiple Program-Multiple Data (MPMD) message passing communication that allows the user to run 3D FE problems together with 2D and/or 3D MHD problems with the respective simulation domains coupled through a common circuit equation. The MPMD coupling capability is used here to model the dynamic coupling of a notional ferroelectric generator with an RP-87 exploding bridgewire detonator. The simulated bridgewire heats up and bursts under current generated by simulated depoling of the ferroelectric generator, as a demonstration of the MPMD capability.

Broadband light absorption enhancement in a–Si:H ultrathin film solar cells with nanophotonic light trapping structures

Light trapping over a wide wavelength range is critical for applications such as thin-film solar cells (TFSCs). Therefore, in this paper, we report a plasmonic light trapping scheme as a solution to overcome the limited absorption of light in hydrogenated amorphous silicon (a-Si:H) thin film solar cells. Here we propose plasmonic nanostructures, which have periodic nanodisks added to the front surface of the cell. These structures combine a variety of photonic effects to reduce reflection, improve light trapping, and increase absorption over a broadband solar spectrum. Initially, to test whether the suggested plasmonic nanoparticles can enhance light-trapping within the absorber layers of the cell, we used the 3D finite difference time domain method to simulate the propagation of electromagnetic waves and the absorbed light in each layer of the cell. Additionally, the obtained optical properties after the FDTD simulation are used to design electrical model simulations using SCAPS software. The results show that the front surface of nanodisk-shaped solar cells with only a 100-nm-thick a-Si:H layer can absorb light at wavelengths ranging from 300 to 800 nm, which is greater than that of flat a-Si:H film devices. With optimized structural parameters, the short circuit current density Jsc could be enhanced by 98 % and 71 % with the addition of Au and Cu nanodisks, respectively. Additionally, the conversion efficiency is improved by 28 % and 26 % for Au and Cu, respectively. The proposed design of the light trapping structure can provide guidelines for ultra-TFSCs with high performance.

Electromagnetic breathing dromion-like structures in an anisotropic ferromagnetic medium

The influence of Gilbert damping on the propagation of electromagnetic waves (EMWs) in an anisotropic ferromagnetic medium is investigated theoretically. The interaction of the magnetic field component of the electromagnetic wave with the magnetization of a ferromagnetic medium has been studied by solving the associated Maxwell’s equations coupled with the Landau–Lifshitz–Gilbert (LLG) equation. When small perturbations are made on the magnetization of the ferromagnetic medium and magnetic field along the direction of propagation of electromagnetic wave by using the reductive perturbation method, the associated nonlinear dynamics is governed by a time-dependent damped derivative nonlinear Schrödinger (TDDNLS) equation. The Lagrangian density function is constructed by using the variational method to solve the TDDNLS equation to understand the dynamics of the system under consideration. The propagation of EMW in a ferromagnetic medium with inherent Gilbert damping admits very interesting nonlinear dynamical structures. These structures include Gilbert damping-managing symmetrically breathing solitons, localized erupting electromagnetic breathing dromion-like modes of excitations, breathing dromion-like soliton, decaying dromion-like modes and an unexpected creation-annihilation mode of excitations in the form of growing-decaying dromion-like modes.

Turbulence-enhanced THz generation by multiple chaotically-distributed femtosecond filaments in air

Remote generation of electromagnetic waves in the terahertz (THz) by the volume of air medium gains increasing scientific interest due to the demand for this spectral range in solving various practical problems including those belonging to the nonlinear atmospheric optics. During self-focusing and filamentation of high-power femtosecond laser pulses in air, the source of THz radiation is the plasma of laser filaments. One of the main challenges of THz generation by a laser filament is increasing the value of optical energy conversion to the long-wavelength band. In this paper, we present the results of our studies on DC-biased THz generation during single-color filamentation in air of focused femtosecond Ti:Sapphire-laser pulses (800 nm, pulse energy up to 40 mJ). The distinctive feature of our study is that a femtosecond optical pulse propagates through a spatially-localized heated air layer containing randomly inhomogeneous refractive index perturbations, which mimics strong air turbulence. For the first time to our knowledge, we show, that the turbulent air layer formed at the beginning of the optical path allows increasing the yield of THz radiation up to 1.5 times due to the formation of multiple chaotically-arranged filaments resulting from random perturbations of the optical beam energy profile that reduces the subsequent THz (re)absorption in the filament plasma.

Evolution of an Overlapped Bandgap and Topological Flat Bands in a Higher‐Order Valley Photonic Insulator Based on Dendritic Structure

AbstractRobust edge states and corner states in photonic topological insulators provide effective ways to manipulate the propagation of electromagnetic waves. Bandgaps of the previously reported photonic topological insulators are independent of each other. In this paper, a higher‐order valley photonic insulator composed of arrays of dendritic structure is designed. The band structure shows an overlapped bandgap is observed, and the overlapped bandgap divides the band structure into three bandgaps. The evolution of the overlapped bandgap is investigated by changing the geometric parameters and increasing the fractal to break the C3v symmetry drastically. Besides, it is notable that the band structure of the proposed valley photonic insulator is flat bands. It is demonstrated that undistorted transmission can be observed as a plane electromagnetic wave transmits through the proposed valley photonic insulator. The interface consisting of two valley photonic structures with distinct topological nontrivial phases is constructed. Edge states and corner states with strong energy localization are obtained in multi‐band frequencies. Remarkably, two triangular structures with different Wannier center configurations both have corner states in the same bandgap, which does not obey the valley selectivity. The phenomenon is caused by the weak valley locking property due to the overlapped bandgap. The proposed valley photonic insulators are expected to benefit applications in optical devices such as topological lasers.

STATISTICAL CHARACTERISTICS OF THE GEOPHYSICAL FIELDS DISTURBED BY WEATHER FRONTS

The Earth (internal spheres) — atmosphere — ionosphere — magnetosphere (EAIM) formation is a single integrated system with direct and reverse, positive and negative coupling, as well as with their combination. The high-energy sources of natural and anthropogenic origins activate coupling between the components of the EAIM. The effects that the sources of various physi- cal nature have on the EAIM system have been studied quite well, while the influence of the weather fronts and other powerful atmospheric sources on the EAIM system and its components has been studied only partly. The scientific objective of this study is to conduct a statistical analysis of variations in the basic parameters of the geophysical fields that accompany the movement of atmospheric fronts. The histograms have been constructed that show the atmospheric pressure difference, atmospheric tem- perature difference, duration of the action of the atmospheric front, and the rate of change in the pressure and temperature, as well as the histograms showing the distribution of variations in the atmospheric electric field, the atmospheric current density, and in the magnetic field. The analysis undertaken has shown that these parameters exhibit variations within a broad range of values. The mean values of these parameters are estimated to be 145 Pa, 6 °C, 70 min, 2.4 Pa/min, 0.23 °C/min, 3.2 kV/m, 63 nA/m2, and 20 nT, respectively. The analysis of the scatter diagrams shows that the correlation between the variation in physi- cal parameters is almost always absent. This means that a single governing parameter along the path of the atmospheric front does not exi st. A simplified analytical relation has been derived to estimate the perturbation in the electric field strength caused by the atmospheric front, which yields ~6–60 kV/m values that increase by an order of magnitude during thunderstorms. Under disturbed conditions, the atmospheric current density is shown to increase from 10 –12 A/m2 to 10–11—10–10 A/m 2. The fol- lowing three mechanisms of an increase in the magnetic induction under the influence of the atmospheric front are considered: the disturbances of the external current density, electromagnetic induction, and the magnetic effect of turbulence. All these mechanisms yield the value of the effect less than ~1 nT. Only the magnetic effect of the ionosphere can explain an increase of 10—70 nT in the magnetic field variations. The energetics of the pressure, temperature, electric, and magnetic fields has been estimated to be (~10 16—10 17 J, ~1013—1014 W), (~1018—1019 J, 1015—1016 W), (~109—1011 J, ~106—108 W), (~1010 — 10 11 J, 107—108 W), respectively. The following channels have been validated through which the components of the EAIM sys- tem couple under the action of atmospheric fronts: atmospheric pressure differences, ionospheric electron density differences, the generation of infrasound and gravity waves, the generation of electromagnetic waves by lightning flashes, and the perturba- tions in the global electric circuit.

Research on high-power and high-efficiency emission of crosswell electromagnetic logging

Crosswell electromagnetic (EM) logging has useful applications in oil, gas, and water monitoring as well as carbon sequestration estimation. Difficulties in the efficient propagation of EM waves through a steel casing inhibit crosswell EM logging at distances greater than 300 m. This study investigates whether high-power transmission and high-efficiency transmitting antennas can resolve the challenges of long-distance crosswell EM logging through steel casings. Theoretical analysis indicates that the emission moment should be at least 12,000 A·m2. By calculating the equivalent relative permeability and selecting the appropriate coil materials and magnetic cores, the maximum emission magnetic moment can create a high-power transmission. Based on series and parallel resonant circuits and the alternating current/direct current cable core multiplexing power supply method, the effective transmission bandwidth is broadened and the transmission efficiency increases by three times. The emission unit is fabricated and tested using single, double, and fiberglass casing. We observe that the crosswell EM technology performs better for nonmetal casing wells than that for metal casing wells. The amplitude and phase curves between two fiberglass casing wells in the range of 425 m are quite smooth. However, the receiving signals in the double-layer steel casing decrease to only a few tenths of the value in the fiberglass casing wells, highlighting the difficulty of long-distance EM wave transmission when using steel casings. Thus, studies on EM transmission through four or more layers of steel casings should be conducted in the future.

On the justification and validity of causality in classical electromagnetism

Determining the causality in electromagnetism is more difficult than determining the causality in classical mechanics. Newton’s second law and the laws of Faraday and of Ampère are very different in character. Whereas Newton’s second law holds for a point in space, the laws of Faraday and of Ampère hold for a region in space. The ultimate aim of this article is to delve into the correct mechanism of propagation of electromagnetic waves. And, in this article, we investigate the wrong reasoning of other authors. It is concluded that an electric field neither generates nor induces a magnetic field and a magnetic field neither generates nor induces an electric field.

A 3-D Global FDTD Courant-limit Model of the Earth for Long-time-span and High-altitude Applications

A new global 3-D finite-difference time-domain (FDTD) model is introduced to simulate electromagnetic wave propagation around the Earth, including the lithosphere, oceans, atmosphere, and ionosphere regions. This model has several advantages over existing global models, which include grids that follow lines of latitude and longitude and geodesic grids comprised of hexagons and pentagons. The advantages of the new model include: (1) it may be run at the Courant-Friedrichs-Lewy (CFL) time step (as a result, it is termed the Courant-limit model); (2) subgrids may be added to specific regions of the model as needed in a straight-forward manner; and (3) the grid cells do not become infinitely larger as the grid is extended higher in altitude. As a result, this model is a better candidate than the others for investigating electromagnetic phenomena over long time spans of interest and for investigating atmosphere-ionosphere-magnetosphere coupling. The new model is first described and then validated by comparing results for extremely low frequency (ELF) propagation attenuation with corresponding analytical and measurement results reported in the literature.

Optimised correction polynomial functions for the Flux Reconstruction method in time-harmonic electromagnetism

The Flux Reconstruction (FR) method is classically used in the Computational Fluid Dynamics field. However, its use for the simulation of electromagnetic wave propagation is not as developed yet. Following on from the development of a priori error estimates for the 1D wave equations, we introduce optimisation problems to allow an adaptation of the FR correction polynomial functions to the discretisation parameters. Showing notable accuracy gains in 1D, especially in the preasymptotic regime, we generalise this procedure to the 3D Maxwell’s equations, leading to similar interesting possibilities to reduce the computational cost for a given accuracy.

Near-Field to Far-Field Approximation Formulas Based on the Asymptotic Expansion Method for Electromagnetic Wave Propagation Across Air–Sea Boundary Due to a Vertical Magnetic Dipole

Near-Field to Far-Field Approximation Formulas Based on the Asymptotic Expansion Method for Electromagnetic Wave Propagation Across Air–Sea Boundary Due to a Vertical Magnetic Dipole

Using Patient-Specific 3D Modeling and Simulations to Optimize Microwave Ablation Therapy for Liver Cancer.

Microwave ablation (MWA) of liver tumors presents challenges like under- and over-ablation, potentially leading to inadequate tumor destruction and damage to healthy tissue. This study aims to develop personalized three-dimensional (3D) models to simulate MWA for liver tumors, incorporating patient-specific characteristics. The primary objective is to validate the predicted ablation zones compared to clinical outcomes, offering insights into MWA before therapy to facilitate accurate treatment planning. Contrast-enhanced CT images from three patients were used to create 3D models. The simulations used coupled electromagnetic wave propagation and bioheat transfer to estimate the temperature distribution, predicting tumor destruction and ablation margins. The findings indicate that prolonged ablation does not significantly improve tumor destruction once an adequate margin is achieved, although it increases tissue damage. There was a substantial overlap between the clinical ablation zones and the predicted ablation zones. For patient 1, the Dice score was 0.73, indicating high accuracy, with a sensitivity of 0.72 and a specificity of 0.76. For patient 2, the Dice score was 0.86, with a sensitivity of 0.79 and a specificity of 0.96. For patient 3, the Dice score was 0.8, with a sensitivity of 0.85 and a specificity of 0.74. Patient-specific 3D models demonstrate potential in accurately predicting ablation zones and optimizing MWA treatment strategies.