Electromagnetic Wave Propagation Research Articles

Lightning and Gravity Wave Signatures Produced by the Hunga‐Tonga Volcanic Eruption on Global Geomagnetic Data

AbstractAcoustic gravity waves (AGWs) have a significant impact on the thermosphere‐ionosphere (T‐I) system by increasing ionisation variability, transporting energy, velocity, momentum, and creating additional horizontal gradients in the T‐I, all of which influence electromagnetic wave propagation and cause changes in the geomagnetic field. Ground magnetic disturbance measurements can thus map the global and local spatial distribution of T‐I current systems. The Hunga‐Tonga volcano eruption released a tremendous amount of mass and energy into the atmosphere on 15 January 2022, causing AGWs. Furthermore, the related lightning strikes disrupt the Global electric circuit. In this study, we look at (a) global geomagnetic disturbances caused by AGW constrained by VTEC amplitudes at two different sectors, (b) Schuman resonances (SR) parameters derived from modulations of ELF observations caused by the intense lightning phenomena that accompanied the volcanic eruption. Our analysis shows that (a) registration timing of geomagnetic disturbance at each observatory indicates the different modes of propagation between 180 and 350 m/s, indicating low‐frequency AGW components, (b) noticeable changes in SR frequency modes (7–21 Hz) occurred in the total power between 04:15 and 05:45 UT hr at Patiyasar, India, linked to heightened lightning activity, (c) velocities are found to be similar at similar distances in the northern and southern hemispheres from Hunga‐Tonga, (d) time difference between the SR and geomagnetic disturbance signature at observatories is found to have no relation with distance from the eruption, (e) fluctuations in VTEC at the Indian and Russian sectors show that the geomagnetic disturbances are linked to ionospheric perturbations.

Electromagnetic loss study of honeycomb structured absorbers with a metal substrate

The broad application prospect of the honeycomb structure wave absorber in industrial and civil fields makes researchers focus on studying its wave absorbing mechanism so as to optimize its structural design and improve its wave absorbing performance. Distinguishing from the equivalent circuit thinking to study the honeycomb structured absorber, a kind of symmetry operation is adopted in this paper for the honeycomb structured absorber from the electromagnetic wave propagation point of view. The reflection loss is assumed to be the result of the loss of the incident electromagnetic wave in the absorbing body and the superposition of multiple refractions, and the symmetry operation can separate the specific physical process of the refracted wave involved in the superposition. The separated electromagnetic wave vector superposition is compared with the simulated and experimental values to verify the correctness of the conjecture. The separation results show that the absorption properties are determined by the internal loss and the phase change caused by the surface structure, which is of positive significance for the optimization and design of honeycomb absorbers.

Switchable frequency‐selective rasorber/absorber based on single‐sheet structure

AbstractA single‐sheet structure‐based switchable broadband FSR/absorber is proposed. The lossy layers I, II, and the FSS are printed along the direction of electromagnetic (EM) wave propagation (z‐direction) at the top, middle, and bottom positions of the substrate, respectively. A PIN diode is used in the lossy layer II and the FSS to switch their operating states. By activating or deactivating the PIN diodes, the design can operate as either an FSR or absorber. The FSR achieves a passband with an insertion loss of 0.64 dB at 3.9 GHz, and two absorption bands with fractional bandwidth of 87.6% and 20.8%, respectively. The absorber has a wide absorption band from 1.6 to 5.4 GHz (109%). It is transparent to EM waves of orthogonal polarization. The measured and simulated results are in close agreement, which exhibits stable performance under 30° of oblique incidence in both the xz‐ and yz‐planes.

Hofstadter butterfly in optical multilayers

This research focuses on the theoretical examination of the propagation of electromagnetic waves in a multilayer structure in which the refractive index in each medium is modulated by a similar expression of Harper’s potential for the electronic 1D model, or, equivalently, to on-site energies in the Aubry–André model. We applied the transfer matrix approach to different multilayers, with a refractive index modulated by a similar expression of Harper’s potential to obtain the optical transmittance spectra for normal incidence. We calculate the transmittance spectrum as a function of frequency and the Harper model phase for two scenarios in order to search for probable edge states that might arise in this system: first, when the quarter wavelength ratio relates to layer thicknesses through njdj=λ0/4, with nj being the refractive index of the jth layer of the 1D photonic crystal and λ0 is the central wavelength; second, we consider the effects when the thicknesses of the layers are related by d2j=2d2j+1. Besides, to obtain the photonic equivalent for Hofstadter butterfly fractal spectra, we calculate the transmittance spectrum as a function of the periodicity control parameter of the Harper model at the critical point.

Spectral Efficiency Improvement Using Bi-Deep Learning Model for IRS-Assisted MU-MISO Communication System.

The intelligent reflecting surface (IRS) is a two-dimensional (2D) surface with a programmable structure and is composed of many arrays. The arrays are used to supervise electromagnetic wave propagation by altering the electric and magnetic properties of the 2D surface. IRS can influentially convert wireless channels to very effectively enhance spectral efficiency (SE) and communication performance in wireless systems. However, proper channel information is necessary to realize the IRS anticipated gains. The conventional technique has been taken into consideration in recent attempts to fix this issue, which is straightforward but not ideal. A deep learning model which is called the long short-term memory (Bi-LSTM) model can tackle this issue due to its good learning capability and it plays a vital role in enhancing SE. Bi-LSTM can collect data from both forward and backward directions simultaneously to provide improved prediction accuracy. Because of the tremendous benefits of the Bi-LSTM model, in this paper, an IRS-assisted Bi-LSTM model-based multi-user multiple input single output downlink system is proposed for SE improvement. A Wiener filter is used to determine the optimal phase of each IRS element. In the simulation results, the proposed system is compared with other DL models and methods for the SE performance evaluation. The model exhibits satisfactory SE performance with a different signal-to-noise ratio compared to other schemes in the online phase.

Dielectric constant and magnetic permeability in the Newtonian gravitational field derived by the elastic energy

The pressure distribution in the Earth’s interior is expressed using the Adams‐ Williamson equation. The elastic energy is stored inside the Earth by the pressure. The Newtonian gravitation is derived by this energy. The Newtonian gravitation refracts light at the surface of the Sun. When light is an electromagnetic wave, this refraction is expressed by the dielectric constant and magnetic permeability in the Newtonian gravitational field. The propagation of electromagnetic waves in a black hole is discussed using the dielectric constant and magnetic permeability.

Photothermal effects of terahertz-band and optical electromagnetic radiation on human tissues

The field of wireless communication has witnessed tremendous advancements in the past few decades, leading to more pervasive and ubiquitous networks. Human bodies are continually exposed to electromagnetic radiation, but typically this does not impact the body as the radiation is non-ionizing and the waves carry low power. However, with progress in the sixth generation (6G) of wireless networks and the adoption of the spectrum above 100 GHz in the next few years, higher power radiation is needed to cover larger areas, exposing humans to stronger and more prolonged radiation. Also, water has a high absorption coefficient at these frequencies and could lead to thermal effects on the skin. Hence, there is a need to study the radiation effects on human tissues, specifically the photothermal effects. In this paper, we present a custom-built, multi-physics model to investigate electromagnetic wave propagation in human tissue and study its subsequent photothermal effects. The proposed finite-element model consists of two segments—the first one estimates the intensity distribution along the beam path, while the second calculates the increase in temperature due to the wave distribution inside the tissue. We determine the intensity variation in the tissue using the radiative transfer equation and compare the results with Monte Carlo analysis and existing analytical models. The intensity information is then utilized to predict the rise in temperature with a bio-heat transfer module, powered by Pennes’ bioheat equation. The model is parametric, and we perform a systematic photothermal analysis to recognize the crucial variables responsible for the temperature growth inside the tissue, particularly for terahertz and near-infrared optical frequencies. Our numerical model can serve as a benchmark for studying the high-frequency radiation effects on complex heterogeneous media such as human tissue.

Hyperbolic Polaritons in Topological Nodal Ring Semimetals.

In mirror-symmetric systems, there is a possibility of the realization of extended gapless electronic states characterized as nodal lines or rings. Strain induced modifications to these states lead to the emergence of different classes of nodal rings with qualitatively different physical properties. Here we study optical response and the electromagnetic wave propagation in type I nodal ring semimetals, in which the low-energy quasiparticle dispersion is parabolic in momentum k_{x} and k_{y} and is linear in k_{z}. This leads to a highly anisotropic dielectric permittivity tensor in which the optical response is plasmonic in one spatial direction and dielectric in the other two directions. The resulting normal modes (polaritons) in the bulk material become hyperbolic over a broad frequency range, which is furthermore tunable by the doping level. The propagation, reflection, and polarization properties of the hyperbolic polaritons not only provide valuable information about the electronic structure of these fascinating materials in the most interesting region near the nodal rings but also pave the way to tunable hyperbolic materials with applications ranging from anomalous refraction and waveguiding to perfect absorption in ultrathin subwavelength films.

Propagation of short-wavelength electromagnetic surface waves along the transition layer between two plasma-like half-spaces in the Voigt geometry

The dispersion properties of surface type electromagnetic waves are studied. The waves are considered to propagate along a slab transition layer located between two infinite homogeneous plasma regions of different particle densities. The wavelength is assumed to be short as compared with the layer width. The waves propagate across a static magnetic field, which is parallel to the layer interface. The influence of the smoothness of the gradient of the plasma particle density within the layer on the surface wave propagation/disappearance is discussed. The conclusions derived in the present paper are of interest in the fields of plasma electronics, nano-technologies, plasma-antenna systems, plasma production, and magnetic confinement fusion.

Chaos Detection by Fast Dynamic Indicators in Reflecting Billiards.

The propagation of electromagnetic waves in a closed domain with a reflecting boundary amounts, in the eikonal approximation, to the propagation of rays in a billiard. If the inner medium is uniform, then the symplectic reflection map provides the polygonal rays' paths. The linear response theory is used to analyze the stability of any trajectory. The Lyapunov and reversibility error invariant indicators provide an estimate of the sensitivity to a small initial random deviation and to a small random deviation at any reflection, respectively. A family of chaotic billiards is considered to test the chaos detection effectiveness of the above indicators.

Physical Aspects of Chemical Carcinogenesis

This study investigated the effects of chemical carcinogenesis induced by 7, 12-dimethylbenz (α) anthracene (DMBA) in mice. The respiratory activity of isolated mitochondria in mouse livers was investigated at various times after the subcutaneous administration of DMBA. Our findings indicated that DMBA derivatives did not exhibit damaging effects on mitochondrial membranes. On the contrary, they showed a stimulating effect on the phosphorylation process compared with the control. This paper discusses the possible role of coherent electromagnetic radiation in biological systems. Additionally, data on the non-chemical interactions between isolated mitochondria and the material (plexiglass and quartz) of the incubation cells were considered. Carcinogenesis was previously considered an exclusive process of biochemical and genetic disorders. However, recent studies have increasingly focused on the physical aspects of carcinogenesis, such as the influence of various wavelengths of electromagnetic radiation on biological systems, the special energy organization of the intracellular space associated with the architectonics of mitochondria and microtubules, and the generation of coherent electromagnetic waves. It was assumed that the biological features of the malignant cells were due to the violation of the electrodynamic parameters of the intracellular space, and the initiating factor was the intrinsic emission of carcinogenic substances. The results of this study indicated that non-chemical factors influenced the mitochondrial poly-enzyme system and confirmed the importance of the non-chemical effect of a carcinogen on bio-objects by examining respiration and phosphorylation of isolated mouse liver mitochondria at various times after the subcutaneous injection of DMBA.

Robust Topological Edge States in C6 Photonic Crystals

The study of photonic crystals has emerged as an attractive area of research in nanoscience in the last years. In this work, we study the properties of a two-dimensional photonic crystal composed of dielectric rods. The unit cell of the system is composed of six rods organized on the sites of a C6 triangular lattice. We induce a topological phase by introducing an angular perturbation ϕ in the pristine system. The topology of the system is then determined by using the so-called k.p perturbed model. Our results show that the system presents a topological and a trivial phase, depending on the sign of the angular perturbation ϕ. The topological character of the system is probed by evaluating the electromagnetic energy density and analyzing its distribution in the real space, in particular on the maximal Wyckoff points. We also find two edge modes at the interface between the trivial and topological photonic crystals, which present a pseudospin topological behavior. By applying the bulk-edge correspondence, we study the pseudospin edge modes and conclude that they are robust against defects, disorder and reflection. Moreover, the localization of the edge modes leads to the confinement of light and the interface behaves as a waveguide for the propagation of electromagnetic waves. Finally, we show that the two edge modes present energy flux propagating in opposite directions, which is the photonic analogue of the quantum spin Hall effect.

Modeling of the Propagation of LF–MF–SF Bands Electromagnetic Waves on Arctic Paths

The article demonstrates that the conditions of LF–MF–SF bands electromagnetic wave propagation over the “ice-sea” structure with highly inductive impedance are more favorable than over the sea without ice because of the appearance of surface electromagnetic waves (SEW). It was determined that the conditions of radio wave propagation over ice paths depend on a frequency, ice thickness and distance from the transmitter within the 100 kHz – 5 MHz range on the paths with ice thickness from 0.6 to 2.7 meters.

Thermal Effects of Electromagnetic Energy on Skin in Contact with Metal: A Numerical Analysis

It has been well recognized that interactions between electromagnetic fields and metals are very strong. The consequence of human tissue in contact with metal, when subjected to an alternating electromagnetic field, is an increase in tissue temperature, which results from metals absorbing the energy obtained through induction. However, the electromagnetic induction characteristics and tissue energy absorbed caused by various electromagnetic field exposure conditions have not been well understood. A computational model was developed and employed in this study to assess the temporal and spatial temperature increases in skin due to contact with a highly conductive metallic plate while subjected to a high-intensity electromagnetic field. The effects of plate material, plate thickness, coil distance, and exposure time on temperature increase in the skin were computationally investigated. The electromagnetic and temperature distributions in skin layers during exposure to electromagnetic fields were achieved using models of electromagnetic wave propagation and an unsteady bioheat transfer. The modeling approach used indicates that the plate thickness, plate material, coil distance, and exposure time have a significant impact on the temperature change in the skin. The most important parameter was found to be the metal type. Iron has the greatest effect on skin temperature increase when subjected to external electromagnetic induction. These results allow the researchers to estimate more precisely the exposure limits for induction coils.

EM wave propagation within plasma-filled rectangular waveguide using fractional space and LFD

This paper aims to investigate the propagation of the electromagnetic (EM) within the rectangular waveguide that is filled with plasma. A rapid Cherenkov free electron laser ( C-FEL) beam was injected into the plasma to excite its natural oscillations and, therefore, an EM wave was generated. We focused on TM-mode propagation through this waveguide. Exact solutions of the EM wave equation have been found using both the Laplacian operator in the fractional D-dimensional space and the local fractional derivative (LFD). The fractional solutions have been converted into classical results to simulate the usual behavior of the waves. It has been found that the well-known Bessel, Neumann, and Mittage–Leffler functions are observed and their propagation is directly proportional to fractional parameters.

Scattering at Temporal Interfaces: An overview from an antennas and propagation engineering perspective

Recent years have witnessed a surge of interest in exotic electromagnetic (EM) wave propagation in time-varying systems. An interesting concept is the one of a temporal interface, the time-analogue of a spatial interface, formed by an abrupt and uniform change of the EM properties of the host medium in time. A time interface scatters the incident wave in a dual fashion compared to its spatial counterpart, conserving momentum but transforming frequency and exchanging energy with the wave. This article provides an overview of the wave-scattering features induced by time interfaces from an antennas and propagation engineering perspective. We first discuss the dualities of wave propagation across spatial and temporal interfaces, by recasting the telegrapher equations in a linear time-variant (LTV) transmission line (TL). Then, we introduce the scattering matrix to describe temporal scattering processes, and derive the conditions for reciprocity and momentum conservation. Understanding temporal scattering through the lens of conventional microwave engineering theory may facilitate the analysis and implementation of next-generation metamaterials encompassing temporal degrees of freedom.

Effect of electron number densities on the radio signal propagation in an inductively coupled plasma facility

Spacecraft entering a planetary atmosphere are surrounded by a plasma layer containing high levels of ionization, due to the extreme temperatures in the shock layer. The high electron number densities cause attenuation of the electromagnetic waves emitted by the on-board antennas, leading to communication blackout for several minutes. This work presents experimental measurements of signal propagation through an ionized plasma flow. The measurements are conducted at the VKI plasma wind tunnel (Plasmatron) using conical horn antennas transmitting in the Ka-band, between 33 and 40 GHz. Testing conditions at 15, 50 and 100 mbar, and powers between 100 and 600 kW cover a broad range of the testing envelope of the Plasmatron as well as a broad range of atmospheric entry conditions. The transmitting antenna is characterized at the UPC anechoic chamber, obtaining the radiation patterns, beamwidth, and gain at the boresight direction; and an optical ray tracing technique is used to describe the electromagnetic waves propagation in the plasma flowfield inside of the Plasmatron chamber. The signal propagation measurements show clear attenuation when the signal is propagating through the plasma, varying between 2 and 15 dB depending on the testing conditions. This attenuation increases with electron number densities, which are driven by the Plasmatron power and pressure settings. Preliminary evidence of Faraday rotation effects caused by the plasma is also observed.

Parallelization of a 3D FDTD code and physics studies of electromagnetic wave propagation in fusion plasmas

Numerical codes for electromagnetic wave propagation in magnetized plasmas are mainly based on frequency-domain asymptotic methods, which provide a fast solution and are thus valuable for experiment design and control applications. However, in several cases of practical interest (e.g. mode conversion), these tools run close to their limits of validity and should be compared to full-wave solutions. The code RFFW solves Maxwell's equations with the finite-difference time-domain method in 3D geometry, for scenarios involving high-frequency waves with arbitrary electric field spectrum in plasmas with axisymmetric equilibrium. In fusion-related problems, the code may conduct investigations of wave propagation and absorption relevant to auxiliary plasma heating and current drive, reflectometry and instability control. The code has been parallelized with a hybrid OpenMP-MPI scheme, which has allowed exploiting the much larger processing power and memory of current-day supercomputers. In this work, we present the main aspects of the physics implemented in the code, and also refer shortly to the parallelization scheme. Furthermore, we show results that exhibit the strong scaling performance of the code, and examine cases of electron-cyclotron heating application in medium-sized tokamaks.

Response of propagation of ELF electromagnetic waves through the morning ionosphere to small density variations caused by infrasonic wave

We consider the problem of the effect of small plasma density variations on the propagation and reflection of ELF (extremely-low-frequency) electromagnetic wave incident on the morning ionosphere from above. Modifications of the electromagnetic wave field near the Earth surface and coefficient of wave energy reflection from ionosphere caused by infrasonic wave are studied. The greatest modifications of the field on the Earth surface and reflection coefficient are related to the density perturbations at altitudes of strong electromagnetic wave attenuation (80–110 km). Reflection of electromagnetic waves is especially sensitive to the plasma density perturbations if the value of horizontal refractive index is close to a unit. In this case, modulation percentage of reflection coefficient can exceed the modulation percentage of density in the infrasonic wave by an order of magnitude. The parametric influence of plasma density perturbations in an infrasonic wave on the ELF electromagnetic field is analyzed. If the values of the horizontal wave numbers of the electromagnetic and infrasonic waves are close to each other, the field of the electromagnetic wave near the Earth surface can increase several times. The obtained results are important for understanding the interconnection of ionospheric wave processes of different nature. The study of the modulation of coefficient of ELF reflection from the ionosphere is relevant for explaining the operation modes of a plasma magnetospheric maser.

Propagation of anisotropic gravitational and electromagnetic waves at very high energies

We analyze the dispersion relation for an anisotropic gravity-electromagnetic theory at very high energies. In particular for photons of very high energy. We start by introducing the anisotropic gravity-gauge vector field model. It is invariant under spacelike diffeomorphisms, time parametrization, and U(1) gauge transformations. It includes high-order spacelike derivatives as well as polynomial expressions of the Riemann and field strength tensor fields. It is based on the Hořava-Lifshitz anisotropic proposal. We show its consistency, and the stability of the Minkowski ground state. Finally, we determine the exact zone at which the physical degrees of freedom, i.e. the transverse-traceless tensorial degrees of freedom and the transverse vectorial degrees of freedom propagate according to a linear wave equation. This is so, in spite of the fact that there exists in the zone a non-trivial Newtonian background of the same order. The wave equation contains spatial derivatives up to the sixth order, in the lowest order it exactly matches the relativistic wave equation. We then analyze the dispersion relation at very high energies in the context of recent experimental data. The qualitative predictions of the proposed model, concerning the propagation of highly energetic photons, are different from the ones obtained from the modified dispersion relation of the LIV models.