Propagation Properties Of Electromagnetic Waves Research Articles

Continuous evolution of Fermi arcs in a minimal ideal photonic Weyl medium

Propagation properties of electromagnetic waves in an optical medium are mainly determined by the contour of equal-frequency states in k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\boldsymbol{k}}$$\\end{document}-space. In photonic Weyl media, the topological surface waves lead to a unique open arc of the equal-frequency contour, called the Fermi arc. However, for most realistic Weyl systems, the shape of Fermi arcs is fixed due to the constant impedance of the surrounding medium, making it difficult to manipulate the surface wave. Here we demonstrate that by adjusting the thickness of the air layer sandwiched between two photonic Weyl media, the shape of the Fermi arc can be continuously changed from convex to concave. Moreover, we show that the concave Fermi-arc waves can be used to achieve topologically protected electromagnetic pulling forces over a broad range of angles in the air layer. Our finding offers a generally applicable strategy to shape the Fermi arc in photonic Weyl media.

Reciprocal and non-reciprocal electromagnetic wave propagation in sub-100 nm epitaxial YIG thin films deposited under different oxygen growth pressure

Directional dependent transport of information in magnetic thin films offers a great opportunity to realize reciprocal and nonreciprocal microwave devices, such as filters, phase shifter, isolators and circulators. Electromagnetic wave (EM) propagation in sub-100 nm thin magnetic film is critical, yet reciprocal and non-reciprocal wave propagation and its accurate measurements remain a challenge. We investigated reciprocal and non-reciprocal wave propagation in 90 nm thick epitaxial thin films of yttrium iron garnet (Y3Fe5O12:YIG) grown by pulse laser deposition (PLD) technique on gadolinium gallium garnet [GGG(100)] substrates. The effect of oxygen growth pressure during deposition of YIG films exhibit directional dependence properties of electromagnetic wave propagation. The reciprocal EM wave propagation was generated by a S-type transmission line to achieve microwave (RF) magnetic fields (hRF) perpendicular to applied dc magnetic fields (HDC), to ensure the ferromagnetic resonance (FMR) condition. The center frequency is tuned up to 20 GHz with an applied magnetic field of 6 kOe. The tuning of the center frequency was achieved as of 85.3 % with HDC of 6 kOe. To achieve non-reciprocal EM-wave propagation one straight microstrip line was used to ensures a parallel configuration (parallel pumping FMR condition) of hRF to HDC. The nonreciprocity observed is due to the presence of gyrotropic properties in the YIG thin films and it enhances when YIG film was placed in asymmetric geometry. Further, oxygen growth pressure (>0.1 mbar) grown YIG films enhances the nonreciprocity by 21.6 %. The experimental results were successfully validated using high-frequency structure simulator (HFSS). Hence, these results indicate that controlled deposition parameters can be a crucial parameter in the design of reciprocal and nonreciprocal microwave signal processing devices.

A refractive index sensor based on the MIM waveguide with a semi-elliptical and a rectangular ring resonant cavity

In this paper, a novel nanosensor comprising the metal–insulator–metal (MIM) plasmonics waveguide with a semi-elliptical and rectangular ring resonant cavity is designed. In near-infrared waveband, the propagation properties of electromagnetic waves in the structure are studied using the finite-difference time-domain (FDTD) method. The results show that, based on the coupling between the semi-elliptical and the rectangular ring resonant cavity, the transmission spectrum of the structure exhibits a sharp Fano resonance shape. Next, the influence of the refractive index and sensor structure parameters on performance is systematically investigated. The simulation results show that the sensor structure has the best sensitivity of 1384[Formula: see text]nm/RIU (refractive index unit), and the figure of merit (FOM) is 28.4. The simple MIM structure could be applied to sensitive plasmonic sensors.

Beam Squint-Aware Integrated Sensing and Communications for Hybrid Massive MIMO LEO Satellite Systems

The space-air-ground-sea integrated network (SAGSIN) plays an important role in offering global coverage. To improve the efficient utilization of spectral and hardware resources in the SAGSIN, integrated sensing and communications (ISAC) has drawn extensive attention. Most existing ISAC works focus on terrestrial networks and cannot be straightforwardly applied in satellite systems due to the significantly different electromagnetic wave propagation properties. In this work, we investigate the application of ISAC in massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite systems. We first characterize the statistical wave propagation properties by considering beam squint effects. Based on this analysis, we propose a beam squint-aware ISAC technique for hybrid analog/digital massive MIMO LEO satellite systems exploiting statistical channel state information. Simulation results demonstrate that the proposed scheme can operate both the wireless communications and the target sensing simultaneously with satisfactory performance, and the beam-squint effects can be efficiently mitigated with the proposed method in typical LEO satellite systems.

Reconfigurable Intelligent Surfaces: Simplified-Architecture Transmitters—From Theory to Implementations

Reconfigurable intelligent surfaces (RISs) offer an entirely new route to alter the propagation properties of electromagnetic waves and thus control their reflection, refraction, and scattering features in arbitrary manners. Such physical attributes are perceived to bring about fundamental influence on the modern wireless communication system due to the possibilities to establish artificial and controllable propagation environments for radio signals, which no longer rely on the complex encoding, decoding, and other signal processing techniques. Recent studies reveal that the wave manipulation is not the only skill of the RISs. With the rapid developments of space–time digital metasurface and information metasurface, there has been increasing attention focused on the information manipulation via these artificial surfaces. In this article, we provide an overview of the theoretical models of the space–time digital metasurface and information metasurface, the mechanisms of wavefront shaping, and the signal modulations in space and time domains during the wave–matter interactions. We will also address some practical issues during implementations of the reconfigurable intelligent metasurfaces and the associated hardware architectures at microwave frequencies to realize simplified radio frequency transmitters. Several modulation schemes and the corresponding demonstration systems are introduced to illustrate the powerful abilities of the reconfigurable intelligent metasurfaces. Potential research directions of this technique are briefly discussed for their potential applications in future wireless networks.

Physical Layer Security: About Humans, Machines and the Transmission Channel

In an increasingly interconnected and globalized world in which the volume but also the confidentiality of transmitted content is becoming ever more important, trust, confidence and trustworthiness are of fundamental importance. Particularly in human societies, this trust is established, sustained and strengthened by personal relationships and experiences. But, in a globally connected world with Cyber-Physical Production Systems (CPPS), Industrial Internet of Things (IIoT) and Digital Twins (DTs), these personal relationships do not longer exist. (Remote) access to systems is possible from anywhere on the globe. However, this implies that there have to be technical solutions to detect, identify and acknowledge entities -people and machines- in the networks and thus to establish an initial level of trust.
 Especially since the proliferation of appropriate use-cases, Physical Layer Security (PhySec) is becoming increasingly popular in the scientific community. Using systems' intrinsic information for security applications provides a lightweight but secure alternative to traditional computationally intensive and complex cryptography. PhySec is therefore not only suitable for the IIoT and the multitude of resource-limited devices and sensors, it also opens up alternatives in terms of scalability and efficiency. Moreover, it provides security aspects regarding the entropy H and Perfect Forward Secrecy (PFS).
 Therefore, this work provides insight into three major branches of PhySec: i) Human - Physically Unclonable Functions (PUFs) ii) silicon/electrical - PUFs, and iii) Channel-PUFs. Based on the PUF operating principle, the silicon derivatives consider the electrical properties of semiconductors. Individual and uninfluenceable deviations during the manufacturing process result in component-specific behavior, which is described in particular for Static- and Dynamic Random Access Memory (S-/DRAM). Following this PUF principle, human characteristics -biological, physiological and behavioral features-, are used to recognize and authenticate them. With respect to the wireless channel, the characteristic properties of electromagnetic wave propagation and the influences on the wireless channel -diffraction, reflection, refraction and scattering-, are used to achieve symmetric encryption of the channel.
 In addition to the "conventional" wireless PhySec, especially the development of the Sixth Generation (6G) Wireless Systems, opens up a wide range of possibilities in terms of PhySec, for example in relation to Visible Light Communication (VLC), Reconfigurable Intelligent Surfaces (RIS) and in general the application of frequencies in the (sub)THz range.
 Thus, the work provides an overview of PhySec fields of application in all areas of the IIoT: in terms of humans, machines, and the transmission channel.

Analysis of Gaussian beam broadening and scintillation index in anisotropic plasma turbulence

In this paper, new expressions for the long-term beam spreading and scintillation index of Gaussian beams in anisotropic plasma turbulent media are derived on the basis of the anisotropic hypersonic plasma turbulent refractive index undulation power spectrum combined with the Rytov approximation theory. Considering the asymmetry of turbulent eddies in the orthogonal xy-plane throughout the path, two anisotropy factors are introduced to parameterize the anisotropy properties of turbulent cells in the horizontal and vertical directions. The spreading and scintillation index of Gaussian beams in plasma turbulence are calculated, and the propagation characteristics of Gaussian beams in anisotropic plasma turbulence are analyzed. Results show that enhancing the anisotropic properties of hypersonic plasma turbulence can significantly improve the propagation performance of Gaussian beams in hypersonic plasma turbulence. The effect of hypersonic plasma turbulence on Gaussian beam increases with the increase of the refractive index undulation variance and the decrease of the turbulent outer scale and anisotropy parameters. The results provide a theoretical basis for the further study of the propagation properties of electromagnetic waves in hypersonic plasma turbulence.

Investigation of near cut‐off properties of electromagnetic wave propagation in homogeneous, collisional plasma slab

AbstractFluctuations in the signal of optical coefficients of propagative electromagnetic (EM) waves in plasma, can cause problems in phase analysis, especially in microwave diagnostic systems which are based on the reflection, and transmission of EM waves in the vicinity of cut‐off layer of the plasma. In this study, optical properties of EM wave propagation in a single layer, homogeneous, and partially ionized plasma slab are investigated. For realistic analysis of propagation characteristics of the EM wave in the plasma slab, multiple reflections of the EM wave from plasma‐vacuum boundaries, known as incoherent internal reflections (IIR) are considered. Optical coefficients of the EM wave are numerically simulated in terms of the plasma parameters and wave frequency, with and without consideration of the incoherent internal reflections effect. It was found that in the low‐loss collision regime, the cut‐off fluctuations of the optical coefficients can be filtered considering the incoherent internal reflections of the EM wave. Such analysis of the EM wave propagation in plasma slab can be considered the primary physical design of diagnostic facilities and EM wave absorbing structures operating in the cut‐off frequency ranges.

Unidirectional propagation based on nonreciprocal defect modes in one-dimensional magneto-optical photonic crystals

In this study, in order to achieve the nonreciprocal propagation properties of electromagnetic waves, a ternary asymmetrical magneto-optical multilayer structure with a defect layer is constructed. It was found that, due to the defect layer, three pair nonreciprocal dispersive curves in three band gaps are formed for forward and backward incident waves. With the increasing thickness of defect layer, the nonreciprocal transmission peaks appear red-shift, and nonreciprocity decrease with enlargement of the space between two transmission peaks. Numerical simulations further indicated that the unidirectional propagation is due to the nonreciprocal resonant modes formed in the magneto-optical material layer of the ternary asymmetrical structure. These nonreciprocal properties are affected by the incident angle and the asymmetric gyrotropic electromagnetic parameters.

Switch design based on magnetic hyperbolic metamaterials

We design a switch based on a switchable magnetic hyperbolic metamaterial that consists of a one-dimensional periodic stacking of dielectric and gyromagnetic layers. The isofrequency curve of the structure can be switched between elliptical and hyperbolic shapes via the external DC magnetic field. The isofrequency curve relates directly to the propagation property of electromagnetic waves. By analyzing the different isofrequency curves, we predict that positive refraction, total reflection, and negative refraction can occur in a TE polarized Gaussian beam incident from air into the structure. The electric field distribution is simulated, and results confirm our predictions. Therefore, our switchable magnetic hyperbolic metamaterial can be used as an efficient switch. To be specific, with the adjustment of the external DC magnetic field, when the isofrequency curve transforms between a circle and a one-sheeted hyperbola, it can switch between positive refraction and total reflection; when the curve transforms between a circle and a two-sheeted hyperbola, it can switch between positive and negative refraction.

Abnormal Wave Propagation in Tilted Linear‐Crossing Metamaterials

The propagation properties of electromagnetic waves depend on media dispersion in momentum space, which can be characterized using isofrequency contours (IFCs). Normal linear‐crossing metamaterials (NLCMMs), which undergo a new type of topological transition between two kinds of hyperbolic media, are attracting attention because of their potential as a new avenue for controlling light propagation and verifying unusual phenomena involving zero‐index and hyperbolic media. Herein, the rotation of the optical axis is treated as a new degree of freedom and a tilted linear‐crossing metamaterial (TLCMM) is theoretically proposed. Upon rotating the optical axis angle such that it is equal to the cone angle, it is found that this special TLCMM has the shape of a type‐III Dirac cone, in condensed matter physics. Boundary conditions and the causality law are used to reveal that electromagnetic waves in this critical TLCMM can achieve abnormal refraction without reflection and filtering. Moreover, these phenomena are observed experimentally in a planar circuit‐based system. The results regarding the manipulation of electromagnetic waves may enable their use in planar‐integrated photonics, including for directional propagation, cloaking, and switching.

Study on propagation properties of electromagnetic waves through a magnetized, collisional and inhomogeneous plasma under oblique incidence

The properties of electromagnetic waves propagation through a collisional, magnetized and inhomogeneous plasma with obliquely incident angles are investigated in this paper. The reflection, transmission, and attenuation ratios are calculated first with the scattering matrix method. Based on the derived formulas, we then analyze the effects of different parameters on the propagation properties under oblique incidence. Simulation results indicate that a larger incident angle causes a longer wave transmission distance in the plasma and is more likely to impede the waves propagation. Under an obliquely incident angle, both the transmission and attenuation ratios are greatly affected by other parameters, such as the effective plasma collisional frequency, background magnetic flux density, plasma thickness and electron density, additionally. These conclusions are of guiding significance to the applications of the interaction between electromagnetic waves and plasma.

Characteristics of dispersion modes supported by Graphene Chiral Graphene waveguide

A theoretical formulation is obtained for a chiral filled waveguide formed by two parallel graphene layers. The thin graphene layers are extended infinitesimally and Kubo formula is used for surface conductivity. The fields expressions in the model are obtained using Maxwell’s equations. It is shown that a chiral filled graphene parallel-plate waveguide can guide hybrid mode instead of quasi-transverse electromagnetic modes. The influence of chirality and or chemical potential on the properties of electromagnetic wave propagation in a planar graphene-chiral-graphene waveguide is discovered under realistic material parameters. A dispersion expression is derived, which covers the achiral graphene-chiral-graphene case. It is observed that when the chirality is raised to certain value the propagating mode is vanished. It is also revealed that chirality and chemical potential might modulate the propagation mode in the waveguide. This work may enrich the electromagnetic theory which is of great importance for Electronic devices. The presented results are compared with published under special cases.

Topology optimization of origami-inspired reconfigurable frequency selective surfaces

Fold-driven reconfigurable devices have a potential to expand functional spaces beyond traditional adaptive wave propagation strategies. In particular, designs inspired by the art of origami leverage the mathematics of origami to map designs defined on two-dimensional surfaces to complex three-dimensional shapes. The design space in this paradigm is vast, so a systematic method is needed to design a device that achieves its goal. In our initial effort, we surveyed electromagnetic wave propagation properties of foldable frequency selective surfaces (FSS) and foldable and deployable antennas based on various known origami designs to identify a number of working principles of functional tuning. We incorporated these findings in the implementation of a design method that finds an origami FSS pattern that achieves the desired frequency tuning. This method is adopted from density-based topology optimization, with a notion that anything functional could be described through a distribution of an effective density of the relevant material property. A substrate is “patterned” with foldable segments parameterized through torsional springs; electromagnetically relevant conductive patterns are described as predefined surfaces that remain unchanged. This talk will discuss the lessons learned from our investigations and remaining challenges of designing fold-driven reconfigurable devices for wave propagation control.

Propagation Characteristics of Electromagnetic Wave in Seawater Channel for Submerged Buoy

The safety of submerged buoy is higher than traditional buoy. The most important problem for submerged buoy is that signal will be attenuated greatly due to ocean wave fluctuation and seawater. On the basis of ocean wave model, propagation characteristics of electromagnetic wave in seawater channel for submerged buoy is analyzed in this letter. It includes the propagation properties of electromagnetic wave in seawater and across the air-sea interface. The results show that the VHF frequency band, first order sea level and water depth of less than 10 cm are acceptable for submerged buoy.

The Optical Properties of Nano-Materials and Electromagnetic Wave Propagation Visualized with MATLAB

The course of electromagnetic fields and waves has properties of abstract concept, strong theory and complex calculation, thus this course is difficult to study and understand, and then is also difficult to teach. In order to make the understanding of the course easier, MATLAB software is used as a platform in classroom teaching of electromagnetic fields and waves. This paper mainly discusses the electrical field intensity distribution of media sphere materials and the properties of electromagnetic wave propagation with MATLAB software. The optical properties of dielectric-metal core-shell multi-layered nano-shell are also studied with Laplace's equation. To enrich the teaching content and improve a better teaching effect, the optical property of nano-materials and electromagnetic wave propagation are visualized with MATLAB software, which makes the properties of nano-materials and electromagnetic wave propagation understand easily.

Propagation characteristics of electromagnetic waves in dusty plasma with full ionization

This study investigates the propagation characteristics of electromagnetic (EM) waves in fully ionized dusty plasmas. The propagation characteristics of fully ionized plasma with and without dust under the Fokker–Planck–Landau (FPL) and Bhatnagar–Gross–Krook (BGK) models are compared to those of weakly ionized plasmas by using the propagation matrix method. It is shown that the FPL model is suitable for the analysis of the propagation characteristics of weakly collisional and fully ionized dusty plasmas, as is the BGK model. The influence of varying the dust parameters on the propagation properties of EM waves in the fully ionized dusty plasma was analyzed using the FPL model. The simulation results indicated that the densities and average radii of dust grains influence the reflection and transmission coefficients of fully ionized dusty plasma slabs. These results may be utilized to analyze the effects of interaction between EM waves and dusty plasmas, such as those associated with hypersonic vehicles.

Magnetic Induction-Based Localization in Randomly Deployed Wireless Underground Sensor Networks

Wireless underground sensor networks enable many applications, such as mine and tunnel disaster prevention, oil upstream monitoring, earthquake prediction and landslide detection, and intelligent farming and irrigation among many others. Most applications are location-dependent, so they require precise sensor positions. However, classical localization solutions based on the propagation properties of electromagnetic waves do not function well in underground environments. This paper proposes a magnetic induction (MI)-based localization that accurately and efficiently locates randomly deployed sensors in underground environments by leveraging the multipath fading free nature of MI signals. Specifically, the MI-based localization framework is first proposed based on underground MI channel modeling with additive white Gaussian noise, the designated error function, and semidefinite programming relaxation. Next, this paper proposes a two-step positioning mechanism for obtaining fast and accurate localization results by: first, developing the fast-initial positioning through an alternating direction augmented Lagrangian method for rough sensor locations within a short processing time, and then proposing fine-grained positioning for performing powerful search for optimal location estimations via the conjugate gradient algorithm. Simulations confirm that our solution yields accurate sensor locations with both low and high noise and reveals the fundamental impact of underground environments on the localization performance.

The Optical Bloch oscillation in chirped one-dimensional superconducting photonic crystal

We exploit theoretically the propagation properties of electromagnetic waves in nanoscale one-dimensional superconducting photonic crystal. The Wannier Stark ladders can be formed in the photonic crystal by varying the thickness of the dielectric layers linearly across the structure. The dynamics behavior of a Gaussian pulse transmitting through the structure is simulated theoretically. We find that photons undergo Bloch oscillations inside tilted photonic bands and the Bloch oscillations are sensitive to the change of temperature in the range of 3–8K. It is demonstrated that our structure is possible to realize tunable optical Bloch oscillations by controlling the temperature of superconducting material.

Flat Terahertz Reflective Focusing Metasurface with Scanning Ability

The ability to manipulate the propagation properties of electromagnetic waves, e.g., divergence, focusing, holography or deflection, is very significant in terahertz applications. Metasurfaces with flat structures are attractive for achieving such manipulations in terahertz band, as they feature low profile, lightweight, and ease of design and installation. Several types of terahertz reflective or transmitting metasurfaces with focusing function have been implemented recently, but none of them can provide scanning ability with controllable focus. Here, a flat reflective metasurface featuring controllable focal shift is proposed and experimentally demonstrated. Furthermore, the principle of designing a focus scanning reflective metasurface is presented and the focusing characteristics are discussed, including focus scanning along a line parallel or orthogonal to the metasurface with a large bandwidth. These interesting properties indicate that this flat reflective metasurface could play a key role in many terahertz imaging and detection systems.