Frequency Of Incident Electromagnetic Wave Research Articles

Multichannel information transmission via a dual-frequency point space-time coding metasurface

Space-time coding (STC) digital metasurfaces enable dynamic control of nonlinear harmonics. To achieve efficient frequency tuning and harmonic control, we propose a one-bit column-controlled temporal coding dual-frequency point STC digital metasurface. Using a field-programmable gate array (FPGA) to control diode switching, the metasurface is encoded to generate multiple target reflected harmonics as independent information transmission channels. The amplitude intensities of these harmonics are defined as independent binary symbols for transmission. The proposed space-time coding digital metasurface can achieve a phase shift of 180° in its unit structure, with reflectivities above 90% at both operating frequencies. We fabricated the designed metasurface and tested its far-field scattering experimentally. When the incident electromagnetic wave frequency is 4.63 GHz, the predicted results are essentially consistent with the experimental findings.

On some computational aspects for electromagnetic-thermal dosimetry of mm waves

This work is on the use of a state-of-the-art hybrid boundary element method/finite element method (BEM/FEM) for electromagnetic (EM) dosimetry and the coupled thermal dosimetry model based on the Pennes’ heat transfer equation (PHE) for biological tissue solved by means of FEM. The distribution of the induced electric field obtained in both homogeneous and non-homogeneous human head models using EM model is used as a distributed heat source in the piecewise homogeneous human head thermal dosimetry model. As the penetration depth is inversely proportional to the frequency of incident EM wave, we consider the heating depth in several human head models, to illuminate whether homogeneous models in the EM part of the model are pertinent in the thermal dosimetry part. If confirmed, the results could be found useful in standardisation efforts related to the assessment of human exposure to EM fields in the high frequency range.

High-performance transparent electromagnetic interference shielding film based on metal meshes

Transparent electromagnetic interference (EMI) shielding films have gained considerable attention for the commercialization of the 5G wireless technology based on electromagnetic waves in the GHz range. In this study, transparent EMI shielding films with embedded metal meshes on a 100 μm thick polyethylene terephthalate film for EMI shielding were fabricated using ultraviolet imprinting and Ag paste filling techniques. The various EMI shielding film types were fabricated by varying the width, aperture size, and height of the mesh electrode to evaluate the efficiency of the EMI shielding according to the incident electromagnetic wave frequency and morphology of the mesh metallic electrodes. The results indicate that the EMI shielding efficiency (SE) increased with a decrease in the aperture size of the metal mesh electrodes and an increase in their height. The average EMI SE values of the fabricated film in the 0.5–18 GHz range reached 48.3 dB and 59.6 dB at a light transmittance of approximately 90% and 77%, respectively. The fabricated EMI shielding films can be used for various applications, such as communications, aerospace, medical equipment, and military.

Self-trapping of nanoparticles by bound states in the continuum

In the first tutorial part of the paper, we show that equilibrium positions of small dielectric particles inside the Fabry-Perot resonator (FPR) are sensitive to a frequency of incident electromagnetic wave and size of particle. That elucidates basic principles of resonant trapping of nanoparticles by excitation of high-$Q$ resonances of FPR. In the second part, we consider a long dielectric cylinder with submicron radius (primary cylinder) integrated into a metallic waveguide which supports symmetry-protected bound states in the continuum (BICs). We consider the case of a slightly shifted cylinder relative to the axis of symmetry of a waveguide that controls the $Q$ factor of quasi-BIC. Then, the extra nanoparticle perturbs quasi-BIC as dependent on the size of the nanoparticle and position relative to the primary cylinder. An interplay between the resonant width of quasi-BIC and a degree of frequency perturbation defines whether a dragging nanoparticle is terminated at a surface of the primary cylinder for an ultrasmall size of nanoparticles or at the definite distances from the cylinder for the larger size of nanoparticles. Thereby, we demonstrate a paradigm of resonant self-trapping and sorting of nanoparticles by use of quasi-BICs. We also show extremal sensitivity of self-trapping to the frequency of an electromagnetic (EM) wave propagating over waveguide.

Far-field steering of beams based on dynamic encoding metasurface

Programmable metasurfaces can realize dynamic control of electromagnetic waves. We propose a 1-bit programmable metasurface based on row-column-encoded dynamic control. The programmable metasurface encodes the cell structure with a sequence of row-column patterns, and controls the on–off of diodes via a field-programmable gate array (FPGA). The proposed programmable metasurface can achieve a 180° phase change of the cell structure, and the reflectivity can reach more than 90 %. We experimentally fabricated the designed programmable metasurface and tested it for far-field scattering. When the incident electromagnetic wave frequency is 11.7 GHz, the programmable metasurface realizes the beam scanning function, and the experimental results are in good agreement with the theoretical results.

Broadband Applications of a Tunable Nano-Rod Metaferrite

The rigorous analytical model of broadband effective electromagnetic response of the two-component metaferrite is presented in this study in the range up to THz frequencies. The metaferrite is a square array of ferric or ferromagnetic infinitely long cylinders of circular cross section symmetrically imbedded into homogenous isotropic dielectric host medium. It is assumed that the cylinders are fully or partially magnetized by a dc biasing magnetic field directed along the cylinder axes. Expressions of the complex effective permeability and permittivity tensors are obtained in the study. Expressions of the complex effective relative permeability and permittivity transverse to the direction of magnetization are derived and analyzed as functions of the frequency of incident electromagnetic wave and constitutive parameters of the metaferrite.It is shown that tuning a dc biasing magnetic field enables to effectively change the transmittivity and reflectivity of the metaferrites in the considered frequency range. We were also able to show that a layer of the metaferrite can be used for exciting surface plasmons at GHz frequencies. Finally, we have discussed the principal possibility of usage of the considered metaferrite for fabricating the substrates of miniaturized patch antennas with improved performance.

Field discrete Monte Carlo simulation of electromagnetic scattering characteristics of plasma sheath

The electromagnetic scattering of an ultra-high-speed plasma covered target is simulated by the field discrete Monte Carlo method. The flow field network is used to simulate the trajectory of electromagnetic wave particles according to the electromagnetic distribution parameters, and the electromagnetic characteristics are calculated according to the statistical parameters of the reflected particles. The computational time-consumption is less correlated with the incident electromagnetic wave frequency [except for the Radar Cross Section (RCS) valley characteristics], and it is convenient for parallel calculation, which realizes the fast calculation of the electromagnetic scattering of the electrically large plasma-covered target. On this basis, the electromagnetic scattering characteristics of the blunt cone hypervelocity target are calculated, and the main RCS reduction and enhancement mechanisms are given.

Simulation and Feature Extraction of the Dynamic Electromagnetic Scattering of a Hypersonic Vehicle Covered with Plasma Sheath

Based on the detection platform of space-borne radar (SBR), the dynamic electromagnetic (EM) scattering characteristics of a hypersonic vehicle covered with plasma sheath are calculated and analyzed by the physical optics (PO) method. Using the angle-time conversion method, the dynamic radar cross section (DRCS) of the vehicle in horizontal flying path and different flying states is solved in the range of L-band to X-band. The relevant effective statistical features are extracted from the time-scale matrix of DRCS based on continuous wavelet transform (CWT). The numerical results show that: At different flying altitudes, the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath has irregular fluctuation and large range reduction in the head region of the vehicle. Generally, the higher the incident EM wave frequency is, the more detailed the fluctuation characteristics of the DRCS can be reflected. Within the same radar illuminate angle range, the time consumed by the vehicle DRCS is inversely proportional to the flying height and flying speed and is directly proportional to the detection altitude of the SBR. Besides, the different kinds of statistical eigenvalues extracted from DRCS will play an important role in hypersonic targets classification and recognition.

Resonant absorption of incident electromagnetic waves in collisional inhomogeneous plasma slabs

Resonant absorption is a process that electromagnetic (EM) energy is converted to plasma energy with a mode conversion on the resonant layer where the incident EM wave frequency equals to the local frequency of a plasma normal modes. With a finite collision between charged and background neutral particles in a plasma, the plasma oscillation is dissipated to widen the resonance layer and heat the plasma. In this work a modified scattering matrix methods (SMM) are applied to study the effects of the collision frequency, incident angle, and plasma thickness on resonant absorption. We analyze the energy absorption caused by resonance in comparison with collisional absorption for different parameters. It is found that the resonant absorption dissipates about nearly half of the incident EM energy in an overdense inhomogeneous plasma when the collision is weak, and the rest half portion is reflected. If the collision is strong, however, the collisional absorption is then more significant than the resonant and affects the entire wave propagation process.

Analysis of the electromagnetic scattering characteristics in two-dimensional time-varying and spatially non-uniform plasma sheath

Hypersonic vehicles are affected by plasma sheath, which influences information transmission and target recognition. This study analyzes the scattering characteristics of different parameters of electromagnetic (EM) waves in a time-varying plasma sheath. The finite-difference time-domain algorithm is applied. An empirical formula of plasma collision frequency is used, and the electron density is assumed to vary with time, causing the plasma frequency to also vary with time and rise exponentially. Different time-varying laws on EM scattering are compared. Radar cross section of different parameters, including the flight altitude, flight Mach number, attack angle, cyclotron frequency of the electron, incident EM wave frequency, and incident EM wave angle, is calculated and analyzed in time-varying plasma.

A layered fluctuation model of electron density in plasma sheath and instability effect on electromagnetic wave at Ka band

The effects of plasma sheath on communication signals are not only power attenuation but also multiplicative noise addition because of the sheath's instability. The fluctuation properties of time-varying electron density are crucial to comprehensively understand the blackout problem. In this paper, the fluctuation laws of time-varying electron density are first comprehensively revealed in space–time–frequency domain. A layered fluctuation model of time-varying electron density is then proposed based on these fluctuation laws. The effects of dynamic plasma sheath on electromagnetic (EM) waves at Ka band are calculated by Monte Carlo quasistatic EM numerical method. Results show that the amplitude and phase of time-varying transmission coefficient both follow Gaussian distribution, whereas the spectrum curves follow a bi-Gauss function because of the effect of second mode instability in the hypersonic boundary layer. Furthermore, the means of amplitudes increase with the increasing of the incident EM wave frequency and the decreasing of the peak electron density, while the standard deviations decrease with the increasing of incident EM wave frequency, the decreasing of the peak electron density and the decreasing of electron density standard deviation.

The Study on Dispersion Characteristic of Dusty Plasma

Dispersion is one of the important characteristics of dusty plasma. In this paper, the real and imaginary parts of the complex refractive index of dusty plasma are first deduced and verified by the Kramers-Kronig dispersion relation. And then, the dependence of dispersion ability on the temperature, pressure, angular frequency of incident electromagnetic wave, as well as the number density, radius, and charge of dust particles is given. Finally, the theoretical results indicate that: 1) the dispersion ability decreases with the increase of angular frequency; 2) the dispersion ability monotonically varies with the pressure approximately, but nonmonotonically varies with the temperature; and 3) the dispersion ability monotonically increases with the increase of dust particle's charge, but nonmonotonically changes with the number density and radius of dust particles. In particular, the involved physical explanations are proposed.

Band structure of one-dimensional doped photonic crystal with three level atoms using the Fresnel coefficients method

We consider a one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics. Electric permittivity and magnetic permeability of this crystal depends on the incident electromagnetic wave frequency. We suppose that three level atoms have been added to the second layer of each dielectric and this photonic crystal (PC) has been doped. These atoms can be added to the layer with different rates. In this paper, we have calculated and compared the band structure of the mentioned PC considering the effect of added atoms to the second layer with different rates through the Fresnel coefficients method. We find out that according to the effective medium theory, the electric permittivity of the second layer changes. Also the band structure of PC for both TE and TM polarizations changes, too. The width of bandgaps related to “zero averaged refractive index” and “Bragg” increases. Moreover, new gap branches appear in new frequencies at both TE and TM polarizations. In specific state, two branches of “zero permittivity” gap appear in the PC band structure related to TM polarization. With increasing the amount of the filling rate of total volume with three level atoms, we observe a lot of changes in the PC band structure.

Effect of external electric field on the electronic structure and optical properties of stanene

In this paper, electronic structure and optical properties of two-dimensional stanene are studied in the absence and also in the presence of external electric fields. Calculations are based on density functional theory using the generalized gradient approximation performance by Siesta code. Stanene, regardless of the spin–orbit effect, has a band gap in order of meV. Studying the optical properties for two directions of light polarization, parallel and perpendicular to stanane’s plane, indicates that these properties are strongly dependent on the direction of light’s polarization. Applying external electric field on stanene cause a slight increase in the bandgap and also makes the structure more pronounce in the buckling. Moreover, it is also observed that external electric filed does not significantly affect the dielectric function. The slight effects are seen just in very low frequency of incident electromagnetic wave, due to which cut-off energy and static dielectric constant change.

Analysis of the Transmission Properties of Terahertz Wave in the Plasma Medium

Take Runge-Kutta exponential time differencing finite-difference time-domain (RKETD-FDTD) method, simulate numerically, analyze the transmission properties of terahertz (THz) wave in the non-magnetized plasma medium, and conclude the regulations of THz wave’s frequency domain transmission characteristics vary with the parameters like plasma electron density and collision frequency. The results show that when the incident electromagnetic wave frequency is lower than 0.1 THz, the transmission coefficient of the plasma slab has close relationship with the electromagnetic wave’s incident frequency, plasma electron density, and plasma collision frequency. The curve is of varied complex. When the incident electromagnetic wave frequency is between 0.1 and 10 THz band, the plasma slab has good transmission characteristics and its transmission coefficients are close to 0 dB. The transmission coefficient is almost not related to the electromagnetic wave incident frequency, the plasma electron density, and the plasma collision frequency. Analysis of these features will help further to apply THz in anti-plasma stealth, biological detection, transport safety checks, and other valuable areas.

Collisional, Nonuniform Plasma Sphere Scattering Calculation by FDTD Employing a Drude Model

In a collisional plasma, the collision frequency between electrons and neutrals may be equal to or greater than incident electromagnetic wave frequency. The complex permittivity can not represent the dielectric property of the plasma perfectly used in the finite difference in time domain (FDTD). Drude model is adopted to characterize a collisional plasma. Using a commercial FDTD package, XFDTD 6.0, the electromagnetic scattering of plasma sphere is calculated. By comparison with Mie method, Drude mode is proven to be suitable. Radar cross-section (RCS) of nonuniform plasma spheres and conductor spheres coated by plasma layer are calculated.