Diffraction Of Electromagnetic Waves Research Articles

A rigorous theory on electromagnetic diffraction by a planar aperture in a perfectly conducting screen

In this paper, we revisit the classic problem of diffraction of electromagnetic waves by an aperture in a perfectly conducting plane. We formulate the diffraction problem using a boundary integral equation that is defined on the aperture using Dyadic Green’s function. This integral equation turns out to align with the one derived by Bethe using fictitious magnetic charges and currents. We then investigate the boundary integral equation using a saddle point formulation and establish the well-posedness of the boundary integral equation, including the existence and uniqueness of the solution in an appropriately defined Sobolev space.

A mathematical study of electromagnetic waves diffraction by a slit in non-thermal plasma

A mathematical study of electromagnetic waves diffraction by a slit in non-thermal plasma

Application of Borehole Geophysical Prospecting Method in Pile Foundation Detection of Existing Buildings

It is particularly important to find out the pile foundation of existing buildings for building safety protection and engineering construction safety during the development and utilization of urban underground space. As a non-destructive, efficient and economic method, the borehole geophysical techniques such as magnetic gradient method, ground penetrating radar method and parallel seismic test method are used to detect the pile foundation of existing buildings, which have obvious advantages. According to the combined abnormal characteristics such as "strong magnetic anomaly, electromagnetic wave in-phase axis change and diffraction wave anomaly at the pile end, P-wave velocity variation", the pile foundation length can be judged.

ELECTRODYNAMIC ALGORITHM FOR CALCULATING AN ANTENNA ARRAY BASED ON AN INTEGRAL REPRESENTATION FOR A COMMON REGION FIELD

The article is devoted to the study of a new approach in the integral equation method. The solution of the electrodynamic problem is carried out based on conditional selection of the common region in the entire area of electromagnetic field definition. In our previous publications, we proposed an integral equation method based on the selection of a penetrating region for solving the problem of electromagnetic wave diffraction on a periodic structure. The legality of using the proposed approach and its equivalence with the previously proposed approach are shown. In this article, the calculation of an infinite antenna array scanning in the H-plane is carried out. The numerical convergence of the proposed approach for reflection coefficients R10 with increasing order of truncation of the system of linear algebraic equations was studied. It was found that the modulus of the reflection coefficient coincides with the exact solution at M = 1 and subsequently does not change with the growth of M. While the phase of the reflection coefficient changes with the growth of M and when M˃11, the difference between the phase value of the exact solution and the calculated value is less than 1%. That is, for the case of scanning in the H-plane, good convergence of the problem solution was obtained for all scanning angles. The aim of the work is to show that for a certain class of problems of applied electrodynamics, it is possible to apply the integral equation method based on the selection of a common region. The methodology consists in the conditional allocation of a common region in the entire area of electromagnetic field determination and the application of the integral equation method. The scientific novelty is that we have shown the correctness of using a new approach based on the selection of the field of the common region for the calculation of periodic structures in the H-plane. The conclusions can be formulated as follows. It is shown that two approaches can be used to calculate the antenna array in the H-plane: the first based on the selection of the integral representation for the full field of the penetrating region, the second based on the selection of the integral representation for the full field of the common region.

Мodel of diffraction of electromagnetic waves on explosive objects

A model of electromagnetic wave diffraction on an explosive object without metal structural substances is proposed. The properties of the materials of the most common anti-personnel mines were analyzed and it was established that their shell is dielectric, and explosive substances are divided into two groups depending on their dipole moment. In particular, the explosive substances such as hexogen, pentaerythritol tetranitrate, and mercury fulminate with zero dipole moment and according to their electromagnetic properties, they belong to ideal dielectrics. The explosives trinitrotoluene, tetryl, lead trinitroresorcinate, and lead azide should be considered as low-loss dielectrics. An electrodynamic model was built to calculate the reflection coefficients and the passage of electromagnetic plane waves of the microwave range through the multilayer structure of an explosive object. To determine the equivalent wave resistance of the multilayer structure of an explosive object, the use of the theory of long lines is proposed. It is established that for microwave radiation, the layers of the case of explosive objects made of dielectric substances can be neglected due to their small thickness. The modeling results show that most anti-personnel mines have a low reflection coefficient, which makes them difficult to detect, but at the same time increases the amount of energy that can pass deep into the body of the explosive substance. It has been shown that explosive objects with dipole explosive substances are capable of absorbing electromagnetic radiation energy. The obtained results allow us to qualitatively assess the susceptibility of explosive substances to their remote detonation by irradiation with powerful pulses of electromagnetic radiation in the microwave range.

Terahertz 3D point cloud imaging for complex targets.

The reconstruction of complex targets using terahertz technology is often hindered by diffraction and interference of electromagnetic waves, leading to the loss of fine target details. In this research article, we have introduced a terahertz synthetic aperture radar (SAR) imaging method that integrates an iterative closest point (ICP) algorithm, referred to as SAR-ICP, to achieve accurate reconstruction of intricate target structures. To accomplish this, multiple sets of point cloud data are acquired by varying the illumination viewpoint. The ICP algorithm is then employed to align and fuse these datasets, resulting in the generation of high-quality three-dimensional (3D) images. The experimental results validate the effectiveness of the proposed SAR-ICP method. The information entropy of the reconstructed 3D image using the SAR-ICP is approximately 0.05 times that of the conventional SAR method, indicating a superior image quality. In the future, we anticipate the widespread application of this method in areas such as security inspection, non-destructive testing, and other complex scenarios.

Diffraction of Electromagnetic Waves on Graphene Metasurfaces in the Terahertz Frequency Range

Diffraction of Electromagnetic Waves on Graphene Metasurfaces in the Terahertz Frequency Range

A Mathematical Model and Results of Analysis of Nonlinear Diffraction of Electromagnetic Waves by Magnetic Nanogratings

A Mathematical Model and Results of Analysis of Nonlinear Diffraction of Electromagnetic Waves by Magnetic Nanogratings

TE-Polarized Electromagnetic Wave Diffraction by a Circular Slotted Cylinder

The problem of diffraction of a TE-polarized electromagnetic wave by a circular slotted cylinder is investigated. The boundary value problem in question for the Helmholtz equation is reduced to an infinite system of linear algebraic equations of the second kind (SLAE-II) using integral summation identities (ISI). A detailed study of the matrix operator of the problem is performed and its Fredholm property in the weighted Hilbert space of infinite sequences is proven. The convergence of the truncation method constructed in the paper for the numerical solution of SLAE-II is justified and the results of computations are presented and discussed, specifically considering the determination of resonance modes.

Refinement of the Heuristic Solution for the Problem of TE-Polarized Electromagnetic Wave Diffraction on a Half-Plane with Two-Sided Impedance Boundary Conditions

A technique for obtaining refined heuristic solutions for problems with electromagnetic wave diffraction by scatterers with non-ideal boundary conditions is proposed. Based on the method of fundamental components for the problem of TE-polarized wave diffraction on a “semitransparent” half-plane with two-sided impedance boundary conditions, an improved heuristic solution for the scattered field is obtained by replacing the primary heuristic formula. A quantitative and qualitative assessment of the accuracy of the heuristic relationship is carried out as well as a physical interpretation of the rigorous solution based upon them. A classification of heuristic solutions is proposed according to the purpose of their application in practical problems.

Diffraction of electromagnetic waves on one-dimensional diffraction gratings formed by slots in an absolutely absorbing screen

Two-sided approximate boundary conditions are obtained for an absolutely absorbing ("black") layer lying on a multilayer dielectric. Paired summation equations (PSEs) are obtained for the tangent components of the electric and magnetic field strengths at the slots. These equations are solved by the Galerkin method with basis functions in the form of Chebyshev and Legendre polynomials. The resulting system of linear algebraic equations has fast internal convergence. To control the accuracy of the obtained solution, a dual problem is solved --- a lattice of "black stripes". In this case, the unknowns in the PSU are the current density on the strips. The properties of lattices are analyzed. Keywords: approximate boundary conditions, "black" screen, diffraction grating, pair summation equations, Galerkin's method.

Diffraction of a Plane Electromagnetic Wave by a Circular Aperture in a Conducting Screen of Finite Thickness

Diffraction of a Plane Electromagnetic Wave by a Circular Aperture in a Conducting Screen of Finite Thickness

A Rigorous Solution to Electromagnetic Wave Diffraction by Junctions of Impedance and Semitransparent Surfaces

Recent studies of surface-wave-based waveguides for terahertz (THz) imaging and spectroscopy have displayed some interest in investigating surface-wave diffraction by junctions of surfaces with different boundary conditions. Generally, many practically applicable surfaces for THz surface waveguides can be described using nontransparent or semitransparent impedance boundary conditions. In this communication, we find rigorous solutions to electromagnetic wave diffraction by the junction of a nontransparent impedance wedge and a semitransparent half-plane, as well as the junction of two semitransparent half-planes. Generalized semitransparent boundary conditions characterize these semitransparent surfaces.

Research on site selection of agricultural internet of things nodes based on rapid terrain sampling

With the development of Internet of Things (IoT) technology, modern agriculture is moving in the direction of 4.0. The Agricultural IoT is inseparable from wireless communication. However, in traditional agricultural IoT router and gateway site selection, the influence of the actual terrain on transmission loss is not considered, which results in node power wastage and increased maintenance costs. Based on a multi-sensor fusion algorithm, a fast terrain sampler is designed in this study to collect point-cloud data of the experimental site terrain. A reasonable objective function is then designed under the premise of consideration of the electromagnetic wave free-space and diffraction losses, and the locations of the routers and gateway are optimized based on k-means and particle swarm optimization (PSO) algorithm. Simulations show that the running time of the PSO algorithm is very sensitive to the changes in the execution parameters, and the improved PSO algorithm converges faster than the genetic algorithm (GA) in all three initialization methods. After collecting field terrain data, five interpolation methods were compared, and the nearest-neighbor algorithm is used to obtain the terrain model. On-site collection of received signal-strength indication (RSSI) shows that the communication quality of the optimal point selected via this algorithm is significantly higher than those of nearby points. At the same time, it is proved that the RSSI data has serious discontinuities, so the traditional gradient descent method is not suitable for solving the objective function in this work. Therefore, the algorithm used herein is of great significance for the site selection of agricultural Internet of Things nodes. However, since there are many ways to calculate the diffraction loss, the objective function of this work still needs more correction studies. The tool proposed in this work can obtain a 3D model of farmland faster than traditional surveying and mapping methods. With future research, the 3D model may be applied to soil moisture analysis, rainfall and moisture direction inversion, and plant light exposure prediction.

Terahertz frequency selective surfaces using heterostructures based on two-dimensional diffraction grating of single-walled carbon nanotubes

ABSTRACT For single-walled carbon nanotubes (SWCNTs) with a length of 1–50 µm, the surface plasmon-polariton (SPP) resonance is within the terahertz frequency range; therefore, SWCNT lattices can be used to design frequency-selective surface (FSS). A numerical model of electromagnetic wave diffraction on a two-dimensional periodic SWCNT lattice can be described by an integro-differential equation of the second-order with respect to the surface current along SWCNT. The equation can be solved by the Bubnov–Galerkin method. Frequency dependence of reflecting and transmitting electromagnetic waves for FSSs near the SPP resonance is studied numerically. It is shown that the resonances are within the lower-frequency part of the terahertz range. We also estimate the relaxation frequency of an individual SWCNT and demonstrate the applicability of the Kubo formula for graphene conductivity to array of strips similar in size to SWCNTs under consideration.

A fundamental approach: E-polarized electromagnetic wave diffraction by two dimensional arbitrary-shaped objects with impedance boundary condition

Abstract In the present study, a new methodology in computational electromagnetics is developed for two-dimensional arbitrarily-shaped objects with impedance boundary conditions. The proposed approach investigates the E-polarized electromagnetic diffraction by a two-dimensional object with the Leontovich boundary condition. The scattered electric and magnetic fields are expressed as the convolution integral of the corresponding Green’s function and the current induced on the obstacle surface. After obtaining integral equations by applying the boundary condition, the integral equations are solved as in the case of the method of auxiliary sources (MAS) which is a well-known method in computational electrodynamics. The results are compared with first, different methods such as the method of moments (MoM), orthogonal polynomials (OP), and second, different boundary conditions such as Dirichlet, Neumann, and fractional boundary conditions. Some results are also obtained for the different shape scatterers at some values of the surface impedance.

Study of electromagnetic wave diffraction by a dielectric coating and metal diaphragm over an endless waveguide antenna array

A study of the diffraction of an electromagnetic wave on a dielectric coating with a diaphragm over an infinite waveguide antenna array has been carried out. The metal diaphragm is located at some distance from the surface of the antenna array. The influence of the geometric dimensions of a metal diaphragm and its distance from the grating surface on the modulus of the reflection coefficient of the incident wave in waveguides is investigated. Dielectric coatings with different values of the dielectric constant are considered.

All-Dielectric Tunable Terahertz Metagrating for Diffraction Control.

Recently, tunable metagratings have attracted substantial attention in manipulating the diffraction of electromagnetic waves with considerable flexibility, but they are usually limited to inherent ohmic loss due to the metal layers. The all-dielectric schemes can address this issue, but its design and optimization remain challenging in the terahertz regime, especially in the 6G communication window. In this work, an all-dielectric tunable terahertz metagrating is demonstrated in theoretical and experimental investigations. The metagrating operating in the 6G communication window bends the electromagnetic waves beam into the T-1 diffraction order by optimizing the unit cell. In the experiments, more than 72.46% of the transmitted energy is concentrated in the desired diffraction order for p-polarized light and more than 66.60% for s-polarized light, which agrees well with the theoretical design. The tunability by angular deflection is reported in this all-dielectric metagrating. Then, based on the all-dielectric metagrating arrays, a metalens with numerical aperture of NA = 0.39 at 0.14 THz is demonstrated. The subwavelength scale focal spot is obtained as 2.0 mm × 2.0 mm with the focusing distance of 117.8 mm. Imaging capability of the metalens is performed utilizing the transmission imaging manner. The measured and anticipated results are satisfactorily congruous with one another, which could validate our design. This work paves the way toward designing highly efficient and tunable devices with potential applications in terahertz communications, sensors, and super-resolution imaging.

Исследование влияния интерференции в кювете на поглощение газа, измеренное с использованием метода нестационарной ТГц спектроскопии

Cell is the important part of the terahertz (THz) spectrometer designed to study the chemical composition of multicomponent gas mixtures, since it is used for supporting the optimal pressure of the gaseous sample. However, the reflection of electromagnetic waves from the cell windows leads to standing-wave interference, which can distort the measured spectrum. Mathematical modeling of the impact of the interference on the measured spectrum was carried out in the paper. The cell was treated as a Fabry-Perot cavity with infinite flat dielectric mirrors. Diffraction of electromagnetic waves, as well as the frequency dependences of the source power and the detector sensitivity, was taken out of the scope of the considered model. The two effects of the interference were described. The interference not only determined the slow frequency dependence of the cell transmission spectrum, but also affected the profile of the gas absorption lines reconstructed from the cell spectrum in accordance with the Bouguer-Lambert-Beer law. Both the processing of the measured spectrum and the setup calibration required for accurate quantitative measurements could be complicated by the effects. However, methods of modulation and non-stationary spectroscopy enabled to eliminate the first effect, they were possibly ineffective to eliminate the second one. Presumably, the detected distortion of the contour of the absorption lines was caused by a shift in the interference pattern and, accordingly, a change in the reflection coefficient of the cell due to the anomalous dispersion of the sample. The correlation of the distortions with the derivatives of the transmission spectrum of the empty cell was revealed. The obtained results could be used to develop algorithms for calibrating the measuring setup and processing experimental data.

Application of the method of continued boundary conditions to the solution of the problems of wave diffraction on various types of scatterers with complex structure

The article considers the application of the method of continued boundary conditions to the two-dimensional problem of diffraction of electromagnetic waves by a dielectric body with a cross section of complex geometry and to the problem of diffraction by a Janus sphere in the form of a permeable sphere partially covered by an absolutely soft or an absolutely rigid spherical screen. The results of calculating the scattering pattern for a large set of bodies of different geometry, including fractal-like scatterers, are obtained. It is illustrated that in the case of a smooth body boundary, the algorithm based on the Fredholm equations of the 1st kind makes it possible to obtain results with greater accuracy than for equations of the 2nd kind. The correctness of the method was confirmed by verifying the implementation of the optical theorem for various bodies and by comparing with the results of calculations obtained by other methods.