Plane Wave Source Research Articles

Electromagnetic Response of a Uniformly Moving Resistive Sheet

ABSTRACTBy using the finite‐difference time‐domain (FDTD) method and a two‐port network model, this letter investigates the response of a uniformly moving resistive sheet to illuminating electromagnetic plane waves, at normal incidence. The numerical Doppler frequency shifts and scattering matrix are matched with curve‐fitting expressions. The effects of motion on the impedance matrix, the chain matrix, and the continuity equations are analyzed. Moreover, the total energy of the transferred and reflected waves are studied for the cases of a resistive sheet moving toward or away from the plane wave source.

Analysis of Moving Bodies with a Direct Finite Difference Time Domain Method

This paper proposes an original and thorough analysis of the behavior of electromagnetic waves in the presence of moving bodies by using the finite difference time domain (FDTD) method. Movements are implemented by changing positions of the objects at each time step, through the classical FDTD time loop. This technique is suitable for non-relativistic speeds, thus for most encountered problems in antennas and propagation domain. The numerical aspects that need to be considered are studied. Then, different bodies in motion are examined: plane wave source with matching resistors, observation point, inclined partially reflecting surface (PRS), line source, and metallic cylinder illuminated by a plane wave. The results are compared with those of special relativity which are considered as the references. Some aspects of special relativity are present in the direct FDTD approach, such as the independence of the velocity of electromagnetic wave propagation with the speed of the source and Lorentz local time (with a different physical interpretation). It is shown that the amplitude of the electric field for a moving plane wave source does not increase with the speed of motion, if the impedance of the source is small. Moreover, for a moving scattering metallic wire, one can observe a phenomenon similar to shock waves.

Electromagnetic analysis of moving structures in a moving reference frame

AbstractIn this work, the finite‐difference time‐domain (FDTD) method is employed to study electromagnetic problems with moving bodies in a moving system. The proposed approach consists in modeling objects with time‐varying positions and using the direct discretization of Maxwell's equations in space and time domains. Doppler effects are investigated for problems with moving observer, source, or reflector, in a moving frame. A distinction is also made between a high‐impedance or low‐impedance plane wave source in motion. The full‐wave electromagnetic simulations are compared with closed‐form equations that agree with wave theory. The proposed analysis shows that, for Doppler radars used every day, the motion of the Earth relative to the Cosmic Microwave Background has a negligible effect and only relative motions in the Earth frame are relevant.

Identification of spectrum of secondary acoustic-gravity waves in the middle and upper atmosphere in a high-resolution numerical model

Considerable attention has recently been paid to the study of so-called “secondary” acoustic-gravity waves (AGWs) that arise as a result of instability and nonlinear interactions of “primary” wave modes propagating from atmospheric sources, among themselves, and with the mean flow. In this paper, for the first time, the horizontal spatial spectra of primary and secondary AGWs are separated at fixed altitude levels in the middle and upper atmosphere at different time moments, which are simulated using a three-dimensional nonlinear high-resolution model AtmoSym. It is shown that in a short time after switching on the plane wave source at the lower boundary of the model, the spectrum consists of a peak corresponding to primary AGW and quasi-white noise generated by random atmospheric disturbances and the numerical model. Later, secondary peaks appear in the spectra at horizontal wave numbers, which are multiples of the wave numbers of primary AGW. The proposed separation of the spectra of primary and secondary AGWs makes it possible to estimate the relative contribution of secondary AGW at different altitudes, at different times, and with different stability of background temperature and wind profiles in the atmosphere.

Выделение спектра вторичных акустико-гравитационных волн в средней и верхней атмосфере в численной модели высокого разрешения

Considerable attention has recently been paid to the study of so-called “secondary” acoustic-gravity waves (AGWs) that arise as a result of instability and nonlinear interactions of “primary” wave modes propagating from atmospheric sources, among themselves, and with the mean flow. In this paper, for the first time, the horizontal spatial spectra of primary and secondary AGWs are separated at fixed altitude levels in the middle and upper atmosphere at different time moments, which are simulated using a three-dimensional nonlinear high-resolution model AtmoSym. It is shown that in a short time after switching on the plane wave source at the lower boundary of the model, the spectrum consists of a peak corresponding to primary AGW and quasi-white noise generated by random atmospheric disturbances and the numerical model. Later, secondary peaks appear in the spectra at horizontal wave numbers, which are multiples of the wave numbers of primary AGW. The proposed separation of the spectra of primary and secondary AGWs makes it possible to estimate the relative contribution of secondary AGW at different altitudes, at different times, and with different stability of background temperature and wind profiles in the atmosphere.

Improved accuracy of plane-wave electromagnetic modelling by application of the total and scattered field decomposition and perfectly matched layers

SUMMARY In 2-D magnetotelluric modelling, the standard application of Dirichlet boundary conditions (BC) may severely diminish the solution accuracy, because the unknown scattered part of the electromagnetic field is erroneously reflected at the domain boundary. Therefore, we adapt the total and scattered field decomposition (TSFD) to geophysical modelling, enabling the application of fully absorbing boundary methods, here perfectly matched layers (PML), to the scattered field. Our novel TSFD divides the modelling domain into two regions. In the total-field region containing the area of interest, the solution is computed for the total field. In the scattered-field region containing the boundaries, the solution is obtained for the scattered field, which is fully absorbed by PML at the boundaries. The plane-wave source is excited at the TSFD interface between both regions. Thus, boundary reflections are eradicated leading to superior solution accuracy, and boundaries can be placed closer to the receivers, shrinking the computational problem. Especially for challenging models with strong lateral changes, the solution accuracy of the TSFD is superior to that of the standard Dirichlet approach. Owing to the linearity of Maxwell’s equations, the inaccuracy introduced to the electric and magnetic fields by using Dirichlet BC can be expected to partly cancel out in the magnetotelluric transfer functions, for example the impedance tensor. In this work, we quantify this cancellation effect. The inaccuracy is less than typical measurement errors in the vast majority of apparent resistivity and phase data, even, when the primary fields are strongly inaccurate.

A TF/SF Plane Wave Source Condition for the Constraint-Preserving FVTD Method

A low-leakage total-field/scattered-field plane wave source condition capable of propagating at any incident angle is developed for a newly-developed DGTD-based FVTD method. This constraint-preserving FVTD method provides solutions up to any order of accuracy, preserves the divergence constraints imposed by Gauss' laws, and may be easily adapted to non-conformal and unstructured meshes. In order to implement the proposed plane wave source condition, several of the steps within the updating loop of the FVTD model, including the Riemann solvers and update equations, must be adapted to ensure the field variables always remain consistent (are consistently designated as either total or scattered fields). The proposed total-field/scattered-field technique is shown to provide numerical leakage errors at the level of machine precision (-300 dB) for second-, third-, and fourth-order constraint-preserving FVTD schemes.

Efficient and Robust Shadowing Determination for Mesh-Based Physical Optics Analysis

Visibility status determination for every mesh element/edge with respect to an illuminating source is routinely required in mesh-based physical optics (PO) methods, where the scatterer is represented by subwavelength sized elements. This article presents an optimally efficient shadowing determination algorithm for both plane wave and point source (Hertzian dipole) illumination of large-scale triangle meshes. It is based on a recursive multilevel field-of-view (image space) subdivision buffer approach, whereby a point’s status is determined by only checking against a small subset of elements. It is error-free and formulated to maintain efficiency for inhomogeneous meshes and grazing incidence, which result in concentration of projected elements in small areas of the buffer plane. A key step is to separate the grazing and nongrazing parts of the mesh. Very challenging test cases affirm the algorithm’s expected optimal and robust linear computational cost scaling of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {O}(N)$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> denotes the number of mesh elements. For fixed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> , almost constant runtimes under extreme illumination and mesh variations, further demonstrate robustness.

Study on the pulse characteristics of cloaked cylindrical objects with pulse radar technique

This paper presents the study of interaction between the cloaked cylindrical object and electromagnetic waves. The 2D scattering width of the cylindrical objects with and without the metasurface is numerically and analytically investigated with the design frequency of 3 GHz. The electromagnetic waves in the presence of the dielectric and metallic of the cylindrical objects with and without metasurface are numerically characterized by the plane waves. Instead of the plane wave source, a resistive antenna whose modulated frequency of 3 GHz is designed and utilized to radiate a short pulse. With the designed resistive dipole antenna, the several scenarios in the far and near region are numerically explored with the conducting cylindrical object with and without the metasurface. The pulse characteristics, such as transmission coefficient, received spectrum, received pulse, and reflected pulse, are then intensively investigated with the conducting cylinder with and without the metasurface.

Wave-equation diffraction imaging using pseudo dip-angle gather

Diffraction images can directly indicate local heterogeneities, such as faults, fracture zones, and erosional surfaces, that are of high interest in seismic interpretation and unconventional reservoir development. We have adopted a new tool called pseudo dip-angle gather (PDAG) for imaging diffractors using the wave equation. PDAG has significantly lower computational cost compared to the classic dip-angle gather (DAG) due to the use of plane-wave gathers, a fast local Radon transform algorithm, and a one-side decomposition assumption. Pseudo dip angle is measured from the vertical axis to the bisector of the plane-wave surface incident angle and scattered wave-propagation angle. PDAG is generated by choosing the zero lag of the correlation of the plane-wave source wavefields and the decomposed receiver wavefields. It reveals diffraction and reflection patterns similar to DAG, that is, diffractions spreading as a flat event and reflections focused on a specular angle, whereas they may have dissimilar coverage for diffraction and different focused locations for reflection compared to that of DAG. A windowed median filter is then applied to each PDAG for extracting the diffraction energy and suppressing the focused reflection energy. In addition, the stacked PDAG can be used to evaluate the migration accuracy by measuring the flatness of the image gathers. Numerical tests on synthetic and field data sets demonstrate that our method can efficiently produce accurate results for diffraction images.

Optimization of gold square-shaped nanopillars arrays for high-efficiency optronics

Parametric optimization of gold (Au) square-shaped nanopillars (AuNPLs) arrays deposited on glass substrate (AuNPLs/glass) was performed through optical characteristics for high-performance optical detection and biosensing purpose from visible to very near-infrared spectral (0.5 ≤λ≤0.8μm). This is aimed at predicting optimum parameters which result in strong enhancement for next-generation optronic devices. The optimization parameters were limited to the AuNPLs height (H), the interslit distance (W1), and the slit width (W2) in investigating the optical characteristics of reflectance, transmittance, and absorption. In achieving this, the extraordinary surface plasmon resonance (SPR) mechanism was explored using 3D finite-differential time-domain (3D-FDTD) algorithm. Based on the periodical nature of the AuNPLs array, periodic boundary conditions (PBCs) and stretched coordinate perfectly matched layers (SCPML) boundaries were employed for the computation region with a plane wave source injection at normal incidence (θ=0°). The results revealed new insights on the AuNPLs/glass structure and might inspire potential applications such as photodetectors and biosensors with optimum device achieved by controlling H from 0.1 to 1.0μm while W1=0.25μm and W2=0.1μm are kept constants and spectroscopy with optimum device by controlling W1 from 0.1 to 1.0μm while H=0.4μm and W2=0.1μm are maintained constants. Besides, application of biosensor performs sensitivity (S) of 380.14 nm/RIU (nanometer/refractive index unit) and 377.32 nm/RIU with corresponding highest figure of merit (FOM) of 8.02 RIU−1 and 11.11 RIU−1 for H=400 nm and H=600 nm, respectively.

Incident Plane-Wave Source Formulations for Leapfrog Complying-Divergence Implicit FDTD Method

The commonly used unconditionally stable finite-difference time-domain (FDTD) methods such as alternating direction implicit (ADI)-FDTD, and its one-step formulation, leapfrog ADI-FDTD, have been found to violate the divergence condition of Gauss's law. The recently proposed leapfrog complying-divergence implicit (CDI)-FDTD not only addresses this problem, but also features many advantages, including unconditional stability, minimal floating-point operations and one-step leapfrog update. To further expand its application, this paper presents the incident plane-wave source formulations for leapfrog CDI-FDTD. Two stable and efficient formulations with different advantages are presented for introducing the far-zone plane-wave source into the FDTD problem space, namely, the scattered-field (SF) formulation and total-field / scattered field (TF/SF) formulation. To deal with the discontinuity and inconsistency across TF/SF boundaries, the fields on the boundaries need special treatments with careful modifications to ensure stability and proper plane-wave injection. Numerical results show that the incident fields can be effectively injected into the problem space with the stability of leapfrog CDI-FDTD maintained in both formulations. In addition, comparisons of radar cross sections computed using leapfrog CDI-FDTD, leapfrog ADI-FDTD and explicit FDTD with both SF and TF/SF formulations are presented. These demonstrate the advantages of leapfrog CDI-FDTD method in solving far-zone plane-wave source problems, including high efficiency, unconditional stability and complying divergence.

Physics-informed neural networks for imaging and parameter retrieval of photonic nanostructures from near-field data

In this paper, we develop a deep learning approach for the accurate solution of challenging problems of near-field microscopy that leverages the powerful framework of physics-informed neural networks (PINNs) for the inversion of the complex optical parameters of nanostructured environments. Specifically, we show that PINNs can be flexibly designed based on full-vector Maxwell’s equations to inversely retrieve the spatial distributions of the complex electric permittivity and magnetic permeability of unknown scattering objects in the resonance regime from near-field data. Moreover, we demonstrate that PINNs achieve excellent convergence to the true material parameters under both plane wave and point source (localized) excitations, enabling parameter retrieval in scanning near-field optical microscopy. Our method is computationally efficient compared to traditional data-driven deep learning approaches as it requires only a single dataset for training. Furthermore, we develop and successfully demonstrate adaptive PINNs with trainable loss weights that largely improve the accuracy of the inverse reconstruction for high-index materials compared to standard PINNs. Finally, we demonstrate the full potential of our approach by retrieving the space-dependent permittivity of a three-dimensional unknown object from near-field data. The presented framework paves the way to the development of a computationally driven, accurate, and non-invasive platform for the simultaneous retrieval of the electric and magnetic parameters of resonant nanostructures from measured optical images, with applications to biomedical imaging, optical remote sensing, and characterization of metamaterial devices.

Design and characterization of a three-dimensional anisotropic additively manufactured pentamode material.

A metamaterial of particular interest for underwater applications is the three-dimensional (3D) anisotropic pentamode (PM), i.e., a structure designed to support a single longitudinal wave with a sound speed that depends on the propagation direction. The present work attempts to experimentally verify anisotropic sound speeds predicted by finite element simulations using additively manufactured anisotropic 3D PM samples made of titanium. The samples were suspended in front of a plane wave source emitting a broadband chirp in a water tank to measure time of flight for wavefronts with and without the PM present. The measurement utilizes a deconvolution method that extracts the band limited impulse response of data gathered by a scanning hydrophone in a plane of constant depth behind the samples. Supporting material takes the form of finite element simulations developed to model the response of a semi-infinite PM medium to an incident normal plane wave. A technique to extract the longitudinal PM wave speed for frequency domain simulations based on Fourier series expansions is given.

Subwavelength probing of surface plasmons in magnetoplasmonic crystals

In this work, we report on near-field studying of propagating surface plasmons (SPs) in one-dimensional magnetoplasmonic crystals (MPCs) by aperture type scanning near-field optical microscopy (SNOM). Optical near-field around the aperture probe is used to drive SPs in the MPC locally. The SNOM signal represents the scattered intensity caused by the interaction of the SNOM probe near-field with the MPC. Scanning the MPC surface with polarization resolving of the scattered radiation shows decreasing of the intensity due to the SP excitation. The observed polarization dependence of the scattered SNOM signal is associated with the selective coupling of the near-field components of the SNOM probe with SPs. Finite-difference time-domain simulations reproduce the experimental SNOM signal. It is shown the excitation of SPs with symmetric (even parity) field distribution, which is forbidden for plane wave source at normal incidence.

Marchenko redatuming, imaging, and multiple elimination and their mutual relations

With the Marchenko method, it is possible to retrieve Green’s functions between virtual sources in the subsurface and receivers at the surface from reflection data at the surface and focusing functions. A macro model of the subsurface is needed to estimate the first arrival; the internal multiples are retrieved entirely from the reflection data. The retrieved Green’s functions form the input for redatuming by multidimensional deconvolution (MDD). The redatumed reflection response is free of internal multiples related to the overburden. Alternatively, the redatumed response can be obtained by applying a second focusing function to the retrieved Green’s functions. This process is called Marchenko redatuming by double focusing. It is more stable and better suited for an adaptive implementation than Marchenko redatuming by MDD, but it does not eliminate the multiples between the target and the overburden. An attractive efficient alternative is plane-wave Marchenko redatuming, which retrieves the responses to a limited number of plane-wave sources at the redatuming level. In all cases, an image of the subsurface can be obtained from the redatumed data, free of the artifacts caused by internal multiples. Another class of Marchenko methods aims at eliminating the internal multiples from the reflection data, while keeping the sources and receivers at the surface. A specific characteristic of this form of multiple elimination is that it predicts and subtracts all orders of internal multiples with the correct amplitude, without needing a macro subsurface model. Like Marchenko redatuming, Marchenko multiple elimination can be implemented as an MDD process, a double dereverberation process, or an efficient plane-wave oriented process. We have systematically examined the different approaches to Marchenko redatuming, imaging, and multiple elimination using a common mathematical framework.

Some Advances in Shooting-Bouncing-Rays Asymptotic Propagation Methodologies

We present an overview of some recent advances including work in progress in different shooting-bouncing-rays asymptotic techniques for electromagnetic modeling of reflection, transmission, and diffraction propagation phenomena. These propagation phenomena computations, coupled with antenna or plane wave source modeling, can cover a wide spectrum of electromagnetic field solutions that offer a versatile approach to modeling of electromagnetic structures and systems at high frequencies.

Empirical formulas for predicting the insertion loss behind wedges

Curves and semi-empirical formulas are presented that predict the diffraction field in the shadow zone behind an infinitely long wedge. They are less accurate than analytical solutions but they reduce the computational time by orders of magnitude. Therefore, they can be of practical interest for a range of applications that involve calculations of diffraction: around complex geometries with a large number of diffracting edges or when the calculation time is crucial. The empirical formulas are further modified to include (i) the effect of the ground on either side of the wedge, (ii) absorptive wedges, and (iii) diffraction by multiple edges. Finally, the family of curves and the semi-empirical formulas are extended to the illuminated regions around the wedge and for all wedge angles. In the cases presented, the proposed formulas are compared against established analytical solutions, as well as available experimental data. Compared to existing empirical formulas, the empirical formulas presented here can be applied to all types of incident sound: coming from plane wave sources, line sources, point sources, both omni-directional and directional. Furthermore, they are applicable for all wedge angles. Finally, they are straightforward in their application.

Prediction of acoustic wave transmission features of the multilayered plate constructions: A review

This study collects all of the existent papers in the field of acoustic transmission across multilayered plate constructions. Herewith, a comprehensive source is proposed wherein approximately 410 references are reviewed and described from the first [Formula: see text] to [Formula: see text]. In the first part, in addition to the presentation of a complete explanation about the importance of the acoustic analysis of these structures, appropriate formulations are also provided. Furthermore, an overview of the thematic correspondent is carried out. Since the type of material used in these constructions can be very important in sound insulation, the significance of this subject is remarked. The papers are then classified based on their acoustic excitation fields containing plane wave, diffuse, random, and point source. After analyzing the research approaches according to different environmental properties, the articles are ordered based on their boundaries as finite and infinite. To present reliable outcomes, it is necessary to investigate a proper theory proportional to the structure’s thickness. Herewith, this issue is also discussed in detail. The review is also expanded to focus on the different vibroacoustic solutions. Before concluding remarks, the authors' research works are presented wherein either optimization algorithms or control techniques improve the acoustic performance of these structures.

Inverse design method of microscatterer array for realizing scattering field intensity shaping

It is a novel and interesting idea to inversely design the scattering structure with the desired scattering field intensity distribution in a given target area as the known information. The inverse design method proposed in this paper does not need to be optimized, and the spatial distribution and dielectric constant distribution of the micro-scatterer array can be quickly analytically calculated according to the desired scattering field intensity in the target area. First, based on the spatial Fourier transform and angular spectrum transformation, the plane wave sources required in all directions are inversely obtained from the electric field intensity distribution required in the target area. Then, based on the theory of induced source, a method of irradiating the array of all-dielectric micro-scatterers with incident electromagnetic field to generate the required plane wave source is proposed. The scattering fields generated by these micro-scatterers will be superimposed on the target area to achieve the desired scattering field strength intensity. Finally, according to the proposed inverse design theory model, a specific three-dimensional (3D) design is carried out. In the 3D example, we study the scattering field intensity distribution of the point-focused shape of the square surface target area, and show an all-dielectric micro-sphere distribution design. Its spatial distribution and permittivity distribution are both obtained through the rapid analytical calculation of the desired scattered field intensity shape in the target area. Finally, based on the principle of linear superposition, we quickly and easily generate the complex shapes of “I”, “T”, and “X” in the target area. The satisfactory results of full-wave simulation show that the proposed inverse design method is effective and feasible.