Total Electromagnetic Field Research Articles

Fast Full-Wave Electromagnetic Forward Solver Based on Deep Conditional Convolutional Autoencoders

This letter proposes a novel deep learning (DL) based fast solver for the electromagnetic forward (EMF) process. This proposed fast full-wave solver for EMF process is designed based on the deep conditional convolutional autoencoder (DCCAE), consisting of a complex-valued deep convolutional encoder network and its corresponding complex-valued deep convolutional decoder network. The encoder network makes use of the input consisting of the incident electromagnetic (EM) wave and the contrast (permittivities) distribution of the target domain, while the corresponding decoder network predicts the total EM field illuminated by the input incident EM wave. The training of the proposed DCCAE solver for EMF is merely based on the simple synthetic dataset. Thanks to its strong approximation capability, the proposed DCCAE can realize the prediction of the EM field of target domain by using the incident EM field and the distribution of contrasts (permittivities). Therefore, compared with conventional methods, the EMF problem could be solved with higher accuracy and the significant reduced computation time. Numerical examples have illustrated the feasibility of the newly proposed DL-based EMF solver. The newly proposed DL-based EMF solver presents its excellent performance for the real-time online application.

PyCharge: An open-source Python package for self-consistent electrodynamics simulations of Lorentz oscillators and moving point charges

PyCharge is a computational electrodynamics Python simulator that can calculate the electromagnetic fields and potentials generated by moving point charges and can self-consistently simulate dipoles modeled as Lorentz oscillators. To calculate the total fields and potentials along a discretized spatial grid at a specified time, PyCharge computes the retarded time of the point charges at each grid point, which are subsequently used to compute the analytical solutions to Maxwell's equations for each point charge. The Lorentz oscillators are driven by the electric field in the system and PyCharge self-consistently determines the reaction of the radiation on the dipole moment at each time step. PyCharge treats the two opposite charges in the dipole as separate point charge sources and calculates their individual contributions to the total electromagnetic fields and potentials. The expected coupling that arises between dipoles is captured in the PyCharge simulation, and the modified radiative properties of the dipoles (radiative decay rate and frequency shift) can be extracted using the dipole's energy at each time step throughout the simulation. The modified radiative properties of two dipoles separated in the near-field, which require a full dipole response to yield the correct physics, are calculated by PyCharge and shown to be in excellent agreement with the analytical Green's function results (<0.2% relative error, over a wide range of spatial separations). Moving dipoles can also be modeled by specifying the dipole's origin position as a function of time. PyCharge includes a parallelized version of the dipole simulation method to enable the parallel execution of computationally demanding simulations on high performance computing environments to significantly improve run time. Program summaryProgram Title: PyChargeCPC Library link to program files:https://doi.org/10.17632/77d5vt43h9.1Developer's repository link:https://github.com/MatthewFilipovich/pychargeLicensing provisions: GPLv3Programming language: Python 3.7 or newerSupplementary material: Documentation is available at pycharge.readthedocs.io. The PyCharge package and its dependencies can be installed from PyPI: pypi.org/project/pychargeNature of problem: Calculating the electromagnetic fields and potentials generated by complex geometries of point charges, as well as the self-consistent simulation of Lorentz oscillators.Solution method: PyCharge calculates the individual contributions from each point charge in the system to calculate the total electromagnetic fields and potentials, and computes the dipole moment of the Lorentz oscillators at each time step by solving their governing equation of motion.Additional comments including restrictions and unusual features: The parallel simulation method is implemented using the mpi4py package [1].

Measurement and Simulation-Based Exposure Assessment at a Far-Field for a Multitechnology Cellular Site up to 5G NR

5G is expected to be the dominant technology for mobile networks in the coming years, but there is concern about the increase in the total electromagnetic field radiation levels due to the deployment of the 5G technology. This paper presents an exposure assessment of electromagnetic field radiation on humans from single base station of a mobile network serving in dense, urban, suburban, and rural area scenarios for single-site transmission with multi-technology, including 2G, 3G, 4G, IoT, and 5G which have recently been deployed. This assessment is performed using simulation to predict the received signal levels and to calculate the related power densities for a typical single site under operating field configurations and settings for each technology. Field measurements were performed using a drive test tool to validate and calibrate the simulation results. The results show the total exposure ratio was very low compared to the international standard exposure limits, and the results show the contribution from each technology for these spesfic sites used in this study.

Application of Wigner Distribution Function for THz Propagation Analysis.

The construction of a transmission line (TL) for a wide tunable broad-spectrum THz radiation source is not a simple task. We present here a platform for the future use of designs of the TL through our homemade simulations. The TL is designed to be a component of the construction of an innovative accelerator at the Schlesinger Family Center for Compact Accelerators, Radiation Sources and Applications (FEL). We developed a three-dimensional space-frequency tool for the analysis of a radiation pulse. The total electromagnetic (EM) field on the edge of the source is represented in the frequency domain in terms of cavity eigenmodes. However, any pulse can be used regardless of its mathematical function, which is the key point of this work. The only requirement is the existence of the original pulse. This EM field is converted to geometric-optical ray representation through the Wigner transform at any desired resolution. Wigner’s representation allows us to describe the dynamics of field evolution in future propagation, which allows us to determine an initial design of the TL. Representation of the EM field by rays gives access to the ray tracing method and future processing, operating in the linear and non-linear regimes. This allows for fast work with graphics cards and parallel processing, providing great flexibility and serving as future preparation that enables us to apply advanced libraries such as machine learning. The platform is used to study the phase-amplitude and spectral characteristics of multimode radiation generation in a free-electron laser (FEL) operating in various operational parameters.

Space-time computation and visualization of the electromagnetic fields and potentials generated by moving point charges

We present a computational method to directly calculate and visualize the directional components of the Coulomb, radiation, and total electromagnetic fields, as well as the scalar and vector potentials generated by moving point charges in arbitrary motion with varying speeds. Our method explicitly calculates the retarded time of the point charge along a discretized grid, which is then used to determine the fields and potentials. The computational approach, implemented in python, provides an intuitive understanding of the electromagnetic waves generated by moving point charges and can be used as a pedagogical tool for undergraduate and graduate-level electromagnetic theory courses. Our computer code, freely available for download, can also approximate complicated time-varying continuous charge and current densities, and can be used in conjunction with grid-based numerical modeling methods to solve real-world computational electromagnetics problems such as experiments with high-energy electron sources. We simulate and discuss several interesting example applications and lab experiments including electric and magnetic dipoles, oscillating and linear accelerating point charges, synchrotron radiation, and Bremsstrahlung.

Lightning return stroke electromagnetic field and energy at close distance by using 3D FDTD simulation

In this paper, the lightning return stroke electromagnetic field at close distance is calculated by the way of transmission line (TL) model and full-wave three-dimensional electromagnetic field simulation software XFDTD, which is based on finite-difference time-domain (FDTD) method. The evolution of distributions of electric field and magnetic field are summarized in the study. Furthermore, the total electromagnetic field and major components are analyzed to clarify the electromagnetic hazard from lightning electromagnetic pulse (LEMP). Then the temporal and spatial distribution characteristic of Poynting vector of the electromagnetic environment is shown to expound the energy distribution of LEMP at close distance. The results based on the analyses of field strength and Poynting vector show that the distribution of electric field, magnetic field and Poynting vector at close distance is akin to multilayered cylinder, and LEMP in the region characterized by large amplitude, transient behavior and high electromagnetic energy is a potential threat to adjacent electronic equipments. Moreover, engineering basis concerning LEMP protection and electromagnetic compatibility (EMC) design in the region closed to the return stroke point can be provided by the synthetical analysis of LEMP.

On transverse radiation pressure cross-sections in the generalized Lorenz–Mie theory and their numerical relationship with the dipole theory of forces

The Rayleigh limit of the generalized Lorenz–Mie theory (GLMT) and its relationship with the dipole theory of forces is investigated for transverse radiation pressure cross-sections and optical forces exerted over very small particles. If, at one hand, the GLMT provides interesting insights in terms of a multipole expansion and becomes restricted to contributions from (n=1)-partial waves, on the other hand the dipole theory incorporates the total electromagnetic fields and their interaction with an electric dipole. Simulations reveal an extreme accuracy between both approaches up to 3000 decimal places, thus reinforcing the conjecture that the Rayleigh limit of the GLMT might exactly identify with the traditional dipole theory of forces, although mathematically such identification remains to be uncovered.

An Inverse Mixed Impedance Scattering Problem in a Chiral Medium

An inverse scattering problem of time-harmonic chiral electromagnetic waves for a buried partially coated object was studied. The buried object was embedded in a piecewise isotropic homogeneous background chiral material. On the boundary of the scattering object, the total electromagnetic field satisfied perfect conductor and impedance boundary conditions. A modified linear sampling method, which originated from the chiral reciprocity gap functional, was employed for reconstruction of the shape of the buried object without requiring any a priori knowledge of the material properties of the scattering object. Furthermore, a characterization of the impedance of the object’s surface was determined.

Electromagnetic Field Imaging in Arbitrary Scattering Environments

In this article, we propose a method to reconstruct the total electromagnetic field in an arbitrary two-dimensional scattering environment without any prior knowledge of the incident field or the permittivities of the scatterers. However, we assume that the region between the scatterers is homogeneous and that the approximate geometry describing the environment is known. Our approach uses field measurements and a compressive sensing inspired algorithm to estimate the incident field and the tangential electric and magnetic fields on the scatterers' surfaces. These estimates are then used to predict the field everywhere using Huygens' principle. Further, we identify the best measurement locations in the environment, which reduces the estimation error to approximately half of the error obtained when using random locations. We show that in an indoor scenario with up to four scattering objects, the total electric field is recovered with less than 10% error when the number of measurements is just 0.3 times the number of unknowns in which the problem is formulated. The formulated problem is solved using `Total field - Compressive sensing based subspace optimization method' - an algorithm that leverages the sparsity of the tangential fields in known transformation domains to obtain an optimal solution.

Comparison of Average Total EMF Exposure for Microcell/Macrocell Topologies Using Novel Methodology Based on Operational Network Measurements

Two outdoor base station macrocell/microcell topologies in operational Global System for Mobile communications (GSM) and Universal Mobile Telecommunications Service (UMTS) networks are compared with respect to average Electromagnetic Field (EMF) exposure over population in an area. A novel joint metric is used, accounting for exposure from both base stations and user equipment. The demonstrated method tends to use as much data as possible that can be extracted from various network systems, for the exact time of measurements or on long-term basis, with the aim of identifying the potential for EMF-awareness of future networks. The reduction of total exposure with the introduction of the microcell layer is shown using the proposed method with experimental measurements and compared by mobile network technologies. The introduction of the micro layer brought reduction to total population exposure of 84.6%, in the micro base station coverage area, mostly due to user device exposure reduction in GSM. UMTS user device exposure reduction was even more pronounced, 97.8%, but having less impact on overall exposure, contributing only 1%. Even with the increase in exposure originating from base stations, the reduction of total exposure was visible over the macro area as well, measuring 2.22%. The uncertainties of the evaluation method are identified and usage of advanced tools and methods is proposed to mitigate them.

Analysis of the hygienic assessment of the electromagnetic environment in residential areas near military airfields

In the purpose to ensure the sanitary and epidemiological well-being of the population living on the territory near the military aerodrome calculated assessment of the geometry and size of the sanitary protection zone (SPZ) was carried out based on aerodrome radiation sources electromagnetic fields (EMF) level and the requirements of current legislation in electromagnetic safety. The analysis showed that the calculated levels of total EMF exposure outside the technical (adjacent) territory are significantly lower than the established maximum permissible for the population. The results obtained allow us to prevent the possibility of developing an inadequate (hyperbolized) perception (radiophobia) of the danger of exposure to this factor, as well as rental behavior of people living in these territories.

Spectral density constraints on wireless communication

Environmental exposure to man-made electromagnetic field (EMF) has been rising as modern technologies have grown and changes in social behavior have generated more synthetic sources. For safety of human health, EMF levels need to be regulated. The level of EMF should be well below levels where there might be harm, hence we do not expect to see any health effects at these levels. Current regulations fail to place a strict limit on EMF in situations where multiple nearby devices transmit simultaneously. The way these regulations are expressed needs great care because it will have an effect on the design of wireless communication systems. In this paper, it is argued that transmitted power constraints on wireless communication devices should be expressed in a different way, namely that devices should limit the EMF spectral density that they generate to the difference between the maximum allowed, by the standard, and the amount currently present, as measured by the device, in the spectral region where it is active. Note that the limit on EMF should be expressed in terms of its EMF spectral density rather than as a total EMF over each of a series of separate bands. If all devices limit their own EMF spectral density, in the spectral region where they are active, in such a way that total EMF spectral density is below the regulated limit in that region, then it is certain that the aggregate EMF spectral density will be below the regulated limit at all frequencies.

An Analytic Algorithm for Electromagnetic Field in Planar-Stratified Biaxial Anisotropic Formation

An analytic algorithm is developed to solve the electromagnetic (EM) field excited by orthogonal magnetic dipoles in the multilayered biaxial anisotropic medium. It allows forward modeling and inversion of EM well logging in the planar-stratified formation without borehole and invasion zones. First, the transverse components of the EM fields are divided into up/down-going waves in the frequency wavenumber domain. A novel concept of reflection/transmission is introduced to describe the propagation of the EM waves through the boundaries. Different from previous work, those reflection/transmission coefficients are concerning the propagation of up/down-going waves directly rather than the amplitude of the total EM field in each layer, which makes the derivation process clearer and easier to understand. Then, we adopt the cubic spline interpolation to calculate the 2-D Fourier integral that transforms the field from the spectral domain to the spatial domain, and an efficient sampling rule is also provided to achieve high accuracy and stability in numerical calculation. For avoiding the singularity when the field locations are close to the source along the vertical direction, the primary field is subtracted in the spectral domain to make the integrand decay fast. Finally, we validate our new formulas compared with another numerical method and analyze the responses of the triaxial induction tool in biaxial anisotropic formations.

Frequency-domain magnetotelluric footprint analysis for 3D earths

Abstract For magnetotelluric (MT) data with a large coverage, inversion interpretation for the whole area is usually impossible, due to the physical limitation of a computer. However, for each MT station, it is only sensitive to a region (called MT footprint) localized immediately underneath the station, much smaller than the whole survey area. Thus the whole large survey area can be subdivided into many sub-areas and inverted using the moving footprint technique efficiently. Therefore, to understand the MT footprint is of great importance for developing such an inversion algorithm. In this paper, we study the influence of frequency, resistivity and existence of anomalous structure in the MT footprint. We first use the finite difference method to evaluate the total electromagnetic (EM) fields, then apply the numerical volume integration of tensor green's function to calculate the total induced fields at the receiver (summation of the contribution for each cell). The footprint is obtained based on the contribution of each cell to the total induced fields. Different models are designed to understand the footprint for MT problems. An increase in frequency or conductivity results in a decrease in the size of footprint. Existence of anomalous bodies within the footprint affects the MT footprint size to a degree, dependent on the overall resistivity. Outside the footprint, the existence of anomalous bodies have little effect on the footprint size and shape.

Proper Equipment Ordinance for Achieving EM Cleanliness in Space Missions: The Case of ELF Electric Sources

A constant electromagnetic compatibility issue in the majority of space missions is the accurate EMI source identification and modeling. This is necessary in order to provide electromagnetic (EM) cleanliness in a specific area inside or outside the spacecraft, where sensitive measurement equipment is placed. Authors in previous work have presented a stochastic process capable to accurately predict the EM signature of a device both for transient and steady-state emissions. In this article, a supplementary methodology is proposed, using the models from the previously established process, to achieve electromagnetic cleanliness. Authors claim that EM cleanliness is possible to be achieved inside or outside a specific area of the spacecraft structure with proper equipment ordinance and if necessary the aid of an additional auxiliary source. The proposed methodology is using a heuristic approach to find the optimum positions of the available equipment. The equipment when placed at these positions presents a minimum total electromagnetic field at a specific point or region. Moreover, if necessary, the total field can be further minimized with the addition of an auxiliary source.

Generalized Electric Field Equations of a Time-Varying Current Distribution Based on the Electromagnetic Fields of Moving and Accelerating Charges

In several studies conducted recently, it was shown that equations pertinent to the electric and magnetic fields produced by electrical charges in motion can be used to calculate the electromagnetic fields produced by current pulses propagating along linearly restricted paths. An example includes the case of current pulses propagating along conductors and conducting channels such as lightning. In this paper, it is shown how the technique can be applied to estimate the electromagnetic fields generated by current and charge distributions moving in arbitrary directions in space. The analysis shows that, depending on the way the problem is formulated using the field equations pertinent to accelerating charges, one procedure leads to the generalized dipole equations, which are independent of the velocity of propagation of the current, and the other procedure leads to a set of equations that depend on the velocity. Using the well-tested transmission line model of lightning return strokes as an example, it is shown that both sets of field equations give rise to the same total electromagnetic field.

The 50 Hz EM method at the Pyhäsalmi massive sulphide deposit

ABSTRACTThe main goal of this research was to develop a simple method to observe the effects of electromagnetic induction in conductors proximal to drillholes at the Pyhäsalmi volcanogenic massive sulphide (VMS) copper − zinc deposit located in central Finland, using electromagnetic fields generated by electrical power lines (50 Hz). The idea is that the mine geologist could interpret the 50 Hz measurements from several holes and infer the boundaries between rock types based on rock samples and the 50 Hz measurements. Three-component dB/dt coils were used to measure the time derivatives of the total electromagnetic field in deep drillholes. Thus, the primary field was present while taking measurements, or the induced field was not separated from the inducing field. Time-domain data were transformed to the frequency domain and three components (x, y, z) of the total 50 Hz magnetic field were extracted. The electromagnetic field down drillholes indicates anomalies, although the difference between the primary and secondary fields is difficult to distinguish. We compared the results of the power line method with those measured using the time- and frequency-domain electromagnetic methods. According to spatial variations in the total field profiles, a strong correlation with electromagnetic data from controlled source methods was observed. The results demonstrate that the electromagnetic field generated by the primary field of power lines in an active mining area can be used to identify conductive targets in the area.

Electromagnetic scattering and emission by a fixed multi-particle object in local thermal equilibrium: General formalism

The majority of previous studies of the interaction of individual particles and multi-particle groups with electromagnetic field have focused on either elastic scattering in the presence of an external field or self-emission of electromagnetic radiation. In this paper we apply semi-classical fluctuational electrodynamics to address the ubiquitous scenario wherein a fixed particle or a fixed multi-particle group is exposed to an external quasi-polychromatic electromagnetic field as well as thermally emits its own electromagnetic radiation. We summarize the main relevant axioms of fluctuational electrodynamics, formulate in maximally rigorous mathematical terms the general scattering–emission problem for a fixed object, and derive such fundamental corollaries as the scattering–emission volume integral equation, the Lippmann–Schwinger equation for the dyadic transition operator, the multi-particle scattering–emission equations, and the far-field limit. We show that in the framework of fluctuational electrodynamics, the computation of the self-emitted component of the total field is completely separated from that of the elastically scattered field. The same is true of the computation of the emitted and elastically scattered components of quadratic/bilinear forms in the total electromagnetic field. These results pave the way to the practical computation of relevant optical observables.

Localized topological states in Bragg multihelicoidal fibers with combined pitch-jump and twist defects

We have studied the influence of pitch-jump defects on the existence of defect-localized states in multihelicoidal Bragg fibers with twist defects. We have shown that the total electromagnetic field energy stored in the defect-localized topologically charged modes essentially depends on the pitch jump and rapidly tends to zero as this increases. This can be used to make the defect mode radiate the stored energy. We have also shown that by tuning the magnitude of the pitch mismatch one can control the wavelength at which the maximal localization takes place. Such fine tuning of the pitch jump can in principle be achieved by piezoelectric modulation.

Revisiting the Low-Frequency Dipolar Perturbation by an Impenetrable Ellipsoid in a Conductive Surrounding

This contribution deals with the scattering by a metallic ellipsoidal target, embedded in a homogeneous conductive medium, which is stimulated when a 3D time-harmonic magnetic dipole is operating at the low-frequency realm. The incident, the scattered, and the total three-dimensional electromagnetic fields, which satisfy Maxwell’s equations, yield low-frequency expansions in terms of positive integral powers of the complex-valued wave number of the exterior medium. We preserve the static Rayleigh approximation and the first three dynamic terms, while the additional terms of minor contribution are neglected. The Maxwell-type problem is transformed into intertwined potential-type boundary value problems with impenetrable boundary conditions, whereas the environment of a genuine ellipsoidal coordinate system provides the necessary setting for tackling such problems in anisotropic space. The fields are represented via nonaxisymmetric infinite series expansions in terms of harmonic eigenfunctions, affiliated with the ellipsoidal system, obtaining analytical closed-form solutions in a compact fashion. Until nowadays, such problems were attacked by using the very few ellipsoidal harmonics exhibiting an analytical form. In the present article, we address this issue by incorporating the full series expansion of the potentials and utilizing the entire subspace of ellipsoidal harmonic eigenfunctions.