Field Distribution Inside Research Articles

Machine Learning for Engineering Meta‐Atoms with Tailored Multipolar Resonances

AbstractIn the rapidly developing field of nanophotonics, machine learning (ML) methods facilitate the multi‐parameter optimization processes and serve as a valuable technique in tackling inverse design challenges by predicting nanostructure designs that satisfy specific optical property criteria. However, while considerable efforts have been devoted to applying ML for designing the overall spectral response of photonic nanostructures, often without elucidating the underlying physical mechanisms, physics‐based models remain largely unexplored. Here, physics‐empowered forward and inverse ML models to design dielectric meta‐atoms with controlled multipolar responses are introduced. By utilizing the multipole expansion theory, the forward model efficiently predicts the scattering response of meta‐atoms with diverse shapes and the inverse model designs meta‐atoms that possess the desired multipole resonances. Implementing the inverse design model, uniquely shaped meta‐atoms with enhanced higher‐order magnetic resonances and those supporting a super‐scattering regime of light‐matter interactions resulting in nearly five‐fold enhancement of scattering beyond the single‐channel limit are designed. Finally, an ML model to predict the wavelength‐dependent electric field distribution inside and near the meta‐atom is developed. The proposed ML based models will likely facilitate uncovering new regimes of linear and nonlinear light‐matter interaction at the nanoscale as well as a versatile toolkit for nanophotonic design.

Thermal runaway of lithium battery based on Star CCM+

Based on the CFD software Star CCM+, the model of square lithium battery is built, and the transient simulation is completed by using the joint simulation and three-dimensional model. The gas venting at the valve is considered. this paper studies the temperature field and flow field distribution inside and outside the cell and battery, and observes physical characteristics such as temperature, volume fraction and flow rate during thermal runaway. It lays the foundation for the subsequent study of the thermal runaway behaviour of the gas injection process and the effective avoidance of thermal runaway.

Magnetic accumulation effect on the inner and outer surfaces of pipeline magnetic penetration in natural environment

In view of the detection requirements of pipeline internal and external surface defects and pipeline special regular structure detection, based on the magnetic shielding effect inside and outside the pipeline, the principle of magnetic field refraction at the interface between the pipe wall and air, and the principle of the magnetic field concentration on the pipe surface and the gap, this article focuses on the natural environment (geomagnetic background). The magnetic field distribution inside and outside the pipeline has been theoretically analyzed. After that, the finite element simulation software is used to model the finite length pipeline, and the internal and external magnetic fields are simulated and researched in combination with the finite element method. Finally, the tunnel magneto resistance (TMR) magnetic sensor is used to collect and process the internal magnetic field of the actual pipeline model, which verifies the correctness of the theoretical analysis. This paper analyzes the magnetic field inside and outside the pipeline by means of principle deduction, finite element simulation, and sensor measurement. The analysis results show that the distribution of the magnetic field in the pipeline under the excitation of the geomagnetic field has a very obvious regularity, which can meet the needs of pipeline defect detection. In addition, because the pipelines of different structures have different magnetic field distribution laws, they can also be used for the detection and analysis of pipelines with special structures.

Prediction of flashover voltage using electric field measurement on clean and polluted insulators

The economy of transporting large amount of power over long distance makes high voltage transmission line an important component of the power system. Outdoor insulators provide electrical insulation as well as mechanical support between energized conductor and grounded parts of the tower. Its performance is closely related to the reliability of power delivery. Various parameters affect the insulator flashover performance, but the measurement and analysis of all those parameters would be a challenging and complex task during online inspection. The performance of the insulators is directly dependent on the electric field distribution inside and surrounding them. The aim of this work is to obtain the relationship between flashover voltage and electric field distribution. Accordingly, a novel electric field measurement technology, which was recently commercially available, was utilized in this paper to measure the electric field distribution around six different varieties of composite and ceramic insulators. The relationship between conductivity of the contamination layer and the environmental relative humidity was initially evaluated. Further, the patterns of the electric field distribution for clean, uniform and non-uniform contamination cases were studied and its relationship with the flashover voltages was explored. Electric field calculation with commercially available package was performed to validate the experimental results and extend the conclusion to higher voltage levels.

Simulation analysis on return conductor configuration for lightning indirect effect test of metal cylinder

Objectives In order to study the lightning indirect effect of metal cylindrical ordnance, a method for constructing the tester for lightning indirect effect of the metal cylindrical flying object is studied, and a cage type frame similar to coaxial line is designed as the coupling device. Methods Firstly, the current resonance of system is analyzed by observing the current waveform of different terminators. Then, through the electromagnetic simulation software CST, the surface current distribution of the metal cylinder is simulated, and the influences of different load impedance and different return conductor arrangement on the uniformity of surface current distribution are analyzed. Finally, according to the simulation results, the surface current intensity of cylinder and the instantaneous electromagnetic field distribution inside and outside the cylinder are analyzed. Results The simulation results show that the cage type injection device similar to coaxial line can be used for indirect lightning effect test of metal cylinders. Conclusions The simulation results provide a basis for the further test.

Electromagnetic Analysis, Characterization and Discussion of Inductive Transmission Parameters for Titanium Based Housing Materials in Active Medical Implantable Devices.

The growing demand for active medical implantable devices requires data and or power links between the implant and the outside world. Every implant has to be encapsulated from the body by a specific housing and one of the most common materials used is titanium or titanium alloy. Titanium thas the necessary properties in terms of mechanical and chemical stability and biocompatibility. However, its electrical conductivity presents a challenge for the electromagnetic transmission of data and power. The proposed paper presents a fast and practical method to determine the necessary transmission parameters for titanium encapsulated implants. Therefore, the basic transformer-transmission-model is used with measured or calculated key values for the inductances. Those are then expanded with correction factors to determine the behavior with the encapsulation. The correction factors are extracted from finite element method simulations. These also enable the analysis of the magnetic field distribution inside of the housing. The simulated transmission properties are very close to the measured values. Additionally, based on lumped elements and magnetic field distribution, the influential parameters are discussed in the paper. The parameter discussion describes how to enhance the transmitted power, data-rate or distance, or to reduce the size of the necessary coils. Finally, an example application demonstrates the usage of the methods.

Earthquake Lights: Mechanism of Electrical Coupling of Earth's Crust to the Lower Atmosphere

AbstractEarthquake lights are an atmospheric luminous phenomenon occurring before, during, and occasionally after earthquakes. In the present work we assume that strong electric currents are produced inside the Earth during earthquakes and model the current and field distribution inside and above the Earth to find the conditions where electrical discharges can appear. The simulation results quantify the effects of various configurations of current dipoles inside the Earth. The results are supported by approximate formulations allowing effective solution of the same problems using an analytical theory. It is shown that a large‐scale dipole with poles located in Earth's crust at 5 and 15 km beneath the Earth's surface requires energy significantly higher than the total seismic wave energy in major earthquakes. The more likely setup to produce earthquake lights is found to be when the upper pole of the source current dipole is shifted close to the Earth's surface, in particular, when locations of current dipoles are tens of meters beneath Earth's surface.

Evaluation of hollow fiber T-type zeolite membrane modules for ethanol dehydration

This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concentration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle. Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.

Resolution criteria in double-slit microscopic imaging experiments.

Double-slit imaging is widely used for verifying the resolution of high-resolution and super-resolution microscopies. However, due to the fabrication limits, the slit width is generally non-negligible, which can affect the claimed resolution. In this paper we theoretically calculate the electromagnetic field distribution inside and near the metallic double slit using waveguide mode expansion method, and acquire the far-field image by vectorial Fourier optics. We find that the slit width has minimal influence when the illuminating light is polarized parallel to the slits. In this case, the claimed resolution should be based on the center-to-center distance of the double-slit.

Metasurface-loaded dielectric rod leaky wave antenna

This paper introduces an analytical solution for a dielectric rod leaky wave antenna loaded by a metasurface. The advantage of adding metasurface on the dielectric rod is that it introduces an additional degree of freedom in the design of this antenna by controlling the outer boundary condition. Modified Generalized Sheet Transition Condition on a cylindrical geometry is used to model the metasurface on the dielectric rod. The analysis is based on developing the characteristic equation of the proposed structure. This characteristic equation is used to obtain the complex propagation constant of this structure and the corresponding field distribution inside and outside the rod including the resulting radiated fields. Parameters of the metasurface are extracted from the reflection and transmission properties of its elements in infinite periodic structure. An example of a dielectric rod loaded by a metasurface is presented analytically based on the introduced analysis and also simulated numerically for comparison. The effect of different polarizabilities of the loading metasurface on the leaky wave properties of the dielectric rod is discussed.

Comparison of two kinds of Ka‐band circular polarisers for use in a gyro‐travelling wave amplifier

This study presents a rigorous theoretical and experimental comparison of two kinds of rectangular waveguide polarisers for use in Ka-band gyro-travelling wave amplifier. It is shown how overall field distribution inside of polariser structures having different kinds of corrugation affects the resulting performances. To the best of the authors’ knowledge, this is the first theoretical estimation of the breakdown power (in watts) of sine-corrugated polariser in competition with conventional polariser having rectangular shaped corrugation. This study also discusses the general practice of smooth structuring in microwave and millimetre-wave component design.

Application of JEMS-FDTD in complicated electromagnetic environment study

This paper demonstrates a massively parallel 3D full-wave electromagnetic field simulation program JEMS-FDTD and its application in complicated electromagnetic environment study. Two numerical examples of application are presented. The computation of radio wave propagation in actual building produces the numerical results of the propagation process of electromagnetic pulse in time domain, which can be used to analyze the characteristics of indoor radio propagation and electromagnetic environment safety. The computation of aircraft transient electromagnetic characteristics gives the transient electromagnetic field distribution inside and outside the compartments, which can be used in HIRF (High Intensity Radiation Field) protection study.

Optical breakdown of multilayer thin-films induced by ultrashort pulses at MHz repetition rates

Multilayer coatings composed of TiO(2), Ta(2)O(5), HfO(2), or Al(2)O(3) as high-index materials and SiO(2) as low-index material were investigated for laser-induced damage using 1 ps, 5 µJ pulses generated by a mode-locked Yb:YAG thin-disk oscillator operating at a wavelength of 1030 nm and repetition rate of 11.5 MHz. Previously reported linear band gap dependence of damage threshold at kHz repetition rates was confirmed also for the MHz regime. Additionally, we studied the effect of electric field distribution inside of the layer stack. We did not observe any significant influence of thermal effects on the laser-induced damage threshold in this regime.

Characterization of the Propagation Properties of the Half-Mode Substrate Integrated Waveguide

The propagation properties of the half-mode substrate integrated waveguide (HMSIW) are studied theoretically and experimentally in this paper. Two equivalent models of the HMSIW are introduced. With the first model, equations are derived to approximate the field distribution inside and outside the HMSIW. Using the second model, an approximate closed-form expression is deduced for calculating the equivalent width of an HMSIW that takes into account the effect of the fringing fields. The obtained design formulas are validated by simulations and experiments. Furthermore, the attenuation characteristics of the HMSIW are studied using the multiline method in the frequency range of 20-60 GHz. A numerical investigation is carried out to distinguish between the contributions of the conductive, dielectric, and radiation losses. As a validation, the measured attenuation constant of a fabricated HMSIW prototype is presented and compared with that of a microstrip (MS) line and a substrate integrated waveguide (SIW). The SIW is designed with the same cutoff frequency and fabricated on the same substrate as the HMSIW. The experimental results show that the HMSIW can be less lossy than the MS line and the SIW at frequencies above 40 GHz.

Direct observation of photonic jets and corresponding backscattering enhancement at microwave frequencies

We report the direct observation of photonic nanojets that emerged from the shadow side of a dielectric cylinder illuminated by plane waves in the microwave frequencies (8–13 GHz). Using our recently developed two-dimensional spatial field mapping system, we carried out a point-by-point measurement of both the phase and intensity of spatial electric field distribution inside and around scattering dielectric cylinders. The direct electric field maps confirm the subwavelength waist of the photonic jet. In addition, we also confirmed the superbackscattering enhancement induced by the presence of a particle much smaller than the initial focusing cylinder within the photonic jet.

Computation of the Electric Field in Cable Insulation in the Presence of Water Trees and Space Charge

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The presence of space charge changes locally the electric field distribution in power cable insulation and may play an important role in tree development, thus accelerating the dielectric breakdown. This paper is concerned with the computation of the electric field in polyethylene-insulated power cables affected by water trees which grow from the following: 1) the inner semiconducting layer; 2) the outer semiconducting layer; and 3) the inner and outer semiconducting layers, taking into account the space charge corresponding to the ions present in the treeing area. Space charge in plane samples where trees have been developed in an accelerated manner was estimated using the thermal step method. Average charge values given by space charge measurements were then used for the electric field computation in cable insulation with continuous or/and individual water trees. For the calculation of the electric field, an analytical and a numerical method have been used. This paper shows that the space charge changes the electric field distribution inside and outside the trees (the field increases in some areas and decreases in others) and that the field variations depend on the magnitude and on the polarity of the space charge, as well as on the dimensions of the water trees developed in the cable insulation. The obtained results show that, in the presence of water trees and space charge, the initiation of electric trees is more probable in the case of individual water trees than in the case of continuous water trees. </para>

Uncoupled modes and all-angle negative refraction in walled honeycomb photonic crystals

Left-handed materials have superlensing effects that enable them to surmount the optical diffraction limit. A photonic crystal is able to mimic some properties of all-angle left-landed materials. In this study, the all-angle negative refraction criteria of photonic crystals are evaluated. The MIT Photonic-Bands program is employed to calculate the band structure of walled honeycomb photonic crystals, and the finite-difference time-domain method is used to provide a snapshot of the electric field distribution inside and outside the honeycomb photonic crystals. The results indicate that the all-angle negative refraction phenomena of the honeycomb photonic crystals are correlated with the orientation of the photonic crystals. Furthermore, the role of the uncoupled modes varies based on their orientation to the all-angle negative refraction photonic crystals, in one case assisting negative refraction and in the other case preventing it. The results suggest that symmetric properties should not be ignored when considering the negative refraction of photonic crystals.

Biorthogonal Multiresolution Time Domain (MRTD) Analysis for In-Vehicle Communications

In this paper, we apply a biorthogonal multiresolution time domain (MRTD) scheme based on the Cohen-Daubechies-Feauveau (CDF) scaling functions for vehicle communication applications. We create a car model using a model based on a 1995 Ford Contour Sedan and simulate the field distribution inside of the car model under the frequency of blue tooth.

Generating homogeneous magnetostatic field inside prolate and oblate ellipsoidal coil

Magnetostatic field distribution inside and outside of prolate and oblate ellipsoidal coil is analytically determined. The results are used to obtain the coil winding function for getting homogeneous magnetostatic field inside the prolate and oblate ellipsoidal coil when uniform current flows through it.

Surface impedance boundary conditions near corners and edges: rigorous consideration

The two-dimensional problem of the magnetic field distribution inside and outside an imperfectly conducting, 90-degree edge is solved using the perturbation technique. The well-known solution of the problem for a perfectly conducting edge is used as an initial approximation. The surface impedance near the edge is represented in the form of asymptotic expansions in the small parameter proportional to the ratio of the skin depth and characteristic size of the conductor surface. An analytical solution for the electric field in the conductor near the edge is obtained. The solution behavior is investigated and the approximate boundary conditions relating the tangential components of the electric and magnetic fields on the conductor surface near the edge are proposed in a form suitable for numerical implementation.