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The purpose of this paper is to discuss a numerically efficient simulation method for the study of the high-frequency behaviour of air-cored coils. The self-resonance phenomenon of coils can be studied which is important, e.g., in wireless power transfer (WPT).

A full-wave and a quasi-stationary integral formulation is introduced. The integral equation is solved by using the Method of Moments. The complex impedance of the coil is calculated and studied in a wide frequency band.

The integral equation method is numerically efficient compared to finite element schemes, making possible its use in design optimisation problems.

The present model can treat homogeneous media only. Future research will focus on the extension of the approach to heterogeneous media.

The method can be used in the design optimisation of WPT systems that apply magnetically coupled resonant coils.

The presented computation scheme is original. Integral equation schemes have not been used for coil modelling before, to the best of the author’s knowledge.

This paper aims to present a SPICE model to represent antennas in receiving mode. The model can be used to evaluate the performance of the antenna when it is coupled to several different nonlinear electric circuits. The proposed methodology is particularly suitable for rectenna applications, as it allows the analysis of different configurations for a rectenna more efficiently than using full-wave analysis simulators coupled directly to each rectifier circuit.

The model presented uses reciprocity theory to calculate the ideal voltage source of the Thevenin-equivalent circuit for an antenna. Vector fitting is then used to approximate the model to rational functions that can be converted to Resistor, Inductor and Capacitor circuits. Additional components are added to the circuit to prevent numerical instability.

Two rectennas are used to illustrate the performance of the proposed model, one based on a 2.45-GHz rectangular patch antenna and another based on a planar spiral antenna. The second antenna has impedance with positive and negative real parts along the frequency range, which could lead to numerical instabilities. The proposed method is shown to be stable while working with these negative resistance values, which may appear during circuit parameterization.

The equivalent SPICE circuit model for the antenna makes it easy to simulate nonlinear circuits connected to the antenna and perform transient analyses. The computational cost of antenna analysis is reduced, being more computationally efficient than methods that involve full-wave simulation. This characteristic makes it an interesting approach for working with rectennas, or any application where the time constant of the circuit is much longer than the period of the incident wave.

For most antenna applications, the numerical stability of the circuit can be achieved using passive enforcement. However, depending on the phase response of the antenna, the impedance that represents its far-field characteristic may present a negative real part, in which case, passive enforcement will fail. In this paper, the problem of numerical instability is solved by introducing an offset resistance and a current-controlled voltage source to the model.

A design procedure for multi-layer absorbers based on carbon nanotubes (CNT) frequency selective surfaces (FSS) sheets is here developed. The paper aims to discuss there issues.

Single layer FSS are first analyzed via finite element (FE). Then equivalent sheets admittances are extracted in a transmission line model. Neural networks (NNs) interpolation over this data and subsequent multi-objective genetic algorithm (GA) based optimizations are then performed to design multiple layers absorbing structures. Designs are finally validated via full wave FEM simulations.

In this paper, some absorbing structures made of three or four FSS sheets with total thicknesses around 6 mm are synthesized.

NNs' accuracy used in the equivalent model can be refined with further training.

Low profile absorbing materials are of relevant industrial interest both for radar cloaking and anechoic chambers.

The transmission line model combined with NNs and GA optimization is capable of speeding up the design procedure with respect to a conventional full-wave FEM approach.

The purpose of this paper is to present an analytical expression for the characteristic impedance of a microstrip line in presence of a dielectric cover.

Assuming a quasi-TEM propagation mode, a rigorous conformal mapping based on the Schwarz-Christoffel transformation is employed to derive the equivalent capacitance model, which can then be applied to derive a closed analytical expression for the effective permittivity and the characteristic impedance of the line.

Such a formulation is not limited to the case of a single cover layer, but an arbitrary number of electric overlays can be considered as well. Comparisons with published numerical results and full-wave simulations in the case of a single cover layer have been also performed to test the validity of the proposed approach.

The new analytical formula for the characteristic impedance of a microstrip line with a single dielectric cover shows better performances compared to the one of closed formulas already presented in the literature.

The purpose of this paper is to present an alternative modeling approach in terms of the determination of a physically equivalent circuit model for one-dimensional (1D) planar metamaterials in the high-frequency regime, without a postprocessing optimization procedure. Thereby, an efficient implementation of physical relationships is aimed.

In this paper, a method based on quasi-stationary simulations and mathematical conversions to derive the values for a physically equivalent circuit model is proposed. Because the electromagnetic coupling mechanisms are investigated in detail, a simplification for the considered multiconductor transmission line structure is achieved.

The results show that the proposed modeling approach is an efficient and physically meaningful alternative to classical full-wave simulation techniques for the investigated inhomogeneous transmission line structure in both the time domain as well as in the frequency domain. In the course of this, the effort is reduced while a comparable accuracy is maintained, whereby specific coupling mechanisms are considered in circuit simulations.

The process to obtain information about physically interpretable lumped element values for a given structure or to determine a layout for known ones is simplified with the aid of the proposed approach. An advantageous adaption of the presented procedure to other areas of application is well conceivable.

The purpose of this paper is to build a neural network (NN) inverse model for the multi-band unequal-power Wilkinson power divider (WPD). Because closed-form expressions of the inverse input–output relationship do not exist, the NN becomes an appropriate choice, because it can be trained to learn from the data in inverse modeling. The design parameters of WPD are the characteristic impedances, lengths of the transmission line sections and the isolation resistors. The design equations used to train the NN inverse model are based on the even–odd mode analysis.

An inverse model of a multi-band unequal WPD using NNs is presented. In inverse modeling of a microwave component, the inputs to the model are the required electrical parameters such as reflection coefficients, and the outputs of the model are the geometrical or the physical parameters.

For verification purposes, a quad-band WPD and a penta-band WPD are designed. The results of the full-wave simulations verify the validity of the design procedure. The resulting NN model outperforms traditional time-consuming optimization procedures in terms of computation time with acceptable accuracy. The designed WPDs using NN are implemented by microstrip lines and verified by using full-wave analysis based on high-frequency structure simulator (HFSS). The results of the microstrip WPDs have good agreements with the corresponding results obtained by using ideal transmission line sections.

The associated time-consuming procedure and computational burden in realizing WPD through optimization are major disadvantages; needless to mention the substantial increase in optimization time because of the multi-band design. NNs are one of the best candidates in addressing the abovementioned challenges, owing to their ability to process the interrelation between electrical and geometrical/physical characteristics of the WPD in a superfast manner.

The paper aims to give the reader a consolidated state of art in the full‐wave modeling of passive interconnection systems using equivalent circuits and presents several advantageous techniques developed by the authors.

The paper presents the theory of generalized partial element equivalent circuit (PEEC) modeling in the frequency domain (FD) and time domain (TD) developed by the authors. The widely spread simplified approaches are derived from this general formulation and the most important issues (e.g. stability in the TD) are considered. The theoretical part is completed by a simulation example, which shows the efficiency of studied methods.

Novel approaches for co‐simulation of passive interconnections in their circuit environment.

The PEEC method is widely used in the practice of computational electromagnetics, e.g. by the authors in the practical electromagnetic compatibility simulation.

The paper is based on the original work of authors carried through over many years.

Selective laser melting (SLM) is an advanced rapid prototyping or additive manufacturing technology that uses high power density laser to fabricate metal/alloy components with minimal geometric constraints. The SLM process is multi-physics in nature and its study requires development of complex simulation tools. The purpose of this paper is to study – for the first time, to the best of the authors’ knowledge – the electromagnetic wave interactions and thermal processes in SLM based dense powder beds under the full-wave formalism and identify prospective metal powder bed particle distributions that can substantially improve the absorption rate, SLM volumetric deposition rate and thereby the overall build time.

We present a self-consistent thermo-optical model of the laser-matter interactions pertaining to SLM. The complex electromagnetic interactions and thermal effects in the dense metal powder beds are investigated by means of full-wave finite difference simulations. The model allows for accurate simulations of the excitation of gap, bulk and surface electromagnetic resonance modes, the energy transport across the particles, time dependent local permittivity variations under the incident laser intensity, and the thermal effects (joule heating) due to electromagnetic energy dissipation.

Localized gap and surface plasmon polariton resonance effects are identified as possible mechanisms toward improved absorption in small and medium size titanium powder beds. Furthermore, the observed near homogeneous temperature distributions across the metal powders indicates fast thermalization processes and allows for development of simple analytical models to describe the dynamics of the SLM process.

To the best of the authors’ knowledge, for the first time the electromagnetic interactions and thermal processes with dense powder beds pertaining to SLM processes are investigated under full-wave formalism. Explicit description is provided for important SLM process parameters such as critical laser power density, saturation temperature and time to melt. Specific guidelines are presented for improved energy efficiency and optimization of the SLM process deposition rates.

The purpose of this paper is to describe the full‐wave modelling of pulsed terahertz systems utilized in non‐destructive testing.

At the outset, some basic information on the terahertz NDT are outlined and then, general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness.

It is possible to model in a relatively simple way a terahertz system for nondestructive evaluation of dielectric materials. In contrast to other published work, the entire measuring setup is modelled, including photoconductive antenna with hemispherical lens, focusing lens and evaluated material with exemplary defect.

This paper gives a description of the terahertz non‐destructive testing system with comparison of simulated and measured results.

The purpose of this research is to efficiently separate incident terahertz (THz) waves into distinct transmission and reflection channels by minimizing the absorption ratio. So, the optical systems operating within the THz frequency range can developed. To achieve a multi-band response, four different periodic arrays of graphene patterns are used. These arrays are strategically stacked on both sides of three SU-8 photoresists, serving as dielectric materials. Consequently, each layer exhibits a unique influence on the device's response, and by applying four external bias voltages, the behavior of the device can be precisely controlled and adjusted.

A novel optoelectronic device operating in the THz frequency range is introduced, using periodic arrays of graphene patterns and SU-8 photoresist dielectrics. The design of this device is based on meta-surface principles, using both the equivalent circuit model (ECM) and transmission line concept. The output of the device is a THz coupler implemented by analyzing the reflection and transmission channels. The structure is characterized using the ECM and validated through comprehensive full-wave simulations. By representing the electromagnetic phenomenon with passive circuit elements, enabling the calculation of absorption, reflection and transmission through the application of the theory of maximum power transfer.

Based on simulation results and theoretical analysis, the proposed device exhibits sensitivity to gate biasing, enabling efficient reflection and transmission of THz waves. The device achieves reflection and transmission peaks exceeding across the five distinct THz bands 90%, and its behavior can be tuned by external gate biasing. Moreover, the device's sensitivity to variations in geometrical parameters and chemical potentials demonstrates its reliable performance. With its outstanding performance, this high-performance meta-surface emerges as an ideal candidate for fundamental building blocks in larger optical systems, including sensors and detectors, operating within the THz frequency band.

The proposed device covers a significant portion of the THz gap through the provision of five adjustable peaks for reflection and transmission channels. Additionally, the ECM and impedance matching concept offers a simplified and time-efficient approach to designing the meta-surface. Leveraging this approach, the proposed device is effectively represented using passive circuit elements such as inductors, capacitors and resistors, while its performance is validated through the utilization of the finite element method (FEM) as a full-wave simulation tool. This combination of circuit modeling and FEM simulation contributes to the robustness and accuracy of the device's performance evaluation.