Editorial

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2 pages, 155 KiB

Open AccessEditorial

Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics

by Alessandro Fedeli and Gian Luigi Gragnani

Electronics 2021, 10(19), 2352; https://doi.org/10.3390/electronics10192352 - 26 Sep 2021

Cited by 1 | Viewed by 1250

Abstract

Few research topics are as broad and pervasive as electromagnetic scattering [...] Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

Research

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18 pages, 1148 KiB

Open AccessFeature PaperArticle

Analysis of a Nonlinear Technique for Microwave Imaging of Targets Inside Conducting Cylinders

by Alessandro Fedeli, Matteo Pastorino, Andrea Randazzo and Gian Luigi Gragnani

Electronics 2021, 10(5), 594; https://doi.org/10.3390/electronics10050594 - 04 Mar 2021

Cited by 4 | Viewed by 1486

Abstract

Microwave imaging of targets enclosed in circular metallic cylinders represents an interesting scenario, whose applications range from biomedical diagnostics to nondestructive testing. In this paper, the theoretical bases of microwave tomographic imaging inside circular metallic pipes are reviewed and discussed. A nonlinear quantitative [...] Read more.

Microwave imaging of targets enclosed in circular metallic cylinders represents an interesting scenario, whose applications range from biomedical diagnostics to nondestructive testing. In this paper, the theoretical bases of microwave tomographic imaging inside circular metallic pipes are reviewed and discussed. A nonlinear quantitative inversion technique in non-Hilbertian Lebesgue spaces is then applied to this kind of problem for the first time. The accuracy of the obtained dielectric reconstructions is assessed by numerical simulations in canonical cases, aimed at verifying the dependence of the result on the size of the conducting enclosure and comparing results with the conventional free space case. Numerical results show benefits in lossy environments, although the presence and the type of resonances should be carefully taken into account. Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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24 pages, 8108 KiB

Open AccessFeature PaperArticle

Scattering from Spheres: A New Look into an Old Problem

by Giuseppe Ruello and Riccardo Lattanzi

Electronics 2021, 10(2), 216; https://doi.org/10.3390/electronics10020216 - 19 Jan 2021

Cited by 8 | Viewed by 2915

Abstract

In this work, we introduce a theoretical framework to describe the scattering from spheres. In our proposed framework, the total field in the outer medium is decomposed in terms of inward and outward electromagnetic fields, rather than in terms of incident and scattered [...] Read more.

In this work, we introduce a theoretical framework to describe the scattering from spheres. In our proposed framework, the total field in the outer medium is decomposed in terms of inward and outward electromagnetic fields, rather than in terms of incident and scattered fields, as in the classical Lorenz–Mie formulation. The fields are expressed as series of spherical harmonics, whose combination weights can be interpreted as reflection and transmission coefficients, which provides an intuitive understanding of the propagation and scattering phenomena. Our formulation extends the previously proposed theory of non-uniform transmission lines by introducing an expression for impedance transfer, which yields a closed-form solution for the fields inside and outside the sphere. The power transmitted in and scattered by the sphere can be also evaluated with a simple closed-form expression and related with the modulus of the reflection coefficient. We showed that our method is fully consistent with the classical Mie scattering theory. We also showed that our method can provide an intuitive physical interpretation of electromagnetic scattering in terms of impedance matching and resonances, and that it is especially useful for the case of inward traveling spherical waves generated by sources surrounding the scatterer. Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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18 pages, 3479 KiB

Open AccessArticle

An Efficient Numerical Formulation for Wave Propagation in Magnetized Plasma Using PITD Method

by Zhen Kang, Ming Huang, Weilin Li, Yufeng Wang and Fang Yang

Electronics 2020, 9(10), 1575; https://doi.org/10.3390/electronics9101575 - 26 Sep 2020

Cited by 4 | Viewed by 1749

Abstract

A modified precise-integration time-domain (PITD) formulation is presented to model the wave propagation in magnetized plasma based on the auxiliary differential equation (ADE). The most prominent advantage of this algorithm is using a time-step size which is larger than the maximum value of [...] Read more.

A modified precise-integration time-domain (PITD) formulation is presented to model the wave propagation in magnetized plasma based on the auxiliary differential equation (ADE). The most prominent advantage of this algorithm is using a time-step size which is larger than the maximum value of the Courant–Friedrich–Levy (CFL) condition to achieve the simulation with a satisfying accuracy. In this formulation, Maxwell’s equations in magnetized plasma are obtained by using the auxiliary variables and equations. Then, the spatial derivative is approximated by the second-order finite-difference method only, and the precise integration (PI) scheme is used to solve the resulting ordinary differential equations (ODEs). The numerical stability and dispersion error of this modified method are discussed in detail in magnetized plasma. The stability analysis validates that the simulated time-step size of this method can be chosen much larger than that of the CFL condition in the finite-difference time-domain (FDTD) simulations. According to the numerical dispersion analysis, the range of the relative error in this method is

10^{- 6}

to

5 \times 10^{- 4}

when the electromagnetic wave frequency is from 1 GHz to 100 GHz. More particularly, it should be emphasized that the numerical dispersion error is almost invariant under different time-step sizes which is similar to the conventional PITD method in the free space. This means that with the increase of the time-step size, the presented method still has a lower computational error in the simulations. Numerical experiments verify that the presented method is reliable and efficient for the magnetized plasma problems. Compared with the formulations based on the FDTD method, e.g., the ADE-FDTD method and the JE convolution FDTD (JEC-FDTD) method, the modified algorithm in this paper can employ a larger time step and has simpler iterative formulas so as to reduce the execution time. Moreover, it is found that the presented method is more accurate than the methods based on the FDTD scheme, especially in the high frequency range, according to the results of the magnetized plasma slab. In conclusion, the presented method is efficient and accurate for simulating the wave propagation in magnetized plasma. Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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15 pages, 7677 KiB

Open AccessArticle

Double-Layer Microstrip Band Stop Filters Etching Periodic Ring Electromagnetic Band Gap Structures

by Xuemei Zheng, Tao Jiang, Hao Lu and Yanyan Wang

Electronics 2020, 9(8), 1216; https://doi.org/10.3390/electronics9081216 - 28 Jul 2020

Cited by 5 | Viewed by 2463

Abstract

The electromagnetic band gap structure (EBGs) is widely used in microwave engineering, such as amplifiers, waveguides, microstrip filters, due to the fact of its excellent band stop characteristics. In this paper, three kinds of microstrip band stop filters were proposed which were etched [...] Read more.

The electromagnetic band gap structure (EBGs) is widely used in microwave engineering, such as amplifiers, waveguides, microstrip filters, due to the fact of its excellent band stop characteristics. In this paper, three kinds of microstrip band stop filters were proposed which were etched with a hexagonal ring EBGs, octagonal ring EBGs and elliptical ring EBGs. Firstly, the etching coefficient of a band stop filter is proposed, and the performance of filters with different etching coefficient was analyzed. Secondly, the equivalent circuit of an EBGs band stop filter is proposed. By comparing the simulation results using advanced design system (ADS) and high frequency structure simulator (HFSS), it was found that the simulation results had the same −10 dB stopband width which verifies the correctness of the equivalent circuit model. Finally, three kinds of microstrip stopband filters were fabricated and measured. The experimental results of the −10 dB stopband width and resonant frequency were in good agreement with the simulation results. The −10 dB stopband fractional bandwidth of the three kinds of microstrip stopband filters was more than 63%. The proposed microstrip band stop filters can be widely used in microwave devices with a wide stopband. Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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21 pages, 597 KiB

Open AccessArticle

Three-Dimensional Time-Harmonic Electromagnetic Scattering Problems from Bianisotropic Materials and Metamaterials: Reference Solutions Provided by Converging Finite Element Approximations

by Praveen Kalarickel Ramakrishnan and Mirco Raffetto

Electronics 2020, 9(7), 1065; https://doi.org/10.3390/electronics9071065 - 29 Jun 2020

Cited by 4 | Viewed by 1884

Abstract

A recently developed theory is applied to deduce the well posedness and the finite element approximability of time-harmonic electromagnetic scattering problems involving bianisotropic media in free-space or inside waveguides. In particular, three example problems are considered of which one deals with scattering from [...] Read more.

A recently developed theory is applied to deduce the well posedness and the finite element approximability of time-harmonic electromagnetic scattering problems involving bianisotropic media in free-space or inside waveguides. In particular, three example problems are considered of which one deals with scattering from plasmonic gratings that exhibit bianisotropy while the other two deal with bianisotropic obstacles inside waveguides. The hypotheses that guarantee the reliability of the numerical results are verified, and the ranges of the constitutive parameters of the media involved for which the finite element solutions are guaranteed to be reliable are deduced. It is shown that, within these ranges, there can be significant bianisotropic effects for the practical media considered as examples. The ensured reliability of the obtained results can make them useful as benchmarks for other numerical approaches. To the best of our knowledge, no other tool can guarantee reliable solutions. Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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16 pages, 3556 KiB

Open AccessFeature PaperArticle

Electromagnetic Field Levels in Built-up Areas with an Irregular Grid of Buildings: Modeling and Integrated Software

by Luca Schirru, Filippo Ledda, Matteo Bruno Lodi, Alessandro Fanti, Katiuscia Mannaro, Marco Ortu and Giuseppe Mazzarella

Electronics 2020, 9(5), 765; https://doi.org/10.3390/electronics9050765 - 06 May 2020

Cited by 4 | Viewed by 2696

Abstract

The knowledge of the electromagnetic field levels generated by radio base stations present in an urban environment is a relevant aspect for propagations and coverage issues, as well as for the compliance to national regulations. Despite the growing interest in the novel fifth [...] Read more.

The knowledge of the electromagnetic field levels generated by radio base stations present in an urban environment is a relevant aspect for propagations and coverage issues, as well as for the compliance to national regulations. Despite the growing interest in the novel fifth generation (5G) technology, several aspects related to the investigation of the urban propagation of the Global System of Mobile Communication (GSM), third generation (3G), and fourth generation (4G) mobile systems in peculiar non-rural environments may be improved. To account for irregular geometries and to deal with the propagation in hilly towns, in this work we present an enhanced version of the COST231-Walfisch–Ikegami model, whose parameters have been modified to evaluate the path loss at distances greater than 20 meters from the radio base station. This work addressed the problem of providing an effective, reliable, and quantitative model for the estimation of electromagnetic field levels in built-up areas. In addition, we also developed and tested a pre-industrial software prototype whose aim is to make the estimated electromagnetic field levels available to the key players in the telecom industry, the local authorities, and the general population. We validated the proposed model with a measurement campaign in the small urban and irregular built-up areas of Dorgali (Nuoro), Cala Gonone (Nuoro), and Lunamatrona (Cagliari) in Sardinia (Italy). Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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10 pages, 2282 KiB

Open AccessFeature PaperArticle

A Hybrid Asymptotic-FVTD Method for the Estimation of the Radar Cross Section of 3D Structures

by Alessandro Fedeli, Matteo Pastorino and Andrea Randazzo

Electronics 2019, 8(12), 1388; https://doi.org/10.3390/electronics8121388 - 21 Nov 2019

Cited by 4 | Viewed by 2360

Abstract

The Finite Volume Time-Domain (FVTD) method is an effective full-wave technique which allows an accurate computation of the electromagnetic field. In order to analyze the scattering effects due to electrically large structures, it can be combined with methods based on high-frequency approximations. This [...] Read more.

The Finite Volume Time-Domain (FVTD) method is an effective full-wave technique which allows an accurate computation of the electromagnetic field. In order to analyze the scattering effects due to electrically large structures, it can be combined with methods based on high-frequency approximations. This paper proposes a hybrid technique, which combines the FVTD method with an asymptotic solver based on the physical optics (PO) and the equivalent current method (ECM), allowing the solution of electromagnetic problems in the presence of electrically large structures with small details. Preliminary numerical simulations, aimed at computing the radar cross section of perfect electric conducting (PEC) composite objects, are reported in order to evaluate the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Electromagnetic Scattering and Its Applications: From Low Frequencies to Photonics)

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