Imperfect Conductors Research Articles

Comparison of Linear Iteration Schemes to Improve the Convergence of Iterative Physical Optics for an Impedance Scatterer

The conventional iterative physical optics (IPO) method updates the surface current based on the Jacobi iteration scheme, which typically diverges for large objects. To control the convergence property of the IPO method, other iteration schemes, such as Gauss–Seidel and successive over-relaxation, can be used. In this study, we compare the convergence properties of three iteration schemes for scatterings by five scatterers comprising electrically perfect or imperfect conductors modeled with an impedance material. The accuracy of the IPO method is compared with that of the multi-level fast multipole method.

Analysis of Hemispherical Dielectric Resonator Antenna With an Imperfect Concentric Conductor

This work presents a full-wave Green’s function approach for the rigorous investigation of a probe-coupled dielectric resonator antenna (DRA) configuration with an imperfect inner conductor. The impedance boundary condition is applied over the imperfect conductor in the formulation to derive the fields inside and outside the dielectric region, considering all higher-order modes. The technique enhances the applicability of the full-wave Green’s function in the evaluation of input impedance and radiation characteristics for an antenna structure with imperfectly conducting spherical surface, which to the best of our knowledge has not been reported before in the DRA literature. The role of the surface impedance on the antenna resonance and quality factor is thoroughly characterized. A suitable choice of the surface reactance depending on the radius of the imperfect conductor and dielectric-coating thickness enables the simultaneous reduction in the resonant frequency and quality factor for the antenna configuration. The effect of the surface reactance with varying coating permittivities is also investigated. The parametric variations in the input impedance, reflection coefficient, and antenna bandwidth with change in the surface impedance and coating permittivity for the antenna configuration are analyzed. The radiation characteristics for the antenna configuration are also examined.

On the Far Field Patterns for Electromagnetic Scattering in Two Dimensions

We consider the problem of scattering time-harmonic electromagnetic plane waves by a dielectric infinitely long cylinder with core which may be a perfect or an imperfect conductor. The corresponding scattering problems are reduced to mixed boundary value problems for the two-dimensional Helmholtz equation . For the far field patterns of these problems, we prove a reciprocity principle and a general scattering theorem. The combination of these theorems with Herglotz wave functions leads to the proof of some properties of the far field operator, which are used in the study of inverse scattering problems. Finally, an optical theorem for the above scattering problems is proved.

Denoising With Inherent Scattering Characteristic for 2-D Radar Cross Section Measurement

Noises from the measurement sensors are inevitable in radar cross section testing due to the thermal agitation of electrons in imperfect conductors. Existing methods represented by wavelet threshold usually regard the measured data as a stationary stochastic signal, ignoring the inherent influence of the target under test, which inevitably removes the signal’s component when noise increases. This paper proposes a novel perspective on 2-D radar cross section measurement denoising, considering the target’s inherent scattering characteristics (ISC). In the proposed method, the noise and the target are firstly separated as far as possible in the generalized Fourier series domain while the target’s component is all preserved. Then, the noise is further suppressed by the scattered field reconstruction of the Hankel function. Finally, a metal sphere being a calibrator is introduced to improve the denoising ability. Both simulations and experimental studies demonstrate the superiority of our method compared with existing algorithms. Results indicate that the proposed method can achieve higher accuracy.

Electromagnetism from 5D gravity: beyond the Maxwell equations

Ever with the work of Kaluza, it has been known that 4D Einstein- and Maxwell-type equations emerge from the equations for 5D gravity, in Ricci-flat space-times having a space-like Killing vector. We revisit these equations and compare them with the Maxwell equations and the Ohm’s law. Although 5D gravity and traditional electromagnetic theory are mathematically related, a paradigm shift in traditional electromagnetic concepts is required for unification. First, both the Maxwell equations and the Ohm’s law are found among the field equations for 5D gravity, which turns Ohm’s law into a field equation. Second, the concept of 4-current density, bringing together electrical charge and current density, is no longer fundamental for the electromagnetic theory resulting from 5D gravity. Third, the 5D gravity equations suggest a generalization for the model of the perfect conductor, to describe a broader range of electromagnetic phenomena and bypass the concept of 4-current density. We thus propose an amendment to the Maxwell equations, based on the field equations for 5D gravity, and discuss a few applications. Namely, we discuss the propagation of electromagnetic waves through an imperfect conductor and topics in electrostatics and magnetostatics, touching ground with the Hall effect and the phenomenon of the persistent current.

A semiclassical Thomas-Fermi model to tune the metallicity of electrodes in molecular simulations.

Spurred by the increasing needs in electrochemical energy storage devices, the electrode/electrolyte interface has received a lot of interest in recent years. Molecular dynamics simulations play a prominent role in this field since they provide a microscopic picture of the mechanisms involved. The current state-of-the-art consists of treating the electrode as a perfect conductor, precluding the possibility to analyze the effect of its metallicity on the interfacial properties. Here, we show that the Thomas-Fermi model provides a very convenient framework to account for the screening of the electric field at the interface and differentiating good metals such as gold from imperfect conductors such as graphite. All the interfacial properties are modified by screening within the metal: the capacitance decreases significantly and both the structure and dynamics of the adsorbed electrolyte are affected. The proposed model opens the door for quantitative predictions of the capacitive properties of materials for energy storage.

Analytical prediction of resonant frequencies of annular stacked dielectric resonator antennas

The method of stacking dielectric resonators for designing multiband and wideband antennas has gained much attention in recent times. However, the existing works lack any theoretical framework for the prediction of resonant frequencies of such stacked structures. In this work, a formal analysis using a cavity model with the mode matching technique is presented to determine all the existing resonant frequencies of annular stacked cylindrical dielectric resonator antennas with and without air gap. The analysis is done separately considering the outermost sidewall of the stack as both perfect magnetic conductor and imperfect magnetic conductor. The theoretical findings are extensively validated against numerous simulations, as well as against a fabricated prototype. It is observed that the perfect magnetic wall condition provides results that are more accurate. The closed-form equation derived in this work not only helps in accurately predicting the resonant frequencies but also reduces the run-time manifolds compared to that of the existing trial and error based methods of design using software simulations.

Application of Whale Optimization Algorithm to Inverse Scattering of an Imperfect Conductor with Corners

In this paper, the whale optimization algorithm (WOA) is applied to the inverse scattering of an imperfect conductor with corners. The WOA is a new metaheuristic optimization algorithm. It mimics the hunting behavior of humpback whales. The inspiration results from the fact that a whale recognizes the location of a prey (i.e., optimal solution) by swimming around the prey within a shrinking circle and along a spiral-shaped path simultaneously. Initially, the inverse scattering is first transformed into a nonlinear optimization problem. The transformation is based on the moment method solution for scattering integral equations. To treat a target with corners and implement the WOA inverse scattering, the cubic spline interpolation is utilized for modelling the target shape function. Numerical simulation shows that the inverse scattering by WOA not only is accurate but also converges fast.

Selective Excitation of the Microwave Sommerfeld—Zenneck Surface Wave on a Conductive Strip

Surface electromagnetic waves (SEWs) on imperfect conductors proposed by A. Sommerfeld and J. Zenneck in the early 20th century have remained unrecognized by academic science for almost a hundred years due to a regrettable misunderstanding of theorists and unsolved radio communication problems. Recognition could have come much earlier if radiophysicists had been able to apply excitation of SEWs in the centimeter range of microwaves, generation of which became possible in the first half of the 20th century with development of radar. Radiophysical experiments on excitation of surface electromagnetic waves on conductors in the centimeter range of radio waves are presented. A method for selective excitation of SEWs is described. Its essence is that the space radio wave radiation is suppressed by screening while the SEW on the conductive strip is excited by isolated currents launched through a slit in the screen.

Linear analysis of traveling sheet electron beam in sine waveguide tubes

A theoretical model is proposed for linear analysis of the beam–wave interaction in a sine waveguide (SWG) with slow-wave structure. The field expressions and “hot” dispersion equation are obtained by means of field matching. The ohmic loss and attenuation constant due to imperfect conductors are also derived using the theoretical model. Moreover, the effects of voltage, current, beam thickness, period, and oscillation amplitude on the linear gain and bandwidth are calculated. The results indicate a peak gain and 3-dB bandwidth of 6.82 dB/cm and 19.5%, respectively, for a 0.22-THz SWG traveling-wave tube upon selecting reasonable structural parameters and electron-beam dimensions. Furthermore, by considering the ohmic losses for the finite conductivities of 5.8 × 107 S/m and 2.2 × 107 S/m, the theoretical results are compared with those of particle-in-cell simulations performed using Computer Simulation Technology Particle Studio.

Analysis and design of sea-water monopole Yagi-Uda antenna with pattern reconfigurability

In this article, a theoretical study of sea-water monopole Yagi-Uda antenna is presented. Unlike the conventional metal one, sea-water monopole is here treated as imperfect conductor. Based on this precondition, a methodology for analyzing sea-water monopole Yagi-Uda antenna is proposed by employing the 3-term theory and voltage-current relation. As such, both its input impedance and radiation pattern can be theoretically predicted. Commercial software packages ANSYS HFSS and CST Microwave Studio are used to verify the proposed methodology. Finally, a prototype is designed, fabricated, and tested. Due to the liquidity of sea water, the parasitic element can work as a director or reflector by altering its height to achieve pattern reconfigurability. Measured results show reasonably good agreement with the simulated and theoretical ones.

Passive Intermodulation Due to Conductor Surface Roughness

The physical mechanism of the experimentally observed dependence of passive intermodulation (PIM) in printed circuits on conductor surface roughness is studied. It is shown that electrothermal (ET) nonlinearity, arising due to heating of imperfect conductors by high-power carriers in a multicarrier system, is correlated with conductor surface roughness and has a unique signature. Carriers modulate the conductor resistivity, skin depth, and surface impedance which generate PIM products. The detailed analysis demonstrates that ET-PIM depends on the conductor resistivity, shape, and roughness profile and also on the electric and thermal properties of the substrate. Their effects on PIM are illustrated by examples of uniform microstrip lines with different conductor and substrate materials, and periodically perturbed and meandered microstrip lines.

Streamer discharges as advancing imperfect conductors: inhomogeneities in long ionized channels

A major obstacle for the understanding of long electrical discharges is the complex dynamics of streamer coronas, formed by many thin conducting filaments. Building macroscopic models for these filaments is one approach to attain a deeper knowledge of the discharge corona. Here, we present a one-dimensional, macroscopic model of a propagating streamer channel with a finite and evolving internal conductivity. We represent the streamer as an advancing finite-conductivity channel with a surface charge density at its boundary. This charge evolves self-consistently due to the electric current that flows through the streamer body and within a thin layer at its surface. We couple this electrodynamic evolution with a field-dependent set of chemical reactions that determine the internal channel conductivity. With this one-dimensional model, we investigate the formation of persisting structures in the wake of a streamer head. In accordance with experimental observations, our model shows that a within a streamer channel some regions are driven towards high fields that can be maintaned for tens of nanoseconds.

Theoretical investigations on equilateral triangular dielectric resonator antenna

Equilateral triangular dielectric resonator antenna (ETDRA) is investigated here analytically for TM z mode. For theoretical analysis, the triangular surfaces on the top and bottom of the isolated ETDRA are modelled either as perfect magnetic conductors (PMC) or imperfect magnetic conductors (IPMC), whereas the side walls having rectangular cross-section are modelled as PMC only. The concept of reduction in effective size due to the avoidance of any corner by the electric field lines is used for the first time to predict the resonant frequency for different TM z mnp modes with an accuracy of 4%. Consequently, an expression is also given here for efficient evaluation of effective dimensions of the ETDRA for various TM z mnp modes. Closed form expressions for the far-field radiation patterns of dominant TM z 101 mode are also presented using both (PMC and IPMC) models. Theoretical results are compared with published data as found in the open literature. One antenna prototype is also fabricated, tested and measured for further verification. It is found that the authors’ theoretical results are in close agreement with measured data.

Derivative expansion for the electromagnetic and Neumann-Casimir effects in2+1dimensions with imperfect mirrors

We calculate the Casimir interaction energy in $d=2$ spatial dimensions between two (zero-width) mirrors---one flat and the other slightly curved---upon which imperfect conductor boundary conditions are imposed for an electromagnetic (EM) field. Our main result is a second-order derivative expansion (DE) approximation for the Casimir energy, which is studied in different interesting limits. In particular, we focus on the emergence of a nonanalyticity beyond the leading-order term in the DE, when approaching the limit of perfectly conducting mirrors. We also show that the system considered is equivalent to a dual one, consisting of a massless real scalar field satisfying imperfect Neumann conditions (on the very same boundaries). Therefore, the results obtained for the EM field hold true also for the scalar field model.

Validated predictive computational methods for surface charge in heterogeneous functional materials: HeteroFoaM™

Abstract Background Essentially all heterogeneous materials are dielectric, i.e., they are imperfect conductors that generally display internal charge displacements that create dissipation and local charge accumulation at interfaces. Over the last few years, the authors have focused on the development of an understanding of such behaviour in heterogeneous functional materials for energy conversion and storage, called HeteroFoaM (www.HeteroFoaM.com). Using paradigm problems, this work will indicate major directions for developing generally applicable methods for the multiphysics, multi-scale design of heterogeneous functional materials. Methods The present paper outlines the foundation for developing validated predictive computational methods that can be used in the design of multi-phase heterogeneous functional materials, or HeteroFoaM, as a genre of materials. Such methods will be capable of designing not only the constituent materials and their interactions, but also the morphology of the shape, size, surfaces and interfaces that define the heterogeneity and the resulting functional response of the material system. Results Relationships to applications which drive this development are identified. A paradigm problem based on dielectric response is formulated and discussed in context. Conclusions We report an approach that defines a methodology for designing not only the constituent material properties and their interactions in a heterogeneous dielectric material system, but also the morphology of the shape, size, surface, and interfaces that defines the heterogeneity and the resulting functional response of that system.

Microwave imaging for half-space imperfect conductors

This article presents an inverse scattering problem for recovering the shape and conductivity of an imperfect conductor buried in a half space by self-adaptive dynamic differential evolution (SADDE). The imperfect conductor of unknown conductivity and shapes is buried in one half-space and illuminated by the transverse magnetic plane wave from the other half-space. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equation is derived and the imaging problem is reformulated into optimisation problem. The SADDE algorithm is employed to find out the global extreme solution of the object function. Numerical results show that the conductivity and the shape of the conductor are well reconstructed. Moreover, the shape function is more sensitive to the scattered field variation than the conductivity. Accurate reconstruction of the shape function can be obtained by using the novel optimisation algorithm. As a result, the electric conductivity can be computed more accurately.

Computation of static and frequency-dependent line parameters of multilayer CPW using static SDA and single layer reduction method

We reformulate the quasi-static SDA applicable to a lossy multilayer CPW that also incorporates two-layer model of a conductor thickness and the concept of effective permeability due to magnetic field penetration in an imperfect conductor. The present static SDA formulation accounts for the effect of conductor thickness and low frequency dispersion on computation of quasi-static effective relative permittivity and characteristic impedance. The paper also presents the single layer reduction (SLR) formulation and circuit model to compute frequency dependent line parameters of a lossy multilayer CPW. The accuracy of formulation is comparable to that of HFSS and CST, without using complex and time consuming full-wave methods. The results of CST for εeff, Z0, αd, αc of multilayer CPW, in the frequency range 1–100 GHz, deviate from results of HFSS up to 1.26%, 2.78%, 11.75%, and 18.7%, respectively; whereas corresponding deviations of present formulation are up to 1.56%, 2.4%, 3.04%, and 7%. The results of the present formulation and HFSS are also compared against the available experimental results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:18–29, 2014.

MODELING FOR DISPERSION AND LOSSES OF MULTILAYER ASYMMETRIC CPW ON ISO/ANISOTROPIC SUBSTRATE

In this paper, we reformulate the quasi-static spectral domain analysis (SDA) applicable to a lossy anisotropic multilayer asymmetric coplanar waveguide (ACPW). The SDA formulation also incorporates two-layer model of a conductor thickness and the concept of efiective permeability to account for the low frequency dispersion due to the magnetic fleld penetration in an imperfect conductor. The paper further presents the single layer reduction (SLR) formulation and circuit model to compute frequency dependent line parameters of a lossy anisotropic multilayer ACPW. The accuracy of formulation is comparable to that of the HFSS and CST, without using complex and time consuming full-wave methods. The results of CST for efi , Z0, fid, fic of multilayer ACPW, in the frequency range 1GHz{100GHz, deviate from results of HFSS up to 0.49%, 1.53%, 2.06% and 10.73% respectively; whereas corresponding deviations of the present SDA and SLR combined formulation are up to 1.38%, 2.09%, 3.57% and 8.87%.

New Absorbing Boundary Conditions and Analytical Model for Multilayered Mushroom-Type Metamaterials: Applications to Wideband Absorbers

An analytical model is presented for the analysis of multilayer wire media loaded with 2-D arrays of thin material terminations, characterized in general by a complex surface conductivity. This includes the cases of resistive, thin metal, or graphene patches and impedance ground planes. The model is based on the nonlocal homogenization of the wire media with additional boundary conditions (ABCs) at the connection of thin (resistive) material. Based on charge conservation, new ABCs are derived for the interface of two uniaxial wire mediums with thin imperfect conductors at the junction. To illustrate the application of the analytical model and to validate the new ABCs, we characterize the reflection properties of multilayer absorbing structures. It is shown that in such configurations the presence of vias results in the enhancement of the absorption bandwidth and an improvement in the absorptivity performance for increasing angles of an obliquely incident TM-polarized plane wave. The results obtained using the analytical model are validated against full-wave numerical simulations.