Perfect Electromagnetic Conductor Research Articles

Interaction of circularly polarized light with an absorptive electromagnetic conductor sphere – Radiation force and spin torque

The concept of a perfect electromagnetic conductor (PEMC) material, which is a class of a magneto-electric metamaterial, has been recently examined in the context of the optical radiation force theory [J. Quant. Spectr. Rad. Transfer, 233 (2019) 21–28; ibid 256 (2020) 107280], with particular emphasis on the rotary polarization effect and the contribution of the cross-polarized waves to the transfer of linear momentum, assuming an illumination of linearly-polarized plane progressive waves. The present investigation shows that additional cross-interference factors, which cannot be ignored, contribute to the time-averaged optical radiation force exerted on an absorptive electromagnetic conductor (AEMC) sphere when the incident field becomes circularly-polarized. Moreover, the analysis is extended to investigate the co-polarized, cross-polarized and cross-interference components of the time-averaged optical spin radiation torque. The multipole series expansion method in spherical coordinates is utilized to derive exact mathematical partial-wave series for the co-polarized, cross-polarized and cross-interference components of the radiation force and torque based on the integration of Maxwell’s radiation stress tensor and its moment over a spherical surface of large radius enclosing the sphere suspended in a lossless medium of wave propagation. Numerical results for the radiation force and spin torque efficiencies and their corresponding co-polarized, cross-polarized and cross-interference components illustrate the analysis with emphasis on the size parameter of the sphere ka, its electromagnetic admittance M as well as its imaginary part amounting to absorption. The computations are of importance from the standpoint of the fundamentals of the linear and angular momenta of circularly-polarized electromagnetic waves transferred to an AEMC and related applications in optical tweezers and particle manipulation of objects exhibiting circular dichroism.

On applying the perturbation theory for the evaluation of near zone scattering properties of a perturbed PEMC cylinder

In this paper, near zone scattering properties of a perturbed perfect electromagnetic conductor (PEMC) cylinder are observed using the perturbation theory (PT). The analytical solution of the scattered field is obtained for both the transverse electric (TE) and transverse magnetic (TM) polarizations of the incident field. The perturbed cross section is generated considering the limits imposed by the PT. The effect of perturbations on the co and cross polarized components of the scattered field from a perturbed PEMC cylinder is observed and compared with the reference scattered field from the circular PEMC cylinder. In particular, the distinctions due to perturbations are observed in the forward and backward scattering. The forward scattering deviates more than the backward scattering. Also, the effect of perturbations for the TE polarization is more evident. The variations in the co and cross polarized scattering are also noted by changing the value of the admittance of the PEMC cylinder.

Diffraction by an interface between perfect electromagnetic conductor and conductive surfaces

The interaction of electromagnetic plane waves by a planar interface between conductive and perfect electromagnetic conductor half-planes is investigated. The method of transition boundary is used for the solution of the problem. The geometry, under consideration, is divided into two parts by using a relation, obtained for a perfect electromagnetic conductor half-plane. After obtaining the diffracted fields for sub-problems, they are combined into a single field for the co- and cross-polarized waves. The behaviors of the total field and its components are analyzed numerically.

Physical optics approach to wave diffraction by a perfect electromagnetic conductor half-plane

The scattering of electromagnetic plane waves by a perfect electromagnetic conductor is investigated. The method of physical optics is used for the analysis of the problem. The reflected fields by a whole-plane are taken into account. The surface electric and magnetic current densities are constructed with the aid of the incident wave and the reflected field from the whole-surface. The scattering integrals are obtained for the electric and magnetic vector potentials. The scattered electric and magnetic fields are expressed in terms of the vector potentials. The scattering integrals are evaluated asymptotically for large values of the wave-number. Some numerical results are given.

Optical trapping of a perfect electromagnetic conductor (PEMC) sphere exhibiting rotary polarization using nonparaxial focused Gaussian single-beam tweezers

A perfect electromagnetic conductor (PEMC) sphere illuminated by linearly-polarized plane progressive waves is known to experience a positive/repulsive force regardless of the sphere size. The present analysis shows that the situation changes when a Rayleigh (small) PEMC sphere is located along the axis of wave propagation of a linearly-polarized nonparaxial focused Gaussian beam. A negative longitudinal force arises as the sphere is translated beyond the center of the focus in the diverging region of the beam along the axis of wave propagation. Mathematical series related to the co-polarized and cross-polarized force components are derived. An exact expression for the on-axis beam-shape coefficients (BSCs) representing the incident nonparaxial focused Gaussian beam is obtained stemming from the complex source-point (CSP) method. The BSCs are compared to the standard solution obtained using the principle of localization. The case of plane progressive waves is recovered for a highly collimated nonparaxial focused Gaussian beam. In addition, the scattering asymmetry parameter is derived. Computations for the longitudinal radiation force efficiency, the dimensionless scattering asymmetry parameter, and the co-polarized and cross-polarized components are presented and discussed. In the Rayleigh regime, the results for the PEMC sphere show that the co-polarized component of the radiation force efficiency is negative beyond the center of the focal spot, while it is positive in the converging region of the beam. Trapping occurs when the longitudinal force vanishes. The cross-polarized radiation force efficiency is always positive, and counteracts the pulling force. Moreover, the scattering asymmetry parameter and its cross-polarized component are always negative while its co-polarized component is positive. Computations for the force efficiency for a radially-polarized nonparaxial focused Gaussian beam are also performed and compared to those obtained using a linearly-polarized focused field. Although the linearly-polarized focused beam induces larger pulling longitudinal force, improved spatial confinement with radial polarization is achieved.

Analytical solution of electromagnetic scattering from PEMC strip located at TI medium

Topological insulator (TI) and perfect electromagnetic conductor (PEMC) are new type of matter with remarkable electromagnetic behavior. Despite of conventional scattered fields terms, cross-component terms are generated when the electromagnetic wave interacts with these matters. In this paper, TI is utilized as host medium for PEMC strip and diffraction of electromagnetic wave from proposed strip is assessed by Kobayashi potential (KP) method which yields exact answer. Pivotal elements in KP are Weber-Schafheitlin integrals which are specific integrals with exact solution. Whereby, boundary and some edge conditions of configurations satisfy automatically and simultaneously. Initially, formulation and theoretical calculations of KP method is provided and far-zone scattered field is calculated. To demonstrate the efficiency of method, convergence analysis is provided and for the validation, comparison with other methods is made. Variations of scattered field pattern due to configuration's parameters are illustrated and discussed meticulously.

Rigorous electromagnetic scattering solution of a PEMC strip placed at interface of dielectric-chiral media using Kobayashi Potential

ABSTRACT In this paper the rigorous solution of transverse electric (TE) and transverse magnetic (TM) plane wave scattering from a Perfect Electromagnetic Conductor (PEMC) strip located at the planar interface of two half spaces (dielectric and chiral medium) is presented by applying Kobayashi Potential (KP) method. Initially, the reflected field in dielectric and also transmitted Beltrami fields in chiral medium are divided into left and right handed fields. Then, contribution of the strip in terms of Bessel eigenfunctions is added as a perturbation to the dielectric and the chiral medium fields. Then, by applying the boundary conditions, utilizing the Weber–Schafheitlin (WS) discontinuous integrals and the Jacobi's polynomials, governing equations of infinite summations with unknown coefficients are derived. The infinite summations are effectively truncated with high numerical accuracy. Next, by solving the matrix equations, the unknown coefficients are calculated. Besides validating the method with the convergence analysis, an asymptotically comparative analysis with other investigations is also provided. Finally, the study of Echo Width (EW) for interesting parameters are depicted. The method is extremely accurate and is applicable to both narrow and wide strips. Also the presented formulations are validated by some methods (KP, physical optic and method of moment).

Dyadic Green’s Function for Electric Dipole Excitation of a Perfect Electromagnetic Conductor Sphere

In this article, we investigate the dyadic Green's function (DGF) of a perfect electromagnetic conductor sphere (PEMCS) due to electric dipoles, theoretically by employing the scattering superposition principle (SSP) and the Ohm-Rayleigh method. Then, the derived DGF is used to calculate the scattered field of a PEMCS due to an arbitrarily oriented infinitesimal electric dipole and also plane wave illumination. Numerical results are compared with those obtained by the FEKO commercial software to demonstrate the efficiency and accuracy of the proposed method. The results are in excellent agreement.

Generalization of Perfect Electromagnetic Conductor Boundary

Certain classes of electromagnetic boundaries satisfying linear and local boundary conditions can be defined in terms of the dispersion equation of waves matched to the boundary. A single plane wave is matched to the boundary when it satisfies the boundary conditions identically. The wave vector of a matched wave is a solution of a dispersion equation characteristic to the boundary. The equation is of the second order, in general. Conditions for the boundary are studied under which the dispersion equation is reduced to one of the first order or to an identity, whence it is satisfied for any wave vector of the plane wave. It is shown that, boundaries associated to a dispersion equation of the first order, form a natural generalization of the class of perfect electromagnetic conductor (PEMC) boundaries. As a consequence, the novel class is labeled as that of generalized perfect electromagnetic conductor (GPEMC) boundaries. As another case, boundaries for which there is no dispersion equation (NDE) for the matched wave (because it is an identity) are labeled as NDE boundaries. They are shown to be special cases of GPEMC boundaries. Reflection of the general plane wave from the GPEMC boundary is considered and an analytic expression for the reflection dyadic is found. Some numerical examples on its application are presented for visualization.

On using the complex conjugate material as coating to observe scattering from a PEMC cylinder buried below a sinusoidal slightly rough surface

In this paper, near and far zone fields scattered from a perfect electromagnetic conductor (PEMC) cylinder coated with complex conjugate material (CCM) and buried below a sinusoidal rough surface is studied. Multiple reflections between the rough surface and the cylinder are evaluated with the help of perturbation theory applied on the plane wave spectrum representation of the cylindrical scattered field. Scattering from CCM coated cylinder is compared with that of a dielectric coated cylinder. Both the CCM and the dielectric material have same refractive index. Difference between the scattered fields is observed due to different impedance of the coating material. Near zone back scattering and forward scattering patterns are very insightful to pronounce the distinctions between the CCM and dielectric coating. It is also noted that for transverse electric (TE) polarized incident field, the forward scattering for CCM and dielectric coated cylinders differs significantly from each other. It is possible to achieve scattering maximization with CCM coating. Moreover, the effects of roughness and the admittance of the PEMC core are also noted on the scattering.

Optical radiation force on a perfect electromagnetic conductor (PEMC) sphere

This work extends the scope of the previous study on the electromagnetic radiation force on a perfect electromagnetic conductor (PEMC) cylinder [F.G. Mitri, J. Quant. Spectr. Rad. Transfer, 233 (2019) 21–28] to the case of a sphere of arbitrary size, illuminated by linearly-polarized plane progressive waves. In contrast with the PEMC cylinder case, the analysis shows that the effect of the cross-polarized waves compensates that of the co-polarized waves such that the optical radiation force is unaffected by the change of the electromagnetic admittance parameter M of the sphere. The multipole series expansion method in spherical coordinates is used to derive exact mathematical series for the co-polarized and cross-polarized components of the longitudinal radiation force. Numerical results for the radiation force efficiency and its co-polarized and cross-polarized components demonstrate the individual contributions. The results show that the cross-polarized component of the radiation force efficiency can be positive or negative as the dimensionless size ka varies. Moreover, it vanishes for ka ≈ 1.78 regardless of the admittance parameter of the PEMC sphere. Notice that the total force (i.e. the sum of the co-polarized and cross-polarized components) is always repulsive (i.e., positive). It is also verified that the results are in complete agreement with the law of energy conservation applied to scattering, where the extinction and scattering energy efficiencies are equal, and independent of M. Furthermore, an equivalent expression for the longitudinal radiation force efficiency is derived stemming from an analysis of the asymmetry parameter and the law of energy conservation applied to scattering. Additional computations for the co-polarized and cross-polarized components of the scattering asymmetry parameter are presented and discussed. The results are of some importance from the standpoint of the basics of the electromagnetic radiation force theory and related applications in particle manipulation.

Analytical study of hybrid surface plasmon polaritons in a grounded chiral slab waveguide covered with graphene sheet

In this paper, we propose a new analytical model for grounded chiral slab waveguides covered with graphene sheets. The general waveguide is constructed of a graphene sheet sandwiched between two different chiral layers (as substrate and cover layers), each one has the permittivity, the permeability and the chirality of $$ \varepsilon_{c} ,\mu_{c} ,\gamma_{c}$$ , respectively. The substrate is supposed to be a perfect electromagnetic conductor, which is able to easily convert to a perfect electric conductor or a perfect magnetic conductor. A novel matrix representation is obtained for the general structure to find its dispersion relation and other propagating parameters. To show the richness of the proposed waveguide, two new structures have been introduced and investigated. It has been shown that the modal properties of these exemplary structures are tunable by changing the chemical potential of the graphene and the chirality. The proposed general structure and its analytical model can be utilized for designing tunable plasmonic devices in THz frequencies.

Optical TM ⇄ TE mode conversion contribution to the radiation force on a cylinder exhibiting rotary polarization in circularly polarized light

Circularly polarized light can induce additional mode conversion when it interacts with a material that rotates the orientation of the plane of polarization, which is known as “optical rotation” or “rotary polarization”. The effect of this additional mode conversion phenomenon is studied in the framework of the optical radiation force theory. The time-averaged force (per-length) acting on an infinitely long perfect electromagnetic conductor (PEMC) circular cylinder is considered. The multipole modal expansion method in cylindrical coordinates is utilized to derive exact series expansions for the components of the longitudinal radiation force per-length (i.e. acting along the direction of wave propagation) applicable to any range of frequencies. Numerical predictions for the radiation force function (which is the radiation force per unit energy density and cross-sectional surface) and its components clearly demonstrate the contribution of the co-polarized and cross-polarized waves. It is shown that the total radiation force is not the mere sum of the TM and TE mode components in a circularly polarized wave-field. There is an additional cross-interference term describing the contributions of TM ⇄ TE mode conversion to the total force that cannot be neglected. The computations show that the interference term can be positive, null or negative as the dimensionless size parameter ka and admittance M of the cylinder vary (where k is the wavenumber in the medium of wave propagation and a is the radius of the cylinder). The results show that the total force is always positive and acts in the direction of wave propagation (i.e., force of repulsion). The analysis is further extended to compute the energy efficiencies, demonstrating the validity of the results from the standpoint of energy conservation. This work generalizes the radiation force formalism for linearly polarized fields by introducing additional terms corresponding to TM ⇄ TE mode conversions in the series expansion for the longitudinal radiation force on cylindrical materials exhibiting rotary polarization in circularly polarized plane progressive waves.

Optical cross-sections and energy efficiencies of a cylindrical material exhibiting circular dichroism in arbitrary-shaped monochromatic light-sheets

Optical scattering, extinction and absorption cross-sections are derived for a cylindrical material exhibiting rotary polarization. A structured light-sheet of arbitrary shape illuminates the cylindrical particle of arbitrary geometrical cross-section. The partial-wave series expansion method in cylindrical coordinates is used and Poynting’s theorem is applied. Exact mathematical series expansions are obtained without any approximations. They demonstrate that the optical cross-sections are not the mere sum of linearly polarized components. Additional terms contributing to the series arise from the cross-interaction of the linearly polarized modes (known also as mode conversion TM ⇆ TE) in the scattering field. Numerical examples for the scattering or extinction energy efficiencies of a left-handed circularly polarized Airy light sheet illustrate the analysis for a circular perfect electromagnetic conductor cylinder in air. The results clearly demonstrate the contribution of mode conversion for a cylinder exhibiting circular dichroism. Under some specific conditions determined by the incident light-sheet characteristics and cylinder size, mode conversion can be zero, or it can contribute in the enhancement or reduction of the scattering.

Gaussian source beam diffraction by a perfect electromagnetic half-plane.

In the present work, diffraction of a Gaussian source beam by a perfect electromagnetic conductor (PEMC) semi-screen is investigated. Due to the special property of the PEMC sheet, which is a combination of perfect electric conductor and perfect magnetic conductor surfaces, the reflected wave from the PEMC surface has a cross-polarized component in addition to the co-polarized component. For an electric line source illumination, the diffracted fields are derived by considering the analogy between the transition boundaries and scattered geometric optics fields. Later, the complex point source technique is applied for evaluation of Gaussian beam diffraction. The finite magnitude values of fields are derived with the aid of an improved version of the well-known uniform theory of diffraction for evanescent plane waves. Also, the resultant waves are plotted and discussed for different groups of parameters.

New analytical investigation of anisotropic graphene nano-waveguides with bi-gyrotropic cover and substrate backed by a PEMC layer

This paper aims to study the magneto-plasmons in an anisotropic graphene nano-waveguide with bi-gyrotropic cover and substrate. The substrate is backed by a perfect electromagnetic conductor (PEMC) layer, a general and ideal boundary, which can be transformed easily into the perfect electric conductor (PEC) or the perfect magnetic conductor (PMC) boundaries. The upper and bottom layers of the graphene sheet are made of different magnetic materials, each one has the permittivity and permeability tensors of $$\bar{\bar{\varepsilon }}$$ and, $$\bar{\bar{\mu }}$$ respectively. The external magnetic field is applied perpendicularly to the structure surface, which can be provided by a permanent magnet placed underneath the ground plane. Hence, the graphene sheet has anisotropic conductivity tensor ($$\bar{\bar{\sigma }}$$). A novel analytical model has been proposed for the general nano-waveguide to find its propagation properties. As special cases of the proposed general structure, two important new waveguides have been introduced and studied to show, first the richness of the proposed general nano-waveguide regarding the related specific plasmonic wave phenomena and effects, and second the validity and the high accuracy of the proposed model. The analytical and the simulation results are in an excellent agreement. It is shown that the modal properties of the proposed structure can be tuned effectively via the external magnetic field and the chemical potential of the graphene. Harnessing the non-reciprocity effect of anisotropic materials and the graphene sheet, the presented analytical model can be exploited to design tunable innovative devices in THz frequencies.

Optical radiation force circular dichroism spectroscopy

This work introduces the method of circular dichroism spectroscopy in the framework of the electromagnetic/optical radiation force theory. This technique is defined here as the difference in radiation force of left-handed and right-handed circularly polarized electromagnetic waves illuminating an object exhibiting rotary polarization. The example of a lossless material, such as the perfect electromagnetic conductor (PEMC) cylinder having a circular geometric cross-section, is considered. The modal expansion method in cylindrical coordinates is used to obtain exact mathematical series expansions for the longitudinal radiation force per-length (i.e. acting along the direction of wave propagation) considering left-handed and right-handed circularly polarized cylindrically diverging waves emanating from a line source. The case of plane progressive waves is recovered when the source is located far from the cylinder. Numerical illustrative results for the dimensionless radiation force functions as well as the scattering, extinction and absorption energy efficiencies and their co-polarized and cross-polarized components are performed with particular emphasis on the size parameter of the cylinder, the dimensionless distance parameter from the line source, and the admittance of the cylinder. The results reveal that the individual radiation force functions for left-handed and right-handed circularly polarized waves can be negative, zero, or positive depending on the cylinder distance from the source. Moreover, the optical radiation force circular dichroism (ORFCD) and the extinction energy efficiency circular dichroism (EEECD) are positive for a negative admittance of the cylinder, while they reverse sign for a positive admittance. While the EEECD shows some form of symmetry versus admittance sign change, the ORFCD does not. The possibility of achieving invisibility cloaking for a small PEMC cylinder is also predicted. The present ORFCD spectroscopy method is applicable to any cylinder material exhibiting rotary polarization such as chiral, topological insulator, plasma, liquid crystal etc.

Locally Strong-Coupled Microwave Resonator Using PEMC Boundary for Distant Sensing Applications

This research study reports on a new coupling structure to demonstrate a constant coupling strength for longer distances in planar microwave sensors. It is shown that there is a positive correlation between the gap size in a pair of gap-coupled transmission lines (GCTLs) and the effective distance of reader and sensing resonators in a planar microwave sensor. On the other hand, the coupling strength in a pair of GCTLs is negatively correlated to the gap size between the two lines, where the larger gap sizes result in weaker coupling strength or vice versa. A technique is introduced to make the coupling strength partially independent of the gap size in GCTLs. The technique enables a sensor designer to increase the gap size, and subsequently, the distance between the reader and sensing resonators of a sensor. Strong electromagnetic coupling is locally demonstrated between a pair of GCTLs using a new artificial perfect electromagnetic conductor (PEMC) boundary, which does not allow electromagnetic power reflect toward the source over larger gap sizes in GCTLs. The concept is experimentally verified with a gap size up to 10 mm between GCTLs with a constantly measured insertion loss of 0.9 dB. Moreover, the structure is employed to design distant microwave resonator for humidity sensing applications. The design has demonstrated the ability of sensing, while the sensing resonator is placed at 35-mm distance from the readout circuitry. The structure is reported to increase the sensing distance with a ratio of about 12 (36:3) compared to the conventional microwave sensors.

Induced radiation force of an optical line source on a cylinder material exhibiting circular dichroism.

The optical radiation force experienced by a cylinder material of circular cross section exhibiting circular dichroism (known also as rotary polarization) in an electric line source illumination is considered. An exact analytical expression for the radiation force (per length) valid for any frequency range is derived assuming an electric line source radiating cylindrically diverging TM-polarized waves without any approximations. The partial-wave series expansion method in cylindrical coordinates utilizing standard Bessel and Hankel functions is used to derive the electric and magnetic field expressions and a dimensionless radiation force function (or efficiency), which depends on the scattering coefficient of the cylinder as well as the distance from the radiating source. To illustrate the analysis, numerical computations for the dimensionless radiation force function for a perfect electromagnetic conductor (PEMC) cylinder are performed with emphasis on its dimensionless size parameter and source distance, which clearly draw attention to the contribution of the cross-polarized scattered waves (resulting from the rotary polarization effect) to the total force. The numerical predictions demonstrate the possibility to pull a circular-shaped cylinder material with rotary polarization toward the illuminating electric line source with TM-polarized waves using a curved wavefront depending on the PEMC material admittance, distance to the source, and size of the cylinder.

Scattering from a Buried PEMC Cylinder due to a Line Source Excitation above a Planar Interface Between Two Isorefractive Half Spaces

A solution to the problem of scattering from a perfect electromagnetic conducting (PEMC) circular cylinder buried inside a half-space and excited by an infinite electric line source is provided. The line source is parallel to the cylinder axis, and is located in the other half-space. The two half spaces are isorefractive to each other. The source fields when incident at the planar interface separating the two half spaces, generate fields that are transmitted into the half-space where the cylinder is. These fields then become the known basic incident fields for the buried PEMC cylinder. Scattering of these incidents fields by the cylinder will consequently generate fields at the interface that get reflected back into the same half-space and transmitted frontward into the source half-space, all of which are unknown. Imposing appropriate boundary conditions at the surface of the buried cylinder and at a specified point on the interface, enables the evaluation of these unknown fields. The refection coefficient at the specified point is then computed for cylinders of different sizes, to demonstrate how it varies with the PEMC admittance of the buried cylinder, the intrinsic impedance ratio of the two isorefractive half-spaces, and the burial depth of the cylinder.