Magnetodielectric Medium Research Articles

Loss-gain compensated anti-Hermitian magnetodielectric medium to realize Tellegen nihility effects.

Generalized duality transformations significantly modify the constitutive relations of electromagnetic media, preserving principal electromagnetic properties. Here, we contemplate transformation of Tellegen nihility as a specific type of extreme-property nonreciprocal bi-isotropic media and show that some intriguing electromagnetic properties of that medium can be realized in a particular class of isotropic magnetodielectric media without magnetoelectric coupling. We show that the permittivity and permeability of the corresponding transformed medium have equal absolute values and opposite signs. Depending on the value of the Tellegen parameter of the original medium, the transformed magnetodielectric medium can be Hermitian, non-Hermitian, or anti-Hermitian, which simultaneously exhibits loss and gain. Focusing on the latter class of anti-Hermitian media, we theoretically and numerically demonstrate that this extraordinary medium allows propagation of electromagnetic plane waves having zero time-averaged Poynting vector, similarly to the original Tellegen nihility media. Hopefully, this work can open novel opportunities for manipulating electromagnetic fields.

Low-loss NiZnCo ferrite composites with tunable magneto-dielectric performances for high-frequency applications

A series of Ni0.5Zn0.3Co0.2Fe2O4/epoxy magnetodielectric composites were synthesized through solvent-assisted method and demonstrate tunable permeability and permittivity, ultralow losses and high refractive index over a broad frequency region of the VHF and UHF bands. Experimental results reveal that the permeability μ' decreases from ~4.2 to ~3.5 while the permittivity ε' was improved from ~5.0 to ~6.1 with an increase in epoxy weight fraction from 1 to 20 wt%. These variations are shown to be intimately related to the microstructures in accordance with effective medium theory and magnetic circuit model. Correspondingly, the characteristic impedance of the magnetodielectric composite medium is varied from ~0.75 to ~0.90 while maintaining a refractive index around 4.5. Typical magnetic loss as tan δμ and dielectric loss as tan δε at 0.5 GHz are as low as in the order of 10−2 and 10−3, respectively. These magnetodielectric materials provide excellent radio frequency results that allowing for the realization of the high-performance miniaturized electronic devices, systems, and platforms.

Strong spatial dispersion in time-modulated dielectric media

We present an effective medium description of time-modulated dielectric media. By taking the averaged fields over one modulation period, the relationship between them is derived, therefore defining the different constitutive parameters. In the most general situation, it is found that the effective material is described by means of a spatially and temporally dispersive transverse dielectric function and a constant longitudinal dielectric function. It has been also found that the frequency dependence in the former is weak, in comparison with its wavenumber dependence (spatial dispersion). Different physical consequences of this spatial dispersion are discussed, with special emphasis on the weak dispersion approximation and the limit in which it is found that the effective material behaves as a resonant and isotropic magnetodielectric medium with no additional longitudinal mode, as it is commonly found in spatially dispersive materials. Time-dependent media therefore opens an alternative way of designing dynamically tunable metamaterials.

Alternative formulation of the macroscopic field equations in a linear magneto-dielectric medium: field equations

We derive an alternative formulation of the field equations for macroscopic electromagnetic fields in a linear magneto-dielectric medium as an identity of the Maxwell–Minkowski equations, complementing a variety of other representations including the Ampère, Chu, Lorentz, and Minkowski formulations of continuum electrodynamics. In the new formulation of the macroscopic field equations, the material properties are carried as a renormalization of the temporal and spatial coordinates instead of as independent material constants. The new representation of the field equations raises some interesting physical issues with relativity and boundary conditions.

Theory of a Strip Antenna Located at a Plane Interface of a Uniaxial Magnetic Metamaterial and an Isotropic Medium

Electrodynamic characteristics of an antenna in the form of an infinitesimally thin, perfectly conducting narrow strip located at a plane interface of a uniaxial magnetic metamaterial and an isotropic magnetodielectric medium are studied. The antenna is placed perpendicular to the anisotropy axis of the metamaterial and excited by a time-harmonic external voltage. Singular integral equations for the antenna current are derived for an infinitely long conducting strip. The solutions to such equations are used to find and analyze the current distribution and input impedance of the antenna. Conditions for applicability of an approximate transmission line method for determining the antenna characteristics are established. Within the framework of this method, the obtained results are generalized to the case of a strip antenna with finite length.

Resonant Interaction of the Transitional Radiation of Charged Particles with Anisotropic Magnetodielectric Filling of the Waveguide Periodically Modulated in Space

The features of the interaction of the transition radiation of a charged particle with an anisotropic magnetodielectric medium periodically modulated in the waveguide in the frequency domain of the “strong” (resonant) interaction of the radiation with the modulated medium are considered. It is assumed that the charged particle moves with a constant velocity perpendicular to the axis of the waveguide. Analytical expressions are obtained for the energy of the transition radiation of transverse electric (TE) and transverse magnetic (TM) fields in a waveguide in the strong interaction region with an accuracy of linear small modulation indices inclusive. Analytical expressions for the frequency and width of the frequency region of the strong interaction are found. The possibility of the appearance of the Cherenkov radiation in the strong interaction region for the case of a rectangular waveguide is analyzed.

Representation independent boundary conditions for a piecewise-homogeneous linear magneto-dielectric medium

At a boundary between two transparent, linear, isotropic, homogeneous materials, derivations of the electromagnetic boundary conditions and the Fresnel relations typically proceed from the Minkowski {E,B,D,H} representation of the macroscopic Maxwell equations. However, equations of motion for macroscopic fields in a transparent linear medium can be written using Ampère {E,B}, Chu {E,H}, Lorentz, Minkowski, Peierls, and other formulations of continuum electrodynamics. We present a representation-independent derivation of electromagnetic boundary conditions and Fresnel relations for the propagation of monochromatic radiation through a piecewise-homogeneous, transparent, linear, magneto-dielectric medium. The electromagnetic boundary conditions and the Fresnel relations are derived from energy conservation coupled with the application of Stokes’s theorem to the wave equation. Our representation-independent formalism guarantees the general applicability of the Fresnel relations. Specifically, the new derivation is necessary so that a valid derivation of the Fresnel equations exists for alternative, non-Minkowski formulations of the macroscopic Maxwell field equations.

Теория ленточной антенны, расположенной на плоской границе раздела одноосного магнитного метаматериала и изотропной среды

A study is made of the electrodynamic characteristics of an antenna having the form of an infinitesimally thin, perfectly conducting narrow strip located at the plane interface of a uniaxial magnetic metamaterial and an isotropic magnetodielectric medium. The antenna is perpendicular to the anisotropy axis of the metamaterial and is excited by a time-harmonic given voltage. Singular integral equations for the antenna current are obtained in the case of an infinitely long strip conductor. Based on the solution of these equations, the current distribution and input impedance of the antenna are found and analyzed. The limits of applicability of an approximate method based on the transmission line theory for determining the antenna characteristics are established. Within the framework of this method, the results obtained are generalized to the case of a finite-length strip antenna.

Резонансное взаимодействие переходного излучения заряженной частицы с периодически модулированным в пространстве анизотропным магнитодиэлектрическим заполнением волновода

The peculiarities of the interaction of the transition radiation of a charged particle with periodically modulated in space anisotropic magnetodielectric medium in the waveguide in the frequency region of the strong (resonant) interaction of the radiation with the modulated medium are considered. It is assumed that the charged particle moves with constant velocity perpendicular to the axis of the waveguide. Analytical expressions are obtained for the energy of transition radiation of transverse-electric (TE) and transverse-magnetic (TM) fields in the waveguide in the region of strong interaction with an accuracy of small modulation indexes in the first degree inclusive. Analytical expressions for the frequency and for the width of the frequency region of strong interaction are found. The possibility of the appearance of Cherenkov radiation in the region of strong interaction in the case of a rectangular waveguide is analyzed.

Interferometric Sounding Using a Metamaterial-Based Compressive Reflector Antenna

This paper describes a new coded interferometric system for sensing the physical temperature radiated from the Earth’s surface. The proposed system consists of a compressive reflector antenna (CRA) coated with metamaterial absorbers (MMAs). The CRA and the MMA are used to code the received electromagnetic (EM) field in space and in frequency, at the focal plane array. The MMA is modeled by an equivalent magnetodielectric medium having a definite thickness. A high-frequency method based on physical optics is used to build the sensing matrix of the system, and the inverse problem is solved using a Nesterov-based compressive sensing (CS) methodology. Numerical examples are carried out in order to reconstruct the physical temperature of the Earth’s surface. The performance of the proposed system is compared to that of the conventional interferometric system, GeoSTAR. Preliminary results show that the metamaterial-based CRA provides comparable performance to the GeoSTAR configuration with only half of the feeding elements while keeping the same physical aperture size for the two configurations.

Canonical relativistic quantization of electromagnetic field in the presence of an anisotropic conductor magneto-dielectric medium

A canonical relativistic quantization of the electromagnetic field is introduced in the presence of an anisotropic conductor magneto-dielectric medium in a standard way in the Gupta–Bleuler framework. The medium is modeled by a continuum collection of the vector fields and a continuum collection of the antisymmetric tensor fields of the second rank in Minkowski space–time. The collection of vector fields describes the conductivity property of the medium and the collection of antisymmetric tensor fields describes the polarization and the magnetization properties of the medium. The conservation law of the total electric charges, induced in the anisotropic conductor magneto-dielectric medium, is deduced using the antisymmetry conditions imposed on the coupling tensors that couple the electromagnetic field to the medium. Two relativistic covariant constitutive relations for the anisotropic conductor magneto-dielectric medium are obtained. The constitutive relations relate the antisymmetric electric–magnetic polarization tensor field of the medium and the free electric current density four-vector, induced in the medium, to the strength tensor of the electromagnetic field, separately. It is shown that for a homogeneous anisotropic medium the susceptibility tensor of the medium satisfies the Kramers–Kronig relations. Also it is shown that for a homogeneous anisotropic medium the real and imaginary parts of the conductivity tensor of the medium satisfy the Kramers–Kronig relations and a relation other than the Kramers–Kronig relations.

Entanglement dynamics of two two-level atoms in the vicinity of an invisibility cloak

We study the entanglement between two identical two-level atoms located near an ideal model of invisibility cloaks, by monitoring the the time evolution of the concurrence measure. We obtain the reduced density operator of the atomic subsystem based on a canonical quantization scheme presented for the electromagnetic field interacting with atomic systems in the presence of an anisotropic, inhomogeneous and absorbing magnetodielectric medium. It is shown that two atoms, which are prepared initially in an unentangled state, are correlated in weak coupling regime via the spontaneous emission and the dipole-dipole interaction of two atoms mediated by the invisibility cloak. We therefore find that the invisibility cloak, independent of the hidden object, works fairly well at frequencies far from the resonance frequency of the object and the cloak, whereas near the resonance frequency, the hidden object becoming detectable due to a sharp reduction of the concurrence.

A Homogenization Technique for Obtaining Generalized Sheet-Transition Conditions for a Metafilm Embedded in a Magnetodielectric Interface

Using the multiple-scale homogenization method, we derive generalized sheet transition conditions (GSTCs) for electromagnetic fields at the surface of a metafilm. The scatterers that compose the metafilm are of arbitrary shape and are embedded between two different magneto-dielectric media. The parameters in these boundary conditions are interpreted as effective electric and magnetic surface susceptibilities, which themselves are related to the geometry of the scatterers that constitute the metafilm.

Spontaneous emission and the operation of invisibility cloaks

As a probe to explore the ability of invisibility cloaks to conceal objects in the quantum mechanics domain, we study the spontaneous emission rate of an excited two-level atom in the vicinity of an ideal invisibility cloaking. On this base, first, a canonical quantization scheme is presented for the electromagnetic field interacting with atomic systems in an anisotropic, inhomogeneous, and absorbing magnetodielectric medium which can suitably be used for studying the influence of arbitrary invisibility cloak on the atomic radiative properties. The time dependence of the atomic subsystem is obtained in the Schrodinger picture. By introducing a modified set of the spherical wave-vector functions, the Green tensor of the system is calculated via exact and discrete methods. In this formalism, the decay rate and as well the emission pattern of the aforementioned atom are computed analytically for both weak and strong coupling interaction, and then numerically calculations are done to demonstrate the performances of cloaking in the quantum mechanics domain. Special attention is paid to different possible orientations and locations of the atomic system near the spherical invisibility cloaking. Results in the presence and the absence of the invisibility cloak are compared. We find that the cloak works very well far from its resonance frequency to conceal a macroscopic object, whereas at near the resonance frequency the object is more visible than the situation where the object is not covered by the cloak.

Canonical Quantization of Electromagnetic Field in the Presence of Nonlinear Anisotropic Magnetodielectric Medium with Spatial-Temporal Dispersion

Modeling a nonlinear anisotropic magnetodielectric medium with spatial-temporal dispersion by two continuum collections of three dimensional harmonic oscillators, a fully canonical quantization of the electromagnetic field is demonstrated in the presence of such a medium. Some coupling tensors of various ranks are introduced that couple the magnetodielectric medium with the electromagnetic field. The polarization and magnetization fields of the medium are defined in terms of the coupling tensors and the oscillators modeling the medium. The electric and magnetic susceptibility tensors of the medium are obtained in terms of the coupling tensors. It is shown that the electric field satisfy an integral equation in frequency domain. The integral equation is solved by an iteration method and the electric field is found up to an arbitrary accuracy.

The theory of transient radiation of a charged particle in a waveguide with an anisotropic magnetodielectric filling

We have considered transient radiation of a charged particle that moves at a constant velocity perpendicularly to the axis of a regular waveguide filled with an anisotropic magnetodielectric medium. Wave equations and analytical expressions for transverse electric (TE) and transverse magnetic (TM) fields in the waveguide have been found. Energies of transient radiation of the particle moving in a rectangular waveguide have been determined. We have obtained conditions of occurrence, the frequency, and the energy of Vavilov–Cherenkov radiation.

Canonical quantization of electromagnetic field in the presence of absorbing bi-anisotropic multilayer magnetodielectric media

A bi-anisotropic magnetodielectric medium is modeled by two independent set of three dimensional harmonic oscillators .A fully canonical quantization of electromagnetic field is demonstrated in the presence of a bi-anisotropic magnetodielectric medium. The electric and magnetic polarization fields of the medium are obtained in terms of the dynamical variable modeling the medium. The Heisenberg equations of the system are solved for a multilayer bi-anisotropic magnetodielectric medium.

Canonical quantization of macroscopic electrodynamics in a linear, inhomogeneous magnetoelectric medium

We present a canonical quantization of macroscopic electrodynamics. The results apply to inhomogeneous media with a broad class of linear magnetoelectric responses, which are consistent with the Kramers-Kronig and Onsager relations. Through its ability to accommodate strong dispersion and loss, our theory provides a rigorous foundation for the study of quantum optical processes in structures incorporating metamaterials, provided these may be modeled as magnetoelectric media. Previous canonical treatments of dielectric and magnetodielectric media have expressed the electromagnetic field operators in either a Green's function or mode expansion representation. Here we present our results in the mode expansion picture with a view to applications in guided wave and cavity quantum optics.

Resonance linewidth and inhomogeneous broadening in a metamaterial array

We examine the effect of inhomogeneous broadening on the collective response of a planar metamaterial consisting of asymmetric split ring resonators. We show that such a response leads to a transmission resonance that can persist when the broadening of individual meta-atom resonance frequencies is roughly one half the frequency characterizing the split ring asymmetry. We also find that larger degrees of inhomogeneous broadening can drastically alter the cooperative response, destroying this resonance. The reduced effect of cooperative response due to inhomogeneous broadening may find applications in producing metamaterial samples that more closely mimic homogeneous magneto-dielectric medium with well-defined susceptibility and permittivity.

MODE SUMMATION APPROACH TO CASIMIR EFFECT BETWEEN TWO OBJECTS

In the last few years, several approaches have been developed to compute the exact Casimir interaction energy between two nonplanar objects, all lead to the same functional form, which is called the TGTG formula. In this paper, we explore the TGTG formula from the perspective of mode summation approach. Both scalar fields and electromagnetic fields are considered. In this approach, one has to first solve the equation of motion to find a wave basis for each object. The two T's in the TGTG formula are [Formula: see text]-matrices representing the Lippmann–Schwinger T-operators, one for each of the objects. Each [Formula: see text]-matrix can be found by matching the boundary conditions imposed on the object, and it is independent of the other object. However, it depends on whether the object is interacting with an object outside it, or an object inside it. The two G's in the TGTG formula are the translation matrices, relating the wave basis of an object to the wave basis of the other object. These translation matrices only depend on the wave basis chosen for each object, and they are independent of the boundary conditions on the objects. After discussing the general theory, we apply the prescription to derive the explicit formulas for the Casimir energies for the sphere–sphere, sphere–plane, cylinder–cylinder and cylinder–plane interactions. First the [Formula: see text]-matrices for a plane, a sphere and a cylinder are derived for the following cases: the object is imposed with Dirichlet, Neumann or general Robin boundary conditions; the object is semitransparent; and the object is a magnetodielectric object immersed in a magnetodielectric media. Then the operator approach developed by R. C. Wittman [IEEE Trans. Antennas Propag.36, 1078 (1988)] is used to derive the translation matrices. From these, the explicit TGTG formula for each of the scenarios can be written down. On the one hand, we have summarized all the TGTG formulas that have been derived so far for the sphere–sphere, cylinder–cylinder, sphere–plane and cylinder–plane configurations. On the other hand, we provide the TGTG formulas for some scenarios that have not been considered before.