Reciprocal Medium Research Articles

Unraveling the effect of circularly polarized light on reciprocal media: Breaking time reversal symmetry with non-Maxwellian magnetic-esque fields

Unraveling the effect of circularly polarized light on reciprocal media: Breaking time reversal symmetry with non-Maxwellian magnetic-esque fields

Nonlocal effective medium theory for phononic temporal metamaterials

We have developed a nonlocal effective medium theory (EMT) for phononic temporal metamaterials using the multiscale technique. Our EMT yields closed-form expressions for effective constitutive parameters and reveals these materials as reciprocal media with symmetric band dispersion. Even without spatial symmetry breaking, nonzero Willis coupling coefficients emerge with time modulation and broken time-reversal symmetry, when the nonlocal effect is taken into account. Compared to the local EMT, our nonlocal version is more accurate for calculating the bulk band at high wavenumbers and essential for understanding nonlocal effects at temporal boundaries. This nonlocal EMT can be a valuable tool for studying and designing phononic temporal metamaterials beyond the long-wavelength limit.

Electromagnetic Doppler effect in non-reciprocal medium

Reflected light from a moving object, such as a mirror, is frequency-shifted via the Doppler effect. This well-known phenomenon is used to determine the speed and direction of an object due to the red or blue shifting of the received electromagnetic radiation frequency. To date, the Doppler theory has focused on the propagation of electromagnetic radiation through reciprocal media where the transiting photons have the same speed, regardless of direction. However, optical birefringence exists in solid-state, liquid, and gas media, which results in spatially dependent, and vector field-dependent, propagation velocities. When combined with the Faraday effect, which is employed routinely in laboratory setups and present at galactic scales, non-reciprocal Doppler effects may occur. A non-reciprocal Doppler effect theory is derived showing frequency shift dependencies on the object velocity and the directional speed of light in the medium. This general Doppler theory is shown to simplify the canonical relations for the Doppler effect in systems without a directional dependence on light. In non-reciprocal systems, when the mirror velocity is much less than the speed of light, the general frequency shift relation simplifies to a dependency on the roundtrip average speed of light. This theory provides a basis for the application of the Doppler effect to estimate the velocity of moving objects in non-reciprocal systems.

Reciprocity condition in synchronously time-periodic bianisotropic materials

In this paper, a sufficient reciprocity condition for general time-periodic modulated bianisotropic media is extracted from first principles. Reciprocity of various cases of significant importance, including stationary bianisotropic media, time-varying (TV) isotropic media, TV anisotropic media, and TV bianisotropic media, are investigated using this condition. We prove that synchronous time modulation of stationary bianisotropic yet reciprocal media (chiral, pseudochiral, and achiral) does not lead to nonreciprocity, unless the modulation function breaks time reversal symmetry. This is in contrast to recently published research. The theoretical results are validated using in-house finite difference time domain simulations.

Simple Derivation of Transfer Functions in Bistatic Scattering Model

We present a simple derivation of the increment of the scattering and impedance parameters among antennas caused by the scattering from a target in an inhomogeneous nonmagnetic reciprocal medium. Although these formulas have been published in the literature, we provide a straightforward and elegant derivation using the electromagnetic (EM) reciprocity theorem and the circuit theory. In this way, we provide a deeper physical insight into the formulas crucial for most microwave imaging (MWI) algorithms.

Gyrotropic reciprocal bianisotropic metamaterial printed dipole antenna: Investigation of negative input impedance and mutual coupling

This paper surveys a new class of electromagnetic materials. The emphasis is on the bianisotropic medium; a complex material which has never been applied in antenna design. In this context, we investigate the behavior of the magnetoelectric elements of the gyrotropic reciprocal bianisotropic medium used as a grounded substrate by studying their effects on the input impedance and mutual coupling of a printed dipole antenna. Numerical integrative equation calculations are carried out using the spectral method of moments (SMoM) based on the analytical derivation of the appropriate spectral Green’s functions for the considered dipole configuration. The obtained results reveal a change in the sign of the real part of the input impedance. This is mainly due to the complex property of the considered medium. The medium has also minimized the input impedance ∼4 times (1kΩ); this can help in device matching. This medium has shown a significant impact on the input impedance as well as the antenna array coupling. The design miniaturization possibility is an important result of this research in the design of antenna arrays.

Incomplete acoustic time reversal, frequency shifting, and matched field processing

In a reciprocal time-invariant medium, sound can travel in both directions along acoustic paths. This bi-directionality enables acoustic retrofocusing via time reversal (TR) and acoustic source localization via matched field processing (MFP). Given this common basis, the simplest frequency-domain formulations of acoustic TR and MFP are essentially identical; both involve a quadratic product of forward- and backward-propagating complex fields. For this presentation, all scenarios begin with the acoustic field from a remote source that propagates forward through a potentially-complicated acoustic environment to a transducer array where it is recorded. The difference between TR and MFP then arises because the second backward-propagating (time-reversed) acoustic field may be (i) a genuine field in the actual environment as in acoustic TR, or (ii) a predicted field developed from a model of the environment as in MFP. This presentation describes a third possibility, frequency-difference MFP or incomplete acoustic TR, that combines (i), (ii), and a multiplicative property of harmonic plane waves to produce frequency-downshifting. The resulting unconventional formulation involves a cubic product of complex fields and allows robust reduced-resolution source localization with sparse arrays in complicated uncertain environments. Example results from simulated, laboratory, and ocean propagation data are shown. [Sponsored by ONR, NAVSEA, NSF].

Effect analysis of the general complex reciprocal gyro-bianisotropic metamaterial medium on the input impedance of a printed dipole antenna

The aim of this paper is to present an analytical study for the investigation of the reciprocal metamaterial gyro-bianisotropy effects on the input impedance of a dipole antenna. This study is based on the numerical resolution, using the spectral method of moments (SMoM), of the integral equation developed through the mathematical derivation of the appropriate spectral Green’s functions of the studied dipole configuration. The original obtained results are discussed and showed good agreements with the isotropic studied cases available in published literature. It is found that the imaginary valued magnetoelectric elements (chiral medium) exhibit an inverse effect on the resonant length compared to purely real elements (Tellegen medium), while negative elements decrease the input impedance. Combination of the two cases has led to more general complex media with further inspiring features.

Dielectric approximation media to reproduce dispersion for field transformation.

Field transformation is complementary to transformation optics as it converts polarization without reflection for any incidence, despite not being impedance-matched to vacuum. However, to ease manufacture, a dielectric approximation may degrade the transmission performance due to the approximate dispersion relation for the exact reciprocal medium. In this paper, we instead propose a different dielectric equivalent medium to guarantee the exact dispersion. We also discuss the birefringence phenomenon in such dielectric media, and their unavoidable induced reflections.

Media Populism on the Example of Right-Wing Political Parties’ Communication in Slovenia

Studies on mediatization have pointed to the “collateralism” of media and politics, a model that emphasizes reciprocal media–politics interactions. This article discusses how various political parties, and in particular right-wing populist parties in the post-socialist Slovenian context, use communication tools on the Internet; to what extent they enable participatory communication; and how they open up to forms of “media populism.” In what ways do right-wing populist parties make use of social media as a megaphone for their positions, to promote their charismatic leaders, to disseminate their “othering” ideologies, and to spread the “politics of fear”? The analysis enables us to detect media populism across the political spectrum, and in particular to theorize contemporary features of right-wing media populism.

Frequency-Domain Integral Equations of Scattering for Complex Scalar Responses

A rigorous frequency-domain forward model of scattering is derived that relates any desired complex-valued scalar response to the vectors of the electromagnetic field. The model is valid in any reciprocal medium. The S-parameter forward model is derived as a special case. The forward model for the open-circuit voltage at the terminals of a receiving antenna is also given. The proposed model is useful in microwave imaging since it eliminates the need to employ inadequate approximations of: 1) Green’s dyadic function and 2) the relation between the field in the antenna vicinity and its response. As a validation, the magnitude and phase distributions of fields are mapped using a small scattering probe in reflection-coefficient measurements. The maps contain both the magnitude and the phase distributions. The application of the proposed model in imaging is also demonstrated.

High Frequency Fields of the PEMC Elliptical Reflector Placed in Chiral Medium Using Maslov’s Method

The high frequency field expressions are analyzed for perfect electromagnetic conducting (PEMC) elliptical reflector embedded in isotropic, homogeneous and reciprocal chiral medium. Geometric optics (GO) method is used to find the caustic region field for the PEMC elliptical reflector. However, GO fields are not valid around the caustic region due to the occurrence of un-realistic singularity around the caustic region. Therefore, Maslov’s method is used to derive the high frequency fields which are also valid in the vicinity of the caustic region. The effect of admittanceM of the PEMC boundary and the chirality parameter kβ on the high frequency fields are illustrated by plotting the numerical results using MATLAB software. A special case of PEMC circular reflector is also discussed.

Asymptotic method based on Maslov’s theory for the focusing of 3D elliptical lens placed in chiral medium

The high-frequency field expressions for the refracted waves from the dielectric 3D elliptical lens embedded in homogeneous and reciprocal chiral medium around the focal region are derived using an asymptotic method based on Maslov’s theory. Ray-based Geometric Optics (GO) technique was initially used to derive the expressions for the electrical field intensities for both left circular polarized and right circular polarized waves which are inherited in the chiral medium. However, GO method is not applicable at the focal points due to the shrinking of ray volume at these points which causes unreal singularities. Therefore, an asymptotic method based on Maslov’s theory is applied to derive the fields at the focal points. Moreover, the effect of chirality parameter on the behavior of focal points electric field intensities are indicated using the line plots obtained from the numerical solution of the derived equations using MATLAB software. A special case of the dielectric 3D elliptical lens placed in achiral medium is also discussed using the expressions.

Elliptical reflector in strong chiral medium supporting PPV and NPV simultaneously

The high-frequency electromagnetic waves reflected from a perfect electric conductor (PEC) elliptical surface placed in homogeneous, reciprocal, and isotropic medium with high value of chirality parameter are analyzed. Negative phase velocity (NPV) and positive phase velocity (PPV) can be obtained by properly adjusting the value of chirality parameter. For the value of only PPV can propagate in the elliptical reflector and out of this range both PPV and NPV are supported by the elliptical reflector in chiral medium. The line plots are given which illustrate the reflected waves at different values of chirality parameter .

Focusing of elliptical reflector covered with chiral medium

Maslov's method has been used to analyze the caustic region high frequency fields of an elliptical reflector covered with isotropic, reciprocal and homogeneous chiral medium. Geometrical Optics (GO) approximation is used at first to describe the desired electromagnetic fields at high frequency but GO become invalid at caustic region due to un-realistic singularity. Therefore, an asymptotic method based on Maslov's theory has been applied to solve the discrepancies in GO. The field patterns are calculated numerically using MATLAB software and the results are plotted. The plots indicate the effects of thickness (d) of the covered chiral medium, chirality parameter (β) of the chiral medium and permittivity (ɛ) of the medium.

Expressions for the high frequency fields in the focal region of symmetrical hyperboloidal focusing lens placed in chiral medium

In this article, Geometric method (GO) and Maslov's method have been used to obtain the expressions for high frequency field refracted by a hyperboloidal focusing lens placed in homogenous and reciprocal chiral medium. High frequency focal region problems are transformed into focal free domain. The high-frequency field expressions that include the focal region obtained from GO method fail at the focal region, so Maslov's method has been used to find the field expressions which are also valid around the focal point. By using hybrid space, Maslov's method combines the simplicity of ray theory and the generality of Fourier transform method. Using the derived expressions numerical results around the focal region are plotted using MATLAB. These results show the effect of chirality parameter β on the focal region fields of hyperboloidal focusing lens placed in chiral medium.

Optical-Theorem-Based Coherent Scatterer Detection in Complex Environments

A new approach is proposed to detect scatterers embedded in reciprocal media from scattering data. The new method is rooted on physical considerations, in particular, on the optical theorem applicable to wavefields (e.g., acoustic, electromagnetic, and optical). The approach exploits insight gained from the optical theorem which assigns physical energy interpretations to the wave data from time reversal mirrors and cavities from which one can deduce the presence of unknown scatterers in unknown background media. The proposed approach is ideally suited for target detection in complex, highly reverberating unknown environments such as indoor facilities, caves, tunnels, and urban canyon.

Chiral Metamaterial Composed of Three-Dimensional Plasmonic Nanostructures

We introduce a top-down fabricated metamaterial composed of three-dimensional, chiral, plasmonic nanostructures for visible and near-infrared wavelengths. Based on a combined spectroscopic and interferometric characterization, the entire complex transmission response in terms of a Jones matrix is disclosed. Particularly, the polarization output state of light after propagation through the nanostructures can be decoded from the measurements for any excitation configuration. We experimentally found a rotation of the polarization azimuth of linearly polarized light exceeding 50° at wavelengths around 1.08 μm. This corresponds to a specific rotation which is significantly larger than that of any linear, passive, and reciprocal medium reported to date.

DYADIC GREEN'S FUNCTIONS FOR UNBOUNDED AND TWO-LAYERED GENERAL ANISOTROPIC MEDIA

The dyadic Green's functions (DGFs) for unbounded and layered general anisotropic media are considered in this paper. First, the DGF for unbounded problem is derived using the eigen- decomposition method. Two difierent approaches are proposed to obtain the DGF for layered problem when the source is located inside the anisotropic region. The flrst approach is to apply the modifled symmetrical property of DGF to obtain the DGF for the fleld in the isotropic region when the source is located inside the anisotropic region, from the DGF for the fleld in anisotropic region when the source is in the isotropic region. This modifled symmetrical property can be applied for the layered geometry with bounded anisotropic region being either reciprocal or non-reciprocal medium. However, this method can not give the DGF for the fleld inside the anisotropic region. Thus, the second approach is presented to obtain the complete set of DGFs for all the regions including the anisotropic region, by applying the direct construction method through eigen-decomposition together with matrix method.

Analysis of the High Frequency Field Expressions at the Caustic Region of a Spherical Reflector Placed in Chiral Medium

High frequency field expressions are derived around the caustic region of a spherical reflector placed in a homogenous, isotropic and reciprocal chiral medium. Firstly Geometrical Optics (GO) field expressions are derived for the spherical reflector placed in chiral medium. As the GO approximation fails at the vicinity of the caustic therefore, Maslov’s method has been used to find the field expressions which are also valid around the caustic region. Present work is an extension of previous work from two dimensional to three dimensional reflector. Some numerical results including line plots around the focal region of spherical reflector placed in chiral medium are obtained using the derived expressions.