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Register a new userElectromagnetic Wave Propagation in Media with Indefinite Permittivity and Permeability Tensors
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We study the behavior of wave propagation in materials for which not all of the principle elements of the permeability and permittivity tensors have the same sign. We find that a wide variety of effects can be realized in such media, including negative refraction, near-field focusing and high impedance surface reflection. In particular a bi-layer of these materials can transfer a field distribution from one side to the other, including near-fields, without requiring internal exponentially growing waves.
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We establish the well-posedness, the finite speed propagation, and a regularity result for Maxwells equations in media consisting of dispersive (frequency dependent) metamaterials. Two typical examples for such metamaterials are materials obeying Drudes and Lorentz models. The causality and the passivity are the two main assumptions and play a crucial role in the analysis. It is worth noting that by contrast the well-posedness in the frequency domain is not ensured in general. We also provide some numerical experiments using the Drudes model to illustrate its dispersive behaviour.
In order to reduce the difficulties in the experimental realizations of the cloak but still keep good performance of invisibility, we proposed a perfect cylindrical invisibility cloak with spatially invariant axial material parameters. The advantage of this kind of TE (or TM) cloak is that only rho and phi components of mu (or epsilon) are spatially variant, which makes it possible to realize perfect invisibility with two-dimensional (2D) magnetic (or electric) metamaterials. The effects of perturbations of the parameters on the performance of this cloak are quantitatively analyzed by scattering theory. Our work provides a simple and feasible solution to the experimental realization of cloaks with ideal parameters.
We describe a method of extrapolation based on a truncated Kramers-Kronig relation for the complex permittivity ($epsilon$) and permeability ($mu$) parameters of a material, based on finite frequency data. Considering a few assumptions, such as the behavior of the loss tangent and the overall nature of corrections, the method is robust within a small relative error, if the assumed hypotheses hold at the extrapolated frequency range.
An equivalent-multishell approach for the approximate calculation of the characteristics of electromagnetic waves propagating in almost circular (azimuthally symmetric), closely packed bundles of parallel, identical, and metallic carbon nanotubes (CNTs) yields results in reasonably good agreement with a many-body technique, for infinitely long bundles when the number of CNTs is moderately high. The slow-wave coefficients for azimunthally symmetric guided waves increase with the number of metallic CNTs in the bundle, tending for thick bundles to unity, which is characteristic of macroscopic metallic wires. The existence of an azimuthally nonsymmetric guided wave at low frequencies in a bundle of a large number of finite-length CNTs stands in contrast to the characteristics of guided-wave propagation in a single CNT. The equivalent-multishell approach yields the polarizability scalar and the antenna efficiency of a bundle of finite-length CNTs in the long-wavelength regime over a wide frequency range spanning the terahertz and the near-infrared regimes. Edge effects give rise to geometric resonances in such bundles. The antenna efficiency of a CNT bundle at the first resonance can exceed that of a single CNT by four orders of magnitude, which is promising for the design and development of CNT-bundle antennas and composite materials containing CNT-bundles as inclusions.
We present a comprehensive study of various electromagnetic wave propagation phenomena in a ferromagnetic bulk Rashba conductor from the perspective of quantum mechanical transport. In this system, both the space inversion and time reversal symmetries are broken, as characterized by the Rashba field $alpha$ and magnetization $M$, respectively. First, we present a general phenomenological analysis of electromagnetic wave propagation in media based on the dielectric tensor. Then, we calculate the microscopic electromagnetic response of the current and spin of conduction electrons subjected to $ alpha$ and $M$, based on linear response theory and the Greens function method. Firstly, it is found that a large $alpha$ enhances the anisotropic properties of the system and enlarges the frequency range in which the electromagnetic waves have hyperbolic dispersion surfaces and exhibit unusual propagations known as negative refraction and backward waves. Secondly, we consider the electromagnetic cross-correlation effects on the wave propagation. These effects stem from the lack of space inversion symmetry and yield $q$-linear off-diagonal components in the dielectric tensor. This induces a Rashba-induced birefringence. In the presence of $M$, there arises an anomalous Hall effect and the dielectric tensor acquires off-diagonal components linear in $M$. These components yield the Faraday effect and the Cotton-Mouton effect. When $alpha$ and $M$ are noncollinear, $M$- and $q$-induced optical phenomena, nonreciprocal directional dichroism is possible. In these nonreciprocal optical phenomena, a toroidal moment, $alphatimes M$, and a quadrupole moment, $alpha_i M_j + alpha_j M_i$, play central roles. These phenomena are strongly enhanced at the spin-split transition edge in the electron band.
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