Wire Medium Research Articles

Longitudinal electromagnetic waves with extremely short wavelength

Electromagnetic waves in vacuum and most materials have transverse polarization. Longitudinal electromagnetic waves with electric field parallel to wave vector are very rare and appear under special conditions in a limited class of media, for example in plasma. In this work, we study the dispersion properties of an easy-to-manufacture metamaterial consisting of two three-dimensional cubic lattices of connected metallic wires inserted one into another, also known as an interlaced wire medium. It is shown that the metamaterial supports longitudinal waves at extremely wide frequency band from very low frequencies up to the Bragg resonances of the structure. The waves feature unprecedentedly short wavelengths comparable to the period of the material. The revealed effects highlight spatially dispersive response of interlaced wire medium and provide a route toward generating electromagnetic fields with strong spatial variation.

Inducing topology in a wire medium based metamaterial [Invited

We review our attempt to tackle topological photonics based on an experimental platform operating in the microwave frequency range. The latter is based on a resonant metamaterial consisting in a dense collection of finite-length resonant metallic wires, known as the wire medium. Inside, the wave propagation is accurately described by a polariton, which exhibits subwavelength propagating modes as well as a hybridization bandgap. Thanks to a relevant design of the relative lengths of the wires and/or on their spatial positioning, we explore different aspects of topology applied to wave propagation.

A Frequency Selective Rasorber by Engineering Transverse Standing Waves of Surface Current

The low RCS level out of operating band is urgent for radome while keeping its communication window. To solve this problem, we propose a frequency selective rasorber (FSR) that exhibits a pass-band between two absorption bands in this paper. The surface currents on a finite metallic wire media is analyzed firstly to elaborate transverse standing waves mechanism. High-efficiency and broadband absorption can be achieved by loading lumped resistors at high amplitude of standing waves. By delicately engineering the transverse standing waves versus frequency, a transparent window can be opened within an absorption wideband and it can be modulated by adjusting structural parameters. The transparent window centered around 10.0 GHz in the absorption band from 5.8 GHz to 18.0 GHz. Prototypes were fabricated and measured. Both the simulated and measured results show that for both x- and y-polarized waves, insertion loss of the transparent window at 9.85 GHz is below 0.2 dB while the absorption is above 90% in the two sidebands of 5.8-7.8 GHz and 11.8-18.0 GHz. Furthermore, the rasorber can also work well under oblique incidence angles up to 45 degrees. This work may find wide applications in electromagnetic compatibility, stealthy radomes, etc.

First principles homogenization of periodic metamaterials and application to wire media

Here, we present an overview of a first principles homogenization theory of periodic metamaterials. It is shown that in a rather general context it is possible to formally introduce effective parameters that describe the time evolution of macroscopic (slowly-varying in space) initial states of the electromagnetic field using an effective medium formalism. The theory is applied to different types of characterized by a strong spatial dispersion in the long wavelength limit. It is highlighted that the spatial dispersion may tailor in unique ways the wave phenomena in wire metamaterials leading to exotic tunneling effects and broadband lossless anomalous dispersion.

Spin Hall Effect of Light with Near‐Unity Efficiency in the Microwave

AbstractThe spin Hall effect of light (SHEL) refers to a transverse and spin‐dependent shift of light in real space at an optical interface. Previous studies of enhancing the SHEL have involved extremely low efficiency, and achieving a large SHEL and high efficiency simultaneously has never been reported. Here, an approach using anisotropic impedance mismatching to attain a large SHEL with near‐unity efficiency in the microwave spectrum is proposed. A wire medium that has a near‐unity transmission for one polarization and low transmission for the other is used to achieve high efficiency. The spin‐dependent splitting is experimentally confirmed by measuring transmission coefficients and the spatial profile of Stokes parameters. The large SHEL with near‐unity efficiency will enable highly efficient devices with spin‐selective functionalities.

Hybrid Metamaterial for the Secondary Radar Antenna System

This paper proposes the gain enhancement of dual-band and dual-polarized asymmetric horn antenna for the secondary radar system using hybrid metamaterial techniques. The hybrid metamaterial is comprised of the structures of woodpile electromagnetic bandgap (EBG) for gain enhancement of the primary main beam of the radar system at the operating frequency of 1,300 MHz with horizontal polarization; and the wire medium structure that is placed beside the EBG structure for gain improvement of the identification friend or foe (IFF) main beam, which is operated at the center frequency of 1,060 MHz with vertical polarization. Meanwhile, the cooperated structures have to function to control the directions of the primary and IFF main beams retaining at 0° and 6°, respectively, too. When the hybrid metamaterial structure is placed at the front of an asymmetric horn’s aperture, with suitable parameters and optimized spacing, it is found to increase the gains of the two beams compared to the single asymmetric horn around 3 dB and retain the directions of original main beams. The comparison of the results between simulation and measurement, such as the reflected power (S<sub>11</sub>), gain, and radiation patterns, are in good agreement.

Robust foil regenerator flow loss and heat transfer tests under oscillating flow condition

A regenerator works as an energy storage component in a Stirling engine. Thus, it is one of the most critical components that makes the Stirling engine highly efficient. Traditionally, the regenerators are made of wire media such as woven screens and random fibers. These wire regenerators experience considerably high flow losses through the regenerator due to the flow separation and the resulting vortices. The high flow losses associated with the flow separation and vortices result in a lower engine efficiency. This research is to test a new robust foil regenerator to investigate its feasibility for free-piston Stirling engine applications. The robust foil regenerator is configured with parallel flow channels and stiffening ribs. Comparing to complex flows patterns in woven screen and random fiber regenerators, the flows in the parallel plates are simple and the flow losses are considerably small, and the heat transfer coefficient is also relatively small. To test the regenerator experimentally, a regenerator test rig was manufactured. To verify the accuracy of the test rig, a woven screen regenerator was made and tested prior to the robust foil regenerator test. The friction factor correlation of the woven screen regenerator shows a good agreement with the published regenerator correlations. The robust foil regenerator tests were conducted under the oscillating flow condition with different Reynolds numbers. The flow losses were measured with dynamic pressure transducers and the friction coefficient was derived from measured pressure drop. The measured temperature difference over the regenerator was used to calculate the heat transfer coefficient and Nusselt number. The figure of merit with two methods of NPH/NTU ratio and j/f ratio was calculated to evaluate the suitability of the robust foil regenerator. The results show that the robust foil regenerator has considerably higher figure of merit and therefore, better performance than other types of regenerator.

Effective Local Permittivity Model for Nonlocal Wire Media

A local permittivity model is proposed to accurately characterize spatial dispersion in non-local wire-medium (WM) structures with arbitrary terminations. A closed-form expression for the local thickness-dependent permittivity is derived for a general case of a bounded WM with lumped impedance insertions and terminated with impedance surfaces, which takes into account the effects of spatial dispersion and loads/terminations in the averaged sense per length of the wire medium. The proposed approach results in a local model formalism and accurately predicts the response of WM structures for near-field and far-field excitation. It is also shown that a traditional transmission network and circuit model can be effectively used to quantify the interaction of propagating and evanescent waves with WM structures. In addition, the derived analytical expression for the local thickness-dependent permittivity has been used in the full-wave numerical solver (CST Microwave Studio) demonstrating a drastic reduction in the computation time and memory in the solution of near-field and far-field problems involving wire media.

An Equivalent ABCD-Matrix Formalism for Non-Local Wire Media With Arbitrary Terminations

A simple analytical model based on the transmission-matrix approach is proposed for equivalent wire-medium (WM) interfaces. The obtained ABCD matrices for equivalent interfaces capture the non-local effects due to the evanescent transverse magnetic (TM) WM mode and in part due to the propagating transverse electromagnetic (TEM) WM mode. This enables one to characterize the overall response of bounded WM structures by cascading the ABCD matrices of equivalent WM interfaces and WM slabs as transmission lines supporting only the propagating TEM WM mode, resulting in a simple circuit-model formalism for bounded WM structures with arbitrary terminations, including the open-end, patch/slot arrays, and thin metal/2D material, among others. The individual ABCD matrices for equivalent WM interfaces apparently violate the conservation of energy and reciprocity, and therefore, the equivalent interfaces apparently behave as non-reciprocal lossy or active systems. However, the overall response of a bounded WM structure is consistent with the lossless property maintaining the conservation of energy and reciprocity. These unusual features are explained by the fact that in the non-local WM the Poynting vector has an additional correction term which takes into account a "hidden power" due to non-local effects. Results are obtained for various numerical examples demonstrating a rapid and efficient solution for bounded WM structures, including the case of geometrically complex multilayer configurations with arbitrary terminations, subject to the condition that WM interfaces are decoupled by the evanescent TM WM mode below the plasma frequency.

Застосування провідникових метаструктур у радіотехнічних засобах для передавання та випромінювання ЕМ хвиль (огляд)

In the presented paper the review of the major possible applications of a wire medium in different radio engineering field is performed. The structures possess the unique properties such as a negative value of permittivity. Three types of wire media shapes are considered which include structures with parallel (superlens), tapered (hyperlens) and irregular (brush) metallic wires allocations. Modern progress allows a number of approaches (from usual mechanic arrangement to chemical synthesis) to realize wire media of different shape for their utilizing in frequency range from microwave to optics and higher. Superlens can be applied to narrow and broadband energy transfer of electromagnetic waves including photovoltaic devices, imaging, endoscopy, spectroscopy and many others. The broadband effect was shown recently in [9] by the investigation of EM power transfer between two waveguides through a wire media slab that became the first experimental evidence of analytical hypothesis of [12]. It was a beginning point to develop of wire media endoscopes in [15] which shown the nature of non-Fabri-Perot minima and maxima of dispersion function as the vortex modes as well as reliability of endoscope operation under the huge bend. The wire media such as hyperlens and irregular one can find applications in antennas development that operate in the wide frequency range. Comparison of Parcell factor dispersions of these two kinds of metamaterials shows different results due to hyperlens, despite the possibility to radiate at interresonant frequencies, stays resonant structure in general. Instead, a wire medium brush is characterized by the continuing Parcell factor spectrum. It is possible in consequence of the structure shape that can be considered as a set of a huge number of local hyperlenses with different parameters that reradiate and amplify EM field of another local hyperlenses and so on. As the result a wide frequency range can be covered (from 1 up to 5 GHz in [18]).

Comb-Like Modal Dispersion Diagram in a Double-Wire Medium Slab

We investigate the guided modes supported by a wire metamaterial slab formed by two mutually orthogonal and nonconnected sets of parallel metallic wires. It is demonstrated that the wire medium slab has a peculiar comb-like dispersion diagram. In the continuum approximation, the metamaterial supports a diverging number of guided mode branches that accumulate near the light line due to a strong hyperbolic response in the static limit. In a realistic system, the number of guided mode branches is finite and is determined by the density of wires. Remarkably, the guided modes may be characterized by a fast field variation along the transverse direction, which can be exploited to detect subwavelength particles or defects.

Interaction of Multiwalled Carbon Nanotube Aerogels with Quasi‐Optical Terahertz Beams

This article presents the measurements of the reflectance from a plane‐parallel aerogel sample formed by multiwalled carbon nanotubes (MWCNTs) in the terahertz range. With an increase in frequency from 100 GHz to 1.5 THz, the reflectance decreases by more than a factor of two. Based on the experimental data and the well‐known wire medium model formed by a three‐dimensional lattice of intersecting conductors, a model of a regular wire medium is constructed using MWCNTs with effective electrophysical characteristics equivalent to those of an irregular aerogel medium. This model reveals that a significant drop in the reflectance in the terahertz frequency range occurs because the plasma frequency of the equivalent medium is located here. The model allows estimating the properties of the aerogel environment in the frequency range extending up to 5 THz and with variations in the packing density of MWCNTs in aerogel. Estimates of the reflection, transmission, and absorption are presented for the case of normal incidence on a thin (submillimeter) layer of such a medium. The aerogel absorption at a given conductivity of CNTs is determined by their packing density.

Frequency-dependent radiation properties of negative permittivity metamaterial reflector antenna

This paper reports a novel type of microwave reflector antenna that uses the frequency-dependent properties of an epsilon negative (ENG) metamaterial medium. The frequency-dependent characteristics of this artificial plasma medium is analyzed using the dispersive auxiliary differential equation finite difference time domain (ADE-FDTD) method by employing a Gaussian pulse and the results are verified experimentally using an artificial plasma medium fabricated by an array of thin conducting wires. The radiation pattern of plain and corner plasma reflector antennas modeled using Drude equations are obtained and are compared with a plasma reflector and conventional metallic reflector antennas. The results obtained for the plasma reflector antenna is experimentally verified using a 90° corner reflector antenna fabricated using wire medium. This new class of plasma antennas show marked variations in radiation pattern for frequencies above and below plasma frequency, which may find potential use in various frequency selective applications.

Homogenization of wire media with a general purpose nonlocal constitutive relation

The wire medium is an important example for a complex artificial electromagnetic material, consisting of metallic nanowires embedded in a non-dispersive, dielectric host medium. It has been explored for various applications, but it is also a prototypical metamaterial that supports a nonlocal optical response. With that, it can be considered as a main research theme for studies revolving around the homogenization of metamaterials. In the past, specific analytical models were derived for the effective properties of the wire medium that were equipped with phenomenologically introduced additional interface conditions. However, the phenomenological approach questions the uniqueness of the effective medium description, as other effective medium theories could capture the optical response equally well. To highlight such issues, we apply here a general purpose nonlocal homogenization theory equipped with rigorously derived additional interface conditions to homogenize a wire medium and compare it to a homogenization theory specifically derived for the wire medium. While the bulk properties can be mapped from one effective medium theory to the other, the interface conditions are different, which renders the models different as well. We discuss the implications of both models in situations where the unit cells are (a) much smaller or (b) only smaller than the operational wavelength.

Transmission of Harmonic Signals Through a Wire Media

This paper is devoted to wire media (WM) investigation for signal transfer devices. Such devices are promising for different applications as imaging, power or signal transfer, sensing etc. However, first WMs could be used as a resonance structures, because the transfer of electromagnetic (EM) waves was possible only at the Fabry-Perot frequencies. It restricts the number of applications. However, the last works has shown the possibility of the broadband power transfer of evanescent electromagnetic waves. It allows using the same source of EM waves and their receiver to transfer the signals with different values of operation frequencies. Another investigation has proved that the WM does not distort the propagation wave. It allowed to suppose the possibility of pixel signal transfer that was studied in the paper and shown the ability of application of the such structures as the multichannel communication systems. With this aim the signals sources were allocated at the same plane with the input WM interface. First of all, the simulation investigations of the electric feld distributions of transferred harmonic signals through the WM have shown the needed period of dipoles allocations for the satisfactory resolution of received harmonic signals. One more conclusion from obtained results is the approvement that in this case the WM is not the resonance structure, but the same one operates with the signals of different frequencies. More detailed results and understanding of this were obtained from the spectrum analysis of the signals received at the output interface. It shown that the period of sources 2a is acceptable along x, y and diagonal directions. The spectrum analysis of the shape of the propagation wave also demonstrated and proven that the propagating signals do not suffer any nonlinear distortions. In the case of using of WM slab it can provide the excellent coupling between the interaction ports.

OVERVIEW OF APPLICATIONS OF WIRE MEDIUM IN RADIO ENGINEERING MEANS

This paper presents an overview of the main possible applications of wire medium in different field of radio engineering. Wire media possesses the unique electromagnetic properties. There is a number for approaches for manufacturing the wire media of different shapes from microwave frequency up to optical one. The wire media that consists of parallel metallic rods finds application for narrow and broadband power radiation in photovoltaic devices, imaging, endoscopy and many others. The wire metastructures such as hyperlens and brush are applicable to the antennas of wide frequency range.

The Usage of Conducting Wire Sphere Models for the Estimation of Electrophysical Properties of Multiwalled Carbon Nanotube Spherical Aerogels

The Usage of Conducting Wire Sphere Models for the Estimation of Electrophysical Properties of Multiwalled Carbon Nanotube Spherical Aerogels

High performance microstrip monopole antenna with loaded metamaterial wire medium superstrate

A novel design of printed monopole antenna loaded with wire medium is developed for radar applications. The advocated design aims to simultaneously enhance the gain and bandwidth of the proposed geometry. The proposed antenna is composed of a circular patch etched with double C-shaped slots and the ground is defected to achieve wide bandwidth. Wire medium superstrate and a metal reflector are implemented to provide high gain. The promising tunable wire medium superstrate consists of a periodic array of parallel metallic wires arranged in a rectangular pattern that mimic the behavior of epsilon-near-to-zero (ENZ) metamaterial. This medium is suspended at a distance of a quarter-wavelength in air above the antenna to provide the optimum gain and reduce the side lobes level. Prototype of the optimized antenna is fabricated using Rogers's substrate to offer −10 dB bandwidth over the entire frequency range (900 MHz to 2.85 GHz). Details of the design process are investigated through full wave electromagnetic simulations performed by CST software. Experimental results of the fabricated prototype are presented and also compared with simulation results where an appreciable agreement between them is demonstrated.

Mode Profile Shaping in Wire Media: Towards An Experimental Verification

We show that an experimentally plausible system consisting of a modulated dielectric wire medium hosted in a metal cavity or waveguide can be used to shape the longitudinal field profile. In addition, a more realistic permittivity is used. These new frequency domain numerical results are a significant step towards justifying the construction of an experimental apparatus to test the field profile shaping in practise.

Beyond Words: The Causal Effects of News on Information

This paper documents systematic inefficiency in the news production of professional financial wire media. When cognitively constrained, wire journalists selectively cover corporate releases that are more visually salient to them. The variation in salience is caused by exogenous shocks that most directly impact wire journalists. Using the salience as an instrument, I find that media coverage affects even sophisticated market participants by increasing institutional investors' information acquisition and analysts' information production. The results are consistent with the hypothesis that sophisticated institutional investors rationally allocate their learning to media-covered events which will have higher price volatility, thus higher reward to their information production. Resource-constrained analysts also cater to the increased information demand by covering more media-reported events. This paper argues that media could impact different market participants through heterogeneous channels.