Wire Medium Research Articles

Double resonant wideband Purcell effect in wire metamaterials

In this paper, we theoretically show that a broadband resonant enhancement of emission may occur for infrared sources located in a polaritonic wire medium. The reason for this enhancement is the overlapping of two topological transitions of the wave dispersion in the medium. The first topological transition has been revealed as an effect inherent to polaritonic wire media at a certain frequency in the mid-infrared range. This work uncovers another topological transition for such wire media which holds at a higher frequency but still in the mid infrared. We show that the first transition frequency can be shifted towards the second one by variation of the design parameters. This shift enables a broadband resonant Purcell factor. We compare the results obtained for two orientations of a subwavelength electric dipole embedded into the wire medium—that along the optical axis and that perpendicular to it—and report on the resonant isotropic radiation enhancement. Also, we reveal the enhancement of radiation to the free space from a finite sample of the wire medium.

Removing image artefacts in wire array metamaterials.

Hyperlenses and hyperbolic media endoscopes can overcome the diffraction limit by supporting propagating high spatial frequency extraordinary waves. While hyperlenses can resolve subwavelength details far below the diffraction limit, images obtained from them are not perfect: resonant high spatial frequency slab modes as well as diffracting ordinary waves cause image distortion and artefacts. In order to use hyperlenses as broad-band subwavelength imaging devices, it is thus necessary to avoid or correct such unwanted artefacts. Here we introduce three methods, namely convolution, field averaging, and power averaging, to remove imaging artefacts over wide frequency bands, and numerically demonstrate their effectiveness based on simulations of a wire medium endoscope. We also define a projection in spatial Fourier space to effectively filter out all ordinary waves, leading to considerable reduction in image distortion. These methods are outlined and demonstrated for simple and complex apertures.

Metamaterial-based lossy anisotropic epsilon-near-zero medium for energy collimation

A lossy anisotropic epsilon-near-zero (ENZ) medium may lead to a counterintuitive phenomenon of omnidirectional bending-to-normal refraction [S. Feng, Phys. Rev. Lett. 108, 193904 (2012)], which offers a fabulous strategy for energy collimation and energy harvesting. Here, in the scope of effective medium theory, we systematically investigate two simple metamaterial configurations, i.e., metal-dielectric-layered structures and the wire medium, to explore the possibility of fulfilling the conditions of such an anisotropic lossy ENZ medium by playing with materials' parameters. Both realistic metamaterial structures and their effective medium equivalences have been numerically simulated, and the results are in excellent agreement with each other. Our study provides clear guidance and therefore paves the way towards the search for proper designs of anisotropic metamaterials for a decent effect of energy collimation and wave-front manipulation.

Creating a Gain Enhancement Technique for a Conical Horn Antenna by Adding a Wire Medium Structure at the Aperture

This paper proposes a technique for improving the conventional conical horn antenna for the X-band frequency using metamaterial on a wire medium structure. The main idea of this research is the application of the wire medium metamaterial to the conical horn’s aperture for the enhancement of the horn’s gain; this is done without changing the antenna’s dimensions. The results show that the wire medium structure can increase the gain of a conventional conical horn antenna from approximately 17.7 dB to 20.9 dB (an increase of approximately 3.2 dB). A prototype antenna was fabricated, and its fundamental parameters including its reflection coefficient (S 11 ), radiation patterns, and directive gain were measured. The simulated and measured results were very good. The wire medium structure of the proposed antenna improved the radiation pattern, enhanced the directivity, increased the gain, and reduced the side lobe level using a simple integrated wire medium structure.

Ultrabroadband perfect imaging in terahertz wire media using single-cycle pulses

Slabs formed by wire medium metamaterials are capable of transmitting evanescent waves over several wavelengths, and enable perfect imaging of field patterns with deeply subwavelength features over such long distances. To date, perfect imaging has been limited to narrow frequency windows defined by the Fabry–Perot (FP) resonance condition. Away from such resonances, backreflections within the slab result in the excitation of surface waves supported by the wire medium. This leads to image distortions, thus severely limiting the use of wire media for broadband subwavelength imaging. Here, we propose and demonstrate that this limitation can be overcome by using ultrashort electromagnetic pulses as the field source, allowing separation of the initial pulse from subsequent backreflections, which cannot be achieved using continuous-wave sources. Using a terahertz (THz) near-field microscope based on a time-domain approach, we demonstrate ultrabroadband transmission of distortion-free images over the entire frequency band of the source (0.1–1.75 THz). Such performance requires the slabs to be sufficiently long; the limits of this approach are also demonstrated by imaging a resonant mode with high Q-factor through a short slab. Our results pave the way for the implementation of wire media in broadband imaging applications based on short electromagnetic pulses, such as THz pulse imaging or optical imaging with ultrashort laser pulses.

Wire-medium loaded planar structures: modal analysis, near fields, and radiation features

A novel transmission-line model is used for the analysis of planar structures, including wire-medium (WM) slabs with vertically aligned wires. The network formalism allows for an effective determination of the relevant spectral Green's functions, of the modal dispersion equation via transverse resonance, as well as of the far-field radiation pattern produced by simple sources via reciprocity, as opposed to the more cumbersome field-matching approach. Numerical results, validated also against state-of-the-art simulation software, confirm the accuracy and effectiveness of the proposed approach. In particular, modal and radiation features are presented for a class of leaky-wave antennas based on planar WM loaded configurations covered by partially reflecting screens, for which leaky unimodal regimes are achieved by minimizing spurious radiation from the quasi-transverse electromagnetic (TEM) mode.

Publisher's Note: Guided modes of a wire medium slab: Comparison of effective medium approaches with exact calculations [Phys. Rev. B91, 155427 (2015)

Publisher's Note: Guided modes of a wire medium slab: Comparison of effective medium approaches with exact calculations [Phys. Rev. B<b>91</b>, 155427 (2015)

Magnetic uniaxial wire medium

It is shown that a racemic array of helical-shaped metallic wires may have a dual electromagnetic response, such that for arbitrarily large wavelengths it concurrently supports two modes with hyperbolic- and elliptical-type dispersions. Importantly, one of the eigenwaves is nearly dispersionless and sees the metamaterial as a medium with extreme magnetic anisotropy. The metamaterial may thus behave as the magnetic analog of the conventional wire medium formed by a set of parallel straight metallic wires. It is demonstrated that the magnetic wire medium enables channeling the subwavelength details of transverse electric (TE) polarized waves.

Phase matching in hyperbolic wire media for nonlinear frequency conversion.

Efficient nonlinear frequency conversion requires a phase matching condition to be satisfied. We analyze the dispersion of the modes of hyperbolic wire metamaterials and demonstrate that phase matching at infrared wavelengths can be achieved with a variety of constituent materials, such as GaAs, in which phase matching cannot easily be achieved by conventional means. Our finding promises access to many materials with attractive nonlinear properties.

Equivalent-Network Analysis of Propagation and Radiation Features in Wire-Medium Loaded Planar Structures

Planar multilayer dielectric structures that include wire-medium (WM) slabs with vertically aligned wires are studied by means of an effective equivalent transmission-line approach based on the homogenized representation of the WM layers. Modal properties are thereby retrieved via transverse resonance, whereas radiative properties of elementary sources are calculated via reciprocity. The proposed approach is employed to show the possibility of suppressing TEM propagation in WM-loaded parallel-plate waveguides as well as of achieving wideband radiation from TM leaky modes in partially open configurations. The features thus gained are of interest for the realization of Fabry–Perot cavity antennas with linearly polarized conical patterns and wide-angular scanning ranges. Numerical results obtained with state-of-art simulation software confirm the accuracy and numerical effectiveness of the proposed formulation.

Wire-Medium Hyperlens for Enhancing Radiation From Subwavelength Dipole Sources

Hyperlens is a metamaterial structure initially proposed for magnifying imaging of subwavelength scattering objects. Here, we show that a wire-medium (WM) hyperlens can be used also for significant enhancement of radiation from small sources to free space and that this enhancement holds in the ultra-wide frequency band. We investigate how the divergence of metal wires modifies the radiated power of a dipole, comparing with an array of parallel wires, and investigate the impact of other design parameters. Next, we implement the optimized hyperlens in the microwave range and verify the theoretical results experimentally. We believe that this work will help to introduce and develop hyperlenses for a number of applications where broadband radiation enhancement of subwavelength sources is needed.

Broadband microstrip antenna using epsilon near zero metamaterials

In this study, the effect of loading microstrip antenna using epsilon near zero (ENZ) metamaterial is investigated. It is known that ENZ material may help to improve the transmission through a boundary condition and that the scattering parameters may be completely independent of such boundary properties. This idea is demonstrated to significantly increase the bandwidth of a simple rectangular microstrip patch antenna. To realise the ENZ material, a periodic wire medium is designed, simulated, fabricated, and tested. Simulation results based on CST Microwave studio have good agreement with measurements.

Side Lobe Reduction in an X-Band Horn Antenna Loaded by a Wire Medium

Through electromagnetic simulation, the present work reports on a comparative study of the enhanced radiation properties of a standard X-band horn antenna loaded by a wire medium. Acting as an artificial dielectric the wire medium consists of an array of parallel metallic wires installed into the antenna with the wires oriented in the direction of the incident electric field. As compared with the properties of the empty antenna, the wire-medium antenna produces appreciable reduction in the side-lobe levels with an improvement of 10 dB at 8.87 GHz in the first side lobe. For the wire-medium antenna, the E- and H-planes look similar, a property desired for precision radar and radiometric mapping systems.

Unbounded spatial spectrum of propagating waves in a polaritonic wire medium

In this paper, we study a topological phase transition in a wire medium operating at infrared frequencies. This transition occurs in the reciprocal space between the indefinite (open-surface) regime of the metamaterial and its dielectric (closed-surface) regime. Due to the spatial dispersion inherent to a wire medium, a hybrid regime turns out to be possible at the transition frequency. Both such surfaces exist at the same frequency and touch one another. At this frequency, all values of the parallel wave vector correspond to propagating spatial harmonics. The implication of this regime is the overwhelming radiation enhancement. We numerically investigate the gain in radiated power for a subwavelength dipole source submerged into such medium. In contrast to previous works, this gain (called the Purcell factor) turns out to be higher for a parallel dipole than for a perpendicular one.

Graphene-loaded wire medium for tunable broadband subwavelength imaging

Graphene-loaded wire medium for tunable broadband subwavelength imaging

Diamagnetism in wire medium metamaterials: Theory and experiment

A strong diamagnetic response of a wire medium with a finite wire radius is reported. Contrary to the previous works where it was assumed that the wire medium exhibits only an electric response, we show that the nonzero magnetic susceptibility has to be taken into account for a proper effective medium description of the wire medium. Analytical and numerical results are supported by experimental measurements.

Tunable dual-band subwavelength imaging with a wire medium slab loaded with nanostructured graphene metasurfaces

In this paper, we demonstrate that a wire medium slab loaded with graphene-nanopatch metasurfaces (GNMs) enables the enhancement of evanescent waves for the subwavelength imaging at terahertz (THz) frequencies. The analysis is based on the nonlocal homogenization model for wire medium with the additional boundary condition at the connection of wires to graphene. The physical mechanism behind this lens can be described as the surface plasmons excitement at the lower and upper GNMs which are coupled by an array of metallic wires. The dual nature (capacitive/inductive) of the GNM is utilized in order to design a dual-band lens in which the unique controllable properties of graphene and the structural parameters of wire medium (WM) slab provide more degrees of freedom in controlling two operating frequency bands. The lens can support the subwavelength imaging simultaneously at two tunable distinct frequencies with the resolution better than λ/6 even if the distance between GNMs is a significant fraction of wavelength (&amp;gt;λ/5.5). The major future challenges in the fabrication of the lens have been demonstrated and a promising approach for the practical configuration of the lens has been proposed.

Analytical Solution for the Stopping Power of the Cherenkov Radiation in a Uniaxial Nanowire Material

We derive closed analytical formulae for the power emitted by moving charged particles in a uniaxial wire medium by means of an eigenfunction expansion. Our analytical expressions demonstrate that, in the absence of material dispersion, the stopping power of the uniaxial wire medium is proportional to the charge velocity, and that there is no velocity threshold for the Cherenkov emission. It is shown that the eigenfunction expansion formalism can be extended to the case of dispersive lossless media. Furthermore, in the presence of material dispersion, the optimal charge velocity that maximizes the emitted Cherenkov power may be less than the speed of light in a vacuum.

A Comparative Study of Software Firewall on Windows and Linux Platform

Nowadays, the communication through World Wide Web (WWW) is growing rapidly. All the gadgets, computer and handheld devices are connected via wire or wireless media and communicated to each others. Thus, network security is the essential requirement of an organization or individuals. Organizations are protecting their communication from unauthorized access by introducing network firewalls. A Firewall is an application program which runs on any platform such as windows, Linux, Solaris, Macintosh etc and protected the networks or systems via implementing policies and rules. In this paper, the performance of firewall is measured and compared on Windows and Linux platform individual. To evaluate the performance, a private network has been setup in which three machines are connected via a switch; one Windows machine running windows firewall, one Linux machine running Linux firewall (IPTable) and one more machine that acting as a client. On both the platforms, the performance is measured in two situations: first when network is traffic free and second network with traffic. When network is traffic free then both the platforms reflect the common normal processing behavior in context of time and packet received per second; and when packets are pumped at a very high speed in the network then the processing time and packet received per second increases exponentially in both the platforms.

An Epsilon-Near-Zero Total-Internal-Reflection Metamaterial Antenna

The total-internal-reflection (TIR) principle and the concept of an epsilon-near-zero (ENZ) material are combined to form an antenna exhibiting sum and difference patterns with good impedance properties. The ENZ material has been realized using a uniaxial wire medium (WM) metamaterial, and the departure from the behavior of an ideal ENZ material is discussed. The radiation pattern of the fabricated antennas has been measured and compared with simulation results.