Uniaxial Wire Medium Research Articles

Experimental verification of magnetic near-field channeling using a helical-shaped wire medium lens

We experimentally verify that a magnetic uniaxial wire medium lens consisting of a racemic array of helical-shaped metallic wires may enable channeling the normal component of the magnetic field of near-field sources with resolution well below the diffraction limit over a broad bandwidth. It is experimentally demonstrated that the helical-shaped wire medium lens can be regarded as the magnetic counterpart of the usual wire medium lenses formed by straight metallic wires. The experimental results are validated with full-wave numerical simulations. We envision that the proposed metamaterial lens may have potential applications in magnetic resonance imaging, near-field wireless power transfer, and sensing.

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.

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.

Super-collimation of the radiation by a point source in a uniaxial wire medium

We investigate the radiation properties of a short horizontal dipole embedded in a uniaxial wire medium. It is shown that the uniaxial wire medium enables a super-collimation of the dipole radiation such that the radiation pattern has a singularity and the radiated fields are non-diffractive in the broadside direction. We derive a closed analytical formula for the power radiated by the dipole in the wire medium. Our theory demonstrates that as a consequence of the ultrahigh density of photonic states of the nanowire array, the power radiated by the dipole is strongly enhanced as compared to the power that would be emitted in the dielectric host with no nanowires.

Imperfections for an equivalent surface impedance of a uniaxial wire medium

A uniaxial wire medium is a medium formed by a two-dimensional array of conducting parallel thin wires. An analytical study of small imperfections in positioning of wires is considered for an equivalent surface impedance of this wire medium. It is studied that effects of these small imperfections in positioning of wires introduce an equivalent additional surface impedance. This additional impedance is taken to be an error impedance which is mainly dependent upon the positioning error standard deviations along two orthogonal directions. It is further studied that an increase in the positioning error standard deviations along two perpendicular directions increases the magnitude of this error impedance. Also, if the propagation of wave is taken to be normal inside the wire medium then the effects of imperfections in a plane along direction of propagation are more pronounced than these imperfections in a plane transverse to the direction of propagation.

A Modified PML in FDTD Modeling of a Uniaxial Wire Medium

Application of wire medium often requires complex models including finite structures or sources and infinite wire medium. In this letter, we propose a modified perfectly matched layer (PML) in which a resonant state similar to the internal computational domain is set up. Numerical results show that compared to other forms of PML, this resonance PML can be used to directly truncate the wire medium with controllable reflections in finite-difference time-domain (FDTD) modeling. Thus, the computation resources can be significantly reduced by using the proposed PML.

Transport model for homogenized uniaxial wire media: Three-dimensional scattering problems and homogenized model limits

A transport-based formulation is used to model three-dimensional objects made of a uniaxial wire medium. The resulting drift-diffusion equation is used to calculate the extinction/scattering cross section of various uniaxial wire medium objects. A comparison is made with measurement and full wave simulation results. This method is faster than full wave simulation and provides physical insight into electrodynamic processes within the homogenized medium. The effect of wire period and thickness on the homogenized model is investigated, and a Debye length parameter is used to access the effect of wire length.

Partial focusing by a bulk metamaterial formed by a periodically loaded wire medium with impedance insertions

In this paper, a uniaxial wire medium periodically loaded with metallic patches and lumped impedance insertions is proposed for partial focusing of electromagnetic radiation due to a magnetic line source. The analysis is based on the nonlocal homogenization model for a bi-layer mushroom structure with generalized additional boundary conditions for loaded vias, and it is extended to a multilayered configuration with the transfer matrix approach. The proposed structure exhibits a high transmission and is nearly insensitive to the losses. The analytical results are validated against full-wave numerical simulations.

Radiation from elementary sources in a uniaxial wire medium

We investigate the radiation properties of two types of elementary sources embedded in a uniaxial wire medium: a short dipole parallel to the wires and a lumped voltage source connected across a gap in a generic metallic wire. It is demonstrated that the radiation pattern of these elementary sources have quite anomalous and unusual properties. Specifically, the radiation pattern of a short vertical dipole resembles that of an isotropic radiator close to the effective plasma frequency of the wire medium, whereas the radiation from the lumped voltage generator is characterized by an infinite directivity and a non-diffractive far-field distribution.

Indefinite dielectric response and all-angle negative refraction in a structure with deeply-subwavelength inclusions

The realization of mesoscopic media that mimic an ideal continuous indefinite material remains a challenging problem, particularly because current designs are plagued by spatial dispersion effects and are based on inclusions whose size may be a significant fraction of the wavelength. Here we show that a structure formed by an array of inductively loaded metallic rods terminated by metallic patches at both ends may enable to largely overcome these problems, and imitate more closely indefinite dielectric media with a local response. In particular, we report a strong all-angle negative refraction effect, even in scenarios where the characteristic size of the material is deeply subwavelength. The response of the proposed structure is characterized using a homogenization model developed for the uniaxial wire medium with impedance loadings.

Characterization of negative refraction with multilayered mushroom-type metamaterials at microwaves

In this paper, it is shown that bulk metamaterials formed by multilayered mushroom-type structures enable broadband negative refraction. The metamaterial configurations are modeled using homogenization methods developed for a uniaxial wire medium loaded with periodic metallic elements (for example, patch arrays). It is shown that the phase of the transmission coefficient decreases with the increasing incidence angle, resulting in the negative spatial shift of the transmitted wave. The homogenization model results are obtained with the uniform plane-wave incidence, and the full-wave results are generated with a Gaussian beam excitation, showing a strong negative refraction in a significant frequency band. Having in mind a possible experimental verification of our findings, we investigate the effect of introducing air gaps in between the metamaterial layers, showing that even in such simple configuration the negative refraction phenomenon is quite robust.

Negative refraction by a uniaxial wire medium with suppressed spatial dispersion

Here, we show that a structure formed by an array of metallic wires loaded with metallic patches may enable strong negative refraction even when the conductivity of the metal is very large, e.g., in the microwave regime. It is shown that the composite structure may be regarded as a uniaxial indefinite material loaded with impedance sheets, and that the negative refraction effect may be characterized using homogenization methods.