Ari J. Viitanen

Dispersion and Reflection Properties of Artificial Media Formed By Regular Lattices of Ideally Conducting Wires

An analytical theory of electromagnetic waves in artificial media formed by a rectangular lattice of thin ideally conducting cylinders using the local field approach is developed. As a result, the transcendental dispersion equation is obtained in closed form and solved numerically. Typical dispersion curves are calculated. Using these results, the reflection problem from an interface between a half space of wire medium and free space is solved for plane-wave excitation. In the low-frequency approximation a simple analytical formula for the frequency dependent effective dielectric permittivity is established.

Surface Wave Character on a Slab of Metamaterial with Negative Permittivity and Permeability

Characteristics of surface wave modes on a grounded slab of negative permittivity and negative permeability parameters are investigated. It is shown that, unlike a slab with positive parameters, the dominant mode can have evanescent fields on both sides of the interface between the slab and the surrounding air. Detailed characteristics of such mode for various combinations of the slab parameters are given.

Chiral slab polarization transformer for aperture antennas

The cross polarization of large aperture antennas can be eliminated by a chiral slab transformer in front of the aperture to obtain a more efficient field pattern. The inhomogeneous chirality distribution required can easily be achieved by using a mixture of right- and left-hand helices so that the total density of the helices is constant inside the slab. Reflection from the slab can be eliminated by a proper design.

Near-field enhancement and subwavelength imaging in the optical region using a pair of two-dimensional arrays of metal nanospheres

Near-field enhancement and subwavelength imaging properties of a device comprising a coupled pair of two-dimensional arrays of resonant nanospheres are studied. The concept of using two coupled material sheets possessing surface mode resonances for evanescent field enhancement is already well established in the microwave region. We show that the same principles can be applied also in the optical region, where the performance of the resonant sheets can be realized with the use of metallic nanoparticles. We present a design of such structures and study the electric field distributions in the image plane of such a device.

Artificial Tellegen particle

Experimental evidence of the nonreciprocal Tellegen magnetoelectric effect is presented. The measured particle consists of a small ferrite sphere and a small piece of a thin metal wire glued to the sphere. The whole system is magnetized by a permanent magnet. The Tellegen effect was observed experimentally when this particle was positioned in a rectangular waveguide and excited by a small wire loop. This result experimentally confirms by a direct observation in the microwave range the known theoretical conclusions and experimental evidences at low frequencies regarding mistakes in some theoretical papers that claimed nonexistence of the Tellegen effect.

Plane waves in regular arrays of dipole scatterers and effective-medium modeling

A simple analytical theory for finding eigensolutions for plane electromagnetic waves propagating along an axis in infinite regular arrays of small dipole particles is presented. The spacing between dipoles in every plane is assumed to be smaller than the wavelength; separation between the planes is arbitrary. The influence of evanescent modes is taken into account. This theory gives a model for an effective propagation constant that can be applied in a wide frequency range from the quasi-static regime to the Bragg reflection (photonic bandgap) region.

Plane wave propagation in a uniaxial bianisotropic medium with an application to a polarization transformer

Uniaxial bianisotropic medium is a generalization of the well-studied bi-isotropic and chiral media. It is obtained, for example, when microscopic helices with parallel axes are positioned in a host dielectric in random locations. Plane wave propagation in such a medium is studied and a simple solution for the dispersion equation and for the eigenwaves are found. As a numerical example, polarization properties of a transverse wave propagating in a uniaxial bianisotropic medium is considered. The results give a simple possibility to construct a polarization transformer with a transversely uniaxial chiral medium for changing the polarization of a propagating plane wave.

Guided waves in uniaxial wire medium slab

Guided waves in a wire medium slab are studied. The wire medium is considered as a continuous medium described in terms of uniaxial permittivity dyadic. Nonlocal model of the wire medium, taking into account spatial dispersion, is used in the analysis. Different cases of an arrangement of the wires are considered. Analytic expressions for the fields in unbounded media and numerical solutions for eigenmodes spectrum in wire medium slab are obtained. Comparison of the results given by old (local) and new model of wire medium is presented.

Electromagnetic wave refraction at an interface of a double wire medium

Plane-wave reflection and refraction at an interface with a double-wire medium is considered. The problem of additional boundary conditions ABC in application to wire media is discussed and an ABC-free approach, known in the solid state physics, is used. Expressions for the fields and Poynting vectors of the refracted waves are derived. Directions and values of the power density flow of the refracted waves are found and the conservation of the power flow through the interface is checked. The difference between the results given by the conventional model of wire media and the model, properly taking into account spatial dispersion, is discussed.

Impedance boundary conditions for regular dense arrays of dipole scatterers

A simple analytical boundary condition to model the electromagnetic properties of planar arrays of dipole particles is developed for the normal plane-wave incidence. The impedance condition connects the averaged tangential electric and magnetic fields in the grid plane. The results for the reflection coefficient are compared with numerical simulations of reflection from arrays of small conducting strips. The model can be used in studies of monomolecular layers, periodic arrays of complex particles, including active arrays, and also in studies of multilayer arrays.