An endoscope based on extremely anisotropic metamaterials for applications in magnetic resonance imaging

The possibility of transfer of the spatial distribution of the near-zone RF magnetic field recorded by receiving coils during magnetic resonance imaging with the use of an endoscope designed from an extremely anisotropic metamaterial is considered. Application of such a material can lead to an increase in the image resolution and/or reduction of the object scanning time in the tomograph. Possibilities of the endoscope for the undistorting transfer of the spatial distribution of the alternating magnetic field through significant distances are theoretically studied and transfer of different spatial field distributions from the isocenter of the tomograph to the region of weak static magnetic field is experimentally demonstrated. The dependence of the quality of obtained images on positions receiving coils in the endoscope is studied. It is found that, in addition to the image transfer with a small distortion, it is possible to significantly increase the signal-to-noise ratio by pumping standing waves in a medium consisting of parallel wires.     

Image transmission with the subwavelength resolution in microwave,terahertz, and optical frequency bands

An image transmission principle related to the transformation of the spatial spectrum of a source into modes propagating in a metamaterial with a flat isofrequency contour is proposed. This principle makes it possible to obtain a resolution much smaller than the wavelength. The proposed principle is implemented in the microwave, terahertz, and optical frequency bands with the use of a medium consisting of parallel metal wires. It is shown that the subwavelength transmission of images can be achieved in the visible optical band via the use of a periodic structure consisting of successive metal and dielectric layers. The resolution, operation bandwidth, and sensitivity to losses in component materials are estimated for all the proposed systems. The applicability of such structures in medicine, in near-field microscopy, and as components of optical data storages with increased capacity is considered.     

A condition imposed on the electromagnetic polarizability of a bianisotropic lossless scatterer

In the dipole and local field approximations, electromagnetic scatterers are modeled in terms of the polarizability tensor. The matrix elements of this tensor, which are determined by the scatterer geometry, are complex even in the absence of losses in the material. There is a criterion that the polarizability tensor must obey if the scatterers possess no dissipative losses. This condition, derived here for bianisotropic scatterers, can be applied to analytical modeling of periodic structures composed of such scattering inclusions.     

Angular stabilisation of resonant frequency of artificial magnetic conductors for TE-incidence

Two novel artificial magnetic conductors (high-impedance surfaces) are suggested that stabilise the resonant frequency of the structure with respect to variations of the angle of incidence of TE-polarised incident electromagnetic waves. The performance is compared to that of the well-known mushroom structure, both in theory and experiment. A possible explanation for the stabilising effect is presented.     

Subwavelength imaging in a superlens of plasmon nanospheres

A structure comprising two lattices of silver or gold nanospheres is considered. It is shown that this structure can be used as a superlens capable of providing subwavelength imaging of a point source and a sub-wavelength spatial resolution of two sources at a distance within one wavelength.     

Electromagnetic study of a ferrite coplanar isolator suitable for integration

The transmission coefficient of a nonreciprocal coplanar waveguide (CPW) using ferrite rods is studied. A new approximate method is proposed to evaluate the propagation constant of such a perturbed waveguide, which is based on the use of numerical data referring to the nonperturbed waveguide. We have estimated the value of the nonreciprocity effect and settled the condition of the validity of our theory. Some experimental data of a CPW with ferrite inclusions are also presented.     

Experimental verification of analytical model for high impedance surfaces

A simple yet accurate analytical model for a high impedance surface comprising an array of capacitive patches over a grounded dielectric slab is experimentally verified. The results are compared for the oblique incidence reflection phase obtained with the analytical model and commercial simulation software with the results of free-space measurements. It is shown that the analytical and simulation results are in very good agreement with the experimental results. To the authors? knowledge, this is the first time the results of the analytical model in question have been experimentally verified.     

Mesoscopic effective material parameters for thin layers modeled as single and double grids of interacting loaded wires

As an example of thin composite layers we consider single and double grids of periodically arranged interacting wires loaded with a certain distributed reactive impedance. Currents induced to the wires by a normally incident plane wave are calculated analytically and the corresponding dipole moment densities are determined. Using this data and calculated averaged fields we assign mesoscopic material parameters for the proposed grid structures. These parameters depend on the number of grids, and measure the averaged induced polarizations. It is demonstrated that properly loaded double grids possess polarization response that over some frequency range can be described by assigning negative values for the mesoscopic parameters. Discussion is conducted on the physical meaningfulness to assign such material parameters for thin composite slabs. The results predicted by the proposed method for the double-grid structures are compared with the results obtained using the commonly adopted S-parameter retrieval procedure.     

Analytical modelling of double-negative composites

Analytical model of metamaterials comprising lattices of small resonant scatterers and (optionally) infinite wires is developed for the case when the planar grids of magnetic dipoles alternate with those of electric dipoles (or those of wires) along the direction of the wave propagation. An important question on the possibility to extract material parameters from measurements or simulations of the plane-wave scattering matrix for finite-thickness slabs of left-handed metamaterials is revisited. It is shown that the class of Bloch lattices (for which this extraction makes sense) is broader than one could judge upon the previous works. Also, it is shown that the spatial dispersion that destroys the operation of double-negative media can arise for the oblique propagation with respect to crystal planes even if it is not revealed from the analysis of the normal propagation.     

Interaction effects in two-dimensional bianisotropic arrays

Electromagnetic excitation of two-dimensional (2-D) arrays of bianisotropic particles by plane waves is considered. Arrays (grids) are assumed to be infinite and the particles to be small compared to the wavelength, so that the dipole approximation is possible. The electromagnetic interaction between all the particles changes the properties of these particles (in particular, chiral and omega particles are studied). The analytical model under consideration allows one to express the electric and magnetic moments induced in each particle through the incident wave fields in terms of collective polarizability dyadics (CPDs). The proposed method to evaluate these dyadics combines numerical and analytical parts. The results of the calculations of the induced electric and magnetic moments by plane waves are presented for a planar arrangement of omega particles