Sergei Kosulnikov

Magnetic hyperbolic metamaterial of high-index nanowires

We show that the axial component of the magnetic permeability tensor is resonant for a wire medium consisting of high-index epsilon-positive nanowires, and its real part changes the sign at a certain frequency. At this frequency the medium experiences the topological transition from the hyperbolic to the elliptic type of dispersion. We show that the transition regime is characterized by extremely strong dependence of the permeability on the wave vector. This implies very high density of electromagnetic states that results in the filamentary pattern and noticeable Purcell factor for a transversely oriented magnetic dipole.

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.

Enhancement of Radiation With Irregular Wire Media

In this communication, we show that broadband enhancement of radiation from subwavelength sources can be achieved by using a new type of metamaterials-irregular random wire media. In contrast to samples of aligned metal wires, which give a narrow-band enhancement at Fabry-Perot resonances, here, the broadband enhancement is achieved due to the internal structure of the sample. Next, in contrast to lenses and hyperlenses, the proposed structure offers this enhancement without enlargement of the radiating aperture.

Multi-Mode Broadband Power Transfer through a Wire Medium Slab (Invited Paper)

It is known that slabs of wire media — dense arrays of thin conducting wires — can transport electromagnetic energy of evanescent plane waves over the slab thickness. This phenomenon was successfully used in superlenses and endoscopes. However, in the known configurations the effective energy transfer takes place only at the Fabry-Perot (thickness) resonances of the slab, making broadband power transfer impossible. In this paper we experimentally demonstrate that power transfer by a wire medium slab can be very broadband, whereas the Fabry-Perot resonances are damped, provided that the wires of the wire medium slab extend into the power-emitting body. As a testbed system we have used two rectangular waveguides and demonstrated that a properly designed and positioned wire medium slab transfers modes of any polarization from the input to the output waveguides. This study is relevant to emerging applications where broadband transport of reactive-field energy is required, especially in enhancing and controlling radiative heat flows in thermophotovoltaic systems.

Optimal parameters of metallic nanorods arrays for subwavelength imaging

The arrays of silver nanorods are known as prospective structures for near-field transmission. However, the available geometries are operating with incoherent sources and do not properly image the coherent ones. In this paper it is demonstrated how the geometry proposed in [Phys. Rev. Lett. 95, 267407 (2005)] can be modified to enable subwavelength imaging of arbitrary coherent sources. The greatly improved performance of the device is demonstrated numerically both through analysis of transmission and reflection coefficients and by full-wave simulation of a particular source imaging.

Unusual eigenmodes of wire-medium endoscopes: impact on transmission properties

Wire-medium endoscopes represent a promising tool of THz sensing/imaging. Bending should not critically harm the endoscope operation and the issue of bending losses is that of key importance for any endoscope. In this paper we show that the frequency-averaged power transmittance of a wire-medium endoscope is weakly sensitive to the bending. However, the frequency dispersion of the power loss/transmittance of the endoscope is strongly oscillating. Frequency maxima of the loss factor result from unusual eigenmodes of an elongated wire medium sample. These modes comprise power vortices and their sensitivity to the sample bending seems to be a critical issue for the future of wire-medium endoscopes.

Broadband power transfer through a metallic wire medium slab

The work contains an experimental confirmation and a theoretical study of broadband power transfer in wire medium slabs. The motivation of this work is a set of novel thermophotovoltaic devices suggested earlier. The key element of these devices is a wire medium slab which electromagnetically connects hot and cold parts without touching them due to a small gap between the ends of the wires and these parts of the system. The electromagnetic connection implies radiative heat transfer. This transfer presumably holds in a very wide band of infrared frequencies. However, this theory was never confirmed experimentally. Even the conceptual possibility of broadband electromagnetic power transfer through a wire medium layer was obtained only in numerical simulations. In the present work, the authors propose a test-bed system, qualitatively mimicking the radiation by a thermal emitter in the radio frequency range. The thermal emitter is replaced by an input waveguide and the photovoltaic (cold) part - by an output waveguide. They are separated by a substantial air gap in which an array of parallel wires is introduced, not touching the waveguide walls.