arXiv subjects

Sergei Tretyakov

Publications and source records attributed to Sergei Tretyakov.

At least 73 records · Page 4Linked to original sources

arXiv2008

A microwave transmission-line network guiding electromagnetic fields through a dense array of metallic objects

We present measurements of a transmission-line network, designed for cloaking applications in the microwave region. The network is used for channelling microwave energy through an electrically dense array of metal objects, which is basically impenetrable to the impinging electromagnetic radiation. With the designed transmission-line network the waves emitted by a source placed in an air-filled waveguide, are coupled into the network and guided through the array of metallic objects. Our goal is to illustrate the simple manufacturing, assembly, and the general feasibility of these types of cloaking devices.

physics.optics↗

arXiv2008

Simple and accurate analytical model of planar grids and high-impedance surfaces comprising metal strips or patches

This paper introduces simple analytical formulas for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied.

physics.class-ph↗

arXiv2008

Impedance-matched microwave lens

A microwave lens with highly reduced reflectance, as compared to conventional dielectric lenses, is proposed. The lens is based on two-dimensional or three-dimensional transmission-line networks that can be designed to have an effective refractive index larger than one, while having almost perfect impedance matching with free space. The design principles are presented and an example lens is studied using commercial simulation software.

physics.optics↗

arXiv2007

A three-dimensional backward-wave network matched with free space

A backward-wave slab based on a capacitively and inductively loaded three-dimensional transmission-line network is designed in such a way that impedance-matching with free space is obtained. To enable field propagation from free space to the network and vice versa, the use of a transition layer is proposed. Matching of the designed network with free space and negative refraction occurring at the slab interfaces are confirmed with full-wave simulations.

physics.gen-ph↗

arXiv2007

Transmission-line networks cloaking objects from electromagnetic fields

We consider a novel method of cloaking objects from the surrounding electromagnetic fields in the microwave region. The method is based on transmission-line networks that simulate the wave propagation in the medium surrounding the cloaked object. The electromagnetic fields from the surrounding medium are coupled into the transmission-line network that guides the waves through the cloak thus leaving the cloaked object undetected. The cloaked object can be an array or interconnected mesh of small inclusions that fit inside the transmission-line network.

physics.class-ph↗

arXiv2007

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 rigorously calculated and the corresponding dipole moment densities are determined. Using this data and the 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.

physics.class-ph↗

arXiv2007

Magnification of Subwavelength Field Distributions at Microwave Frequencies Using a Wire Medium Slab Operating in the Canalization Regime

Magnification of subwavelength field distributions using a wire medium slab operating in the canalization regime is demonstrated using numerical simulations. The magnifying slab is implemented by radially enlarging the distance between adjacent wires, and the operational frequency is tuned to coincide with the Fabry-Perot resonance condition. The near-field distribution of a complex-shaped source is canalized over an electrical distance corresponding roughly to $3λ$, and the distribution details are magnified by a factor of three. The operation of the slab is studied at several frequencies deviating from the Fabry-Perot resonance.

physics.class-ph↗

arXiv2007

Modeling and Analysis of Composite Antenna Superstrates Consisting on Grids of Loaded Wires

We study the characteristics and radiation mechanism of antenna superstrates based on closely located periodical grids of loaded wires. An explicit analytical method based on the local field approach is used to study the reflection and transmission properties of such superstrates. It is shown that as a result of proper impedance loading there exists a rather wide frequency band over which currents induced to the grids cancel each other, leading to a wide transmission maximum. In this regime radiation is produced by the magnetic dipole moments created by circulating out-of-phase currents flowing in the grids. An impedance matrix representation is derived for the superstrates, and the analytical results are validated using full-wave simulations. As a practical application example we study numerically the radiation characteristics of dipole antennas illuminating finite-size superstrates.

physics.class-ph↗

arXiv2007

On the Definition of Effective Permittivity and Permeability For Thin Composite Layers

The problem of definition of effective material parameters (permittivity and permeability) for composite layers containing only one-two parallel arrays of complex-shaped inclusions is discussed. Such structures are of high importance for the design of novel metamaterials, where the realizable layers quite often have only one or two layers of particles across the sample thickness. Effective parameters which describe the averaged induced polarizations are introduced. As an explicit example, we develop an analytical model suitable for calculation of the effective material parameters $ε_{\rm{eff}}$ and $μ_{\rm{eff}}$ for double arrays of electrically small electrically polarizable scatterers. Electric and magnetic dipole moments induced in the structure and the corresponding reflection and transmission coefficients are calculated using the local field approach for the normal plane-wave incidence, and effective parameters are introduced through the averaged fields and polarizations. In the absence of losses both material parameters are purely real and satisfy the Kramers-Kronig relations and the second law of thermodynamics. We compare the analytical results to the simulated and experimental results available in the literature. The physical meaning of the introduced parameters is discussed in detail.

physics.class-ph↗

arXiv2007

Subwavelength resolution with three-dimensional isotropic transmission-line lenses

Dispersion, impedance matching and resolution characteristics of an isotropic three-dimensional flat lens ("superlens") are studied. The lens is based on cubic meshes of interconnected transmission lines and bulk loads. We study a practical realization of the lens, based on the microstrip technology. The dispersion equations that have been previously derived, are verified with full-wave simulations. The isotropy of the structure is verified with analytical as well as simulation results. The resolution characteristics of a practically realizable, lossy lens are studied analytically.

physics.optics↗

arXiv2006

On geometrical scaling of split-ring and double-bar resonators at optical frequencies

In this paper we consider the resonant frequency of split-ring resonators and double-bar resonators used to create artificial magnetic response at terahertz and optical frequencies. It is known that geometrical scaling of the resonant frequency of split rings breaks down at high frequencies (in the visible) due to electromagnetic properties of metals at those frequencies. Here we will discuss this phenomenon in terms of equivalent inductance and capacitance of the ring, derive an approximate formula for the resonant frequency of split rings in the visible and show how the limiting value of the resonant frequency of extremely small split rings and double bars depends on particle shape.

cond-mat.mtrl-sci↗

arXiv2006

On Impedance Bandwidth of Resonant Patch Antennas Implemented Using Structures with Engineered Dispersion

We consider resonant patch antennas, implemented using loaded transmission-line networks and other exotic structures having engineered dispersion. An analytical expression is derived for the ratio of radiation quality factors of such antennas and conventional patch antennas loaded with (reference) dielectrics. In the ideal case this ratio depends only on the propagation constant and wave impedance of the structure under test, and it can be conveniently used to study what kind of dispersion leads to improved impedance bandwidth. We illustrate the effect of dispersion by implementing a resonant patch antenna using a periodic network of LC elements. The analytical results predicting enhanced impedance bandwidth compared to the reference results are validated using a commercial circuit simulator. Discussion is conducted on the practical limitations for the use of the proposed expression.

physics.class-ph↗

arXiv2006

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

Near-field enhancement and sub-wavelength imaging properties of a system 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. This paper shows 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. In this paper we present design of such structures and study the electric field distributions in the image plane of such superlens.

physics.optics↗

arXiv2006

Microstrip antenna miniaturization using partial dielectric material filling

In this paper we study microstrip antenna miniaturization using partial filling of the antenna volume with dielectric materials. An analytical expression is derived for the quality factor of an antenna loaded with a combination of two different materials. This expression can be used to optimize the filling pattern for the design that most efficiently retains the impedance bandwidth after size reduction. Qualitative design rules are given, and a miniaturization example is provided where the antenna performance is compared for different filling patterns. Results given by the analytical model are verified with numerical simulations and experiments. Key words: Microstrip antenna, miniaturization, partial filling, impedance bandwidth, quality factor.

physics.class-ph↗

arXiv2006

Vector circuit theory for spatially dispersive uniaxial magneto-dielectric slabs

We present a general dyadic vector circuit formalism, applicable for uniaxial magneto-dielectric slabs, with strong spatial dispersion explicitly taken into account. This formalism extends the vector circuit theory, previously introduced only for isotropic and chiral slabs. Here we assume that the problem geometry imposes strong spatial dispersion only in the plane, parallel to the slab interfaces. The difference arising from taking into account spatial dispersion along the normal to the interface is briefly discussed. We derive general dyadic impedance and admittance matrices, and calculate corresponding transmission and reflection coefficients for arbitrary plane wave incidence. As a practical example, we consider a metamaterial slab built of conducting wires and split-ring resonators, and show that neglecting spatial dispersion and uniaxial nature in this structure leads to dramatic errors in calculation of transmission characteristics.

physics.class-ph↗

arXiv2006

Generalized Permeability Function and Field Energy Density in Artificial Magnetics Using the Equivalent Circuit Method

The equivalent circuit model for artificial magnetic materials based on various arrangements of split rings is generalized by taking into account losses in the substrate or matrix material. It is shown that a modification is needed to the known macroscopic permeability function in order to correctly describe these materials. Depending on the dominating loss mechanism (conductive losses in metal parts or dielectric losses in the substrate) the permeability function has different forms. The proposed circuit model and permeability function are experimentally validated. Furthermore, starting from the generalized circuit model we derive an explicit expression for the electromagnetic field energy density in artificial magnetic media. This expression is valid at low frequencies and in the vicinity of the resonance also when dispersion and losses in the material are strong. The presently obtained results for the energy density are compared with the results obtained using different methods.

physics.class-ph↗

arXiv2006

Magneto-Dielectric Substrates in Antenna Miniaturization: Potential and Limitations

In the present paper we discuss antenna miniaturization using magneto-dielectric substrates. Recent results found in the literature reveal that advantages over conventional dielectric substrates can only be achieved if natural magnetic inclusions are embedded into the substrate. This observation is revised and the physical background is clarified. We present a detailed discussion concerning magnetic materials available in the microwave regime and containing natural magnetic constituents. The effects of magnetic dispersion and loss are studied: constraints on the microwave permeability are used to estimate the effect of magnetic substrates on the achievable impedance bandwidth. Microwave composites filled with thin ferromagnetic films are considered as a prospective antenna substrate. We calculate the impedance bandwidth for a $λ/2$-patch antenna loaded with the proposed substrate, and challenge the results against those obtained with conventional dielectric substrates. It is shown that the radiation quality factor is strongly minimized with the proposed substrate even in the presence of realistic losses. Estimates for the radiation efficiency are given as a function of the magnetic loss factor.

physics.class-ph↗

arXiv2006

Experimental verification of the key properties of a three-dimensional isotropic transmission line based superlens

Design and experimental realization of a three-dimensional superlens based on LC-loaded transmission lines are presented. Commercially available components and materials are used in the design. Transmission properties of the designed structure are studied experimentally and the observed lens properties are compared with analytical predictions. Backward-wave propagation and amplification of evanescent waves in the prototype structure are verified both analytically and experimentally.

physics.optics↗