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In this paper, we study the efficiency of several types of all-dielectric, non-resonant, antireflection, and light-trapping coatings for the enhancement of photovoltaic absorption in thin-film silicon solar cells. We compare the enhancement of the photovoltaic absorption offered by a square array of nano-pillar shaped voids in the dielectric covering of the cell with that granted by a flat blooming layer, and a densely packed array of dielectric nanospheres. We optimize these coatings and show that the newly proposed nanostructure allows a significant increase of the photovoltaic absorption. The dependence of antireflection and light-trapping properties on the angle of incidence is numerically investigated, and it is shown that the array of voids keeps optimal also after averaging over the incidence angles. [ABSTRACT FROM AUTHOR]

Recently, we suggested the idea of an optical superlens based on the extraordinary dispersion properties of plasmonic nanochains. In the present paper we discuss the results of numerical simulations of the imaging of point sources in this superlens. The simulations show that sub-wavelength resolution can be obtained in much thicker structures than usual. A distance of nearly λ/2 between the source and the image plane is achieved. In addition the effects of stochastic deviations in geometrical parameters are studied. [ABSTRACT FROM AUTHOR]

Introduces an exact method used for determining the electric potential in an infinite lattice of particles described by curvilinear coordinates in which Laplace's equation separates. Problem formulation and description of the method; Case of spherical inclusions; Numerical results and comparison with other methods.

Here, we develop a theory of radiative heat transfer based on an equivalent electrical network representation for the hot material slabs in an arbitrary multilayered environment with arbitrary distribution of temperatures and electromagnetic properties among the layers. Our approach is fully equivalent to the known theories operating with the fluctuating current density, while being significantly simpler in analysis and applications. A practical example of the near-infrared heat transfer through the micron gap filled with an indefinite metamaterial is considered using the suggested method. The giant enhancement of the transferred heat compared to the case of the empty gap is shown. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we suggest, numerically simulate and discuss a tapered plasmonic nanostructure which allows efficient transmission of the wave beam energy into a weakly subwavelength (λ/4… λ/2) spatial region within a broad frequency range. The frequency stable location of this region becomes possible due to unusual plasmonic modes we have theoretically revealed and used. Our structure is promising for prospective transducers between conventional optical waveguides and subwavelength nanoguides or nanocircuits. [Copyright &y& Elsevier]

Near-field heat transfer between two closely spaced media can exceed in orders radiation through the interface of a single black body. This effect is caused by exponentially decaying (evanescent) waves, which form the photon tunnel between two transparent boundaries or boundaries supporting surface waves. However, in the infrared range this huge energy transfer holds only in the case when the gap between two media is as small as a few tens of nanometers. We propose a different paradigm of the radiation heat transfer, which makes possible the strong photon tunneling (and therefore giant radiative heat transfer) for micron-thick gaps. For it the air gap between two media should be modified, so that evanescent waves are transformed inside it into propagating ones. This modification is possible without increasing the phonon thermal conductance between two media. The suggested structure containing arrays of nanotubes or nanowires is designed so that the photovoltaic conversion of the transferred heat will not be altered by these arrays. [ABSTRACT FROM AUTHOR]

In this paper, propagation properties of a parallel-plate waveguide with tunable artificial impedance surfaces as sidewalls are studied both analytically and numerically. The impedance surfaces comprise an array of patches over a dielectric slab with embedded metallic vias. The tunability of surfaces is achieved with varactors. Simple design equations for tunable artificial impedance surfaces, as well as dispersion equations for the TE and TM modes are presented. The propagation properties are studied in three different regimes: multimode waveguide, single-mode waveguide, and below-cutoff waveguide. The analytical results are verified with numerical simulations. [ABSTRACT FROM AUTHOR]

Simple analytical formulas are introduced 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. [ABSTRACT FROM AUTHOR]

The work presented in this paper concerns a theoretical study on frequency selective surfaces (FSS) with application to artificial magnetic conductors or high-impedance surfaces (HIS). Current realizations of HIS are based on a planar FSS at the interface of a metal-backed dielectric slab either including vertical vias or not. A stable resonance was found for the case of series-resonance grids without vias in the slab. The resonance turns out to be unique in theory for all angles of incidence and both polarizations of plane waves illuminating the HIS. It was shown that vias destroy the stabilization effect and introduce a frequency shift. The analytical model was validated by HFSS simulations. [ABSTRACT FROM AUTHOR]

We report free space transmission and the first reflection measurements of a composite double negative (DNG) metamaterial, also known as a left-handed material (LHM). The metamaterial composes of the split-ring-resonators and discontinuous thin wires. Very high transmission values of the metamaterial are observed within a frequency range for which both effective permeability and permittivity are expected to be negative. [ABSTRACT FROM AUTHOR]

An analytical model is presented for a rectangular lattice of isotropic scatterers with electric and magnetic resonances. Each isotropic scatterer is formed by putting appropriately 6 Ω-shaped perfectly conducting particles on the faces of a cubic unit cell. A self-consistent dispersion equation is derived and then used to calculate correctly the effective permittivity and permeability in the frequency band where the lattice can be homogenized. The frequency range in which both the effective permittivity and permeability are negative corresponds to the mini-band of backward waves within the resonant band of the individual isotropic scatterer. [Copyright &y& Elsevier]

Antenna systems based on some improved metallic photonic bandgap (MPBG) structures are introduced. A useful modification is introduced by replacing each wire in a two-dimensional MPBG structure by a chain of many identical conducting elements of a certain shape. Each such chain forms an effective wire of capacitive impedance. The optimal design for maximal radiation efficiency and directivity is obtained by choosing an appropriate value of the impedance per unit length for the effective wire and the geometry of the modified MPBG structure. The optimal impedance is realized by using elements of various shapes, including broken wire elements and planar H-shaped elements. Numerical results have shown that the modification can increase the efficiency of the MPGB antenna by a factor of 1000, as well as reduce the thickness of the MPGB structure to about λ/3 in the presence of a metal background plane. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 214–221, 2001. [ABSTRACT FROM AUTHOR]

Presents information on a study that proposed a method to calculate the plane wave reflection from a planar rectangular array of C-shaped wire elements. Background on electromagnetic response for some complex particles such as the C-shaped wire elements; Details on the explicit expression for the reflection coefficient; Information on the radiated field of the array of dipoles; Conclusion.

Antenna or array antenna systems based on metallic photonic bandgap structures are considered. An explicit method is introduced to quickly obtain the radiation characteristics for such an antenna system. Numerical results for the radiation pattern and the radiation resistance are presented, and are compared with those obtained by the method of moments. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 67–73, 2000. [ABSTRACT FROM AUTHOR]

A planar rectangular array of C-shaped wire elements is placed over a Dallenbach absorbing layer to further reduce the reflection from a metallic plane. An analytical formula for the reflection coefficient for such a structure is given, and numerical results are presented to illustrate the antireflection effect of the C-particle array. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 302–307, 2000. [ABSTRACT FROM AUTHOR]

Presents information on a study that featured electromagnetic excitation of two-dimensional arrays of bianisotropic particles by plane waves. Formulation of the problem; Evaluation of interaction dyadics; Example of collective polarizability dyadics for arrays of omega particles; Conclusions.

Discusses a study that examined the problem of electromagnetic mutual coupling of scatters in the three-dimensional regular infinite arrays. Information on the polarizability dyadics for the elements of the two-dimensional infinite planar grid; Description of the Floquet harmonic expansion of the wave field of the dipole array; Numerical example and conclusion.

A correction to the article "Electromagnetic characterization of planar and bulk metamaterials: A theoretical study" published in the January 3, 2012 issue is presented which discusses expressions for surface susceptibilities and reflection and transition coefficients.

We propose the enhancement of the photovoltaic absorption in thin-film solar cells using densely packed arrays (not obviously regular) of non-absorbing submicron or micron-sized dielectric spheres located on top of the cell. The spheres can decrease reflection forming an effective blooming layer. Simultaneously, they can suppress the transmission through the photovoltaic layer transforming the incident radiation into a set of collimated beams. The focusing of the light inside the photovoltaic layer allows enhanced absorption in it leading to the increase of the photovoltaic current. Every sphere focuses the incident wave separately-this mechanism does not require collective effects or resonances and therefore takes place in a wide spectral range. Since the fabrication of such the coating is easy, our light-trapping structure may be cheaper than previously known light-trapping ones and perhaps even than flat anti-reflecting coatings. [ABSTRACT FROM AUTHOR]

Authors demonstrate numerically the magnification of subwavelength field pattern using a wire medium slab operating in the canalization regime. The magnifying slab is implemented by radially enlarging the distance between adjacent wires, and the operational frequency is tuned to coincide with the Fabry-Pérot resonance condition. The near-field pattern of a complex-shaped source is canalized over an electrical distance corresponding roughly to three wavelengths (3λ), and the pattern details are magnified by a factor of 3. The performance is also studied at several frequencies deviating from the one of the Fabry-Pérot resonance. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of numerical and experimental investigations of a prospective antenna which can be used, for example, as a base-station antenna in cellular telecommunication systems. The antenna is a half-wavelength dipole surrounded by periodically arranged capacitively loaded wires. Its operation is based on the recently suggested principle of the wire-medium artificial lens. The development of this concept can possibly lead to the design of compact (0.2–0.5 wavelength in diameter) electrically controllable base-station antennas. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 467–469, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20503 [ABSTRACT FROM AUTHOR]

In this article, we suggest and study a novel omnidirectional wireless power transfer (WPT) system based on unusual double-toroidal helix coils. The suggested antenna is a double-helix coil wounded around a torus. It creates two mutually orthogonal magnetic fields. One is toroidal and confined inside the torus, and another one is poloidal and is distributed outside it. The intensities of these two fields can be independently tuned via the geometry of the turns. The coupling coefficients are tailored to ensure high efficiency regardless of the receiver position and orientation, without active circuitry for tuning or control. This topology provides self-tuning functionality which is achieved when the coupling between the transmitter and receiver is minimized while the coupling in the pairs transmitter–repeater and repeater–receiver is strong. The system consists of three transmitter–repeater pairs orthogonal to each other, ensuring omnidirectional functionality. Experimental results confirm self-tunability and high efficiency for any position and orientation of receivers. The proposed double-helix antenna is applicable to different WPT applications where the coupling/decoupling between coils can be freely controlled. [ABSTRACT FROM AUTHOR]

A novel approach for designing an element of an arrayed radio frequency coil for ultrahigh field magnetic resonance imaging (UHF MRI) is presented. The purpose of this approach is to achieve the dual-band transceiver regime in a compact array of magnetic antennas. Our work qualitatively develops the concept of the so-called high-impedance coil (HIC), combined with the adequate interfacing circuitry, which offers the decoupling of the HICs in the array due to the very high self-impedance compared to the mutual impedance. This concept has not been previously thought applicable to dual-band transceiver arrays. We show that, by slightly modifying only the cable shield, we achieve a dual-band transceiver high-impedance coil (dual-band TRHIC). The needed modification implies two asymmetric gaps granting two useful eigenmodes to the cable loop. The resonant excitation of these modes will allow the magnetic resonant scanning of both hydrogen and Phosphorus in the 7 T dc magnetic field. To verify our ideas, we simulated and measured a single TRHIC in both transmitting and receiving regimes and similarly studied two linear arrays made of two and three proposed TRHICs. The method of asymmetric gaps, in our opinion, allows one to engineer the targeted multifrequency operation of arrayed TRHICs decoupled at these frequencies. [ABSTRACT FROM AUTHOR]

In the literature on composite materials with extreme or unusual electromagnetic properties (so-called metamaterials), it is common to retrieve the effective material parameters from the scattering parameters (complex reflection and transmission coefficients) of the metamaterial layer. Most often, this retrieval is done by using the well-known Nicolson-Ross-Weir method or its modifications. It is commonly known that one of the two effective parameters of many metamaterials retrieved in this way (either effective permittivity or permeability) exhibits the so-called anti-resonance, which is a nonphysical feature. This effect has been understood as a manifestation of spatial dispersion in the sample. Many previous works have either claimed or assumed that the anti-resonance is an effect caused by the periodicity of the composite material. To our knowledge, this claim was never supported by comparisons of periodical and random samples. In some other works, it has been theoretically shown that the anti-resonance of the retrieved material parameters can be avoided, e.g., by the introduction of additional surface parameters into the retrieval procedure. If it is so, the anti-resonance has nothing to do with the internal periodicity of the bulk medium. In the present work, we numerically and experimentally investigate the question if the internal periodicity of metamaterial layers is essential for the appearance of anti-resonances in extracted material parameters. We show that it is not so. Therefore, our result is in favor of the theory which treats the anti-resonance as a deficiency of the Nicolson-Ross-Weir retrieval procedure applied to spatially dispersive media. [ABSTRACT FROM AUTHOR]

A correction to the article "Isotropic negative refractive index at near infrared" that was published in the January 10, 2013, issue is presented.

In this paper we suggest and study a metamaterial composed of non-magnetic spherical particles, which according to both approximate analytical theory and exact simulations possesses an isotropic negative refractive index in the near-infrared frequency range. The effect of negative refraction has been confirmed by full-wave simulations of the Gaussian beam diverted by a metamaterial prism. The disagreement between predictions of the theory for an infinite lattice and the results of full-wave simulations for the prism is discussed. [ABSTRACT FROM AUTHOR]

A correction to the article "Simple and Accurate Analytical Model of Planar Grids and High-Impedance Surfaces Comprising Metal Strips or Patches," by Olli Luukkonen and colleagues is presented.

We present a general methodology for electromagnetic homogenization and characterization of bianisotropic metasurfaces formed by regular or random arrangements of small arbitrary inclusions at interfaces of two different isotropic media. The approach unites and generalizes the earlier theories developed independently by two joint research groups: that of profs. Holloway and Kuester and that of profs. Simovski and Tretyakov. We analyze the features of both formalisms and discuss their peculiarities in several example cases. Our theory can be used in the analysis and synthesis of a wide spectrum of metasurfaces. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate an approach for local reduction of the electric field amplitude of the transmitted radio-frequency signal in ultrahigh-field magnetic resonance imaging (MRI). We excite a suitable combination of three coupled dipole hybrid resonances composing a single transmit antenna array element. Using numerical optimization, we designed a feeding network for three coupled dipoles placed over an electromagnetic phantom mimicking a human body. This network of discrete elements provides the appropriate amplitudes and phases of three dipole currents excited by a single input port. It allows controlling the electric field distribution in the vicinity of the antenna. Our goal was to obtain a minimum of the electric field at the given relatively small depth inside the phantom, where body implants are typically located while keeping a tolerable level of the magnetic field toward the phantom’s center. We designed and manufactured a three-dipole antenna prototype optimized for MRI of the human body at 7 T (proton Larmor frequency of 298 MHz). The experimental validation showed a 40 dB reduction of the electric field amplitude at a depth of 4 cm compared to a conventional single-dipole antenna. The coupling network can be rearranged to target different depths. Therefore, a principle of electric field minimization at a controllable position inside the body has been shown, which may be useful for designing transmit MRI antennas with improved safety of implants. [ABSTRACT FROM AUTHOR]

Megahertz-range wireless power transfer has become a promising approach for increasing spatial freedom of charging. This article proposes a cylindrical-shaped coil, which can produce the homogeneous magnetic field in a plane. The coil consists of two helical windings, which are wound to guide the current in opposite directions. A single power source is used to excite the transmitter without any current amplitude or phase control circuits. Furthermore, since the parasitic capacitance of the coil is not negligible due to the complexity of the coil shape, we develop a general equivalent model with parasitic capacitance for the analysis of complex coils. The system efficiency of the proposed omnidirectional wireless power transfer device is validated by a practical experiment. The measured dc-to-dc efficiency of approximately 72.4% and the load power of 13 W are demonstrated for the proposed wireless charging system at 6.78-MHz operating frequency. Finally, we verify that the electromagnetic exposure satisfies the safety regulations. [ABSTRACT FROM AUTHOR]

Bloch analysis in conjunction with a full-wave simulation is used in order to design a composite right/left-handed (CRLH) transmission line (TL). We analyze the parasitic components introduced by loading elements and inter-cell coupling, and present details to the compensation required in order to maintain the balanced state of the periodic TL. The method is shown to yield a useful tool for the design of CRLH periodic TLs up to millimeter-wave frequencies for structures with arbitrary metallization. The performance of the method is shown numerically at 26 and 77 GHz. Experimental verification is done at 26 GHz, comparing radiative properties, dispersion, and attenuation constant of a through-broadside scanning leaky-wave antenna. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate experimentally a simple approach for achieving superdirectivity of emitted radiation for electrically small antennas based on a spherical dielectric resonator with a notch excited by a dipole source. Superdirectivity is achieved without using complex antenna arrays and for a wide range of frequencies. We also demonstrate the steering effect for a subwavelength displacement of the source. Finally, unlike previously known superdirective antennas, our design has significantly smaller losses, at the operation frequency radiation efficiency attains 80%, and matching holds in the 3%-wide frequency band without any special matching technique. [ABSTRACT FROM AUTHOR]

We address the question of the optimal choice of loading material for antenna miniaturization. A new approach to identify the optimal loading material (dielectric or magnetic) for maximization of bandwidth of resonant antennas is introduced. Instead of equivalent resonant circuits or transmission-line resonators, we use the analysis of radiation mechanism to identify the fields contributing mostly to the stored energy and determine the beneficial material type. The formulated rule is qualitatively illustrated using a dipole and a patch antenna, as well as a planar inverted-L antenna where the conventional analysis of circuit or a transmission-line resonator leads to incorrect conclusions. Guidelines are presented for miniaturizing different antenna types. [ABSTRACT FROM AUTHOR]

Low-profile antennas comprising a horizontal dipole above a high-impedance surface are analyzed. The emphasis of this paper is on the additional resonances of the radiating structure caused by surface waves propagating on the high-impedance surface. It is shown that such resonances can be favorably used for broadening the bandwidth of the antenna. The phenomenon is thoroughly modeled by exploiting a parallel between the HIS structure and a waveguide resonator. In the second part of the paper we discuss homogenized approaches for modeling the radiating properties of the antenna with emphasis to the phenomenon discussed in the first part. As it turns out, it is necessary to take into account the spatially dispersive properties of high-impedance surfaces, and most of the simplified models commonly used for analyzing high-impedance surface based antennas fail in predicting the discussed resonance mode. [ABSTRACT FROM AUTHOR]

A design for planar electromagnetic absorbers is presented. The performance of this absorber is maintained over a wide incidence angles and for both TE and TM polarization. The absorber is composed of a high-impedance surface comprising an array of patches over a grounded lossy dielectric slab perforated with metallic vias (wire medium). The main contribution of the paper is to demonstrate and practically use the presence of an additional resonance when the plasma frequency of the wire medium in the dielectric substrate is close to the original resonance of the high-impedance surface. The presence of the vias between FSS and the ground plane is discussed both for the case of a high-permittivity absorber and for a low permittivity one, through the derivation of simple and efficient analytical expressions, specifically derived for the problem at hand. We show that the presence of the vias influences the oblique incidence TM absorption, and when properly designed, the insertion of the vias into the absorber structure results in a bandwidth enlargement and higher absorption performance. [ABSTRACT FROM AUTHOR]

The effect of artificial magnetodielectric substrates on the impedance bandwidth properties of microstrip antennas is discussed. We review the results found in the literature and then focus on practically realizable artificial magnetic media operating in the microwave regime. Next, a realistic dispersive behavior of a practically realizable artificial substrate is embedded into the model. It is shown that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of reduced size patch antennas loaded with dispersive magnetodielectric substrates and high-permittivity substrates are compared. It is shown that unlike substrates with dispersion-free permeability, practically realizable artificial substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This conclusion is experimentally validated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Phased antenna arrays of dipoles are widely used in ultrahigh field (UHF) magnetic resonance imaging for creating the controllable radio frequency (RF) magnetic field distributions in a human body. Due to safety and imaging quality reasons each individual channel of the array should be decoupled—electromagnetically isolated from the others. The required number of channels is large and in some techniques the dipole antennas should be located in the close proximity of the human body. Their ultimately dense arrangement leads to a strong mutual coupling and makes the conventional decoupling structures inefficient. This coupling needs to be suppressed without a significant distortion of RF fields in the imaged area. In this work, we propose and study a novel decoupling technique for two UHF transceiver on-body dipole antennas. The decoupling is performed by a periodic structure of five parallel resonant wires referred to as a metasurface (MS). In contrast to conventional decoupling with a single resonant wire, the MS decoupled by means of excitation of a higher order coupled mode of the wires, which field is highly confined. The main advantage is a low distortion of the RF-field in the central region of the body. [ABSTRACT FROM AUTHOR]

A theoretically revealed effect [Belov et al., Opt. Lett. 34, 527 (2009)] of the significant enhancement of evanescent harmonics inside a wire medium slab is experimentally verified in the microwave frequency range. The phenomenon originates from resonant pumping of standing waves into which evanescent waves are converted inside the slab. We find a good agreement between experimental data, numerical simulations and theory. [ABSTRACT FROM AUTHOR]

Conventional wireless power transfer systems consist of a microwave power generator and a microwave power receiver separated by some distance. To realize efficient power transfer, the system is typically brought to resonance, and the coupled-antenna mode is optimized to reduce radiation into the surrounding space. In this scheme, any modification of the receiver position or its electromagnetic properties results in the necessity of dynamically tuning the whole system to restore the resonant matching condition. It implies poor robustness to the receiver location and load impedance, as well as additional energy consumption in the control network. In this paper, we introduce a new paradigm for wireless power delivery based on which the whole system, including transmitter and receiver and the space in between, forms a unified microwave power generator. In our proposed scenario, the load itself becomes a part of the generator. Microwave oscillations are created directly at the receiver location, eliminating the need for dynamical tuning of the system within the range of the self-oscillation regime. As a proof-of-concept demonstration, we experimentally show that, such self-oscillating wireless power delivery systems can provide robust operation against changes in the environment or in the location of the load. The proposed concept has relevant connections with the recent interest in parity-time symmetric systems, in which balanced loss and gain distributions enable unusual electromagnetic responses. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

We review the basic physics and applications of a special class of planar metamaterials, often called metasurfaces , which are composed of optically thin and densely packed planar arrays of resonant or nearly resonant subwavelength elements. Electromagnetic properties and functionalities of such metasurfaces are defined by the structure and specific features of the subwavelength elements and their coupling type and strength, and they are often influenced by an underlying substrate. Metasurfaces may provide a full control of the reflected and transmitted fields, and they can be designed to possess many required properties replacing bulky optical components. Here, we describe different types of metasurfaces suggested in the past and recent years for a broad range of the operational wavelengths ranging from microwaves to the visible, and emphasize their important functionalities. We demonstrate that, despite a wide functional and structural diversity, all suggested metasurfaces can be associated with only several broad classes depending on intrinsic physical mechanisms of their polarizability. We suggest the functionality-based classification of metasurfaces, and clarify a link between their polarization response and field control capabilities. We also suggest a general approach to an optimal design of metasurfaces for many specific applications. [ABSTRACT FROM AUTHOR]

The Purcell effect is usually described as a modification of the spontaneous decay rate in the presence of a resonator. In plasmonics, this effect is commonly associated with a large local-field enhancement in "hot spots" due to the excitation of surface plasmons. However, high-index dielectric nanostructures, which become the basis of all-dielectric nanophotonics, cannot provide high values of the local-field enhancement due to larger radiation losses. Here, we demonstrate how to achieve a strong Purcell effect in all-dielectric nanostructures, and show theoretically that the Purcell factor can be increased by two orders of magnitude in a finite chain of silicon nanoparticles. Using the eigenmode analysis for an infinite chain, we demonstrate that the high Purcell factor regime is associated with a Van Hove singularity. We perform a proof-of-concept experiment for microwave frequencies and observe the 65-fold enhancement of the Purcell factor in a chain of 10 dielectric particles. [ABSTRACT FROM AUTHOR]

The Purcell effect is defined as a modification of the spontaneous emission rate of a quantum emitter at the presence of a resonant cavity. However, a change of the emission rate of an emitter caused by an environment has a classical counterpart. Any small antenna tuned to a resonance can be described as an oscillator with radiative losses, and the effect of the environment on its radiation can be modeled and measured in terms of the antenna radiation resistance, similar to a quantum emitter. We exploit this analogue behavior to develop a general approach for calculating the Purcell factors of different systems and various frequency ranges including both electric and magnetic Purcell factors. Our approach is illustrated by a general equivalent scheme, and it allows resenting the Purcell factor through the continuous radiation of a small antenna at the presence of an electromagnetic environment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In this paper, we propose, design, theoretically study, and experimentally test a simple periodical array which provides perfect absorptivity when one of its surfaces is illuminated and controllable reflectivity for illuminations of the other side. The proposed structure does not contain any ground plane and relies on the bianisotropic properties of the unit cells forming the absorbing layer. The absence of the ground plane makes the new design suitable for applications where the absorber should not block transmission outside the absorption band. The proposed structure is realized as an array of nonidentical conducting patches imprinted on the two sides of a thin dielectric slab. This ultra-thin ($\sim\lambda/150$, where $\lambda$ is the operational wavelength) metasurface absorber is optimized, fabricated, and tested. The test results confirm nearly perfect absorption (from one direction) and controllable reflection (from the other direction) at the resonance frequency, as well as partial transparency outside of the absorption band. [ABSTRACT FROM PUBLISHER]

In this paper we propose and study some electromagnetic properties of a thin composite layer formed by metal stripes of resonant length located on two sides of an elastic polymer film. We show that in the THz range the structure offers multiple functionalities such as high sensitivity to applied mechanical strain and polarization transformation properties. We suggest a method of fabrication for such composite layers, prepare the experimental sample and measure the dependence of the transmission coefficient on stretching. [ABSTRACT FROM AUTHOR]