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This paper presents a comparative analysis of the mixture models used in radio physics to describe the effective properties of composite materials and formulates the limits of their applicability and criteria for checking their correctness. Two of the most general models have been chosen, which take into account the transformation of the composite structure upon changes in its composition. The correspondence of the chosen model to the experimental results is considered. The effect of the composite structure on the frequency of the maximum and the shape of its dielectric absorption line is shown. The analysis shows that the complication of the models in comparison with those already known and an increase in the number of parameters determined from the experiment is inappropriate at the existing level of the composition and material parameters (permittivity and permeability) measuring error and due to a significant contribution of the size and surface effects, which is not taken into account in quasi-static mixture models.

Methods for measuring the microwave permittivity and permeability of materials are considered. The specific features and applicability conditions of measurement methods in transmission lines and in free space are shown, and the measurement errors are analyzed along with the calibration procedures applied for reducing the errors. Individual sections of the articles contain descriptions of scalar, resonance, quasistatic, and quasioptic methods. It has been determined that out of many existing techniques, the NicolsonRossWeir measurement method in a coaxial line and also the method for measuring the permeability of thin ferromagnetic films with the use of a shortcircuited strip cell are most widely applied. By using these methods, the majority of matters concerned with studying the microwave properties of materials can be solved.

Protective SiO2 coating deposited to iron microparticles is highly demanded both for the chemical and magnetic performance of the latter. Hydrolysis of tetraethoxysilane is the crucial method for SiO2 deposition from a solution. The capabilities of this technique have not been thoroughly studied yet. Here, two factors were tested to affect the chemical composition and the thickness of the SiO2 shell. It was found that an increase in the hydrolysis reaction time thickened the SiO2 shell from 100 to 200 nm. Moreover, a decrease in the acidity of the reaction mixture not only thickened the shell but also varied the chemical composition from SiO3.0 to SiO8.6. The thickness and composition of the dielectric layer were studied by scanning electron microscopy and energy-dispersive X-ray analysis. Microwave permeability and permittivity of the SiO2-coated iron particles mixed with a paraffin wax matrix were measured by the coaxial line technique. An increase in thickness of the silica layer decreased the real quasi-static permittivity. The changes observed were shown to agree with the Maxwell Garnett effective medium theory. The new method developed to fine-tune the chemical properties of the protective SiO2 shell may be helpful for new magnetic biosensor designs as it allows for biocompatibility adjustment.

We present investigation of microwave permeability of thin supermalloy films deposited on a flexible substrate. The permeability measurements are performed by transmission-reflection technique in a coaxial line under external magnetic bias in the frequency range of 100 MHz–20 GHz. It is shown that demagnetization does not affect the measurements when bias is above 150 Oe. Magnetic characteristics of the films are determined by two approaches: (i) fitting of the resonant frequency dependence on magnetic bias by Kittel's equation and (ii) calculation of the parameters from the Landau–Lifshitz–Gilbert dispersion law. Both approaches give close results for values of magnetoelastic field, anisotropy field, saturation magnetization, and damping factor.

The microwave permeability of nickel is determined from constitutive parameters of paraffin–bound composites filled with nickel flakes or spheres. The metal permeability is calculated with account for skinning. The measurements of constitutive parameters are performed using the reflection–transmission coaxial-line within the frequency band of 0.001–20 GHz. The effects of filling factor, particle shape, and size on permittivity and permeability spectra are analyzed. The retrieval of inclusion permeability is based on the treatment of measured dependence of composite constitutive parameters on frequency and on volume fraction of inclusions. The retrieval procedure is based on the generalized Sihvola mixing model simplified for a single-dimension composite. The model describes the wide contrast of component susceptibility, accounts for inclusion shape and the Bergman–Milton spectral linewidth. The retrieved microwave permeability is close to the values reported for measurements with thick wires and foils.

In this chapter, various techniques are reviewed with focus on the identification of complex biological agents such as bacteria, viruses, proteins, and enzymes using SERS-active silver substrates. Biological targets have multiple peculiarities that add to the challenges of the SERS biosensing. In regards to the direct non-labeled sensing of bacteria, it was discovered that all bands in the registered SER spectra were generated by metabolites released from bacterial cells. It undermined the prior notion of non-labeled detection and identification of bacteria based on the presumed spectra of cellular walls. However, it also provides new opportunities for the SERS analysis of bacteria. The SERS measurements of viruses can be performed with SERS-active surfaces or colloidal solutions of silver nanoparticles. However, the use of surfaces requires extensive sample preparation and often lacks sensitivity, while colloidal SERS substrates have another problem—most types of silver nanoparticles are negatively charged and have a poor interaction with likewise predominantly negatively charged virions. Thus, a challenge is posed to develop SERS-ready positively charged silver nanoparticles or use other methods to enforce the non-specific binding of viruses to the silver surfaces. Meanwhile, SER spectra of proteins are nearly impossible to acquire at adequate sensitivity. Thus, non-direct measurements are the only way. SERS provides the most benefits when working with relatively small molecules, so small molecules serving as Raman probes can be used as an intermediary to produce SER spectra. For enzymes like butyrylcholinesterase, it means measuring SER spectra of substrates and products of the relevant reaction, while for other proteins, specialized techniques must be developed. It can be concluded that biological targets require a case-by-case approach. Prior experiences with direct SERS measurements of highly Raman-active molecules like R6G and others often used in fundamental studies might not be relevant in bioanalytics.

Spectroscopy based on surface enhanced Raman scattering (SERS) is widely used as a method with extremely high sensitivity for molecular and chemical analysis. We have developed thin-film sandwich structures, in which, when used as sensitive elements for detecting organic compounds at low concentrations, high-amplitude spectra of surface enhanced Raman scattering are observed. Using gas-phase cryochemical synthesis and thermal sputtering in vacuum, SERS active sandwich structures Ag&ndash, poly(chloro-p-xylylene)&ndash, Ag (Ag&ndash, PCPX&ndash, Ag) were obtained. In the process of creating sandwich structures, the upper silver film takes the form of a complex island topology with submicron sizes. A series of samples were made with different thicknesses of the polymer and upper silver layers. SERS spectra of the analyte chemically adsorbed on the film surface were obtained, demonstrating a significant amplification (up to 104) compared with the control sample. The dependence of the gain on the silver concentration is characterized by a maximum polymer layer thickness of 600 nm and a 30 nm thick upper silver layer. A selective amplification of the low molecular weight compound spectra with respect to proteins was observed. A semi-empirical model is proposed that is in good agreement with the experimental results.

Anomalous optical response of the metasurface, fabricated from regular silicon resonators is investigated. The resonators have form of two-dimensional regular bars that are covered by nano-thin silver film. Computer simulations as well as real experiment demonstrate deep minima in the reflectance in the optical spectral range. We believe the resonances are due to the excitation of propagating and localized surface em waves. The multiple metal-dielectric resonances result in much enhanced local electromagnetic fields on the surface of the resonators. To investigate the surface enhanced Raman scattering (SERS) effect the metasurface is covered by molecules of 4-mercapto-phenylboronic acid that form covalent bonds with the silver layer. We obtain over $$10^5$$ enhancement of the Raman scattering, by direct matching Raman signals from the metasurface and the flat silver surface. The designed metasurface is used as an effective SERS substrate.

Virus detection is often performed using antibody-based and polymerase chain reaction-based techniques. Such methods have major deficiencies, caused by time-consuming and labor-intensive incubation and purification steps. In this contribution, a novel SERS substrate for qualitative virus detection was developed and described. The substrate is composed of a thin silver film with folded surface structure containing pore-like nanoscale cavities and indentations, deposited on mica substrate by electron beam physical vapor deposition method. Pore-like structures are semi-regularly arrayed, with a rough surface in between, allowing for SERS activity, and their size and periodicity can be manipulated in the manufacturing process. It was speculated that viral particles could be trapped in these structures and would generate easily detectable enhanced Raman signals. The SERS substrate was tested against detection of four virus species – rabbit myxomatosis virus, canine distemper virus, tobacco mosaic virus and potato virus X. Specific spectra were obtained and analyzed for each virus. Data analysis demonstrated successful differentiation between tested species. The reported results demonstrate that novel SERS substrate is suitable for detection and identification of viral particles.

The magnetic permeability of alsifer was restored from the frequency dependences of the dielectric and magnetic permeabilities of powder alsifer (AlSiFe alloy)–wax matrix composites. The permeabilities were measured using the coaxial line technique within a frequency range of 0.05–20 GHz. The effect of the concentration, shape, and size of powder particles on the microwave magnetic properties of composites was considered. A good agreement between the measurement results and the Maxwell–Garnett formula generalized with consideration for the particle shape, the percolation threshold, and the skin-effect was obtained. The found sizes of particles agreed with electron microscopy and granulometry data. Both the frequency and the ferromagnetic resonance line figure of merit (FOM) for lamellar particles proved to be higher than for spherical ones. Alsifer powders were shown to be promising fillers for radioabsorbing materials.

A resonant RLC circuit with a magnetic core has been investigated experimentally and theoretically as a promising metamaterial cell design. Laminates of multilayer ferromagnetic films serve as a magnetic core. The ferromagnetic resonance frequency of the bare laminate core is above 1 GHz. An intensive magnetic absorption peak is obtainable at lower frequencies due to a resonant wire coiled around the core. Such magnetic metamaterials seem promising for applications that require high magnetic loss at frequencies of hundreds of megahertz. This paper focuses on efficient approaches to adjusting the location of magnetic loss peak in magnetic metamaterials. High-frequency permeability of the metamaterial samples has been measured in a rectangular waveguide. It is shown that by varying the geometry, structure, and composition of the measured metamaterial samples, the magnetic spectra can be radically changed. Excitation of electromagnetic resonance in the ferromagnetic core with the resonant wire is discussed within the frame of the quasi-static approximation.

Iron powder particles were coated with a thin SiO 2 shell for protection of corrosion. Dynamic magnetic behavior of the as-synthesized material was studied in comparison with uncoated metal in terms of frequency dispersion of the microwave permeability and permittivity. A uniform 100-nm SiO 2 shell provides durable corrosion resistance to a 4.5-μm carbonyl iron powder. The shell was deposited through tetraethyl orthosilicate hydrolysis of technical grade chemicals. It was shown that the shell did not influence the magnetic properties of the iron powder. Electron microscopy, particle size analysis, and γ-resonance spectroscopy were applied in the study. The deposited SiO 2 decreased the microwave permeability value and prevented percolation conductivity in a composite with a paraffin wax dielectric matrix.

The paper considers the application of mixing rules to the analysis of the microwave effective material parameters, the permittivity and permeability, of composites. It is suggested to perform the analysis in terms of the normalized inverse susceptibility defined as the volume fraction of inclusions divided by the effective dielectric or magnetic susceptibility of the composite. This allows the volume fraction dependence of the effective material parameters to be represented in a form that is convenient for the analysis, so that distinguishing features of the dependence become more pronounced and helpful for understanding the factors that affect the effective properties of the composite. The proposed approach is illustrated by the analysis of the measured data on the microwave material parameters of composites comprising Sendust powder with either spherical or platelet powder particles, and Permalloy powders with particles of the stone-like shape. The microwave material parameters are measured with paraffin-based composite samples in the 7/3-mm coaxial air-filled waveguide by the Nicolson‒Ross‒Weir technique. It is shown that for Sendust particles, the interaction between inclusions is low. For the composites comprising spherical particles, the Maxwell Garnet mixing rule is a good approximation of the volume fraction dependence of microwave permeability. For the platelet powder particles, the magnetic performance is governed by the Wiener mixing rule. For composites filled with Permalloy powder, the contribution of the interaction between inclusions to the effective permeability is essential. Therefore, the suggested approach allows the type of mixing rule suitable for description of material parameters of a given composite to be determined.

Original multiscale flaked silver SERS-substrate (MFSS substrate) was applied for glycated albumin (GA) biosensing. The substrate is composed from silver flakes that have three orders of magnitude size dispersion: from 50 nm to 2 μm. The multiscale silver structure refracts the incident light and various surface plasmons are excited. Some of the internal plasmons are localized and give rise of the large local electric field. It was demonstrated that Raman scattering signal strongly depends: a) on “hot spots” formation at the edges and points of contact of silver plates, and b) on the angle of incidence. As a result the silver structure operates as an effective SERS substrate. To achieve the selectivity to glycated part, the surface of SERS-substrate was modified with 4-mercaptophenylboronic acid (4-mPBA). Various saccharides (Fru, Glc, Suc, Dex) were taken as model compounds for the glycated proteins determination. The saccharides contain cis-diol groups that form five- or six-membered ethers with boronic acid. Spectrum of SERS-substrate changes after sugar/glycated albumin treatment. Main differences in the SERS-spectra of sugar/glycated albumin treated SERS-substrate and control are referred to phenylboronic acid vibrations (999, 1021, 1072 and 1589 cm−1). Principal component analysis (PCA) and Partial Least Squares Regression (PLS-R) were used to discriminate spectra and to construct calibration curve, as well as to measure GA values in real samples of human plasma. Multiscale flaked silver SERS-substrate modified with 4-mPBA allows quantitative one-step biosensing of glycated albumin in 15 μl of human plasma.

Metal-dielectric micro/nano-composites have surface plasmon resonances in visible and near-infrared domains. Excitation of coupled metal-dielectric resonances is also important. These different resonances can allow enhancement of the electromagnetic field at a subwavelength scale. Hybrid plasmonic structures act as optical antennae by concentrating large electromagnetic energy in micro- and nano-scales. Plasmonic structures are proposed for various applications such as optical filters, investigation of quantum electrodynamics effects, solar energy concentration, magnetic recording, nanolasing, medical imaging and biodetection, surface-enhanced Raman scattering (SERS), and optical super-resolution microscopy. We present the review of recent achievements in experimental and theoretical studies of metal-dielectric micro and nano antennae that are important for fundamental and applied research. The main impact is application of metal-dielectric optical antennae for the efficient SERS sensing.

Reactive sputtering of permalloy typically reduces crystallite size in films, if the concentration of reactive gas is low. This advances magnetic properties: decreases coercivity and increases good in-plane magnetic anisotropy. But oxygen is rarely applied for this purpose. Here, peculiar deposition conditions, including the geometry of the vacuum deposition system and large polymer substrate, allowed for the deposition of supermalloy with unusually high admixture of oxygen. Evolution of both static and dynamic magnetic properties with an increase in oxygen concentration proved to be dealt with the balance between grain size, surface structure, disordering of atomic structure and internal stresses. The critical concentration when supermalloy shows indications of oxidation is 5% of O2. Coercivity, resistivity, roughness and ferromagnetic resonance frequency are the parameters that are most sensitive to oxidation.

Observation of the surface enhanced Raman scattering (SERS) is hampered by the background surface luminescence. We investigate the metasurface made of periodic silicon micro bars. Bars are covered by the silver nanolayer. Computer simulations as well as real experiment reveal an anomalous optical response of the metasurface, which is due to the excitation of various metal-dielectric surface resonances. We demonstrate the enhancement of the Raman signal from a monolayer of 4-Mercaptophenylboronic acid (MPBA) when it is deposited on the microbar metasurface. The micro-bar metasurface exhibits large Raman/luminescence (signal/noise) ratio. As result it operates as a very efficient SERS substrate.

Anomalous optical response for the metasurface fabricated from silicon resonators is investigated. Resonators have form of 3D micro cones – tips that are covered by semicontinuous silver film. Thus prepared metasurface exhibits anomalous optical response due to the excitation of metaldielectric resonances in visible and near IR spectral ranges. We investigate the effect of the “extraordinary” optical diffraction by tip-shaped metasurface. The multiple metal-dielectric resonances result in huge enhancement of the local electric field in-between metal particles placed on the surface of dielectric cones. SERS phenomenon is investigated by immobilization of DTNB (5,5’- dithio-bis-[2-nitrobenzoic acid]) molecules of on the metasurface.

Observation of the wanted Raman signal from SERS substrates is hampered by the background luminescence. We investigate the metasurface made of periodic silicon micro bars with thin silver layer on the top. The computer simulations as well as real experiment reveal the anomalous optical response of the metasurface is due to the excitation of the metal-dielectric surface resonances. We demonstrate the enhanced Raman signal from the organic molecules of 5,5-dithio-bis[2-nitrobenzoic] acid deposited on the microbar metasurface. The microbar metasurface exhibits large Raman/luminescence (signal/noise) ratio. As result it operates as an efficient SERS substrate.

Anomalous optical response for the metamaterial fabricated from silicon bar resonators is investigated. The resonators are manufactured in form of two-dimensional bars and covered by semicontinuous silver film. The calculations as well as real experiments demonstrate Wood anomalies in visible and near IR spectral ranges associated with excitation of the surface waves in metamaterial by means of diffraction of the incident light on the periodic bars. The multiple metal-dielectric resonances result in much enhanced local electromagnetic fields in-between metal particles placed on the surface of dielectric bars. The resonances can be tuned by varying angle of incidence, polarization, and geometry of the dielectric bars. It opens new venue in R&D SERS substrates including sensors detecting specific substances.

In this paper, we investigate the potential of facet structures of cerium dioxide for the purpose of increasing the intensity of the surface enhancement Raman scattering (SERS) signal. During the studies, a new metamaterial is developed. The metamaterial is based on facet cerium dioxide films and plasmonic nanoparticles that are immobilized on its surface. The new metamaterial provides an additional SERS signal amplification factor of more than 200. Thus developed material offers the prospect of increasing the sensitivity and selectivity of biochemical and immunological analysis.

The possibility of amplification of local electric fields on the surface of thin dielectric films of complex structure is considered. Amplification of the optical field enables an increase in the intensity of the Raman scattering signal and provides broad opportunities for the development of novel biochemical sensors.

Optical properties of two-dimensional periodic systems of the dielectric micro bars and micro cones are investigated. Computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric and metal-dielectric resonances, which are excited in-between metal nanoparticles and dielectric cones and bars. In the metal-dielectric resonance local electric field can be orders on magnitude larger than the field in the plasmon resonance only. To investigate local electric field the signal molecules were deposited on the metal nanoparticles. We demonstrate the enhancement of the electro- magnetic field by detecting the Raman signal from the of organic acid molecules deposited on the investigated metasurface.

Optical properties of two dimensional periodic system of the silicon micro-cones are investigated. The metasurface, composed of the silicon tips, shows enhancement of the local optical field. Finite element computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric resonances. Various electromagnetic resonances are considered in the dielectric cone. The metal-dielectric resonances, which are excited between metal nanoparticles and dielectric cones, are also considered. The resonance local electric field can be much larger than the field in the usual surface plasmon resonances. To investigate local electric field the signal molecules are deposited on the metal nanoparticles. We demonstrate enhancement of the electromagnetic field and Raman signal from the complex of DTNB acid molecules and gold nanoparticles, which are distributed over the metasurface. The metasurfaces composed from the dielectric resonators can have quasi-continuous spectrum and serve as an efficient SERS substrates.

Application of metamaterials for creation of new types of radar absorbers (RAs) is investigated. Typical frequency dependences of the permittivity and permeability of composites fabricated from various inclusions employed in designing RAs are considered. It is shown that the structures of RAs can contain metamaterials with both positive and negative values of the real parts of permittivity and permeability. An RA having a low reflection coefficient over a wide range of the incidence angles of an electromagnetic wave for both wave polarizations is developed. It is based on a metamaterial with negative values of the permittivity and permeability.

Microwave magnetic performance of thin ferromagnetic films is of interest in view of many technical problems. For measuring the microwave permeability, a shorted stripline technique is in common use. Recently, a coaxial technique has been developed for permeability measurements of films deposited onto a flexible substrate. The coaxial technique is reported to be advantageous over the conventional stripline method in wideband operating range and accuracy. In this paper, measurement results are presented which are obtained with these two techniques for Fe–N films. It is found that the magnetoelastic effect contributes greatly to the measured microwave permeability of the films. With the coaxial measurements under an external magnetic bias, this effect may be accounted for to estimate the permeability of a plane film sample. Additional information on the properties of the film can also be extracted from these data, such as estimations of average magnetic anisotropy field and of the magnetostriction constant of the film.

Magnetic spectra of composites filled with carbonyl iron powder were measured at frequencies of up to 30 GHz. Two previously unknown intensive high-frequency peaks of magnetic absorption have been found at frequencies surpassing the ferromagnetic resonance frequency. The peaks may be attributed to Aharoni exchange resonance modes. The resonances are excited inside magnetically isolated nanocrystallites that constitute carbonyl iron grains. Features of homogeneous ferromagnetic resonance in carbonyl iron powder grains are also discussed.

Magnetron sputtered nanocrystalline thin Fe70Co30 metal and (Fe70Co30)95(SiO2)5 composite films show a differently broadened Mossbauer sextet, which is interpreted as an increase in CsCl-type solid solution ordering degree for the composite film. It is suggested that the effective magnetic field at iron nuclei increases by 15 kOe when an Fe atom is substituted by Co in the first coordination sphere. The ordering degree and the composite structure are shown to vary the lattice parameter by up to 0.5%.

The light transmission through metallic films with different types of nano-structures was studied both theoretically and experimentally. It is shown that the positions of the surface plasmon resonances depend on nano-structural details. Those can be changed from sample to sample or in given sample by applying an external dc electric or magnetic field. The dependence of transmission spectrum on the shape of holes (inclusions) and external fields can be used for manipulation of the light transmission, as well as the polarization of the transmitted light and other optical properties, by external field. Two complementary situations are considered: a metal film with dielectric holes and a dielectric film with metallic islands. A new analytical asymptotic approach for calculation of the optical properties of such plasmonic systems is developed.

The structure of the Tamm state localized at the interface between anisotropic magnetophotonic crystal (anisotropic MPC) and a photonic crystal (PC) made of isotropic dielectrics is studied. It is shown that if the frequency of this state appears within the degenerate band gap then its structure qualitatively differs from the structure of a well-known Tamm state localized at the interface between two one-dimensional PC made of isotropic materials. Since inside the degenerate BG the real part of the Bloch wavenumber differs from the Brillouin value, two Bloch waves with different signs in the real part of the wavenumber and the same sign in the imaginary part have different input impedance values. Moreover, contrary to the case of a PC made of isotropic materials the impedance of each Bloch wave is a tensor. As a consequence to construct a surface state at least three evanescent Bloch waves are required. The conditions that determine the Tamm state frequency also change.

Results of studies in the influence of losses on the superresolution achieveability are presented. The studies involve modeling and realization of superresolution devices. It is found that rigorous electrodynamic models that are not based on homogenization of composites can be effectively used in modeling devices with metamaterials. The possibilities to compensate losses in near-optic metamaterials by means of “active” inclusions are discussed; they appear to be rather doubtful. Alternatively, new designs are suggested for applications where losses are desirable.

Layered structures fabricated from thin ferromagnetic films (including structured ones) are proposed as bulk materials with high values of microwave permeability. Experimental data on microwave properties of such structures based on monolayer and multilayer nitrogen-doped iron films are presented. The influence of the skin effect, magnetostriction, and other physical phenomena on the microwave properties of such materials is discussed. The problem of the limiting values of permeability in the microwave band is considered in detail. Possible applications of such materials as radio-wave absorbing coatings and substrates for miniature stripline antennas are analyzed.

Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability. To produce a bulk massive sample from thin films, multi-layer films made of a number of many thin films may be used. The paper reports on an experimental study of microwave and static magnetic properties of multi-layer iron-based films and composite samples made of these. The multi-layer films under study are deposited onto a mylar substrate by a magnetron-sputtering process performed in Ar atmosphere with controlled N2 admixture. The sputtered iron layers are alternated with SiO2 layers. The measured static and microwave magnetic properties of the bulk sample are found to differ from the properties of constituent films. This is an evidence for strong interactions between the magnetic layers in the sample, which interact at distances exceeding greatly the distance between adjacent magnetic layers. A theoretic model is developed to account for magneto-dipole interactions between iron films in a multi-layer system. The model explains the anomalously high demagnetization field of the sample observed in the measurements.

The problem regarding top possible (hopefully, total) fleld suppression of a fll- amentary source placed above nonuniform impedance plane is discussed. New designs of the electromagnetic fleld absorbers and resonators are suggested which may be engineered with the use of metamaterials. 1. INTRODUCTION | ABSORPTION OF THE ENERGY OF A POINT SOURCE BY A HALF-SPACE Interest to the fleld propagation along the imperfect surface has about century-old history, the beginnings of which trace back to the Sommerfeld's solution of the classical problem for the dipole radiating above the plane with flnite conductivity. Later, as the radio broadcasting evolved, a lot of publications appeared which dealt with electromagnetic fleld propagation in the presence of an absorbing half-space with the aim to minimize the signal losses. Now certain practical needs (1) set questions about what value of impedance of a plane should be chosen to absorb the maximum portion of energy radiated by a point source (say, fllamentary current), how much the amount of the absorbed energy is and how to create such an impedance. Note, in view of the symmetry of the radiation pattern of the fllament, at the absence of the plate (in the free space) equal power ∞uxes are radiated into upper and lower half-spaces, and exactly one half of the radiated energy penetrates through the plane y = 0, see Fig. 1.

The idea to inverse the radiation pattern of the microwave antenna due to appli- cation of the isotropic metamaterial screen with negative refractive index in S band is demon- strated at the flrst time in this investigation. The electromagnetic simulation of waveguide antenna patterns by moment's methods demonstrates an agreement modeling antenna patterns with measured antenna diagrams for values of metamaterial efiective parameters (permittivity and permeability) extracted from measured S-parameters of metamaterial sheet sample.

The paper touches upon the correspondence between the widely used homogenized approach and integral equation technique in simulating electromagnetic excitation of metamaterials. The attention is drawn to metamaterials with helix-type inclusions, their properties are briefly discussed. Special attention is paid to the thin metamaterial sheets as they are the primary candidates to manufacture the so-called “superlenses” that can reveal the resolution overcoming the well-known diffraction limit (about half a wavelength). Experimental results are compared to computer simulation using both homogenized model and a rigorous approach. A physical interpretation is suggested of the development of an image with superresolution in a real device.

The study is conducted of thin Fe–N films produced by magnetron sputtering on mylar substrate. The correlations between morphology, structure, and magnetic static and dynamic properties of the films are found. The films under study have a columnar morphology. Both the average granule size and the length-to-width ratio of the granules increase with the film thickness that causes an increase of the effective anisotropy field. A small variation of nitrogen fraction in Ar+N 2 gas mixture in the sputtering chamber allows the location of magnetic loss peak to be controlled within the frequency range of 1–5 GHz. Therefore, the frequency dependence of permeability is determined not only by the crystalline structure and composition of the film but also by its morphology, thickness, and effective magnetic anisotropy. In particular, with the fixed concentration of nitrogen in the film, the frequency dependence of microwave permeability is determined greatly by the distribution of nitrogen atoms over different vacancies in the film structure.

The microwave permeability of multi-layered Fe fllms is under study. The multi- layer fllms are found to possess more rigid magnetic structure and larger damping factor of ferro- magnetic resonance compared to those of single-layer fllms. Bulk materials with high microwave permeability may be produced as laminated structures of these multi-layer ferromagnetic fllms. In the paper, experimental data are presented on the microwave permeability of such laminated regular structures based on Fe fllms. Possible technical applications of the materials under study include thin wideband radar absorbers and miniaturized patch antennas. For many microwave applications, materials with high microwave permeability values are needed. The frequency dependence of microwave permeability is typically due to the ferromagnetic reso- nance. In many magnetic materials, the permeability varies slightly with frequency until an abrupt drop appears at the ferromagnetic resonance frequency. Above the resonance, the permeability takes values that are close to unity. Hence, an estimate of microwave permeability of a magnetic material may be made from its static permeability "s and resonance frequency fr. The static per- meability characterizes the magnetic performance in the operating frequency band. The resonance frequency is an estimate for the cutofi frequency, above which the material is no more permeable enough and magnetic loss increases greatly. For high microwave permeability be attained, both fr and "s must be as high as possible. These values often reveal a complex dependence on the material composition, magnetic and crystalline structure, features of manufacturing and processing, etc. However, "s and fr are related closely to each other by well known Snoek's law: an increase of one leads to a decrease of another, with the product of these being dependent only on the saturation magnetization Ms of the material. The anisotropy fleld or other structure-dependent values are not involved in Snoek's law. For thin fllms with in-plane magnetization, "s is reciprocal to squared fr in difierence to con- ventional Snoek's law (1): ("s i 1)f 2 r = (∞4…Ms) 2 (1) where ∞ … 3GHz/kOe is the gyromagnetic ratio. Eq. (1), which is referred to as Acher's law in the literature, also has the right-side part depending on the saturation magnetization only. Therefore, Eq. (1) provides a constraint for the microwave permeability of magnetic fllms that is determined by the composition and is independent of structure, the same as Snoek's law does for bulk materials. When fr < ∞4…Ms, which is several GHz or several dozens GHz for typical high-permeability fllms, Eq. (1) produces far higher values of "s and, therefore, higher microwave permeability compared to Snoek's law. Therefore, thin ferromagnetic fllms are promising materials for microwave applications. However, most applications require bulk samples. With the increase of fllm thickness, the microwave permeability of the fllm degrades because of the efiect of eddy currents and out-of-plane magnetization. For these efiects to be avoided, laminates of thin ferromagnetic layers are useful. Since the thickness of substrate is large compared to that of ferromagnetic fllm, multi-layer fllms may be used to obtain high volume fractions of ferromagnetic material in the laminate. Therefore, this study presents experimental data on the microwave performance of both multi-layer thin Fe fllms and laminates made of such fllms. 2. EXPERIMENT

New dielectric metamaterial based on the Bragg filter comprising ten dielectric bilayers was investigated. Each bilayer is the thin films of silicone dioxide ( SiO 2 ) and another film of zirconium dioxide ( ZrO 2 ). The surface of the multilayer film is profiled. It has a form of periodic system of rectangles separated by the open gaps. We use the computer simulation as well as analytical solution to find the reflectance of the multilayer as a function of the wavelength and electromagnetic (em) field distribution. The multilayer system reveals the enhancement of em fields at the surface. The considered Bragg filter was modified by Raman-active structure made of gold nanoparticles with chemically attached 3,3-thio-bis(6- nitrobenzoic acid) - (TNB). The high Surface Enhanced Raman Scattering (SERS) signal was detected.