MULTIPATH ANTENNA SYSTEM OF THE VHF BAND BASED ON A LENS MADE OF GRANITE RUBBLE

Предложена конструкция приземной многолучевой антенной решетки на основе линзы из гранитного щебня, позволяющая одновременно формировать до нескольких десятков лучей в длинноволновой области УКВ-диапазона волн. Эффективная диэлектрическая проницаемость гранитного щебня оценивалась с помощью формулы Лихтенекера для мелкодисперсных смесей; ее величина приблизительно равна 3. Для оценки величины замедления поверхностных волн в линзе использовалась методика анализа дисперсионных характеристик зеркального диэлектрического волновода; при высоте линзы 1.8 метра эффективная диэлектрическая проницаемость эквивалентного зеркального диэлектрического волновода равна 2.1. В качестве облучателей линзы - несимметричные электрические вибраторы, расположенные на окружности по периметру линзы, диаметр которой составляет 30 метров; диаметр подстилающей стальной поверхности составляет 40 метров. Предложенная антенная система характеризуется потерями в щебне около 3 дБ при диаметре линзы около 3,8 длин волн; показано, что коэффициент направленного действия у каждого луча может составлять около 15,5 дБ, при ширине главного лепестка в азимутальной плоскости по уровню половинной мощности около 10 градусов We propose a design of a surface multi-beam antenna array based on a lens of crushed granite, which makes it possible to simultaneously form up to several tens of beams in the long-wave region of the VHF wave range. We estimated the effective dielectric constant of crushed granite using the Lichtenecker formula for fine mixtures; its value is approximately equal to 3. To estimate the magnitude of the deceleration of surface waves in the lens, we used a technique to analyze the dispersion characteristics of a mirror dielectric waveguide; at a lens height of 1.8 meters, the effective dielectric constant of the equivalent mirror dielectric waveguide is 2.1. As irradiators of the lens - asymmetric electric vibrators located on a circle around the perimeter of the lens, the diameter of which is 30 meters; the diameter of the underlying steel surface is 40 meters. The proposed antenna system is characterized by a loss in rubble of about 3 dB with a lens diameter of about 3.8 wavelengths; the directivity of each beam can be about 15.5 dB, with the width of the main lobe in the azimuthal plane at half power level of about 10 degrees

Analysis Method of Bending Effect on Transmission Characteristics of Ultra-Low-Profile Rectangular Microstrip Antenna

With the advent of wearable communication devices, microstrip antennas have developed multiple applications due to their ultra-low-profile properties. Therefore, it is essential to analyze the problem of frequency shift and impedance mismatch when the antenna is bent. For the case of a rectangular patch antenna E-plane bent on the cylindrical surface, (1) this paper introduces the effective dielectric constant into the cavity model, which can accurately predict the resonance frequency of the antenna, and (2) according to the equivalent circuit model of the antenna resonance mode, the lumped element parameters are calculated based on the above effective dielectric constant, so that impedance characteristics and the S-parameter matching the port can be quickly constructed. From the perspective of circuit frequency characteristics, it explains the change in the transmission performance of the curved antenna. The experimental results show that the maximum difference between the experimental and theoretical calculation frequencies is less than 1%. These results verify the validity and applicability of the theory in the analysis of ultra-low-profile patch antennas and wearable electronic communication devices. It provides a theoretical basis for the fast impedance matching of patch antennas under different working conditions.

Performance Improvement of Aperture Coupled MSA through Si Micromachining

In recent times rectangular patch antenna design has become the most innovative and popular subject due to its advantages, such as being lightweight, conformal, ease to fabricate, low cost and small size. In this paper design of aperture coupled microstrip patch antenna (MSA) on high index semiconductor material coupled with micromachining technique for performance enhancement is discussed. The performance in terms of return loss bandwidth, gain, cross-polarization and antenna efficiency is compared with standard aperture coupled antenna. Micromachining underneath of the patch helps in to reduce the effective dielectric constant, which is desirable for the radiation characteristics of the patch antenna. Improvement 36 percent and 18 percent in return loss bandwidth and gain respectively achieved using micromachined aperture coupled feed patch, which is due to the reduction in losses, suppression of surface waves and substrate modes. In this article along with design, fabrication aspects on Si substrate using MEMS process also discussed. Presented antenna design is proposed antenna can be useful in smart antenna arrays suitable in satellite, radar communication applications. Two topologies at X-band are fabricated and comparison between aperture coupled and micromachined aperture coupled are presented. Index Terms—Microstrip Patch Antenna, Aperture Coupled, Micromachining, High Resistivity Silicon

Recognition of kinetic transient process in corrosion scales of fuel elements by impedance spectroscopy

The presented study concerns with the corrosion kinetics of two zirconium alloys: Zr-Nb-Sn-Fe and Zr-Nb-Fe. Alloy samples were pre-exposed at 360 °C in a LiOH solution containing 70 mg/l of lithium ions. Ex-situ electrochemical impedance spectroscopy (EIS) performed in 0.5 M potassium sulphate solution at 25 °C was used to study the properties of the oxide and kinetic transient effect. Evaluation of the impedance spectroscopy data was based on application of a simple equivalent circuit. The setup of the equivalent circuit conformed to Jonscher´s universal law of dielectric response. The analysis of the impedance data was aimed at estimation of non-dispersive capacitance of the oxide formed during the pre-exposure. Effective values of dielectric constant were calculated using the non-dispersive capacitance and the oxide thickness values, calculated from weight gains. For the pre-transient samples relatively higher values of dielectric constants were obtained. Typical pre-transient dielectric constants for Zr-Nb-Sn-Fe alloy ranged between 20–21, while slightly lower values were obtained for Zr-Nb-Fe alloy. In both alloys steep and significant decrease in effective dielectric constant (e_ef = 9–13) was found for the transient samples. The decrease correlated very well with the drop in percentage of tetragonal oxide determined by Raman spectroscopy and corresponded to the increase of the weight gains of the transient samples. Literature data indicate values of dielectric constants for tetragonal zirconium oxide between 38–46, while those for monoclinic oxide are usually presented between 12–22. The evidenced changes in dielectric constants are therefore in agreement with the expected decrease of tetragonal phase fraction in the oxide layer during the transient. In the Zr-Nb-Sn-Fe post-transient samples values of dielectric constant increased again to 18–20, therefore almost to the pre-transient level. This increase was not evidenced with Raman spectroscopy data, which show constant low content of the tetragonal fraction. Possible explanation of this disagreement is the location of the newly formed post-transient tetragonal oxide presumably at the metal/oxide interface. Oxide thickness of the post-transi-ent samples is 4–7 m and the oxide/metal interface is beyond access of the laser beam of Raman spectrometer. We can conclude that using ex-situ EIS, the transient was observable in both alloys; the change in the ratio of monoclinic and tetragonal phase can be evaluated based on the difference of effective dielectric constant of the two phases. The Zr-Nb-Sn-Fe alloy showed the onset of the transient after the 105th day of pre-exposure, but the change in the ratio of the monoclinic and tetragonal phases was less significant than in the Zr-Nb-Fe alloy, in which, however, the transient could be observed only after 147 days of pre-exposure. The resulting values of the effective dielectric constant of oxides correlated well with the percentage of tetragonal oxide determined by Raman spectroscopy and with the results of the weight gain method.

Effective dielectric permeability and electrical conductivity of polycrystalline PbTe films with disturbed stochiometry

This paper presents the study of the effective dielectric constant and electrical conductivity of polycrystalline PbTe films with disturbed stoichiometry. It is shown that superstoichiometric additions of Te and Pb within the limits of solubility by doping with PbTe contribute to a change in a wide range of concentrations of electrically active impurities and, consequently, to an increase in the dielectric constant (ɛ), electrical conductivity (σ) and absorption coefficient (α), in addition, the excess of these components strongly affects the amount of polarization.

Scaling of energy gaps in phosphorene nanoflakes

Electronic structure of phosphorene nanoflakes which consist of hundreds of phosphorus atoms are studied in the framework of unrestricted Hartree-Fock approach. On the base of Pariser-Parr-Pople model for electron-electron interactions, a simplified Bethe-Salpeter formalism is established for the calculation of excitation states of the system. Taking into account the electron-hole interaction in various dielectric environments, the optical gap of a triangular phosphorene nanoflake is shown to increase as the screening effect becomes stronger while its graphene counterpart exhibits just the opposite dependence. After confirming an exponential dependence of the optical gap on the effective dielectric constant, the quasiparticle and optical gaps are also found to obey an exponential scaling rule against the total number of atoms in the nanoflakes, respectively. By extrapolating the dependence on the size of the system, one is able to estimate the exciton binding energy of a monolayer phosphorene sheet on a SiO2 substrate to be 0.894 eV. The result is found to agree well with the previous experimental result of $ 0.9 eV.

Prospects for the Development of High Energy Density Dielectric Capacitors

In this paper, the design of high energy density dielectric capacitors for energy storage in vehicle, industrial, and electric utility applications have been considered in detail. The performance of these devices depends primarily on the dielectric constant and breakdown strength characteristics of the dielectric material used. A review of the literature on composite polymer materials to assess their present dielectric constants and the various approaches being pursued to increase energy density found that there are many papers in which materials having dielectric constants of 20–50 were reported, but only a few showing materials with very high dielectric constants of 500 and greater. The very high dielectric constants were usually achieved with nanoscale metallic or carbon particles embedded in a host polymer and the maximum dielectric constant occurred near the percolation threshold particle loading. In this study, an analytical method to calculate the dielectric constant of composite dielectric polymers with various types of nanoparticles embedded is presented. The method was applied using an Excel spreadsheet to calculate the characteristics of spiral wound battery cells using various composite polymers with embedded particles. The calculated energy densities were strong functions of the size of the particles and thickness of the dielectric layer in the cell. For a 1000 V cell, an energy density of 100–200 Wh/kg was calculated for 3–5 nm particles and 3–5 µ thick dielectric layers. The results of this study indicate that dielectric materials with an effective dielectric constant of 500–1000 are needed to develop dielectric capacitor cells with battery-like energy density. The breakdown strength would be 300–400 V/µ in a reverse sandwich multilayer dielectric arrangement. The leakage current of the cell would be determined from appropriate DC testing. These high energy density dielectric capacitors are very different from electrochemical capacitors that utilize conducting polymers and liquid electrolytes and are constructed much like batteries. The dielectric capacitors have a very high cell voltage and are constructed like conventional ceramic capacitors.

Dual Metal Triple-gate-dielectric (DM_TGD) Tunnel Field Effect Transistor: A Novel Structure for Future Energy Efficient Device

Background: Power reduction is a severe design concern for submicron logic circuits, which can be achieved by scaling the supply voltage. Modern Field Effect Transistor (FET) circuits require at least 60 mV of gate voltage for a better current drive at room temperature. The tunnel Field Effect Transistor (TFET) is a leading future device due to its steep subthreshold swing (SS), making its ideal device at a low power supply. Steep switching TFET can extend the supply voltage scaling with improved energy efficiency for digital and analog applications. These devices suffer from a sizeable ambipolar current, which cannot be reduced using Dual Metal Gate (DMG) alone. Gate dielectric materials play a crucial role in suppressing the ambipolar current. Objective: This paper presents a new structure known as triple-gate-dielectric (DM_TGD) TFET, which combines the dielectric and work function engineering to solve these problems. Method: The proposed structure uses DMG with three dielectric gate materials titanium oxide (TiO2), aluminum oxide (Al2O3), and silicon dioxide (SiO2). The high dielectric material alone as gate oxide increases the fringing fields, which results in higher gate capacitance. This structure has been simulated using 2-D ATLAS simulator in terms of drive current (Ion), ambipolar current (Iamb) and transconductance (gm). Results: The device offers better gm, lower SS, lower leakage and larger drive currents due to weaker insulating barriers at the tunneling junction. Also, higher effective dielectric constant gives better gate coupling and lower trap density. Conclusion: The proposed structure suppresses the ambipolar current and enhance the drive current with reduced SCEs.

SYNTHESIS AND CHARACTERIZATION OF (ZNO)–(CO3O4) NANOCOMPOSITE VIA SPRAY PYROLYSIS PROCESS: THE USE OF THE BRUGGEMAN MODEL ON OPTICAL PROPERTIES PREVISION

In the present paper, (ZnO)–(Co3O4) nanocomposite thin films have been prepared by using spray pyrolysis deposition on a glass substrate at 350∘C. After that, the as-obtained films have been characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the double beam UV-visible (UV-vis) spectrophotometer. Furthermore, the Bruggeman model is used to predict the evolution of the optical dielectric constant (real and imaginary parts: [Formula: see text] and [Formula: see text] to compare them with those obtained from the experimental results. The XRD pattern reveals that the nanocomposite film has diffraction peaks 2[Formula: see text], 36.95∘ corresponding respectively to the (220), (311) planes of cubic Co3O4 and another about of 2[Formula: see text] corresponding to the (101) plane of Wurtzite ZnO. Using the Debye Scherrer formula, the crystallite size of (ZnO)[Formula: see text]–(Co3O[Formula: see text] nanocomposite is found about 32[Formula: see text]nm, while the obtained thickness of this nanocomposite is about 780[Formula: see text]nm using the DekTak Stylus profilometer. Besides, the morphology analysis shows that the nanocomposite sample is well covered without holes and/or cracks and it has uniform dense grains. The evaluation of the transmittance, reflectance, refraction index, extinction coefficient, real and imaginary parts of dielectric constant as function of wavelength illustrates that the optical response of nanocomposite thin film (ZnO)[Formula: see text]–(Co3O[Formula: see text] depends on the influence of two mediums of pure materials ZnO and Co3O4 and their interaction. In addition, the direct band gap vs incident photon energy obtained from the Tauc plot equation shows that this nanocomposite has three values of band gap energy which are [Formula: see text][Formula: see text]eV, [Formula: see text][Formula: see text]eV (correspond to pure Co3O4 film) and [Formula: see text][Formula: see text]eV (correspond to pure ZnO film). Besides, the application of the Bruggeman equation indicates that the influence of the values of volume concentration and optical dielectric constant of the ingredient nanomaterials (ZnO and Co3O[Formula: see text] is significant on the value of the effective dielectric constant of nanocomposite thin film. The specific result of this study is the similarity between the spectra obtained from the Bruggeman model and the measured one, which proves that the application of this model is useful for the prediction of the optical properties of the composite.

Ferroelectric, Piezoelectric and Dielectric Properties of Novel Polymer Nanocomposites

In this chapter, the Ferroelectric, Piezoelectric and Dielectric behavior of novel polymer/ceramic nano-composite (PCC) based on ferroelectric polymer [polyvinyledene fluoride (PVDF)] & nano Barium Titanate (n-BaTiO3) with different volume fractions of n-BaTiO3 (fBaTiO3), prepared through the novel cold pressing method has been discussed. The ferroelectric parameters of PCC are attributed to spherulites of PVDF, the increase of n-BaTiO3 and the ordered homogenous structure due to the novel cold pressing. The clustering of ceramic fillers is responsible for randomization of the structures of these composite ferroelectrics for some samples, leading to decrease of electrical polarisations. The piezoelectricity and piezoelectric coefficients of these composites ferroelectrics, increases with increase of ceramic filer content and remains constant beyond a certain ratio. However, the dielectric properties increase linearly as a function of ceramic content due to increase of interfaces/interfacial polarisations. The enhancement of effective dielectric constant (ɛeff) is attributed to the large interfacial polarization arising due to the charge storage at the spherulites of PVDF and at the polymer/filler interfaces of PCC and have been explained on the basis of sum effect with the help of the standard models. The achieved lower loss tangent (Tan δ) for the PCC as compared to the polymer/metal composites (PMC) is attributed to the highly insulating nature of PVDF & semiconducting n-BaTiO3. The thermal stability of the composites is also maintained due to the higher melting temperature (170°C) of PVDF. The cold pressed PCC based on PVDF are going to act as better polymer ferroelectric/dielectrics for memory and electrical energy storage applications.