Trapped Coupled Dielectric Overlay Guide Configuration at Millimeter Wave Frequencies

Trapped coupled dielectric overlay guide has several interesting characteristics useful for millimeter wave applications. Dispersion characteristics and wave impedance for even and odd modes are computed by using Effective Dielectric Constant (EDC) method. Dispersion curves realized for Trapped coupled overlay guide for various dielectric materials and dimensional parameters as a function of frequency. Conductor and dielectric loss in the above configuration have also been studied. Polystyrene (µ_r = 2.56) and Stycast (µ_r = 3.4) have been used as dielectric materials.     

Ordered 3D Thin‐Shell Nanolattice Materials with Near‐Unity Refractive Indices

The refractive indices of naturally occurring materials are limited, and there exists an index gap between indices of air and available solid materials. With many photonics and electronics applications, there has been considerable effort in creating artificial materials with optical and dielectric properties similar to air while simultaneously being mechanically stable to bear load. Here, a class of ordered nanolattice materials consisting of periodic thin‐shell structures with near‐unity refractive index and high stiffness is demonstrated. Using a combination of 3D nanolithography and atomic layer deposition, these ordered nanostructured materials have reduced optical scattering and improved mechanical stability compared to existing randomly porous materials. Using ZnO and Al₂O₃ as the building materials, refractive indices from 1.3 down to 1.025 are achieved. The experimental data can be accurately described by Maxwell Garnett effective media theory, which can provide a guide for index design. The demonstrated low‐index, low‐scattering, and high‐stiffness materials can serve as high‐quality optical films in multilayer photonic structures, waveguides, resonators, and ultra‐low‐k dielectrics.     

The effect of the base composition and microstructure of nickel-zinc ferrites on the level of absorption of electromagnetic radiation

Promising absorbing materials include Ni—Zn ferrites, as they quite intensively absorb electromagnetic waves in the frequency range from 50 to 1000 MHz. The electromagnetic properties of Ni—Zn ferrite absorbing materials obtained by different technological methods were studied in this paper. A model making it possible to evaluate the dielectric permeability of the ferrite material, depending on the microstructure parameters and electrophysical properties of grain boundaries, was proposed. The influence of base composition and microstructure on the amount of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials was determined. It was stated that the increase of the content of excess Fe₂O₃ to 51.0 mol % leads to the shift of the frequency range of the absorption of electromagnetic radiation towards lower frequencies. It can be explained by the increase of the dielectric and magnetic permeability of ferrite. Moreover, the introduction of an excess of Fe₂O₃ in the grinding stage of the synthesized burden is more efficient. It was revealed that increasing the sintering temperature to 1350°C also shifts the frequency range of absorption of electromagnetic radiation towards lower frequencies. Probably it is caused by the increase of the dielectric and magnetic permeability of ferrite and the shift of the resonance frequency of domain walls as a result of the formation of a coarse-grained structure.     

Improving the Magnetic Properties of Li-Zn-Ti Ferrite by Doping with H3BO3-Bi2O3-SiO2-ZnO Glass for LTCC Technology

Li-Zn-Ti ferrite doped with 0.5 wt.% to 16 wt.% H₃BO₃-Bi₂O₃-SiO₂-ZnO (BBSZ) glass was synthesized using a low-temperature ceramic sintering process. Selected parameters of saturation induction (B _S), coercivity (H _C), Curie temperature (T _C), and complex permeability spectra were measured as functions of doping content, and their relationships with ferrite density and microstructure are discussed. It was found that Li-Zn-Ti ferrite can be fired at low temperature (900°C) with BBSZ glass content varying from 0.5 wt.% to 2 wt.%. The real permeability increased from 80 to 190 in the frequency range from 1 MHz to 3 MHz, the saturation induction B _S increased from 105 mT to 150 mT at 1 kHz, whereas the coercivity H _C decreased from 165 A/m to 65 A/m at 1 kHz and the Curie temperature T _C slightly declined from 155°C to 143°C. These results confirm that this new ferrite material could be used in low-temperature cofired ceramic (LTCC) devices.     

Electromagnetic Properties and Impedance Matching Effect of Flaky Fe–Si–Al/Co2Z Ferrite Composite

Fe–Si–Al/Co₂Z ferrite composites were prepared by ball-milling. The microstructure, microwave electromagnetic properties, and impedance-matching performance of a series of composites were determined and the results are discussed. Experimental results indicated that, in frequency range 1–18 GHz, the permittivity and permeability of the complexes can be adjusted by changing the Fe–Si–Al-to-Co₂Z weight ratio. Calculated reflection losses indicate that the absorption performance of Fe–Si–Al/Co₂Z ferrite composites is superior to that of the pure Fe–Si–Al and Co₂Z ferrites. It was found that the impedance-matching performance of the materials, which contributes to perfect absorption, can be improved by use of an appropriate weight ratio for the Fe–Si–Al/Co₂Z ferrite composite.     

Duplexer designed on the basis of microstrip filters using high dielectric constant substrates

A microstrip duplexer for a modification of a PCS communication system operating at frequencies of 1.84?C1.87 and 1.75?C1.78 GHz is described. The duplexer containing microstrip bandpass filters on high dielectric constant substrates (? _r = 92) are compared with duplexers manufactured on microwave ceramic materials with high values of ? _r . The microstrip bandpass filters use stepped-impedance resonators placed one near another with a gap of 0.1?C0.2 mm. It is shown that the microstrip duplexer has slightly lower insertion loss and occupies smaller volume than a duplexer using coaxial dielectric resonators having a rectangular cross section of 3 × 3 mm and ? _r = 92.     

Novel Method of Preparation of Gold‐Nanoparticle‐Doped TiO2 and SiO2 Plasmonic Thin Films: Optical Characterization and Comparison with Maxwell–Garnett Modeling

SiO₂ and TiO₂ thin films with gold nanoparticles (NPs) are of particular interest as photovoltaic materials. A novel method for the preparation of spin‐coated SiO₂–Au and TiO₂–Au nanocomposites is presented. This fast and inexpensive method, which includes three separate stages, is based on the in situ synthesis of both the metal‐oxide matrix and the Au NPs during a baking process at relatively low temperature. It allows the formation of nanocomposite thin films with a higher concentration of Au NPs than other methods. High‐resolution transmission electron microscopy studies revealed a homogeneous distribution of NPs over the film volume along with their narrow size distribution. The optical manifestation of localized surface plasmon resonance was studied in more detail for TiO₂‐based Au‐doped nanocomposite films deposited on glass (in absorption and transmittance) and silicon (in specular reflectance). Maxwell–Garnett effective‐medium theory applied to such metal‐doped nanocomposite films describes the peculiarities of the experimental spectra, including modification of the antireflective properties of bare TiO₂ films deposited on silicon by varying the concentration of metal NPs. The antireflective capabilities of the film are increased after a wet etching process.     

Methods of accounting for inclusion-shape randomness in calculating the effective dielectric characteristics of heterogeneous textured materials

Two methods of accounting for the inclusion-shape randomness, an analytical method and a method for simulating a medium with several inclusion types, are considered for calculating the effective permittivity tensor of a textured heterogeneous matrix-type medium with inclusions of a random ellipsoidal shape. The methods are based on the generalized Maxwell–Garnett model. The rotation group representations are used to consider the distribution of inclusion orientations. The results of calculations by these methods of the effective dielectric characteristics of porous silicon models in an alternating electromagnetic field in the frequency range of 10₃–10₈ Hz are compared.     

A fractal metamaterial based printed dipoles on a nickel oxide polymer palm fiber substrate for Wi-Fi applications

In this paper, a novel antenna circuit based metamaterial (MTM) structures is proposed for Wi-Fi applications. The antenna consists of two dipoles with 3 × 5 Hilbert-shaped MTM array printed with Sliver Nanoparticles Conductive Ink (SNPCI). The antenna substrate is mainly created from INP composite of: Iraqi Palm Tree Remnants (IPTR) and Nickel Oxide Nanoparticles (NONP) with Polyethylene (PE) mixture. The relative permittivity (ε_r) and permeability (μ_r) are measured using an open-stub microstrip resonator to find ε_r = 3.106 − j0.0314 and μ_r = 1.548 − j0.0907 at the frequency band of interest. Numerically, Finite Integral Technique (FIT) and Finite Element Method (FEM) of CSTMWS and HFSS formulations, respectively, are invoked to investigate the antenna performance. Experimentally, the antenna exhibits two resonances, |S₁₁| < −10 dB, at 2.45 GHz and 5.8 GHz with gain of 2.6 dBi and 4.8 dBi, respectively. The antenna shows a bandwidth of 500 MHz around the first resonance and 2 GHz at the second resonance. The measured radiation patterns at the two resonances are found to be mainly directed toward the antenna end fire with radiation efficiency of 0.8 and 0.65 at the first and second modes, respectively. Finally, the proposed antenna performance is compared against a reference antenna to reveal the excellent enhancements.     

Electronic Structure Regulation of Layered Vanadium Oxide via Interlayer Doping Strategy toward Superior High‐Rate and Low‐Temperature Zinc‐Ion Batteries

Currently, development of suitable cathode materials for zinc‐ion batteries (ZIBs) is plagued by the sluggish kinetics of Zn²⁺ with multivalent charge in the host structure. Herein, it is demonstrated that interlayer Mn²⁺‐doped layered vanadium oxide (Mn_0.15V₂O₅·nH₂O) composites with narrowed direct bandgap manifest greatly boosted electrochemical performance as zinc‐ion battery cathodes. Specifically, the Mn_0.15V₂O₅·nH₂O electrode shows a high specific capacity of 367 mAh g^?1 at a current density of 0.1 A g^?1 as well as excellent retentive capacities of 153 and 122 mAh g^?1 after 8000 cycles at high current densities up to 10 and 20 A g^?1, respectively. Even at a low temperature of ?20 °C, a reversible specific capacity of 100 mAh g^?1 can be achieved at a current density of 2.0 A g^?1 after 3000 cycles. The superior electrochemical performance originates from the synergistic effects between the layered nanostructures and interlayer doping of Mn²⁺ ions and water molecules, which can enhance the electrons/ions transport kinetics and structural stability during cycling. With the aid of various ex situ characterization technologies and density functional theory calculations, the zinc‐ion storage mechanism can be revealed, which provides fundamental guidelines for developing high‐performance cathodes for ZIBs.     

Quasi-static effective permittivity of periodic compositescontaining complex shaped dielectric particles

A methodology is described for computing the quasi-static effective permittivity of a two-dimensional (2-D) or three-dimensional (3-D) lattice of dielectric particles. The particles in this composite material may have complicated shapes. This methodology uses a moment method based technique to determine the electric dipole moments of the particles immersed in a uniform electric field. The effective permittivity is then obtained using an appropriate macroscopic model. With this methodology, the mutual interaction between particles can be accounted for accurately. The computed effective permittivity for round cylinders and spheres suspended in a host are compared with our previous T-matrix method results as well as the Maxwell Garnett (MG) formula predictions. Three additional examples involving square (2-D), rounded square (2-D), and spherical (3-D) dielectric inclusions are also given, illustrating the shape effects on the computation of the quasi-static effective permittivity. While the square- and cubic-shaped particles can possess great mutual interaction, surprisingly their effective permittivity is well predicted for all volume fractions by the simple MG formula in both 2-D and 3-D problems     

Heterogeneous Interface Engineering of Bi-Metal MOFs-derived ZnFe2O4–ZnO-Fe@C Microspheres via Confined Growth Strategy Toward Superior Electromagnetic Wave Absorption

Heterogeneous interface regulation plays an important role in tailoring the intrinsic electromagnetic (EM) properties for obtaining excellent EM wave absorption, which still faces huge challenge. In this work, bi-metal MOFs-derived ZnFe₂O₄–ZnO-Fe@C (ZZFC) microspheres with custom-built heterogeneous interfaces are successfully fabricated via a confined growth strategy. Bi-metal Fe–Zn–ZIF with tailored coordination structure and chemical bonding are first selected as the precursor template. After undergoing the annealing process, the metal Fe²⁺ host is converted into magnetic Fe nanoparticles (NPs). The Zn²⁺ host is transformed into semiconductor zinc oxide (ZnO) with increasing (101) crystal-oriented growth. At the same time, metal hosts Fe²⁺ and Zn²⁺ are further reacted to synthesize the zinc ferrite (ZnFe₂O₄). Formed Fe nanoparticles catalyze organic ligands to constitute graphitized carbon layers, which confine the further growth of ZnFe₂O₄, ZnO, and Fe NPs. Combined with the well impendence and synergy absorption mechanism (magnetic loss, interface polarization, and conduction loss), optimized magnetic–dielectric ZnFe₂O₄–ZnO-Fe@C microspheres exhibit outstanding EM wave absorption with the minimum reflection loss −66.5 dB at only 2.0 mm thickness. Bi-metal MOF-derived magnetic–dielectric absorption materials with tailored heterogeneous interfaces provide a new sight to design an efficient EM wave absorption system.     

Effects of Heat-Treatment Temperature on the Microstructure, Electrical and Dielectric Properties of M-Type Hexaferrites

M-type hexaferrite BaCr _x Ga _x Fe_12?2x O₁₉ (x = 0.2) powders have been synthesized by use of a sol–gel autocombustion method. The powder samples were pressed into 12-mm-diameter pellets by cold isostatic pressing at 2000 bar then heat treated at 700°C, 800°C, 900°C, and 1000°C. X-ray diffraction patterns of the powder sample heat treated at 1000°C confirmed formation of the pure M-type hexaferrite phase. The electrical resistivity at room temperature was significantly enhanced by increasing the temperature of heat treatment and approached 5.84 × 10⁹ Ω cm for the sample heat treated at 1000°C. Dielectric constant and dielectric loss tangent decreased whereas conductivity increased with increasing applied field frequency in the range 1 MHz–3 GHz. The dielectric properties and ac conductivity were explained on the basis of space charge polarization in accordance with the Maxwell–Wagner two-layer model and Koop’s phenomenological theory. The single-phase synthesized materials may be useful for high-frequency applications, for example reduction of eddy current losses and radar absorbing waves.     

Direct Conversion of Fe2O3 to 3D Nanofibrillar PEDOT Microsupercapacitors

Microsupercapacitors (µSCs) are attractive electrochemical energy storage devices serving as alternatives to batteries in miniaturized portable electronics owing to high‐power density and extended cycling stability. Current state‐of‐the‐art microfabrication strategies are limited by costly steps producing materials with structural defects that lead to low energy density. This paper introduces an electrode engineering platform that combines conventional microfabrication and polymerization from the vapor phase producing 3D µSCs of the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT). A sputtered Fe₂O₃ precursor layer enables deposition of a 250 nm thick polymer coating comprised of a high packing density of vertically aligned PEDOT nanofibers possessing exceptional electrical conductivity (3580 S cm^?1). The 3D µSCs exhibit state‐of‐the‐art volumetric energy density (16.1 mWh cm^?3) as well as areal (21.3 mF cm^?2) and volumetric (400 F cm^?3) capacitances in 1 m H₂SO₄ aqueous electrolyte. These figures of merit represent the highest values among conducting polymer‐based µSCs. Electrochemical performance is controlled by investigating coating thickness, gap distance, fractal geometry, and gel electrolyte (1 m H₂SO₄/polyvinyl alcohol). The quasisolid‐state µSCs exhibit extended rate capability (50 V s^?1), retain 94% of original capacitance after 10 000 cycles and remain thermally stable up to 60 °C.     

Structural,Magnetic, and Reflection Loss Characteristics of Ni/Co/Sn-Substituted Strontium Ferrite/Functionalized MWCNT Nanocomposites

Ni/Co/Sn-substituted strontium ferrite [SrFe_12?x (Ni_0.5Co_0.5Sn) _x/2O₁₉]/multiwalled carbon nanotube (MWCNT) nanocomposites were produced by assembling ferrite particles on the external surfaces of MWCNTs. Various techniques including x-ray diffraction (XRD) analysis, transmission electron microscopy, field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared (FTIR) spectroscopy were used to demonstrate the successful attachment of ferrite particles onto the external surfaces of the MWCNTs. XRD analysis and FTIR spectroscopy confirmed the presence of strontium ferrite and carbon nanotube phases in ferrite and nanocomposite samples, respectively. FE-SEM micrographs indicated the formation of ferrite particles on the outer surfaces of MWCNTs in nanocomposite samples. Furthermore, vibrating-sample magnetometer (VSM) and reflection loss (RL) measurements were performed to assess the magnetic and microwave characteristics of the synthesized samples. VSM loops confirmed a relatively strong dependence of the saturation magnetization and coercivity on the volume percentage of MWCNTs. With the introduction of MWCNTs or an increase in the substitution, the saturation magnetization and coercivity were decreased. The RL properties of the nanocomposites were investigated in the 8 GHz to 12 GHz frequency range. The sample with 80 wt.% nanocomposite content showed a maximum RL of ?35 dB at 8.3 GHz with a 4 GHz absorption bandwidth over the extended frequency range of 8 GHz to 12 GHz for absorber thickness of 1.8 mm. The RL evaluations indicated that these nanocomposites have high potential for application as wide-band electromagnetic wave absorbers at GHz frequencies.     

Conversion of red and infrared luminescence centers as a result of electron bombardment and annealing of CdS and CdS:Cu single crystals

The luminescence centers and their conversion as a result of electron bombardment and annealing in CdS single crystals which were not specially doped and which were doped with copper have been investigated. The Cu atoms, which interact mainly with defects in the cadmium sublattice, form Cu_Cd, which are responsible for luminescence at wavelengths λ_m=0.98−1.00 μm. At annealing temperatures above 50 °C, conversion of the defect complexes, which are responsible for the green (λ_m=0.514 μm), red (λ_m=0.72 μm), and infrared (λ_m=0.98 μm) luminescence, occurs as a result of an increase in the mobility of point defects in the cadmium and sulfur sublattices of CdS:Cu. Fiz. Tekh. Poluprovodn. 31, 1013–1016 (August 1997)     

Quasioptical measurement of ferrite material parameters at terahertz frequencies by a new method: Faraday angle resonance

A new method for measuring the dielectric constant? _r and the saturation magnetizationM _S of ferrites in the terahertz frequency region is introduced in theory and experiment. The method, which bases on a resonance effect of the Faraday angle, gives an estimation of the loss factor tan δ, too. The derivation of the effect is based on a simple 4-port model of the ferrite disc which is axially premagnetized. Using the scattering matrix from the 4-port model the resonance effect is described and the extraction of the material parameters of some special data from the measurement record is explained. The measurement setup at 290 GHz is described and records of the ferrite Trans Tech TT 1–105 are evaluated, including an error calculation. Data for the hard ferrite Philips Ferroxdure FXD 330 are given, too. Using error minimizing algorithms which fit the material parameters to the measurement data a further increase in accuracy can be achieved.     

Diketopyrrolopyrrole‐Based Conjugated Polymers Synthesized via Direct Arylation Polycondensation for High Mobility Pure n‐Channel Organic Field‐Effect Transistors

High‐performance unipolar n‐type conjugated polymers (CPs) are critical for the development of organic electronics. In the current paper, four “weak donor–strong acceptor” n‐type CPs based on pyridine flanked diketopyrrolopyrrole (PyDPP), namely PPyDPP1‐4FBT, PPyDPP2‐4FBT, PPyDPP1‐4FTVT, and PPyDPP2‐4FTVT, are synthesized via direct arylation polycondensation by using 3,3′,4,4′‐tetrafluoro‐2,2′‐bithiophene (4FBT) or (E)‐1,2‐bis(3,4‐difluorothien‐2‐yl)ethene (4FTVT) as weak donor unit. All four polymers exhibit low‐lying highest occupied molecular orbital (≈ ?5.90 eV) and lowest unoccupied molecular orbital energy levels (≈ ?3.70 eV). Top‐gate/bottom‐contact organic field‐effect transistors based on all four polymers display unipolar n‐channel characteristics with electron mobility (µ_e) above 1 cm² V^?1 s^?1 in air, and presented linear |I_SD|^1/2 ?V_GS plots and weak dependence of the extracted moblity on gate voltage (V_GS), indicative of the reliability of the extracted mobility values. Importantly, the devices based on PPyDPP1‐4FBT and PPyDPP2‐4FBT show a pure unipolar n‐channel transistor behavior as revealed by the typical unipolar n‐channel output characteristics and clear off‐regimes in transfer characteristics. Attributed to its high crystallinity and favorable thin film morphology, PPyDPP2‐4FBT shows the highest µ_e of 2.45 cm² V^?1 s^?1, which is among the highest for unipolar n‐type CPs reported to date. This is also the first report for DPP based pure n‐type CPs with µ_e greater than 1 cm² V^?1 s^?1.     

Enhanced Photocatalytic Activity of Two-Pot-Synthesized BiFeO<Subscript>3</Subscript>–ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Heterojunction Nanocomposite

BiFeO₃–ZnFe₂O₄ heterojunction nanocomposites have been produced by a chemical synthesis method using one- and two-pot approaches. X-ray diffraction patterns of as-calcined samples indicated formation of pure zinc ferrite (ZnFe₂O₄) and bismuth ferrite (BiFeO₃) phases, each retaining its crystal structure. Diffuse reflectance spectrometry was applied to calculate the optical bandgap of the photocatalysts, revealing values in the range from 2.03 eV to 2.17 eV, respectively. The maximum photodegradation of methylene blue of about 97% was achieved using two-pot-synthesized photocatalyst after 120 min of visible-light irradiation due to the higher probability of charge separation of photogenerated electron–hole pairs in the heterojunction structure. Photoluminescence spectra showed lower emission intensity of two-pot-synthesized photocatalyst, due to its lower recombination rate originating from greater charge separation.     

Percolation Conduction in Hybrid Thermoelectric Material Consisting of Bi0.88Sb0.12 and Barium Ferrite Particles

A hybrid material consisting of thermoelectric Bi_0.88Sb_0.12 and Ba ferrite Bi_0.88Sb_0.12(BaFe₁₂O₁₉) _x (x = 0, 0.025, 0.04, and 0.08) was synthesized using sintering. Powder x-ray diffraction patterns and scanning electron microscopy images of the hybrid indicate that the BaFe₁₂O₁₉ particles were well distributed in the host Bi_0.88Sb_0.12 phase. The temperature dependence of the electrical resistivity ρ of the host Bi-Sb exhibits metallic behavior. By the addition of Ba ferrite particles, the ρ at 300 K increases intensively, and ρ(Τ) then behaves similarly to a semiconductor. However, it is noted that the thermoelectric power S is unchanged. Inhibition of current and heat flows by a restricted conduction path and the unchanged electromotive force generated by the Seebeck effect in the conduction path can be understood based on a site-percolation model consisting of conducting Bi-Sb and insulating Ba ferrite. The critical volume fraction p _c of this system was estimated experimentally as p _c = 0.68.