Papers by Keyword: Microwave Properties

Abstract: An urgent task in the field of creating new functional oxide materials is to obtain products with specified properties for specific requirements, which will expand the field of application of such materials in practice. The result of work on this problem will be discussed. The paper presents the results of obtaining and studying the structure and properties of nickel-zinc ferrites doped with cobalt, with the general formula Ni_0.3Zn_0.7-xCo_xFe₂O₄ (with the substitution x equal to 0; 0.1; 0.3; 0.5). The samples were obtained by solid-phase synthesis in a tube furnace with silicon carbide heaters at a temperature of 1150 °C. The porosity of the materials obtained was calculated. For porous ceramic materials, it is one of the quality criteria.

Abstract: Typically microwave properties of High Temperature Superconducting films are defined in terms of surface resistance R_s computed from Q-factor measurements obtained using one of resonant techniques. While NdBaCuO films are known to have higher T_C and J_C than YBaCuO films, not much is known about their loss at high frequencies. In this paper we report on microwave properties of NdBaCuO films of varying quality and thickness based on measurements with a 25GHz sapphire Hakki Coleman resonator and computations using two approaches: the surface resistance and the complex conductivity as primary variables for rigorous electromagnetic solutions.

Abstract: Mn-Ti substituted Barium - Strontium Hexaferrite and Barium – Lanthanum Manganite both well established materials which have been shown poses microwave absorbtion properties. As the properties of composite system are a composition sensitive, composite materials must be properly designed to meet a specific application. In this paper, we report our recent investigation on microwave absorbtion properties of composite Ba_0.5Sr_0.5Fe_11.7Mn_0.15Ti_0.15O₁₉/La_0.7Ba_0.3MnO₃ system. Composite components respectively Ba_0.5Sr_0.5Fe_11.7Mn_0.15Ti_0.15O₁₉ and La_0.7Ba_0.3MnO₃ were prepared through mechanical alloying route employing a planetary ball mill for 20 hrs. The two milled powders were sintered at a temperature 1100 °C for 10 hours to ensure the crystallization towards fully crystalline materials. Composites with 2 different compositions were studied by FTIR and VNA from which results were compared with that of each component. Results of the investigation concluded that, the composite of Ba_0.5Sr_0.5Fe_11.7Mn_0.15Ti_0.15O₁₉/La_0.7Ba_0.3MnO₃ system is a good microwave absorbing material in the frequency range 9 GHz-15 GHz, particularly, sample with coded A03B07 has a wide range frequencies absorption.

Abstract: The microwave properties of Glass-coated FeCuNbVSiB and CoFeNiSiB microwires/dielectric composite with different microwires diameters were studied. Relative complex permeability and complex permittivity was measured by transmission/reflection (T/R) coaxial line method at the frequency range of 2-18 GHz for composite samples. The results show that the microwave permeability and permittivity increases with the lengthening of the microwires in composite. The microwave permeability, natural resonance frequency and microwave permittivity increase with the decrease of the diameter of the microwires.

Abstract: The Ferrite term is used to refer to all magnetic oxides containing iron as major metallic component which has great to technological applications because of their ferromagnetic and insulating properties at room temperature. Among such ferrites, the hexagonal ones (hexaferrites) have long been used for permanent magnets and are of interest for microwave applications. The hexaferrite M-type has a structure built up from the S blocks interposed by the R block and are symbolically described as RSR*S*. In the last decades there has been great interest in the hexaferrites M-Type for applications as electronic components for mobile and wireless communications at microwave/GHz frequencies, electromagnetic wave absorbers for electromagnetic compatibility (EMC), radar absorting material (RAM) and stealth technologies and as composite materials. This review aimed study the structure, magnetic and dielectric properties of the hexaferrite Ba_xSr_1-xFe₁₂O₁₉, which is a promising material for electronic devices and for small dielectric resonator antennas (MRA).The outline of this Review Paper is as follows:

Abstract: The microwave permeability of glass-coated magnetic alloy microwires / dielectric composite was investigated by apparent permeability linked with intrinsic permeability calculated based on Landau-Lifshitz function. The effect of diameter, length and microwires content on the composite effective permeability was simulated. The simulated results show that the complex permeability decreases with the increase of the microwires diameter and the wire content in the composite. The microwave magnetic resonance frequency increase distinctly with the lengthening of the glass-coated microwires. The full width at half maximum of the ferromagnetic resonance peak increases with the lengthening of the microwires and the decrease of the wire content.

Abstract: Ceramic samples based on barium nanotitanate (Ba₂Ti₉O₂₀) have been produced for application as dielectric resonators aiming at good microwave properties as high dielectric permittivity, low dielectric loss, and high frequency stability. Two different samples were prepared: first a Ba₂Ti₉O₂₀ specimen and second a 1wt% Nb₂O₅-added Ba₂Ti₉O₂₀ composition, using BaO and TiO₂ as precursor materials. Variation of resonant frequency with temperature is commonly represented by temperature coefficient. Experimental tests were carried out to determine the dielectric permittivity (ε) and the temperature coefficient (τ) using a metal box where the specimen was placed between parallel metal surfaces. The resonant frequencies were measured as function of temperature from-20°C to +50°C in a programmable climatic chamber. As a result, the ceramics presented relatively good microwave properties: ε₁=34.6, τ₁=20.5 ppm/°C from initial frequency f₁=7.23 GHz for the former composition, and ε₂=27.5, τ₂=10.1ppm/°C from initial frequency f₂=7.80 GHz for the latter.

Abstract: The structural-phase composition, magnetic and microwave properties of Fe_x(SiO₂)_1-x (x=30, 70, 90, 95) nanocomposites have been studied. The composites are produced by high-energy ball milling with either Ar or acetone as a milling medium and milling time of 1 to 64 h. The microwave magnetic properties of the composite in the frequency range of 0.1 to 6 GHz are shown to depend slightly on the phase composition and be governed mainly by the particle size. Reduction of the particle size to about 1 μm results in elimination of magnetic loss at frequencies below 1 GHz, which is attributed to the domain walls motion.

Abstract: Corundum-type magnesium niobate (Mg₄Nb₂O₉) ceramics were synthesized by the conventional solid-state method, the effect of ball milling time on microwave properties was studied in detail. Xrd results showed that the major phase was identified as the ordered corundum structure Mg₄Nb₂O₉ with minor secondary phase of orthorhombic-symmetry Mg₅Nb₄O₁₅. The morphology was obviously affected by ball milling times at sintering process, and then the relationships between the morphology and microwave properties were discussed. The results indicated that ball milling times at sintering process could obviously affect the microstructure and microwave properties of Mg₄Nb₂O₉ ceramics. When ball milling time was 10h, the Mg₄Nb₂O₉ ceramics were prepared with the conditions of calcination at 1100°C for 2h and sintered at 1350°C for 6h, and the optimal microwave properties were ε_r~13, Q·ƒ~120,000GHz and ƒ~-60ppm/°C.

Abstract: Corundum-type magnesium niobate (Mg₄Nb₂O₉) ceramics were synthesized by the conventional solid-state method, the effect of holding time during calcination and sintering process on microwave properties was studied in detail. The xrd results showed that the major phases were identified as the ordered corundum structure Mg₄Nb₂O₉ with minor secondary phases of orthorhombic-symmetry Mg₅Nb₄O₁₅. The morphology was obviously affected by holding times at sintering process and the relationships between the morphology and microwave properties were discussed. The results indicated that holding time at calcination process had negligible effect on the microstructure and microwave properties, while holding time at sintering process could obviously affect the microstructure and microwave properties of Mg₄Nb₂O₉. When calcination at 1100°C for 2h and sintered at 1350°Cfor 6h, the optimal microwave properties were ε_r~13, Q·ƒ~130,000GHz and τ_f~-50 ppm/°C.