Papers by Keyword: Permittivity

Abstract: In this paper, C/SiO₂ bulk composite was prepared via SiO₂ microspheres’ self-assembly process combined with heat treatment. SEM and impedance analyzer was used to investigate the microstructure and high-frequency dielectric properties of the composites. The results show that SiO₂ microspheres constituted the composite matrix, whose porosity was slightly higher than the densest hexagonal stacking. Sheet carbon distributed in pores formed by SiO₂ microspheres. The real and imaginary parts of the dielectric constant of the composite material increased with the content of carbon, but decreased with the frequency. The permittivity of C/SiO₂ composite could be adjusted by control the concentration of PVA solution.

Abstract: Materials with relative permittivity or dielectric constant near to that of air (εr~1) are known as ‘ultra-low k’ materials. They find a number of applications in inter-connects of micro-electronic circuits, antennae, high-speed communication substrates etc. Among the inorganic materials, porous silica is the widely studied candidate. Porous silica can be of many types depending upon the extent of porosity and size and connectivity of pores. This paper presents the details of measurement of permittivities and the results of silica beads and silica aerogels. Silica beads, prepared by microwave heating of silica gels, are spherical beads of average 1mm size. Hydrophobic silica aerogels, prepared by ambient pressure drying of silica gels, are irregular chunks of 5-10 mm size. Both are potential bulk fill insulation materials and hence the permittivity can be measured as an aggregate filling a definite volume. The permittivities of these have been measured upto 1 MHz by 3-terminal method using a precision LCR meter and a powder-paste cell as per ASTM-D150-11. The εr values of silica aerogels and silica beads in 20 Hz-1 MHz range could be measured and are less than 1.6 at 1 MHz.

Abstract: In the dielectric heating by using microwave, both the interior and exterior of fiber materials can be evenly heated simultaneously. Especially, in case of heating the material of low thermal conduction by normal furnaces, thermal loss is great and it takes long time to finish the required treatment. However, if microwave is applied to fibrous materials, it can be treated rapidly. Also, application of microwave system has the results of remarkably enhancing productivity and improving working environment owing to no air pollution. Thus, in this study, the bonded polypropylene (PP) fibers and PP/PET nonwovens have prepared by dielectric heating with various organic solvents, and their morphological structures and debonding force have investigated with different treatment time.

Abstract: Amorphous hydrogenated carbon thin films were deposited on Si and glassceramics substrates by reactive ion-plasma magnetron sputtering. Thin films were without (a-C:H) and with Ni nanoparticles (a-C:H:Ni). Measurement of absorption coefficient in 220-850 nm spectral range using spectrophotometer and following approximation applying of Tauc method shows that obtained a-C:H thin films material has near 3.6 eV optical band gap and confirmed that this material is amorphous semiconductor. Thin films with Ni nanoparticles have a high complex permittivity ε* and permeability μ* (ε′ ≈ 1000–10000, ε′′ ≈ 100–1500, μ′ ≈ 10–70, μ′′ ≈ 0.4-10). Some magnetic parameters of thin films were determined.

Abstract: This paper describes an interesting approach aimed at analysis of material properties. This work is based on simulated measurements of transmission coefficients of multi-layered materials. These measurements (in a waveguide) are taken as a product of a certain situation, therefore there is an inverse problem in which we try to estimate the original properties of the layers. This study employs analysis of closed-form solutions and numerical multi-parameter optimization.

Abstract: The effect of sintering temperature and Mn-Ti (x = 0.1 and 0.5 % mol) doped in Barium hexaferrite (BaFe₁₂O₁₉) on the microwave absorption properties have been investigated. The BaFe_(12-2x)Mn_xTi_xO₁₉ samples were prepared by using a solid state reaction method from technical grade materials of BaCO₃, Fe₂O₃, MnO₂, and TiO₂. The permagraph and vector network analyzer (VNA) measurement with frequency of 4 – 10 GHz were used to determine the magnetic properties and microwave absorbing properties, respectively. The magnetic induction and magnetizing force (B-H) curve analysis of BaFe_(12-2x)Mn_xTi_xO₁₉ revealed that by increasing the Mn-Ti dopant concentrations, the remanence (Br) and BH(max) increases, meanwhile, the H_CB value decreases for both 1100 and 1150^oC. The frequency dependence of reflection loss (RL) measurement given anoptimum value of-26.15 dB at frequency of 9.18 GHz which obtained by x = 0.1% mol Mn-Ti (1100^oC). The maximum absorption peak was achieved for 0.5 % mol Mn-Ti sample with ~98.3 % at 9.18 GHz. By controlling the sintering temperature and Mn-Ti dopant concentration, the RL and absorption behavior can be modified to desirable values and also indicates that higher Mn-Ti dopant concentration (0.5% mol) possess better absorbing characteristics. Furthermore, it was found that complex permitivitty and permeability values of BaFe₁₂O₁₉ can be modified by controlling the Mn-Ti dopant concentration.

Abstract: Different porosity Y₃Fe₅O₁₂ (YIG) ceramics (32% - 62%) were prepared from ceramic powders, which was synthesised by high temperature solid-phase reactions, and the effects of porosity on their electromagnetic properties were investigated. XRD and SEM were used to analyze the phase composition and microstructure of the porous composites. Electromagnetism properties including alternate current conductivity, permittivity and permeability of the composites were tested by HP4991 impedance analyzer (10 MHz~1 GHz). The results indicated that, the porosity and pore diameter were increasing with the addition of pore former by pressureless sintering; the real permeability and permittivity of YIG ceramic decreased when the porosity increasing, at the same time, the peaks of magnetic loss were moved to high frequency. That is to say, the electromagnetism properties of YIG ceramic composites could be adjusted by its porosity. Yttrium iron garnet ceramic can be widely used for high frequency devices due to its excellent and tunable magnetic properties.

Abstract: A planar capacitive sensor is designed for security detection. The different length of the sensor electrodes are design and the experiments are presented. For the relations between sensor structure parameters and the sensor potential distribution, detailed analyses are presented and the qualitative conclusions are discussed. The signal strength and measurement range of the sensor can be improved by enlarge the length of the sensor electrodes. The experimental results indicate that the sensor is more portable, easy to minimize, and applicable to the detection of a variety of sizes of containers. It is feasible to be applied to security detection.

Abstract: In this paper electromagnetic properties of composite materials based on polymethylmethacrylate and multiwall carbon nanotubes (MWCNTs) are investigated. Carbon nanotubes are received with application of various types of catalysts and have various structural parameters. Calculation of dielectric permeability of the synthesised materials is carried out. Dependence of electromagnetic properties of composite materials on concentration and structure used multilayer carbon nanotubes is shown.

Abstract: This study presents the research of water-alcohol solution phase transition by permittivity changing. Complex permittivity was measured by open-end-coaxial method in frequency range 500 MHz – 40 GHz. We varied temperature from 240 K to 310 K and ethanol content from 10 % to 80 %. Temperature dependencies of permittivity for water-alcohol solutions were obtained and the patterns of variation of those solidification temperatures were established.