Papers by Keyword: Dielectric Constant

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Authors: Soo Woong Lee, Nam Jin Song, Jinwook Burm, Chul An
Authors: Fei Yu Lian, Qing Li
Abstract: In this paper, we proposed a punctuated target identification method for underground homogeneous medium based on dielectric constant inversion algorithm. Its main idea is that, initially, Hough transform is used to locate the target characterized by hyperbola in a radar profile map, then a layer-by-layer waveform inversion algorithm is used to invert the dielectric constant on the location where the target lies. To guarantee the correctness of inversion, the transmission beam method is adopted to obtain initial parameters and calibration factors required by inversion. Through numerical analysis of the dielectric constant of the target, the classification of multiple targets in an underground medium can be confirmed. This method not only overcomes the failure of the traditional phase-comparison method to distinguish different kinds of targets in the same region, but also overcomes the limitation of the image processing method, in which it only classifies the target in a coarse-grained manner. Experimental results show that this method has many advantages, such as fine-grained classification, high precision, and multiple target identification, in the identification of underground targets.
Authors: Hong Tao Yu, Wen Bo Zhang, Jing Song Liu, Lin Hong Cao, Han Xing Liu
Abstract: In this work, we have proposed a simple model to predicte the dielectric constant of CaCu3Ti4O12-SrTiO3 composite ceramics. The model has been established based on the analysis of composition and microstructure. Two different compositions in the composite ceramics correspond to two different grain sizes, large for CaCu3Ti4O12, and small for SrTiO3, which has been identified by the x-ray diffraction, the scanning electron microscope and the energy spectrum analysis. All specimens have been assumed to be the barrier layer dielectrics in the model, according to the complex impedance spectra. The dielectric constant of serial, parallel, and logarithmic mixture models has been discussed. Compared with the experimental results, the model shows the similar variation tendency as SrTiO3 content increases.
Authors: Heng Feng Li, Guo Wen He, Jun Li, Jun Chen, Jiang Cong Chen
Abstract: A series of polyimide composites with various mass fractions of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization. MWNTs were treated with an acid mixture and sulfoxide chloride in turn to increase the chemical compatibility of carbon nanotubes with the polyimide matrix. The modified MWNTs are dispersed homogeneously in the matrix while the structure of the PI and MWNTs structures are stable in the preparation process. The composite films hold preferable thermal stability as same as the pure PI. The dielectric constants of the composites decreased with the increasing frequency and increase sharply with the adding of MWNTs.
Authors: G. Berchiesi, F. Farhat, G. Vitali
Authors: G. Asghar, S. Nasir, M.S. Awan, G.H. Tariq, M. Anis-ur-Rehman
Abstract: Strontium hexa-ferrite nanoparticles were prepared successfully by simple co-precipitation method. The XRD analysis confirmed the formation of single phase MFe12O19 (M=Sr). Parameters such as crystallite size, lattice constant, X-ray density and porosity were calculated from the X-ray diffraction data. The crystallite sizes were in the range 12-26 nm. The temperature dependent dc electrical resistivity measurements showed that the material was highly. Dielectric constant and dielectric loss factor (tanδ) were measured in the frequency range 20Hz-3MHz. The anomalous behavior of dielectric loss revealed a very important behavior of the prepared sample of SrFe12O19 in different frequency regions and that could be used for new applications of this material. The magnetic properties were determined from the hystersis loop obtained from vibrating sample magnetometer (VSM). The Curie temperature was determined by susceptometer. This material is potentially suitable for use as a recording medium in identification cards and credit cards and for the fabrication of permanent magnets.
Authors: Nan Li, Ji Huan Tian, Wei Deng, Hui Gang Sun
Abstract: The applicability of functionally graded materials (FGM) for solid insulator of gas insulated switchgear (GIS) was investigated. First, a new fabrication method based on layer-by-layer casting technique was demonstrated to prepare FGM insulator possessing spatial distribution of dielectric constants. Then, electric field strength in the FGM spacer model was calculated and optimized by using finite element method (FEM). Three types of truncated cone spacers were fabricated according to the optimization results. Finally, surface flashover tests were performed under AC voltage and lightning impulse voltage applications. Results in both circumstances indicated an evident improvement of flashover voltage when FGM insulator was employed. As a result, we verified the fabrication technique and the applicability of FGM insulator for enhancement of insulation performance in GIS device.
Authors: R. Zhang, Lian Gao, Hai Long Wang, Hong Liang Xu, Jing Kun Guo
Authors: Young Ho Kim, Jeonghun Ahn, Sung Woon Cha
Abstract: An experiment was conducted to confirm how changes in characteristics due to the porous structure apply to the electrical characteristics as the pore size decreases in polymer foam. ABS material, whose foaming process is relatively easy to control, was used to control the foaming ratio by adjusting the foaming temperature. A change in capacitance was observed as a result of the experiment. When the foam structure was analyzed and numerically recorded, it was confirmed that the changes in distribution, according to the specific volume and variation in capacitance, showed similar tendencies.
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