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Three dimensional diamond structure photonic crystals with planar defects and heterostructure fabricated by rapid prototyping and gel casting with alumina were studied. The influence of ordinary planar defect and twinned planar defect on the transmission properties of the electromagnetic wave in the photonic crystals was first investigated. The normalized resonant intensities are 0.5 and 0.58 for ordinary and twinned planar defect photonic crystals (PCs). The resonant intensity of electromagnetic wave in the twinned planar defect PC is stronger than that in the ordinary planar defect PC and the resonant peak width of the twinned planar defect PC is narrower and steeper than that of the ordinary planar defect PC. The resonant peak intensity and frequency of planar defect modes increase firstly and then decrease with the increase of the planar defect sizes. The strongest resonant peak intensity lies at the defect size with 0.5 mm. If the defect size is more than 2.5 mm, the resonant mode will disappear. In the heterostructure PC, which was realized by combining two perfect PCs with different lattice constants of 9 mm and 12 mm, the band gaps of the two different PCs can be united together. [ABSTRACT FROM AUTHOR]

Three dimensional diamond structure photonic crystals with line defects fabricated by rapid prototyping and gel casting with alumina were studied. The influence of the line defect shapes, which include rectangular, ellipse, circle, and square shapes of the cross section, on the transmission properties of the electromagnetic wave was first studied. The resonant mode of the rectangular line defect is the strongest with the guiding band from 11.0 to 11.75 GHz and the normalized resonant intensity is 0.8. If the TE10 mode of the propagating electromagnetic wave is parallel to the polarization direction of the rectangular line defect, the property of the line defect will be strengthened. Two separate line defects with a point defect between them can realize the properties of a straight complete line defect through the coupling between them. The bending properties of the line defect were investigated with the bending angle from 0° to 90° at 15° interval. With the increasing of the bending angle, the guiding bandwidth was reduced slowly while the resonant intensity did not change too much. [ABSTRACT FROM AUTHOR]

Three dimensional diamond structure photonic crystals (PCs) with point defects fabricated by rapid prototyping and gel casting with alumina were studied at microwave frequencies. The sphere, ellipsoid, and cylinder point defects were introduced in the PCs first and it was found that the localization of electromagnetic wave is the strongest in ellipsoid point defect photonic crystals. Then, the size change of the ellipsoid point defect was studied to find out the optimal size. When the size of the ellipsoid point defect is close to one unit cell, the Q factor, which represents the localization intensity of the electromagnetic wave, will be the biggest. Based on the optimal size of ellipsoid point defect, more ellipsoid point defects were introduced into one diamond PC structure. Three point defect resonant modes were found in a photonic crystal with three ellipsoid point defects and the distance between each defect was twice of the lattice constant. A guided band was observed in the forbidden band gap in a photonic crystal with five ellipsoid point defects, in which the distance between each defect was of one lattice constant. [ABSTRACT FROM AUTHOR]

Due to the high sensitivity of the electrical properties of electronic ceramics to various factors, knowledge about the possible influence of the processing procedure on their electrical performance is critical for applying a new technique to the fabrication of the materials. In this study, various electrical parameters, complex impedance spectra, ferroelectric hysteresis loops, and microstructures of soft lead zirconate titanate (PZT) ceramics formed by the gelcasting technique from suspensions with various dispersants were investigated in comparison with those of the conventional dry pressed ones. We found that the sodium ion, which is the main cation in many commercial surfactants, exhibited obvious hard doping effects; thus causing deteriorated performance of the gelcast PZT ceramics. While a certain impurity ion introduced by a dispersant was also found to induce soft doping characteristics and improve the electrical performance of the materials. The results suggest that the doping effects of the metal ions or impurities introduced by the dispersants, or other additives, should be generally considered for applying a wet processing technique to forming multicomponent electronic ceramics. [ABSTRACT FROM AUTHOR]

Gelcasting is a well established process for ceramics manufacturing which recently has been proved to be successful for soft ferrites as well. This approach is particularly interesting for power electronics application in which the magnetic components (e.g. transformers and inductors) are three dimensionally integrated on the power module substrate. This paper proposes a gelcasting process adapted to make it more effective for 3D heterogeneous integration. The main novelties in this direction consist of low solid load (65wt%) and gelation without catalyst to improve casting and de-airing steps. The magnetic properties of gelcast samples are compared with commercial materials and correlated with the microstructure. [ABSTRACT FROM AUTHOR]

A new kind of heterostructures containing 3D diamond and 2D holes structures, and diamond-structure photonic crystals and 2D holes-structure photonic crystals fabricated by stereolithography and gel-casting with alumina were studied at microwave range, respectively. The heterostructures were designed by 2D holes structure embedded in 3D diamond structure, in which the lattice of three kinds of structures was equivalent. It was found that the band gaps of photonic crystal heterostructure were broadened by 124.6% and 150% comparing to that of diamond-structure crystal and 2D aerial holes structure. Experimental results showed the band gap broadened was not connected with a linear superposition of the band gap of 2D and 3D photonic crystals, which was the superposition of partial overlap. [ABSTRACT FROM AUTHOR]

Due to the drastic aerodynamic heating effect in supersonic aircrafts, the operational performance of wave-transmitting dielectric ceramics functionalized radomes strongly depends on the temperature and oxidation. In this paper, the evolution of microwave dielectric responses in Si3N4 ceramics via gelcasting over a wide temperature range (25°C∼800°C) is investigated experimentally and theoretically. Specifically, the relative increment rate of real permittivity over evaluated temperature range is 4.46% at 8.2GHz and 8.67% at 12.4GHz, while the imaginary permittivity remains less than 0.06. Taking temperature-dependent polarized bound charge and damping coefficient into consideration, a revised dielectric relaxation model with Lorentz correction for Si3N4 ceramics has been established, which agrees well with evolution of experimental results. Furthermore, the best fitting results indicate that the activation energy of electrons Ea (15.46 ∼17.49 KJ/mol) is less than that of lattice Eb (33.29∼40.40 KJ/mol), which could be ascribed to the binding force between the electrons and nucleus is lower than covalent bonding force of lattice. Besides, excellent restorable feature of permittivity after heat-treatment lays a solid foundation for radome materials serviced in high temperature circumstances. [ABSTRACT FROM AUTHOR]