Search results

To study the photonic band‐gap (PBG) characteristics constructed by periodic conducting vias on various guided transmission‐line structures.

The finite difference time domain (FDTD) method is adopted to analyze various PBG via structures. Conventionally, PBG characteristics on guided‐wave structures, such as microstrip lines or coplanar waveguides (CPW), are constructed through a series of perforations on the ground plane(s). PBG characteristics can, however, also be realized through periodic arrangements of conducting vias located on the respective ground planes.

Through studies of the scattering parameters, it has been found that all analyzed PBG via structures exhibit strong band‐gap characteristics in a particular frequency range. Different harmonic patterns are also observed when the dimensional sizes of the conducting vias vary with respect to the PBG period.

Research has been mainly limited to study solely the PBG via structures, guided‐wave transmission lines. More studies may be conducted in analyzing the overall performance when they are combined with other microwave components.

The proposed PBG via structures can be applied to various microwave areas, ranging from signal suppressions in microelectronics and mobile communications, to electro‐magnetic interference studies in other practical electronic circuit structures.

The ideas of applying conducting vias on the guided‐wave transmission lines and the proposed via patterns to induce the PBG characteristics are the research's claim to originality one.

To demonstrate the flexibility and advantages of a non‐uniform pseudo‐spectral time domain (nu‐PSTD) method through studies of the wave propagation characteristics on photonic band‐gap (PBG) structures in stratified medium

A nu‐PSTD method is proposed in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain‐rule property in calculus together with the transformed space technique in order to make the algorithm flexible in terms of non‐uniform spatial sampling.

Through the studies of the wave propagation characteristics on PBG structures in stratified medium, it has been found that the proposed method retains excellent accuracy in the occasions where the spatial distributions contain step of up to five times larger than the original size, while simultaneously the flexibility of non‐uniform sampling offers further savings on computational storage.

Research has been mainly limited to the simple one‐dimensional (1D) periodic and defective cases of PBG structures. Nevertheless, the findings reveal strong implications that flexibility of sampling and memory savings can be realized in multi‐dimensional structures.

The proposed method can be applied to various practical structures in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled.

The method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more complicated structures.

This study aims to investigate the effect of high temperature (600°C) on the compressive strength of concrete covered with a mixture of polypropylene fiber and gypsum plaster (PFGP).

To study the compressive strength of concrete specimens exposed to temperature, 16 cubic specimens (size: 150 mm × 150 mm × 150 mm) were made. After 28 days of processing and gaining the required strength of specimens, first, polypropylene fiber was mixed with gypsum plaster (CaSO4.2H2O) and then the concrete specimens were covered with this mixture. To cover the concrete specimens with the PFGP, the used PFGP thickness was 15 mm or 25 mm. The polypropylene rates mixed with the gypsum plaster were 1, 3 and 5 per cent. A total of 14 specimens, 12 of which were covered with PFGP, were exposed to high temperature in two target times of 90 and 180 min.

The results show that the PFGP as covering materials can improve the compressive strength lost because of the heating of the concrete specimens. The results also show that the presence of polypropylene fiber in gypsum plaster has the effect on the compressive strength lost because of the heating of the PFGP-covered concrete. The cover of PFGP having 3 per cent polypropylene fiber had the best effect on remained strength of the specimens.

The cover of PFGP having 3 per cent polypropylene fiber has the best effect on remained strength of the PFGP covered specimens exposed to temperature.