Kamariah Noor Ismail

Coaxial feed Archimedean spiral antenna for GPS application

This work highlights the design, simulation and analysis of an Archimedean spiral antenna (ASA) for GPS application. The antenna was fed using coaxial feed and a prototype was fabricated on FR4 of dielectric constant, εr = 4.9 with thickness of 1.54 mm while the center frequency was 1.575 GHz. The design and simulation of the ASA were carried out b y using commercial electromagnetic simulator, CST. The prototype was fabricated, measured and analyzed using Vector Network Analyzer (VNA), ZVA40. 2D radiation pattern was obtained by using antenna training system, ED3200. It was observed that the measured and simulated values of the parameters of the ASA were close with each other. The frequency independent of the ASA was achieved by having the same values of inner radius r, width of arm w and the spacing, s between each turn of the ASA. The radiation pattern obtained illustrated an omni-directional pattern.

Sierpinski gasket fractal antenna with defected ground structure (DGS)

This paper presents the design and fabrication of Sierpinski gasket fractal antenna with defected ground structure (DGS) with center frequency at 5.8 GHz. A slot was used as a DGS. The antenna was designed and simulated using Computer Simulation Technology (CST) software and fabricated on FR-4 board with a substrate thickness of 1.6 mm and dielectric constant, er of 5.0 and dielectric loss tangent 0.025. Measurement of the parameters of the antenna was carried by using a Vector Network Analyzer. The result shows a good agreement between simulation and measurement and a compact size antenna was realized.

Microwave Characterization of Silicon Wafer Using Rectangular Dielectric Waveguide

A non-destructive and easy to use method is presented to characterize p-type and n-type silicon semiconductor wafers using a rectangular dielectric waveguide measurement (RDWG) system. The measurement system consists of a vector network analyzer (VNA), a pair of coaxial cable, coaxial to waveguide adapter and dielectric-filled standard gain horn antenna. In this method, the reflection and transmission coefficients, S11 and S21 were measured for silicon wafer sandwiched between the two Teflon, the dielectric that filled the standard gain horn antenna. It was observed that, the dielectric constant of the silicon wafers are relatively constant, varying slightly over the frequency range of 9 to 12 GHz. The loss factor, loss tangent and conductivity of the doped wafers are higher than the undoped type

Thermal Stability Study of Ce0.75-Zr0.25O Nanostructures Synthesized via Water-in-Oil Microemulsion Method

Fundamentally, ceria particle had ability to store, transport and release oxygen, which was identified as oxygen storage capacity (OSC). Due to this OSC ability, ceria became the most important component in the three-way catalyst. With the addition of zirconia into the ceria resulting in better performance in three-way catalyst as it increased or improved thermal stability and also promotes the redox properties. This study was conducted to investigate the effects of heat treatment on the structure and physical property of nanocrystalline Ce-Zr-O solid solution. Microemulsion method was used for preparation of Ce-Zr-O solid solution, and heat treatment investigation was applied towards the synthesized nanocrystalline Ce-Zr-O solid solution. The phase and crystal structure of Ce-Zr-O solid solution were determined using XRD analysis. While, the modification of surface area and porosity size over the wide range of calcination temperatures range from 300°C to 700°C was investigated using BET Analyzer. XRD analysis confirmed the Ce0.75Zr0.25O2 solid solution was succesfully synthesized in the research. The results exhibited the effect of heat treatment on the decreasing of surface areas and porosity profiles of the Ce0.75Zr0.25O2. Despite of the reduction of surface areas at elevated temperatures, the study found the promising results that the enhancement of thermal stability of ceria by addition of zirconia.

Surface Structure Study of CeZrO2 Nanocatalyst Doped with Different Transition Metals

CeZrO2 nanocatalysts doped with three transition metals of Cu, Ni and Co were synthesized via sequence method of microemulsion and deposition-precipitation method. The crystallinity phase was studied by using X-ray diffraction (XRD) while the textural analysis was performed by N2 adsorption desorption analysis. XRD results exhibited the transition metals peaks were detected on the CeZrO2 pattern. N2 adsoption–desoption depicted that Ni/CeZrO2 produced higher BET surface area of 35.19 m2/g as compared to Cu/CeZrO2 and Co/CeZrO2. Therefore, this result suggested that the CeZrO2 nanocatalyst doped with Ni has a great potential to enhance the catalytic activity.

Overview: Modification of Cerium Oxide in Three-Way Catalysts

An overview of modification of cerium oxide, CeO2 which is employed in the three-way catalyst (TWCs) is presented in this article. The modifications of cerium oxide, CeO2 incorporated with the metal oxides for the improvement of thermal stability, microstructure and oxygen storage capacity (OSC) are discussed. In view of that, the types of metal oxide are grouped into transition metals, rare earth metals, and alkaline metals and the effect of each group into cerium oxide, CeO2 are elaborated.

Study on the structure and morphology of CexZr(1-x)O2 mixed oxides

A series of CexZr(1-x)O2 mixed oxides with different ratio (0 x 1) have been synthesized using microemulsion method. The structure and morphology of the mixed oxides have been investigated via X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The results showed that the synthesized mixed oxides were of nanoscale size and the cubic phase was obtained with the application of a ratio of x > 0.5. Additionally, it was found that the tetragonal phase existed with lower ceria content. The average crystallite size of the CexZr(1-x)O2 series were found to be in the 5 - 10 nm range. Moreover, the roughness of these mixed oxides had also decreased with increasing ceria content.

Modification of PdO/CeZrO2 doped with transition metals (Y and Fe) for reducibility properties

This paper describes the synthesis of modified nanocatalysts of PdO/CeZrYO2(PdO/CZY), PdO/CeZrFeO2(PdO/CZF) and PdO/CeZrO2(PdO/CZ) via microemulsion followed by deposition – precipitation method. The structural, textural and redox properties of the synthesized nanocatalysts were investigated. The diffractogram of XRD showed that all the synthesized nanocatalysts indicate a symmetrical pattern of cubic phase crystallinity. The amount of PdO was detected using EDX analysis and PdO/CZF portrayed the highest Pd contents of about 4.63 %. Therefore it shows a good potential to have reducibility properties and can be manifested active at low temperature reduction.

Catalytic activity of calcium-based mixed metal oxides nanocatalysts in transesterification reaction of palm oil

Nowadays, biodiesel has become the forefront development as an alternative diesel fuel derived from biological sources such as oils of plant and fats. Presently, the conventional transesterification of vegetable oil to biodiesel gives rise to some technological problem. In this sense, heterogeneous nanocatalysts of calcium-based mixed metal oxides were synthesized through sol-gel method. It was found that significant increase of biodiesel yield, 91.75 % was obtained catalyzed by CaO-NbO2 from palm oil compared to pure CaO of 53.99 % under transesterification conditions (methanol/oil ratio 10:1, reaction time 3u2005h, catalyst concentration 4 wt%, reaction temperature 60 °C, and mixing speed of 600u2005rpm). The phase structure and crystallinity as well as the texture properties of the prepared catalysts were characterized by X-ray Diffraction (XRD) and the textural properties were characterized by N2 adsorption-desorption analysis. Sol-gel method has been known as versatile method in controlling the structural an...

Effect of calcination temperature on the structure and catalytic performance of 80Ni20CO/SiO2 catalyst for CO2 methanation

The 80Ni20Co/SiO2 catalysts prepared using co-precipitate and incipient wetness impregnation method were used for production of methane through CO2 methanation reaction between CO and H2 gases. The effect of a range of calcination temperature on the structure and catalytic performance of 80Ni20Co/SiO2 catalyst was investigated using microactivity fixed bed reactor. It was found that the catalyst calcined at 400°C for 4.5u2005h under air atmosphere has shown the best catalytic performance for CO2 methanation. Characterization of 80Ni20Co/SiO2 catalyst calcined fresh samples was carried out using TPR-H2 analysis, Brunauere Emmette Teller (BET) measurements and X-ray diffraction (XRD. It was observed that calcination temperature influenced the structure, morphology and catalytic performance of the catalysts.