Wan Khairuddin Wan Ali

Measurement of pyramidal microwave absorbers using RCS methods

In this work, a commonly used measurement techniques were used to define the reflection loss performance of pyramidal microwave absorbers mounted on a wall. The technique is namely, Radar Cross Section (RCS) measurement method. Six set of pyramidal microwave absorbers and flat square absorbers were installed at one side wall, in an RF shielded room in order to investigate the performance. Two types of cable losses measurement techniques were applied to compare its performance under different loss conditions. The reflection loss values resulting from this investigation were then analyzed and discussed.

Effect of Oxidizer-Fuel Mixture Ratio to the Pressure Exponent of Ammonium Perchlorate Based Composite Propellant

In this paper, experimental investigation of pressure exponent in burning rate of composite propellant was conducted. Four sets of different propellant compositions had been prepared with the combination of Ammonium Perchlorate (AP) as an oxidizer, Aluminum (Al) as fuel and Hydroxy-Terminated Polybutadiene (HTPB) as fuel and binder. For each mixture, HTPB binder was fixed at 15% and cured with isophorone diisocyanate (IPDI). By varying AP and Al, the effect of oxidizer-fuel mixture ratio (O/F) on the whole propellant can be determined. The propellant strands were manufactured using compression molded method and burnt in a strand burner using wire technique over a range of pressure from 1atm to 31atm. The results obtained shows that the pressure exponent n, increases with increasing O/F. The highest pressure exponent achieved was 0.561 for propellant p80 which has O/F ratio of 80/20.

A theoretical development to simplify the analysis of rectangular patch microwave sensor built on multi-layer substrate

This paper presents a method to simplify the analysis of a square patch microwave sensor built on a multi-layer substrate. The main feature of this method is the simplification of a multi-layer sensor structure into a sensor structure with a single homogeneous layer. The equivalent dieletric constant for the new single homogenous layer was discriminated using the method proposed in this paper. Effectively it eliminates the problem of mode matching between layers and thus reduces the amount of calculation and computing time. The method was compared with the experimental results and was found to give an error less than 4% in the worse case.

Review on Typical Ingredients for Ammonium Perchlorate Based Solid Propellant

Ammonium perchlorate (AP) based solid propellant is a modern solid rocket propellant used in various applications. The combustion characteristics of AP based composite propellants were extensively studied by many research scholars to gain higher thrust. The amount of thrust and the thrust profile, which may be obtained from a specific grain design, is mainly determined by the propellant composition and the manufacturing process that produces the solid propellant. This article is intended to review and discuss several aspects of the composition and preparation of the solid rocket propellant. The analysis covers the main ingredients of AP based propellants such as the binder, oxidizer, metal fuel, and plasticizers. The main conclusions are derived from each of its components with specific methods of good manufacturing practices. In conclusion, the AP based solid propellant, like other composite propellants is highly influenced by its composition. However, the quality of the finished grain is mainly due to the manufacturing process.

Microwave Absorber Coating Material Using Oil Palm Ash

The most important part to be highlighted in developing a reliable microwave absorber is the material used to fabricate the absorber. As an alternative in managing the increase of the oil palm residues throughout the country, this study is focusing on developing a microwave absorber coating using oil palm fly ash. The software uses for design and simulation of microwave absorber is CST Microwave Studio (CST MWS) which enables the fast and accurate analysis of high frequency devices. The simulation design is fabricated to a number of layers which is coated by oil palm ash as a lossy element. The measurement and performance are carried out in the high broadband frequency of 8 to 12 GHz (X-band).

Studies of potential carbon coating for high frequency microwave absorber

An electromagnetic (EM) wave absorber is used to absorb the reflected wave that occurs on the wall of the chamber in the anechoic chamber. To date findings show that the construction of the absorber material used for the absorbers, ferrite is in the lead. A survey on materials that can be used as a carbon for the absorber is performed and the best carbon content is a mix of wood. The absorbers are made of elephant board and then coated with carbon. The absorber is measured for 10GHz frequency. The performances of the designed absorber are compared to commercial absorbers available in terms of the absorption performance.

Synthesis of Hydroxyl Terminated Epoxidized Natural Rubber as a Binder for Solid Rocket Propellant

Hydroxyl terminated epoxidized natural rubber (HTENR) was prepared by oxidative degradation of epoxidized natural rubber (ENR) with cobalt (II) acetylacetonate (co (II) aa) as a chemical agent in toluene as a solvent. Different of cobalt amount and reaction time used to study the effect on molecular weight. It was found that the number average molecular weight (Mn) and weight average molecular weight (Mw) depended on the reaction time and cobalt amount. Burning rate of solid propellant based on HTENR binder is 2.93mm/s which is approximately same with HTPB binder with 3.0mm/s. As a conclusion, HTENR binder is suitable to be used as a binder for solid rocket propellant.

Design of portable mini anechoic chamber using low cost composite absorber

This paper presents the absorber in which it is designed and shaped to absorb incident radio frequency (RF) radiation. The absorber is designed using composite material since the significance of the project is to find a potential solution to construct a low cost anechoic chamber. This model of mini anechoic chamber, which is consisting of the new designed absorber, is portable and small in size so that it is more user friendly. The performance of the designed absorber are compared to commercial absorber available. The absorber that has been developed is a low cost absorber with the absorption rate is 16.6% less compared to the commercial absorber.

Effect of Various Alcohols and Reaction Time on the Properties of Hydroxyl Terminated Natural Rubber Synthesized via Oxidative Degradation

The oxidative degradation of deproteinized natural rubber (DPNR) using cobalt bis(acetyl acetonate) in the presence of different alcohols and various reaction time; followed by reduction with sodium borohydride (NaBH4) for the synthesis of hydroxyl terminated liquid natural rubbers (HTNRs) was carried out. The synthesis of HTNRs from natural rubber is particularly important as an alternative to hydroxyl terminated polybutadiene (HTPB); one of the current leading synthetic rubber for the production of rubber binders for composite solid propellants. Four different alcohols (i.e. methanol, ethanol, propanol and hexanol) were investigated in order to achieve degraded DPNR with lowest molecular weight. The structure of the obtained HTNRs were analysed using gel permeation chromatography (GPC) and fourier transform infrared (FTIR). Based on GPC analysis, it was found that the use of ethanol at 1 h reaction time resulted in lowest molecular weight of approximately 6,690 g/mol. Analysis of chain scission of the HTNRs were consistent with the molecular weight attained. FTIR analysis, on the other hand confirmed the presence of hydroxyl functional group in the synthesized HTNRs with the highest amount of hydroxyl group presence in the HTNR prepared using ethanol. Overall, the properties of synthesized HTNRs (molecular weight and functional groups) displays a potential material for the production of propellant binder and are comparable to the properties of commercially available HTPB.

Improvement study of the reflectivity for hollow pyramidal shape absorbers

This paper presents an investigation of the reflectivity performance for hollow pyramidal shape microwave absorbers. The pyramidal absorbers used in this study is constructed using four 15cm-pyramidal absorbers stacked on each other to equal the height of one single 45cm-absorber. The wave frequency ranging from 8GHz to 12 GHz was chosen for simulation and measurement of the absorber performance. The reflectivity performances of the stacked pyramidal absorbers were compared to single level pyramidal absorbers in term of their reflectivity performances. The result shows that the stacked pyramidal absorber has higher absorption level an average absorption of −24 dB for the above frequency range.