Key Engineering Materials Vols. 594-595

Abstract: Explosive growth of bandwidth demand together with advance in latest communication services and emerging applications have inspired interest in optical code division multiple access (OCDMA). The work focuses on analysis and demonstration of two-dimensional (2-D) modified double weight (MDW) OCDMA wavelength-time. The 2-D MDW uses balance-detection for mitigating multiple access interference. The property of cross-correlation results in optimum phase induces intensity noise suppression (PIIN). The proposed code achieves high scalability; below 10^-9 BER error floor the code cardinality reaches 254 simultaneous numbers of users which is double the 2-D PDC performance. The lowest effective power (P_sr) for minimum optical transmission requirement for smallest number of users is achieved at-17.5dBm. The 2-D MDW OCDMA simulation model is developed to validate the realization of the code for BER and distance performance. The 2-D MDW OCDMA code successfully suppresses PIIN and mitigating MAI which result in high cardinality, reduce P_sr and improved distance.

Abstract: This paper focuses on the performance of different channel spacing with AND as well as modified-AND subtraction detection techniques emphasizing the spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems. Modified double-weight (MDW) codes are used as the signature codes for SAC-OCDMA systems. This study has been carried out through simulation of a real-like SAC-OCDMA system by using OptiSystem software from optiwave^TM. It has been found that the modified-AND subtraction detection technique able to provide a good transmission of 0.8nm that close to 1nm channel spacings performance thus show that it is a good solution which able to provide bandwidth efficiency factor to the incoherent SAC-OCDMA system that can cut down 25% of the bandwidth usage.

Abstract: Thermal oxidation of Ge was performed in dry oxygen ambience at atmospheric pressure at temperature ranging between 375 and 575°C. From SE analysis, the slope of Ge oxide growth and extinction coefficient (k) increases while refractive index (n) does not change with oxidation temperature. The reduction of activation energy for Ge thermal oxidation was explained by the retardation of diffusion oxidant through GeO₂ film during Ge oxidation. The generation of an oxygen-defect region in the Ge oxide layer at 490°C oxidation was confirmed by XPS analysis and an O₂ anneal at 375°C was effective to reduce this oxygen deficiency.

Abstract: Perylene tetracarboxylic diimide (PTCDI), derivatives have attracted the attention of the scientific community owing to their thermal stability, electron affinity-enabling n-type semiconductor behaviour and useful photophysical properties. Thin films of six new perylene tetracarboxylic diimides were fabricated on glass substrate by spin coating. The contact angles made by water on these six substrates, some with alkyl chain derivatives and the others with polar side chains, were measured using a precision contact angle goniometer. The alignment of these films on glass substrates are inferred from the contact angle data and the results are compared with those of the (self) alignment in liquid state. Derivatives with alkyl chains were seen to interact more with water, causing a lower contact angle compared to the more polar derivatives. This counter-intuitive result is interpreted in terms of molecular alignment of samples on the glass substrates.

Abstract: Subspace-based Model Predictive Control (SMPC) is a combination of a result in subspace system identification with Model Predictive Control (MPC) method. Particularly, it uses the subspace linear predictor equation to predict the future value of the system in the MPC implementation, instead of the usual state-space representation. The recursive subspace identification which updates the estimation of the extended observability matrix online is presented here for a Multi Input-Multi Output (MIMO) system specifically for a nonlinear Biological Waste Water Treatment Process. Givens rotation is applied for recursive updating of QR decomposition of a matrix in this SMPC. In SMPC, the need to have an explicit state-space representation of the system is abolished, resulting in a control algorithm that performs system identification and controller design in a single simultaneous step. Additionally, SMPC algorithm will inherit the numerical robustness typical of subspace-based methods thus giving us an easily deployable control implementation in adaptive framework.

Abstract: The ProTEX^® PSB thin film as a photosensitive layer has been released in the market as an alternative replacement for silicon nitride or silicon oxide wet etch masks. In this work, this film has been deposited on SiC-on-Si wafer for the back-etching of the bulk Si to leave SiC thin film to be used as a pressure sensor diaphragm. This paper will discuss the process flow to estimate the optimized ProTEX^® PSB thin film thickness for the sufficient back-etching of the 300um bulk Si. This thickness is defined by the following parameters: spin-coating rotational speed, final cure temperature and hard bake time of coating. Several samples of ProTEX^® PSB thin films have been preliminary characterized by infinite focus microscopy (IFM) and scanning electron microscopy (SEM) to examine the substrate surface conditions and the effects of undercut edges structure. Based on these data, it was determined that the optimum thickness of ProTEX^® PSB for this project is 2.133 μm with the spin speed of 3000 rpm, the first bake temperature of 110 °C in 120 seconds and the second bake temperature of 240 °C in 60 seconds. We conclude that ProTEX^® PSB can withstand the etch mask with etch rate of 1.28 μm/min for 8 hours and gives good quality effect of undercut edge on the SiC-on-Si wafer.

Abstract: Laminated polyurethane foam composite was produced by incorporating Cloisite 30B clay as filler and aluminium sheet as the skin. Initially, PU foams were synthesized with reaction of natural oil polyol and isocyanate with ratio of 1:1.1 by weight. Water was used as the blowing agent and appropriate surfactant and catalyst were added to ensure better performance of end product. Cloisite 30B was added as filler and the percentages were varied from 1 to 5 wt%. Al skin was attached at the top and bottom of the foam to increase the stiffness of the composite and improve its mechanical properties. In order to evaluate its impact characteristic, drop weight impact test was done and the drop height was varied from 5 cm to 20 cm. The results showed that there was no pattern that exists in the impact force, but found the results for the control PU foam (PU foam without filler) has a high impact force values at 5cm, 10 cm and 15 cm drop heights. The incorporation of clay particles were found to give lower impact force to the sample, especially at low filler percentage of 1%. It was found that the addition of clay particles has decrease the impact force of PU foam due to brittleness. Besides, the impact force of the laminated composite is higher than PU foam at the same drop height. For laminated composite at 10 cm, the impact force is higher with an average value of 817% as compared to PU foam. This shows that the addition of Al sheets have improved mechanical characteristics of foam and its ability to withstand higher impact force.

Abstract: Toxicity characteristic leaching procedure was executed on solidified petroleum sludge to investigate the metal ions release in leaching medium extractant fluid number 2, U.S.EPA SW-846 TCLP. Nine metal ions from solidified sludge in ordinary Portland cement were evaluated at water to cement ratio of 0.4 to 0.5 and incorporation of 5-15% cement replacement materials. Five cement replacement materials namely, rice husk ash, condense silica fume, activated carbon, fly ash and meta kaolin were selected for solidified sludge in the cement. Solidified sludge with cement replacement materials indicates minimum leachability of metal ions.

Abstract: SILASTIC P-1 Silicone, a hyper elastic material, supplied by Dow Corning^® is considered for the current research of the development of a soft actuator. The uniaxial tensile testing and compression testing according to ASTM standards are conducted to find its mechanical material properties. The measured stress-strain data are then applied to three kinds of constitutive non-linear models and their respective non-linear material constants are computed by least square fit. The first order Ogden model shows the better agreement with the experimental data. The mechanical properties such as ultimate tensile strength, compressive strength, shear modulus and non-linear material constants of the selected material are finally presented which will further be used for the design and analysis of the soft actuator.

Abstract: Fatigue crack initiation and growth of aluminum alloys with stress ratio were investigated due to it was widely used in aircraft production parts. Various types of aluminium alloy have been selected (6063-T6, 7075-T6, and 2024-T351). Compact design standard based on ASTM standard E647-11 was used for specimen. Cyclic loading experiment was conducted using Instron 8801 Hydraulic Server Machine with da/dN software for setup and parameter setting. Investigations on crack propagation and fracture surface were done by using Scanning Electron Microscope (SEM) to obtain the image of the specimen surface. Further analysis was done on the image to study on the crack initiation and propagation. Various stress ratio effects were set for the compact specimens having thickness 12.7 mm. Relationship between crack growth rate and the stress intensity factor range were further identified with the stress ratio effects. The gradients of crack growth rate increase while the stress ratio, R increase. Higher R-ratio results in higher value range of minimum load applied. Paris law and Modified Forman law were used as comparison with the experimental data for validation purposes and to provide the level of precision.