Permanent URI for this collection
Browse
2712 results
Search results
Publication Optimization of surface micromachined patch antenna(2000) Wong, S.; Ooi, B.L.; Kooi, P.S.; Ng, T.H.; Liu, A.Q.; ELECTRICAL ENGINEERINGAlthough Microelectromechanical system (MEMS) technology has been used extensively in constructing microelectronic and micromechanical structures, there are very few reports on the research and development of MEMS antenna. This paper reports the investigation results of MEMS patch antennas in different shapes and structures. Like conventional patch antenna, MEMS patch antenna has narrow bandwidth, however, it is found among three basic shapes: circular, square and triangular. Square patch antenna has the best overall performance. Two simple methods to improve the performances of MEMS patch antenna are also proposed. When the feed inset position in polysilicon layer of a MEMS microstrip patch antenna is optimized, the impedance bandwidth of the antenna can be enhanced without deteriorating the radiation pattern of the antenna. Also, the resonance frequency of MEMS patch antenna is reduced by etching holes on the radiating patch.Publication Packet reservation multiple access in a metropolitan microcellular radio environment(1993-08) Wong, Wai-Choong; ELECTRICAL ENGINEERINGWe examine the performance of a Packet Reservation Multiple Access (PRMA) protocol in a metropolitan microcellular radio environment using computer simulations. Call characteristics, mobility, and channel conditions have an impact on PRMA performance which we measure in terms of the average packet dropping rate per call. In order to maintain a reasonable level of service quality for calls in progress, teletraffic loading can be controlled by introducing a call setup queue and limiting the number of active subscribers. Call mobility is found to have a minor impact on PRMA performance. PRMA is also fairly robust against adverse channel conditions with a drop in performance of about 15 percent when the channel packet loss rate is less than 0.01. Performance comparisons to other protocols are also carried out.Publication A neural fuzzy power system stabilizer based on α-level sets(1999) Eng, Y.W.; Elangovan, S.; ELECTRICAL ENGINEERINGA new type of fuzzy logic power system stabilizer is proposed in this paper. It is constructed using a five-layered neural fuzzy network architecture based on α - level fuzzy sets. The workability of this neural fuzzy power system stabilizer is first demonstrated using regularly spaced and triangular fuzzy sets. Then, it is shown that the fuzzy sets can be tuned so as to improve the damping performance of the stabilizer. To obtain the desired output for backpropagation to be applied, the network output is altered at a randomly chosen time instant. The altered output is then taken as the desired output if the stabilizer performs better than without the alteration. Simulation results show that the performance of the neural fuzzy network can be improved within 30 training cycles.Publication Optical detection of laser plasma interaction during laser ablation(1999) Hong, M.H.; Lu, Y.F.; ELECTRICAL ENGINEERING; DATA STORAGE INSTITUTELaser plasma interaction during pulsed laser ablation is investigated by ultrafast phototube detection. There are two peaks in an optical signal with the first peak attributed to laser scattering and the second one to plasma generation. As laser fluence increases, the second peak rises earlier to overlap with the first one. The signal is fitted by different distribution functions for the laser scattering and the plasma generation. Peak amplitude and its arrival time, full width at half maximum (FWHM), starting time and termination time of the distributions are studied for different laser fluences and detection angles. Laser pulse is mainly scattered from the plasma during the laser ablation. Peak amplitude of the laser scattering increases but its FWHM decreases with laser fluence. Angular distribution of the peak amplitude can be fitted with cosn θ (n=4) while detection angle has no obvious influence on the FWHM. In addition, FWHM and peak amplitude of the plasma increase with laser fluence. However, its starting time and peak arrival time reduce with laser fluence. Time interval between plasma starting and scattered laser pulse termination is proposed as a quantitative parameter to characterize laser plasma interaction. Threshold fluence for the interaction can be estimated to be 3.5 J/cm2 for KrF excimer laser ablation of silicon. For laser fluence above 12.6 J/cm2, the plasma and scattered laser pulse distributions tend to saturate.Publication Automatic contingency selection and ranking using an analytic hierarchical process(1996) Zhu, J.; Irving, M.R.; Guoyu, X.U.; ELECTRICAL ENGINEERINGA new approach in the power system analysis to automatic contingency selection (ACS) and ranking, using an analytic hierarchical process (AHP) is developed. ACS for the real and reactive power subproblems is solved by network flow programming, based on the existence of weak coupling between real and reactive quantities in power systems. The performance indices to assess the severity of contingencies are defined as the total real and reactive load to be curtailed. In the rank calculation, this paper takes into consideration the relative importance of transmission lines and the situation that the real and reactive power security constraints may be violated as the line outage appears, so that the precise information for the real time security analysis can be provided. The results on IEEE-14 bus test system are given in the paper.Publication Characterization of proton-exchanged optical waveguides in ZnO:LiNbO3(1995) Hou, W.X.; Chong, T.C.; ELECTRICAL ENGINEERINGWe report the first demonstration of proton-exchanged optical planar waveguides in x-cut and z-cut LiNbO3 doped with 6 mol% ZnO using adipic acid as proton source. These waveguides exhibit a graded index profile which can be modeled by a linear step function with a surface index increase of 0.135 and 0.14 for x-cut and z-cut waveguides, respectively. The diffusion constant D0 and the activation energy Q are characterized optically to be 1.64×109 μm2/h and 88.8 KJ/mol for x-cut waveguides, and 1.478×109 μm2/h and 91.25KJ/mol for z-cut waveguides, respectively. The diffusion rate along the z-axis is slower than that along the x-axis, whereas the surface index increase on z-cut waveguides is larger than that on x-cut waveguides.Publication Role of hole fluence in gate oxide breakdown(1999-11) Li, M.F.; He, Y.D.; Ma, S.G.; Cho, B.-J.; Lo, K.F.; Xu, M.Z.; ELECTRICAL ENGINEERINGA simple model which links the primary hole and Fowler-Nordheim (FN) electron injections to oxide breakdown is established and the calculation based on this model is in good agreement with our experiments. When the sum of the active trap density Dpri due to primary hole injection and the active trap density Dn due to FN electron injection reaches a critical value Dcri, the oxide breaks down. The hole is two orders of magnitude more effective than FN electron in causing breakdown. These new findings are imperative in predicting oxide reliability and device lifetime.Publication Formation of voids in Ti-salicided BF+ 2-doped submicron polysilicon lines(2000-06-15) Chua, H.N.; Pey, K.L.; Lai, W.H.; Siah, S.Y.; ELECTRICAL ENGINEERINGThe physical characteristics and distribution of voids in TiSi2/p +-Si system as a function of polycrystalline silicon (polySi) linewidths were investigated in detail using scanning electron microscopy, cross-sectional transmission electron microscopy, and the focused ion beam technique. Surface and subsurface voids were found in Ti-salicided BF+ 2-implanted polycrystalline silicon (polySi) lines that were annealed at temperatures ranging from 650 to 850 °C. Most of the subsurface voids were found in the TiSi2 film as well as at the TiSi2/polySi interface. The void density, shape irregularity, and void size increase with decreasing polySi linewidth, especially when it is smaller than 0.24 μm, indicating that stress associated with narrow polySi lines may play an important role in the voiding phenomenon. It was also shown that the TiN film overlying the TiSi2 film and the etch-back process could not be responsible for the void formation process. Instead the absence of voids in B+-implanted polySi and the segregation of fluorine into the TiSi2/polySi and TiN/TiSi2 interfaces from BF+ 2-implanted polySi after the first salicidation rapid thermal annealing suggest a fluorine-assisted voiding mechanism. © 2000 American Institute of Physics.Publication Correlation statistics distribution convolution (csdc) modeling for studying cdma indoor wireless systems with rake receiver, power control & multipath fading(1996) Chen, X.H.; Lang, T.; Oksman, J.; ELECTRICAL ENGINEERINGA new scheme to study the performance of a DS/CDMA indoor wireless system, the correlation statistics distribution convolution (CSDC) modeling, is introduced in this paper. With the aid of the CSDC modeling, the bit error rate versus number of simultaneous interfering transmitters can be directly evaluated, considering the effects of Rayleigh fading, power control, multipath and co-channel interference. The performance of two CDMA receiver structures, conventional correlator and RAKE receiver, is compared. It is shown that the RAKE receiver is effective in improving the system performance under indoor multipath fading. However, its effectiveness under transmitter power control is sensitive to the severity of multipath interference in the indoor channel. When the multipath fading is severe, a tight power control over the main paths may not be able to improve the performance of the RAKE receiver.Publication Growth of compressive strained in GaAs/GaAs multiple quantum well structures by MBE(1997-07) Sanjeev, S.; Vaya, P.R.; Chua, S.J.; Shen, Y.; O'Connor, J.; King, V.B.; ELECTRICAL ENGINEERINGThe aim of the present work is to grow compressive strained InGaAs/GaAs quantum well structures and study energy levels in them. Multiple layers of 20 InGaAs/GaAs quantum wells were grown by MBE. The energy for the C1-HH1 transition of the grown structure was measured using Photoluminescence and Electroluminescence. Low energy ion scattering was carried out on the samples to study the depth profile of the multiple quantum wells.