Journal Articles

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Journal Articles (Electrical and Electronics Engineering)

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Open Access
Adaptive electrical echo canceller for telephone networks
(IEEE, 2005-11) Oyerinde, Olutayo; Yesufu, Kokumo Thomas
Echo in telephones is generally undesirable but inevitable. Impedance mismatch and acoustic coupling between the receiver and microphone circuit(s) respectively produce electric and acoustic echoes in a telephone network. There is therefore a need to develop an echo canceller that can be used to reduce these echoes in telephone networks. In this work, a model for electrical echo in telephone networks for varied echo-path delay was designed. This was with a view to implementing an adaptive electrical echo canceller based on a combination of the normalized least mean square (NLMS) and Geigel speech detector algorithms (GSD). Subsequently, the performance indices (convergence rate and efficiency) of the echo canceller implemented were obtained using error function, echo return loss enhancement (ERLE) and the mean squared error (MSE) for various echoes with varied round-trip delay according to the minimum requirement of ITU-T (International Telecommunication Union) Recommendations. The results obtained show that there was a 3 dB improvement over the NLMS algorithm. The developed adaptive electrical echo canceller is therefore suitable for reduction of echoes in telephone networks
Open Access
Analysis of a synchronous reluctance machine with an auxiliary single-phase winding
(International journal of Electronic and Electrical Engineering, 2003-10-01) Ojo, Olorunfemi; Omoigui, Michael; Dong, Gan
A three-phase synchronous reluctance machine having an axially laminated rotor structure and an auxiliary DC-source-fed single-phase control winding has utility as either a high-speed generator or a high-torque low-speed motor. This paper provides an understanding of its operation using electric circuit and electromagnetic field concepts in the process of which some insights are provided into the design of the windings, conditions for torque production and generation of electric power when operating in the motoring or generating modes. Some confirmatory experimental results of analytical developments are provided showing performance characteristics of an experimental machine.
Open Access
Analysis of multi-terminal unified power flow controller for power transfer
(IEEE, 2008-09) Omoigui, Michael; Karugaba, Sosthenes; Ojo, Olorunfemi
The paper reports the results of analysis of a multi-terminal UPFC used for power transfer and stability improvement of power systems. The analysis employed abc to qd0 transformation technique to obtain a time-invariant equation describing the system. A simulation of a-two transmission network rated at 20 and 15 MVA at 33 kV was investigated. Results confirm that converters rated appropriately can be used to transfer power between the lines. Converter power and current optimization were carried out to determine their operational limits.
Open Access
Assessment of electrical energy use efficiency in Nigeria food industry
(IEEE, 2009-09) Aderemi, A.O.; Aderemi, Helen olubunmi; Ilori, M.O.; Akinbami, john -felix kayode
This study examined various patterns of energy consumption; it identified the sources of energy wastage, and assessed the effectiveness of the strategies that were employed to reduce energy waste in the food companies. This was with a view to recommending policy measures that would enhance effective electrical energy savings in the industry. Random sampling technique was used to select the food companies in South-western Nigeria which represent more than 50% of the Nigerian food and beverage companies. Structured questionnaire, interview and direct observation were employed as research instruments. Analytical procedure as given by Knutson and ANSI/NEMP for calculating electrical energy lost to heat per hour (Wh/h) and power factor respectively was adopted for the study. The study showed that the pattern of electrical energy consumption in the food companies was mainly from generating set; this was due to either low voltage or epileptic power supply from national grid. Direct and indirect sources that lead to electrical energy waste and in-efficient energy utilization in the industry were identified such as energy loss as a result of worn out or slack / misaligned belts that need timely replacement or tensioning, training and retraining of staff, power factor of electrical equipment among others. Three out of eleven strategies were effective in reducing the companies' electricity bill by 3% for the same quantity of production. These include: switching off most lighting during day time; instant replacement / tensioning of worn out / slack belts or chains and; disconnection of all faulty equipment. This finding shows that 72.8% of all the acclaimed strategies to reduce energy consumption were not effective. The study concluded that the factors that constituted electrical energy waste and energy use inefficiency in the food companies in the study area were very identical and recommendations for effective energy use efficiency in the firms were proposed.
Open Access
Compositional studies of various metal oxide coatings on glass
(Thin Solid Films, 9019-02) Ajayi, E.O.B; Akanni, M.S; Lambi, John Ngolui; Jeynes, Chris
Oxide films were deposited on soda-lime glass substrates by pyrolysis of indium, copper, chromium and aluminium acetylacetonates. Ion beam analysis and X-ray photoelectron spectroscopy were performed showing that the appropriate metal oxides were deposited. The indium and chromium oxide films appeared to be quite clean but the copper and aluminium oxide films were porous and had very high concentrations of carbon with associated oxygen. The copper film also had significant free copper near the surface. Significant leaching of sodium and potassium from the substrate in these two latter films was also observed. Promising optical absorbance was observed for the chromium film
Open Access
A control strategy for optimum efficiency operation of high performance interior permanent magnet motor drives
(IEEE, 2003-11) Ojo, O.; Wu, Zhiqiao; Osaloni, F.; Omoigui, Michael
This paper, using the concept of input-output linearization with decoupling, sets forth the speed control of the interior permanent magnet motor drives which simultaneously ensures the minimization of the losses-the copper and core losses. This control scheme is unique in that saturation dependent parameters such as the d and q axis inductances and the armature reaction dependent magnet flux linkage are included in the controller structure formulation and implementation. The proposed control scheme differs from known schemes which are either based on perturbation and search methods or on steady curve fitted graphs that map the command q and d axis currents based on reference torque. Unlike these methods, an optimization formulation that dynamically determines the reference currents/voltages required to achieve high performance speed control and total loss minimization is used. The control structure methodology, the nature of the variations of the machine parameters and how they influence the machine efficiency are clearly laid out.
Open Access
Correlation studies of VHF radiowave propagation and radiometeorological conditions
(IEEE, 2001-02-01) Aboaba, O.A.; Jegede, O.O.
This article presents the radiometeorological factors contributing to specific fluctuations of signal level in the southwestern part of Nigeria. Earlier in this region, diurnal and seasonal signal level variations in the VHF band were studied in over-the-horizon radiowave propagation (Aboaba 2000). The large variation in the received field strength was correlated with radiometeorological parameters such as atmospheric pressure, temperature and water vapour pressure measured during the period Oct. 1998-Nov. 1998
Open Access
Cross polarization on line-of-sight links in a tropical location: Effects of the variation in canting angle and rain dropsize distributions
( IEEE Transactions on Antennas and Propagation, 1999-09) Ajewole, O; Kolawole, L; Ajayi, G
The effects of the variation in canting angle of falling raindrops and the distribution of raindrop sizes in different types of rain on cross polarization discrimination (XPD) on line-of-sight propagation paths in a tropical location in the frequency range 1-50 GHz are investigated. The dropsize distribution (DSD) model of Adimula and Ajayi (see Ann. Telecomm., vol.51, no.1/2, p.87-93, 1996) has been used. Although, some previous studies of XPD assumed equi-orientation of the raindrops along the propagation paths, the present study employs the more realistic distribution of canting angles along the path. The results obtained show that the XPD improves by about 4-7 dB over those based on the equi-orientation model. It is also shown that for the same copolar fade and for frequencies greater than about 10 GHz, the variation of the XPD with copolar attenuation (CPA) is relatively insensitive to the assumed DSD in rain and that the deterioration in signal quality or outage will be influenced more by the signal attenuation rather than by the cross-polarization interference
Open Access
Deep level transient spectroscopy study of the damage induced in n-type silicon by a gate oxide etching in a CHF3/Ar plasma
(Journal of vacuum science & technology B, 1997-06) Adegboyega, G.; Perez, I.V; Poggi, Antonella; Susi, E
Deep level transient spectroscopy was used to detect the presence of deep levels correlated to the defects induced in the Si substrate by a CHF ₃ /Ar dry etch of a 550 Å gate oxide as a function of the rf power. Several energy levels were observed; some of them were due to the processing before the dry etching. Three traps produced by the dry etching, with Arrhenius plot activation energies, respectively, E_na1=350 meV , E_na2=220 meV , and E_na3=100 meV , and capture cross sections around 10^-20 cm ² were detected. The correlation with the surface recombination velocity variations and the F and C diffusion in the Si substrate was investigated. © 1997 American Vacuum Society
Open Access
Dynamic and steady-state operation of a five phase induction machine with an open stator phase
(IEEE, 2008-09) Karugaba, Sosthenes; Olorunfemi, Ojo; Wang, Ge; Omoigui, Michael
The analysis of an open phase fault for a five phase induction motor is presented. A circuit based model is developed which can help to predict not only the steady-state performance but also the dynamics including the pulsating torque and to evaluate the small-signal stability of the faulted machine. This is made possible by the utility of the harmonic balance technique on the model of the machine in the stationary reference frame. The resulting model is used in determining the small-signal stability of the five-phase induction motor under open-phase fault. At low speeds the machine exhibits instability on the rotor flux linkages but it is stable at higher speeds. Simulation results and steady state results are presented which also predict the speed harmonic components as well as the torque pulsations.
Open Access
The effects of oxygen precipitates on the electrical properties of silver impurities in p-type silicon
(1996-07) Adegboyega, G.A; Passari, L; Butturri, M.A; Susi, E
Some characteristics of the silver impurity in silicon with and without oxygen precipitates are studied by means of the four-point probe, minority carrier lifetime, and infra-red absorption spectroscopy measurements. The relative effect of varying contents of oxygen precipitate on the impurity is also investigated. Silver proved to be a donor-type impurity in p-type silicon and its presence led to a reduction, by up to a factor of 21, in the lifetime of the minority carriers by the formation of deep level traps. While the presence of oxygen precipitate in the substrate has little or no effect on the donor-type behaviour, it improved slightly the value of the minority carrier lifetime by gettering some of the Ag impurities and there appears to be a linear dependence of the improved lifetime on the quantity of precipitated oxygen.
Open Access
Electrical properties of CuPbBr3
( Solid State Ionics, 1989-05) kuku, T.A; Chioba, E.R; Chiodelli, G.
Electrolyte characterisation of CuPbBr3 has shown the material to be appreciably conductive with a room temperature conductivity of 2.3×10−4(Ω cm)−1, and a value of 1.37×10−2 (Ω cm)−1 at 210°C. Conductivity is mainly by anionic type defects, with ionic transport numbers greater than 0.98 for all temperatures considered in the range from 22 to 215°C. The activation energy for bromine vacancy motion is 0.27 eV. X-ray, DTA and TG analyses also show that the material is characterised by a cubic lattice with lattice parameter a0 = 9.08 Å, melts at 271°C and is thermally stable up to 450°C.
Open Access
Electrical Properties of Silver Impurities and their Annealing Behaviour in p-Type Fz Silicon
(Journal de Physique III, 1691-12) Adegboyega, G.A; Passari, L; Butturri, Maria Angela; Poggi, Antonella
The electrical activity of silver as well as its annealing properties in 10 Omega cm p-type Fz silicon substrate are studied by means of the four-point probe and minority carrier lifetime measurements. Silver atom concentration in the range 10^{14} to 10^{15} cm^{-3} consistently showed a donor type behaviour in the material and its presence led to a reduction of up to two orders of magnitude in the lifetime of minority carriers by the formation of deep-level traps. Isochronal annealing of silver contaminated specimens showed some gettering of the Ag impurities with resulting temperature dependent changes in the resistivity as well as the minority carrier lifetime values. Analysis of our results shows that a large fraction of the silver impurity atoms present forms the deep level defects and both the deep- and donor-levels appear to originate from the same source
Open Access
Electrical properties of vacuum evaporated PbSnS 3 thin films
(International Journal of Materials Science, 2006-02) Kuku, T.A; Osasona, O.; Azi, Samuel
Electrical conduction of evaporated PbSnS3 films of thickness ranging between 0.1 and 2.0 μm were studied by measuring the dc current in both parallel (planar) and transverse (cross plane) directions to the substrate surface. Conduction mechanisms relevant to various regions of the current-voltage characteristics are discussed. The obtained film conductivities were of the order 10−5 S cm−1 at room temperature and increased exponentially with increasing temperature. No consistent modification of the conductivity values and nature were observed when the films are doped with CdCl2, PbCl2 and CuI impurities. While planar conductivity activation energies were constant with voltage and increased slightly with deposition temperature, the cross plane values were found to depend on both voltage and film deposition temperature.
Open Access
Evaluation of bistatic intersystem interference due to scattering by hydrometeors on tropical paths
(International Journal of Satellite Communications, 1999-09) Ajewole, Oludare; Kolawole, L.B; Ajayi, G.O
Evaluation of bistatic transmission loss cumulative distribution is very useful in assessing the effect of interference due to hydrometeor scatter between the communication links operating at the same frequency. Out of the many factors that could be responsible for the intersystem interference between the microwave communication systems, this paper presents the result of computation of intersystem interference resulting from the hydrometeor scatter on tropical paths. Interference is computed in terms of the cumulative distribution of transmission loss. The effect of varying common volume formed by the intersection of the antenna beams on the transmission loss is investigated. Results show that at frequencies higher than 10 GHz, for antenna separation longer than 100 km, common volume will be in the ice region, leading to a higher interference level at the interfered terminal. Also, results obtained show that because total path attenuation at 30 GHz is lower than at 20 GHz (this is due to the decrease in water vapour attenuation in the 22·2–30 GHz window), transmission loss tends to be higher at 20 GHz than at 30 GHz. In addition, increasing the antenna gain of the interfering station will result in the increasing interference level at the interfered station. Evaluation of the effective transmission loss shows that this parameter gives a better assessment of interference on the tropical propagation paths noted for high-intensity convective precipitation. In this case, the effective transmission loss has been evaluated in terms of the joint occurrence of additional rain attenuation on the wanted path, and the cumulative distribution of transmission loss on the intersecting paths. Copyright © 1999 John Wiley & Sons, Ltd.
Open Access
The Functions of Language in Herbalist-Client Interaction in Yoruba Traditional Medicine
(1991) Adegbite, Wale
A piece of language in use or 'text' can be studied from three vantage points. While sociological, socio-linguistic or socio-psychological approach will be interested in studying the social uses of (parts of) the text or the pragmatic activities of the speaker and interpretant accompanying its production and reception, a textual approach will be more interested in analysing its linguistico-pragmatic features such as the function(s) and message(s), and a linguistic approach will most probably focus the description of form (grammar and lexis) and meaning in the text.
Open Access
Hybrid Online Labs
(IJOE, 2012-11) Ayodele, Kayode.P; Komolafe.A, Olusola; Kehinde, L.O
One of few limitations of remote laboratory technology is the fact that access and usability of such laboratories depend largely on the existence of favorable bandwidth conditions between the remote user and the system under test. This dependence is regrettable because some of the institutions likely to find remote laboratories attractive are also those most likely to have severe bandwidth limitations. Also, a typical remote laboratory will be completely unusable to remote students in the event of an outright network downtime. In this paper, we propose a hybrid online laboratory architecture that allows the automatic generation of accurate software models of remote laboratories. Such models can be hosted closer to the student and during periods of unfavorable bandwidth conditions, students can successfully interact with such models in lieu of the real hardware. We identify the challenges that need to be resolved for such a scheme to be useful and discuss the process by which suitable modeling bases were chosen. Finally we present and discuss data from a first test of the system and conclude that such a scheme holds considerable promise in changing the way remote laboratories are used and viewed
Open Access
Implementable soft decision decoding schemes
(International Journal of Electronics, 1989-03) Olaniyan, O.O
An implementable soft decision decoding algorithm is described. The scheme, which can be used to improve the performance of any hard decision decoder, is based on an iterative search method that tests relatively few possible code words from which the code word at nearest minimum distance from the received word is chosen. Computer simulations of the (7, 4) and (15, 7) codes on an additive white gaussian noise channel using the soft decision scheme were undertaken. A coding gain of at least 0-7 dB at an error rate of 10~3 was obtained when compared with that of the hard decision decoder
Open Access
The influence of magnetic saturation and armature reaction on the performance of interior permanent magnet machines
(IEEE, 2003) Ojo, O; Osaloni, F.; Zhiqiao, Wu; Omoigui, Michael
These effects are reflected in the classical qdo equivalent circuit model of the machine in the following fashion: the core loss is represented with a stator flux linkage dependent core loss resistance, the armature reaction effect is accounted for by the changing magnet flux linkage and magnetic saturation effect is reflected in the changing d and q-axis inductances of the machine. The steady-state modeling and analysis of the machine, the nature of the variations of the machine parameters and how they influence the machine torque and efficiency are clearly laid out and eventually confirmed by simulation and experimental results. The balance of the paper provides finite element analysis results for an experimental 2 hp IPM to further validate the conclusions drawn from calculation and experimental results.
Open Access
Inspiring next generation of engineers through service-learning robotics outreach and mentorship programme
(IEEE, 2016-10) Ilori, Olusoji; Watchorn, Andrew
. The programme is designed to tackle the problem of lack of integrative courses inengineering programmes and the lack of interest in science technology engineering and mathematics subjects among primaryand secondary school students. Under the programme, a robotic team is formed consisting of undergraduate engineeringstudents as mentors/coaches and primary and secondary school students as team members. The team members are taughthow to design, build, and program robots to solve challenges by their mentors

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