Department of Electrical and Electronics Engineering
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- ItemOpen AccessAdaptive electrical echo canceller for telephone networks(IEEE, 2005-11) Oyerinde, Olutayo; Yesufu, Kokumo ThomasEcho 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
- ItemOpen AccessAnalysis 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, GanA 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.
- ItemOpen AccessAnalysis of multi-terminal unified power flow controller for power transfer(IEEE, 2008-09) Omoigui, Michael; Karugaba, Sosthenes; Ojo, OlorunfemiThe 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.
- ItemOpen AccessAssessment of electrical energy use efficiency in Nigeria food industry(IEEE, 2009-09) Aderemi, A.O.; Aderemi, Helen olubunmi; Ilori, M.O.; Akinbami, john -felix kayodeThis 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.
- ItemMetadata onlyBefore the Dawn of Molecular Electronics(2000-07-11) Adegboyega, G.A.Today, civilization has passed the threshold of the second industrial revolution. The first industrial revolution which was based upon the steam engine, enabled man to multiply his physical capacity to do work. The second Industrial revolution, which is based upon semiconductor (or solid-state) electronics, is enabling man to multiply his intellectual capabilities. In other words, what technology has done to the world to modernize it is what solid-state electronics is doing to technology. Ultra large scale integration (ULSI) electronics, as it is presently termed, is the most advanced state of semiconductor electronics, and represents a remarkable application of scientific knowledge to the requirements of technology. In this lecture, we will highlight the past and present stages of development of this science and technology and elucidate the trend for the future of what is becoming a giant scale integration electronics. In addition, we will highlight Nigeria's position in the acquisition of this technology and proffer the way forward. Electronics, by definition, is that field of science and engineering that deals with electron devices and their utilisation. An electron device is one in which conduction is principally by electrons moving through a vacuum, gas or semiconductor. In elementary science, we say matter is made up of gas, liquid or solid. Electrically, the solid can be classified as a conductor, a semiconductor or an insulator. This lecture will deal, in the main, with the art, science and technology of semiconductor devices fabrication. Having said this, I must be quick to add that semiconductor devices cannot be fabricated in the absence of the conductor and the insulator. Neither will it be possible to fabricate semiconductor devices without the use of liquids and gases. What we are, therefore, dealing with here is an encompassing materials science with a special emphasis on semiconductor devices.
- ItemOpen AccessCompositional studies of various metal oxide coatings on glass(Thin Solid Films, 9019-02) Ajayi, E.O.B; Akanni, M.S; Lambi, John Ngolui; Jeynes, ChrisOxide 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
- ItemOpen AccessA control strategy for optimum efficiency operation of high performance interior permanent magnet motor drives(IEEE, 2003-11) Ojo, O.; Wu, Zhiqiao; Osaloni, F.; Omoigui, MichaelThis 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.
- ItemOpen AccessCorrelation 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
- ItemOpen AccessCross 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, GThe 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
- ItemOpen AccessDeep 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, EDeep 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
- ItemOpen AccessDesign and Construction of an Electronic Heart Beat Monitor.(Obafemi Awolowo University, 1986) Oladunjoye, Olunu Akintunde; Kehinde, L. O.The design of safe monitors of physiological events in humans is of paramount importance in the field of medical electronics, and this report describes the development of a safe computer-based heart beat monitor for hospital use. The heart beats are detected by passing light through a finger into a photo-diode. Each time the heart beats, it pumps blood round the body and this causes the density of many parts of the body to vary, particularly the finger tips. By passing light through the finger tip onto a photodiode, this variation in density is converted into electrical signal that varies with the heart beat. The output of the photodiode is amplified in detection and amplification circuit to produce a CMOS compatible pulse each time the heart beats. An electronic method that does not employ a computer is first designed as a basis for comparison with the computer based method. In this method the time interval between successive three heart beats is measured and on the basis of the measured interval, the heart rate is computed by employing digital division method. This method, like others employing digital division method in computing the heart rate, has a reliable narrow operating frequency from 40 to 200 BPM, and a resolution of IBPM. Its main problem arises from truncation error. In the computer based method, the heart beat detection and amplification circuit is interfaced with a digital micro-computer. The microcomputer is programmed to measure the time interval between successive three heart beats, to compute the heart beat rate and to provide both graphical and numerical indications of the heart beat rate. This method has a wide operating range (10 to 10920 BPM), and a resolution less than BPM.
- ItemOpen AccessDesign and Simulation of a Programmable Logic Controller for Remote Monitoring and Control of Satellite Oil and Gas Wells(2015-09-30) Ikono, Nsikan-Abasi MichaelThis study investigated development of an automatic controller for remote production restoration of oil and gas wells with a view to minimizing downtime by giving electronic logic alerts of problem areas to the system operator. The conceptual design was based on the development of a ladder logic circuitry with variable input data such as high pressure, low pressure and valves position signals sensed as "ON" or "OFF" signal levels. These input data were scanned at predetermined time intervals using the Programmable Logic Controller (PLC). The "TRIlogi 5.3" educational computer application simulator was used to simulate the workability of the ladder logic program. A remotely operated PLC system constructed with transceivers was used to demonstrate the operations by running the ladder logic program with physical model using On/Off switches as inputs and light emitting diodes (LED) as output indication. The results showed that operating the PLC logic program can achieve input variable monitoring by indicating the current statuses of the inputs with "ON" state as high pressure, "OFF" state as low pressure and "ON/OFF" as opened and closed valve positions respectively. The simulator did not require any physical connection to the target PLC, thereby offering the most effective way of testing and debugging ladder logic program prior of the hardware. Programming and debugging time were greatly reduced by making good use of the simulator feature to eliminate as many logic errors as possible before testing the program on the actual hardware. In addition, it reduced the chances of costly damage to the PLC machine due to programming errors. Moreover, it controlled the opening and closing of well production with the PLC output signals acting as feedback from the logical decision to operate end devices actuator coils with changed statuses indicated by the output LED. In conclusion, the result of the system test established the workability of remote restoration of oil and gas production using a PLC for quick decision making.
- ItemOpen AccessDevelopment of a Rainfall Attenuation Map for Microwave Terrestrial Application in Nigeria.(Obafemi Awolowo University, 1987) Anazodo, Chiedu Charles; Ajayi, G. O.The growing need to utilize frequencies above 10GHz for high capacity terrestrial and space radio links due to the congestion at low frequencies has enhanced the necessity to develop a map of attenuation due to rainfall at these frequencies. There is a dearth of instantaneous rainfall data in Nigeria hence the long-term total rainfall data and other meteorological data obtained from some 37 stations in Nigeria have been used to study the attenuation due to rainfall for microwave terrestrial applications in Nigeria. A database has been created for all the data and statistical analysis carried out on them. The Dutton and Dougherty (1974) prediction model used for predicting short integration time rainfall rate from long-term rainfall data for Europe has been modified for use in the Nigerian climatic conditions. Regression techniques have been utilized to obtain a mathematical relationship between the rainfall rate, the average annual rainfall and the number of thunderstorm days for all the available meteorological stations. The computed one-minute integration time rain rate has been used to predict the specific attenuation for some microwave frequencies for each station and the results are presented in form of contour maps. The attenuation map shows that specific attenuation due to rainfall is higher in the southern parts of Nigeria compared with the northern parts. The results obtained in this study will be useful in the design of terrestrial microwave links in Nigeria, especially in the estimation of necessary fade margin to take care of attenuation due to rainfall.
- ItemOpen AccessDevelopment of a Self-Coordinated Communication System for Scaring Birds on Rice Farms(2015-06-23) Badru, Rahmon AriyoThe study appraised techniques for communicating hazards to birds and developed a self-coordinated electronic communication system for scaring birds. It also determined the optimal placement of the bird-sensory electronic devices on the rice farms. This was with a view to solving the problem of menace of birds on rice farms. Static (e.g. scarecrow) and dynamic (e.g. drumming) methods of communicating hazards to birds through their tactile sensory cells bristle feathers, vibration sensors (Herbot's corpuscles), hearing tubes, rods and cones sensory cells were appraised in relation to their practical implementation and cost effectiveness. A prototype system was simulated by designing an infrared (IR) transmitter and receiver circuits, which were constructed using relevant combination of electronic techniques. Subsequently, an electronic IR motion detection system comprising of pyroelectric infrared sensor, Fresnel’s lens, amplifier and comparator circuits were developed and implemented. In addition, the architecture of the system was fitted with air vibration mechanisms human eye-structured and sound producing units. The overall assembly was covered with sheet of rust-free metallic sunlight reflector. The results showed that the effective coverage field and detection range for the simulated IR transmitter and receiver system were 10° and 1.5m respectively. This system was characterized with low quality siren output, faulty triggering during systems stand misalignment and inability to electronically facilitate other actuators for the effective scaring of birds. Furthermore, the self-coordinated communication system had a coverage field of 95° and a detection range of 27.4 m. The prototype of this system was observed to scare birds when the air vibration mechanism produced artificial oscillation of air molecules. The illumination produced by the human eye-structured unit coupled with the reflection of diffused sunlight rays from the body of the system disturbed the sight of the birds. Also, sound of triangular waveform signals with frequencies from 0.6 kHz to 1.5 kHz in periodic bursts of 3.0 seconds was interpreted by the birds as scare signals. In conclusion, the device was found to be suitable for the communication of hazard to birds attacking rice plants which is fundamental to improving the yield per hectare of the protected area.
- ItemOpen AccessDevelopment of a Synchronous Data Transmission System.(Obafemi Awolowo University, 1986) Agomo, Uchenna Udochukwu; Kehinde, L. O.The development of a 2 - channel synchronous data transmission system is presented. The system is capable of accepting at the input two separate analog voltage signals that have zero to 1 kHz frequency range and amplitude not greater than 2.5 volts. The two analog voltage signals are multiplexed at the input of the-system and converted to corresponding digital representations. These digital representations are then transmitted by means of digital gates from the transmitting section serially and with transmission clock frequency of 6.6 MHz, through cable wire to a remote receiving section, where the received digital representations are re-converted to analog voltage signals and demultiplexed to produce at the output, two separate analog voltage signals plus noise. The noise level does not exceed 5% of the signal level when filtered and leaves analog voltage signals with the same characteristics as those at the input of the system. The designed system is simple and can be used for laboratory demonstration on synchronous data transmission system. It may be useful as a communication medium for data exchange between two data processing terminals. The system may be used to transmit voltage signals from a central storage facility to a remote destination. In such circumstance the signals may be those derived from research results, medical findings and student/staff records. A computer base may then be set up and made accessible to users.
- ItemOpen AccessDevelopment of a Text-Independent Speaker Identification System(2015-04-22) Fisusi, Abimbola AdeolaAccess control to confidential information and facilities is conventionally through the use of passwords, smart cards or keys that can be stolen or forgotten. In this work, a software-based access control system that identifies users by the unique features in their voices, which cannot be easily breached, was developed with a view to overcome the limitations of conventional access control methods. The implementation of the system involved two phases - the training and testing phases. During the training phase, speech samples were collected from seven male and five female speakers by recording their voices with a microphone connected to a computer system. Speaker's unique features were extracted from the speech samples in form of Mel-Frequency Cepstrum Coefficients (MFCCs) which estimated the unique shape of the spectral envelope of each user. The extracted MFCCs features were used to build speaker models in form of codebooks for the speakers using the Vector Quantization (VQ) approach. The speaker models created were stored in a database. During the testing phase, another set of speech samples were collected from the same set of speakers of the training phase. MFCC features were extracted from each of the testing speech samples and compared with the codebooks created during the training phase. For each testing speech sample, the speaker whose codebook gave the lowest average distortion was identified as the true speaker. Codebooks of different sizes ranging from 16 to 256 were used to perform the identification task. In the same vein, the performance of the system as a text-dependent system was also evaluated using the same words for both training and testing phases. The performance of the text-independent speaker identification system was evaluated by comparing the speakers' testing phase MFCCs with their training phase codebooks. The results showed that the identification rate of the text-independent speaker identification system increased with increase in codebook size. "The identification rate of the system was 57.14% when 16-vector codebooks were used as speaker models. It was 71.43% and 85.71% for 32-vector and 64-vector codebooks respectively. The speaker identification system was able to achieve 100% identification rate at codebook sizes of 128 and 256. The average distortions of speakers from testing speech samples were found to decrease with increase in codebook size. The 128-vector codebooks are preferred over 256-vector codebooks because the time required to perform the identification task is shorter for 128-vector codebooks although both give 100% identification rate. 1n conclusion, the developed text-independent speaker identification system could distinguish between speakers correctly and provide security for confidential information and facilities better than conventional methods if the codebook size used for the identification task is large enough.
- ItemOpen AccessDynamic 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, MichaelThe 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.
- ItemOpen AccessThe 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, ESome 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.
- ItemOpen AccessElectrical 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.
- ItemOpen AccessElectrical 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, AntonellaThe 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