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- 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
- 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 AccessModelling of Raindrop Size Distribution in Nigeria for Microwave and Millimetre Wave Application.(Obafemi Awolowo University, 1986) Adimula, Isaac Abiodun; Ajayi, G. O.Raindrop size data collected using a distrometer measuring system at three geographical locations in Nigeria namely Calabar, Ile-Ife and Zaria have been analysed for the prediction of rainfall attenuation at centimeter and millimetre wave frequency bands. The modeling of the raindrop size distributions has been carried out using the lognormal and exponential distributions. Models for the three stations as well as a Southern, Northern and a general model for the country have been proposed for the prediction of the effect of tropical rainfall on electromagnetic propagation at microwave and higher frequencies. Rain induced specific attenuation values were computed for a frequency range of 1 to 400GHz using the models obtained for thunderstorm and shower which are very important for communication systems design.
- 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 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 AccessRainfall Attenuation on Earth-Satellite Microwave Link in a Tropical Environment(Obafemi Awolowo University, 1987) Odunewu, Paul Adekunle; Ajayi, G.O.Rainfall is a major impairment to radiowave propagation at centimeters and millimetre wavebands, moreso in the tropics because of the intensity, frequency of occurrence and presence of large drops in tropical rainfall. In order to determine the vertical extent of rain (rain height) in the tropics, the characteristics of 0°C isotherm height have been studied using radiosonde data collected at three stations in Nigeria for three years at each station. One year rain rate data collected at Ile-Ife using an electronic rapid response rainguage have been analysed in order to obtain the cumulative rain rate distribution. The existing rainfall attenuation prediction models have been examined. Three attenuation models viz: CCIR, Global and SAM, have been utilized to predict slant path attenuation at Ile-Ife from the one-year rain rate distribution. Cumulative distributions of predicted attenuation were obtained for different frequencies, earth station's elevation angles and polarizations. Attenuation distributions from the three models have been compared. The result obtained shows that 0°C isotherm height during rainy season decreases from the southern to the northern part of Nigeria. A mean 0°C isotherm height of 4. 8 km for the rainy season has been obtained for Nigeria. The rain intensity exceeded for 0.01% year at Ile-Ife was obtained to be 87 mm/h. The differences in the attenuation values predicted by the three remodels vary for different percentages of time, frequencies, elevation angle and polarizations. The results obtained in this work could be used for providing necessary fade margin in satellite link budgets in Nigeria and other similar tropical environment.
- ItemOpen AccessTransport properties of PbSnI4(Solid State IonicsA, 1988-10) kuku, titilayo A.; adeosun, O.S; akande, A.R; adiguel, osmanPbSnI4 has been prepared from equimolar amounts of PbI2 and SnI2. X-ray and DSC measurements show the material to be uniphase in the temperature range 30 to 400°C; it has a tetragonal structure and melts at 379°C. The electrical conductivity is mainly ionic with an ionic transport number greater than 0.99 at 200°C. Conductivity at room temperature is 2.56 × 10−8 Ω−1 cm−1 while the value at 200°C is 1.25 × 10−6 Ω−1 cm−1.
- ItemOpen AccessImplementable soft decision decoding schemes(International Journal of Electronics, 1989-03) Olaniyan, O.OAn 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
- 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 AccessOxidation-induced changes in the electro-optical properties of thin copper films(Il Nuovo Cimento D, 1989-07) Adegboyega, G.AThe room temperature oxidation of vapour deposited copper films has been investigated as a function of film thickness and time by the sheet resistance and optical transmittance measurements. An increase of both sheet resistance and transmittance with a tendency to saturation has been observed. Time variation of the sheet resistance shows that the kinetics of oxidation could be described by a model whereby an initial logarithmic oxide growth changes to an inverse logarithmic one as time progresses; the thicker the film, the longer the change-over time. Absorption coefficients of oxidized films show that the resulting oxide is most probably Cu2O. Evaluation of the oxidized films for possible use as transparent electrode material shows the existence of an optimum thickness value
- ItemOpen AccessStructural and ionic transport properties of some A2BX4 (A=Cu, B=Pb, Sn, X=Br, I) compounds.(1990) Kuku, T.A; Erharhine, P.O; Chiodelli, G.; Akande, A.R.The compounds Cu2PbBr4, Cu2SnI4, and Cu2PbI4 have been synthesized as stable phases in the CuBr-PbBr2, CuI-SnI2, or CuI-PbI2 binary systems. Cu2PbBr4 is cubic (a0=9.170 A ̊), whereas Cu2SnI4 and Cu2PbI4 are hexagonal with a=9.050, c =9.706 A ̊, and a=8.064, c=15.128 A ̊, respectively. These materials are characterized mainly by a rather high anionic defect conductivity over the temperature range 20-270°C. The activation energy for the ionic defect mobility is 0.27 eV for Cu2PbBr4, 0.28 eV for Cu2SnI4 and 0.31 eV for Cu2PbI4
- ItemOpen AccessSome aspects of tropical rainfall and their effect on microwave propagation(International Journal of Satellite Communications, 1990-05) Ajayi, G.OlalereSome characteristics of tropical rain rate and raindrop size distribution are briefly reported, making use of the data obtained at locations in Nigeria. Models and empirical relations have been obtained for the computation of the effects of tropical rain on radiowave propagation at centimetre and millimetre waves. Results are presented for the effect of integration time on rain rate as well as the rain-rate duration characteristics, rain-induced phase shift, attenuation and depolarization, in addition to the relationship between the rain rate and other rainfall parameters. Comparisons have also been made in many cases with the CCIR reports and results from other locations
- ItemOpen AccessIntrinsic gettering of Cr impurities in p-type Cz silicon( physica status solidi (a, 1990-09) Adegboyega, G.A; Poggi, AntonellaThe gettering of chromium impurities by means of high temperature oxygen precipitates is studied by means of resistivity, lifetime, and infrared absorption spectroscopy measurements. The results show that the density of interstitial oxygen, following an oxygen precipitation step, is rather low, and the presence of this interstitial oxygen is closely connected with the formation of the so-called new donor defect. Most of the high temperature (T = 1000°C) oxygen precipitates seem to appear in the form of SiO2 and there is a strong evidence of a redissolution of the oxygen precipitates due to Cr diffusion. The presence of this high temperature oxygen precipitate shows a high efficiency in the gettering of Cr impurities.Das Gettern von Chromverunreinigungen mittels Hochtemperatur-Sauerstoffpräzipitaten wird mittels Widerstands-, Lebensdauer- und Infrarotspektroskopiemessungen untersucht. Die Ergebnisse zeigen, daß die Dichte des Zwischengittersauerstoffs nach dem Sauerstoffpräzipitationsschritt ziemlich niedrig ist, und die Anwesenheit dieses Zwischengittersauerstoffs eng verbunden ist mit der Bildung von sogenannten „new-Donor”-Defekten. Die meisten der Hochtemperatursauerstoffpräzipitate (T = 1000°C) scheinen in Form von SiO2 vorzuliegen, und es existiert ein starker Hinweis auf die Wiederauflösung der Sauerstoffpräzipitate infolge der Cr-Diffusion. Die Anwesenheit dieser Hochtemperatursauerstoffpräzipitate zeigen einen hohen Wirkungsgrad für die Getterung der Cr-Verun-reinigungen
- ItemOpen AccessPrecision Measurement of Rotor Angle of a Microsynchronous Alternator(IEEE Xplore, 1991) Omoigui, MichaelA precision instrument used for the measurement of rotor angles of a laboratory microalternator is described. The measurement is performed by integrating digital signals derived from a phase-locked loop (PLL) reference (i.e. laboratory infinite busbar or the terminals of another machine in a multimachine system) and an optical encoder mounted on the shaft of the machine. The integration is executed by synchronous up-down binary counters. A 12-b digital-analog converter enables both transient and dynamic movement of the rotor to be displayed on an oscilloscope or other suitable recorder. When used on a four-pole 3-MVA microalternator, the resolution of the encoder is 0.2 electrical degrees. Relatively slow and fractional movements of the rotor angle arising from dynamic power imbalances as well as fast and large rotor excursions arising from severe transient disturbances, which sometimes result in pole slipping, are reliably and precisely recorded. It is possible to obtain constant information on the stability or lack thereof for the machine under every operating condition. With appropriate transducers, the principle may easily be applied to continuously monitor changes in the rotor angle of large alternators in interconnected power systems
- ItemOpen AccessThe Functions of Language in Herbalist-Client Interaction in Yoruba Traditional Medicine(1991) Adegbite, WaleA 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.
- ItemOpen AccessSome Features of Language Use in Yoruba Traditional Medicine(1993) Adegbite, WaleYoruba traditional medicine (YTM) is a system which basically incorporates a four-square intersection of two pairs of terms in relation to medicine, viz. positive/negative and personal/communal. In the intersection of 'positive personal' medicine which is catered for by the data for this study, the goal is for a herbalist, or a priest of some divinity, to diagnose and treat an illness of a client or patient where the patient is a child, friend or relation of the client. Herbalists deal in various kinds of medicine though many of them may treat cases of different types, they normally have different areas of specialty e.g. gynaecology, paediatrics, traditional midwifery, orthopaedics, psychiatry etc. However, the diviners or priests are well reputed for handling complex cases that are linked to supernatural causation.
- ItemOpen AccessPhotoconductivity of MOCVD CdS thin films(Journal of Materials Science Letters, 1995-01) Eleruja, Marcus Adebola; Adedeji, A.U; Azi, samuel; Okulaja, Oluwabukola... [2,3,4] Many techniques have been reported in deposition of CdS thin films. These include evaporation, sputtering, spray pyrolysis, molecular beam epitaxy (MBE) technique, photochemical deposition, successive ionic layer adsorption and reaction (SILAR) method [5][6][7][8][9][10][11][12].In all of these deposition methods there are some problems in each of them, for example , it is difficult to obtain a stiochiometric CdS films by evaporation technique and a high substrate temperature is required in spray deposition. [13] The chemical bath deposition (CBD) method appears to be a relatively simple, in expansion method to prepare a homogenous films with controlled composition [14]. ...
- ItemOpen AccessElectrons and Technology(Obafemi Awolowo University Press, 1995-05-27) Williams, V.A.The existence of electrical phenomena, and of static electrical charges, had first been recognized and recorded over 2,500 years ago by Thales of Miletus (640-548 BC). The word electricity itself was derived from the Greek word for amber, a substance upon Which electrical phenomena was first observed. The idea that electricity has structure derives directly from the classical studies of Michael Faraday on electro-chemistry. Michael Faraday occupies a very unique and honored place in the story of electrical science and technology. These studies were 'those which in particular led to the famous laws of electrolysis published in 1833. It is indeed one of those quirks of fate that he could not have brought himself to believe the natural conclusion of his own studies i.e. that charges exist as discrete quanta.
- ItemOpen AccessVariations in raindrop size distribution and specific attenuation due to rain in Nigeria(annals of telecommunications - annales des télécommunications, 1996-01) Adimula, I.A; Ajayi, G.OLes distributions des tailles des gouttes de pluie ont été mesurées en trois lieux du Nigéria (Calabar, Ile-Ife et Zaria). Les données collectées pendant trois ans ont servi à obtenir des modèles de ces distributions pour divers types de pluie : bruine, averse, pluie étendue, orage. La distribution lognormale constitue un bon ajustement pour tous les types de pluie en des lieux tropicaux, sauf pour la bruine où le modèle exponentiel convient. On discute aussi les conséquences de ces modèles pour des calculs de l’affaiblissement linéique dû aux pluies tropicales. The raindrop size distributions had been measured at three locations in Nigeria - Calabar, Ile-Ife and Zaria. The data collected over a period of three years have been utilized to obtain models of drop size distributions for drizzle, shower, widespread and thunderstorm rain. The lognormal distribution provides a good fit for all the rain types at these tropical locations except drizzle, where the exponential model is adequate. The implications of the models for specific attenuation calculations for tropical rain are discussed. Mots clésPluie-Zone tropicale-Distribution statistique-Goutte eau-Dimension particule-Ajustement-Loi lognormale-Loi exponentielle-Onde radioélectrique-Affaiblissement Key wordsRain-Tropical zone-Statistical distribution-Water drop-Particle size-Fitting-Lognormal distribution-Exponential distribution-Radio wave-Attenuation
- 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.